RU2124812C1 - Method for transmission of signals in digital fiber-optical systems using spectral-code multiplexing and device which implements said method - Google Patents

Abstract

FIELD: equipment for multichannel fiber-optical communication system, in particular, multiplexing signals of synchronous digital flows in systems which use spectral channel multiplexing. SUBSTANCE: method involves modulation of output signals of m channel optical transmitters by transmitting terminal. Goal of invention is achieved by encoding of set of N input characters of N channel signal of synchronous transmission system (N>m) for each clock interval before modulation of output of channel optical emitters. Said encoding is done by means of clock set of m microwave sub-carriers, which are generated by special synthesizer, so that m, n and N conform to condition

, where A $\genfrac{}{}{0ex}{}{\text{m}}{\text{n}}$ is number of arrangements out of n elements taken m at a time. After beam detection at receiving terminal method involves detection of set of microwave sub-carriers that has been transmitted during given clock interval, decoding this set into sequence of N binary characters which is identical to source signal. Corresponding device has switching encoder, synthesizer of microwave sub-carriers, and m channel optical emitters at transmitting terminal, and m channel photodetectors, m devices for detection of sub-carrier, synthesizer of n microwave sub-carriers and decoder at receiving terminal. EFFECT: increased throughput capacity using larger number of synchronous digital channels than number of channel optical emitters with output of different wavelengths, decreased requirements for members of optical path, since no tuning of wavelength of these members is required during device operations. 3 cl, 2 dwg

Description

 The claimed invention relates to the field of technology of multi-channel fiber-optic transmission systems, in particular to multiplexing signals of synchronous digital streams in systems using spectral multiplexing of channels.

 The method of increasing the capacity of a fiber-optic channel is widely known, which consists in transmitting several digital streams on different fibers on different optical carriers within the transparency region of a linear fiber, called spectral channel multiplexing - QMS [1, 2]. The method is characterized in that each pair of terminals of the fiber optic path — transmitting and receiving — uses a constant operating wavelength to transmit one digital stream. To change the correspondent terminal, a change in the working wavelength can be used, but the total number of channels simultaneously transmitted through the system is limited by the number of multiplexed optical carriers (and for partially inactive terminals, it is less than this number).

 The closest in technical essence to the claimed one and chosen as a prototype is a method [3] for improving efficiency with QMS, which consists in organizing the flexible provision of unused for any reason working wavelengths (from the set provided by the system equipment) to any pair of terminals upon special request a connection sent to the controller of operating wavelengths, in which the presence of unused wavelengths is analyzed and a control signal is generated that is transmitted on a specially selected case ebnoy wavelength in functional units connected optical path terminals and, if necessary, optical switches, where the information contained in the control signal, is tuned to the selected wavelength of unused respective transmitting and receiving units of these terminals.

 Using this method allows you to eliminate the "simple" potentially possible optical channels, ie if there are requests, almost continuous loading of all optical carrier systems is achieved, which means that the maximum throughput is realized for a system with a known method of spectral multiplexing.

 The disadvantage of the known prototype method and device that implements it is the limitation of the capacity of the system with QMS to the number of optical carriers (wavelengths) provided by the equipment.

 In addition, as follows from the description of the prototype patent [3], the transmitting and receiving blocks of the terminals should be tuned to the indicated (selected from among the unused) operating wavelengths according to the control signal of the controller. Such requirements are associated technically with a significant complication of the design of the transmitting and receiving terminals of the system with QMS (especially laser emitters, filters) and, consequently, the deterioration of the technical and economic characteristics of the equipment - an increase in the cost of equipment, a decrease in the reliability of its operation.

 The problem that the proposed technical solution solves is to increase the amount of information transmitted, namely the transmission of a larger number of synchronous digital channels than the number of channel optical transmitters with different radiation wavelengths, as well as simplifying the requirements for the elements of the optical path, consisting in the fact that in the proposed the invention does not require any adjustment of the operating wavelengths of these elements during the operation of the transmission system.

The specified problem in the proposed method is solved due to the fact that in the method for transmitting synchronization signals of digital fiber-optic systems using spectral-code multiplexing, which modulates at the transmitting terminal signals m transmitted digital signals from m channel optical transmitters with different wavelengths, transmitting signals various digital channels on any of the used working optical wavelengths, in accordance with the distribution of working wavelengths controlled by the unit board switching the used optical wavelengths between the transmitting and receiving terminals of the communication system, combining the spectrally-spaced output optical signals of all m channel optical transmitters into a group optical linear signal, transmitting a group optical linear signal along a linear optical path, dividing the group optical signal into a receiving terminal m components based on the difference in optical wavelengths, photodetection of each component of the optical signal with an optical photodetector, before modulating the emissions of channel optical transmitters, the set of N input symbols of the N-channel signal of the digital synchronous transmission system generated during each clock interval is encoded by a clock set of m microwave subcarriers from among n microwave subcarriers generated by the subcarrier synthesizer, m, n and N are related by A $\genfrac{}{}{0ex}{}{\text{m}}{\text{n}}$ + n ≥ 2 ^N , where A $\genfrac{}{}{0ex}{}{\text{m}}{\text{n}}$ is the number of arrangements of n elements with respect to m, and the emission modulation of m channel optical transmitters, differing in optical wavelengths, is carried out by a clock set of m microwave subcarriers with simultaneous input into the optical signal of information about the clock frequency of the digital synchronous transmission system, after photodetection of each component at the receiving terminal optical signal determine what value of the microwave subcarrier was transmitted for each of the m optical channels in a given clock interval with simultaneous selection of clock cycles th frequency of the digital synchronization of the transmission system, form the equivalent of the clock set of m microwave subcarriers, similar to that obtained by encoding the input set of N symbols at the transmitting terminal, decode the equivalent of the clock set of m microwave subcarriers with the formation of a set of N binary symbols distributed over the weekend channels of the receiving terminal in the same way as at the input of the transmitting terminal.

 In addition, in a spectral-code multiplexing device for synchronous digital channels of optical transmission systems, comprising a transmitting terminal, which in turn includes a signal input device of an N-channel synchronous digital transmission system, m channel optical transmitters with different operating lengths waves, a device for combining spectrally-separated channels, a linear optical path, a receiving terminal, which, in turn, contains a device for separating spectrally-separated optical channels, m channel photodetectors, a terminal for outputting N signals and a clock frequency of a synchronous digital transmission system, inputs of N synchronous digital channels are connected to N information inputs of an encoder switch, a clock input is connected to clock inputs of an encoder switch, a microwave subcarrier synthesizer and channel optical transmitters, n microwave outputs of the microwave subcarrier synthesizer are connected to n microwave inputs of the encoder switch, m microwave outputs of the encoder switch are connected respectively to the mode inputs headers of m channel optical transmitters, the optical outputs of m channel optical transmitters are connected to m inputs of a spectral diversity optical combining device, the output of which is connected to an input of an optical transmission path of a linear signal, the output of a transmission path is connected to an input of a spectral diversity optical device, m the outputs of which are connected respectively to the optical inputs of m channel photodetectors, the first microwave outputs of which are connected respectively to the information to the microwave inputs of the subcarrier detection devices, the second microwave outputs are connected to the inputs of the clock synchronization device, the outputs of which are connected to the clock inputs of the subcarrier detection devices, the decoder and the clock input of the microwave subcarrier synthesizer, the microwave outputs of which are connected in parallel to the inputs of the microwave subcarriers in all m devices subcarrier determination, the outputs of the subcarrier determination devices are connected respectively to m by n information inputs of the decoder, and N information outputs of the decoder p dklyucheny to the N inputs of the output device from the output terminal of synchronization of digital signals and clock frequency.

 The condition for solving the additional switching problem of the SCS is that a device for outputting excess clock sets of microwave subcarriers is inserted into the decoder at the receiving terminal, the outputs of which are connected to the inputs of the decoder of the switching signals, the decoder output is connected to the input of the controller for synchronizing digital channels, the controller output is connected to the control input this switch, N information inputs of which are connected to information outputs of the decoder, N information outputs are connected to N inputs of devices output from the output terminal of synchronous digital channels, and the transmitting terminal switching signal input is connected to the switching input of the encoder-switch.

At the heart of the proposed solution to the problem, i.e. of obtaining N> m, the fact is that the number of possible clock sets of microwave subcarriers, i.e. combinations (arrangements) of n microwave subcarriers on m spectrally separated optical channels is
A $\genfrac{}{}{0ex}{}{\text{m}}{\text{n}}$ + n = (n!) / (nm)! + n,
while the number of possible combinations of binary symbols in N synchronous digital channels generated on the transmission clock interval is 2 ^N.

число размещений из n элементов по m, а также реализующие их функциональные узлы и связи между ними, указанные в формуле изобретения и на фиг. 1, 2, обеспечивают решение поставленной задачи. Это позволяет сделать вывод, что заявляемый способ и устройство связаны единым изобретательским замыслом.Based on the foregoing, it is the claimed sequence of operations on the input set of signals of the SCS when fulfilling the relations between N, n and m, determined by the formula
A $\genfrac{}{}{0ex}{}{\text{m}}{\text{n}}$ + n≥2 ^N ,
Where

the number of placements of n elements in m, as well as the functional units implementing them and the relationships between them, as indicated in the claims and in FIG. 1, 2, provide a solution to the problem. This allows us to conclude that the claimed method and device are connected by a single inventive concept.

 The described method is implemented using the device shown in FIG. 1.

The block diagram of the receiving terminal corresponding to claim 3 of the claims (the transmitting terminal in this case remains the same as in FIG. 1), is presented in FIG. 2. On these diagrams and further in the description text, the following notation is adopted:
1 - input device to the terminal of the signals of the N-channel synchronous digital transmission system, clock frequency and switching signals;
2 - encoder switch;
3 - microwave subcarrier synthesizer;
4 - channel optical transmitters with spaced wavelengths λ _i ;
5 - a device for combining / separating spectrally separated optical channels;
6 - optical transmission line signal;
7 ₁ ... 7 _m - channel photodetectors;
8 ₁ ... 8 _m - channel subcarrier determination devices;
9 - device clock synchronization;
10 - decoder;
11 - output device from the receiving terminal of synchronous digital channels and clock frequency;
12 - decoder signal switching;
13 - controller switch synchronous digital channels;
14 - switch synchronous digital channels;
15 - transmitting terminal;
16 - receiving terminal;
SCS - synchronous digital channel;
F _t - clock frequency;
"Sync" - a clock synchronization signal that defines the boundaries of the clock interval;
SC - switching signal of synchronous digital channels.

 A device that implements a method of transmitting signals of synchronous digital fiber optic systems by the method of spectral-code multiplexing, operates as follows.

N transmitting synchronous channels, a clock frequency F _{t of a} synchronous transmission system and a switching signal of SC channels at the output of the receiving terminal 16 are fed to the input of the transmitting terminal 15.

The clock frequency is fed to the input of the microwave subcarrier synthesizer 3, which generates n harmonics of the clock frequency, the frequency and number of which are determined by the operating frequency band of the optoelectronic nodes of the transmitting and receiving terminals (channel optical transmitters 4 _i (i = 1, ... m), channel photodetectors devices 7 _i ), as well as the initial technical parameters (the number of transmitted synchronous digital channels N, the number of spectrally multiplexed optical channels m), at which the ratio required by the formula electricity. These n harmonics, intended for further use as microwave subcarriers of the transmitted signals, are fed to the microwave inputs of the encoder switch 2, and N synchronous input channels, as well as the clock frequency F _t , are fed to the video inputs of the encoder switch Encoder switch 2 is a variation of a known encoding device that "displays" a combination of N input characters ("zeros" and "ones") generated during each clock interval, a combination of m specific microwave subcarriers (m∈n) uniquely corresponding to this combination . Such a mapping can be performed by known circuitry using high-speed electronic logic and microwave diode keys. This clock set of m microwave subcarriers is fed simultaneously to m channel optical transmitters 4. The transmitters emit signals, each at its own wavelength (λ ₁ ... λ _m ), modulated by these microwave subcarriers during a given clock interval. At the end of each clock interval, the clock synchronization signal resets the installation of the diode microwave keys switching the subcarriers, then the new clock combination on the N video inputs of the encoder switch 2 is mapped (encoded) into a new distribution of m microwave subcarriers (of n possible) that uniquely corresponds to it and the whole the procedure is repeated step by step.

The output paths of the optical channel transmitters 4, having the same optical length, are connected to the inputs of the device for combining spectrally-spaced optical channels 5, usually performed in systems with spectral multiplexing based on optical filters. The device 5 summarizes m optical signals with different wavelengths (λ ₁ ... λ _m ), modulated at each clock cycle with "its" distribution of microwave subcarriers into a group linear optical signal, which is input into the optical transmission path of linear signal 6 (into a linear optical fiber) .

At the input of the receiving terminal 16, after passing along path 6, the group linear signal is first subjected, using the same device 5, but turned on in the opposite direction, to split into m spectrally separated optical channels, each of which is connected to the input of its own channel photodetector 7 . In channel photodetectors 7 ₁ . . . 7 _m , the optoelectronic conversion of the received radiation of the corresponding channel and its preliminary amplification in the frequency bands of all n possible microwave subcarriers are performed. Output signals of channel photodetectors 7 ₁ . ..7 _m are fed to the inputs of the clock synchronization device 9, as well as to the inputs of the channel devices for determining the subcarrier 8 ₁ ... 8 _m, respectively.

The clock synchronization device 9 restores the clock frequency F _t from its harmonics contained in the photocurrents of the channel photodetector devices 7, and generates the signals necessary for clock synchronization of all functional units of the receiving terminal. The distribution of clock signals F _t and clock signals "sync" from the outputs of the device 9 is shown in the diagrams of FIG. 1 and 2. The recovered clock frequency F _t from the output of the clock synchronization device 9 is fed to the input of the microwave subcarrier synthesizer 3 similarly to the synthesizer in the transmitting terminal 15, with the only difference being that the set of n synthesized microwave subcarriers from the outputs of the synthesizer goes to more than one device (encoder -switch 2), and on the microwave inputs of all m channel devices for determining the subcarrier 8 ₁ ... 8 _m , in which this set is used to heterodyne the signals supplied from the outputs of the channel photodetector devices 7.

The principle of operation of the device for determining the subcarrier 8 is very simple: the signal from the output of the channel photodetector 7 _i is fed to the input of the channel device for determining the subcarrier 8 _i , amplified and divided into n signals, each of which is supplied to its own mixer (there are n total of them), to which one of the n microwave subcarriers produced by the synthesizer 3. At the output of the mixers, low-pass filters (low-pass filters) are installed, so that a nominal signal at the output of the low-pass filters will be formed only when the same esuschih. This signal will determine the subcarrier received in this channel. At the boundaries of the clock intervals, the sync signal resets the previous value.

m-channel set of subcarriers thus determined from the outputs of devices 8 ₁ . ..8 _{m is} fed to the information inputs of the decoder 10 as the equivalent of the received clock set of microwave subcarriers and is displayed by the decoder 10 in the clock distribution of N binary symbols at the outputs of the decoder, repeating the distribution of symbols at the input of the encoder-switch 2.

When a switching signal transmitted by the SCC encoder is fed to the switching input of the encoder-switch 2, the “service” clock set of microwave subcarriers corresponding to this signal is formed, which is not included in the encoding table of binary binary information sets, but is contained in the service signal encoding table. If the number of switching (service) signals provided during the operation of the communication system is K, then the number n of subcarriers is taken so that (A $\genfrac{}{}{0ex}{}{\text{m}}{\text{n}}$ + n) - 2 ^N ≥ K.
The passage of a service clock set along the optical path of the device does not differ from the passage of an information clock set, but in decoder 10, a service clock set that is not included in the decoding table of information clock sets is output to the input of the signal decoder 12, in which the service clock set is decrypted with the formation the corresponding control signal transmitted to the input of the controller of the switch SCS 13, in which, in turn, the corresponding command I am the combination for the required switching, transferred to the switch 14. After performing these switching, the arrangement of synchronous channels that existed at the input of the transmitting terminal 15 and transmitted to the output of the decoder 10 will change to another one specified by the switching signal SK and implemented by the switch 14. In this new order the set of SCS through the output device 11 is supplied to the equipment of the receiving subscribers, i.e. to the SCS outputs (Fig. 2).

 We also note that the use of service clock sets of microwave subcarriers and additional service coding / decoding is possible not only for switching, but also for telecontrol, service communication, etc.

 The technical and economic effectiveness of the proposed method and device and their industrial applicability are confirmed by the following examples.

 Let it be required to transmit as many synchronous digital channels as possible with a speed of 155 Mbps, i.e. without switching to high-speed transmission media, with the minimum cost of manufacturing and operating equipment.

 In principle, to increase the capacity of the fiber optic path without increasing the bit rate of the linear signal, systems with spectral multiplexing of channels can be used. However, it is known [1] that with the increase in the number of optical QMS channels (m≥5 ... 6), the complexity of the optical scheme, the requirements for spectral selectivity and stability of optical and optoelectronic nodes, and therefore the cost of the equipment, increase sharply. In addition, the energy potential at the transmission site is reduced due to unrecoverable optical losses, as well as the operational reliability of the optical path with the QMS due to drift of working wavelengths, difficulties with spare parts. Therefore, systems with a small number of multiplexed optical carriers are most preferred.

 Suppose we have a FOTS with QMS, where only two wavelengths are used (i.e. m = 2). In the usual way, we can transmit along its path only 2 digital channels.

If we use a device operating according to the claimed method, and use channel optical transmitters and photodetector devices operating in the frequency range 1.5 ... 3.5 GHz (and this is a well-developed working range of modern optoelectronics), then, having microwave subcarrier synthesizer, forming, for example, n = 8 harmonics of the clock frequency (namely, from the 10th harmonic, F $\genfrac{}{}{0ex}{}{\text{(ten)}}{\text{t}}$ = 1550 MHz, according to the 17th, F $\genfrac{}{}{0ex}{}{\text{(17)}}{\text{t}}$ = 2635 MHz), it is possible to transmit already up to N = 6 synchronous channels, because

A $\genfrac{}{}{0ex}{}{\text{m}}{\text{n}}$ + n = A $\genfrac{}{}{0ex}{}{\text{2}}{\text{eight}}$ +8 = 8 • 7 + 8 = 64 = 2 ⁶ = 2 ^N.
In the case of FOTS with QMS with three operating wavelengths (m = 3), it is possible to add one more microwave subcarrier (for example, F $\genfrac{}{}{0ex}{}{\text{(18)}}{\text{t}}$ = 2790 MHz), transmit up to 9 synchronous digital channels, as

A $\genfrac{}{}{0ex}{}{\text{3}}{\text{nine}}$ +9 = 516> 2 ⁹ = 512.
When using the entire specified operating range, i.e. assuming n = 12, i.e., to the microwave subcarrier F $\genfrac{}{}{0ex}{}{\text{(22)}}{\text{t}}$ = 3410 MHz, it is possible to transfer 10 synchronous digital channels at 155 Mbps and the number of redundant combinations for service use (switching, telecontrol) will be K = 308.

 Microwave electronics nodes (microwave subcarrier synthesizer, encoder switch, decoder, subcarrier determination devices) required to achieve such a gain according to this method and device can be manufactured using standard methods of hybrid-film technology, well-developed and ensuring relative cheapness and stability of the equipment, which confirms the possibility of manufacturing the claimed device and the implementation of the claimed method in industry.

Sources of information
1. Brackett CA "Dense WDM Networks". Fourteenth European Conference on Optical Communications (ECOC '88), 11-15 Sept 1988 Techn. Digest, part I, p. 533, Brighton, UK.

 2. S. Suzuki, K. Nagashima. "Optical Broadband Communications Network Architecture Utilizing Wavelength - Division Switching Technology", in Conf. Digest, Optical Soc. America, Topical Meeting on Photon Switching, March 1987, paper Th A2, Lake Tahoe, Navada, USA.

 3. Y. Tadahiko, U. Arimoto. Wavelength assignable optical communication system.

U.S. Patent 5,319,485, MKI ⁵ H 04 J 14/02; Mitsubishi Denki KK N 878487; declared 5.5.92; publ. 7.6.94; prior. 5.10.91, N 3 - 104583 (Japan); NCI 359/128.

Claims (3)

1. A method of transmitting signals of synchronous digital fiber-optic systems by the method of spectral-code multiplexing, which consists in modulating at the transmitting terminal the signals of the transmitted digital signals of the radiation of m channel optical transmitters with different wavelengths, transmitting signals of various digital channels to any of the used optical wavelengths in accordance with the distribution of operating wavelengths by a controlled control unit switching the used optical wavelengths between the transmit transmitting and receiving terminals of communication systems, combining spectrally-spaced output optical signals of all m channel optical transmitters into a group optical linear signal, transmitting a group optical linear signal along a linear optical path, dividing the group optical signal into m components at the receiving terminal based on the difference in optical lengths waves, photodetection of each component of the optical signal channel photodetector, characterized in that before modulation and radiation channel optical transmitters, the set of N input symbols of the N-channel signal of the digital synchronous transmission system, generated during each clock interval, is encoded by a clock set of m microwave subcarriers from among n microwave subcarriers generated by the subcarrier synthesizer, m, n and N are related by
A $\genfrac{}{}{0ex}{}{\text{m}}{\text{n}}$ + n ≥ 2 ^N ,
where a $\genfrac{}{}{0ex}{}{\text{m}}{\text{n}}$ = the number of placements of n elements in m,
and the modulation of the emissions of m channel optical transmitters, differing in optical wavelengths, is carried out by a clock set of m microwave subcarriers with simultaneous input into the optical signal of information about the clock frequency of the digital synchronous transmission system, after photodetection at the receiving terminal of each component of the optical signal, determine what value of the microwave subcarrier was transmitted over each of the m optical channels on a given clock interval with the simultaneous allocation of the clock frequency of the digital synchronous system s transmit, form the equivalent of the clock set of m microwave subcarriers, similar to that obtained by encoding the input set of N symbols at the transmitting terminal, decode the equivalent of the clock set of m microwave subcarriers with the formation of a set of N binary symbols distributed over the N output channels of the receiving terminal during this clock interval same as at the input of the transmitting terminal.  2. A spectral-code multiplexing device for synchronous digital channels of optical transmission systems, comprising a transmitting terminal, which, in turn, includes an input device for signals of an N-channel synchronous digital transmission system, m channel optical transmitters with different operating wavelengths, a device for combining spectrally-spaced channels, a linear optical path, a receiving terminal, which, in turn, contains a device for separating spectrally-spaced optical channels, m channel photodetectors, a device for outputting from the terminal N signals and a clock frequency of a synchronous digital transmission system, characterized in that the inputs of N synchronous digital channels are connected to N information inputs of the encoder switch, the clock input is connected to the clock inputs of the encoder switch, synthesizer microwave subcarriers and channel optical transmitters, n microwave outputs of the synthesizer microwave subcarriers are connected to n microwave inputs of the encoder switch, m microwave outputs of the encoder switch are connected respectively to I will give modulators of m channel optical transmitters, the optical outputs of m channel optical transmitters are connected to the m inputs of the spectral diversity optical combining device, the output of which is connected to the input of the optical transmission line of the linear signal, the output of the transmission path is connected to the input of the spectral diversity optical device, m outputs of which are connected respectively to the optical inputs of m channel photodetectors, the first microwave outputs of which are connected respectively information to the microwave inputs of the subcarrier determination devices, and the second microwave outputs are connected to the inputs of the clock synchronization device, the outputs of which are connected to the clock inputs of the subcarrier detection devices, the decoder and the clock input of the microwave subcarrier synthesizer, the microwave outputs of which are connected in parallel to the microwave subcarrier inputs in all m subcarrier determination devices, the outputs of the subcarrier determination devices are connected respectively to m at n information inputs of the decoder, and N information outputs the decoder is connected to the N inputs of the output device from the receiving terminal of synchronous digital signals and clock frequency.  3. The device according to claim 2, characterized in that the output terminal introduces a device for outputting excess clock sets of microwave subcarriers, the outputs of which are connected to the inputs of the decoder of the switching signals, the decoder output is connected to the input of the switch controller of synchronous digital channels, the controller output is connected to the control input of this switch, N information inputs of which are connected to N information outputs of the decoder, N information outputs are connected to N inputs of the output device from the receiving terminal of synchronous circuits digital channels, and in the transmitting terminal, the input of the switching signal is connected to the switching input of the encoder-switch.

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