JPH0657011B2 - Group simultaneous broadcast method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to a communication system for performing communication between a center and terminals by performing time division multiplex transmission on a CATV network, and particularly to group simultaneous broadcasting. The present invention relates to a communication method that enables communication.

[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. In addition, a coaxial cable is generally used as a cable forming a transmission line in the CATV network, 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 At the center, as shown as the delay control signal A in FIG. 6B, the response signal from the terminal control device at an intermediate distance from the center is delayed like the delay control signal A, although it is considerably delayed. Less delay than. 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.

Therefore, it is conceivable to use the idle time of the downlink signal to carry out the simultaneous broadcast communication, but the simultaneous broadcast to all subscriber terminals is not always an effective simultaneous broadcast. That is, when the message that the content of the broadcast is not valid for all subscribers, for example, when sending a message to a specific group (members of a specific residents 'association among multiple residents' associations or members of a circle) etc. , Unnecessary messages are also transmitted to non-members of other residents' associations and circles, and in some cases, it is possible that they may not want to be known, and hesitate to notify by simultaneous broadcast.

[Means for Solving the Problems]

The present invention eliminates such drawbacks and provides a communication system for easily performing broadcast communication for each group in a CATV network. That is, according to the present invention, the center is provided with means for inserting the broadcast information including the group designation information in the idle time of the downlink signal, and each terminal control device has the group designation information included in the broadcast information. Only when the group setting information previously set in the terminal control device agrees with the group setting information, means for sending the content of the broadcast to an external audio output device provided separately from the communication function such as a telephone is provided. By doing this, simultaneous broadcasting for each group can be performed.

[Action]

According to the present invention, it is possible to enhance the frequency utilization efficiency by effectively using the idle time of the downlink signal, and to provide the broadcast communication in units of groups.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. First
The figure shows 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 is shown with the same time width, but the signal width differs depending on 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 is generated. For example, when the timing control signal G1 is generated, the frame synchronization signal generated by the synchronization signal generation unit 22 is output. When the timing control signal G2 is generated, a delay control signal (delay time measurement instruction + terminal ID and delay time designation information + terminal ID in FIG. 3) created by the delay control signal creating section 23 is output, and so on. To multiplex. The input signal to the modulator 23 (the output of the multiplexer 21) can be arranged as shown in FIG. 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 24 is activated when broadcast is required, and creates the on / off signal and group designation information of the broadcast control signal unit shown in FIG. That is, for example, if the broadcast information is included in the corresponding cycle, it is set to on (= 1), and if it is not included (not activated), it is set to off (= 0). Although not shown, for example, the number is controlled so as to insert a numerical code or the like set by a rotary switch or a DIP switch.

The broadcast message creating unit 25 A / D-converts a message sound source (for example, a recorded tape recorder) 26 by a codec unit 27 and an A / D-converted signal within a frame period by a TDM speed converting unit 28. The speed corresponding to 1 bit of is converted into the speed on the transmission path, and the timing control signal G4
Is transmitted to the terminal device via the multiplexing unit 21.
The speed conversion unit 28 needs to be synchronized with the timing control signal G4, but it is omitted because it is not directly related to the present invention. Further, it can be easily understood that the A / D conversion codec unit 27 is used for telephones for 3.4 kHz, 7 kHz, or a multi-bit conversion element different from these, which affects the sound quality.

Communication control signal creation unit 29, call time slot control unit 3
Although 1 to 32 are controlled in the same manner as described above, it is possible that they are multiplexed by the switching equipment and input to the multiplexing unit 21.

Although not shown, timing control signals G4 and G5
, There may be a vacant time, that is, a difference between the simultaneous broadcast signal occupation time and the vacant time in the conventional method. In this case, for example, 0 or 1 is fixedly set. The multiplexing unit 21 controls the transmission. In this way, the downlink signal shown in FIG. 3 is sent to the tree type transmission line via the modulator 23 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 34 of the broadcast control unit 33 extracts a signal in the time zone in which the broadcast signal is accommodated (broadcast control signal) by these synchronization signals and clock signals, and determines whether or not there is broadcast information. Check the information (on / off) to indicate, for example, if this information is on, continue,
This terminal control device compares the contents of the group setting unit 35 in which the group setting information is set in advance with the contents of the received group designation information, and if they match, the speed conversion unit 3
6. The codec unit 37 outputs the broadcast message information to the external output unit (eg speaker) 38.

On the other hand, the information (on / off) indicating the presence or absence of broadcast information is off.
And the content of the group designation information does not match the setting content of the group setting unit 33, the speed conversion unit 3
6. The codec unit 37 is not activated. In this case, although not shown, it is necessary for the codec unit 37 to send out the non-call pattern data or control the external output unit 38 so as not to 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 28 and the codec unit 27, respectively. Also, the delay control unit 13, I
D setting unit 14, call control unit 17, telephone 16, switching unit 1
No. 5 and the like will not be described because they are controlled similarly to the conventional method.

Further, in the case of the terminal control device that does not receive the simultaneous broadcast, it is not necessary to provide the broadcast control unit 33, and it can be easily understood that these broadcast messages have no influence on this terminal control device. The idle time of the downlink signal may be provided at any other position in the frame without being provided between the delay control signal and the communication control signal. In any case, the group broadcast signal is inserted in this idle time. To do.

[Effects of the Invention] In the digital multiplex communication facility for performing delay control in the CATV network as described above, means for inserting a broadcast signal including information designating a group in the idle time zone of the downlink delay time at the center The terminal control device determines the signal for simultaneous broadcast, and when there is a signal and the group information matches, this signal is output to the external output device to use the idle time to perform simultaneous broadcast for each group. It is expected that the system will be able to provide CATV broadcasting services, communication services, and simultaneous broadcasting services with a system that is unified with effective use of frequencies. In addition, although higher quality than that of a normal telephone is desirable in broadcast communication, in ISDN basic service, two call channels and one control channel are one line.
The quality of the broadcast signal can be improved by using kHz audio ADPCM.

[Brief description of drawings]

1 is a block diagram showing 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. 3 is a terminal control from a center according to the present invention. FIG. 4 is a diagram showing an embodiment of a downstream signal format transmitted to the device, FIG. 4 is a diagram showing an embodiment of the time relationship of timing control signals in the center according to the present invention, and FIG.
FIG. 6 is a block diagram showing a conventional terminal control device, FIG. 6 is a diagram showing signals between conventional center terminal control devices, and FIG. 7 is a diagram showing signal timing of signal transmission / reception 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. In a communication network in which time division digital multiplex communication is performed with a plurality of terminal control devices having more communication time slots and the center, the terminal control devices are divided into a plurality of groups and delay time control is performed in the center. Broadcast message containing information for identifying the group in the idle time of the downlink signal caused by A means for inserting a message, and the terminal control device is provided with a means for extracting the message signal from the received signal and outputting a voice to an external output device when the group identification information of the terminal control device matches. Group broadcast communication system characterized by