JP2009111466A - Mobile station, base station, radio communication system, and radio communication method - Google Patents

Abstract

When performing wireless communication with a base station connected to another base station using a real-time data transfer protocol (RTP) over an IP communication network, silence is prevented from occurring even when a handover is executed.
In a mobile station that performs radio communication with a base station connected to another base station using a real-time data transfer protocol (RTP) over an IP communication network, a first buffer that accumulates a received signal from a handover source base station CS1 224, the second buffer 226 that accumulates the received signal from the handover destination base station CS2, and the received signal accumulated in the first buffer 224 and the second buffer 226 are compared to determine the time difference between the received signals. And a terminal control unit 210 that switches a signal to be played back from the first buffer 224 to the second buffer 226 based on the time difference detected by the time difference detection unit.
[Selection] Figure 4

Description

  The present invention relates to a mobile station, a base station, a radio communication system, and a radio communication method in a radio communication system in which a base station transmits packets using a real-time data transfer protocol (RTP) over an IP communication network.

  In recent years, mobile stations such as PHS (Personal Handy phone System) and mobile phones have become widespread, making it possible to make calls and obtain information regardless of location or time. Such a mobile station connects to a communication network by performing wireless communication with base stations arranged at a predetermined interval. Then, the base station communicates with a base station within the communicable range of the communication partner to establish voice communication between the mobile stations. Such base stations are currently connected by an integrated digital network (ISDN).

  The total digital communication network is a public telephone network formed as a digital line, can communicate at a signal transmission rate of 64 kbps with at least one channel, and can improve the stability of voice communication between mobile stations. On the other hand, ADSL (Asymmetric Digital Subscriber Line), which has been rapidly spreading in recent years, has a transmission speed of several M to several tens of Mbps, and further, FTTH (Fiber To The Home) using an optical fiber transmits several hundred Mbps. Allows for speed. Therefore, in the wireless communication system by the mobile station, it is considered to replace the general digital communication network, which was initially superior in transmission speed and stability, with an IP (Internet Protocol) communication network having a higher transmission speed. Yes.

  If the VoIP (Voice over Internet Protocol) or real-time data transfer protocol (RTP: Real-time Transport Protocol, hereinafter simply referred to as RTP) is used instead of the general digital communication network, the transmission speed can be improved. The communication occupancy time can be shortened by packetizing data, and one communication line can be shared for a plurality of calls, so that the cost required for one line call can be reduced. Become. Under such a background, a wireless communication system (VoIP: Voice Over IP) using an IP communication network has been put into practical use.

  FIG. 7 is a block diagram for explaining a radio communication system using the RTP in the IP communication network. In the wireless communication system 10, the mobile station PS1 and the mobile station PS2 perform voice communication. Accordingly, as shown in FIG. 7 (a), the mobile station PS1 performs radio communication with the base station CS1 within the wireless coverage, the mobile station PS2 performs radio communication with the base station CS3, and the base station CS1 and the base station CS3. Are connected through the IP communication network 40.

  Here, when the mobile station PS1 moves in the direction of the arrow, a distance from the base station CS1 is generated, and the radio wave that arrives weakens. Therefore, so-called handover is performed in which communication is maintained by switching the connected base station CS1 to another base station CS2. However, if the communication path is switched suddenly by handover, a silent time occurs until the packet arrives through another path. In order to avoid such an adverse effect, in recent years, when a handover is performed as shown in FIG. 7B, a communication line is opened in advance with the base station CS2 to which the handover is switched, and both the base stations CS1 and CS2 are connected. A method of executing wireless communication in parallel is adopted.

  In the state of FIG. 7B, the mobile station PS1 and both base stations CS1 and CS2 connect RTP sessions, and packets are transmitted and received in both sessions. The packet transmission from the mobile station PS2 to the mobile station PS1 at this time will be described. The packet transmitted from the mobile station PS2 is duplicated by the base station CS3, and either the switching source base station CS1 or the switching destination base station CS2 Also sent to. Then, the mobile station PS1 that has received the packet from both the base stations CS1 and CS2 discards the packet from the switching destination base station CS2, and reproduces the packet of the switching source base station CS1.

  Further, the transmission of a packet from the mobile station PS1 to the mobile station PS2 will be described. The mobile station PS1 transmits the same packet to both the base stations CS1 and CS2, and the packet passes through both base stations CS1 and CS2. Are aggregated in the base station CS3. The base station CS3 discards the packet from the switching destination base station CS2, and transmits the packet of the switching source base station CS1 to the mobile station PS2.

  When the mobile station PS1 further moves and communication between the mobile station PS1 and the base station CS1 becomes difficult, as shown in FIG. 7C, a handover is executed, and a session between the mobile station PS1 and the base station CS1 is established. To be released. After the handover, the mobile station PS2 reproduces the packet that has passed through the switching destination base station CS2, and similarly the mobile station PS1 reproduces the packet that has passed through the switching destination base station CS2.

In the handover, since the arrival time of the voice differs depending on the line switching, there may be a silent time due to delay. Patent Document 1 includes a silence detection unit that detects a silence signal from voice data and a memory that accumulates voice data. The voice data is stored in the memory from the start of communication or when silence is detected, and at the time of handover or channel switching. There has been proposed a mobile phone system that reproduces voice based on voice data in the memory even when there is no voice data. In Patent Document 2, the voice is D / A converted at the time of reception and stored in a buffer, and the stored voice is D / A converted and output for a speaker during handover, so The structure which shortens the interruption of the produced silence is disclosed.
Japanese Patent Laid-Open No. 2001-45560 Japanese Patent Laid-Open No. 9-009326

  However, when base stations are connected by RTP (VoIP), the dispersion of line delay is larger than that of the integrated digital communication network (ISDN).

  Furthermore, since RTP (VoIP) is not aware of the interval and order of arrival of packets, it is necessary to provide a jitter buffer in order to absorb delay and fluctuation. For this reason, it takes time to accumulate the jitter buffer in the handover destination base station, which may cause a delay larger than that of the integrated digital communication network (ISDN).

  Therefore, even if wireless communication is executed in parallel with both the mobile station and the handover source / destination base stations as described above, the delay cannot be absorbed and there is a possibility that silence is generated. In addition, when a specific sound (sound just before silence) is reused as in Patent Document 1 and Patent Document 2, if the delay difference becomes large, the repeated sound is played back longer, and there is a possibility of feeling uncomfortable. .

  Therefore, the present invention can prevent silence from occurring even when a handover is performed when wireless communication is performed with a base station connected to another base station using a real-time data transfer protocol (RTP) over an IP communication network. An object is to provide a mobile station, a base station, a wireless communication system, and a wireless communication method.

  In order to solve the above problems, a typical configuration of a mobile station according to the present invention is a mobile station that performs wireless communication with a base station connected to another base station using a real-time data transfer protocol (RTP) over an IP communication network. The first buffer for storing the received signal from the handover source base station, the second buffer for storing the received signal from the handover destination base station, and the received signals stored in the first buffer and the second buffer are compared. A time difference detection unit that detects a time difference when each received signal is received, and a control unit that switches a signal to be played back from the first buffer to the second buffer based on the time difference detected by the time difference detection unit. It is characterized by.

  According to the above configuration, the time difference between the handover source / destination audio signals is detected in the mobile station, and the deviation of the audio signals at the time of executing the handover is synchronized using the data in the first buffer or the second buffer based on the time difference. Therefore, it is possible to prevent silence from occurring.

  When the received signal arriving from the handover destination base station is delayed from the handover source base station, the control unit may shift the head address of the second buffer backward based on the time difference detected by the time difference detection unit. Good. “Back” means the rear in the arrival order (time) direction. As a result, a voice signal arriving late from the handover destination base station can be carried forward, and synchronization can be achieved.

  In a case where the received signal arriving from the handover destination base station is ahead of the handover source base station, the control unit may extend the accumulation amount of the second buffer based on the time difference detected by the time difference detection unit. That is, by increasing the audio signal stored in the second buffer, the second buffer relatively accumulates the audio signal for a longer time, and stops the progress of the audio signal that has advanced and synchronizes. It becomes possible to plan.

  The first buffer starts storing when a voice call starts, when a handover start is predicted, or when a buffer once stored is used, and the second buffer starts when a connection with the handover destination base station starts Accumulation may be started at the opportunity. In other words, the first buffer may be stored in advance from the beginning of the voice call, but storing in the buffer causes a delay in voice even when a call is made without moving, for example. Therefore, delay can be suppressed as much as possible by starting accumulation after the start of handover is predicted.

  The time when the handover start is predicted may be a case where the communication quality of the mobile station or the currently connected base station is lowered to a predetermined standard or lower. As the communication quality, for example, a received signal strength indicator (RSSI) can be suitably used.

  When the handover is completed, the control unit expands the storage amount of the second buffer and stores and supplements the received signal when the capacity of the second buffer is less than the capacity of the first buffer. Also good. When the next handover is performed, the second buffer is used as the first buffer. According to the above configuration, the second buffer can be used smoothly as the first buffer.

  The control unit expands or intermittently reproduces the sound from the first buffer, and reproduces the sound signal read out from the sound signal reaching the first buffer over a longer time, thereby causing the sound signal to be output to the first buffer. May be accumulated. This makes it possible to store a buffer during a voice call.

  A typical configuration of a base station according to the present invention is a base station connected to another base station by a real-time data transfer protocol (RTP) by an IP communication network, with respect to a mobile station that performs radio communication with the base station. A handover prediction notifying unit is provided that transmits a signal for notifying that buffering of a received signal should be started when the communication quality with the mobile station falls below a predetermined standard.

  In a wireless communication system including a mobile station and a plurality of base stations that perform wireless communication with the mobile station, the mobile station includes a first buffer that accumulates reception signals from the handover source base station, and reception from the handover destination base station. A second buffer for accumulating signals, a time difference detecting unit for detecting a time difference for receiving each received signal by comparing the received signals accumulated in the first buffer and the second buffer, and a time difference detected by the time difference detecting unit And a control unit that switches a signal to be reproduced from the first buffer to the second buffer based on the base station, the base station is connected to another base station by a real-time data transfer protocol (RTP) by an IP communication network, and When the communication quality with a mobile station that performs wireless communication with a base station falls below a predetermined standard, buffering of received signals should be started. Wireless communication system comprising the handover prediction notification unit for transmitting a signal for notifying that.

  A representative configuration of a radio communication method according to the present invention is that a mobile station that performs radio communication with a base station connected to another base station using a real-time data transfer protocol (RTP) by an IP communication network, Are stored in the first buffer, the received signal from the handover destination base station is stored in the second buffer, and the received signals stored in the first buffer and the second buffer are respectively compared. And a step of detecting a time difference when the received signal is received and a step of switching a signal to be played back from the first buffer to the second buffer based on the time difference detected by the time difference detection unit.

  According to the present invention, when wireless communication is performed with a base station connected to another base station using a real-time data transfer protocol (RTP) over an IP communication network, silence can be prevented from occurring even when a handover is executed. Mobile station, base station, wireless communication system, and wireless communication method can be provided.

  An embodiment of a mobile station, a base station, a wireless communication system, and a wireless communication method according to the present invention will be described. Note that dimensions, materials, and other specific numerical values shown in the following embodiments are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified.

  Mobile stations such as mobile phones and PHS can communicate (call) with other mobile stations in remote locations via a wireless communication system. At this time, the mobile station has established wireless communication with base stations arranged at predetermined intervals. In this embodiment, instead of or in addition to an existing integrated digital communication network (ISDN), an IP communication network capable of reducing operation costs is used, and communication between base stations is realized by RTP. Thus, it is possible to make a voice call seamlessly even when handover is necessary.

  The RTP described above corresponds to a session layer equivalent to VoIP, and also functions as an upper protocol of UDP (User Datagram Protocol). In addition, RTCP (RTp Control Protocol) that performs minimum delivery confirmation and monitoring is attached as a control protocol. Such RTP is suitable for transferring video and audio data in real time, and data in a session to be transferred can be packetized in units of a predetermined time and transferred with a time stamp added to the packet. Since RTP can be reproduced independently in units of packets without depending on other packets, even if a past packet has not arrived or a part of data is missing, Such a packet can be ignored and reproduced.

  The base station that has received the transferred packet sequentially decodes the packet, converts it into a voice signal, and transmits it to the mobile station. As wireless communication between a base station and a mobile station, for example, a TDMA-TDD system (TDMA: Time Division Multiplex) in which a plurality of time slots obtained by time-dividing frames in a base station are assigned to channels of the mobile station, respectively, for communication. Access: time division multiplexing, TDD: time division duplex, OFDMA (Orthogonal Frequency Division Multiplex Access), etc. are used.

(Wireless communication system)
FIG. 1 is a system block diagram for explaining the radio communication system 100. The wireless communication system 100 includes a mobile station PS (PS1, PS2), a base station CS (CS1, CS2, CS3), an IP communication network 130 such as the Internet, and a management server 140.

  In the wireless communication system 100, when a user attempts to make a call to another mobile station PS1 using the mobile station PS2, according to the user's operation of the mobile station PS2, the user can communicate with the base station CS3 in the wireless communicable area. Wireless communication is established, and the base station CS3 requests the management server 140 to establish a communication connection with the mobile station PS1 via the IP communication network 130, as indicated by (1) in FIG.

  As shown in (2) in FIG. 1, the management server 140 selects the base station CS1 in the wireless communicable area of the mobile station PS1 and sets a voice call with the mobile station PS1 that the communication partner has.

  Then, when the setting of the base station CS1 necessary for the voice call is completed, the management server 140 passes the voice call processing between the base stations, and the base stations CS3 and CS1 are transferred as shown in (3) in FIG. Directly sends and receives audio signals. At this time, the management server 140 shifts to a standby state for assigning an appropriate base station CS according to a change in the communication environment of each mobile station PS1, PS2.

  Here, when the mobile station PS1 of the communication partner moves and it becomes difficult to continue communication with the base station CS1 that has been communicating wirelessly until then, a new base station CS2 within the wireless communicable range of the mobile station PS1 is added to the management server. 140 is selected and the handover is performed. Then, as shown in FIG. 1 (4), communication with the new base station CS2 is started.

  Hereinafter, the configurations of the mobile station PS1, the aggregation station, and the base station CS in the radio communication system 100 will be described, and then the radio communication method at the time of handover will be described.

(Mobile station)
FIG. 2 is a functional block diagram showing the configuration of the mobile station PS. In this embodiment, a PHS terminal is used as the mobile station PS. However, the present invention is not limited to such a case. A game machine, a DVD player, a remote controller, etc. can also be used as the mobile station PS.

  The mobile station PS includes a terminal control unit 210, a terminal memory 212, a display unit 214, an operation unit 216, a voice input unit 218, a voice output unit 220, a wireless communication unit 222, a first buffer 224, The second buffer 226 and a time difference detection unit 230 realized by the terminal control unit 210 are included.

  The terminal control unit 210 manages and controls the entire mobile station PS by a semiconductor integrated circuit including a central processing unit (CPU). The terminal control unit 210 naturally performs a call function and a mail delivery function using the mobile station PS using a program stored in the terminal memory 212. It also functions as a time difference detection unit 230, which will be described later.

  The terminal memory 212 is composed of ROM, RAM, EEPROM, nonvolatile RAM, flash memory, HDD (Hard Disk Drive), etc., and stores programs processed by the terminal control unit 210, software provided by service providers, and the like. To do. The terminal memory 212 is also used by the terminal control unit 210 for developing programs and temporarily storing data.

  The display unit 214 is composed of a liquid crystal display, and is stored in the terminal memory 212 or provided from an application relay server (not shown) via the IP communication network 130, and is a GUI (Graphical User Interface) of a Web browser or application. ) Can be displayed. The display unit 214 may be configured by EL (Electro Luminescence), PDP (Plasma Display Panel), or the like.

  The operation unit 216 includes switches such as a keyboard, a cross key, and a joystick, and receives a user operation input.

  The voice input unit 218 is composed of a voice recognition device such as a microphone, and converts the user's voice input during a call into an electrical signal that can be processed in the mobile station PS.

  The voice output unit 220 includes a speaker, and converts the voice signal of the other party received by the mobile station PS into voice and outputs the voice. In addition, a ring tone, an operation sound of the operation unit 216, an alarm sound, and the like can be output.

  The radio communication unit 222 performs radio communication with the base station CS in the PHS telephone network. As such wireless communication, there is a time division multiplexing method in which a plurality of time slots obtained by time division of frames in the base station CS are allocated to the channel of the mobile station PS to perform communication.

  The first buffer 224 accumulates reception signals from the handover source base station. The first buffer 224 can start accumulation from the start of a voice call. However, the first buffer is mainly used for handover, and storing the received signal in the first buffer causes a delay from the arrival of voice to the output, so that the start of handover is predicted. Accumulation may be started from that time. The time when the start of handover is predicted can be a case where the communication quality of the mobile station or the currently connected base station has dropped below a predetermined standard. Received electric field strength (RSSI) can be suitably used for communication quality. The first buffer can start to be stored when a buffer once stored by handover is used. This makes it possible to always prepare a certain amount of buffer.

  When the accumulation of the first buffer 224 is started during a voice call, there is no surplus data if the reproduction is performed as it has reached the mobile station PS1, and therefore the accumulation cannot be performed. Therefore, the audio read out from the first buffer 224 is expanded, and the audio signal read out over a longer time than the audio signal reaching the first buffer can be reproduced to generate a surplus, and the audio is stored in the first buffer 224. A signal can be accumulated. Similarly, it is possible to generate surplus data by extending the silence period or repeatedly reproducing the same data in a short time that humans cannot perceive, and by intermittently reproducing the actual data. 1 buffer 224 can be stored.

  The second buffer 226 stores received signals from the handover destination base station. When the second buffer does not execute the handover, for example, when talking without moving, the received signal is not accumulated. When handover is started and reception of a signal from the handover destination base station is started, accumulation of received signals is started.

  The time difference detector 230 detects the time difference at which each received signal is received by comparing the received signals accumulated in the first buffer and the second buffer. As a comparison, the received signals (audio signals) accumulated in both buffers are extracted for a predetermined time, the correlation value is calculated while relatively moving in the time direction, and the correlation value is equal to or greater than a predetermined threshold. By detecting, the time difference between the data can be derived.

  When the handover is executed, that is, when switching from the base station CS1 serving as the switching source to the communication with the base station CS2 serving as the switching destination, the terminal control unit 210 is based on the time difference detected by the time difference detecting unit 230. The signal for audio reproduction is switched from the first buffer to the second buffer.

(Base station CS)
FIG. 3 is a functional block diagram showing the configuration of the base station CS. The base station CS includes a base station control unit 250, a base station memory 252, a base station radio communication unit 254, a handover prediction notification unit 256, and an IP connection unit 258.

  The base station control unit 250 manages and controls the entire base station CS by a semiconductor integrated circuit including a central processing unit. The base station control unit 250 uses the program in the base station memory 252 to support a call or communication between the mobile stations PS1 and PS2.

  The base station memory 252 includes a ROM, a RAM, an EEPROM, a nonvolatile RAM, a flash memory, an HDD, and the like, and stores a program processed by the base station control unit 250 and data transmitted / received between mobile stations.

  The base station wireless communication unit 254 performs wireless communication based on the mobile station PS and the PHS telephone network. For example, in the present embodiment, a time division multiplexing method (TDMA-TDD method) is employed in which a plurality of time slots obtained by time-dividing frames in the base station CS are assigned to channels and communication is performed.

  The handover prediction notification unit 256 should monitor the received electric field strength (RSSI) with the mobile station PS and start buffering of the received signal when the received electric field strength with the mobile station PS falls below a predetermined standard. A signal for notifying is sent out. As a result, the mobile station PS can recognize that there is a high possibility that a handover will occur, and can start accumulating received signals in the first buffer 224. Although it is conceivable that the handover does not actually occur, in this case, the accumulated data in the first buffer is continuously used while the voice call is continued. If the mobile station PS has already been stored in the first buffer when receiving the notification signal, the mobile station PS does not particularly need to perform the storage operation.

  However, in the case where the mobile station PS predicts the handover by viewing the communication quality such as the received electric field strength, the base station CS does not need the handover prediction notification unit 256, and it is sufficient to predict the handover by either one. It is.

  The IP connection unit 258 transmits / receives a setting signal to / from the management server 140 through the IP communication network 130, and then transmits / receives a packet directly to / from the base station CS1 and the base station CS2. The IP connection unit 258 includes a packet transmission / reception unit 270 and a jitter buffer 272.

  The packet transmitting / receiving unit 270 transmits or receives a packet exchanged with another base station CS connected through the IP communication network 130. Accordingly, not only packets with the handover source base station CS1 to which the mobile station PS1 is connected, but also packets with the handover destination base station CS2 can be transmitted and received simultaneously.

  The jitter buffer 272 is a buffer that absorbs a shift in packet reception timing in RTP communication. In RTP (VoIP), a packet is transmitted through an IP communication network. In the IP communication network, packets follow various routes, and the interval and order of packet arrival are not conscious. For this reason, the base station accumulates the packets in the jitter buffer, and aligns the packets in time series based on the time stamps attached to the received packets, thereby absorbing delays and fluctuations. The aligned packets are decoded into voice signals by the base station control unit 250, converted to time division multiplexing packets by the base station radio communication unit 254, and transmitted to the mobile station PS.

(Wireless communication method)
A wireless communication method using the above system will be described. FIG. 4 is a block diagram for explaining a wireless communication system in an IP communication network, and FIG. 5 is a flowchart for explaining a wireless communication method. Here, it is assumed that the mobile station PS1 moves and performs handover via the two base stations CS1 and CS2.

  In FIG. 4 (a), the mobile station PS1 performs radio communication with the base station CS1. In the mobile station PS1, when the start of the handover is predicted due to the reception field strength weakening, the reception of the received signal is started in the first buffer 224 (S102 in FIG. 4). At this time, if the data transmitted from PS2 is D1 to D3, the data is first stored in the first buffer and then reproduced in PS1. In the example shown in FIG. 4A, D1 is reproduced, and D2 and D3 are in the first buffer 224.

  When the handover between the mobile station PS1 and the base station CS1 is started, the mobile station PS1 is connected to the handover destination base station CS2 while maintaining the connection with the handover source base station CS1 (S104).

  In FIG. 4 (b), the voice signal transmitted from the mobile station PS2 reaches the mobile station PS1 via both the handover source / destination base stations CS1 and CS2, and the PS1 from the base station CS1 that is the handover source. Play the received audio signal. At this time, the received signal that has arrived from the base station CS1 continues to be accumulated in the first buffer 224, and the received signal that has arrived from the base station CS2 starts to be accumulated in the second buffer 226 (S106). Assuming that the data transmitted from the mobile station PS2 at this time is D4 to D6, the received signal that has arrived via the base station CS1 is reproduced at the mobile station PS1, and D5 and D6 are in the first buffer 224.

  Here, since it is necessary to accumulate a jitter buffer in the base station CS2, the reception signal received from the base station CS2 arrives later than the reception signal received from the base station CS1. Accordingly, the received signals that have arrived through the base station CS2 are only D4 and D5 and are stored in the second buffer 226, and D6 is still in the jitter buffer of the base station CS2. That is, the data is shifted by one data.

  Then, the time difference detection unit 230 of the mobile station PS1 compares the received signals stored in the first buffer 224 and the second buffer 226 to detect the time difference at which the received signals are received (S108). As a comparison, the received signals (audio signals) accumulated in both buffers are extracted for a predetermined time, the correlation value is calculated while relatively moving in the time direction, and the correlation value is equal to or greater than a predetermined threshold. By detecting, the time difference between the data can be derived. When a correlation value equal to or greater than the threshold value cannot be acquired, it is assumed that synchronization cannot be acquired, and the comparison is performed again after a predetermined time has elapsed.

  Next, as shown in FIG. 4C, a handover is executed (S110). That is, the session between the mobile station PS1 and the base station CS1 is released, and the connection between the base stations CS1 and CS3 is also released. At this time, the sound reproduction in the mobile station PS1 is also switched from the first buffer to the second buffer based on the time difference detected by the time difference detection unit 230. At this time, since the session between the mobile station PS1 and the base station CS1 is released, no new received signal is accumulated. However, by reproducing the data corresponding to the time difference from the first buffer 224, the base station CS2 It waits for the received signal to be accumulated in the second buffer 226. Then, by switching the signal to be reproduced to the received signal stored in the second buffer 226, the audio signals of the base stations CS1 and CS2 can be synchronized.

  In FIG. 4C, when the data transmitted from the mobile station PS2 is D7 to D9, the session with the base station CS1 is released in the mobile station PS1, but is stored in the first buffer 224. D7 is reproduced, and D8 stored in the second buffer 226 is reproduced at the next timing. That is, reproduction is performed by skipping D7 in the second buffer 226. In this way, when the received signal arriving from the handover destination base station CS2 is delayed with respect to the handover source base station CS1, the terminal control unit 210 sets the second buffer 226 based on the time difference detected by the time difference detection unit 230. Synchronization can be performed by shifting the head address backward.

  Here, shifting the head address of the second buffer 226 backward means that the capacity of the second buffer 226 is reduced. Therefore, in preparation for the next handover, the capacity of the second buffer 226 is expanded so as to satisfy the capacity of the first buffer, and accumulation of received signals is started. Similar to the accumulation in the first buffer 224, the accumulation of the reception signal in the second buffer 226 can be realized by generating a surplus by expansion or intermittent reproduction of the reception signal.

  In the above-described embodiment, the case where the received signal arriving from the handover destination base station CS2 is delayed, but the received signal arriving from the handover destination base station CS2 is ahead of the handover source base station CS1. In some cases, the audio signals of the base stations CS1 and CS2 can be synchronized by expanding the accumulated amount of the second buffer 226. As described above, since the base station CS2 needs to accumulate a jitter buffer, the handover destination tends to be delayed. However, since the dispersion of the line delay in the communication network 130 is large, the handover destination voice signal is more delayed. This is because it is possible to reach the destination in advance.

  FIG. 6 is a diagram for explaining a case where a reception signal reaching from the handover destination base station CS2 advances. In FIG. 6A, data arriving from the base station CS1 is D1 to D3, D1 is reproduced, and D2 and D3 are stored in the first buffer. Here, the data that arrives from CS2 advances, D2 is discarded, and D3 and D4 are stored in second buffer 226.

  First, the time difference between the two data is derived. Then, based on the obtained time difference (here, one piece of data), the accumulation amount of the second buffer 226 is expanded, and the reception signal is accumulated in the second buffer. In FIG. 6B, the data that arrives from the base station CS1 is D3 to D5, D3 is reproduced, and D4 and D5 are stored in the first buffer 224. Since the second buffer 226 is expanded, D4 to D6 are accumulated in the second buffer 226 for the data that arrives from CS2.

  At this time, since the data in the second buffer 226 is originally discarded, the data can be quickly stored (filled) in the second buffer 226 by stopping the output from the second buffer 226. Similarly to the accumulation in the first buffer 224, it can also be realized by generating a surplus by expansion of the output signal or intermittent reproduction.

  As a result, in the second buffer 226, the progress of the audio signal that has arrived from the base station CS2 can be stopped, and the data of the first addresses of the first buffer 224 and the second buffer 226 are synchronized. Therefore, as shown in FIG. 6C, the terminal control unit 210 can smoothly perform handover by simply switching to the data stored in the second buffer 226.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  The present invention is used as a mobile station, a base station, a wireless communication system, and a wireless communication method in a wireless communication system in which a base station transmits packets using a real-time data transfer protocol (RTP) over an IP communication network. Can do.

It is a system block diagram for demonstrating a radio | wireless communications system. It is the functional block diagram which showed the structure of mobile station PS. It is the functional block diagram which showed the structure of base station CS. It is a block diagram for demonstrating the radio | wireless communications system in an IP communication network. It is a flowchart for demonstrating a radio | wireless communication method. It is a figure explaining the case where the received signal which arrives from base station CS2 of a handover destination is advancing. It is a block diagram for demonstrating the radio | wireless communications system especially using RTP in an IP communication network.

Explanation of symbols

CS ... base station, PS ... mobile station, 100 ... wireless communication system, 130 ... communication network, 140 ... management server, 210 ... terminal control unit, 212 ... terminal memory, 214 ... display unit, 216 ... operation unit, 218 ... voice Input unit, 220 ... voice output unit, 222 ... wireless communication unit, 224 ... first buffer, 226 ... second buffer, 230 ... time difference detection unit, 250 ... base station control unit, 252 ... base station memory, 254 ... base station Wireless communication unit, 256 ... Handover prediction notification unit, 258 ... Connection unit, 270 ... Packet transmission / reception unit, 272 ... Jitter buffer

Claims (10)

In a mobile station that performs radio communication with a base station that is connected to another base station via a real-time data transfer protocol (RTP) over an IP communication network,
A first buffer for accumulating received signals from the handover source base station;
A second buffer for accumulating received signals from the handover destination base station;
A time difference detection unit that detects a time difference of receiving each received signal by comparing the received signals accumulated in the first buffer and the second buffer;
A control unit that switches a signal to be reproduced from the first buffer to the second buffer based on the time difference detected by the time difference detection unit;
A mobile station comprising: When the received signal arriving from the handover destination base station is delayed from the handover source base station,
The mobile station according to claim 1, wherein the control unit shifts the head address of the second buffer backward based on the time difference detected by the time difference detection unit. In the case where the received signal arriving from the handover destination base station is ahead of the handover source base station,
The mobile station according to claim 1, wherein the control unit expands an accumulation amount of the second buffer based on the time difference detected by the time difference detection unit. The first buffer starts storing when a voice call starts, when a handover start is predicted, or when a buffer once stored is used,
2. The mobile station according to claim 1, wherein the second buffer starts accumulation at the start of connection with a handover destination base station.   The mobile station according to claim 4, wherein the time when the handover start is predicted is a case where the communication quality of the mobile station or the currently connected base station is lowered to a predetermined standard or less.   When the handover is completed, the control unit expands an accumulation amount of the second buffer and accumulates a reception signal when the capacity of the second buffer is less than the capacity of the first buffer. 5. The mobile station according to claim 4, wherein the mobile station is replenished.   The control unit decompresses or intermittently reproduces audio from the first buffer, and reproduces the audio signal read out over the audio signal reaching the first buffer over a long time. 2. The mobile station according to claim 1, wherein an audio signal is stored in the buffer. In a base station connected to another base station by a real-time data transfer protocol (RTP) by an IP communication network,
Handover that sends a signal for notifying the mobile station that performs radio communication with the base station that the buffering of the received signal should be started when the communication quality with the mobile station falls below a predetermined standard A base station comprising a prediction notification unit. In a wireless communication system including a mobile station and a plurality of base stations that perform wireless communication with the mobile station,
The mobile station
A first buffer for accumulating received signals from the handover source base station;
A second buffer for accumulating received signals from the handover destination base station;
A time difference detection unit that detects a time difference of receiving each received signal by comparing the received signals accumulated in the first buffer and the second buffer;
A control unit that switches a signal to be reproduced from the first buffer to the second buffer based on the time difference detected by the time difference detection unit;
With
The base station
Connected to other base stations via the real-time data transfer protocol (RTP) over the IP communication network,
Handover that sends a signal for notifying the mobile station that performs radio communication with the base station that the buffering of the received signal should be started when the communication quality with the mobile station falls below a predetermined standard A wireless communication system comprising a prediction notification unit. In a mobile station that performs radio communication with a base station that is connected to another base station via a real-time data transfer protocol (RTP) over an IP communication network,
Accumulating received signals from the handover source base station in the first buffer;
Storing the received signal from the handover destination base station in the second buffer;
Detecting a time difference of receiving each received signal by comparing the received signals stored in the first buffer and the second buffer;
And a step of switching a signal to be played back from the first buffer to the second buffer based on the time difference detected by the time difference detection unit.

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