JP2019068456A - System and method for bidirectional radio communication - Google Patents

Abstract

To provide a bidirectional radio communication system which enables bidirectional communication between a multicast transmission station and a multicast reception station, without using the number of lines to the possible extent in 1-to-N communication through a communication satellite.SOLUTION: In the bidirectional radio communication system which configures a VSAT system capable of bidirectional radio communication through a communication satellite 3, Each 1-to-N communication line between one multicast transmission station 1 and N (N: a natural number) multicast reception stations 2A, 2B, 2C is allocated by a DAMA method. One line in the uplink direction from each multicast reception station 2A, 2B, 2C toward the multicast transmission station 1 is shared by performing communication in time division at slot timing ta, tb, tc allocated to each multicast reception station 2A, 2B, 2C for each slot period T1, which is preset as a transmission period, by using a frame conforming to a radio frame format of the TDMA method.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a two-way wireless communication system and a two-way wireless communication method, and more particularly to a two-way wireless communication system and a two-way wireless communication method which can be suitably applied to connection type communication by 1 to N communication via communication satellites. .

  One of two-way wireless communication systems via communication satellites is the VSAT (Very Small Aperture Terminal) system. In the VSAT system, a large number of earth stations on the ground can jointly use one to one or one to N communication by using repeaters (transponders) mounted on communication satellites. . Here, in one-to-one or one-to-N communication, 1 means that it is a single station, and N means that it is a plurality of stations.

  In the VSAT system, since the number of lines possessed by a repeater (transponder) of a communication satellite is usually limited, in order to use the line efficiently, Japanese Patent Laid-Open No. 2002-164828 "Digital Satellite Communication" As described in “System and its control method” and the like, a DAMA (Demand Assign Multiple Access) scheme is adopted.

  The outline of the operation of the DAMA method will be described below. The earth station requests the control station to assign a communication line only when communicating between the earth stations. The control station allocates a communication line to the earth station that made the line allocation request and the earth station that communicates with the earth station. When the earth station does not need to communicate, the earth station itself performs line disconnection (line release) processing. The earth station which performed the line disconnection returns to the state waiting for the original communication line assignment request.

  Also, when performing 1-to-N communication according to the DAMA method, the earth station serving as a multicast transmitting station requests 1-to-N communication channel assignment from the control station, and the control station belongs to the same group as the multicast transmitting station. The same earth station as a multicast reception station, and assigns the same 1 to N communication line. Which earth station belongs to which group is registered in advance with the control station.

  Also, in the case of 1-to-N communication in the conventional VSAT system, allocation of only one line in the direction from the multicast transmitting station to the multicast receiving station is normally performed, and for the line from the multicast receiving station to the multicast transmitting station As needed, it makes an allocation request for a one-to-one line each time. That is, assuming that the number of multicast transmitting stations is one and the number of multicast receiving stations is N, to perform bidirectional communication between the multicast transmitting station and all multicast receiving stations, The number of (1 + N) lines is required.

  Furthermore, in the conventional VSAT system, the 1-to-N communication is used for the purpose of simultaneous delivery of video and audio, simultaneous transfer of file data, and the like. Because of this, it is necessary to communicate in both directions between the multicast transmitting station and all the multicast receiving stations.

  That is, when performing file data transfer, it is necessary to divide the file data into a plurality of packets and transmit them, and if there is a packet loss or a wrong order in assembling the packets, the receiving file It can not be restored to data. For this reason, in file data transfer, it is necessary to detect packet loss and to retransmit at the time of packet loss, so it is necessary to assign a sequence number to a packet. In addition, since it is necessary to send a response signal notifying that the packet has been successfully received from the packet receiving station to the packet transmitting station, detection of packet loss is premised on bidirectional communication.

  Incidentally, a bidirectional communication system having the above-mentioned function is called connection-type communication, and there is a TCP (Transmission Control Protocol) system as a representative connection-type communication system. The TCP method is widely spread in general, and is a communication method adopted in almost all transmitting and receiving terminals that perform IP (Internet Protocol) communication. Therefore, in file data transfer, it is ideal that the TCP method can be adopted from the viewpoint of versatility.

  However, the TCP method is a communication method assuming one-to-one communication, and is not suitable for one-to-N communication. Therefore, in the conventional VSAT system, file data transfer by 1 to N communication is a unique communication method limited to the present application. Then, a dedicated data transmission terminal and data reception terminal having the unique communication method are respectively installed in the network of the multicast transmission station and in the network of the multicast reception station, and all the packets from the data transmission terminal are all data This is realized by repeating packet retransmission until it is received at the receiving terminal. Since data transmission terminals and data reception terminals having communication systems unique to this kind have limited applications as described above compared with terminals that adopt the TCP system, the purchaser layer is also limited accordingly. Terminal prices tend to be expensive.

  In addition, in communication using a communication satellite line, a method different from general connection type communication is adopted also for response signal reception confirmation. That is, in the case of general connection-oriented communication, the next packet transmission is performed after the transmission side receives the response signal from the reception station. On the other hand, in the case of communication using a communication satellite link, since the communication satellite is far above, the transmission distance is long and the propagation delay is large. The amount of delay in a communication satellite link is the amount of delay until an electrical signal reaches the other party when an electrical signal is sent from one earth station to another earth station via the communication satellite, and the communication satellite is stationary. When operated on a satellite orbit, in consideration of the distance to the communication satellite, the amount of delay in the round trip communication satellite link between two earth stations is theoretically about 500 ms. For this reason, when the system waits for response signals one by one, the packet transmission interval increases and the throughput significantly decreases. Therefore, after transmitting as many packets as possible at one time, the system waits for response signals.

JP, 2002-164828, A

  As described above, when connection-oriented communication is performed by 1-to-N communication in the conventional VSAT system, the following problems occur.

  The first problem is that the consumption of the number of lines increases. That is, connection-oriented communication in the conventional VSAT system is premised on two-way communication, and when performing one-to-N two-way communication between a multicast transmitting station and a multicast receiving station, the number of channels is multicast from the multicast transmitting station Since one line to the receiving station and N lines from the multicast receiving station to the multicast transmitting station are required, and a total of (1 + N) lines are required, the number of lines is consumed significantly.

  The second problem is that the communication efficiency and the line use efficiency deteriorate. That is, in the conventional VSAT system, the multicast transmitting station retransmits the packet until all the response signals can be received unless all the response signals from all the multicast receiving stations for the transmitted multicast packet have arrived. It is a mechanism to do it repeatedly. For this reason, if there is a receiving station where packet reception is bad and packet loss occurs frequently, packet retransmission from the transmitting station will occur many times, and even in a station with good reception status, data transfer operation is quite easy Can not be completed, and the communication function remains occupied only for this data transfer operation, resulting in deterioration of communication efficiency and line use efficiency.

  The third problem is that an expensive dedicated data transmission / reception terminal is required, and there is a problem that the facility cost is increased. That is, since connection-type communication in the conventional VSAT system is a 1-to-N communication method, a data transmission / reception terminal of a connection-type communication method based on a 1-to-1 communication method such as TCP which has already prevailed in general is used. Since it is impossible to do so, it is necessary to prepare a data transmission / reception terminal of a unique communication scheme, which makes the cost of the terminal expensive, as compared with the commonly used data transmission / reception terminal, and the facility cost increases. .

  The fourth problem is that there is a limit to improvement in throughput. That is, in the conventional VSAT system, regardless of the number of packets transmitted at one time, since it is a method of waiting for reception of the response signal one by one, improvement of the reduction in throughput due to the influence of delay with the communication satellite There is a limit to

(Object of the present invention)
The present invention has been made in view of the problems described above, and in 1-to-N communication via communication satellites, bidirectional communication between a multicast transmitting station and a multicast receiving station without using the number of channels as much as possible. It is an object of the present invention to provide a two-way wireless communication system and a two-way wireless communication method that make it possible.

  Furthermore, in 1-to-N communication via communication satellites, even if there is a receiving station whose packet reception status is worse than that of other receiving stations, the communication efficiency of the reception status with good reception status is reduced as much as possible. It is another object of the present invention to provide a two-way wireless communication system and a two-way wireless communication method that make it possible to perform line disconnection control for a receiving station with poor reception conditions.

  Furthermore, even in a connection-oriented communication environment where 1-to-N communication is performed, communication based on 1-to-1 connection-oriented communication such as TCP is assumed for communication with a data transmission terminal and with a data reception terminal. It is another object of the present invention to provide a two-way wireless communication system and a two-way wireless communication method that can adopt a scheme.

  Furthermore, it is another object of the present invention to provide a two-way wireless communication system and a two-way wireless communication method capable of improving throughput reduction due to delay in a communication satellite link in 1-to-N communication via a communication satellite.

  In order to solve the above-mentioned problems, the two-way wireless communication system and the two-way wireless communication method according to the present invention mainly adopt the following characteristic configurations.

  (1) A two-way wireless communication system according to the present invention is a two-way wireless communication system constituting a VSAT (Very Small Aperture Terminal) system capable of two-way wireless communication via a communication satellite, and one multicast transmitting station And assigns a 1-to-N communication link between N and N (N: natural number) multicast receiving stations by DAMA (Demand Assign Multiple Access) method, and the uplink direction from the multicast receiving station to the multicast transmitting station One line assigned as a line is assigned to each of the N multicast receiving stations in each slot cycle predetermined as a transmission cycle, using a frame conforming to a radio frame format of the TDMA (Time Division Multiple Access) system. In time-division communication at different slot timings Ri, characterized by shared.

  (2) A two-way wireless communication method according to the present invention is a two-way wireless communication method in a two-way wireless communication system constituting a VSAT (Very Small Aperture Terminal) system capable of two-way wireless communication via a communication satellite. Assign a 1-to-N communication channel between one multicast transmitting station and N (N: natural number) multicast receiving stations by DAMA (Demand Assign Multiple Access) method, and transmit the multicast from the multicast receiving station One of the channels assigned as the uplink channel toward the station is a frame conforming to the radio frame format of the TDMA (Time Division Multiple Access) system, and N of the multicasts per slot cycle predetermined as the transmission cycle At the slot timing assigned to each receiving station And by communicating with, characterized by shared.

  According to the two-way wireless communication system and the two-way wireless communication method of the present invention, the following effects can be mainly obtained.

  That is, in communication from multiple (for example, N) multicast receiving stations toward one multicast transmitting station, by sharing one line among multiple (for example, N) multicast receiving stations in a time division manner, The number of allocated lines can be reduced from a plurality of (e.g., N) lines in the conventional system to one line, and a significant saving of the number of used lines can be achieved.

FIG. 1 is an entire configuration diagram for explaining an example of the entire configuration of a multicast communication system according to the present invention. FIG. 7 is a schematic view showing an example of a frame format of each of a downlink radio frame, an uplink radio frame, and a data portion in the downlink radio frame in the multicast communication system shown in FIG. 1; It is a sequence chart which shows an example of operation | movement at the time of implementing the multicast packet transmission from a transmitting station to a receiving station in the multicast communication system shown in FIG. It is a sequence chart which shows an example of the multicast packet resending operation (the first half part) by the receiving failure by the side of one of the receiving stations which generate | occur | produced at the time of multicast packet transmission from a transmitting station to a receiving station in the multicast communication system shown in FIG. It is a sequence chart which shows an example of the multicast packet retransmission operation (latter half part) by the receiving failure by the side of one of the receiving stations which generate | occur | produced at the time of multicast packet transmission from a transmitting station to a receiving station in the multicast communication system shown in FIG. FIG. 6 is a sequence chart showing an example of a multicast packet retransmission operation due to a partial packet loss that occurs in any of the receiving stations at the time of multicast packet transmission from the transmitting station to the receiving station in the multicast communication system shown in FIG. A sequence showing an example of an operation of controlling a line disconnection of a corresponding receiving station when a reception degradation state occurs in any of the receiving stations at the time of multicast packet transmission from a transmitting station to a receiving station in the multicast communication system shown in FIG. It is a chart. In the multicast communication system shown in FIG. 1, for the receiving station other than the receiving station, the receiving station is deregistered from the multicast packet transmission destination receiving station registration list held by the transmitting station during transmission and reception of multicast packets. On the other hand, it is a sequence chart which shows an example of the operation | movement which resends the multicast packet which has been transmitted.

  Hereinafter, preferred embodiments of a two-way wireless communication system and a two-way wireless communication method according to the present invention will be described with reference to the attached drawings. Note that the two-way wireless communication method according to the present invention may be implemented as a two-way wireless communication program that can be executed by a computer, or alternatively, the two-way wireless communication program may be recorded on a computer readable recording medium. It goes without saying that it is good. Further, reference numerals in the drawings attached to the following drawings are for convenience added to the respective elements as an example for aiding understanding, and it is needless to say that the present invention is not intended to be limited to the illustrated embodiment. Yes.

(Features of the present invention)
Before describing the embodiments of the present invention, the features of the present invention will first be outlined. The present invention relates to a VSAT (Very Small Aperture Terminal) system capable of two-way wireless communication via a communication satellite, and two-way wireless communication between one multicast transmitting station and a plurality of multicast receiving stations. In a two-way wireless communication system that performs communication,
One line from the multicast transmitting station to each multicast receiving station, and one line from each multicast receiving station to the multicast transmitting station
The multicast sender is
A means for assigning a sequence number to each multicast packet;
Means for transmitting a plurality of multicast packets towards each multicast receiver at one time;
A means for retransmitting the packet if the sequence number in the response signal from the multicast receiving station is confirmed and if it is confirmed that the update has not been performed for a predetermined fixed period or if the sequence number missing has occurred;
A means for changing the packet transmission cycle according to the degree of update of the sequence number in the response signal;
Means for monitoring the reception status information in the response signal, and controlling the line disconnection to the corresponding multicast reception station if the reception status information indicates the reception degradation status, and means for excluding it from the multicast reception stations for packet transmission;
A means for performing communication based on a connection type communication method such as TCP for one-to-one communication with a data transmission terminal;
Equipped with
On the other hand, each multicast receiver is
A means for sharing one circuit to the multicast transmission station by time division;
The oldest signal sequence number of the multicast packet corresponding to the response packet received from the data receiving terminal, and when a packet loss is detected, further stores the sequence number corresponding to the packet loss in the response signal and transmits it to the multicast transmitting station Means,
The reception level or BER (Bit Error Rate) of the own station in communication with the multicast transmission station is monitored, and the reception deterioration state is multicast transmission station when the reception level or BER is lower than a preset reception allowance threshold. Means for disconnecting the line of the own station while transmitting to
Means for performing communication based on a connection-type communication method such as TCP for one-to-one communication with a data receiving terminal;
The main feature is the provision of

(Function of means to bring effect)
By providing each means as described above in the two-way wireless communication system according to the present invention, the following effects can be obtained.

  That is, the multicast transmission station takes over all the data from the data transmission terminal using communication based on the connection-oriented communication method such as TCP of one-to-one communication, and stores it in the storage device in the multicast transmission station. Then, the multicast transmission station creates a multicast packet of the taken data, assigns a sequence number to each multicast packet, and multiplexes it into a radio frame having an error detection function. Thereafter, the multicast packet to which the sequence number is assigned is transmitted as one or more sets to each of a plurality of multicast receiving stations registered as multicast target stations.

  Each multicast packet receiving station transmits the multicast packet received from the multicast transmitting station to each data receiving terminal using communication based on a connection-oriented communication method such as TCP for one-to-one communication. Each data receiving terminal that has received the multicast packet transmits a response packet to the received multicast packet to each multicast packet receiving station. After that, each multicast receiving station that receives the response packet from each data receiving terminal responds that the oldest reception sequence number of the multicast packet held for responding to the multicast transmitting station has been confirmed from the data receiving terminal The oldest packet sequence of the multicast packet in which the packet was updated is updated to the oldest sequence number of the multicast packet, and the oldest slot sequence of the updated multicast packet is assigned to the line to the multicast transmitting station at the transmission slot timing previously assigned to each multicast receiving station. Send a numbered response signal. In addition, the response signal also stores a sequence number of a packet midway drop, information indicating that the reception deterioration state of the own multicast receiving station has occurred, and information indicating that the reception deterioration state has been recovered.

  The multicast transmitting station transmits the multicast packet to each multicast receiving station at a timing determined in advance as a multicast packet transmission period regardless of the reception timing of the response signal from each multicast receiving station. This reduces the effect of delay in the communication satellite link and suppresses the decrease in throughput.

  Also, with regard to the occurrence of packet loss, the multicast transmitting station may not have updated the oldest number sequence number indicating that it has already been received in the response signal from each multicast packet receiving station, or may not transmit multicast packets It is judged whether it has not been updated by a fixed number of times (number of times it is possible to set variably to any number including one time) predetermined by the number, or whether or not there is a packet missing sequence number. Do. Thus, when occurrence of packet loss is detected, the multicast transmission station performs retransmission processing of the multicast packet.

  Furthermore, when the update interval of the received sequence number of the response signal is longer than the transmission period of the multicast packet, the multicast transmitting station determines whether to change the transmission period of the multicast packet. . In addition, the multicast transmission station monitors the reception status of the response signal and the reception status in the response signal, and repeats the retransmission process, or, for multicast reception stations that may have quality deterioration, another multicast packet In order to prevent a decrease in communication efficiency at the receiving station, line disconnection control is performed, and a process of excluding the receiving station of the multicast target from the registration list registered is performed.

  Note that the above judgment criteria for multicast packet retransmission processing and disconnection control to the multicast receiving station can be arbitrarily changed and set by the setting in the multicast transmitting station, and the multicast transmitting station can Retransmission processing of multicast packets and control of disconnection from a multicast receiving station are performed in accordance with the set judgment criteria. After transmitting all multicast packets, if necessary, change the judgment criteria for retransmission and line disconnection mentioned above, and there will be multicast receiving stations excluded from the registration list registering the multicast target receiving stations. If yes, the transmission of the multicast packet is performed again to the multicast receiving station.

(Configuration Example of Embodiment of the Present Invention)
Next, an example of the configuration of the multicast communication system according to the present invention will be described in detail with reference to FIG. FIG. 1 is an entire configuration diagram for explaining an example of the entire configuration of a multicast communication system according to the present invention, and as an example configuration of a multicast communication system via communication satellites, bidirectional wireless communication via communication satellites is possible It shows the case where the VSAT (Very Small Aperture Terminal) system is configured.

  In the multicast communication system of FIG. 1, reference numeral 1 denotes an earth station serving as a multicast transmitting station (hereinafter referred to as transmitting station), and reference numerals 2A, 2B, and 2C denote earth stations serving as a plurality of multicast receiving stations Hereinafter, it is described as a receiving station, and the code 3 is a communication satellite. Reference numeral 4 denotes a data transmission terminal, reference numerals 5A, 5B, and 5C denote a plurality of respective data reception terminals, and reference numeral 6 denotes a storage device provided in the transmission station 1. Reference numeral 11 denotes a communication cable for connecting the transmitting station 1 and the data transmitting terminal 4. Reference numerals 12A, 12B and 12C denote receiving stations 2A, 2B and 2C and data receiving terminals 5A, 5B and 5C, respectively. Is a communication cable that connects

The data transmission terminal 4 is connected to the transmission station 1 by the communication cable 11 and transmits data D7 from the data transmission terminal 4 to the transmission station 1 via the communication cable 11.
The data receiving terminals 5A, 5B and 5C are connected to the receiving stations 2A, 2B and 2C by the communication cables 12A, 12B and 12C, respectively, and via the communication cables 12A, 12B and 12C, respectively. Data packets D8a, D8b and D8c from the respective receiving stations 2A, 2B and 2C are received, and response packets D9a, D9b and D9c to the respective receiving stations 2A, 2B and 2C are returned.

  The transmitting station 1 and each of the receiving stations 2A, 2B, 2C are wirelessly connected by a communication satellite channel via the communication satellite 3 assigned using the DAMA (Demand Assign Multiple Access) method, and each of the transmitting stations 1 A plurality of multicast downlink radio frames D1a and D1b for each of the receiving stations 2A, 2B and 2C, in a predetermined multicast packet transmission cycle, using one downlink going to the receiving stations 2A, 2B and 2C. , D1c, D1d, D1e, D1f, D1g, D1h, D1i, D1j, D1k, D1l toward each receiving station 2A, 2B, 2C at a time, while each receiving station 2A, 2B, The slot timings ta, tb, and tc allocated in advance in units of one slot for each slot period T1 on one uplink going from the 2C to the transmitting station 1 Used, in divided state when, the uplink radio frame D2a to transmission station 1, D3a, D4a, D2b, D3b, sequentially transmits D4b.

  In the example shown in FIG. 1, the number of receiving stations is three in the receiving stations 2A, 2B and 2C, but in the present invention, the number of receiving stations is limited to such a case. Instead, N stations (N: any natural number) may be installed. In the following description, for convenience of explanation, the earth station performing multicast transmission is the transmitting station, and the earth station performing multicast reception is the receiving station. However, in the earth station of the present invention, both functions of multicast transmission and reception are provided. It goes without saying that any earth station can be either a transmitting station or a receiving station.

(Description of the operation of the embodiment)
Next, the flow of operations of the entire multicast communication system shown in FIG. 1 will be described in detail with reference to the overall configuration diagram of FIG.

  The data transmission terminal 4 transmits data D7 to the transmission station 1 via the communication cable 11 using a one-to-one connection-type communication method such as TCP. The transmitting station 1 temporarily stores all the data D7 received from the data transmitting terminal 4 in the storage device 6 in the own station. The data D7 is stored in the storage device 6 in the own station in units of packets when transmitted and received between the data transmission terminal 4 and the transmission station 1.

  The transmitting station 1 stores all the data D7 from the data transmitting terminal 4 in the storage device 6 in the own station, and then transmits 1 to the receiving stations 2A, 2B, 2C from the transmitting station 1 by the DAMA (Demand Assign Multiple Access) method. A request for assignment of a book line (hereinafter referred to as downlink) and one line (hereinafter referred to as uplink) from the receiving stations 2A, 2B and 2C to the transmitting station 1 is made. When the requested line assignment is completed, the transmitting station 1 generates a sequence number indicating the transmission order of each packet of the data D7 stored in the storage device 6 in the own station. Although the transmitting station 1 does not particularly change the data in the packet or the like for the packet of the stored data D7, in order to simplify the following description, this packet will be referred to as 'multicast packet' hereinafter. I will write.

  The transmitting station 1 stores the multicast packet and the sequence number data in the transmission frame having the error detection function, respectively, and then makes them into one set, and the downlink radio frame currently to be transmitted (first transmission in FIG. If it is time, it is stored in the data portion of the downlink radio frame D1a) for multicast.

  If the frame length of one set of transmission frames is longer than the length of the data portion in one frame of the downlink radio frame, the one set of transmission frames is divided and a plurality of downlink radio frames (for example, multicast Are stored across the data portions of a plurality of downlink radio frames D1a to D1d). Also, even during a period in which there is no multicast packet transmission, a value defined as empty data (for example, ALL 1 in HDLC format) is stored in the data section at each predetermined multicast packet transmission cycle, and defined as the empty data Keep transmitting the downlink radio frame in which the value is stored in the data part.

  The multicast packet transmitted from the transmitting station 1 via the downlink, the downlink radio frames D1a to D1l storing the sequence numbers, that is, the downlink radio frames D1a to D1l for multicast in the downlink direction, are transmitted via the communication satellite 3 , And received by each receiving station 2A, 2B, 2C. The details of the elements and operation of the downlink radio frame will be described later with reference to FIG.

  Next, each of the receiving stations 2A, 2B, 2C converts the multicast packet received through the downlink into data packets D8a, D8b, D8c of a format that can be transmitted to the data receiving terminals 5A, 5B, 5C, respectively. Then, it transmits to each of the data receiving terminals 5A, 5B, 5C via the communication cables 12A, 12B, 12C using a one-to-one connection type communication method such as TCP. After that, in each of the receiving stations 2A, 2B, and 2C, the response packets D9a, D9b, and D9c indicating that the data receiving terminals 5A, 5B, and 5C have successfully received the packets, respectively, correspond to the data receiving terminals 5A, 5B, and 5C, respectively. I will wait for the return from. Here, each of the response packets D9a, D9b and D9c is also a response packet in a communication system used between each of the receiving stations 2A, 2B and 2C and the data receiving terminals 5A, 5B and 5C.

  For uplink communication, in the present invention, a TDMA (Time Division Multiple Access) system is adopted, and one uplink line is shared by time division among a plurality of receiving stations 2A, 2B, 2C, Each of the receiving stations 2A, 2B, and 2C transmits the transmitting station 1 to the transmitting station 1 at predetermined intervals (slot period T1) at the slot timings ta, tb, and tc of the slot numbers preset for the receiving stations 2A, 2B, and 2C, respectively. The uplink radio frame to be transmitted is continuously transmitted to the communication satellite 3 via the uplink.

  In the example shown in FIG. 1, the receiving station 2A receives uplink radio frames D2a and D2b, the receiving station 2B receives uplink radio frames D3a and D3b, and the receiving station 2C receives uplink radio frames D4a and D4b. At the respective slot timings ta, tb and tc described in the above, it is transmitted to the communication satellite 3. At this time, each of the receiving stations 2A, 2B, and 2C transmits the uplink radio frames D2a and D2b, the uplink radio frames D3a and D3b, and the uplink radio frames D4a and D4b, respectively, to the data receiving terminals 5A, 5B, and 5C. The oldest number sequence number etc. of the multicast packet corresponding to the response packets D9a, D9b, D9c received from each are stored as a response signal.

  Also, as described above, the transmission period of the uplink radio frame in each of the receiving stations 2A, 2B, 2C is defined as the slot period T1, and is preset as a value unified to each of the receiving stations 2A, 2B, 2C. ing. The set value of the slot cycle T1 is variable. Further, the positions of slot timings ta, tb and tc for uplink in the next receiving stations 2A, 2B and 2C are identified by referring to the information stored in the downlink radio frames D1a to D1l. The detailed operation regarding the reception slot number will be described later with reference to FIG. Also, one slot length is equal to or longer than two downlink radio frames, and can be arbitrarily changed. Here, the length of one slot is assumed to be set in advance for each of the transmitting station 1 and the receiving stations 2A, 2B, and 2C.

  Next, details of the elements and operations of the downlink radio frame and uplink radio frame will be described in detail with reference to FIG. FIG. 2 is a schematic diagram showing an example of the frame format of each of the downlink radio frame, uplink radio frame and data portion of the downlink radio frame in the multicast communication system shown in FIG. The line radio frame format is shown in FIG. 2B, and the frame format of the data portion of the downlink radio frame is shown, and the line radio frame format is shown in FIG. 2C.

  As shown in FIG. 1, uplink radio frames D2a, D3a, D4a, D2b, D2b, D3b, D4b transmitted from the receiving stations 2A, 2B, 2C via the communication satellite 3 respectively have one slot period T1. At each of the slot timings ta, tb, and tc, the transmission station 1 sequentially receives the data in time series. The transmitting station 1 confirms the response signal information in the uplink radio frames D2a, D3a, D4a, D2b, D3b, D4b from the receiving stations 2A, 2B, 2C, respectively, and retransmits the multicast packet as needed. Control line disconnection to the corresponding receiving station. Detailed operations relating to packet retransmission and line disconnection control will be described later with reference to FIGS.

  The downlink radio frame format shown in FIG. 2 (A) and the uplink radio frame format shown in FIG. 2 (C) are similar to the radio frame format of the TDMA system generally used in the conventional radio communication system. It has become. However, in the present invention, it is important to use the TDMA method and to use only one uplink frequency channel to reduce the number of used CH (channels) as much as possible, as long as such a point is realized, The detailed configuration of the downlink radio frame format and the uplink radio frame format may not be as shown in FIG.

  First, the configuration of the downlink radio frame format shown in FIG. 2 (A) will be described. As shown in FIG. 2A, the downlink radio frame D1a includes elements of a UW (Unique Word) D11a, a frame information unit D12, a control signal unit D13, and a data unit D14a. The subsequent downlink radio frames D1b, D1c and D1d are also similar to the frame configuration of D1a, and UW D11b, D11c and D11d and data parts D14b, D14c and D14d are respectively identical to UW D11b and data part D14a. It is an element. Note that components other than the components described above in the subsequent downlink radio frames D1b, D1c, and D1d are not important in the present invention, and thus the description thereof is omitted.

  Downlink radio frames are grouped in groups of two or more frames to form one slot unit. The example shown in FIG. 2A shows an example in which one slot unit is configured by a group of two frames of downlink radio frames D1a and D1b, but the number of downlink radio frames in one slot is As long as it is two or more frames, it may be any frame. By the way, the uplink radio frame size can be increased as the number of downlink radio frames in one slot is increased, so the amount of data that can be transmitted at one time is increased at the time of uplink transmission. be able to. However, the transmission cycle of the uplink radio frame of each of the receiving stations 2A, 2B, 2C becomes long.

  Next, each element of the downlink radio frame will be further described by taking the downlink radio frames D1a, D1b, D1c, and D1d of FIG. 2A as an example.

  In UW D11a, UW D11b, UW D11c, and UW D11d in FIG. 2A, values uniquely determined in all downlink radio frames are stored, and each receiving station 2A that receives downlink radio frames is received. , 2B, 2C side, used for identification of the head of the downlink radio frame and frame synchronization. Further, at the time of uplink radio frame transmission, the UW D 22 of the uplink radio frame shown in FIG. 2C is set to the second frame in the same slot in the downlink radio frame of FIG. It is also used to adjust timing at the time of uplink transmission so as to synchronize with the UW (UW D11b in the example of FIG. 2A) of the frame in which the multicast packet is stored in the data section.

  Further, in the frame information section D12 of FIG. 2A, a specific value which is known as the transmission timing of the leading frame is stored in the leading frame of the youngest slot in the transmission cycle of the uplink radio frame. In the receiving stations 2A, 2B, 2C, the slot timings ta, tb, tc of the own station slot number at the time of uplink transmission are used for identification. That is, each of the receiving stations 2A, 2B, 2C counts the number of received frames from the detection of the top frame of the lowest numbered slot, thereby to transmit slot timings ta, tb of its own station slot number for transmitting uplink radio frames. , Tc can be identified.

  Further, the control signal unit D13 of FIG. 2A is used to store control signals exchanged in a wireless section between the transmitting station 1 and the receiving stations 2A, 2B, and 2C. The data part D14a of FIG. 2A is used to store a multicast packet or a sequence number. In the example shown in FIG. 2B, the sequence number D53 is stored in the data section D14a of FIG. 2A, and the multicast packet D63 is stored in the data section D14b of FIG. 2A. Both the multicast packet and the sequence number are stored in a frame having an error detection function. When one piece of data does not fit in the data part D14a, for example, as shown in FIG. 2A, the data parts D14b, D14c, D14d of the subsequent downlink radio frames D1b, D1c, D1d are straddled. Stored.

  Next, the configuration of the uplink radio frame format shown in FIG. 2 (C) will be described. As shown in FIG. 2C, the uplink radio frame D2a transmitted by the receiving station 2A is composed of a preamble D21, a UW (Unique Word) D22, and a response signal D23. The time D24 and the rear guard time D25 are inserted.

  The configuration of the subsequent uplink radio frame D3a transmitted by the receiving station 2B is also the same as the configuration of the uplink radio frame D2a, and is configured of the preamble D31, UWD32, and the response signal D33, and the uplink radio frame D2a. Similarly, the front guard time D34 and the rear guard time D35 are inserted. As shown in FIG. 1, each of the receiving stations 2A, 2B, 2C transmits uplink radio frames D2a, D3a,... At slot timings ta, tb, tc of the slot numbers of the receiving stations 2A, 2B, 2C, respectively.

  Next, taking uplink radio frame D2a shown in FIG. 2C as an example, each element of uplink radio frame, that is, preamble D21, UW D22, response signal D23, forward guard time D24, backward guard time D25 will be described.

  The preamble D21 in FIG. 2C is data in which binary '1's and' 0's are alternately continued, and gives synchronization timing to the transmitting station 1 receiving the uplink radio frame. Used for Further, UW D22 in FIG. 2C stores a value uniquely determined in the uplink radio frame, and the transmitting station 1 that receives the uplink radio frame stores the beginning of the frame excluding the preamble D21. Used for identification and frame synchronization.

  Further, the response signal D23 of FIG. 2C is used to store the response signal transmitted from the receiving station 2A side to the transmitting station 1 side. If the response signal has a number identifying the receiving station 2A, the oldest serial number of the multicast packet corresponding to the response packet received from the data receiving terminal 5A, and a sequence number of a halfway defect, it corresponds to a halfway defect A sequence number to be stored and a value indicating whether the reception state is good or not are stored. In addition, any data such as an IP (Internet Protocol) packet may be connected after the response signal if it does not exceed the range of one slot length.

  Further, the front guard time D24 and the rear guard time D25 in FIG. 2C are arbitrary non-signal times, respectively, and absorb fluctuations in transmission timing in the uplink radio frame, and can be used in the front slot or the rear slot. , And is used to prevent collisions with uplink radio frames D2b,... Transmitted by other receiving stations 2B, 2C. The uplink radio frame D2a shown in FIG. 2C is transmitted at the same timing within one slot so as to be synchronized with the two downlink radio frames D1a and D1b shown in FIG. 2A.

  Next, the configuration of the frame format of the data portion of the downlink radio frame shown in FIG. 2 (B) will be described. As shown in FIG. 2B, for example, in the case of downlink radio frames D1a and D1b, the data section frame is an HDLC (High level Data Link Control) frame forming a data section D14a in the downlink radio frame D1a. It comprises one set of D5a and a PPP (Point to Point Protocol) frame D6a forming a data section D14b in the downlink radio frame D1b.

  In the conventional VSAT system, unlike the case of the present embodiment, since the sequence number data is not assigned, the data part frame is only the PPP frame. In this embodiment, as shown in FIG. 2B, in addition to the PPP frame D6a, the sequence number D53 is stored in the HDLC frame D5a having an error detection function, and arranged at the front stage of the PPP frame D6a. They are connected to form one set.

  The reason for storing the sequence number D53 in the HDLC frame D5a having an error detection function is that, similar to the multicast packet, the error detection needs to be performed on the receiving side also for the sequence number D53. If not, even if an error occurs in the sequence number D53, the reception side will receive the packet normally, and the certainty of the packet order will be lost. Then, in order to ensure the certainty of both the order and data of the multicast packet, the reception side makes normal reception only when there is no error in both the sequence number D53 of the pair and the multicast packet D63. . If an error occurs in either one, the properly received sequence number D53 or the multicast packet D63 is also discarded as abnormal data.

  As for the HDLC frame D5a, the same one as the frame format prevailing in the conventional system is only used as an example also in this embodiment, and in the case of a frame having an error detection function, other frames It goes without saying that the format may be used.

  As shown in FIG. 2B, the HDLC frame D5a includes a forward flag D51, identification information D52, a sequence number D53, an FCS (Frame Check Sequence) D54, and a backward flag D55, and a mark D56 is inserted at the end of the frame. Be done. The HDLC frame D5b forming the data section D14c in the downlink radio frame D1c is also similar to the configuration of the HDLC frame D5a, and a mark is inserted at the end of the HDLC frame D5b as in the case of the HDLC frame D5a.

  Further, as shown in FIG. 2B, the PPP frame D6a is composed of a forward flag D61, a PPP header D62, a multicast packet D63, an FCS D64, and a backward flag D65, and the mark D66 is inserted at the end of the frame. The PPP frame D6b forming the data portion D14d in the downlink radio frame D1d is also similar to the configuration of the PPP frame D6a, and a mark is inserted at the end of the PPP frame D6b as in the PPP frame D6a.

  The forward flag D51, the FCS D54, the backward flag D55, and the mark D56, which are components of the HDLC frame D5a, are general standards for the HDLC frame, and thus the description thereof will be omitted. Further, the forward flag D61, the PPP header D62, the FCS D64, the backward flag D65, and the mark D66, which are components of the PPP frame D6a, are also general standards in the PPP frame, so the description here is omitted.

  Next, an HDLC frame D5a forming the data portion D14a of the downlink radio frame D1a shown in FIG. 2B and a PPP frame D6a forming the data portion D14b of the downlink radio frame D1b are taken as an example. Among the elements constituting each of the frames D6a, each element other than the above-described elements whose description is omitted will be described.

  The identification information D52 in the HDLC frame D5a of FIG. 2B is used for type identification of the HDLC frame. The identification information D52 is used to distinguish from the PPP frame D6a in the receiving stations 2A, 2B and 2C, and the following applications are also conceivable.

  In FIG. 2B, as in the HDLC frame D5a and the PPP frame D6a, a one-to-one configuration of the HDLC frame and the PPP frame is described as a basic configuration with respect to the data portion of the downlink radio frame. For example, in order to improve transmission efficiency, a configuration such as a plurality of PPP frames for HDLC frame 1 frame is also permitted as a one-to-multiple configuration, and identification information D52 is used to identify such a frame configuration. It is also possible to use.

  Further, although the HDLC frame D5a is described on the basis of storing the sequence number D53 in FIG. 2 (B), the HDLC frame D5a can also be used for other applications, and the identification information D52 can also be used to identify such HDLC frame applications.

  The sequence number D53 in the HDLC frame D5a of FIG. 2B stores the sequence number of the multicast packet D63 in the PPP frame D6a of FIG. 2B. The multicast packet D63 is a packet transmitted from the network on the transmitting station 1 side to the networks on the receiving station 2A, 2B, 2C side.

  Next, the frame format relating to the HDLC frame D5a and the PPP frame D6a forming the data parts D14a and D14b of the downlink radio frames D1a and D1b in FIG. 2B will be described in detail. .

  The multicast packet D63 to be transmitted from the network on the transmitting station 1 side to the networks on the receiving station 2A, 2B, 2C side is stored in the PPP frame D6a having an error detection function in the transmitting station 1. Thereafter, the transmitting station 1 stores the sequence number D53 and the identification information D52 to be added to the multicast packet D63 in the HDLC frame D5a having an error detection function, and transmits the HDLC frame D5a and the PPP frame D6a via the mark D56. Connect in pairs. The same operation is performed for the subsequent multicast packets, and is further connected behind the HDLC frame D5b and the PPP frame D6b. The number of combinations of HDLC frames and PPP frames to be linked is variable.

  Next, the details of the communication method between the transmitting station 1 and the receiving stations 2A, 2B and 2C will be described with reference to the sequence charts shown in FIGS. In the sequence charts shown in FIGS. 3 to 7, the communication satellite 3, the data transmission terminal 4 and the data reception terminals 5A, 5B and 5C shown in FIG. 1 are omitted. Further, in the sequence chart of FIG. 6, the description of the receiving stations 2A and 2B is also omitted. It is assumed that the storage of data from the data transmission terminal 4 in the transmission station 1, the line assignment request, and the line assignment have already been performed by the start of each sequence in FIGS. Furthermore, in the sequence charts of FIG. 3 to FIG. 5, transmission of each multicast packet of sequence numbers 1 to 5 from the transmitting station 1 to the receiving stations 2A, 2B, 2C has ended, and the data receiving terminals 5A, 5B, It is assumed that the receiving stations 2A, 2B and 2C have already received response packets indicating that they have been received normally from 5C.

(Example of multicast packet transmission and reception operation)
First, an example of operation when transmitting a multicast packet from the transmitting station 1 to the receiving stations 2A, 2B, 2C will be described using the sequence chart of FIG.

  FIG. 3 is a sequence chart showing an example of the operation when multicast packet transmission from the transmitting station 1 to the receiving stations 2A, 2B, 2C is performed in the multicast communication system shown in FIG. In the sequence chart of FIG. 3, as described above, the transmission operation from the transmitting station 1 to the receiving stations 2A, 2B, and 2C has already ended for each of the multicast packets of sequence numbers 1 to 5. , And an operation of transmitting a multicast packet with a sequence number of 6 or later.

  In the sequence chart of FIG. 3, the transmitting station 1 generates five multicast packets CS1 of sequence numbers 6 to 10 for transmission data received from the data transmitting terminal 4 and stored in the storage device 6, and received. A downlink radio frame is continuously transmitted toward the stations 2A, 2B, and 2C in synchronization with the multicast packet transmission cycle T2 (step S1). The number of multicast packets transmitted from the transmitting station 1 at one time is variable.

  Each of the receiving stations 2A, 2B, 2C receives the multicast packet CS1 of sequence number 6 to 10 from the transmitting station 1, and edits it into a packet for the data receiving terminals 5A, 5B, 5C, respectively, and receives the data receiving terminal 5A. , 5B, and 5C, and waits for response packets from the data receiving terminals 5A, 5B, and 5C, respectively.

  Receiving each of the response packets from the data receiving terminals 5A, 5B and 5C, each of the receiving stations 2A, 2B and 2C generates a response signal storing the oldest number sequence number of the multicast packet corresponding to the response packet. Then, at slot timings ta, tb and tc assigned to the respective receiving stations 2A, 2B and 2C, they are transmitted to the transmitting station 1 as uplink radio frames.

  In the example shown in the sequence chart of FIG. 3, for the receiving station 2A, the multicast packet CS1 of sequence numbers 6 to 10 from the transmitting station 1 is not received at the time of the slot timing ta for transmission to the uplink. Therefore, it transmits to the transmitting station 1 the response signal CS2a storing the sequence number 5 corresponding to the oldest sequence number of the multicast packet which has already received the response packet indicating that it has already been received from the data receiving terminal 5A ( Step S2a).

  As for the receiving station 2B, at the time of the slot timing tb for transmission to the uplink, as in the case of the receiving station 2A, the multicast packet CS1 of sequence numbers 6 to 10 from the transmitting station 1 has not been received, The response signal CS2b storing the sequence number 5 corresponding to the oldest sequence number of the multicast packet which has received the response packet indicating that it has already been received from the data receiving terminal 5B is transmitted to the transmitting station 1 (step S2b ).

  On the other hand, for the receiving station 2C, at the time of the slot timing tc for transmission to the uplink, the multicast packet CS1 of sequence numbers 6 to 10 from the transmitting station 1 is received and transmitted to the data receiving terminal 5C. Then, since a response packet to the effect that reception has already been received from the data receiving terminal 5C, the response signal CS2c storing the sequence number 10 corresponding to the oldest sequence number of the multicast packet is sent to the transmitting station 1 (Step S2c).

  The transmitting station 1 constantly monitors the response signal returned from each of the receiving stations 2A, 2B, 2C, and the sequence number of the oldest number stored in each response signal is the response signal in the previous slot cycle. It has been checked whether or not it has been updated. The transmitting station 1 updates the sequence numbers of the oldest response signals of the response signals CS2a, CS2b, CS2c from the receiving stations 2A, 2B, 2C, respectively, from the sequence number of the oldest number of response signals in the previous slot cycle. If it is confirmed that the packet transmission / reception operation is performed, it is determined that the packet transmission / reception operation is normally performed with each of the receiving stations 2A, 2B, 2C.

  In addition, as long as a line assigned at the management station is secured, the transmitting station 1 receives the response signal from each of the receiving stations 2A, 2B, and 2C for the multicast packet transmitted earlier, regardless of whether or not the received signal. An operation of transmitting a multicast packet (or an empty multicast packet if there is no data to be transmitted) to the receiving stations 2A, 2B and 2C is performed at each multicast packet transmission cycle T2 set in advance. Therefore, after the multicast packet transmission cycle T2 has elapsed after the transmission of the multicast packet CS1 of sequence numbers 6 to 10, the transmitting station 1 generates five multicast packets CS3 of sequence numbers 11 to 15 to be transmitted next. , And transmit continuously as downlink radio frames to the receiving stations 2A, 2B, and 2C (step S3).

  The multicast packet transmission cycle T2 is variable, and is changed in accordance with the update condition of the sequence number of the response signal received from each receiving station 2A, 2B, 2C. For example, the difference between the value of the oldest sequence number in the response signal from each of the receiving stations 2A, 2B and 2C and the value of the sequence number of the multicast packet transmitted from the transmitting station 1 may not expand (case On the contrary, control is performed to change the multicast packet transmission cycle T2 or the like so as not to shrink. For example, the difference between the oldest sequence number in the response signal from each of the receiving stations 2A, 2B, 2C and the sequence number of the transmission multicast packet transmitted from the transmitting station 1 is expanded to a predetermined threshold value or more. When it detects that, it controls so that multicast packet transmission period T2 may be lengthened by predetermined length. At this time, the response signal to be referred to may be the response signal of all the receiving stations 2A, 2B, 2C, or may be the response signal of the receiving station arbitrarily selected.

  Each of the receiving stations 2A, 2B, 2C receives the multicast packet CS3 of sequence numbers 11 to 15 from the transmitting station 1, and edits it into packets for the data receiving terminals 5A, 5B, 5C, respectively, and receives the data receiving terminal 5A. , 5B, 5C, and when receiving response packets from the data receiving terminals 5A, 5B, 5C, generate a response signal storing the oldest number sequence number of the multicast packet corresponding to the response packet, At slot timings ta, tb, and tc assigned to the respective receiving stations 2A, 2B, and 2C, transmission is performed as an uplink radio frame toward the transmitting station 1 at preset slot cycles T1.

  In the example shown in the sequence chart of FIG. 3, for the receiving station 2A, when the slot period T1 elapses after transmitting the response signal CS2a storing the sequence number 5 first, transmission to the next uplink is performed. At the time of the slot timing ta, the transmitting station transmits the response signal CS4a storing the sequence number 10 corresponding to the oldest sequence number of the multicast packet CS1 which has already received the response packet indicating that it has already been received from the data receiving terminal 5A. It transmits for 1 (step S4a).

  Further, with regard to the receiving station 2B, as in the receiving station 2A, a slot timing tb at which a slot cycle T1 has elapsed since transmission of the response signal CS2b storing the sequence number 5 first, that is, transmission to the next uplink. The transmitting station 1 is sent a response signal CS4b storing the sequence number 10 corresponding to the oldest sequence number of the multicast packet CS1 which has already received the response packet indicating that it has already been received from the data receiving terminal 5B. Send (step S4b).

  On the other hand, the receiving station 2C receives the multicast packet CS3 with the sequence number 11 to 15 from the transmitting station 1 at the slot timing tc for transmission to the uplink, and transmits it to the data receiving terminal 5C. Then, since a response packet to the effect that reception has already been received from the data receiving terminal 5C, the response signal CS4c storing the sequence number 15 corresponding to the oldest sequence number of the multicast packet CS3 is transmitted to the transmitting station 1 To send (step S4c).

  Thereafter, the same transmission / reception operation of the multicast packet and the response signal as described above is repeated, and finally, when the multicast packet transmission operation regarding the last data of the transmission data transmitted from the data transmission terminal 4 is reached, the transmitting station 1 receives the multicast packet CS5 storing sequence numbers (n-4) to n (n: sequence number of the last multicast packet) when the multicast packet transmission cycle T2 has elapsed since the previous multicast packet transmission, It transmits toward 2A, 2B, 2C (step S5). Thereafter, when the transmitting station 1 receives the response signals CS6a, CS6b, CS6c storing the last sequence number n from the respective receiving stations 2A, 2B, 2C (steps S6a, S6b, S6c), the transmitting station 1 and the receiving station 1 receive The transmission / reception operation of multicast packets with the stations 2A, 2B, 2C is ended.

  Thereafter, the transmitting station 1 receives a response signal CS6a, CS6b, CS6c storing the last sequence number n from each of the receiving stations 2A, 2B, 2C, and then the time preset as the non-communication time T3 has elapsed. If no new data to be transmitted as a multicast packet is received from the data transmitting terminal 4 until then, the transmitting station 1 receives all data when the time equivalent to the no-communication time T3 has elapsed. The disconnection signal CS7 specifying the stations 2A, 2B, 2C is continuously sent to all the receiving stations 2A, 2B, 2C continuously until the predetermined disconnection signal transmission time T4 expires (step S7) .

  Each of the receiving stations 2A, 2B, and 2C that receives the disconnection signal CS7 from the transmitting station 1 disconnects the line of the own station (steps S8a, S8b, and S8c). Furthermore, when the disconnection signal continuous transmission time T4 has expired, the transmission station 1 also disconnects the line of its own station (step S9). As a result, the communication satellite circuit assigned as the multicast circuit by the management station to each of the transmitting station 1 and the receiving stations 2A, 2B and 2C is released.

(Example of multicast packet retransmission operation)
Next, when a multicast packet is transmitted from the transmitting station 1 to the receiving stations 2A, 2B, and 2C using the sequence charts of FIGS. 4A and 4B, a multicast packet is generated because a reception failure occurs on one of the receiving stations. An example of the multicast packet retransmission operation for retransmitting.

  FIGS. 4A and 4B show an example of a multicast packet retransmission operation due to a reception failure at one of the receiving stations that occurred when transmitting a multicast packet from the transmitting station 1 to the receiving stations 2A, 2B and 2C in the multicast communication system shown in FIG. Is a sequence chart showing 4B is continuous at the bottom of FIG. 4A, and the sequence charts of FIG. 4A and FIG. 4B are preferably drawn on one sheet of paper, but the former part of the multicast packet retransmission operation is shown in FIG. And the second half of the multicast packet retransmission operation is shown in FIG. 4B. The sequence charts of FIGS. 4A and 4B show the case where a reception failure occurs in the receiving station 2C among the receiving stations 2A, 2B, and 2C. Also in the sequence charts of FIGS. 4A and 4B, as in the case of FIG. 3, the transmission operation from the transmitting station 1 to the receiving stations 2A, 2B, and 2C has already ended for each multicast packet of sequence numbers 1 to 5. , And shows an operation of transmitting a multicast packet with a sequence number of 6 or later.

  In the sequence charts of FIGS. 4A and 4B, the transmitting station 1 generates five multicast packets CS10 of sequence numbers 6 to 10 for the transmission data received from the data transmitting terminal 4 and stored in the storage device 6. The mobile station continuously transmits downlink radio frames toward the receiving stations 2A, 2B, and 2C in synchronization with the multicast packet transmission cycle T2 (step S10). At this time, it is assumed that the receiving station 2C can not receive the multicast packet CS10 due to some factor (step S11).

  Receiving stations 2A and 2B receive multicast packets CS10 with sequence numbers 6 to 10 from transmitting station 1 and edit them into packets for data receiving terminals 5A and 5B, respectively, as in the case of FIG. It is transmitted to the terminals 5A and 5B, and waits for response packets from the data receiving terminals 5A and 5B. However, unlike the case of FIG. 3, since the receiving station 2C does not receive the multicast packet CS10, the transmitting operation to the data receiving terminal 5C is not performed.

  When each receiving station 2A, 2B, 2C receives a response packet from the data receiving terminal 5A, 5B, 5C, respectively, it receives a response signal in which the oldest sequence number of the multicast packet corresponding to the response packet is stored. It generates and transmits as an uplink radio frame at the slot timings ta, tb and tc assigned to the respective receiving stations 2A, 2B and 2C.

  In the example shown in the sequence charts of FIGS. 4A and 4B, as for the receiving station 2A, as in the case of FIG. Since the multicast packet CS10 has not been received, the response signal CS12a stores the sequence number 5 corresponding to the oldest sequence number of the multicast packet which has already received the response packet indicating that it has already been received from the data receiving terminal 5A. Are transmitted to the transmitting station 1 (step S12a).

  As for the receiving station 2B, as in the case of FIG. 3, at the time of the slot timing tb for transmission to the uplink, as in the case of the receiving station 2A, the multicast packets of sequence numbers 6 to 10 from the transmitting station 1 Response signal CS12b storing sequence number 5 corresponding to the oldest sequence number of the multicast packet which has not received CS 10 and has already received a response packet indicating that it has already received from data receiving terminal 5B as transmitting station 1 And send the information (step S12b).

  Also, with regard to the receiving station 2C, unlike in the case of FIG. 3, reception of the multicast packet CS10 of sequence numbers 6 to 10 from the transmitting station 1 has failed, so slot timing tc for transmission to the uplink At this time, it transmits to the transmitting station 1 the response signal CS12c storing the sequence number 5 corresponding to the oldest sequence number of the multicast packet which has already received the response packet indicating that it has already been received from the data receiving terminal 5C. (Step S12c).

  As described above, the transmitting station 1 constantly monitors the response signal returned from each of the receiving stations 2A, 2B, 2C, and the sequence number of the oldest number stored in each response signal is the previous one. It is confirmed whether the response signal in the slot cycle is updated or not. In step S12a, S12b, and S12c, the transmitting station 1 responds to the oldest sequence number in the response signals CS12a, CS12b, and CS12c from the receiving stations 2A, 2B, and 2C, respectively. Make sure that it is updated from the oldest sequence number in the signal. Therefore, it is determined that the packet transmission / reception operation is normally performed with each of the receiving stations 2A, 2B, and 2C.

  The transmitting station 1 periodically transmits multicast packets to the receiving stations 2A, 2B, and 2C every multicast packet transmission cycle T2 set in advance, as long as the line allocated by the management station is secured. To do the action. Therefore, after the multicast packet transmission cycle T2 has passed after the transmission of the multicast packet CS10 of sequence numbers 6 to 10, the transmitting station 1 generates five multicast packets CS13 of sequence numbers 11 to 15, and the receiving station 2A, It continuously transmits as a downlink radio frame toward 2B and 2C (step S13).

  The receiving stations 2A and 2B receive the multicast packet CS13 of sequence numbers 11 to 15 from the transmitting station 1 as in the case of FIG. 3, but the receiving station 2C receives the multicast packet CS13 again due to some factor. It is assumed that it could not be done (step S14).

  The receiving stations 2A and 2B having received the multicast packet CS13 are respectively edited into packets for the data receiving terminals 5A and 5B and transmitted to the data receiving terminals 5A and 5B as in the case of FIG. It is in a state of waiting for response packets from the terminals 5A and 5B. However, unlike the case of FIG. 3, since the receiving station 2C does not receive the multicast packet CS1, the transmitting station 2C does not perform the transmission operation to the data receiving terminal 5C.

  As described above, each of the receiving stations 2A, 2B, 2C stores the oldest sequence number of the multicast packet corresponding to the response packet upon receiving the response packet from the data receiving terminals 5A, 5B, 5C, respectively. The response signal is generated, and the uplink radio signal is transmitted to the transmitting station 1 at the slot timings ta, tb, and tc allocated to the receiving stations 2A, 2B, and 2C at each preset slot period T1. Send as a frame.

  In the example shown in the sequence charts of FIGS. 4A and 4B, for the receiving station 2A, when the slot period T1 elapses after the response signal CS12a storing the sequence number 5 is transmitted first, that is, transmission to the next uplink The response signal CS15a storing the sequence number 10 corresponding to the oldest sequence number of the multicast packet CS10 which has already received the response packet indicating that it has already been received from the data receiving terminal 5A at the time of the slot timing ta Transmit to the transmitting station 1 (step S15a).

  Further, as for the receiving station 2B, similarly to the receiving station 2A, when the slot period T1 elapses after the response signal CS12b storing the oldest sequence number 5 is transmitted first, that is, the transmission to the next uplink is performed. At the time of the slot timing tb to be performed, it transmits the response signal CS15b storing the sequence number 10 corresponding to the oldest sequence number of the multicast packet CS10 which has already received the response packet indicating that it has already been received from the data receiving terminal 5B. Transmit to station 1 (step S15b).

  However, for the receiving station 2C, not only the reception of the multicast packet CS10 of sequence numbers 6 to 10 from the transmitting station 1 but also the reception of the multicast packet CS13 of sequence numbers 11 to 15 has failed. That a slot cycle T1 has elapsed since transmission of the response signal CS12c storing the sequence number 5 of 1, that is, at the slot timing tc at which transmission to the next uplink is to be performed, from the data receiving terminal 5C The response signal CS 15 c storing the sequence number 5 corresponding to the oldest sequence number of the multicast packet receiving the response packet is transmitted to the transmitting station 1 (step S 15 c).

  The transmitting station 1 constantly monitors the response signal returned from each of the receiving stations 2A, 2B, 2C, and the sequence number of the oldest number stored in each response signal is the response signal in the previous slot cycle. It has been checked whether or not it has been updated. As described above, the transmitting station 1 is updated from the response signals CS12a and CS12b in the previous slot cycle with respect to the oldest sequence number in the response signals CS15a and CS15b from the receiving stations 2A and 2B, respectively. It is determined that the packet transmission and reception operation is normally performed. However, since the sequence number of the oldest number in the response signal CS15c from the receiving station 2C is the same as the response signal CS12c in the previous slot cycle and has not been updated, some abnormality has occurred in the packet transmission / reception operation. Judge as a thing.

  Since the transmitting station 1 has only one channel for the receiving stations 2A, 2B, 2C, it is determined that a reception failure has occurred in any of the receiving stations 2A, 2B, 2C which is the transmission destination of the multicast packet. In this case, the process shifts to a multicast packet retransmission operation for all the receiving stations 2A, 2B, 2C. Here, the case of shifting to the retransmission operation immediately when receiving the response signal of the oldest sequence number not yet updated even once from any of the receiving stations 2A, 2B, 2C will be described. The case where the response signal of the sequence number not updated is continuously received until it reaches a certain number of times predetermined as the number threshold (the number threshold is variable including the case of one) instead of once. It may be made to shift to the resending operation.

  Therefore, the transmitting station 1 determines that the packet transmission / reception operation is defective as the first retransmission operation when the predetermined multicast packet transmission cycle T2 elapses after the transmission of the multicast packet CS13 of sequence numbers 11 to 15 In order to retransmit the multicast packet CS10 transmitted next to the multicast packet corresponding to the oldest sequence number 5 stored in an unupdated state in the response signal from the receiving station 2C, The retransmission multicast packet CS16 is generated and retransmitted to the receiving stations 2A, 2B and 2C (step S16).

  Even in the first retransmission operation, the receiving stations 2A and 2B receive the retransmission multicast packet CS16 of sequence numbers 6 to 10 from the transmitting station 1, but the receiving station 2C re-transmits the multicast by another factor. It is assumed that the packet CS16 can not be received (step S17).

  The receiving stations 2A and 2B that have received the retransmission multicast packet CS16 have already received the multicast packet CS10 corresponding to the sequence numbers 6 to 10 of the retransmission multicast packet CS16, and have received the data reception terminals 5A and 5B. Since it has already been transmitted, the operation of retransmitting retransmission multicast packets CS16 of sequence numbers 6 to 10 to the data receiving terminals 5A, 5B is not performed. On the other hand, since the receiving station 2C has not received the retransmission multicast packet CS16, the transmitting operation to the data receiving terminal 5C is not performed.

  As described above, each receiving station 2A, 2B, 2C generates a response signal storing the oldest numbered sequence number of the multicast packet corresponding to the response packet from the data receiving terminals 5A, 5B, 5C, respectively, At slot timings ta, tb and tc allocated to each of the receiving stations 2A, 2B and 2C, it transmits as an uplink radio frame toward the transmitting station 1 every slot cycle T1 set in advance.

  In the example shown in the sequence charts of FIGS. 4A and 4B, for the receiving stations 2A and 2B, respectively, for example, when the process is immediately shifted to the retransmission operation by the reception of the response signal of the oldest sequence number not updated. At the time when the slot cycle T1 has elapsed since the response signals CS15a and CS15b storing the oldest sequence number 10 first, that is, at the slot timings ta and tb at which transmission to the next uplink is performed, For the transmitting station 1, response signals CS18a and 18b storing the sequence number 15 corresponding to the oldest sequence number of the multicast packet CS13 which has already received a response packet indicating that it has already been received from the receiving terminals 5A and 5B. It transmits (steps S18a and S18b).

  However, for the receiving station 2C, not only the multicast packets CS10 of sequence numbers 6 to 10 from the transmitting station 1 but also the reception of the multicast packets CS13 of sequence numbers 11 to 15 and the retransmission multicast packets CS16 of sequence numbers 6 to 10 Since all have failed, at the time of slot timing tc for transmission to the uplink, it corresponds to the oldest number sequence number of the multicast packet which has received a response packet indicating that it has already been received from the data receiving terminal 5C. The response signal CS 18 c storing the sequence number 5 to be transmitted is transmitted to the transmitting station 1 (step S 18 c).

  After that, although the transmitting station 1 repeatedly performs the resending operation of the resending multicast packet similar to the above, there is a situation where the oldest serial number stored in the response signal from the receiving station 2C is not updated in one direction. Similarly, even in the last Nk-th retransmission operation predetermined as the retransmission execution frequency threshold, if it is not updated, the operation shifts to an operation of excluding the receiving station 2C from the multicast packet transmission targets.

  That is, even if the transmitting station 1 generates the retransmission multicast packet CS19 of sequence numbers 6 to 10 as the last Nk-th retransmission operation, the transmitting station 1 may retransmit it to the receiving stations 2A, 2B, and 2C (step S19). The receiving stations 2A and 2B normally receive the retransmission multicast packet CS19, but the receiving station 2C can not receive the retransmission multicast packet CS19 for some reason (step S20). .

  As in the case of the first retransmission operation, the transmitting station 1 receives, from each of the receiving stations 2A and 2B, a response signal CS21a storing the sequence number 15 corresponding to the oldest sequence number of the received multicast packet CS13, 21b and a response signal CS21c storing a sequence number 5 corresponding to the oldest sequence number of the already received multicast packet from the receiving station 2C at slot timings ta, tb and tc (step S21a, S21b, S21c).

  Even if the transmitting station 1 repeatedly performs the retransmission operation up to the last Nk-th time, it is detected that the oldest serial number stored in the response signal of the receiving station 2C is not updated at all. At the same time, delete the registration of the receiving station 2C from the registration list of multicast target receiving stations held in its own station (that is, the multicast packet transmission destination receiving station registration list, in other words, the packet retransmission target station registration list). (Step S22).

  Thereafter, the transmitting station 1 further disconnects the disconnecting signal CS23 for the receiving station 2C to the receiving stations 2A, 2B, and 2C in order to disconnect the receiving station 2C from the multicast packet target station. Continuous transmission is performed during the signal continuous transmission time T4 (step S23). The receiving station 2A, 2B ignores the disconnecting signal CS23 because the target of the disconnecting signal CS23 received is the receiving station 2C, but the receiving station 2C receiving the disconnecting signal CS23 disconnects its own line. (Step S24).

  In addition, after the transmitting station 1 continuously transmits the disconnection signal CS23 for the receiving station 2C, if the multicast packet to be transmitted still remains, the remaining receiving stations 2A other than the line-disconnected receiving station 2C , 2B, perform the remaining multicast packet transmission operation. After that, the transmitting station 1 completes transmission of all multicast packets to be transmitted, and receives a response signal storing the last sequence number of the transmitted multicast packet from each of the remaining receiving stations 2A and 2B. If no data to be newly transmitted occurs before the time set in advance as the non-communication time T3, the receiving stations 2A and 2B are targeted at the time when the non-communication time T3 has elapsed. The line of the receiving stations 2A and 2B is also disconnected by continuously transmitting the disconnection signal for the predetermined disconnection signal transmission time T4.

  If the response signal CS15c from the receiving station 2C does not reach the transmitting station 1 in step S15c, the response signal CS12c from the receiving station 2C can not be compared with the immediately preceding response signal CS12c. There is no opportunity to shift to step S16 in which the retransmission operation is performed. Therefore, the transmission and reception operation of the multicast packet of FIG. 3 described above is continued without performing the retransmission operation.

  As a result, even if the transmitting station 1 happens to receive the response signal from the receiving station 2C, the sequence number of the received response signal from the receiving station 2C is the oldest by the normal transmitting / receiving operation. If the difference between the sequence numbers of response signals from the other receiving stations 2A and 2B whose sequence numbers are successively updated and the difference between the predetermined sequence and the predetermined value has expanded, or in some cases, When the response signal from the receiving station 2C can not be confirmed continuously for a predetermined time, the process does not shift to the re-sending operation, but immediately shifts to step S22 to receive the receiving station 2C as a multicast target. It is decided to delete from the multicast packet transmission destination receiving station registration list which has registered the receiving station of and to disconnect.

  Also, the above-described retransmission execution number threshold Nk is an arbitrary value and is variable. In some cases, it is also possible not to perform the retransmission operation itself. As described above, when the re-transmission operation is not performed at all, it may be operated to shift to step S22 immediately after the execution of step S15 c.

(Example of retransmission operation when multicast packet loss occurs)
Next, when transmitting a multicast packet from transmitting station 1 to receiving stations 2A, 2B, 2C using the sequence chart of FIG. 5, packets related to some multicast packets due to some error at any of the receiving stations An example of the multicast packet retransmission operation when a loss occurs will be described.

  FIG. 5 shows an example of the multicast packet retransmission operation due to partial packet loss occurring in any of the receiving stations at the time of multicast packet transmission from transmitting station 1 to receiving stations 2A, 2B, 2C in the multicast communication system shown in FIG. Is a sequence chart showing In the sequence chart of FIG. 5, the loss of some packets in the receiving station 2C among the receiving stations 2A, 2B, and 2C (the packet with the sequence number 8 among the five multicast packets of sequence numbers 6 to 10) In the case of a loss of Also in the sequence charts of FIGS. 4A and 4B, as in the case of FIG. 3, the transmission operation from the transmitting station 1 to the receiving stations 2A, 2B, and 2C has already ended for each multicast packet of sequence numbers 1 to 5. , And shows an operation of transmitting a multicast packet with a sequence number of 6 or later.

  In the sequence chart of FIG. 5, the transmitting station 1 generates five multicast packets CS30 of sequence numbers 6 to 10 for transmission data received from the data transmitting terminal 4 and stored in the storage device 6, and received. A downlink radio frame is continuously transmitted toward the stations 2A, 2B, and 2C in synchronization with the multicast packet transmission cycle T2 (step S30). At this time, it is assumed that the receiving station 2C generates a packet list due to some error and can not receive the packet with the sequence number 8 among the five packets of the multicast packet CS30 (step S31). ).

  Receiving stations 2A and 2B receive multicast packets CS10 with sequence numbers 6 to 10 from transmitting station 1 and edit them into packets for data receiving terminals 5A and 5B, respectively, as in the case of FIG. It is transmitted to the terminals 5A and 5B, and waits for response packets from the data receiving terminals 5A and 5B. However, unlike the case of FIG. 3, the receiving station 2C does not receive the packet of the sequence number 8 in the middle of the five packets of the multicast packet CS30. Therefore, the sequence other than the sequence number 8 in which the packet loss occurs Data corresponding to the numbers 6, 7, 9, 10 are transmitted to the data receiving terminal 5C.

  When each receiving station 2A, 2B, 2C receives a response packet from the data receiving terminal 5A, 5B, 5C, respectively, it receives a response signal in which the oldest sequence number of the multicast packet corresponding to the response packet is stored. It generates and transmits as an uplink radio frame at the slot timings ta, tb and tc assigned to the respective receiving stations 2A, 2B and 2C.

  In the example shown in the sequence chart of FIG. 5, with respect to the receiving station 2A, as in the case of FIG. 3, the multicast of sequence numbers 6 to 10 from the transmitting station 1 at the time of slot timing ta for transmission to the uplink Since the packet CS30 has not been received, the response signal CS32a storing the sequence number 5 corresponding to the oldest sequence number of the multicast packet which has already received the response packet indicating that it has already been received from the data receiving terminal 5A is transmitted. Transmit to station 1 (step S32a).

  As for the receiving station 2B, as in the case of FIG. 3, at the time of the slot timing tb for transmission to the uplink, as in the case of the receiving station 2A, the multicast packets of sequence numbers 6 to 10 from the transmitting station 1 Response signal CS32b storing sequence number 5 corresponding to the oldest sequence number of the multicast packet which has not received CS 30 and has already received a response packet indicating that it has already received from data receiving terminal 5B as transmitting station 1 To send (step S32b).

  On the other hand, for the receiving station 2C, at the time of the slot timing tc at which transmission to the uplink is performed, of the multicast packets CS1 of sequence numbers 6 to 10 from the transmitting station 1, a sequence during the packet loss due to some cause The data corresponding to the sequence numbers 6, 7, 9, 10 other than the sequence number 8 which has received a packet other than the number 8 and which has a packet loss is transmitted to the data receiving terminal 5C The reception terminal 5C receives a response packet indicating that it has already been received. Therefore, the receiving station 2C sends the response signal CS32c storing the sequence number 10 and the packet loss occurrence sequence number 8 corresponding to the oldest sequence number of the multicast packet for which the data receiving terminal 5C has been received to the transmitting station 1 (Step S32c).

  As for the packet loss occurrence sequence number 8, for example, a value '2' obtained by subtracting the sequence number 8 in which the packet loss occurred from the oldest sequence number 10 may be stored as a packet loss value. In such a case, the transmitting station 1 performs an operation of subtracting the packet loss value '2' from the oldest sequence number 10 in the received response signal to calculate the sequence number 8 in which the packet loss has occurred. You should do it.

  The transmitting station 1 constantly monitors the response signal returned from each of the receiving stations 2A, 2B, 2C, and the sequence number of the oldest number stored in each response signal is the response signal in the previous slot cycle. It is checked whether or not it has been updated, and whether or not packet loss has occurred. The transmitting station 1 is updated from the sequence number of the oldest number in the response signal in the previous slot cycle with respect to the sequence number of the oldest number in the response signals CS32a and CS32b from the receiving stations 2A and 2B, respectively. And, if it is confirmed that the packet loss occurrence sequence number is not stored either, it is determined that the packet transmission and reception operation is normally performed with each of the receiving stations 2A and 2B.

  On the other hand, although the transmitting station 1 has been updated from the sequence number of the oldest number in the response signal in the previous slot cycle, the packet loss occurs with regard to the sequence number of the oldest number in the response signal CS32c from the receiving station 2C. Since it is confirmed that the sequence number is also stored, in the next multicast packet transmission cycle T2, it is determined that it is necessary to retransmit the packet of the sequence number in which the packet loss has occurred.

  Since the transmitting station 1 has only one downlink for the receiving stations 2A, 2B, 2C, it is assumed that a packet loss has occurred in any of the receiving stations 2A, 2B, 2C which is the transmission destination of the multicast packet. If it is determined, the operation shifts to the retransmission operation of the multicast packet including the packet of the sequence number in which the packet loss has occurred for all the receiving stations 2A, 2B, 2C.

  Therefore, transmitting station 1 retransmits data of sequence number 8 in which a packet loss has occurred in receiving station 2C when a predetermined multicast packet transmission cycle T2 elapses after transmission of multicast packet CS30 of sequence numbers 6 to 10 In addition to the four packets of sequence numbers 11 to 14, a multicast packet CS33 including a retransmission packet of sequence number 8 in which a packet loss has occurred is generated and transmitted toward receiving stations 2A, 2B, and 2C. (Step S33).

(An example of the line disconnection control operation of the receiving station)
Next, using the sequence chart of FIG. 6, each of the receiving stations 2A, 2B, and 2C determines whether or not it is in the reception degradation state by its own determination on the receiving station side, and falls into the reception degradation state. If it is determined that the response signal is included in the response signal, it is reported to the transmitting station 1, and if the reception deterioration state continues, the receiving station side autonomously determines the line of the own station. An example of the control operation in the case of disconnecting will be described. In the example described above with reference to FIGS. 4A and 4B, even if one of the receiving stations 2A, 2B, and 2C repeats the retransmission operation for the number of times predetermined by the transmitting station 1 as the threshold for the number of retransmissions The case has been described where, when the multicast packet can not be received normally, the disconnect signal is continuously sent from the transmitting station 1 side to forcibly disconnect the line of the corresponding receiving station. On the other hand, in the case of the sequence chart of FIG. 6, when the reception deterioration state continues, the line of the own station is disconnected by the autonomous control of the receiving station side, and the line is disconnected more reliably. The case where the line of the corresponding receiving station is forcibly disconnected is also described under the control from the transmitting station 1 which has received the notification of the occurrence of the reception deterioration state from the receiving station side in order to perform control.

  FIG. 6 shows a line of a corresponding receiving station when a reception degradation state occurs in any of the receiving stations when transmitting a multicast packet from transmitting station 1 to receiving stations 2A, 2B, 2C in the multicast communication system shown in FIG. It is a sequence chart which shows an example of operation which controls cutting. Although the receiving stations 2A, 2B and 2C constantly monitor the reception level or BER (Bit Error Rate) indicating the receiving state of the own station, in the sequence chart of FIG. And 2C, in the receiving station 2C, detection that the reception level or BER of the signal from the transmitting station 1 has fallen below the receivable threshold predetermined as the receivable limit value, and the occurrence of the reception degradation state It shows about the case where it detected.

  In the sequence chart of FIG. 6, although the receiving station 2C constantly monitors the reception level or BER indicating the reception state of the own station as described above, it has been transmitted from the transmitting station 1 through the satellite channel. When it is detected that the reception level or BER of the signal is lower than a predetermined receivable threshold (step S41), it is determined that the reception degradation state has occurred in the own station, and the receiving station At the time of slot timing ta assigned to 2C, in addition to the sequence number corresponding to the oldest sequence number of the received multicast packet, a value indicating the reception degradation state of the own station (receiving station 2C) is received degradation state A response signal CS42 stored as occurrence information is generated and transmitted to the transmitting station 1 (step S42).

  Furthermore, in the receiving station 2C that has detected the occurrence of the reception degradation state, the timer is started when the occurrence of the reception degradation state in the own station is detected, and the reception degradation state monitoring time continues to be determined beforehand. It is monitored whether it is continuously generated during T5. If the reception degradation state continues to occur during the reception degradation state monitoring time T5, the receiving station 2C autonomously disconnects the line of its own station (step S44). If the reception degradation state of the own station is improved and recovered to a good reception state before the reception degradation state monitoring time T5 elapses, at the timing of the slot timing ta assigned to the receiving station 2C, In addition to the sequence number corresponding to the sequence number of the oldest of the already received multicast packets, a response signal storing a value indicating recovery information for recovery from reception degradation is generated to generate a transmitting signal 1 At the same time, it is controlled to stop the clock operation of the timer and not to shift to the disconnection operation of the line of the own station.

  On the other hand, when the transmitting station 1 confirms that the receiving deterioration state occurrence information indicating the occurrence of the receiving deterioration state is stored in the receiving station 2C in the response signal CS42 received from the receiving station 2C (step S43), the receiving station To continuously monitor whether or not reception degradation state recovery information indicating recovery to a good reception state is stored in a response signal from 2C during a predetermined reception station recovery state recovery waiting time T6. To start the timer.

  When the transmitting station 1 receives, from the receiving station 2C, a response signal storing reception degradation state recovery information indicating recovery to a good reception state before the reception station recovery state recovery waiting time T6 elapses, The temporal operation of the timer is stopped, and the normal packet transmission / reception operation as shown in FIG. 3 is restored. On the other hand, even if the receiving station reception state recovery waiting time T6 has elapsed, the receiving station 2C can not receive the response signal storing the reception degradation state recovery information indicating recovery to the good reception state. In this case, the transmitting station 1 deletes the registration of the receiving station 2C from the multicast packet transmission destination receiving station registration list (in other words, the registration list of packet retransmission target stations) held in the own station (step S45) .

  Furthermore, in order to separate the receiving station 2C from the multicast packet target station, the transmitting station 1 sends the disconnection signal CS46 for the receiving station 2C not only to the receiving station 2C but also to the receiving stations 2A, 2B and 2C. , And continuously transmit for a predetermined disconnection signal transmission time T4 (step S46). The receiving station 2A, 2B ignores the disconnecting signal CS46 because the target of the disconnecting signal CS46 received is the receiving station 2C, but the receiving station 2C that has received the disconnecting signal CS46 still has its own line. If it has not been disconnected autonomously, the line of the own station is forcibly disconnected based on the disconnection signal CS46.

  In general, since the reception station reception state recovery waiting time T6 at the transmission station 1 side is set as a time longer than the reception deterioration state monitoring time T5 at the reception station 2C side, as shown in FIG. Under normal circumstances, when the receiving station 2C receives the disconnection signal CS46 from the transmitting station 1, the receiving station 2C has already recovered from the reception deterioration state even once to a good state. , It is in a state of disconnecting the line autonomously.

  In addition, after the transmitting station 1 continuously transmits the disconnection signal CS46 for the receiving station 2C, if the multicast packet to be transmitted still remains, the remaining receiving stations 2A other than the line-disconnected receiving station 2C. , 2B, perform the remaining multicast packet transmission operation. After that, the transmitting station 1 completes transmission of all multicast packets to be transmitted, and receives a response signal storing the last sequence number of the transmitted multicast packet from each of the remaining receiving stations 2A and 2B. If no data to be newly transmitted occurs before the time set in advance as the non-communication time T3, the receiving stations 2A and 2B are targeted at the time when the non-communication time T3 has elapsed. The line of the receiving stations 2A and 2B is also disconnected by continuously transmitting the disconnection signal for the predetermined disconnection signal transmission time T4.

(An example of the line disconnection control operation of the receiving station)
Next, using the sequence chart of FIG. 7, among the receiving stations 2A, 2B, and 2C of the multicast target stations, the multicast packet transmission destination receiving station registration list (held by the transmitting station 1 during transmission and reception of multicast packets) In other words, an example of an operation of retransmitting a multicast packet which has been transmitted to a receiving station other than the receiving station to a receiving station whose registration has been deleted from the registration list of the packet retransmission target station) will be described. .

  As described in the sequence charts of FIGS. 4A and 4B, during the transmission and reception operation of the multicast packet, any of the receiving stations 2A, 2B and 2C (the receiving station 2C in the example of FIGS. 4A and 4B) When it is detected that the reception failure state occurs and the update of the oldest sequence number stored and returned in the response signal from the receiving station is not detected, the transmitting station 1 performs the resending operation of the multicast packet. Launch However, even if the resending operation of the multicast packet is repeated until the Nkth time predetermined as the resend execution frequency threshold, the sequence number of the oldest number stored in the response signal from the receiving station is not updated. When the state continues, the transmitting station 1 deletes the registration of the receiving station from the multicast packet transmission destination receiving station registration list (in other words, the registration list of the packet retransmission target station) and instructs the line disconnection. Transmit to the receiving station.

  In addition, as described in the sequence chart of FIG. 6, during the transmission and reception operation of the multicast packet, the reception deterioration in any of the reception stations 2A, 2B and 2C (reception station 2C in the example of FIGS. 4A and 4B) When a state occurs and a state in which the reception level or BER is lower than a predetermined reception allowance threshold occurs, a response signal storing information indicating that fact is returned to the transmitting station 1. The transmitting station 1 having received the response signal can receive from the receiving station a response signal storing information indicating recovery to a good reception state until the receiving station reception state recovery waiting time T6 is reached. If not, the registration of the receiving station is deleted from the multicast packet transmission destination receiving station registration list (in other words, the registration list of packet retransmission target stations) registering the receiving station of the multicast target, and Send an instruction to the receiving station.

  Note that, as described in the sequence chart of FIG. 6, after the occurrence of a reception degradation state in which the reception level or BER is lower than a predetermined reception allowable threshold, the reception station monitors the reception degradation state monitoring time T5 in advance. When it is detected that the reception degradation state continues until the set time is reached, the receiving station autonomously disconnects the line.

  7 is registered from the multicast packet transmission destination receiving station registration list (in other words, the registration list of packet retransmission target stations) held in the transmitting station 1 during transmission and reception of multicast packets in the multicast communication system shown in FIG. It is a sequence chart which shows an example of operation | movement which resends the multicast packet which has been transmitted with respect to receiving stations other than the said receiving station with respect to the deleted receiving station. In the sequence chart of FIG. 7, among the receiving stations 2A, 2B, and 2C which are multicast target stations, the multicast packet transmission destination receiving station registration list (in other words, the receiving destination 2C registers the receiving stations for multicasting). It shows about the case where registration deletion was carried out from the registration list | wrist of the station which is a packet resending object.

  Although not shown in the sequence chart of FIG. 7, the transmitting station 1 receives the receiving stations 2A and 2B other than the receiving station 2C whose registration has been deleted, that is, the multicast packet transmission destination receiving station registration list (in other words, When all multicast packets to the receiving stations 2A and 2B of the multicast target station registered in the packet retransmission target station registration list) are transmitted, the lines of the receiving stations 2A and 2B are also disconnected.

  Thereafter, the transmitting station 1 starts an operation of retransmitting a multicast packet which has already been transmitted to the receiving stations 2A and 2B other than the receiving station 2C with respect to the receiving station 2C whose registration has been deleted. However, even for the receiving station 2C whose registration has been deleted, the line has already been disconnected, so the transmitting station 1 sends the control station the line to the receiving stations 2A, 2B and 2C. In order to reset, the allocation request of the 1-to-N communication line is made again. As described in the background art, in the VSAT system, the control station performs line management as to which earth station is to be allocated a line in 1-to-N communication.

  That is, since the control station manages as a circuit for multicasting between the transmitting station 1 and the receiving stations 2A, 2B and 2C of the multicast target station, the allocation request of the 1 to N communication line from the transmitting station 1 is Even if it is received, only the line of the receiving station 2C can not be set, and all the lines of the receiving stations 2A, 2B, 2C of the multicast target station will be set. Therefore, not only the receiving station 2C whose registration has been deleted but also the receiving stations 2A and 2B for which transmission of all the multicast packets has already been completed, the line is set again.

  Therefore, in the sequence chart of FIG. 7, first, in order to disconnect the line set up in the receiving stations 2A and 2B for which transmission of all the multicast packets has already been completed, disconnection for the receiving stations 2A and 2B is performed. The signal CS51 is continuously sent not only to the receiving stations 2A and 2B but also to the receiving station 2C for a predetermined disconnection signal continuous transmission time T4 (step S51). Each of the receiving stations 2A, 2B, and 2C that has received the disconnection signal CS51 confirms whether or not the local station is designated as the target station, and the target station of the disconnection signal CS51 is the local station. Each of the receiving stations 2A and 2B disconnects its own line (steps S52a and S52b).

  As for the receiving station 2C, since the target station of the disconnection signal CS51 is not the local station, the line setting state continues as it is. Therefore, the transmitting station 1 takes out the latest response signal which has been received so far from the receiving station 2C, and confirms the oldest serial number of the multicast packet indicating that it has already been received. The operation of retransmitting to the receiving station 2C is started from the data corresponding to the next sequence number of the sequence number of. Here, since the line of the receiving station 2C is reconfigured again, the sequence number of the retransmission multicast packet also starts from the first '1'.

  Therefore, as shown in the sequence chart of FIG. 7, the transmitting station 1 transmits three multicast packets CS53 of sequence numbers 1 to 3, for example, to the data to be retransmitted to the receiving station 2C first. It is generated and continuously transmitted as a downlink radio frame to the receiving station 2C (step S53). After that, if there is still data to be retransmitted to the receiving station 2C, the multicast packet with the next sequence number 4 and subsequent sequence numbers attached in each multicast packet transmission cycle T2 set in advance. Are sequentially generated, and are continuously transmitted to the receiving station 2C as downlink radio frames.

  Also, although the transmitting station constantly monitors the response signal from the receiving station 2C, even in the case of FIG. 7, the same operation as in the sequence chart of FIGS. 4A and 4B is performed, and the response from the receiving station 2C When the signal is sent back, if the oldest sequence number stored in the response signal is updated from the response signal in the previous slot cycle, transmission / reception of the multicast packet with the receiving station 2C It is determined that the operation has recovered normally. On the other hand, when the sequence number of the oldest number is not updated, the operation shifts to a multicast packet resending operation similar to the case of FIGS. 4A and 4B.

  In the case of FIG. 7, in the transmitting station 1, the values of the number of multicast packets to be transmitted at one time, the multicast packet transmission cycle T2, the number of retransmission executions threshold Nk, the receiving station reception state recovery waiting time T6, etc. , B and FIG. 6 may be changed. Furthermore, as to the judgment criteria for retransmission processing of multicast packets and line disconnection control to the receiving stations 2A, 2B and 2C as shown in FIGS. 4A and 4B, and FIG. 6 and FIG. The transmitting station 1 operates to perform retransmission processing of the multicast packet and control of line disconnection to the receiving stations 2A, 2B and 2C according to the judgment criteria set and changed. be able to.

(Description of the effect of the embodiment)
As described above in detail, in the embodiment according to the present invention, the following effects can be achieved.

  The first effect is that in communication from a plurality of (for example, N) multicast receiving stations (receiving stations 2A, 2B and 2C) toward one multicast transmitting station (transmitting station 1), a plurality of one line (a plurality of For example, the number of allocated lines can be reduced from a plurality (e.g., N) lines in the conventional system to one by sharing time-divisionally in N multicast receiving stations (receiving stations 2A, 2B, 2C) , Significant savings in the number of lines used.

  The second effect is to disconnect the link of a multicast receiving station (for example, receiving station 2C) having a bad reception state of packets and to delay file transfer to the multicast receiving station (for example, receiving station 2C). The point is that it is possible to improve the communication efficiency of a multicast receiving station (for example, receiving stations 2A and 2B) in a good reception state.

  The third effect is the assignment of sequence numbers required for connection-oriented communication, transmission of response signals, and communication control using them, the multicast transmitting station (transmitting station 1) and the multicast receiving stations (receiving stations 2A, 2B) , 2C), and performs connection-type communication with the data transmission terminal 4 on a one-to-one basis with the multicast transmission station (transmission station 1), and performs communication with the data reception terminals 5A, 5B, 5C. Connection-type communication is performed on a one-to-one basis with a multicast receiving station (receiving stations 2A, 2B, 2C), so that one communication partner can be seen from the data transmitting / receiving terminal side. It is possible to adopt a general-purpose communication method on the premise of one-to-one communication in comparison with the case where an expensive data transmission / reception terminal adopting a unique communication method for one-to-N communication is adopted. , It is that it is possible to expect a reduction of equipment costs.

  The fourth effect is that the response signal is always monitored after waiting for the response signal, instead of transmitting the next multicast packet, and if necessary, the packet is determined in each predetermined cycle as the multicast packet transmission cycle T2. If there is no need for retransmission, it is possible to further improve the reduction in throughput even if the delay in the communication satellite channel is taken into account by setting it as a communication method for transmitting multicast packets one after another. , It is possible to maintain the packet retransmission function.

(Supplementary note)
As is clear from the detailed description of the embodiment according to the present invention as described above, part or all of the above-described embodiment can be described as the following supplementary notes. It goes without saying that the invention is not limited to such a case.

  (Supplementary Note 1) A two-way wireless communication system constituting a VSAT (Very Small Aperture Terminal) system capable of two-way wireless communication via a communication satellite, comprising one multicast transmitting station and N (N: natural number) A one-to-N communication line with a multicast receiving station is assigned according to a DAMA (Demand Assign Multiple Access) method, and one line assigned as an uplink line from the multicast receiving station to the multicast transmitting station is Communication is performed by time division at a slot timing assigned to each of the N multicast receiving stations at each slot period predetermined as a transmission period using a frame conforming to a radio frame format of TDMA (Time Division Multiple Access) system Two-way wireless communication system shared by .

  (Supplementary Note 2) The multicast transmission station stores all data transmitted from the data transmission terminal in a storage device installed in the local station, and then divides the stored data into one or more multicast packets, and A sequence number indicating a transmission order is generated for each of the divided multicast packets, and further, each of the divided multicast packet and the generated sequence number is stored in each of two radio frames having an error detection function. After that, the two radio frames are connected in a set, and when there are a plurality of divided multicast packets, the two connected frames are further connected by a predetermined number, In the multicast packet transmission cycle predetermined as a transmission cycle, the communication Through the star, two-way radio communication system according to the Appendix 1 to the downlink radio frame, serially toward the N of the multicast receiving stations constituting a multicast target station.

  (Supplementary Note 3) Each of the multicast receiving stations transmits the data of the multicast packet in the downlink radio frame received from the multicast transmitting station via the communication satellite to a data receiving terminal, and the data receiving terminal Receiving the reception confirmation response indicating that the reception confirmation has been completed, the sequence number of the oldest number is taken out of the multicast packets in which the data corresponding to the reception confirmation response is stored, and is stored. A response signal storing the old sequence number is generated and stored in a frame having an error detection function, and the multicast is performed via the communication satellite for each slot timing allocated to each of the multicast receiving stations. The two-way wireless communication system according to supplementary note 2, which transmits toward a transmitting station.

  (Supplementary Note 4) The multicast transmitting station is receiving the sequence number of the oldest number in the response signal from each of the multicast receiving stations received via the communication satellite in the previous slot cycle The multicast reception station compares the sequence number with the oldest number in the response signal from the multicast reception station and, as a result of comparison, a predetermined number of multicast reception stations among one or more of the multicast reception stations. It is detected that the sequence number of the oldest number in the response signal received this time a fixed number of times is not updated from the sequence number of the oldest number in the response signal received in the previous slot cycle In the event of a failure, a multicast with a sequence number later than that of the oldest The door packet in the next said multicast packet transmission period, two-way radio communication system according to the appendix 3 to the via communication satellite retransmits towards each of said multicast receiving stations.

  (Supplementary Note 5) The multicast transmitting station re-sends the multicast packet, and then the sequence number of the oldest number in the response signal from the multicast receiving station that has triggered the re-transmission is The sequence number of the oldest number in the response signal received in the slot cycle is compared and, as a result of the comparison, the sequence number of the oldest number in the response signal received in the slot cycle of the previous time If it is detected that it has not been updated, the retransmission operation is activated again, and even if the retransmission operation is repeated a predetermined number of times as the retransmission frequency threshold value, within the response signal received in the previous slot cycle of the previous time When it is detected that the update has not been performed from the sequence number of the oldest of the The receiving station deletes the receiving station from the multicast packet transmission destination receiving station registration list in which the receiving station for multicast is registered, and simultaneously sends a disconnection signal for instructing disconnection of the line to the multicast receiving station. The two-way wireless communication system according to claim 4, wherein continuous transmission is performed for a time.

  (Supplementary Note 6) The multicast transmission station adds the sequence number of the oldest number in the response signal from each of the multicast reception stations received via the communication satellite to a transmission multicast packet transmitted from the own station. When it is detected that the difference between the two sequence numbers is greater than or equal to a predetermined threshold value as a result of comparison with the corresponding sequence numbers, the multicast packet transmission cycle is lengthened by a predetermined length. The two-way radio communication system according to any of the above remarks 3 to 5, wherein:

  (Supplementary Note 7) Each of the multicast receiving stations monitors the continuity of the sequence number attached to the multicast packet from each of the multicast receiving stations received via the communication satellite, and the omission of the sequence number occurs. If it is detected, it is determined that a packet loss of the multicast packet corresponding to the sequence number is occurring, and the packet loss in addition to the sequence number of the oldest number indicating reception confirmation completed. Creating a response signal in which the sequence number assigned to the multicast packet in which the event occurred is stored as a packet loss occurrence sequence number, and via the communication satellite at the slot timing assigned to the multicast receiving station Supplementary note 3 for transmitting toward the multicast transmitting station 6 two-way radio communication system according to one of.

  (Supplementary Note 8) In the response signal from each of the multicast receiving stations received via the communication satellite, the multicast transmitting station may receive the packet loss in addition to the oldest serial number indicating reception complete. When it is detected that an occurrence sequence number is stored, a multicast packet to which a sequence number corresponding to the packet loss occurrence sequence number is attached is designated as a multicast packet to be transmitted next, for retransmission. Together with a multicast packet to which a sequence number is assigned after the oldest sequence number indicated, and in the next multicast packet transmission cycle, retransmitting toward each of the multicast receiving stations via the communication satellite An interactive wireless communication system according to appendix 7.

  (Supplementary Note 9) Each of the multicast receiving stations monitors a reception level or BER (Bit Error Rate) indicating the reception state of the own station, and the reception level or BER can be received from a threshold that can be determined in advance as a limit that can be received. When it is detected that the reception deterioration state of the own station has occurred, it is determined that the reception deterioration state of the own station has occurred, and the occurrence of the reception deterioration state of the own station is indicated in addition to the sequence number of the oldest number indicating reception confirmation completed. The response signal storing the reception degradation state occurrence information is prepared, and transmitted toward the multicast transmitting station via the communication satellite at the slot timing allocated to the multicast receiving station The two-way wireless communication system according to any of the above.

  (Supplementary note 10) If each of the multicast receiving stations determines that the reception degradation state has occurred, it starts a timer and continues the reception degradation state monitoring time set in advance for a predetermined reception degradation state monitoring time. It is monitored whether or not it is occurring, and when the reception degradation state continues to occur for the reception degradation state monitoring time, the line of the own station is disconnected autonomously. A two-way wireless communication system according to claim 1.

  (Supplementary note 11) If each of the multicast receiving stations recovers from the reception degradation state of its own station to a good reception state before the time until the reception degradation state monitoring time elapses, the timer operation of the started timer In addition to the sequence number of the oldest number indicating reception confirmation completed, the response signal storing the reception deterioration state recovery information indicating recovery from the reception deterioration state is created and assigned to the multicast receiving station. The two-way radio communication system according to claim 10, wherein the communication is transmitted toward the multicast transmission station via the communication satellite at the slot timing.

  (Supplementary Note 12) The multicast transmitting station monitors the response signal from each of the multicast receiving stations received via the communication satellite, and the oldest of the reception number indicating the reception confirmation has been received in the received response signal. In addition to the sequence number, when it is detected that the reception degradation state occurrence information is stored, the timer is activated and the reception degradation state occurrence occurs before the predetermined reception station reception state recovery waiting time elapses. When it is not possible to receive the response signal storing the reception deterioration state recovery information indicating that the reception state has been restored to a good reception state from the multicast receiving station that has sent back the response signal in which the information is stored Delete the multicast reception station concerned from the multicast packet transmission destination reception station registration list in which the reception stations targeted for multicast are registered. Two-way radio communication system described in conjunction with, a disconnect signal for instructing the line disconnection with respect to the multicast receiving station, between the disconnect signal successive sending time predetermined, the note 11 to be continuous transmissions to.

  (Supplementary Note 13) The multicast transmission station may perform the multicast reception station in which the oldest sequence number in the response signal is not updated even in the retransmission operation repeatedly performed the number of times corresponding to the retransmission frequency threshold, or The multicast reception in which the response signal storing the reception degradation state recovery information indicating recovery to a good reception state is not received until the reception station reception state recovery waiting time elapses Station is deleted from the multicast packet transmission destination reception station registration list, and the multicast packet to be transmitted still remains after continuously transmitting a disconnection signal instructing the multicast reception station to disconnect the line. If the line is disconnected, the remaining multicast receivers other than the multicast receiver are disconnected. Two-way radio communication system according to the appendix 5 or 12 performed on each preparative receiving station, the transmitting operation of the remained multicast packets.

  (Supplementary Note 14) The multicast transmitting station completes transmission of all the multicast packets to be transmitted to the remaining multicast receiving stations other than the multicast receiving station whose line has been disconnected, and the remaining multicast receiving stations respectively After receiving the response signal storing the last sequence number of the transmitted multicast packet, no new data to be transmitted is generated until a predetermined time as a no-communication time elapses The bidirectional signal according to supplementary note 13, wherein a disconnection signal for instructing a disconnection of the line to the remaining multicast receiving stations is continuously sent during the disconnection signal continuous transmission time when the non-communication time has elapsed. Wireless communication system.

  (Supplementary Note 15) The multicast transmitting station continuously transmits the disconnection signal to each of the remaining multicast receiving stations other than the disconnected multicast receiving station, and then transmits the disconnection signal to the multicast receiving station. The two-way wireless communication system according to claim 14, wherein the line via the communication satellite is reconfigured again, and the transmission operation of the remaining multicast packets to be transmitted to the disconnected multicast receiving station is resumed.

  (Supplementary note 16) The multicast transmission station communicates with a data transmission terminal on the premise of a connection-oriented communication method of one-to-one communication, and each multicast reception station performs connection-oriented communication with a data reception terminal in one-to-one communication. The two-way wireless communication system according to any one of the above-mentioned additional claims 1 to 15, which performs communication based on a scheme.

  (Supplementary note 17) A two-way wireless communication method in a two-way wireless communication system constituting a VSAT (Very Small Aperture Terminal) system capable of two-way wireless communication via a communication satellite, comprising: N: A natural number) 1-to-N communication line with the multicast receiving stations is allocated by DAMA ((Demand Assign Multiple Access) method, and is assigned as an uplink line from the multicast receiving station to the multicast transmitting station Slot timing allocated to each of the N multicast receiving stations at each slot cycle predetermined as a transmission cycle, using a frame conforming to a radio frame format of TDMA (Time Division Multiple Access) system, using Communication by time division in Two-way radio communication method to use.

  (Supplementary note 18) The multicast transmission station stores all data transmitted from the data transmission terminal in a storage device installed in the local station, and then divides the stored data into one or more multicast packets, and A sequence number indicating a transmission order is generated for each of the divided multicast packets, and further, each of the divided multicast packet and the generated sequence number is stored in each of two radio frames having an error detection function. After that, the two radio frames are connected in a set, and when there are a plurality of divided multicast packets, the two connected frames are further connected by a predetermined number, In the multicast packet transmission cycle predetermined as the transmission cycle, the communication Via satellite, as downlink radio frame, two-way radio communication method according to the appendix 17 to be transmitted consecutively towards the N of the multicast receiving stations constituting a multicast target station.

  (Supplementary note 19) Each of the multicast reception stations transmits data of the multicast packet in the downlink radio frame received from the multicast transmission station via the communication satellite to a data reception terminal, and the data reception terminal Receiving the reception confirmation response indicating that the reception confirmation has been completed, the sequence number of the oldest number is taken out of the multicast packets in which the data corresponding to the reception confirmation response is stored, and is stored. A response signal storing the old sequence number is generated and stored in a frame having an error detection function, and the multicast is performed via the communication satellite for each slot timing allocated to each of the multicast receiving stations. 24. The two-way wireless communication method according to appendix 18, which transmits toward a transmitting station.

  (Supplementary Note 20) The multicast transmitting station is receiving the sequence number of the oldest number in the response signal from each of the multicast receiving stations received via the communication satellite in the previous slot cycle The multicast reception station compares the sequence number with the oldest number in the response signal from the multicast reception station and, as a result of comparison, a predetermined number of multicast reception stations among one or more of the multicast reception stations. It is detected that the sequence number of the oldest number in the response signal received this time a fixed number of times is not updated from the sequence number of the oldest number in the response signal received in the previous slot cycle In the case of a multi-key device with a sequence number that is later than the sequence number of the oldest Strike packet in the next said multicast packet transmission period, through the communication satellite, two-way radio communication method according to the appendix 19 to be retransmitted toward each of the multicast receiving stations.

  (Supplementary note 21) The multicast transmitting station re-sends the multicast packet, and then the sequence number of the oldest number in the response signal from the multicast receiving station that has triggered the re-sending is The sequence number of the oldest number in the response signal received in the slot cycle is compared and, as a result of the comparison, the sequence number of the oldest number in the response signal received in the slot cycle of the previous time If it is detected that it has not been updated, the retransmission operation is activated again, and even if the retransmission operation is repeated a predetermined number of times as the retransmission frequency threshold value, within the response signal received in the previous slot cycle of the previous time When it is detected that the update has not been performed from the sequence number of the oldest of the The receiving station is deleted from the multicast packet transmission destination receiving station registration list in which the receiving station for multicast is registered, and a disconnection signal continuously instructing a disconnection signal to the multicast receiving station is established. 20. The two-way wireless communication method according to supplementary note 20, wherein continuous transmission is performed for a time.

  (Supplementary note 22) The multicast transmitting station adds the sequence number of the oldest number in the response signal from each of the multicast receiving stations received via the communication satellite to a transmission multicast packet transmitted from the own station. When it is detected that the difference between the two sequence numbers is greater than or equal to a predetermined threshold value as a result of comparison with the corresponding sequence numbers, the multicast packet transmission cycle is lengthened by a predetermined length. The two-way wireless communication method according to any one of appendices 19 to 21 which is controlled as described above.

  (Supplementary Note 23) Each of the multicast receiving stations monitors the continuity of the sequence number attached to the multicast packet from each of the multicast receiving stations received via the communication satellite, and the omission of the sequence number occurs. If it is detected, it is determined that a packet loss of the multicast packet corresponding to the sequence number is occurring, and the packet loss in addition to the sequence number of the oldest number indicating reception confirmation completed. Creating a response signal in which the sequence number assigned to the multicast packet in which the event occurred is stored as a packet loss occurrence sequence number, and via the communication satellite at the slot timing assigned to the multicast receiving station Appendix 19 for transmitting toward the multicast transmission station Bidirectional radio communication method according to one of the stone 22.

  (Supplementary Note 24) The multicast transmitting station may include, in the response signal from each of the multicast receiving stations received via the communication satellite, the packet loss in addition to the oldest serial number indicating reception complete. When it is detected that an occurrence sequence number is stored, a multicast packet to which a sequence number corresponding to the packet loss occurrence sequence number is attached is designated as a multicast packet to be transmitted next, for retransmission. Together with a multicast packet to which a sequence number is assigned after the oldest sequence number indicated, and in the next multicast packet transmission cycle, retransmitting toward each of the multicast receiving stations via the communication satellite 24. A two-way wireless communication method according to appendix 23.

  (Supplementary note 25) Each of the multicast receiving stations monitors a reception level or a bit error rate (BER) indicating the reception state of the own station, and the reception level or BER can be received from a threshold that can be determined in advance as a limit that can be received. When it is detected that the reception deterioration state of the own station has occurred, it is determined that the reception deterioration state of the own station has occurred, and the occurrence of the reception deterioration state of the own station is indicated in addition to the sequence number of the oldest number indicating reception confirmation completed. The response signal storing the reception degradation state occurrence information is prepared, and transmitted toward the multicast transmitting station via the communication satellite at the slot timing allocated to the multicast receiving station The two-way wireless communication method according to any one of the above.

  (Supplementary note 26) If each of the multicast receiving stations determines that the reception degradation state has occurred, it starts a timer, and continues the reception degradation state monitoring time set in advance for a predetermined reception degradation state monitoring time. It is monitored whether or not it is occurring, and when the reception degradation state continues to occur during the reception degradation state monitoring time, the line of the own station is disconnected autonomously. The two-way wireless communication method according to

  (Supplementary note 27) If the multicast reception station recovers from the reception degradation state of its own station to a good reception state before the time until the reception degradation state monitoring time elapses, the timer operation of the started timer In addition to the sequence number of the oldest number indicating reception confirmation completed, the response signal storing the reception deterioration state recovery information indicating recovery from the reception deterioration state is created and assigned to the multicast receiving station. The two-way wireless communication method according to appendix 26, wherein the communication is transmitted to the multicast transmission station via the communication satellite at the slot timing.

  (Supplementary note 28) The multicast transmitting station monitors the response signal from each of the multicast receiving stations received via the communication satellite, and the oldest of the reception number indicating the reception confirmation has been received in the received response signal. In addition to the sequence number, when it is detected that the reception degradation state occurrence information is stored, the timer is activated and the reception degradation state occurrence occurs before the predetermined reception station reception state recovery waiting time elapses. When it is not possible to receive the response signal storing the reception deterioration state recovery information indicating that the reception state has been restored to a good reception state from the multicast receiving station that has sent back the response signal in which the information is stored Delete the multicast reception station concerned from the multicast packet transmission destination reception station registration list in which the reception stations targeted for multicast are registered. As well as, a disconnection signal for instructing the line disconnection with respect to the multicast receiving station, between the disconnect signal successive sending time a predetermined two-way wireless communication method according to the appendix 27 to continuous transmission.

  (Supplementary note 29) The multicast transmission station, even in the retransmission operation repeatedly performed the number of times corresponding to the retransmission frequency threshold, the multicast reception station in which the oldest serial number in the response signal is not updated, or The multicast reception in which the response signal storing the reception degradation state recovery information indicating recovery to a good reception state is not received until the reception station reception state recovery waiting time elapses Station is deleted from the multicast packet transmission destination reception station registration list, and the multicast packet to be transmitted still remains after continuously transmitting a disconnection signal instructing the multicast reception station to disconnect the line. If the line is disconnected, the remaining multicast receivers other than the multicast receiver are disconnected. Bidirectional radio communication method according to the appendix 21 or 28 carried out for each preparative receiving station, the transmitting operation of the remained multicast packets.

  (Supplementary note 30) The multicast transmitting station completes transmission of all the multicast packets to be transmitted to the remaining multicast receiving stations other than the multicast receiving station whose line has been disconnected, and the remaining multicast receiving stations respectively After receiving the response signal storing the last sequence number of the transmitted multicast packet, no new data to be transmitted is generated until a predetermined time as a no-communication time elapses The bidirectional signal according to supplementary note 29, wherein a disconnection signal for instructing a disconnection of the line to the remaining multicast receiving stations is continuously sent during the disconnection signal continuous transmission time when the non-communication time has elapsed. Wireless communication method.

  (Supplementary Note 31) The multicast transmitting station continuously transmits the disconnection signal to each of the remaining multicast receiving stations other than the multicast receiving station whose line has been disconnected, and then transmits the disconnection signal to the multicast receiving station whose line is disconnected. 30. The two-way wireless communication method according to claim 30, wherein the line via the communication satellite is reconfigured again, and the transmission operation of the remaining multicast packets to be transmitted to the multicast receiving station whose line is disconnected is resumed.

  (Supplementary note 32) The multicast transmission station communicates with a data transmission terminal on the premise of a connection-oriented communication method of one-to-one communication, and each multicast reception station performs connection-oriented communication with a data reception terminal at one-to-one communication. The two-way wireless communication method according to any one of appendages 17 to 31, which performs communication based on a scheme.

  The configuration of the preferred embodiment of the present invention has been described above. However, it should be noted that such an embodiment is merely an example of the present invention and does not limit the present invention. It will be readily understood by those skilled in the art that various modifications and variations can be made according to a particular application without departing from the scope of the present invention.

1 Multicast transmitter (transmitter)
2A, 2B, 2C multicast receiver (receiver)
3 communication satellite 4 data transmitting terminal 5A, 5B, 5C data receiving terminal 6 storage device 11 communication cable 12A, 12B, 12C communication cable D1a, D1b, D1c, D1d, D1e, D1f, D1g,
D1h, D1i, D1j, D1k, D1l downlink radio frame
(Radio frame from transmitting station to receiving station)
D2a, D2b, D3a, D3b, D4a, D4b Uplink Radio Frame
(A radio frame from the receiving station to the transmitting station)
D5a, D5b HDLC frame D6a, D6b PPP frame D7 Data from the data transmission terminal D8a, D8b, D8c Data packet to the data reception terminal D9a, D9b, D9c Response packet from the data reception terminal D11a, D11b, D11c, D11d UW Unique Word)
D12 Frame information section D13 Control signal sections D14a, D14b, D14c, D14d Data section D21 Preamble D22 UW (Unique Word)
D23 Response signal D24 Forward guard time D25 Backward guard time D31 Preamble D32 UW (Unique Word)
D33 response signal D34 forward guard time D35 backward guard time D51 forward flag D52 identification information D53 sequence number D54 FCS (Frame Check Sequence)
D55 Backward flag D56 Mark D61 Forward flag D62 PPP header D63 Multicast packet D64 FCS (Frame Check Sequence)
D65 Backward flag D66 Mark T1 Slot cycle T2 Multicast packet transmission cycle T3 No communication time T4 Disconnected signal continuous transmission time T5 Reception degradation status monitoring time T6 Receiving station reception status recovery waiting time ta, tb, tc Slot timing

Claims (9)

A two-way wireless communication system constituting a VSAT (Very Small Aperture Terminal) system capable of two-way wireless communication via a communication satellite, comprising one multicast transmitting station and N (N is a natural number) multicast receiving stations The one-to-N communication line between them is assigned by the DAMA (Demand Assign Multiple Access) method, and one line assigned as an uplink line from the multicast receiving station to the multicast transmitting station is assigned to the TDMA (Time Division). Communication is performed by time division at slot timings assigned to each of the N multicast receiving stations in each slot cycle determined in advance as a transmission cycle using a frame conforming to a radio frame format of the Multiple Access scheme. , Share,
The multicast transmission station stores all data transmitted from the data transmission terminal in a storage device installed in the local station, divides the stored data into one or more multicast packets, and divides the data. A sequence number indicating the transmission order is generated for each multicast packet, and further, each of the divided multicast packet and the generated sequence number is stored in each of two radio frames having an error detection function. When two radio frames are connected in a set, and there are a plurality of divided multicast packets, the two connected frames are further connected by a predetermined number, and they are transmitted in advance as a transmission period. At the specified multicast packet transmission cycle, via the communication satellite As downlink radio frame, two-way radio communication system, characterized by continuously transmitted toward to the N of the multicast receiving stations constituting a multicast target station.   Each of the multicast receiving stations transmits the data of the multicast packet in the downlink radio frame from the multicast transmitting station received via the communication satellite to a data receiving terminal, and the reception confirmation from the data receiving terminal When the reception confirmation response indicating completion is received, the sequence number of the oldest number is taken out and stored among the multicast packets in which the data corresponding to the reception acknowledgment is stored, and the stored oldest sequence A response signal storing a number is generated and stored in a frame having an error detection function, and directed to the multicast transmission station via the communication satellite for each slot timing allocated to each of the multicast reception stations. The two-way radio communication system according to claim 1, characterized in that   The multicast transmission station receives the sequence number of the oldest number in the response signal from each of the multicast reception stations received via the communication satellite, and receives the corresponding multicast received in the previous slot cycle. As a result of comparison with the sequence number of the oldest number in the response signal from the station, as a result of comparison, a predetermined number of times in a predetermined number of multicast receiving stations among one or more of the multicast receiving stations When it is detected that the sequence number of the oldest number in the received response signal is not updated from the sequence number of the oldest number in the response signal received in the previous slot cycle, A multicast packet to which a sequence number later than the sequence number of the oldest number is attached The, in the next said multicast packet transmission period, two-way radio communication system according to claim 2, wherein via the communication satellite, characterized by retransmission toward each of the multicast receiving stations.   The multicast transmitting station receives the sequence number of the oldest number in the response signal from the multicast receiving station that triggered the retransmission after resending the multicast packet in the previous slot cycle. As a result of comparison with the sequence number of the oldest number in the response signal that was being sent, as a result of comparison, the sequence number of the oldest number in the response signal that was received in the previous slot cycle is not updated If it is detected, the retransmission operation is activated again, and even if the retransmission operation is repeated a predetermined number of times as the retransmission frequency threshold, the oldest in the response signal received in the previous slot cycle is also received. If it is detected that the sequence number has not been updated, the multicast reception station that triggered the retransmission is While deleting the multicast packet transmission destination receiving station registration list registering the receiving station to be multicasted and instructing the multicast receiving station to disconnect the line during the disconnection signal continuous transmission time determined in advance The two-way wireless communication system according to claim 3, wherein the continuous transmission is performed.   The multicast transmitting station is the sequence number of the oldest number in the response signal from each of the multicast receiving stations received via the communication satellite, the sequence number assigned to the transmission multicast packet transmitted from the own station, and When it is detected that the difference between the two sequence numbers is greater than or equal to a predetermined threshold value as a result of comparison and comparison, control is performed to lengthen the multicast packet transmission cycle by a predetermined length. The two-way wireless communication system according to any one of claims 2 to 4, characterized in that:   Each of the multicast receiving stations monitors the continuity of the sequence number assigned to the multicast packet from each of the multicast receiving stations received via the communication satellite, and it is determined that a missing sequence number has occurred. When it is detected, it is determined that a packet loss of the multicast packet corresponding to the sequence number has occurred, and the packet loss has occurred in addition to the sequence number of the oldest number indicating reception confirmation completed. The response signal storing the sequence number attached to the multicast packet as a packet loss occurrence sequence number is created, and the multicast transmission station is transmitted via the communication satellite at the slot timing assigned to the multicast reception station Sending the information to the destination. Two-way radio communication system according to one of stone 5.   In the response signal from each of the multicast receiving stations received via the communication satellite, the multicast transmitting station has the packet loss occurrence sequence number in addition to the oldest serial number indicating reception confirmation completed in the response signal from each of the multicast receiving stations. When it is detected that the packet is stored, the multicast packet to which a sequence number corresponding to the packet loss occurrence sequence number is attached for retransmission is used as the multicast packet to be transmitted next, the oldest indicating the reception confirmation completed. The multicast packet is retransmitted toward each of the multicast receiving stations via the communication satellite in the next multicast packet transmission cycle together with a multicast packet to which a sequence number later than a sequence number is assigned. The two-way wireless communication system according to claim 6.   Each of the multicast receiving stations monitors the reception level or bit error rate (BER) indicating the reception status of the own station, and the reception level or BER is lower than a predetermined receivable threshold as a receivable limit value. If it detects a reception degradation condition of its own station, it will determine that a reception degradation condition has occurred that indicates the occurrence of a reception degradation condition of its own in addition to the sequence number of the oldest number indicating reception confirmation completed. 8. A response signal storing information is prepared, and transmitted toward the multicast transmission station via the communication satellite at the slot timing assigned to the multicast reception station. The two-way wireless communication system according to any one of the above.   A two-way wireless communication method in a two-way wireless communication system constituting a VSAT (Very Small Aperture Terminal) system capable of two-way wireless communication via a communication satellite, comprising one multicast transmitting station and N (N: natural number) 1 line assigned as an uplink line from the multicast receiving station to the multicast transmitting station by assigning a 1-to-N communication line to and from each of the multicast receiving stations according to the DAMA (Demand Assign Multiple Access) method Time division using the frame conforming to the radio frame format of the TDMA (Time Division Multiple Access) system, at slot timings allocated to each of the N multicast receiving stations at each slot period predetermined as a transmission period, Share and communicate with each other The multicast transmission station stores all the data transmitted from the data transmission terminal in a storage device installed in the local station, divides the stored data into one or more multicast packets, and divides the data. A sequence number indicating the transmission order is generated for each multicast packet, and further, each of the divided multicast packet and the generated sequence number is stored in each of two radio frames having an error detection function. When two radio frames are connected in a set, and there are a plurality of divided multicast packets, the two connected frames are further connected by a predetermined number, and they are transmitted in advance as a transmission period. At the specified multicast packet transmission cycle, A two-way wireless communication method comprising: continuously transmitting toward the N multicast receiving stations constituting a multicast target station as a reverse link wireless frame.

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