DE3539378A1 - COMMUNICATION SYSTEM - Google Patents

Description

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Applicant: Stuttgart, November 5th, 1985

Communications Patents Limited P 4800 S / Pi 187 Coombe Lane West

Kingston-upon-Thames

Surrey, KT2 7DJ,

Great Britain

Representative:

Kohler Schwindling Späth
Patent attorneys
Hohentwielstrasse 41
7000 Stuttgart 1

Communication system

The present invention relates to a communication system and particularly one in which television signals are transmitted to subscribers over fiber optic cables will.

There has been a large number of proposals for the distribution of television signals from a central source so far of the television signals have been turned into participants. Older systems include electrically conductive networks, however Systems based on the use of optical fibers are increasingly being proposed, and in some cases also Installed.

Ss is known in telecommunication systems for signal transmission to use pulse code modulation (PCM). In PCM systems, the signals are periodically sampled and serially transmitted digital data which are characteristic of the sampled signal values or samples. At the The system's receiving end requires the original Signal by appropriately decoding the PCM signal transmitted through the system.

In known PCM systems, the transmitted contain bit streams always address data which determine the receiver for the data characterized by the bit streams. These "Labeling" the various transmitted data elements is not a problem if the data receiver is specified. in the However, in the case of a television signal distribution system, other requirements apply, since it is necessary to know about the System to make a large number of television signals available and to give participants the opportunity to use the Select the television signals to be fed to your own receivers yourself. In it lies presumably the reason that PCM technology, which is well known in other fields of telecommunications, has hitherto been used has not found application in general cable network systems.

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The invention is therefore based on the object of a communication system to create which makes use of the technique of pulse code modulation to convert signals of a number Distribute signal sources to a large number of participants.

Accordingly, the invention provides a communication system which comprises a plurality of subscriber stations and a plurality of distribution points, of which the subscriber stations each have a plurality of connections at which television signals broadcast via the system are made available, and the distribution points each with an assigned group are connected by subscriber stations, the subscriber stations of which are each connected via at least one glass fiber to the assigned distribution point, and in which the distribution points and a plurality of television signal sources are connected to one another by a plurality of optical fiber cables. A plurality of PCM television signals are transmitted over each fiber of the fiber cable in such a way that the samples of each PCM television signal are assigned a corresponding time interval in a cyclical sequence of time intervals. Each distribution point has a selection device for each connection of each of the subscriber stations connected to it, which can be controlled from the corresponding connection of the subscriber station and enables the selection of a desired television signal by selecting the samples of this television signal appearing in the respective time intervals. The distribution point includes means for assigning the selected television signals to corresponding time intervals in a repeating sequence of time intervals on the fiber leading to the subscriber did ion. Finally each Anscnl'iß de includes the subscriber station a device for Aaswahl _t * samples

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which appear in corresponding time intervals, and for Decoding the received signals to produce the desired one Television signal.

Accordingly, in the system according to the invention, PCM-coded Television signals distributed throughout the system so that they are generally available at every distribution point, however, the ultimate determination of the bit streams fed to the distribution points is made by the recipients of these bit streams and not determined by the sender or distributor side of the system.

The use of optical fibers instead of conductive cables reduces the volume required in the distribution points required facilities for a given number of participants, so that a larger number of subscriber stations can be supplied from a reasonable size distribution point. The use of optical fibers also offers the advantage that the maximum distance between distribution point and subscriber can be greater than when using conductive cable.

Preferably, the PCM television signals transmitted to the fibers of the optical fiber cables are fed, synchronized and are resynchronized in the distribution points. The resynchronization can be achieved through the use of shift registers and short cable sections after the detection of the signals received at the distribution points.

An embodiment of the invention is described, for example, with reference to the accompanying drawing. Show in it

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Pig. 1 shows the schematic representation of the in a distribution point for a single subscriber existing facility that feeds three connections enables the subscriber station

2 shows a schematic representation of the in the subscriber station existing device for receiving by means of the device shown in Fig. 1 of Distribution station generated signals and

Pig. 3 shows an embodiment of circuit breakers of a alternative arrangement for generating the three connections of the subscriber station in the correct Timing of the output signals to be supplied.

Before going into detail on the attached drawing, the general structure of the system will be briefly described to which the distribution station ji-it in Pig. 1 The facility shown belongs to.

The system described is intended for the subscriber stations 30 TV channels, 20 FM audio channels and data to feed. The 30 TV channels can be up to 10 satellite direct broadcast channels (DBS = direct broadcast from satellite) in MAC format and the rest for channels in Act PAL 1 format. The 20 FM audio channels are predominantly in Stereo.

Each subscriber station can have up to three connections, and any television channel in DBS or PAL 1 format can be used on any connection from the distribution point All of the FM audio channels and the 64 kbit / s data channel

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to be delivered. In addition, the subscriber has the option of sending a message to the assigned distribution point of the channels he wishes to see, 64 kbit / s data and one upstream, i.e. towards the distribution point Broadcast television channel. You can also use two-way connections made available to selected participants at 2 MHz. These different channels can be used in the procedure described below to bit streams higher Following speed can be combined.

The structure of the network is based on a complete separation of the upstream and downstream signal paths and uses a multi-point, branched, primary downstream network made up of fiber optic cables which connect signal sources to distribution points, a secondary network with special power supply and downstream connections in the form of individual optical fibers extending between a subscriber station and the associated Extending distribution point, and an upstream primary network of the distribution points that of the Format used by the telecommunications authorities, such as in the UK Telecom format and in Germany from the format of the German Federal Post Office.

Good quality PCM television in PAL I format can be obtained are, if the color subcarrier with three times its frequency, so with 13.5 MHz, sampled and the sample is quantized into 8 bits. Sampling takes place every 75 ns, which requires 106.4 Mbit / s. It can be occasional It may be necessary to transmit such signals over standard lines for 140 Mbit / s, as used by the telecommunications authorities be made available so that

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additional capacity is available that can be used for parity bits, synchronization codes, television sound insert high quality and auxiliary data channels. The current modulation rate of lasers is approaching 1 G-bit / s with a typical rise time of 0.5 ns, so that 3 to 4 Bit streams, each derived from a corresponding television signal, time-interleaved on a fiber can be.

The signal format used for DBS transmissions is based on direct reception and therefore does not need the standard of the telecommunications authorities. Its sampling rate is about 1.5 times the sampling rate of PAL I, and it is easier to decode the digital parts of the deck signals, if the clock frequency is an exact multiple of 20.25 MHz.

3 x HO Mbit / s can therefore be 3 PAL I or 2 DBS channels record using a basic synchronization interval of 6 samples, which corresponds to 450 ns.

4 PAL I channels or 2 DBS channels with 140 Mbit / s capacity in 4 x 18 ns blocks for other services can be carried at 4 x 140 Mbit / s in a frame of 8 samples which is equivalent to 600 ns.

It would theoretically be possible to convert FM band to PCM. The implementation of the band from 88 to 108 MHz would, however Require 1.79 Gbps, which is not practical. However, it is possible to use the individual FM channels in the signal sources to an intermediate frequency and to bring it down to the band of 150 to 300 kHz before coding Coding of 20 eolfhpri: '«. Next.i» n in ni; w: i P M:

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Pulse code at a sampling frequency of, for example, 750 kHz would require 120 Mbit / s and could therefore be used in PCM television signal channels which require a similar bit rate. The theoretical signal-to-noise ratio of the recovered FM signals is sufficient to provide near perfect stereo sound.

The separate coding of the FM channels also allows the Application of a method for channel selection, which is the method used for the selection of the television signals is the same, and avoids problems with FM receivers lower RF selectivity and linearity. The delivery of data at 64 kbit / s to each subscriber station is possible under Using the 4.7 microsecond blanking interval that follows each line of a conventional television signal and is currently is not used. Provided that the various television signals at the head end of the system have a Line synchronization is imposed and that delays that occur in transmission over the fiber optic cable result, are balanced in the distribution points, only one of the channels needs the normal line synchronization pulses respectively. The remaining channels can transmit data signals.

Each distribution point can have 600 single-channel connections for corresponding Serving subscriber stations using a duplicate address system for each sector of the system. Thus, one television channel can be used to transmit data to each of the distribution points, and one Line to feed data to a subscriber who is served by this distribution point, from which 30 χ 600 = 18,000 single-channel data connections per sector result - each

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Participants would receive 25 data groups, each using a duration of 4 μβ (of the 4.7 μβ available) 640 Mbit / s, i.e. 64 kbit / s. The downstream data distribution with 2 Mbit / s gets along well with the clock frequency of the system, which is coupled to the DBS data frequency of 20.25 MHz.

A 140 Mbit / s channel intended for this would have a capacity for up to 70 2Mbit / s channels for downstream data.

In the system described above, the facilities for Transmission of 64 kbit / s and 2 Mbit / s data is provided on the basis of fiber input amplifiers, which are grouped in this way are that each data feed unit 30 distribution points supplied with a potential of a total of 18,000 single-channel connections. Larger or less data capacities can be achieved by changing the groupings in the central structure of the system accordingly.

The structure of the device present in a distribution point, which is shown schematically there, is now illustrated with reference to FIG reproduced. Five fibers 1 to 5 of a fiber optic cable feed PCM television signals to the distribution point. The detectors convert the optical signals fed on the fibers of the cable into electrical signals. The cable fibers 1 to 5 supplied signals are originally synchronous, but require resynchronization at the distribution point, which is carried out with the aid of runtime equalizers 7.

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The output signals of the transit time equalizers are corresponding Bus lines 8 "to 12. Each subscriber unit, which is generally sufficient to supply the home of a participant, is set up to three of each other to receive independent signals fed to the respective terminals, each of which is used for supply a corresponding receiver, video recorder or the like. serves. Therefore there is a switch for each subscriber line 13, which makes it possible to select one of the fibers 1 to 5 from which the television signal is received target. In the configuration shown in Fig. 1 of Switches, fibers 2, 4 and 2 were selected for the three connections of the subscriber station from left to right. The switches 13 are controlled by signals which form a clock switch and a selection control Circuit arrangement 14 are generated as a function of control signals for the signal selection desired by the subscriber characteristic and derived from suitable connections between the distribution point and the subscriber station are.

The output signals of the switches 13 are fed to corresponding multiplex switches 17, which in turn are fed by the Control circuit 14 can be controlled. The multiplex switches 17 close to the selected fibers 1 to 5 existing signals only at specified time intervals transmitted, which are assigned to the special signal that the appearing at the inputs 15 control signals of the Identified the participant as the desired signal. So the three are at the outputs of the multiplex switch 17 signals appear in the same, original time intervals as on the input fiber lines.

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The output signals of the multiplex switch 17 are adjustable Delay elements 18 are supplied, the setting of which is in turn determined by the control circuit 14. The delay elements are designed and adjusted so that they ensure that the three by means of the Multiplex switch 17 selected signals in consecutive Time intervals fall which correspond to the channels that are desired at the individual connections, so that the three signals via an OR gate 19 and an electro-optical converter diode 20 of a common optical fiber which leads to the subscriber unit.

In Fig. 1, the switching elements are shown as if she actuates the relay. It is understood, however, that in practice the required switching speeds will make the application make of solid-state switching elements necessary and that the relay-like representation used in Fig. 1 is only simple was chosen for explanatory purposes.

The arrangement of FIG. 1 essentially selects three digital ones Bit streams from the signals applied to the optical fibers 1 to 5 and effects a rearrangement of the digital bit streams in such a way that the decoding takes the facilities present in the subscriber station can be left. Fig. 2 then shows the facilities present in the subscriber station. The optical signal, the optical fiber 16 leading to the subscriber station has been given is converted into an electrical signal by a detector 21 and three parallel to each other switched switches 22 supplied. The switches 22 are controlled by a decoding logic 23 which also supplies digital / analog converters 24 with a clock signal. The on

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the D / A converter 24 become corresponding low-pass filters 25 whose outputs are in turn connected to video connections 26 and also to the inputs of modulators 27 which provide UHF output signals 28.

The decoding logic is designed so that it closes the switch 22 only during the time intervals that the signals are assigned which are to be supplied to the assigned output 26 or 28.

After in a general way the structure of the facilities required in the distribution point and the subscriber station has been described, a possible configuration of the signal distribution to the various Time intervals described.

Because of the above-mentioned relationship between the PAL I and the DBS signals, the two services can only then be integrated when a common sample frame is chosen in which any combination of 3 PAL I and DBS signals can be nested without interference. Since PAL I must be scanned every 75 ns and DBS every 50 ns, the shortest is common time interval 150 ns. However, to avoid interference it is necessary to use the DBS and PAL I signals offset against each other in such a way that each uses its own time intervals, except in those cases in which a paser carries three signals of one type and no signal of the other type. This leads to the need for that available 150 ns into 12 intervals of 12.5 ns each. An 8-bit sample requires a bit rate of 640 Mbit / s in 12.5 ns.

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A possible arrangement of the intervals is shown in the following table. The odd intervals are the DBS samples and the even intervals are assigned to the PAL I samples, except for those cases in which the intervals assigned either 3 PAl I signals or 3 DBS signals are.

interval 1DBS 1 2 3 4th 5 6 7 8th 9 10 11th a 2DBS D1 D1 D1 b 3DBS D1 D1 D2 D1 D2 C. 1PAL D1 D3 D2 D1 D3 D2 D1 £ 1 D2 d 2PAL P1 P1 e 3PAL P1 P2 P1 P2 f 1D + 1P P1 P2 P3 P1 P2 il S. 2D + 1P D1 P1 D1 P1 D1 H 1D + 2P D1 P1 D2 D1 D2 P1 D1 D2 i D1 P1 P2 D1 P1 Tue P2

Options a to i in the table above illustrate the possible combinations of signals that can be used in a Participants are fed from a distribution point. The assignment of the five pasers 1 to 5 of the fiber cable (Fig. 1) supplied signals to the time intervals can be done in the manner shown in the table below:

Fiber 1 d1 d2 d3 d4 d-1 d2 d3 d4 d1 d2 d3 d4 Fiber 2 d5 d6 d7 d8 d5 d6 d7 d8 d5 d6 17 d8 Fiber 3 d9 d10 - - d9 diO - - d9 diO -

Fiber 4 p1 p2 p3 p4 p5 p6 pi p2 p3 p4 p5 po Fiber 5 p7 p8 p9 p10 p11 pi 2 p7 p8 p9 p10 pll p12

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It can be seen that using only five pasers of the fiber cable can easily accommodate 10 DBS signals, but only 12 PAL I signals. More system capacity can be made available by adding more cable fibers. For example, could be a sixth Fiber effect the transmission of further 6-PAL I-channels.

To make a selection, such as the one specified in line i of the first of the two tables above, in which the single DBS signal corresponds to the signal d7 of the second table and the two PAL I signals P1 and P2 the signals p4 and p11 of the second of the preceding Table, the following settings must be made in the distribution point:

For d7: Choose fiber 2, take the signals and appearing in time intervals 3, 7 and 11 delay by 4 intervals.

For p4: choose fiber 4, time intervals 4 and

10 and delayed by 4 intervals.

For p11 - choose fiber 5, time intervals 5 and

11 and delay by 5 intervals.

It is necessary to provide a processor in the distribution point, which is set up by the subscriber station Requirements are recorded and the selection of fibers, time intervals and delays controls in an appropriate manner. He must then supply the subscriber unit with information that enables the subscriber unit to receive information from the distribution point to separate the three signals supplied and to connect the

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sen to be assigned to which the three signals are to be fed. For example, the subscriber station must be informed of this that the intervals 7, 11 and 3 belong to the DBS signal, that the connection 1 is to be fed that the intervals and 2 belong to a PAL I signal which the connection 2 is to be supplied, and that the intervals 10 and 4 belong to an EAL I signal which is to be supplied to the terminal 3. the Set up the participant as they are in Pig. 2 can select the correct signals and the three Feed connections.

FM radio channels are in intervals 6 and 12. As mentioned above, 20 FM channels can be accommodated in the time intervals that are normally used by a single one PAL-I channel can be taken. Both intervals 6 and 12 are free, unless there are 3 DBS signals from a subscriber station be requested. This case is very unlikely because it has 3-DBS compatible televisions or VCR in an apartment would require, and it is therefore easily possible to have FM radio service in one Reduce situation. On the other hand, there are no requirements regarding the time relationships between neighboring Channels exist, the content of time interval 6 could be moved to time interval 4 or 8.

The beginning of a decoding sequence of 10 to 12 time intervals (1.5 M-s) would be coded in the partial strap station Synchronization data recognized in the line blanking intervals, and the desired! FM-Karial assigned Time intervals fed to the D / A converter 24. However, a frequency converter would be required to convert the selected To convert the channel to a free frequency in the FM band.

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The line blanking intervals that make a downstream communication from the head end to the individual subscriber using 64 kbit / s data can be used to transfer data to transmit and to supply texts to the subscriber, v / o teletext converters for viewing on the screen, Printers or memories of computers can be fed.

The data will be stored in the distribution point after the restoration the specified logic level and after the extraction of clock signals, separated from all signals. That the The signal assigned to the distribution point would be routed to suitable output lines by logic and delayed in such a way that it matches the channel selected for a single subscriber line. This method only works if PAL I signals are used, as DBS signals have no free blanking gaps. However, there is no particular problem here, since there are opportunities for correspondence are not offered in the DBS system.

The construction of the distribution point described with reference to FIG. 1 forms only one of many different structures that could be used. For example, it would be possible to spatially subdivide the inputs of the distribution point by they are extracted only once from their time-interleaved multiplex format with which they are transmitted to the input fibers 1 to 5 arrive. These individual signals can then be rearranged in time due to delays to take all scans or samples at the same time. The samples present at the same time could are then made available with a delay of 1, 2 or 3 units, so that the circuit arrangement,

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which "repackages" the samples for transmission to the subscriber station, only the channels coming from a given port be asked to identify and then bring them together. For example, it is possible for a shared PAL I and DBS system a 54-way bus for 18 PAL signals (and also for DBS signals). This leads to a considerable simplification, because on the one hand all Signals, once they have been put onto the bus in a synchronized manner, remain synchronized and therefore the Signal distribution circuits can be simplified. In this case, buffers could be clocked to prevent a disturbed clocking Need to improve. Second, a channel selection only requires a one-time switching of a logic or of diodes with low speed so that high speed logic circuits be avoided. The basic device assigned to the subscriber only requires a 54-bit register, 54 diode switches and an LED driver.

Because the first, second and third ports are one Subscriber station would only have 0, 1 or 2 delay units, the channels could do so be organized so that the bus is in three groups of 18 and only one channel of each group can be selected for each output. This would be deploying of one and two connections if necessary.

A schematic representation of an arrangement for separating samples in the manner described above is shown in FIG Fig. 3 shown. Six optical fibers 29 to 34 are fed to fiber optic receivers 35, which receive the incoming convert optical signals into electrical signals. The signals on all six fibers 29 to 34 can do just that

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have the same format as the signals which the five optical fibers 1 to 5 according to Pig. 1 are fed. A number of six sample disconnectors 36 distribute the to the corresponding optical pas received signals on several groups of three delay lines 37, 38, 39, where the number of groups corresponds to the number of channels carried by each paser. Each of the Delay lines 37, 38 and 39 of each group introduce a time delay which synchronizes the channels with one another and also adds either 1, 2 or 3 time intervals. The signals required for a first connection of the Subscriber station are determined, are selected from the delayed by a time interval output signals from which there is now one for each channel. The samples for connections 2 and 3 are made in the same way by the others separated.

Each subscriber station can now use three channels for the three connections, which are fed without further delay are selected by each of the versions of the input signal delayed by one, two and three units will.

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Claims (2)

Claims §Y communication system comprising a plurality of subscriber stations and a plurality of distribution points, of which the subscriber stations each have a plurality of connections at which television signals broadcast via the system are made available, and the distribution points are each connected to an assigned group of subscriber stations, their subscriber stations are connected to the assigned distribution point via at least one glass fiber each, and in which the distribution points and a large number of television signal sources are connected to one another by a large number of optical fiber cables, characterized, that over each fiber (1, 2, 3, A, 5) of the fiber cable several PCM television signals are transmitted in such a way that the samples of each PCM television signal are assigned a corresponding time interval in a cyclical sequence of time intervals, that each distribution point for each Connection of each of the subscriber stations connected to it has a selection device (13, 14) which can be controlled from the corresponding connection of the subscriber station and enables the selection of a desired television signal by selecting the samples of this television signal appearing in the respective time intervals, so that the distribution point has a facility (17, 18) for assigning the selected television signals to corresponding time intervals in a repeating sequence of time intervals on the leading to the subscriber station BATH ORIGINAL the paser (16), and that each connection (26, 28) the subscriber station a device (22) for the selection of the samples, which in corresponding time intervals and for decoding the received signals to produce the desired television signal. 2. System according to claim 1, characterized in that those of the fibers (1, 2, 3, 4, 5) of the optical fiber cable supplied television signals are synchronized and the distribution points have devices (7) for resynchronizing the signals. 3 · System according to claim 2, characterized in that the means (7) for resynchronizing comprise shift registers and short cable sections. BAD ORiGINAL