JP2000013774A - Bidirectional CATV system, center device and terminal device thereof, and communication method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform transmission that has a satisfactory throughput characteristic even in the case of transmission of packets of various lengths that are long and short by detecting data signal length, comparing the data signal length with data signal length threshold that is set in advance, deciding an incoming frequency channel and deciding an incoming transmission slot time in the decided up frequency channel. SOLUTION: Center equipment 200 receives incoming control data, performs scheduling with a 2nd incoming information data channel when information data length is larger than threshold, makes an information channel change flag 'changed' and outputs it to a CATV circuit 300. A cable modem 100 changes it to the frequency of a 2nd incoming information data channel because a read information channel change flag has 'changed' and transmits it to the equipment 200. The 2nd information data is outputted to a router 600. Outgoing information data supplied from the Internet 700 is transmitted to the modem 100.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a CATV (Cabl
The present invention relates to a two-way CATV system for performing high-speed packet communication using an e-television network, and more particularly to a communication system for multiple access between a center device and each terminal device.

[0002]

2. Description of the Related Art In recent years, a system for performing packet communication between a center device (head end) and a terminal device using a CATV network has attracted attention. In this system, for example, personal computers are connected to a CATV network via a cable modem, and these personal computers are selectively connected to a head end of the CATV network, that is, a center device, to perform packet communication such as data and voice. Things.
The use of this system makes it possible to easily perform a high-speed access to an external network such as the Internet, in addition to a survey of audience ratings and on-demand communication of each subscriber. By the way, in this type of system, since the center device sends out a signal in a unified manner on the downlink transmission line, transmission with a so-called effective frame usage rate, which is the ratio of frames actually used for information transmission, is possible. is there. However, since many terminal devices arbitrarily transmit signals on the uplink transmission line, collisions are likely to occur and efficient transmission is difficult. further,
Since the length of information data transmitted by a large number of terminal devices is various, a variable length packet system which is a highly efficient transmission system is desired rather than a fixed length packet system in which the data length is divided into fixed lengths and transmitted. ing.

For this reason, the development of an access method that can reduce the occurrence of collisions on the uplink transmission path and that can transmit variable-length packets and that increases the effective frame utilization rate has become an important theme. Therefore, the CSMA / CD method (international standard: ISO / DIS 8802/3) conventionally used in the random access method, Ethernet and the like,
Furthermore, F used in digital mobile phone systems
/ TDMA method (frequency division / time division multiple access method, Radio Industry Association Standard RCR-STD 27
F) has been proposed.

In the random access method, each terminal device performs transmission at random timing based on the generation of each packet transmission request, and the effective frame use rate is improved as compared with the polling method. However, Aloha (Alo
ha) or slotted-Aloha (S-Aloh)
a) In the random access method called the method, not only does the average transmission delay increase as the transmission delay increases, but also as the traffic, that is, the traffic increases, the frequency of collisions increases, and the throughput, that is, the processing capacity deteriorates. Still remain. In the CSMA / CD system, which is one of the random access systems, a terminal device that intends to perform transmission monitors the presence or absence of a carrier on an uplink transmission path, performs transmission only when there is no carrier, and detects a collision. In this case, the transmission is stopped at that time, and since the occurrence of collision is small and the occupation time of the transmission medium by the collision signal is short, efficient transmission can be performed.

However, when one of the terminal devices transmits a packet having a long packet length, the terminal devices that have been waiting for transmission during the transmission period start transmitting at the same time at the end of transmission of the long packet. Therefore, the probability that a collision will occur at this point becomes very high. In addition, CA
Since a plurality of bidirectional amplifiers are installed on a TV line (transmission line), there is a problem that collision of transmission signals by a CSMA / CD terminal device cannot be detected. The F / TDMA system used in the digital mobile phone system has an uplink frequency band and a downlink frequency band that are frequency-divided, and each of them is divided into a plurality of time slots on a time axis and transmitted. The access method at the start of packet transmission of each terminal device is random access. In addition, the time slot length is fixed for both uplink and downlink, and the fixed-length packet system is used. This is because packets having a fixed length may be used due to the characteristic of transmitting voice. As an example, the transmission rate after voice encoding is 6.7 kbps (full rate codec VSELP, Vector Suppler).
m code ExcitedLinear Pred
icting), one slot length is 280 bits (including a ramp bit and a preamble), and one slot time is 20
msec (at full rate).

On the other hand, when data such as a computer data signal is transmitted, its data length varies in length, so if it is divided into fixed-length packets, it is redundant due to a preamble added in the packet or a header. And the transmission efficiency decreases. In addition, since a terminal device transmitting a long packet occupies many time slots, another terminal device having information data to be transmitted waits for transmission (also referred to as transmission suspension), and there is a problem that transmission cannot be performed forever. For this reason, a variable-length packet system capable of transmitting requested information data in one packet is desired.

[0007]

As described above, the various access methods proposed in the prior art cause extreme degradation of the effective frame utilization rate when the number of terminals is large, and may cause packets of various lengths, long and short. In the case where the transmission is performed, there is a problem that transmission suspension increases and the throughput is deteriorated. SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a bidirectional CATV system capable of performing transmission with good throughput characteristics even when packets of various lengths are transmitted. And its center device and its terminal device.

[0008]

In order to achieve the above object, a bidirectional CATV system according to the present invention comprises a center device and a plurality of terminal devices connected to the center device via a common transmission line. Means for temporally dividing a transmission period of an uplink signal for information communication with the center device into a reservation signal transmission period and a data signal transmission period; and, prior to data transmission, the reservation signal Control signal transmitting means for transmitting a control signal including a data signal length to the center device in a transmission period, and variable length data transmitting means for transmitting variable length information to the center device,
The center device compares the data signal length with a preset data signal length threshold value, and detects if the data signal length is smaller than the data signal length threshold value. Determines the first uplink frequency channel as the uplink frequency channel of the terminal device, and if the data signal length is greater than the data signal length threshold, sets the second uplink frequency channel to the uplink frequency of the terminal device. Channel determination means for determining a channel, transmission time determination means for determining an uplink transmission slot time in the uplink frequency channel determined by the channel determination means, and data relating to the determined uplink frequency channel and the uplink transmission slot time. Transmitting means for transmitting to the terminal device.

In the bidirectional CATV system, the center device includes a variable length data receiving means for receiving the variable length information during the data signal transmission period. Further, in this bidirectional CATV system, the center device includes a statistical processing unit that statistically processes the detected data signal length to determine the data signal length threshold. Further, in the bidirectional CATV system, the terminal device performs information communication with the center device by multiple access to the center device by a plurality of uplink frequency channels via the common transmission path.

A center device according to the present invention divides an uplink signal transmission period into a reservation signal transmission period and a data signal transmission period in time and transmits the uplink signal from a terminal device transmitted through a common transmission path. Means for receiving a signal, detection means for detecting a data signal length, and comparing the data signal length with a preset data signal length threshold value, wherein the data signal length is greater than the data signal length threshold value If it is smaller, the first uplink frequency channel is determined as the uplink frequency channel of the terminal device, and if the data signal length is larger than the data signal length threshold, the second uplink frequency channel is set to the Channel determination means for determining an uplink frequency channel; and transmission time determination means for determining an uplink transmission slot time of the uplink frequency channel determined by the channel determination means. And a transmitting means for transmitting the data and the uplink transmission slot time relating to the determined uplink frequency channel to the terminal device.

In the center apparatus, a variable length data receiving means for receiving the variable length information during the data signal transmission period is provided. Further, the center device is provided with statistical processing means for statistically processing the detected data signal length to determine the data signal length threshold value. In the terminal device according to the present invention, a means for connecting to the center device via a common transmission path, and a transmission period of an uplink signal for performing information communication with the center device are divided into a reservation signal transmission period and a data signal transmission period. Prior to data transmission, control signal transmitting means for transmitting a control signal including a data signal length in the reservation signal transmission period to the center device, and variable control for transmitting variable length information to the center device. Long data transmission means.

In the communication method according to the present invention, a plurality of terminal devices are connected to a center device via a common transmission path,
The terminal device is multiple-accessed to the center device via the common transmission path by a plurality of uplink frequency channels, and a transmission period of an uplink signal for information communication from the terminal device to the center device is a reservation signal transmission period. , Time-divided into a data signal transmission period, and prior to the data transmission transmission period, from the terminal device to the center device,
A control signal including a data signal length is transmitted in the reservation signal transmission period, and the center device detects the data signal length,
The data signal length is compared with a preset data signal length threshold, and if the data signal length is smaller than the data signal length threshold, the first uplink frequency channel is set to the uplink of the terminal device. If the data signal length is larger than the data signal length threshold, the second uplink frequency channel is determined to be the uplink frequency channel of the terminal device if the data signal length is larger than the data signal length threshold value. To send data specifying that channel,
The center device determines an uplink transmission slot time of the determined uplink frequency channel, transmits the determined time to the terminal device, and transmits variable-length information from the terminal device to the center device.

Further, in the communication method according to the present invention, a plurality of terminal devices are connected to the center device via a common transmission line, and the plurality of terminal devices are connected to the center device via the common transmission line. Multiple access by the uplink frequency channel, the transmission period of the uplink signal for information communication from the terminal device to the center device is temporally divided into a reservation signal transmission period and a data signal transmission period, and the data transmission transmission period Prior to this, a control signal including a data signal length is transmitted from the terminal device to the center device in the reservation signal transmission period, the center device detects the data signal length, and statistically processes the data signal length. Determining a data signal length threshold, comparing the data signal length with the data signal length threshold, wherein the data signal length is smaller than the data signal length threshold. Expediently, it transmits the data specifying the channel of the first uplink frequency band to determine the uplink frequency channel of the terminal device to the terminal device,
If the data signal length is greater than the data signal length threshold, determine a second uplink frequency channel as the uplink frequency channel of the terminal device, and transmit data specifying the channel to the terminal device, From the center device to the terminal device, the determined uplink transmission slot time of the determined uplink frequency channel is determined by the center device and transmitted to the terminal device, and the variable length information is transmitted from the terminal device to the center device. Has been sent.

In a preferred CATV system according to the present invention, uplink control data including an information data length is formed according to an Internet connection request signal, and uplink information data is transmitted at a transmission time designated by the downlink control data from the center device. A control unit for performing control for transmission, a transmission unit for transmitting the uplink control data to the center device, a reception unit for receiving the downlink control data transmitted from the center device, and reading the downlink control signal to obtain uplink information A terminal device including a channel switching control unit that specifies a channel to the transmission unit, a reception unit that receives the uplink control data transmitted from the terminal device, and a threshold setting unit that sets a threshold value of information data length A comparing unit that compares a threshold value from the threshold value setting unit and the information data length of the uplink control data, Schedule processing unit for setting a transmission start time and the uplink information channel based on the output from the serial comparison unit, a downlink control data structure portion constituting the downlink control data in response to a command from the scheduling processing unit,
A center device including a transmission unit for transmitting the downlink control data; and means for connecting the center device and a plurality of the terminal devices via a common CATV line.

In the bidirectional CATV system, the center device is provided with a statistical processing unit for statistically processing the length of information data received in the past and resetting the threshold value of the threshold value setting unit. In a preferred terminal device of the present invention, means for connecting to a center device via a CATV line, and uplink control data including an information data length in response to an Internet connection request signal, and downlink control data transmitted from the center device A control unit that performs control for transmitting uplink information data at a transmission time specified by data, a transmission unit that transmits the uplink control data to the center device, and the downlink control data transmitted from the center device. A receiving unit that receives the downlink control signal and designates an uplink information channel as the transmitting unit;

In this terminal device, a buffer memory for storing the Internet connection request signal is provided. Furthermore, in this terminal device, the control unit controls the transmission unit so as to start transmitting the uplink control data at a predetermined time. Also, a preferred center device of the present invention is a terminal device connecting means for connecting a terminal device via a CATV line, a receiving unit for receiving uplink control data including the information data length transmitted from the terminal device, A threshold setting unit that sets a threshold, a comparison unit that compares a threshold value from the threshold setting unit with the information data length of the uplink control data, and based on an output from the comparison unit. A schedule processing unit that sets an uplink information channel and a transmission start time, a downlink control data configuration unit that configures the downlink control data according to a command from the schedule processing unit, and a transmission unit that transmits the downlink control data And In this center device, a statistical processing unit is provided for statistically processing the length of information data received in the past and resetting the threshold value of the threshold value setting unit.

According to a preferred embodiment of the present invention, in order to solve the above-mentioned problem, a transmission period of an uplink signal for performing information communication from a terminal device to a center device is divided into a reservation signal transmission period and a data signal transmission period. And the terminal device comprises:
Prior to data transmission, a control signal including a data signal length is transmitted to the center device in the reservation signal transmission period, and the center device detects the data signal length and sets the data signal length to a preset data value. Compared with the signal length threshold, if the data signal length is smaller than the data signal length threshold, determine the current uplink frequency channel as the uplink frequency channel of the terminal device, the data signal length is the data If greater than the signal length threshold, determine an uplink frequency channel different from the current uplink frequency channel of the terminal device, in the uplink frequency channel,
The uplink transmission slot time is determined, uplink frequency channel data and the uplink transmission slot time are transmitted to the terminal device, and the terminal device transmits variable-length information to the center device during the data signal transmission period. Transmit variable length data.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a bidirectional CAT according to the present invention will be described.
An embodiment of a V system, its center device, its terminal device, and its communication method will be described using examples. FIG. 1 is a block diagram showing one embodiment of a bidirectional CATV system according to the present invention. In FIG. 1, 100,
1005 and 1008 are cable modems, 200 is a center device, 300 is a CATV line, 400, 1006, and 10
09 is a personal computer, 500, 1007, 1
010 is a TV receiver, 600 is a router, 1001 is a router connection terminal, 700 is the Internet network, 800 is MP
EG (Moving Picture Experts)
Group: An international standard for compression and decompression of moving images and sounds, and multiplexing and demultiplexing thereof. ISO / IEC138
18-1, -2, -3) server, 1002 is a compressed video input terminal, 1003 is a compressed audio input terminal, 1004 is a video input terminal, 1012, 1013, and 1014 are distributors. The center device 200 receives, for example, a compressed video and a compressed audio data which are stored in the MPEG server 800 and are data-compressed by the MPEG2 method, for example. Further, the computer data signal from the Internet 700 is
0, and receives the MPEG video signal, the MPEG audio signal, and the computer data signal to the CATV line 300 through the downstream data (the center device 2).
From 00, the cable modems 100, 1005,
1008), multiplex and transmit.

An uncompressed analog video signal input from a terminal 1004 is directly transmitted to the center device 20.
0 is supplied. Since the center device 200 has a built-in MPEG encoder, the analog video signal is compressed here, converted into downlink data, and transmitted to the CATV line 300. At homes that have subscribed to CATV, the TV receivers 500, 1007, and 1010 normally view programs, movies, and voluntary broadcast programs of CATV stations transmitted from the center device 200. . Cable modems 100, 1005, 10 for bidirectional CATV
By using 08, it is possible to connect to the Internet from a personal computer (hereinafter referred to as a personal computer) and browse a homepage on the Internet at the same time as watching TV images. Cable modem 100, 1005, 10
08 receives a downlink signal from the CATV line 300 and outputs a computer data signal to the personal computer 400. The cable modems 100, 1005, and 1008 further transmit an Internet access request signal from the personal computers 400, 1006, and 1009 to the CATV line 300.
The signal is converted into an uplink signal and transmitted. The center device 200 is C
Uplink data from the ATV line 300 (from the terminal device cable modems 100, 1005, 1008 to the center device 20)
0 is received, the uplink information data is converted and output to the router 600.

Next, a bidirectional C according to the present invention will be described with reference to FIG.
The frequency allocation used in the embodiment of the ATV system will be described. FIG. 2 shows a bidirectional CATV according to the present invention.
FIG. 2 is a schematic diagram showing one embodiment of frequency allocation of the system. 2, reference numeral 302 denotes a frequency band for downlink control data and downlink information data; 304, a frequency band for downlink information data; 306, a frequency band for uplink control data;
8 is the frequency band of the first information data, and 310 is the frequency band of the second information data. Here, the information data is transmission information that is originally desired to be transmitted, other than control data used for communication control. In the case of the cable modem 100, the upward direction indicates a signal input from the personal computer 400. The down direction indicates a computer data signal input from the router 600 to the cable modem 100 via the center device 200 and the distributor 1012.

In FIG. 2, control data such as designation of an uplink frequency channel and transmission start time performed from the center device 200 to the cable modem 100 is time-division multiplexed with information data, and is centered around 767.0 MHz. .0
It is allocated to a frequency band 302 having a width of MHz. Similarly, the downlink information data is 6.0M centered at 761.0 MHz.
It is assigned to a frequency band 304 having a Hz width. Commands for requesting transmission of information data from the cable modem 100 to the center device 200 and control data such as terminal device IDs are allocated to a frequency band 306 having a width of 0.8 MHz centered on 20.4 MHz. Similarly, information data is 0.8 at 21.4 MHz and 22.0 MHz, respectively.
It is assigned to frequency bands 308 and 310 having a MHz width.

Next, an embodiment of the center device 200 shown in FIG. 1 will be described with reference to FIG. FIG. 3 is a block diagram showing one embodiment of the center device used in the bidirectional CATV system according to the present invention. In FIG. 3, 202
Is a duplexer, 204 and 210 are high-frequency transmitters, 206 and 2
12 is a modulator, 208 is a control data encoder, 214 is an encoder, 216, 230, 238 are high-frequency receivers, 2
18, 232 and 240 are demodulation units, 220 is a control data decoding unit, 224 is a threshold value setting unit, 226 is a comparison unit,
28 is a schedule processing unit, 234 and 242 are decoding units, 236 is a high-frequency switch, 244 is an interface unit, 246 is a control unit, 248 is a CATV line terminal, and 25 is a CATV line terminal.
0 is a router I / F unit, and 1001 is a router connection terminal.

Next, referring to FIG. 4, the cable modem 1 shown in FIG.
00 will be described. FIG. 4 shows the bidirectional CAT shown in FIG.
FIG. 2 is a block diagram showing one embodiment of a cable modem used in a V system. 4, reference numeral 102 denotes a branching filter, 104 denotes a high-frequency transmission unit, 106 denotes a modulation unit, 108 denotes an encoding unit, 110 denotes a channel switching control unit, 112 denotes a high-frequency reception unit, 114 denotes a demodulation unit, and 116 denotes a decoding unit. , 1
18 is a control unit, 120 is an Ethernet I / F unit, 122
Is a CATV line terminal, 124 is a personal computer terminal, and a buffer memory 126.

FIG. 5 is a schematic diagram showing one embodiment of a downstream signal format of the bidirectional CATV system according to the present invention. In FIG. 5, reference numeral 821 denotes a header, which includes a synchronization word 836 for searching for a synchronization signal and reading information after that, and a 3-byte header 837 indicating control information. The downlink transport packet 820 is, for example, an MPE.
It comprises a header 821 and a payload 822 containing a video or audio signal compressed by G. The payload 822 includes a header 831 and a numerical value part 835,
The header 831 is a message type 8 indicating the type of information.
32, an uplink channel frequency 833 for notifying a channel used by the cable modem 100, and a service ID 834 for transmitting an ID for outputting uplink information. The numerical value part 835 includes channel description information 840 such as a downlink channel, a contention slot time, and an uplink information channel frequency initial value, and H / indicating synchronization time information held by the center device 200, ie, the head end (H / E). An E time stamp 841, a transmission start time at the time of single cast on the control data channel, an information channel change flag, a frequency value part 842 at the time of single cast of the up information channel, and a numerical value part 844 of the video and audio information data channel. Have been.

FIG. 6 is a schematic diagram showing an embodiment of the bidirectional CATV upstream signal format according to the present invention. In FIG. 6, the uplink control data 846 includes the preamble 84
8, frame type 850, MAC parameter 852,
It comprises a service ID 854, an information data length 856, a header check sequence 858, and an error correction code 860. Signal format 86 in information data channel
2 is preamble 848, frame type 850, MA
It has information data 864 in addition to the C parameter 852 service ID 854, header check sequence 858, and error correction code 860. The information data 864 is DA (D
(estination Address) 866, SA
(Source Address) 868, LEN (D
data Length 870, user data 872, and CRC (Cyclic Redundancy Che).
ck code) 874.

One embodiment of the specifications of the upstream signal and the downstream signal of the bidirectional CATV system according to the present invention will be described below.
The specifications of the upstream signal are: multiplexing method: frequency division / time division multiplexing, modulation method: QPSK, symbol rate: 640 ksym / sec, data transmission rate: 1.28 Mbps, transmission bandwidth: 0.8 MHz / ch, waveform shaping filter roll OFF rate: 0.25.

The specifications of the downlink signal are as follows: multiplexing method: frequency division / time division multiplexing, modulation method: 64 QAM, symbol rate: 5.274 Msym / sec, data transmission rate: 31.644 Mbps, transmission bandwidth: 6.0 MHz / ch, waveform Shaping filter roll-off rate: 0.13.

The operation of the embodiment of the bidirectional CATV system according to the present invention will be described below with reference to FIGS. The center device 200 periodically transmits the frequency of the uplink control data channel, the transmission start time, and the like on the downlink control data frequency channel. Specifically, in the form of a transport packet 820, it is the uplink channel description information 840 included therein. This signal is intended for all the cable modems 100, 1005, 1008 connected to the CATV line 300, and is a so-called broadcast.

On the other hand, when the power is turned on, the cable modem 100 receives the downlink control data channel, performs the frequency conversion in the high frequency receiving section 112, and performs the frequency conversion in the demodulating section 114.
4QAM demodulation is performed, and decoding is performed by the decoding unit 116. The control unit 118 controls the decrypted transport packet 82
Among the 0s, a packet whose message type 832 is broadcast is read. Then, the uplink control channel frequency 833 specified by the control data is set in the channel switching control unit 110, and the service ID 834 is set as the service ID for its own transmission packet. Also, an uplink information channel frequency initial value 840 is stored. Normal,
The cable modem 100 is waiting in this state.

In this state, when the user operates the personal computer 400 shown in FIG. 1 to connect to the Internet, the personal computer terminal 124 shown in FIG.
, An Internet connection request signal is input. The Ethernet I / F unit 124 temporarily stores the input signal in the buffer memory 126. This method uses Ethernet (I
SO / DIS 8802/3), the format of the stored Internet connection request signal is DA866, S
A868, LEN870, user data 872, CRC
874. The control unit 118 configures the uplink control data 846 from the already stored service ID 854, the frame type 850 indicating the contention slot, the MAC parameter 852 indicating the transmission request, and the information data length 856, and further specifies the designated transmission start. The uplink control data 846 is transmitted to the encoding unit 108 at a timing such that the time comes.

The uplink control data 846 is transmitted to the encoder 108
, And QPSK-modulated by the modulator 106, frequency-converted by the high-frequency transmitter 104, and output to the CATV line 300 via the duplexer 102. Center device 200
Receives the uplink control data 846 input from the CATV line terminal 248 and receives the uplink control data 846 via the duplexer 202.
16 where the frequency conversion is performed.
The signal is QPSK-demodulated at 18 and decoded by the control data decoding unit 220. If the service ID 854 matches the service ID 834 of the downlink control data 846, the control unit 246 determines that the uplink control data 846 is valid data.

If the data is valid, the comparing unit 226
Compares the information data length 856 with the threshold value of the threshold value setting unit 224, and sets “SHORT” when the information data length 856 is smaller than the threshold value and “LONG” when the information data length 856 is larger than the threshold value. Output to switch 236. In the case of “SHORT”, the schedule processing unit 228 sets the first uplink information data channel (frequency band) 30
At 8, the scheduling is performed, the transmission start time 842 is calculated, and the calculated transmission start time 842 is transmitted to the control data encoding unit 208. The control data coding unit 208 configures the single-cast downlink control data 302 in which the information channel change flag is set to “no change”, and the information channel change flag and the transmission start time are set to the numerical value unit 835, and the modulation unit 206 Send to

The downlink control data 302 is transmitted to the high frequency
4 and is output to the CATV line 300 via the branching filter 202 and the CATV line terminal 248.
Here, scheduling in the schedule processing unit 228 means that uplink transmission is performed by a plurality of cable modems 100, 1 and 2.
005 and 1008 perform time division multiplexing, so that the center device 200
5, 1008 means to calculate and allocate the transmittable time so that the transmission does not overlap. Cable modem 10
0 receives single-cast downlink control data and reads information channel change flag and transmission start time information 842. Since the read information channel change flag 842 is “no change”, the channel switching control unit 110
Uplink information channel frequency initial value 840 already stored
Is set in the high-frequency transmitting unit 104.

The control unit 118 controls the Ethernet I / F unit 120 so that the Internet connection request signal is output from the buffer memory 126 so that transmission can be performed at the designated time. The coding unit 108 incorporates the Internet connection request signal into the information data 864 to form the uplink information data 862. The uplink information data 862 is
6, high-frequency transmitter 104, duplexer 102, terminal 122,
The signal is transmitted to the CATV line 300 through the distributor 1012. The first information data transmitted in the frequency band 308 of the first information data from the cable modem 100 via the CATV line 300 is supplied to the high frequency receiving unit 230 through the duplexer 202, where the frequency is converted. The signal is QPSK-demodulated by the demodulation unit 232, decoded by the decoding unit 234, and transmitted to the interface unit 244 and the router I / F unit 250.
Is output to the router 600. As described above, the Internet connection request signal from personal computer 400 is transmitted to center device 200. Next, an operation when the comparing unit 226 of the center device 200 outputs “LONG” to the schedule processing unit 228 and the high-frequency switch 236 will be described.

In the case of “LONG”, the schedule processing section 228 sets the second uplink information data channel (frequency band) 3
At 08, scheduling is performed, and transmission start time 842 is calculated and transmitted to control data coding section 208. The control data coding unit 208 sets the information channel change flag to “changed”, and sets the information channel change flag, the uplink information channel frequency (frequency of the second uplink information data channel), and the transmission start time 842 to the numerical value unit 835. The single control downlink control data 302 is configured and transmitted to the modulation unit 206. Thereafter, it is output to the CATV line 300 in the same manner as in the case of "SHORT".

The high-frequency switch 236 is connected to the “LON
G "is received, the switch 236 is turned on, and the duplexer 20 is turned on.
2 and the high-frequency receiving unit 238. Control unit 246
Sets the high-frequency receiving unit 238 so that it can receive the second uplink information data channel. Cable modem 100
Receives the single-cast downlink control data 302, and reads the information channel change flag and the transmission start time 842. Since the read information channel change flag is “changed”, channel switching control section 110 changes the already stored uplink information channel frequency initial value 840 to the frequency of second uplink information data channel 308. ,
It is set in the high-frequency transmission unit 104 The control unit 118 controls the Ethernet I / F unit 120 to output an Internet connection request signal from the buffer memory 126 so that transmission can be performed at the designated time. Hereafter, "SHORT"
The Internet connection request signal is transmitted to the center device 200 in the same manner as in the above case.

In this way, the scheduling of the upstream time slot can be performed according to the information data length of the upstream signal. From the cable modem 100 via the CATV line 300, the second information data frequency band 31
The second information data transmitted at 0 is supplied to the high-frequency receiving unit 238 through the duplexer 202 and the switch 236,
Here, the frequency is converted, QPSK demodulated by the demodulation unit 240, decoded by the decoding unit 242, and
44, output to the router 600 through the router I / F section 250. Downlink information data supplied from the Internet 700 to the center device 200 through the router 600 is encoded by the encoding unit 214, modulated by the modulation unit 212,
After being frequency-converted by the high-frequency transmitting section 210, the demultiplexer 20
2 to the CATV line 300 and transmitted to the cable modem 100 or another cable modem 1005 or 1008 as downlink information data.

Next, the operation when a plurality of cable modems transmit a transmission request will be described with reference to FIGS. 7 to 10 are timing charts for explaining the operation of one embodiment of the bidirectional CATV system according to the present invention. 7, reference numeral 302 denotes a frequency band for downlink control data and downlink information data, 304 denotes a frequency band for downlink information data, 306 denotes a frequency band for uplink control data, 308 denotes a frequency band for first information data, and 31
0 is the frequency band of the second information data, and 846 is the uplink control data. HEM means a head-end modem, that is, a modem provided in the center device 200.
In the drawing, t represents time, and the subscripts of fDC and fUT are as follows:
D: Downstream, that is, down, C: Co
control channel, ie, control channel, U: Upstream, ie, uplink, T: T
trafficchannel, that is, a traffic channel. In FIG. 8, reference numeral 820 denotes a downlink transport packet, in FIG. 9, reference numeral 862 denotes uplink information data, and in FIG. 10, reference numeral 829 denotes a downlink transport packet. As described above, when the cable modem 100 is in the standby state, the personal computer 4
It is assumed that an Internet transmission request signal has been input from 00. At this time, as shown in FIG.
When the cable modem CM # 2 is input first and the cable modem CM # 2 is input later, the uplink control data 846 is received by the modem HEM (not shown) of the center device 200 in the order of CM # 1, CM # 2. .

The modem HEM of the center device 200 compares the information data length with the threshold value in the comparing section 226 as described above. At this time, it is assumed that the information data length of the cable modem CM # 1 is shorter than the threshold, and the information data length of the cable modem CM # 2 is longer than the threshold. Comparison section 22
6 shows "SHORT" to the cable modem CM # 1,
“LONG” is output to the schedule processing unit 228 and the high frequency switch 236 for the cable modem CM # 2.
The schedule processing unit 228 is a cable modem CM # 1
Is the first uplink information data channel (or frequency band) 30
8 (see FIG. 2), and the cable modem CM # 2 performs scheduling on the second uplink information data channel (or frequency band) 310 (see FIG. 2). The transmission start time of each of the calculated results is transmitted to control data encoding section 208.

The control data encoding unit 208 first outputs the CM #
From the transmission start time of the transport packet 820
Is transmitted to the modulation section 206, and then the transport packet 820 is composed from the transmission start time of CM # 2 and the like, and transmitted to the modulation section 206. As shown in FIG. 8, these transport packets 820 are single-cast to the cable modems CM # 1 and CM # 2 in the downlink control data frequency band 302, respectively. Each of the cable modems CM # 1 and CM # 2 receives the transport packet 820 and reads the transmission start time, the information channel change flag, and the uplink information channel frequency.

As a result, as shown in FIG. 9, the cable modem CM # 1 transmits an Internet connection request on the first information data channel (or frequency band) 308,
The cable modem CM # 2 transmits an Internet connection request on the second information data channel (or frequency band) 310. As shown in FIG. 9, the information data of the cable modem CM # 2 that occupies a time slot for a long time is
Since the second information data was transmitted in the frequency band 310, the frequency band 308 of the first information data has a vacant time slot after transmission of the cable modem CM # 1, and signals from other cable modems are transmitted. It is possible. Thus, highly efficient transmission is possible in the variable-length packet system. In the figure, 86
2 is information data. Further, as an example of operation, the cable modems CM # 1 and CM # 2 are
When there is information data 844 to be transmitted from the 0 modem HEM side, the operation shown in FIG. 10 is performed. In the frequency band 304 of the downlink information data, the cable modems CM # 1, C #
Transport packets 820 are single-cast in the order of M # 2.

Next, the center device 200 of the present invention shown in FIG.
Another embodiment will be described. FIG. 11 is a block diagram showing another embodiment of the center device of FIG. 1 according to the present invention. The center device in FIG. 11 is different from the center device in FIG. 3 in that a statistical processing unit 222 is provided between a connection point between the control unit 246 and the control data decoding unit 220 and the threshold value setting unit 224. Are the same. In addition,
The description of the reference numerals of the same circuit blocks as in FIG. 3 is omitted.

In the standby state of the cable modem 100 shown in FIG. 4, in order for the user to connect to the Internet, FIG.
Is operated, the Internet connection request signal is input to the personal computer terminal 124 of FIG. Ethernet I / F section 120
Temporarily stores the input signal in the buffer memory 126.

The control unit 118 includes a service ID 854 which has already been stored, a frame type 850 indicating a contention slot, and a MAC parameter 85 indicating a transmission request.
2 and the uplink control data 846 from the information data length 856
And transmits the uplink control data 846 to the encoding unit 108 at a timing such that the designated transmission start time comes. Uplink control data 846 is encoded by encoding section 108, QPSK-modulated by modulating section 106, frequency-converted by high-frequency transmitting section 104, and output to CATV line 300 via duplexer 102. Center device 200
Receives the uplink control data 846, and
6, the frequency conversion is performed, the demodulation unit 218 performs QPSK demodulation, and the control data decoding unit 220 decodes. Control unit 24
6 indicates that if the service ID 854 matches the service ID 834 of the downlink control data,
6 is determined as valid data. If the data is valid, the statistical processing unit 222 performs a statistical process on the information data length 856 in addition to the past information data length of, for example, 99 data items, and calculates a threshold value. Part 224
Output to

The comparison unit 226 calculates the information data length 856 by
When the information data length 856 is smaller than the threshold value, “SHORT” is output to the schedule processing unit 228 and the high-frequency switch 236 when the information data length 856 is larger than the threshold value. Schedule processing unit 2
28 is “SHORT”, the scheduling is performed on the first uplink information data channel 308, the transmission start time 842 is calculated, and the calculated transmission start time 842 is transmitted to the control data encoding unit 208. The control data encoding unit 208 configures the single-cast downlink control data with the information channel change flag = “no change”, the information channel change flag, and the transmission start time 842 as the numerical value unit 835, and configures the modulation unit 2
06.

The downlink control data is frequency-converted by the high-frequency transmitting unit 204, passed through the duplexer 202 and the terminal 248,
Output to CATV line 300. Cable modem 10
0 receives the single-cast downlink control data, and reads the information channel change flag and the transmission start time 842.
Since the read information channel change flag is “no change”, the channel switching control unit 110 transmits the already stored uplink information channel frequency initial value to the high-frequency transmission unit 104.
Set to. The control unit 118 controls the Ethernet I / F unit 120 to transmit the Internet connection request signal from the buffer memory 126 so that the signal is transmitted at the designated time. The encoding unit 108 incorporates the Internet connection request signal into the information data 864 and
62. The uplink information data 862 is
6. The signal is transmitted to the CATV line 300 via the high-frequency transmitting unit 104, the duplexer 102, and the terminal 122. As described above, the Internet connection request signal from personal computer 400 is transmitted to center device 200.

Next, the comparison unit 22 of the center device 200
6 will be described when “LONG” is output to the schedule processing unit 228 and the high-frequency switch 236. In the case of “LONG”, the schedule processing unit 228 performs scheduling on the second uplink information data channel (or frequency band) 310 and sets the transmission start time 84
2 is calculated and transmitted to the control data encoding unit 208. The control data encoding unit 208 sets the information channel change flag to “changed”, and sets the information channel change flag, the uplink information channel frequency (frequency of the second uplink information data channel), and the transmission start time 842 to the numerical value unit 835. did,
The single-cast downlink control data is configured and transmitted to the modulation section 206. Thereafter, as in the case of "SHORT", the data is output to the CATV transmission path.

The high-frequency switch 236 is connected to the “LON
G "is received, the switch is turned on, and the duplexer 202 and the high frequency receiving unit 238 are made conductive. The control unit 246 sets the high frequency receiving unit 238 to receive the second uplink information data channel. The cable modem 100 receives the single-cast downlink control data, and reads the information channel change flag and the transmission start time 842. The channel switching control unit 110 determines that the read information channel change flag is “changed”. Therefore, the already stored uplink information channel frequency initial value 840 is changed to the frequency band 310 of the second uplink information data, and is set in the high frequency transmitting section 104.

The control unit 118 controls the Ethernet I / F unit 120 to transmit the signal at the designated time, and causes the buffer memory 126 to output an Internet connection request signal. After that, as in the case of "SHORT",
An internet connection request signal is transmitted to center device 200. In this way, scheduling of an uplink time slot can be performed according to the information data length of the uplink signal.

As described above, the present invention is an extremely effective technique for providing an inexpensive transmission / reception device that can use a high-speed network for a computer.

[0051]

According to the present invention, since bidirectional communication capable of transmitting variable-length data can be realized, a bidirectional CATV system using a CATV transmission line, a center device thereof, a terminal device thereof, and a communication method thereof are provided with a computer. A high-speed network can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a bidirectional CATV system according to the present invention.

FIG. 2 is a schematic diagram showing one embodiment of frequency allocation of a bidirectional CATV system according to the present invention.

FIG. 3 is a block diagram showing one embodiment of a center device used in the bidirectional CATV system according to the present invention.

FIG. 4 is a block diagram showing one embodiment of a cable modem used in the bidirectional CATV system shown in FIG.

FIG. 5 is a schematic diagram showing one embodiment of a downlink signal format of the bidirectional CATV system according to the present invention.

FIG. 6 is a schematic diagram showing one embodiment of an uplink signal format of a bidirectional CATV according to the present invention.

FIG. 7 is a timing chart for explaining the operation of one embodiment of the bidirectional CATV system according to the present invention.

FIG. 8 is a timing chart for explaining the operation of one embodiment of the bidirectional CATV system according to the present invention.

FIG. 9 is a timing chart for explaining the operation of one embodiment of the bidirectional CATV system according to the present invention.

FIG. 10 is a timing chart for explaining the operation of one embodiment of the bidirectional CATV system according to the present invention.

FIG. 11 is a block diagram showing another embodiment of the center device of FIG. 1 according to the present invention.

[Explanation of symbols]

100, 1005, 1008 ... set-top box,
200: center device, 300: CATV line, 40
0, 1006, 1009 ... personal computer, 5
00, 1007, 1010: TV receiver, 600: router, 700: Internet, 800: MPEG server, 202: duplexer, 204, 210: high frequency transmission unit,
206, 212: modulation section, 208: control data encoding section, 214: encoding section, 216, 230, 238: high frequency reception section, 218, 232, 240 ... demodulation section, 220 ...
Control data decoding unit, 222 statistical processing unit, 224 threshold setting unit, 226 comparison unit, 228 schedule processing unit, 234, 242 decoding unit, 236 high frequency switch, 244 interface unit, 246 ... Control unit,
248: CATV line terminal, 250: Router I / F
, 1001 ... Router connection terminal, 102 ... Diplexer, 1
04: high-frequency transmission unit, 106: modulation unit, 108: encoding unit, 110: channel switching control unit, 112: high-frequency reception unit, 114: demodulation unit, 116: decoding unit, 118 ...
Control unit, 120: Ethernet I / F unit, 122: CA
TV line terminal, 124 personal computer terminal,
126 ... buffer memory.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Tsutomu Noda 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture F-term in Hitachi Multimedia Systems Development Division 5C064 BA01 BB05 BC10 BC16 BC20 BD01 BD13

Claims (17)

[Claims] 1. A center device and a plurality of terminal devices connected to the center device via a common transmission path, wherein the terminal device sets a transmission period of an uplink signal for information communication with the center device. Means for temporally dividing a reservation signal transmission period and a data signal transmission period, and control signal transmitting means for transmitting a control signal including a data signal length in the reservation signal transmission period to the center device before data transmission. And a variable-length data transmitting unit for transmitting variable-length information to the center device. The center device includes a detecting unit for detecting the data signal length, and a data signal in which the data signal length is set in advance. If the data signal length is smaller than the data signal length threshold, the first uplink frequency channel is determined to be the uplink frequency channel of the terminal device. If the data signal length is greater than the data signal length threshold, the channel determination unit determines the second uplink frequency channel as the uplink frequency channel of the terminal device, and the uplink determined by the channel determination unit. Transmission time determining means for determining an uplink transmission slot time in a frequency channel, and transmitting means for transmitting data on the determined uplink frequency channel and the uplink transmission slot time to the terminal device, Interactive CATV system. 2. The two-way CATV system according to claim 1, wherein said center device transmits said data signal during said data signal transmission period.
A bidirectional CATV system comprising variable length data receiving means for receiving the variable length information. 3. The bidirectional CATV system according to claim 1, wherein said center device has statistical processing means for statistically processing the detected data signal length to determine said data signal length threshold value. Bidirectional CATV system. 4. A two-way CATV system according to claim 1, wherein said terminal device performs information communication with said center device by multiple access through a plurality of uplink frequency channels via said common transmission path. Characteristic bidirectional CA
TV system. 5. A means for dividing an uplink signal transmission period into a reservation signal transmission period and a data signal transmission period in time and receiving an uplink signal transmitted from a terminal device through a common transmission path. And detecting means for detecting a data signal length, and comparing the data signal length with a preset data signal length threshold value. If the data signal length is smaller than the data signal length threshold value, 1 uplink frequency channel is determined as the uplink frequency channel of the terminal device, and when the data signal length is larger than the data signal length threshold,
Channel determination means for determining a second uplink frequency channel to be the uplink frequency channel of the terminal device; transmission time determination means for determining an uplink transmission slot time of the uplink frequency channel determined by the channel determination means; And transmitting means for transmitting data relating to the uplink frequency channel and the uplink transmission slot time to the terminal device. 6. The center apparatus according to claim 5, further comprising a variable length data receiving means for receiving said variable length information data during said data signal transmission period. 7. The center device according to claim 5, further comprising statistical processing means for statistically processing the detected data signal length to determine the data signal length threshold value. 8. A means for connecting to a center device via a common transmission line, and a transmission period of an uplink signal for information communication with the center device is temporally divided into a reservation signal transmission period and a data signal transmission period. Means for transmitting a control signal including a data signal length in the reservation signal transmission period to the center device prior to data transmission, and variable length data transmission for transmitting variable length information to the center device. And a terminal device. 9. A plurality of terminal devices are connected to a center device via a common transmission line, and the terminal devices are multiplex-connected to the center device via the common transmission line by a plurality of uplink frequency channels. The transmission period of an uplink signal for information communication from the terminal device to the center device is temporally divided into a reservation signal transmission period and a data signal transmission period, and prior to the data transmission transmission period, A control signal including a data signal length is transmitted to the center device during the reservation signal transmission period, the data signal length is detected by the center device, and the data signal length and a preset data signal length threshold are detected. If the data signal length is smaller than the data signal length threshold value, the first uplink frequency channel is determined as the uplink frequency channel of the terminal device, and Transmitting data specifying a channel, if the data signal length is greater than the data signal length threshold, determining a second uplink frequency channel as the uplink frequency channel of the terminal device and specifying the channel; The center device determines the uplink transmission slot time of the determined uplink frequency channel, transmits the determined time to the terminal device, and transmits variable length information from the terminal device to the center device. Communication method. 10. A plurality of terminal devices are connected to a center device via a common transmission line, and the terminal devices are connected to the center device via the common transmission line by a plurality of uplink frequency channels. The transmission period of an uplink signal for information communication from the terminal device to the center device is temporally divided into a reservation signal transmission period and a data signal transmission period, and prior to the data transmission transmission period, A control signal including a data signal length is transmitted to the center device in the reservation signal transmission period, the data signal length is detected by the center device, the data signal length is statistically processed, and a data signal length threshold value is transmitted. And comparing the data signal length with the data signal length threshold value. If the data signal length is smaller than the data signal length threshold value, the first uplink frequency channel is determined. A data channel length is determined to be an uplink frequency channel of the terminal device, and data specifying the channel is transmitted to the terminal device. If the data signal length is larger than the data signal length threshold value, the second uplink frequency A channel is determined as an uplink frequency channel of the terminal device, and data specifying the channel is transmitted to the terminal device. From the center device to the terminal device, the determined uplink transmission slot time of the determined uplink frequency channel Is determined by the center device and transmitted to the terminal device, and the terminal device transmits variable-length information to the center device. 11. An uplink control data including an information data length is configured in accordance with an Internet connection request signal, and control for transmitting uplink information data at a transmission time specified by downlink control data from the center device is performed. Control unit,
A transmission unit that transmits the uplink control data to the center device; a reception unit that receives the downlink control data transmitted from the center device; and a channel switch that reads the downlink control data and designates an uplink information channel to the transmission unit. A terminal device including a control unit, a receiving unit that receives the uplink control data transmitted from the terminal device, a threshold setting unit that sets a threshold value of an information data length, A comparing unit that compares a threshold value and the information data length of the uplink control data,
A schedule processing unit that sets an uplink information channel and a transmission start time based on the output of the comparison unit, a downlink control data configuration unit that configures the downlink control data in response to a command from the schedule processing unit, and the downlink control data A center unit including a transmitting unit for transmitting a signal, and a CATV common to the center unit and a plurality of the terminal units.
A bidirectional CATV system comprising: means for connecting via a line. 12. A bidirectional CATV system according to claim 11, wherein a statistical processing section for statistically processing information data length received in the past and resetting a threshold value of said threshold value setting section is provided in said center device. Bidirectional C characterized by providing
ATV system. 13. A means for connecting to a center device via a CATV line, and comprising uplink control data including an information data length in response to an Internet connection request signal and designated by downlink control data transmitted from said center device. A control unit for controlling transmission of uplink information data at the transmission time, a transmission unit for transmitting the uplink control data to the center device, and a reception unit for receiving the downlink control data transmitted from the center device. And a channel switching control unit that reads the downlink control signal and specifies an uplink information channel to the transmitting unit. 14. The terminal device according to claim 13, further comprising a buffer memory for storing said Internet connection request signal. 15. The terminal device according to claim 13, wherein the control unit controls the transmission unit so as to start transmitting the uplink control data at a predetermined time. 16. A terminal device connecting means for connecting a terminal device via a CATV line, a receiving unit for receiving uplink control data including an information data length transmitted from the terminal device, and setting a threshold value of the information data length. A threshold setting unit, a comparison unit that compares the information data length of the uplink control data with the threshold value from the threshold setting unit, and an uplink information channel based on an output from the comparison unit. A schedule processing unit that sets a transmission start time, a downlink control data configuration unit that configures the downlink control data according to a command from the schedule processing unit, and a transmission unit that transmits the downlink control data. Characteristic center device. 17. The center device according to claim 16,
A center apparatus, comprising: a statistical processing unit that statistically processes information data lengths received in the past and resets a threshold value of the threshold value setting unit.