JPH10262016A - Two-way communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent useless dial operations by broadcasting the presence or absence of the plural idle information channels via a control channel of an outgoing channel and selecting at random plural control channels to access them via a terminal when an idle information channel is available. SOLUTION: A center device is constituted of a switchboard 11, an interface device 12, a time division multiplex access device 13, etc. Then every terminal connected to a transmission line performs the two-way communication, via a center device by making use of the time division multiplex channels of communication bands which are separated in each frequency bands of both incoming/ outgoing-transmission bands. Each of incoming/outgoing-channels consists of plural information and control channels, and the control channel of the outgoing- channel led from the center device broadcasts the presence or absence of the plural idle information channels. Then a terminal selects at random plural control channels and accesses them, when an idle information channel is available.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cable television system (hereinafter referred to as CA) capable of two-way communication between terminals.
TV system).

[0002]

2. Description of the Related Art The CATV system currently constructed is mainly provided with a service of distributing an existing TV broadcast or independent broadcast from a center device to a plurality of terminals of participants.
In recent years, a broadcasting / communication integrated service that realizes two-way communication between subscribers by adding a repeater having a two-way communication function to this CATV system has been realized by, for example, an ISDN communication service. In this ISDN communication service, as will be described later, the communication frequency band of the transmission path is divided into an upstream transmission band and a downstream transmission band. That is,
Increase the frequency of the transmission line and increase the transmission area, for example, 10 to 5 OMH.
For z, a downstream transmission band is allocated to, for example, 70 to 300 MHz. Among them, the bandwidth for one TV channel (6 MHz)
z) 30 to 36 MHz corresponding to the upstream communication band, 2
34 to 240 MHz is used for the downstream communication band. This band is subjected to QPSK modulation to secure a digital communication path of 8,912 Mbps and use it as a time division multiplexing communication path (TDM).

[0003] In such a transmission frame of the TDM communication path, a plurality of information channels are multiplexed and transmitted in order to transmit communication information such as voice, facsimile, and data.
Conventionally, there are a fixed assignment method in which a fixed channel is assigned as an information channel for each terminal, and a demand assignment method in which an empty time slot is assigned each time a call occurs in each terminal. Two of the assignment methods have been put to practical use.

The above-mentioned fixed assignment method does not require a control channel and is easy to control. However, since the number of terminals that can be accommodated is the same as the number of time slots in a transmission line, it can be applied only to small-scale communication systems. No, the efficiency of transmission line use is very poor.

On the other hand, in the demand assignment system, a procedure such as time slot allocation and release is performed between a terminal and a center device at the start and end of communication. Therefore, a plurality of control channels are multiplexed on a plurality of information channels and transmitted. The need to do so complicates the device. However, with the same number of time slots as in the above-mentioned fixed assignment method, a large number of terminals can be accommodated by a large grouping effect within a predetermined traffic volume and blocking rate. Therefore, as a time slot control method for a TDM communication path for a bidirectional communication system such as a CATV system, it is possible to flexibly cope with a small to medium or large-scale communication system, and the use efficiency of the transmission path is high.
The demand assignment method that is excellent in economic efficiency is promising.

FIG. 14 shows an example of a transmission frame configuration of a TDM communication path in the conventional demand assignment system. In the figure, the uplink and downlink transmission frames are respectively composed of one control channel 141a, 142
a and an information channel group 141 including a plurality of information channels
b and 142b.

FIG. 15 shows a center device 15 in a CATV system having an upstream and downstream transmission frame configuration.
1 shows a series of communication sequences from the assignment of an information channel due to the occurrence of a call, communication, and disconnection between the terminal 1 and the terminal 152. The center device 151 includes, for example, an interface with a TDM transmission line and a transmitting terminal 152.
And an exchange for exchanging an information channel with a terminal (not shown) of the other party number designated by
Reference numeral 2 has, for example, a voice communication function and incorporates an interface with a TDM transmission line. As shown in the figure, in the communication sequence between these, as shown in the figure, when the terminal 152 detects an off-hook and enters a dial number, the uplink channel sends an information channel allocation request 15
3 is transmitted. The center device 151, upon receiving this, searches for a free information channel, and if there is a free information channel, executes connection and exchange processing to the partner terminal, and confirms information channel assignment 1 including the number of the free information channel.
54 is transmitted to the terminal 152 via the downlink control channel. When the vacant information channel is allocated, a call can be made between the terminals by transmitting and receiving the user information 155 including voice information by using the uplink and downlink information channels.

[0008]

In the conventional two-way communication system as described above, first, a dial pulse (DP) or a push button (P) input by a subscriber is input.
B) etc., the dial number indicating the destination is temporarily stored on the terminal side, and the dial numbers are digit-by-digit or collectively, for example,
TTC standard JT-Q. It is necessary to notify the center device by a call request procedure such as a call control procedure according to 931 rules. For this reason, if the dialing operation is not completed, the empty information of the time slot cannot be understood, the operation is wasted, the traffic of the control channel used as the notification unit increases, and retransmission of the same channel occurs frequently. A problem arose. Furthermore, it is necessary to temporarily store the dialed number in the terminal, which increases the size of the terminal,
There was a disadvantage that it became expensive.

Accordingly, an object of the present invention is to provide a two-way communication system in which the terminal can know the time slot vacancy information before the terminal completes the dial operation, in order to solve the above-mentioned problems in the conventional system. It is in.

[0010]

According to the present invention, there is provided a communication system in which a center device and a plurality of terminals are connected on a transmission line, and the terminals are separated for each frequency band of an upstream transmission band and a downstream transmission band. In a two-way communication system that performs two-way communication via the center device using a time-division multiplex communication channel of a band, each of the upstream and downstream communication channels includes a plurality of information channels and a plurality of control channels. In the control channel of the downlink communication path from the center device, the presence or absence of an empty information channel among the plurality of information channels is broadcast, and the terminal receives the broadcast and transmits to the control channel. Upon access, the plurality of control channels are randomly selected in a state where the free information channel exists. The above problems can be solved by Shin system.

Further, the present invention provides the above-mentioned upstream transmission band,
Further, it has a time-division multiplexing channel arranged in a plurality of frequency bands, each of which comprises a plurality of information channels and at least one control channel. In the control channel of the road,
It has a function of broadcasting the presence or absence of a free information channel in each of the plurality of uplink frequency bands.

Further, the present invention is characterized in that a terminal status monitoring field is provided for each of the information channels.

Further, the present invention is characterized in that an error detection / correction code is added to the status monitoring field.

Further, the present invention is characterized in that the on-hook / off-hook information of the terminal is provided in the status monitoring field.

Further, according to the present invention, according to the call state at the time when an error is detected in the state monitoring field, the state monitoring field is discarded, and the state monitoring field is replaced or switched to disconnect the call. It is a feature.

Further, the present invention is characterized in that the status monitoring field is provided with terminal layer 1 information.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a diagram showing a configuration of a CATV system which is one embodiment of a two-way communication system according to the present invention.

As shown in FIG. 1, the CATV system extends a tree-type coaxial cable from a center apparatus 1 having a TV broadcast distribution facility and an exchange to terminals 2a to 2d in a plurality of subscriber premises. A relay amplifier 3 having a bidirectional communication function is connected to a branch point on the way. Each of the terminals 2a to 2d is located in the home of a user (subscriber), and each of the terminals 2a to 2d has a TV set including a television (TV) and a video tape recorder (VTR), and a telephone and a facsimile. Communication equipment is connected.

FIG. 2 is a block diagram showing the configuration of the center device 1, which comprises an exchange 11, an interface device 12, a time division multiple access device (hereinafter referred to as a TDMA device) 13, and a head end 14. Exchange 11
Performs a connection for a local call and a connection to an external network. The exchange 11 has a capacity (connection capacity) of, for example, 1,024 units.
2 is connected by 32 signal lines. Since 125 μs is taken as one frame, and one frame is multiplexed and transmitted with 32 time slots (TS) of 64 Kbps,
A total of 32 between the exchange 11 and the interface device 12
There is a transmission capacity of TS × 32 (number of signal lines) = 1,024 TSs. The TDMA device 13 transfers the TS set by the interface device 12 to a TS on a transmission line connecting the center device 1 and each of the terminals 2a to 2d as described later.

Here, in the above-described ISDN communication service, the communication frequency band of the transmission line is generally divided into an upstream transmission band 131 and a downstream transmission band 132 as shown in FIG. Of the downlink transmission band 132, for example, 234 to 240 MHz is allocated as a downlink communication band, and this band is subjected to QPSK modulation to obtain a 8,192 Mbps (4, 192 Mbps).
096 baud) and a digital communication path of 30 to 3 is set as the upstream communication band of the upstream transmission band 131.
6 MHz is allocated, and although not shown, this is further divided into four, for example, with the center frequency of 30.9 MHz and 32.3 M
Hz, 33.7 MHz, and 35.1 MHz, QPSK modulation is performed with a width of 1.4 MHz, and 2.048 Mb.
Secure digital communication path of ps (1,024 baud)
These communication paths are used as time division multiplex transmission paths. In other words, in this system, the upstream and downstream configurations are asymmetric,
Downlink 8,192 Mbps, Uplink 2,048 Mbps × 4
Has been assigned. Here, the uplink communication paths are called f0, f1, f2, and f3 for each center frequency to be distinguished.

Next, the TDMA device 13 shown in FIG. 2 works together with the exchange 11 to efficiently perform communication between the terminals 2a to 2d so that uplink signals transmitted from the terminals 2a to 2d do not collide with each other. Center device 1 and each terminal 2
A round-trip signal time between a and 2d is measured, and control is performed so that a farther terminal, for example, the terminal 2d, transmits an uplink signal earlier. FIG. 10 shows the concept of transmission control of an uplink signal. That is, in order to match the phases of the uplink / downlink frame signals on the center device side, this control is performed after the terminal receives the TS from the center device, and then Td (downlink delay time) + Tu
(Uplink delay time) An uplink signal is transmitted earlier. This precision is about 1/10 of 1 bit (symbol) time or less (1/16 in the present invention).
), The T received by the center device
S is synchronized with the clock of the center device. This enables a highly efficient frame configuration in which the preamble for each TS is removed. However, in the range of the timing accuracy, a deviation may occur from the optimum timing in the punching of the reception signal in the center device, and therefore, it is necessary to stabilize the reception timing of the uplink signal in the center device (transmission timing of the terminal). .

The head end 14 shown in FIG. 2 is connected to a video signal such as a TV broadcast and an independent broadcast and a time division multiplex access (hereinafter referred to as TD).
This is a device that performs multiplexing / demultiplexing with a signal multiplexed by the MA and transmits and receives (communicates) the TDMA signal to and from the terminals 2a to 2d.

In such a center device, a frame of a TDMA signal between the exchange 11 and the interface device 12 has a plurality of, for example, 32 time slots # 0 as shown in FIGS. 7 (a) and 8 (a). # 31. Here, the upstream and downstream frames have the same configuration.

As shown in FIG. 4, the interface device 12 includes a downlink TS transfer unit 41 and an uplink TS transfer unit 4.
2. It has an interface main controller 43.

The interface device 12 is connected to the terminal 2a
2d or according to a call control signal from the exchange 11,
The uplink or downlink time slot CTS on the TDMA device 13 side (terminal side) is dynamically allocated according to the idle state (demand assignment), and the downlink TDM from the exchange 11 is assigned.
The A signal (downlink time slot: PTS) is converted to a downlink TDMA signal (downlink time slot: CTS) to the TDMA device 13 (terminal side), and conversely, an uplink TDMA signal (uplink) to the TDMA device 13 (terminal side). Time slot: CT
S) is replaced with an uplink TDMA signal (uplink time slot: PTS) on the exchange 11 side.

As shown in FIG.
Reference numeral 1 includes a downstream frame receiving unit 41a, a downstream frame receiving buffer 41b, and a downstream frame transmitting unit 41c. The interface main control unit 43 includes an interface device control unit 43a, a CTS-PTS correspondence table storage unit 43b.
And a terminal status table storage unit 43c. The interface device control unit 43a transmits and receives the call control signals to and from the exchange 11, and the demand assignment control channels 72c and 82b to and from the terminals 2a to 2d shown in FIGS. And CTS- shown in FIG.
Based on the PTS correspondence table, an empty CTS is searched from among the CTSs # 0 to # 87, and control for assigning a CTS number corresponding to the PTS number is performed. Further, the terminal status table storage unit 43c stores the information of the terminal attributes, the information channels 72e and 82c (uplink / downlink CT) shown in FIGS. 7 (b) and 8 (b), respectively.
S) describes whether the information can be used or not. If a call request (although it is impossible originally) or a call request to a terminal that cannot use the information channel is received from a terminal that cannot use the information channel,
The call control is rejected. This state table storage unit 43c stores the TD
It shall be shared with the MA device 13.

In the downstream frame receiving section 41a, FIG.
(B) Two downstream frame reception buffers 41b for each 5 ms time interval of the frame 72 on the TDMA device 13 side.
# 0 and 41b # 1 are alternately switched to write the downstream PTS to the same buffer.

The downstream frame transmitting section 41c reads out the downstream PTS based on the CTS-PTS correspondence table shown in FIG.
7B is written in a predetermined CTS of the frame 72, and the control information for the TDMA device 13 is set on the control channel 72b, and the idle channel (CTS) for the terminal is written.
The information is written to the demand assignment control channel 72c and transmitted to the TDMA device 13.

The upstream TS transfer unit 42 shown in FIG.
The upstream frame receiving unit 42a comprises an upstream frame receiving buffer 42b, an upstream frame receiving buffer 42b, and an upper reframe sending unit 42c. The upstream frame receiving unit 42a has a time interval of 5 ms between the frames 82 of the TDMA device 13 shown in FIG. Two uplink frame reception buffers 42b # 0, 42b for each
# 1 is alternately switched, and based on the CTS-PTS correspondence table shown in FIG. 9, the upstream CTS is written into the same buffer at a predetermined upstream PTS position, and the TDMA shown in FIG.
The control information (control channel 82a) from the device 13 and the free channel (CTS) acquisition information (demand assignment control channel 82b) from the terminal are transmitted to the interface device control unit 43a.

Similarly, the upstream frame transmitting unit 42c alternately switches the upstream frame receiving buffers 42b # 0 and 42b # 1, and the information (upstream CTS) of the buffer written by the upstream frame receiving unit 42a is shown in FIG. It is read out based on the CTS-PTS correspondence table shown and transmitted to the exchange 11.

Next, as shown in FIG. 5, the TDMA device 13 comprises a TDMA device main control unit 51, a downstream processing unit 52, an upstream processing unit 53, and the like.

The TDMA main controller 51 has a TDMA having a memory such as a microprocessor and a RAM / ROM.
The device control unit 51a includes the terminal status table storage unit 43c described above. The TDMA device control unit 51a is control information of the interface device 12 or the terminals 2a to 2d from the control channel receiving unit 52b of the downlink processing unit 52 and the uplink delay measurement control channel receiving unit 53d of the uplink processing unit 53. Control channel 72b shown in FIG.
The delay measurement control channel 83a shown in FIG. 8C is received, appropriate processing (for example, calculation of transmission timing) is performed, and the response is set to the control channel transmission unit 53e and the downlink delay measurement control channel transmission unit 52c. I do. When the transmission timing is determined for the terminal and the information channels 72e and 82c (uplink / downlink CTS) shown in FIGS. 7 and 8 become available, the fact is described in the terminal state table storage unit 43c.

The downlink processing section 52 includes a downlink frame receiving section 52a, a control channel receiving section 52b, a downlink delay measurement controlling channel transmitting section 52c, and a downlink frame transmitting section 52d.
It is composed of In the downstream frame receiving unit 52a,
The control channel 72b of the downlink TDMA signal 72 shown in FIG. 7B transmitted from the interface device 12 is set in the control channel receiving unit 52b, and the downlink frame transmitting unit 52d transmits the downlink delay measurement control channel transmitting unit 52c.
Is transmitted to the terminal set in the downlink T shown in FIG.
The DMA signal 73 is set to the delay measurement control channel 73b and transmitted to the modulation unit at the head end.

The upstream processing section 53 includes an upstream frame receiving section 53a, a phase determining section 53b, a phase adjusting section 53c, an upstream delay measurement control channel receiving section 53d, a control channel transmitting section 53e, and an upstream frame transmitting section 53f. Have been.

In the upstream frame receiving section 53a, FIG.
The uplink TDMA signal 83 shown in (c) is received, the delay measurement control channel 83a is set in the phase determination unit 53b, and the remaining channels are set in the uplink frame transmission unit 53f.

The phase determining unit 53b has a clock generating unit, generates a clock of 64 MHz of 1/16 of 1 bit time, synchronizes with the preamble pattern 83a1 of the delay measurement control channel 83a, and 12 (4 MHz) and the terminal (2a-2)
The phase difference from the upstream TDMA signal 83 shown in FIG.

In the phase adjusting section 53c, the measured 1/1
Adjust the phase in units of 6 bits to “shift” in units of bits,
The frame synchronization pattern 83a2 shown in FIG. 8C and the frame synchronization signal (200H
z), the bit difference is measured, and the obtained phase and bit difference (reception timing) and the received data of the delay measurement control channel 83a are set in the uplink delay measurement channel receiving unit 53d.

Although not shown, the phase adjustment unit 53c has a CRC check unit and an error correction (FEC) unit, and refers to an error correction bit 83a4 shown in FIG. Channel information section 84 and CRC
After error correction of bit 83a3, CRC bit 8
With reference to 3a3, the error detection of the same information section 84 is performed. When an error is detected by error correction / detection, the fact is similarly set in the uplink delay measurement control channel receiving unit 53d.

As shown in FIG. 6, each of the terminals 2a to 2d includes a demultiplexing unit 61, a downstream processing unit 62, an upstream processing unit 63, and a main control unit 64.

The splitter 61 has a splitter 61a.
The splitter 61a receives a CATV signal X (a plurality of program signals such as a television program, an audio program and a teletext program, a communication signal, etc.) from the center device 1 shown in FIG. A control signal and the like are collectively referred to as a signal obtained by frequency-division multiplexing, and only desired signals are distributed to the downstream processing unit 62, and the communication signal and the control signal Y output from the upstream processing unit 63 are also The data is transmitted to the center device 1 via the input / output terminal A.

The downlink processing section 62 includes a distribution section 62a, a demodulation section 62b, a downlink delay measurement control channel receiving section 62c,
It is composed of an audio output unit 62d. As shown in FIG. 3, the distribution unit 62 a performs frequency band pass for the downstream band of 70 to 300 MHz, and sends the signal X1 carrying the existing analog TV service to the output terminal B to the output terminal B.
The signal X2 in the 234 to 240 MHz band in which the DMA signal is secured is distributed to the demodulation unit 62b.

The signal X1 distributed by the distributor 62a
Is sent to the antenna terminal of the TV receiver via the output terminal B. The demodulation unit 62b demodulates the signal X2 from the distribution unit 62a into a digital signal.

Downlink delay measurement control channel receiving section 62c
Receives the downlink TDMA signal, extracts the signal corresponding to the own address (terminal ID) of the delay measurement control channel 73b, and distributes it to the terminal control unit 64a of the main control unit 64. The terminal ID is input from an input terminal E to a terminal ID storage 64 composed of a nonvolatile storage device such as a ROM or a hard disk device.
b and is set in advance.

The audio output section 62d has a D / D converter for converting the digital signal demodulated by the demodulation section 62b into an analog signal.
An A conversion circuit is provided.

The upstream processing section 63 includes a modulation section 63a, a transmission timing adjustment section 63b, an uplink delay measurement control channel transmission section 63c, an audio input section 63d, and the like. The audio input unit 63d outputs the audio information input from the terminal D to the transmission timing adjustment unit 63b. The voice input unit 63d is provided with a D / A conversion circuit that converts input voice information (including a dial signal as well as a voice signal) into a digital signal. The transmission timing adjusting unit 63b determines the transmission timing based on the transmission timing value 74d shown in FIG. 7C, which is input from the downlink processing unit 62, and converts the audio information input at that timing into the timing shown in FIG. It is transmitted to the center device 1.

The transmission timing adjustment unit 63b has a clock generation unit. Under the control of the main control unit 64a, the transmission timing adjustment unit 63b adjusts the accuracy of the delay measurement to 64 MHz of about 1/16 of the Ebit time. A clock is generated, and the transmission timing is controlled by the clock.

Next, referring to FIGS. 7 and 8, TDs communicated between center device 1 and terminals 2a to 2d will be described.
The frame configuration of the MA signal will be described.

Of the TDMA signals communicated in a time-division multiplex manner between the center apparatus 1 and the terminals 2a to 2d,
The signal frame is composed of a frame used between the interface device 12 and the TDMA device 13 shown in FIG. 7B and a frame used between the TDMA device 13 and the terminal shown in FIG. 7C. I have. The former is 5m
s is one frame (40,960 bits), and a frame synchronization bit 72 in which a specific pattern for frame synchronization is described.
a, a control channel 72 for controlling a TDMA device
b, information channel 7 including delay measurement control channel 73b, demand assignment control channel 72c, broadcast channel 72d, and 88 channels CTS # 0 to CTS
2e and the like. This information channel 72e
Is referred to as downlink CTS for convenience. Channel CTS # 0-C
Each of TS # 87 has 40 pieces of 8-bit information (8 bits).
(Bit × 40 = 320 bits). The information channel 72e is further provided with a state monitoring field 74a relating to call control such as ringing (calling) of the terminal, as shown in FIG.

The control channel 72b is connected to the TDMA device 1
3 and the interface device 12, the TDM
Used to control device A.

Next, the latter is the former control channel 72b.
Is replaced by the delay measurement control channel 73b, except that the former is the same as the frame configuration.

The delay measurement control channel 73b is
In communication between the DMA device and the terminal, the command type 74 is used for controlling the terminal, and as shown in FIG.
a, a terminal ID (address) 74b, an information channel transmission flag 74c, a transmission timing value 74d, and the like. The information channel transmission flag 74c indicates whether or not the information channel 72e can be transmitted to the terminal. In the disabled state, the terminal is prohibited from transmitting the information channel 72e and uses the delay measurement control channel 73b. It is assumed that only communication can be performed. Transmission timing value 74d
Indicates the timing (bit and phase value) at which the terminal should transmit the uplink TDMA signal frame shown in FIG. 10 as described above.

The vacant CH broadcast channel 72c has a flag 76a for each of the uplink communication paths (frequency) f0 to f3 as shown in FIG. 72e indicates whether or not there is, and is transmitted from the center apparatus 1 to the terminal 2 in a broadcast format, so that all the terminals 2 can know the free information. Here, the broadcast format means that all the terminals, for example, the channel 72
The communication format is such that information of a specific channel, such as c, can always be received, so that all terminals can simultaneously receive the same information.

When performing communication, the terminal 2 determines the presence or absence of an idle information channel 72e for each uplink frequency based on the information of the same channel, and determines whether or not there is an idle uplink signal control channel 82e.
b, requesting that device 1 allocate information channels 72e and 82c. In addition, the center device 1 confirms the terminal 2 using the control channel 72d.
Send to

Four control channels 72d (# 0 to # 3) are prepared, which are the same as the number of uplink frequencies. The center device 1 corresponds to the control channel 82b of the uplink frequency f0 to f3, respectively. For example, in response to a request from the terminal 2 using the control channel 82b of the uplink frequency f0, the center device 1 uses the downlink control channel # 0. respond. As shown in FIG. 11E, a code 7 indicating the type of command / response
5a, a terminal ID (address) 75b, and control data 75c which is a parameter determined for each code 75a.

Further, the frame of the uplink TDMA signal corresponds to the interface device 12 and the TDM signal shown in FIG.
It is composed of a frame used between the A device 13 and a frame used between the TDMA device 13 and the terminal shown in FIG. The former is as shown in FIG.
As in the case of the downlink TDMA signal, 5 ms corresponds to one frame (40,
960 bits) and includes a control channel 82a, a delay measurement control channel 83a, a demand assignment control channel 82b, and 88 information channels 82c. The information channel 82c has, in addition to the 40 information bits (8 bits × 40 = 320 bits) similar to the downlink frame described above, 8 bits in front and 8 bits in the rear for absorbing the delay due to the delay detection of the center apparatus 1 in the information bits. A guard bit 82c1 and a 64-bit error correction bit (FEC) 82c2 are added to eight bits. The range of the error correction (FEC) is set to 40 information bits, and the information bits and the error correction bits are set to the output range of the carrier (transmission signal).

Next, the latter is the former control channel 82a.
Is replaced by a delay measurement control channel 83a, except that the former is the same as the former frame configuration.

The delay measurement control channel 83a is shown in FIG.
As shown in (c), command type 84a, terminal ID
(Address) 84b, information channel transmission flag 84c,
Transmission timing value 84d and random pattern 84e
In addition, a 64-bit preamble 83a1 that describes a specific pattern for clock synchronization, a 16-bit frame synchronization (FS) bit 83a2 that describes a specific pattern for frame synchronization, and a 16-bit CRC for error detection It is composed of a bit 83a3, a 16-bit error correction bit (FEC) 83a4, and a guard (G) bit 83a5 of 8 bits in front and 8 bits in back.
The range of CRC for error detection is 128 bits of spare bits from the command type, and the range of error correction (FEC) is 12 bits.
It is assumed to be 144 bits including a CRC bit in 8 bits.
Then, the error correction bits 83 are converted from the preamble 83a1.
The range up to a4 is set as the carrier output range (preamble 8
The error correction bits 83a4 from 3a1 are the output data of the terminal 2. Here, the length of the delay measurement control channel 83a is set to 488 bits, and in the initial state (information channel transmission “impossible” state), the output data from the terminal 2 depends on the distance from the center apparatus 1. Channel 83a
Since the output data from the terminal 2 fluctuates within the range, the transmission timing is controlled so that the WA 85 has 8 bits. That is, when the WA 85 has 8 bits, the state of the information channel transmission is “enabled”.

The control channel 82b is used when the terminal makes a request for information channel allocation at the start of communication in a state where information channel transmission is enabled. As shown in FIG. 9E, a code 85a indicating the type of command / response and a terminal ID (address) 85 are provided similarly to the downlink control channel.
b, control data 85c which is a parameter determined for each code 85a. Further, similarly to the information channel 82c and the delay measurement channel 83a, a guard bit, an error correction bit, and the like are added.

Next, the operation of the CATV system configured as described above will be described. A plurality of terminals 2a to 2 shown in FIG.
When a voice call is made between any two of the devices d, for example, 2a and 2b, the center device 1
7a and 7b, respectively, to the terminals 2a and 2b, and the downlink delay measurement control channel 73b and the terminals 2a and 2b.
a, 2b, and measures the time “shift” from the uplink delay measurement control channel 83a to the center apparatus 1, and sets the terminals 2a, 2b so that the phases of the uplink and downlink frames match.
Is instructed to transmit an upstream frame (transmission timing). The terminal 2a, 2b
In this example, the precision of the delay measurement is controlled by about 1/16 of 1 bit. Until the phases match (actually, a tolerance of ± α is given), the terminal 2 is connected to the demand assignment control channel 7.
The use (transmission / reception) of 2c, 82b, the broadcast channel 72d, and the information channels 72e, 82c is prohibited (the terminal does not transmit / receive).

The center device 1 uses the downlink demand assignment control channel 72c to notify (broadcast) the numbers of the free information channels 72e and 82c to the terminal 2, and when the phases of the uplink and downlink frames match, , TDM
The A device 13 notifies the terminals 2a and 2b of the information channel transmission flag 74c as "OK".
a and 2b are demand assignment control channels 72c and 82
b can be used.

The terminals 2a and 2b check the vacant information of the notified channel number, request the center device 1 to allocate an information channel using the up-link demand assignment control channel 82b, and thereafter request the allocated information channel. Use the channel to connect and talk with the other party. At this time, the CTS-P of the center device 1 in the ascending and descending directions
The correspondence table of FIG. 9 shows the correspondence between TSs. Unused (empty) CTS for both uplink and downlink is indicated by "-", and IDs are ID1 and ID2 (for example, terminals 2a, 2a,
The terminal of b) has CTS ml, m2,
Indicates that the PTS uses nl, n2 time slots. Similarly, for terminals with IDs of ID3 and ID4, the CTS is m3 and m4, and the PTS is n3 and n4. Of course, the CTS and PTS numbers for uplink and downlink may differ depending on the order of channel reservation.

FIG. 12 shows a sequence of transmitting and receiving a TDMA signal between the center apparatus 1 and the terminal 2.

As shown in the figure, the transmission / reception sequence between the TDMA device 13 and the terminal 2 is basically the transmission / reception of the command A, response A ', and command B every 5 ms. This basic sequence is repeated for each terminal 2 for the number of registered terminals (here, 1024), and the terminal 2 goes round. That is, from an individual terminal, about 15 seconds (15 seconds)
(ms × 1024 units), command / response transmission / reception with the TDMA device is performed.

Here, in command A, uplink frequency number 7
In step 7e, an uplink frequency (f0 to f3) to be used is specified in the response from the terminal. The terminal transmits a response A 'at the instructed uplink frequency. Similarly, in the uplink frequency number 77e of the command B, the next uplink frequency in which transmission and reception to and from another terminal circulates is specified. For example, after processing f0 first, it is sequentially designated like fl. That is, the transmission timing for each uplink frequency is determined by this basic sequence. TDM
Since the A device 13 first requests a response from the terminal 2, "A" is added to the type 74a of the command 74 in FIG.
Is transmitted to the terminal in order to identify the terminal. In the initial state, the information channel transmission flag 74c is "impossible", and a provisional value is described in the transmission timing value 74d. In terminal 2
As shown in FIG. 2, upon receiving the command A in which the own address (terminal ID) is described, a response A 'in which the terminal ID is described in 84b of FIG. 8C is transmitted at the transmission timing instructed by the command. . The format of the response A 'is shown as 84 in FIG.

The information channel 84c and transmission timing value 84d of the response are used for confirmation in the TDMA device 13, and describe the same value described in the command A. (The code type 84a is for future expansion and has only one type of response in the present system, so it is vacant 0.) When the TDMA device 13 receives the response A 'from the terminal to the previously transmitted command A, And the phase difference (reception timing) between the downlink frame and the downstream frame, and the transmission timing is updated as TXT + RXT → TXT. Here, TXT is transmission timing, RXT
Is the reception timing. This updated value is stored in the command type 7
4a is "B", which is transmitted as command B. At this time, when the reception timing is 0 (or within a certain allowable range), that is, when the phase difference is 0, the information channel transmission flag 74c is set to “OK”.

At this time, if a response from the terminal is not received due to a power failure of the terminal or the like, and a terminal ID 84b is a response from another terminal and is incorrect, a CRC error is detected (transmission path failure). Etc.), the content notified by the command A first is transmitted again by the command B without applying the update formula.

When receiving the command B, the terminal 2 controls the transmission timing and the use state of the information channel as described in the transmission timing value 74d and the information channel transmission flag 74c.

By repeating such a basic sequence several times, the shift of the reception timing converges to 0, the optimum transmission timing is obtained, and the information channel can be transmitted. ,
When a failure such as an error in the terminal ID is detected a specified number of times, the information channel transmission is disabled again.

When the above processing is performed and any of the uplink frequencies is in a state where the information channel transmission is “permitted”, communication using the uplink frequency, specifically, the control channels 72d and 8
2b, the use (transmission / reception) of the vacant CH broadcast channel 72c and the information channels 72e and 82c is enabled. FIG. 13 shows an outline of the transmission / reception sequence of the call control after this state.

As described above, the center device 1 has an empty C
Using the H broadcast channel 72c, the terminal is notified whether there is a free space in the information channel 72e of each uplink frequency. When the telephone connected to the calling terminal 2a goes off-hook, the calling side terminal 2a determines that any of the uplink frequencies is in a state of “enabled” for information channel transmission and that there is an empty information channel 72e at that frequency. Uplink control channel 8 of frequency
Using 2b, the center device 1 is requested to be assigned an uplink and downlink information channel. If all uplink frequencies are not available or there is no free information channel,
The terminal outputs BT (busy tone) to the telephone. If a plurality of uplink frequencies are available, a random selection is made from among them. The terminal control unit 64a generates a random number Xn each time a call is set, for example, by the following equation based on a linear congruential method (Iinearcongruentialmethod), and determines an uplink frequency number based on the value (for example, the upper 7 or 8 bits of Xn). . The initial value X0 is set based on the terminal ID and the like.

[0072] _{X n = a · X n-} 1 + b (mod m) a = 17, b = 499, m = center apparatus which receives two ¹⁶ data channel assignment request 131, as shown in FIG. 9 CTS- PTS correspondence table 4
3b, uplink and downlink empty information channel (CTS)
And assigns that number to the information channel assignment confirmation 132
To the terminal 2a.

The terminal 2a to which the upstream and downstream information channels are assigned uses the same channel and inputs a dial number to the exchange 11. First, the center device 1
On the side, the link (conduction) bit 74a1 of the state monitoring field 74a of the downstream information channel 74 shown in FIG.
In the terminal 2a, the link (conduction) bit 84b1 and the hook bit 84b2 of the status monitoring field 84b of the uplink information channel 84 shown in FIG.
The conduction of the terminal 2a and the center device 1 is confirmed.

If the continuity can be confirmed in the down state monitoring field 74a, the terminal indicates the dial number of the other party input from the telephone by using the hook bit 84b2 for DP (dial pulse) and for the PB (push button). This is notified by the information bit 84c. The center apparatus 1 that has recognized the other party by the dial number indicates that the other party terminal 2b is in a state where any of the uplink frequencies is “information channel transmittable”, as in the procedure on the calling side, and It is determined whether there is a vacant frequency, and if these conditions are satisfied, the terminal 2b
The information channel numbers of the free uplink and downlink are notified by the information channel assignment display 133 (if the conditions are not satisfied, the fact is notified to the calling terminal 2a). Then, terminal 2
If the information channel assignment confirmation 134 from b is confirmed, the link bit 74a1 of the status monitoring field 74a of the assigned downstream information channel 74 is set to 1 and the ringing (ringing) bit 74a2 is alternately set to 1,0.

The terminal 2b outputs the ringing to the telephone. Thereafter, if the off-hook is confirmed, the link (conduction) of the status monitoring field 84b of the upstream information channel 84 is established.
The bit 84b1 and the hook bit 84b2 are set to 1 to notify the center device 1 of conduction, and the call setting is completed.

At this time, the CTS-PTS correspondence table 43b shown in FIG.
b) The terminal has an uplink CTS of m of the uplink frequency f0.
l, m2 and PTS are nl and n2, respectively, and
It shows that TS uses l1 and l2 and PTS uses n1 and n2. The empty CTS, as described above,
This is indicated by "-".

The terminals 2a and 2b respectively transmit an information channel assignment request 131 and an information channel assignment confirmation 132.
Will use the uplink control channel 82b,
Since the same channel is used in common by other terminals, it is assumed that a collision occurs and the signal does not reach the center device, and no response is received within the expected fixed time (information channel assignment request 131).
In the case of (1), the information channel assignment confirmation 132 is performed. In the case of the information channel assignment confirmation 134, the link bit 74a1 is set to 1).

When the communication ends and the terminal goes on-hook, the terminal 2
For a and 2b, the hook bit 84b2 is set to 0 (on-hook), and after the link bit 74a1 from the center device 1 is confirmed to be 0, the link bit 84b1 is set to 0.

FIG. 11 shows the upstream link bit 84b1 and the hook bit 84b2. When the state where the link bit is 1 and the state where the hook bit is 0 continues for a certain period of time, it is considered that the on-hook has been performed.

The state monitoring field 74a of the downlink information channel 74 shown in FIG.
In the status monitoring field 84b of the upstream information channel 84 shown in FIG.
Although not shown, an error detection / correction code such as a Hamming code is added to empty bits other than 84b1, the ring bit 74a2, or the hook bit 84b2, and transmission / reception is performed to prevent the influence of noise. That is,
When an error is detected by the status monitoring fields 74a and 84b, the center device 1 monitors the status of the call by the terminal, and if an error is detected during dial transmission, there is a possibility of erroneous connection. The call is disconnected. Otherwise, for example, when the influence of noise can be ignored, such as during a call, the status monitoring fields 74a and 84b are discarded and replaced with the status monitoring fields 74a and 84b before and after the status monitoring fields 74a and 84b.

In the case of an ISDN terminal, layer 1 information corresponding to on-hook / off-hook information of an analog telephone is provided in the hook bit 84b2 of the state monitoring field 84b.

[0082]

As described above, according to the present invention, the terminal determines whether or not there is a free information channel and determines whether or not to reserve the same channel. There is no indication that the free information channel could not be secured, and the operation is not wasted.

Also, the center device broadcasts only the presence or absence of an empty information channel, and the terminal judges this, requests the center device to allocate an information channel, and then has the center device notify the information channel number. The terminal does not need to manage a large number of information channel numbers, etc., as compared to the case of broadcasting empty information channel numbers, which simplifies the processing and makes it possible to process even relatively inexpensive and low-function processors. Become.

Further, since a plurality of control channels are selected at random, the traffic of the same channel can be distributed.

According to the present invention, in addition to the above two-way communication system, the upstream transmission path is further divided into time division multiplex communication paths arranged in a plurality of frequency bands. Since a plurality of control channels are provided and selected at random, the traffic of the same channel can be distributed.

Further, according to the present invention, a terminal status monitoring field is provided for each of the information channels, so that it is not necessary to temporarily store dial numbers and the like on the terminal side, and a storage means for that purpose is not required. , Terminals can be realized at low cost.

Further, according to the present invention, an error detection and a correction code are added to the field, so that errors in the field are reduced and the frequency of erroneous connection is reduced, thereby improving reliability.

[Brief description of the drawings]

FIG. 1 shows a CA capable of two-way communication according to an embodiment of the present invention.
It is a schematic structure figure of a TV system.

FIG. 2 is a block diagram showing a configuration of a center device in the CATV system shown in FIG.

FIG. 3 is a diagram showing a frequency domain assigned to a communication service of the CATV system shown in FIG. 1;

FIG. 4 is a block diagram showing a configuration of the interface device 12 shown in FIG.

FIG. 5 is a block diagram showing an internal configuration of the TDMA device 13 shown in FIG.

FIG. 6 is a block diagram showing a configuration of terminals 2a to 2d shown in FIG.

FIG. 7 is a downlink TD in the CATV system shown in FIG.
FIG. 3 is a diagram illustrating a frame configuration of an MA signal.

FIG. 8 is an uplink TD in the CATV system shown in FIG. 1;
FIG. 3 is a diagram illustrating a frame configuration of an MA signal.

9 is a diagram showing each CTS-PTS correspondence table for uplink / downlink and an empty CTS table in the CATV system shown in FIG. 1;

FIG. 10 is a diagram illustrating the principle of delay measurement control, which is uplink transmission timing control.

FIG. 11: LK (conduction bit) and HK (hook bit)
It is a key map showing handling of.

FIG. 12 is a schematic diagram of a transmission / reception sequence before a center device and a terminal set a call.

FIG. 13 is a schematic diagram of a transmission / reception sequence of call control between the center device and the terminal.

FIG. 14 is a schematic configuration diagram of a conventional TDM transmission line format.

FIG. 15 is a schematic diagram of a transmission / reception sequence between a center device and a terminal using a conventional TDM transmission line.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Center apparatus 2a-2d ... Terminal 3 ... Relay amplifier 11 ... Switch 12 ... Interface apparatus 13 ... TDMA
Device 14 Head end 131 Uplink transmission band 132 Downlink transmission band 41 Downlink T
S transfer unit 41a ... down frame receiving unit 41b ... down frame receiving buffer 41c ... down frame transmitting unit 42 ... up T
S transfer unit 42a ... Up frame receiving unit 42b ... Up frame receiving buffer 42c ... Up frame transmitting unit 43 ... Interface device main control unit 43a ... Interface device control unit 43b ... CT
S-PTS correspondence table 43c Terminal status table 51 TDM
A device main control unit 51a TDMA device control unit 52 Downlink processing unit 52a Downlink frame receiving unit 52b Control channel receiving unit 52c Downlink delay measurement control channel transmitting unit 52d Downlink frame transmitting unit 53 Uplink system Processing unit 53a Uplink frame receiving unit 53b Phase determining unit 53c Phase adjusting unit 53d Uplink delay measurement channel receiving unit 53e Control channel transmitting unit 53f Uplink frame transmitting unit 61 Demultiplexing unit 61a Demultiplexer 62 ··· Downlink processing unit 62a · Distribution unit 62b · Demodulation unit 62c · Downlink delay measurement control channel receiving unit 62d · · · Audio output unit 63 · Uplink processing unit 63a · Modulation unit 63b · Transmission timing adjustment unit 63c · Uplink delay measurement Control channel transmitting unit 63d Voice input unit 64 Main control unit 64a Terminal control unit 64b Terminal ID Storage unit 71: Downlink TDMA from exchange to interface device
Signal 72: Downlink T from interface device to TDMA device
DMA signal 72a: frame synchronization bit 72b: control channel for controlling the TDMA device 72c: demand assignment control channel 72e: information channel 73: downlink TDMA signal from the TDMA device to the terminal 73b: delay control Delay measurement control channel 74: Detailed diagram of delay measurement control channel for delay measurement control 74a: Command type 74b Terminal ID (address) 74c: Information channel transmission flag 74d: Transmission timing value 81: From the interface device to the exchange Up TDMA
Signal 82: Up T from the TDMA device to the interface device
DMA signal, 82a ... Control channel, 82b ... Demand assignment control channel 82c ... Information channel 83 ... Uplink TDMA signal from terminal to TDMA device 83a ... Delay measurement channel 83a1 ... Preamble pattern 83a2 ... Frame synchronization pattern 83a3 ... C
RC bit 83a4: error correction pit, 84: delay measurement channel information section 91: uplink CTS-PTS correspondence table 92: downlink C
TS-PTS correspondence table

Claims (7)

[Claims] 1. A center device and a plurality of terminals are connected on a transmission line, and each terminal uses a time-division multiplexing communication channel of a communication band separated for each frequency band of an upstream transmission band and a downstream transmission band. In the two-way communication system for performing two-way communication via the center device, each of the uplink and downlink communication paths includes a plurality of information channels and a plurality of control channels, and the downlink from the center device. In the control channel of the communication channel, the presence / absence of the vacant information channel among the plurality of information channels is broadcast, and the terminal receives the broadcast and, when accessing the control channel, has the vacant information channel. In the state described above, the plurality of control channels are randomly selected. 2. The uplink transmission band further includes a time division multiplexing channel arranged in a plurality of frequency bands, and each of these channels includes a plurality of information channels and at least one control channel. 2. The bidirectional communication system according to claim 1, further comprising a function of broadcasting a presence / absence of a free information channel in each of the plurality of uplink frequency bands on a control channel of a downlink communication path from the center device. 3. Communications system. 3. A terminal status monitoring field is provided for each of said information channels.
A two-way communication system as described. 4. The two-way communication system according to claim 3, wherein an error detection / correction code is added to said status monitoring field. 5. The two-way communication system according to claim 3, wherein the on-hook / off-hook information of the terminal is provided in the status monitoring field. 6. The method according to claim 1, wherein the status monitoring field is discarded and replaced with the status monitoring field, or the call is disconnected, according to a call status at the time when an error is detected in the status monitoring field. Item 6. The two-way communication system according to Item 5. 7. The two-way communication system according to claim 3, wherein the status monitoring field includes terminal layer 1 information.