GB2110034A

GB2110034A - Private communication system

Info

Publication number: GB2110034A
Application number: GB8225183A
Authority: GB
Inventors: Wolfgang Andrich; Gunter Bertsch; Klaus Reh; Horst Rosenbaum
Original assignee: International Standard Electric Corp
Current assignee: International Standard Electric Corp
Priority date: 1981-09-04
Filing date: 1982-09-03
Publication date: 1983-06-08
Also published as: GB2110034B; DE3135005A1

Abstract

From a central station, television picture signals are sent as modulated light, via optical fibres (VLKI...VLKm), to the terminal stations (TInI). The sound portion of television programs, the radio broadcasting sound signals and data signals, after converted to a digital format, are combined by a multiplexor (MUX) to form a time- division multiplex (TDM) signal and transmitted as pulse-modulated light, via an optical fibre (TLK) to such terminal stations. At the terminal stations, the light signals are coupled out, reconverted into electric signals and by them, using a television monitor (VM), television pictures are displayed together with the accompanying sound. The data are displayed on a data display unit (V) and the radio broadcasting programs are reproduced either by the sound section of the monitor (VM) or can be heard via separate earphones (H), or possibly loudspeakers. <IMAGE>

Description

SPECIFICATION Private communication system This invention relates to a private communication system for transmitting picture, sound and/or data signals from a central station to terminal stations. Such systems are used, for example, in hotels to permit the reception of television and/or radio programs in the individual rooms. Usually, such systems use community antenna systems, with television and/ or radio receivers in the rooms. For radio broadcasts, however, there are known systems in which the radio programs are sent over lines, program selection being by connecting a loudspeaker via a selection switch to one of the lines. A disadvantage of such systems is that electrical noise can affect the lines, which affects received signal quality.

It is thus an object of the invention to provide a private communication system permitting noise-free transmission of television and/or radio programs involving a relatively small investment at the terminal stations. In addition it shall also be sought to be able to transmit data from the central station to the individual stations, and possibly also in the opposite direction.

According to the invention there is provided a communication system for transmitting picture, sound and/or data signals from a central station to a plurality of terminal stations, wherein in a said central station, television programs conveyed either by wireless or over cables in a high-frequency modulated form are demodulated into video-frequency form, wherein such video-frequency signals are applied to the inputs of analogue-operating optical fibre transmitter modules, wherein light modulated with such a video-frequency signal is applied at the output of the transmitter module to an optical fibre cable, wherein at a said subscriber terminal station, from this light, using an optical fibre receiver module the video-frequency signal is recovered as an electrical signal, and wherein after the selection of a wanted television program the electrical signal therefor is fed to a display device wherein the sound and/or data programs to be transmitted are obtained by receiving sections from wireless-transmitted radio programs or from sound or data stores, and using a multiplexer, are converted into a pulse-modulated time-division multiplex (TDM) signal, wherein the said TDM signal is fed to the input of an optical fibre transmitter module, wherein the said TDM signal is transmitted as a pulse-modulated light beam, over an optical fibre cable to the said terminal stations, and wherein the TDM signal received at a said terminal station is re-converted into an electrical signal from which, using a demultiplexer the individual sound and/or data channels are recovered, with the desired radio program being selected therefrom and fed to the respective reproducing equipment units.

An embodiment of the invention will now be explained with reference to the accompanying drawings, which Fig. 1 is a block diagram of a system embodying the invention, and Fig. 2 is a more detailed block diagram of the sound and data parts of the system of Fig.

1.

Referring to Fig. 1 at the central station m picture signals VS1. .VSm are received via m television tuners VTU,...VTUm, a video-frequency form. The sound portions of these television programs are received as sound channels TK,...TKm. Moreover, receivers TTUm+i...TTUn2 supply at their outputs further sound programs as sound channels TKm+,...TKn~2 which, as shown with respect to TK,~,, may also be taken from recording media via tape recorders or record players.

Data signals are put in over sound channel TKn by a data input equipment.

The picture signals VS1. .VSm in video-frequency form, are each fed to the input of an analogue fibre optical transmitter module VSM1. . VSMrn, each of which modules sends its video-frequency picture signal in amplitude modulated form as a light signal to an optical fibre cable VLK. For each individual television program there is one transmitter module VSM and an optical fibre cable VLK. Thus for the m video signals m modules VSM and m cables VLK are used.At the central station, the sound signals on the chanels TKI...TKn ,are each applied to the input of an analogue-todigital converter, the digital output signals thereof, and also the data output on the channel TKn, are fed to the n inputs of a multiplexer (MUX), which forms therefrom a pulse-modulated time-division mulitplex (TDM) signal TDMS. This TDM signal is fed to the input of a fibre optical transmitter module TSM, and the pulse-modulated light from its oupput is sent over an optical fibre calbe TLK.

Thus for all n sound signals only one transmitter module TSM and one optical fibre cable TLK are needed.

The light signals from the modules VSMI...VSMm and TSM of the central station, are to be sent to a large number of subscribers' terminal stations Tln. Thus a number of subscribers have to be supplied with the modulated light from one transmitter module.

Before we consider the question of the multiple branching thus needed, the construction of a terminal station will be explained. The modulated light beams arriving at the terminal station, are fed to optical fibre reciever modules VEM,...VEMm and TEM, the picture signals VS1.. VSm then being available at the outputs of the modules VEM where they can be selected, e.g., by a selector switch, and fed to a television monitor VM.

The pulse-modulated TDM signal TDMS appears at the output of the module TEM and is fed to the input of a demultiplexer DEMUX at whose outputs there appear the digitized sound signals of the channels TKI...TKn ,, plus the digital data signal of channel TKn. The data signal controls a data display unit to display the transmitted data. A selector switch selects the sound signal for a selected picture signal, and thus, by a digital-to-analogue converter, is reconverted to analogue and reproduced by the sound section of the monitor VM.

The indpendent sound channels TKm+,...TKn~, can similarly be selected by selector switches following the digital-to-analogue conversion, and reproduced by the sound section of the monitor VM if no simultaneous picture reproduction is required. The independent sound channels TK,.,...TK, TKm+,...TKn~" however, may also be separately selected by a separate selector switch and, following digitalto-analogue conversion and amplification by an amplifier V, can be reproduced by an earphone H or a loudspeaker. The television monitor VM can also be used to display the data of Videotext (or "Teletext" to use British terminoloy), provided that this monitor has a Videotext decoder, as the Videotext signals are within the video-frequency picture signal and are thus also sent by the central station.

Fig.2 shows the sound and data transmission system in more detail. To convert the analogue sound signals to be transmitted, into digital pulse-modulated signals, and to quantize them into a TDM a scanning clock is needed whose repetition frequency is at double the frequency of the highest overtone to be sent. Since in colour television picture transmission the chrominance subcarrier with a frequency of 4.433 MHz is available, a highly accurate scanning clock can be obtained from a frequency division of that subcarrier. It is also possible, however, to use other e.g. crystal-stabilized frequencies. In Fig. 2, the chrominance subcarrier is frequency divided by 120, to give a clock frequency of 36.94 kHz.The analogue-to-digital converters which digitize the individual sound channels are each preceded by a low-pass filter (in the present case, one with an upper cutoff frequency of 1 6 kHz) to preventing such frequency components from reaching the input of the analogue-to-digital converter, which in their frequency exceed one half of the clock frequency.

The multiplexer MUX assigns the scanning values of the individual sound channels as transmitted by the analogue-to-digital converters, to the pulse-modulated TDM signal TDMS, any further frequencies needed for the group or channel formation, being likewise derived from the basic clock frequency. This signal, as mentioned with reference to Fig. 1, is applied to the input of the optical fibre transmitter module TSM, which modulates a light beam which, from the output of the module, via an optical fibre cable TLK, is sent to the subscriber terminal station Tln.

The frequencies needed at the terminal for the demultiplexer DEMUX, may be obtained from the light signal demodulated in the receiver module TEM. Here also the digital-toanalogue converters are followed by low-pass filters to prevent interference due to the clock.

As far as concerns the data display unit, note that during the input, all terminal stations are controlled simultaneously or the individual terminal stations can be controlled discretely by addressing. It is also possible for the central station to be selected during a gap (interval) in the TDM signal, so that discrete messages, confirmations or data requests may be sent to the central station.

We now consider the question of multiple branching, of which there are a number of methods. Thus the individual stations Tln can be supplied via individual optical fibres respectively associated with each video signal and with all sound signals, these optical fibres being coupled out at each terminal by an optical fibre coupler. As every coupler causes some insertion loss, the number of stations to be supplied, is limited. However, one can also use optical fibre cables with several optical fibres, e.g. 1 9 fibres, the individual fibres of such a cable being coupled out to the fibres of a further optical fibre cable by couplers.

Since the number of series-arranged optical fibre couplers can be reduced, the number of terminal stations to be connected, can be enlarged. Another possibility is to be seen in the use of multi-core optical fibre cables in which there is one optical fibre per terminal station and from which, at a said terminal station, the fibre for that terminal station, is spliced out. Which possibility to be used in each case depends on the number of the subscriber terminal stations Tln to be supplied, and on the line conduction possible in the respective case. The aforementioned second possibility, i.e. the changeover from one optical fibre of a multi-core optical fibre cable to another type of optical fibre cable, makes it possible, for example, to divide the supply to individual floors.

Thus with the system described, the supply of a number of subscribers with a greater number of television and radio broadcasting programs can be achieved with a relatively small investment.

Claims

1. A communication system for transmitting picture, sound and/or data signals from a central station to a plurality of terminal stations, wherein in a said central station, television programs conveyed either by wireless or over cables in a high-frequency modulated form are demodulated into video-frequency form, wherein such video-frequency signals are applied to the inputs of analogue-operat ing optical fibre transmitter modules, wherein light modulated with such a video-frequency signal is applied to at the output of the transmitter module to an optical fibre cable, wherein at a said subscriber terminal station, from this light, using an optical fibre receiver module the video-frequency signal is recovered as an electrical signal, and wherein after the selection of a wanted television program the electrical signal therefor is fed to a display device wherein the sound and/or data programs to be transmitted are obtained by receiving sections from wireless-transmitted radio programs or from sound or data stores, and using a multiplexer, are converted into a pulse-modulated time-division multiplex (TDM) signal wherein the said TDM signal is fed to the input of an optical fibre transmitter module, wherein the said TDM signal is transmitted as a pulse-modulated light beam, over an optical fibre cable to the said terminal stations, and wherein the TDM signal received at a said terminal station is re-converted into an electrical signal from which, using a demultiplexer the individual sound and/or data channels are recovered, with the desired radio program being selected therefrom and fed to the respective reproducing equipment units.

2. A system as claimed in claim 1, wherein to transmit the video programs there is provided one separate optical fibre cable per video program, and wherein to transmit said pulse-modulated TDM signals (TDMS) there is a further optical fibre cable.

3. A system as claimed in claim 2, wherein the coupling of said video-frequency signals and said pulse-modulated TDM signal out of the optical fibre cable uses optical fibre couplers.

4. A system as claimed in claim 1, wherein the outputs of the optical fibre transmitter modules for all signals to be sent are connected to respective optical fibres of one multi-core optical-fibre cable, and wherein one fibre each in said multicore optical-fibre cables is provided for each of the terminal stations served.

5. A system as claimed in claim 1, wherein the data signals as transmitted in said pulse-modulated TDM signal (TDMS) are displayed on a data display unit, and wherein for this purpose, from said central station, only the data display unit at the desired terminal station is controlled discreetly by addressing.

6. A system as claimed in claim 1, wherein the radio broadcasting program of a selected sound channel is reproduced using the sound section of the television display devices.

7. A system as claimed in claim 1, wherein the radio broadcasting program of the selected sound channel is amplified by a separate amplifier, and is reproduced via an earphone.

8. A system as claimed in claim 1, and wherein the television monitor has a Videotext (Teletext) decoder.

9. A system as claimed in claim 1, wherein said terminal stations have returnindicating devices via which discrete messages, confirmations and data requests addressed to the central station, can be sent.

1 0. A system as claimed in any one of claims 1 to 9, and which is used as a hotel communication system.

11. A system as claimed in any one of claims 1 to 9, and which is used as a television and radio broadcasting distributing system for large residential buildings.

1 2. A private communication system, substantially as described with reference to the accompanying drawings.