JPS63294144A - Inter-terminal communication system in catv network - Google Patents

Abstract

PURPOSE:To reduce up-joining noises, by respectively using an FDM and TDM for an up-channel and down-channel and reproduction-repeating both of the channels by means of a collective demodulator and TDM modulator provided in a center device. CONSTITUTION:To a center device 101 of a branched network of CATV, LAN, etc., plural FDM waves are collectively converted into digital signals by means of one AD converter 136. Then incoming signals sent from terminals 103-105 through up-channels with FDM waves by means of a collective demodulator 112 which separates and demodulates each FDM wave by performing digital signal processing and a TDM demodulator 114 which multiplexes demodulated signals on a time base, are collectively demodulated by means of the collective demodulator 112. After the incoming signals are again modulated by means of the TDM modulator 114, the signals are converted into outgoing signals by means of a frequency converter 115 and returned to the terminals 103-105 by using down-channels. Thus communication of a non-delay service, etc., is carried out among the terminals 103-105. Therefore, upjoining noises can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a communication system between terminals in a CATV network such as a CATV system.

Conventional technology In dendritic networks such as CATV and LAN, a single coaxial cable is provided with upstream and downstream broadband transmission paths (upstream channel, downstream channel) with different frequencies, and these are transmitted within a seven-channel computer. Two-way transmission is achieved by combining the signals using a frequency converter. Conventionally, the C3MA/CD method (for example, "
Draft Eye Standard 802.3
Broadband Medium Attachment Unit and Medium Specifications J
('“DraftIEEE 5standard 8
02.3 Broadband MediumAtt
achment Unit and MediumS
peciftcations”, IEEE Pro
jects 802Local Area Netwo
rk 5tandars, Revision F (Ma
rch 1985) ), Token-Passin
g Bus method (for example, [ANSI/IEEE Easterners 802.4 Oaken Hassing Method and Physical Layer Specifications] (ANSI/IEEE Stand
ars 802.4 Token-Passing M
ethod and physical layer
5 specifications”.

IEEE Project 802.4 Local
AreaNetwork 5tandars(Dec,
(1984)), and for circuit-switched services, the FDM method is multi-channel communication using MCA radio.
Channel access method (e.g. National Technical Report's li'cATV-based two-way communication device)
(National Technical Report
t Vol, 32A 38 (Jun, 1986
)), but the TDM system is a system that combines TDMA modulation and a digital converter (for example, ``Control window time slotted bus system'', Journal of the Institute of Electronics and Communication Engineers).
86/10■○L, J69-BNolo), etc.

Problems to be solved by the invention Among these conventional communication methods, the C8MA/CD method and the Token-Passing Bus method are essentially packet switching services, and are suitable for data communication such as PC communication. However, there was a problem in that switching services such as voice calls were not possible.

In the multi-channel access method, the upstream signal sent in FDM waves using the upstream channel is simply converted into a downstream signal by a frequency converter in the center equipment, and then sent back to the terminal using the downstream channel. , the noise in the upstream signal is directly folded into the downstream signal. C
In a dendritic network such as an ATV, there is a problem of so-called "upstream noise" in which all the noise in the signal band gathers at the center device. However, there was a problem in that the code error rate could not be reduced especially when performing digital communication.

Time slotted bus with control window
In the DM system, it is necessary to accurately control the transmission timing of the time slot of the uplink signal from the terminal, but CAT
In a wide-area network spanning several tens of kilometers like the V system, there are problems such as the propagation delay time varying depending on the connection location on the network, making it difficult, and various methods have been proposed so far. There is a problem in that the terminal becomes more complicated and expensive than the FDM method.

The present invention has been made in view of this point, and uses FDM for the upstream channel and TDM for the downstream channel, and regenerates and repeats both channels using a collective demodulator and a TDM modulator placed in the center device. Terminal-to-terminal communication in a CATV network that reduces the influence of incoming noise and enables highly reliable terminal-to-terminal communication with a simple configuration and low-cost terminals equivalent to the FDM method, and enables line-switched services. The purpose is to provide a method.

Means for Solving the Problems The present invention solves the above problems by using CATV and LAN.
After converting multiple FDM waves into a digital signal at once using one A/D converter, each FDM wave is converted into a digital signal by digital signal processing.
A "batch demodulator" that separates and demodulates DM waves and a TDM modulator that multiplexes the demodulated signals on the time axis are installed, and uplink 61\ is sent from the terminal as an FDM wave using an uplink channel.

The signals are demodulated all at once by the batch demodulator, further modulated again by the TDM modulator, and then converted to a downlink signal by a frequency converter and sent back to the terminal using the downlink channel. It realizes communications such as system) services.

Operation With the above configuration, uplink signals sent from the terminal in the form of FDM waves using uplink channels are once demodulated in a batch demodulator, then modulated again in a TDM modulator, and then frequency-converted into downstream signals. Since the signal is sent back to the terminal using the downlink channel, the center equipment performs regenerative relaying, which eliminates the noise in the uplink signal! , it will not be looped back to the downbound signal. Each FDM wave of the upstream signal is once demodulated by a batch demodulator, and if necessary, it can be re-modulated by a TDM modulator after error correction after demodulation. Therefore, the S/N ratio is much better than the conventional FDM method (multi-channel access method, etc.), which simply converts the frequency of the upstream signal into the downstream signal using a frequency converter in the center equipment. High-quality communication between terminals can be realized, and as a result, the code error rate when performing digital communication can be significantly reduced.

In addition, in this method, since the uplink signal from the terminal is sent by FDM, there is no need to precisely control the sending timing of the time slot of the uplink signal as in the TDM method, so there is no need for a control circuit or system. F of
Similar to DM type terminals, the terminal can be manufactured with a simple configuration and at low cost.

Embodiment FIG. 1 is an overall block diagram of an example in which voice communication between terminals, which is one of the typical circuit-switched services, is realized on a CATV network according to the present invention. In Figure 1, 102 is C
This is an ATV network, and a center device 101 is arranged at the node part of the CATV network, and a plurality of terminals 103 to 105 are arranged at the core part. The center device 101 includes a video service section 111 that provides video services. Collective demodulator 11
2° error correction circuit 113. It is composed of a TDM modulator 1142 and a frequency converter 115. The terminal is a video processing section 131. Mike 135. A/D converter 136. F
DM modulator 132. Tuner 134°TDM demodulator 13
3. D/A converter 138. It is composed of a speaker 137. FIG. 2 is a block diagram for explaining the signal processing process within the center device.

The signal processing process of the center device will be explained with reference to FIG. Uplink signals of uplink channels going up the CATV network from each terminal (frequency f1.f2°T3..., fn)
are extracted all at once by one band pass filter (BPF) 201, and then passed through a frequency converter 202 for reducing the sample frequency of A/D conversion, and then extracted by one A/D conversion sample frequency.
The D converter 203 converts all the signals into digital signals.

The converted digital signal is input to the batch demodulator 204 and subjected to digital signal processing (polyphase digital signal processing).
filter, digital demodulator, etc.). The demodulated base node signal is corrected by error correction circuits 205 to 208.

After being corrected, it is input to TDM modulator 209.

In the TDM modulator 209, the error-corrected baseband signal is, for example, frequency f1 of the uplink signal from each terminal.
, T2. T3. -=Tfn and time slot) TI, T
2. ..., Tn are TDM modulated accordingly.

The TDM modulated signal is input to the frequency converter 210, converted to the frequency of a downlink signal, and sent back to the terminal via the downlink channel of the CATV network.

In the case of a CATV system, signals for communication between terminals are transmitted together with other video signals, so it is convenient in terms of frequency arrangement to set the bandwidth of the upper and lower channels for communication between terminals to 6 MHz, matching the bandwidth of the video signal. be. If GMSK is used to modulate uplink signals, and the transmission speed is 64 Kbps, the occupied bandwidth per wave will be about 100 KHz, and 60 waves can be used per channel. This allows 30 lines of terminal-to-terminal communication to be performed simultaneously.

The downlink transmission speed in this case is 3.84 Mbps.
become.

Next, an embodiment of voice communication according to the present invention will be described using FIG. 1, taking as an example a case where terminal 103 and terminal 104 perform inter-terminal communication. The voice input from the microphone 135 at the terminal 103 is converted into a digital signal by the D/D converter 136, then modulated by the FDM modulator 132 at frequency f1 in the uplink channel, and input to the center device 1Q1 through the CATV network. The center device 101 receives the frequency f1°T2 from each terminal as described above.
．． T3. ... r f ” signal in time slot T1
, T2. T3. , Tn and is converted into a TDM signal, fl corresponds to T1. The signal converted to TDM is input to the terminal 2 through the CATV network using the downlink channel, and after being selected by the tuner 134, the TDM signal is
It is demodulated by the DM demodulator 133 and the time slot T1 is demodulated here.
is extracted. The extracted signal is sent to the D/A converter 13
8, the signal is converted into an audio signal and reproduced by the speaker 137.

In a similar manner, the audio from the terminal 104 can be played back on the terminal 103, so that audio communication can be performed between the terminal 104 and the terminal 103.

Effects of the Invention As described above, according to the present invention, FDM is applied to the upstream channel.
We decided to use TDM for the downlink channel and regenerate and relay both channels using a collective demodulator and TDM modulator placed in the center equipment.
N's: To provide a terminal-to-terminal communication method that can realize highly reliable terminal-to-terminal communication with a low-cost terminal with a simple configuration equivalent to the FDM method, and also enables line-switched services. can.

According to the present invention, the FDM wave of the upstream signal is once demodulated by the batch demodulator placed in the center device, and then modulated with TD1v+ again into the downstream signal, so that multiple upstream channels can be combined on one time axis. It is also easy to multiplex with
Even if the number of uplink channels increases due to an increase in the number of lines, this can be easily handled by simply increasing the transmission speed of the downlink channels without making major changes to the channel control method, etc. .

According to the present invention, by employing a batch demodulator that uses digital signal processing to demodulate upstream FDM waves, A
Since the /D converter and bandpass filter can be shared by all FDM waves, as in the case of using a normal demodulator configuration in which a bandpass filter is provided for each modulated wave... It does not increase proportionally, and since the processing in this part is digital signal processing, it is suitable for IC and LSI implementation, and a highly reliable regenerative repeater system can be realized at low cost with a relatively simple configuration. 3゜ is also effective

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the present invention, and is an overall block diagram of an example in which voice communication is realized on a CATV network. FIG. FIG. 101...Center device, 111...Video service section, 112...Batch demodulator, 113...
・Error correction circuit, 114...TDM modulator, 11
513... Frequency converter, 102... CATV network, 103-105... Terminal, 131... Video system processing unit, 132... FDM modulator, 133...・・・
TDM demodulator, 134... tuner, 135...
-Microphone, 136...A/D converter, 137...Speaker, 138...D/A converter, 201...Banthus filter, 202...Frequency converter, 203... ...A/D converter, 204...Batch demodulator, 205-208...Error correction circuit, 20
9...TDM modulator, 210...frequency converter.

Claims (1)

[Claims] In dendritic networks such as CATV and LAN, batch demodulation is used in a central device to convert multiple FDM waves into digital signals using one A/D converter, and then separate and demodulate each FDM wave using digital signal processing. and a TDM modulator that multiplexes the demodulated signals on the time axis, and the batch demodulator collectively demodulates the uplink signals sent from the terminal in the form of FDM waves using the uplink channel, and the An inter-terminal communication system in a CATV network characterized by realizing real-time communication between terminals by modulating the signal again with a TDM modulator, converting it into a downlink signal with a frequency converter, and sending it back to the terminal using a downlink channel.