JPH0657013B2 - Broadcast communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a communication system for performing communication between a center and each terminal by performing time division multiplex transmission in a CATV network, and particularly broadcast communication. The present invention relates to a communication method that enables

[Conventional technology]

Conventionally, CATV networks provide television broadcasting, but it is considered to provide communication services such as telephones by using a transmission line routed to each subscriber's house. Frequency division multiplex communication with frequency division was considered as a telephone service using this CATV network, but this method is analog communication and it is difficult to provide an ISDN service, so digital signals are time-divided. It is proposed to communicate.

In general, CATV networks have tree-like transmission lines, and ordinary communication networks are star networks. For this reason, in the CATV network, there is a tree structure between the center and a plurality of terminal control devices, and by the TDMA (Time Division Multiplex Demand Assign) method, different frequencies are assigned to the downlink and the uplink, and a pair of transmission lines is provided to connect with the center. It has been considered to allocate a communication channel (time slot) every time a digital communication with each terminal control device is required by time division multiplex transmission. Also, in CATV networks, coaxial cables are generally used as the cables that make up the transmission line, and the signal transmission time (propagation time) of the cable changes depending on the distance between the terminal control device and the center equipment and temperature conditions. In order to adopt the TDMA method, it is necessary to measure the delay time to the center for each terminal control device and automatically control the timing of sending an upstream signal from the terminal control device.

Therefore, the downlink signal is transmitted by digital modulation from the center in the format shown in FIG. 6A. This downlink signal is provided with a sync signal at the beginning of a frame, a delay control signal next thereto, a communication control signal after a vacant time, and then n speech time slots are sequentially provided. The downlink signal of this format is transmitted at a constant period T as shown in FIG. 7, but in the measurement of the delay time,
A delay time measurement instruction and a device-specific terminal ID (identification) indicating a specific terminal control device are transmitted in the delay control signal. In the terminal control device, as shown in FIG.
The digital signal received by the frame synchronization detection circuit 12 is converted into a digital signal, the frame synchronization detection circuit 12 detects the synchronization signal from the digital signal to establish synchronization, and the delay control circuit 13 receives the digital signal according to the instruction from the frame synchronization detection circuit 12. The delay control signal is extracted from among these, and the terminal ID included in the extracted delay control signal is compared with the ID given to the terminal control device set in the ID setting circuit 14. When the delay control signal is a delay time measurement instruction, a response signal including the delay measurement time and its terminal ID is prepared, and the response signal is modulated / demodulated via the switching unit 15 in synchronization with the detection of the synchronization signal in the next cycle. It is modulated by the device 11 and sent to the center.

The center receives the response signal from the terminal control device, and measures the time t ', which is the difference between the transmission time of the frame synchronization signal transmitted from the center and the reception time of the response signal. From this time t ', the delay time between the terminal control device and the center is detected. One half of the measurement time t'is the delay time t between the terminal control device and the center. Strictly speaking, it is necessary to consider the signal processing time. At the center, the delay time designation information and the I of the terminal control device are used as the delay control signal.
D and delay time t are set, and the signal is transmitted as a downlink signal in the next cycle. The terminal control device detects frame synchronization in the same manner as described above, and when the ID included in the delay control signal and the ID held by the terminal control device match, the received delay time t is the delay control unit 13
The delay control circuit 13 is controlled so that the communication signal stored in the terminal control unit and transmitted from the terminal control device to the center is delayed by (T-t) time from the received frame synchronization signal and relayed.
In this way, a delay time corresponding to the delay with the center is set for each terminal control device. Therefore, the communication time slot assigned at the time of communication is also transmitted with a delay of the delay time (T−t) set in the terminal control device, that is, the delay time adjusted to the specific time slot position designated prior to the call. By performing control for each individual terminal, upstream signals from each terminal control device at the center are arranged in an orderly manner, and a time-division digital transmission line without overlapping between a plurality of communication time slots is configured. As for the communication time slot, every time there is a communication request from the terminal controller, the center allocates an empty communication time slot, and each terminal controller further delays the allocated communication time slot with respect to the delay time set above. Send a signal. Further, as described above, setting the delay time for each terminal so that the signals reaching the center are temporally matched is referred to as delay time control.

The center may send (T-t) as a delay time instruction. Generally, the internal processing delay time of the center and the terminal control device and the difference in the delay time due to the up / down frequency bands are ignored because they are so small, but it is easy to add them to the delay time designation if they can be measured in advance. Let's do it.

As a method of using the communication time slot, for example, a communication control signal may be used to allocate a vacant communication time slot based on a channel request from a terminal control device that has a transmission request by a demand assign method.
The transmission timing of the upstream call signal from 6 to the center is controlled by delaying the call signal by instructing the call control unit 17 with a signal indicating the difference in the transmission time of the transmission communication control signal from the reception frame synchronization from the delay control unit 13. Will reach the center. In the center, in order to perform delay control according to the installation distance for each terminal control unit device that makes a call,
It is possible to prevent the received call time slot signals from overlapping. Although not shown in the figure in order to cover the control accuracy, it is necessary to consider providing a guard time between call time slots, but this is omitted because it is not directly involved in the present invention.

[Problems to be Solved by the Invention]

In such a delay control method, the center arrival time of the response signal based on the delay time measurement instruction signal differs depending on the distance from the center of the terminal control device, and the response signal from the terminal control device installed at the farthest end in the system. Is considerably delayed at the center with respect to the synchronizing signal as shown as the delay control signal A in FIG. 6B, but the response signal from the terminal control device at the intermediate distance from the center is the delay control signal B like the delay control signal. Less delay than A. Since the reception time of the response signal with respect to the frame synchronization signal varies depending on the distance of the terminal control device, the reception time range of the response signal is set so that the response signal from the farthest position can be received without overlapping with other signals. There is a need to. On the other hand, since the delay control signal of the downlink signal has a fixed time width and is inserted at a fixed time with respect to the frame synchronization signal, the delay control signal time width of the downlink signal and the waiting time of the response signal of the uplink signal The time difference from the range is a free time that is not used for downlink signals at all. Although the idle time is provided between the delay control signal and the communication control signal in FIG. 6A, it may be provided at any position in the frame.

In the method of performing delay control as described above, there is a drawback that an idle time is generated in the downlink signal and the use efficiency of the frequency is poor accordingly.

[Means for Solving the Problems]

In order to eliminate such drawbacks, the present invention provides a communication system capable of performing simultaneous broadcast communication in a CATV network. That is, according to the present invention, the center is provided with a means for inserting the broadcast information in the idle time of the downlink signal, and each terminal control device displays the contents of the time slot of the time when the broadcast information is stored in the telephone or the like. In addition to the communication function, a means for transmitting to an external audio output device provided is provided for simultaneous broadcast.

[Action]

According to the present invention, the broadcast communication can be provided by effectively using the idle time of the downlink signal to improve the frequency utilization efficiency.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. First
The figure shows the construction of a center according to the invention. Although not shown in the center, as shown in FIG. 4, the timing control signals G1 to G7 are repeatedly created every frame period T. In the figure, each timing control signal G1
G7 is shown with the same time width, but the signal width is different corresponding to each signal length. In FIG. 1, the multiplexing unit 21 is configured to output the signal of each corresponding generation unit when each timing control signal G is generated. For example, when the timing control signal G1 is generated, the synchronization signal generation unit 22 is used. The generated frame synchronization signal is output, and when the timing control signal G2 is generated, the delay control signal created by the delay control signal creation unit 23 (delay time measurement instruction + terminal ID, delay time designation information + in FIG. 3). The terminal IDs) are output, and the terminals are sequentially multiplexed. In this way, the input signal to the modulator 24 (the output of the multiplexer 21) is the third signal.
The arrangement may be as shown in the figure. The circled numbers shown as an output signal in FIG. 4 correspond to the circled numbers given to each signal in the signal format of FIG. In the conventional method, the timing control signals G3 to G4 are not generated.

The broadcast instruction creating unit 25 is activated when broadcast is required, and creates the on / off signal of the broadcast signal unit shown in FIG. That is, for example, when the broadcast information is included in the corresponding period, it is controlled to be on (= 1), and when it is not included (not activated), it is controlled to be off (= 0).

The broadcast message creating unit 26 outputs the output of the sound source of the message (for example, a recorded tape recorder) to the codec unit 28.
A / D conversion is carried out by the TDM speed converter, and the speed corresponding to 1 bit of the A / D converted signal within the frame period by the TDM speed converter 29 is converted into the speed on the transmission path, and the timing control signal G
4 is transmitted to the terminal device via the multiplexing unit 21. The speed conversion unit 29 needs to be synchronized with the timing control signal G4. Also, it can be easily understood that the codec unit 28 for A / D conversion affects the sound quality by the multi-bit conversion elements used for telephones of 3.4 kHz, 7 kHz or different from these.

Communication control signal creation unit 31, call time slot control unit 3
Outputs 2 to 33 are controlled in the same manner as above, but are multiplexed by the switching equipment and input to the multiplexing unit 21.

There is a vacant time between the timing control signals G4 and G5 as shown in FIG. 3, which is due to the difference between the time width of the broadcast signal and the vacant time in the conventional system. ,
In this portion, the multiplexing unit 21 controls so that 0 or 1 is fixedly transmitted. In this way, the downlink signal shown in FIG. 3 is transmitted to the tree type transmission line via the modulator 24 of FIG.

On the other hand, the terminal control device shown in FIG. 2 restores the signal of FIG. 3 via the modulator / demodulator 11, and the frame synchronization detection circuit 12 extracts a synchronization signal and a control clock signal (not shown). The control circuit unit 35 of the broadcast control unit 34 extracts a signal (broadcast signal) in a time zone in which the broadcast signal in the frame is accommodated by these synchronization signals and clock signals, and outputs the broadcast information. Information (on / off) indicating presence / absence is checked. For example, when the information indicates that the information is on, the speed changing unit 36 and the codec unit 37 output the broadcast information to an external output unit (for example, a speaker) 38. .

On the other hand, the information (on / off) indicating the presence or absence of broadcast information is
When f is indicated, the speed conversion unit 36 and the codec unit 37
Does not start. In this case, although not shown, in this case, the codec unit 37 transmits the no-call pattern data,
It may be necessary to control the external output section 38 so that it does not operate.

It can be easily understood that the speed conversion unit 36 and the codec unit 37 have functions opposite to those of the center speed conversion unit 29 and the codec unit 28. Further, the delay control unit 13, the ID setting circuit 14, the call control unit 17, the telephone set 16, the switching unit 15 and the like are controlled and operated in the same manner as in the conventional system, and will not be particularly described.

Further, in the case of the terminal control device which does not receive the broadcast, it is not necessary to provide the broadcast control unit 33, and in this case, the broadcast message does not have any influence on the device which does not have the broadcast control unit 34. It's easy to understand that.

It should be noted that the idle time of the downlink signal may not be provided between the delay control signal and the communication control signal but may be provided at another position in the frame. In any case, the broadcast signal is inserted in the idle time.

〔The invention's effect〕

As described above, in digital multiplex communication equipment that performs delay control in a CATV network, a means for inserting a broadcast signal in the down idle time zone at the center is used to determine the presence or absence of a broadcast signal in the terminal control device. However, when there is a signal, a means for outputting this signal to the external output section is provided so that the broadcast information is provided by utilizing the idle time. It is expected that the simultaneous broadcasting service will be available. In addition, although higher quality is desired for broadcast communication than for ordinary telephones, ISDN basic service requires 2
One call channel and one control channel,
Therefore, the cordic parts 28 and 37 are set to 7 kHz audio ADP
The voice can be improved by using commercials.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a center according to the present invention, FIG. 2 is a block diagram showing an embodiment of a terminal control device according to the present invention, and FIG. A format showing an example of a downlink signal format transmitted to a terminal control device, FIG. 4 is a diagram showing an example of a time relationship of timing control signals in a center according to the present invention, and FIG. FIG. 6 is a block diagram showing a terminal control device, FIG. 6 is a diagram showing signals between a conventional center and a terminal control device, and FIG. 7 is a diagram showing signal timing of signal transmission / reception in delay control between center terminal control devices. .

Claims (1)

[Claims] 1. In a tree-like CATV network, upstream and downstream frequency bands are paired and used as a transmission path, and a delay control time slot for performing delay time control and a plurality of communication channel time slots are provided within the frequency band. , The delay control time slot designates the terminal control device from the center to give a delay time measurement instruction, and the terminal control device which has received the delay time measurement instruction responds the reception delay time to the center by the delay control time slot. However, in a communication network that performs time division digital multiplex communication with a plurality of terminal control devices having more communication slots than the communication time slot and the center, the broadcast is simultaneously broadcast to the idle time of the downlink signal generated by performing the delay time control on the center. Means for inserting the message is extracted, and the broadcast message is extracted and output to the terminal control device. A broadcast communication system characterized in that it is provided with means for transmitting to the device.