RU2454805C1 - Method to transfer digital data streams along fibre optic communication line - Google Patents

Abstract

FIELD: information technologies.

SUBSTANCE: information data streams are broken into blocks of fixed size, so called clusters, which are coded by special optical signals in the form of optical pulses following each other. The number of pulses in groups may differ, within a group each pulse is characterised by its individual wavelength of optical radiation. Coding optical signals are combined into frames, accompanied with marker optical pulses with a fixed wavelength of optical radiation, different from wavelengths of coding optical signals. Frames are sent along a fibre optic track. At a receiving end of the fibre optic track return conversions take place, information data streams are restored in their initial form.

EFFECT: higher noise immunity and reliability of transferred information, lower requirements to an optic fibre of a fibre optic track, higher speed of data transfer, higher protection of transferred information.

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Description

The invention is a method, relates to the field of information transmission systems, and can be used for backbone and object fiber-optic systems for transmitting digital information along fiber-optic paths and relates to the data link layer of the transmission system (media access control sublevel).

A known method of high-speed transmission of digital data streams over fiber-optic communication lines [1].

The method consists in the fact that, under the combined action of dispersion and nonlinear effects in the region of anomalous (negative) dispersion, a laser source of radiation in an optical fiber excites optical solitons, waves of a special shape propagating in the fiber over significant distances practically without distorting their shape, while the peak power the initial pulse must be greater than some threshold value. The optical solitons are modulated by the signals of the digital data stream, at the receiving end of the transmission line (fiber-optic path), the optical solitons are converted into the original electric digital data stream.

Soliton communication lines can be used to increase the length of the regeneration section (at least twice as compared with the usual one) and to transmit information over very long distances (several thousand kilometers) without the use of regenerators.

A soliton pulse in a communication line plays the role of an information pulse. With an increase in the speed of information transfer, the distance between such pulses, and hence the solitons, becomes so small that their interaction cannot be avoided. At a certain small distance between them, such an interaction can periodically cause collapse of solitons, which is undesirable, since this leads to errors in the transmitted information. If special measures are not taken, then soliton systems can provide transmission at speeds of the order of 40 Gbit / s with minimal mutual influence, if pulses with a width of 2-3 ps are used. Using special measures, for example, solitons polarized in orthogonal planes, it is possible to bring the transmission rate to 160 Gbit / s.

Thus, the disadvantages of the method of data transmission using solitons are the following:

- low reliability of the transmission associated with the possibility of collapse of solitons, in violation of one of the many conditions under which the soliton can exist;

- stringent requirements for the parameters of the fiber optic path: attenuation at the working wavelength of optical radiation, chromatic and polarization-mode dispersion;

- speed limit of transmitted information (theoretical speed limit - 160 Gbit / s);

- lack of protection against unauthorized access to information.

Another well-known method of transmitting information over fiber-optic communication lines is the method of spectral compression of transmitted signals (WDM), described in [2].

The method consists in forming structured parallel digital data streams, converting the electrical signals in these streams into optical signals with different wavelengths of optical radiation for each stream, combining (multiplexing) these signals into one aggregate stream, amplifying the optical power of the aggregate stream and transmitting it through fiber -optical path, decomposition of the aggregate stream at the output of the fiber-optic path into component signals (spectral demultiplexing i) the conversion of component optical signals (spectral components of the aggregate stream) into electric digital streams.

The advantage of the considered method of information transfer is its versatility, determined by the independence of the type of transmitted digital streams (digital streams can be formed by various information transfer technologies: SDH, PDH, IP, ATM, etc.).

The disadvantages of the considered method are:

- low reliability of information delivery;

- high requirements for the parameters of the optical fiber of the fiber optic path;

- speed limit of transmitted information (speed cannot be higher than the result of multiplying the number of wavelengths of component flows by their speed);

- lack of protection against unauthorized access at the physical level.

The low reliability of information transmission is due to the fact that while the optical fiber propagates many spectral components of optical radiation, local bursts of the optical power density in the fiber core are possible, which can lead to such undesirable phenomena as [1, 3]:

- phase self-modulation;

- forced inelastic scattering, such as Raman (Raman) and Mandelstam-Brillouin (Brillouin);

- modulation instability;

- four-wave mixing;

- the occurrence of optical discharge, which can lead to the destruction of the optical fiber.

High requirements for the parameters of the optical fiber are associated with the requirements of minimizing the possible cross-influence of spectral channels on each other. For example, the influence of channels on each other can occur due to nonlinear refraction, which manifests itself in the fact that there is a dependence of the refractive index of the core of the optical fiber not only on the frequency of the optical signals, but also on the intensity of these signals.

In case of unauthorized connection of a fiber-optic path to an optical fiber, a transmitted schedule can be obtained, since the encoding of the traffic does not involve the considered method.

Closest to the technical solution to the proposed method is a method of symbolic transmission of information over a fiber-optic communication line, described in [4] and consisting in the fact that they form a digital electrical signal (CES) at a speed of P bits / s. CECs are divided into equal clusters of K bits in each and encoded with optical signals. The coding optical signals, which are optical pulses with wavelengths of optical radiation, depending on the content of the clusters, transmit one core of the optical fiber path.

At the output of the fiber optic path, the optical signals are demultiplexed by the wavelength of the optical radiation, converted into electrical signals and their levels are compared. A signal with a maximum level is selected and converted into a cluster of K bits, the content of which corresponds to the wavelength of the received optical signal.

The advantages of the proposed method are:

- reduction of requirements for fiber optic links in comparison with the WDM method;

- better noise immunity and reliability of transmission compared to WDM, since the transmission speed decreases, and therefore, the signal-to-noise ratio increases and the bit error parameter determined by this ratio decreases;

- the transmitted traffic is protected from unauthorized access (information retrieval), since the information bits during transmission are encoded by the wavelengths of the optical pulses.

The disadvantages of the considered method are:

- limitation of the information transfer rate, due to the fact that the method is designed to transmit only one digital information stream (the speed limit is 40 Gbit / s [5], determined by the production technology of the modern electronic component base);

- insufficient noise immunity and reliability of information transmission over long distances due to a slight decrease in speed in the fiber-optic transmission channel compared to the speed of the transmitted digital stream (to reduce the transmission speed by 8 times, it will be necessary to form clusters of one byte in size, for encoding such clusters it is necessary the use of 256 wavelengths of optical radiation, which is a technologically difficult task);

- poor information security from unauthorized access (with a cluster size of one byte, for decoding it will be necessary to sort out a total of 256 possible combinations).

The proposed method solves the problem of increasing the noise immunity and reliability of the transmitted information, further reducing the requirements for the optical fiber of the fiber optic path, increasing the speed of information transfer, increasing the protection of the transmitted information from unauthorized access at the physical level.

The essence of the invention lies in the fact that in the method of transmitting digital data streams over a fiber-optic communication line, which consists in forming a digital data stream, breaking it into clusters containing equal volumes of digital information, the clusters are encoded with optical signals that are transmitted via optical fiber of the fiber optic transmission path, at the receiving end of the transmission path, the optical signals are demultiplexed by the wavelength of the optical radiation, converted into electrical and decoded, in contrast to of the prototype method, increase the number of generated digital data streams to N, each of the N streams is divided into clusters, and the clusters are encoded with optical signals in the form of Y successive groups of optical pulses, each group can have from one to V optical pulses with different lengths waves of optical radiation, moreover, the bit composition of each of the clusters is uniquely determined by the composition of the optical signal encoding it, which differs in the sequence and the composition of the groups of optical pulses encoding opt The physical signals are combined into frames of N signals, an optical pulse with a fixed wavelength of optical radiation different from the wavelengths of the pulses in the optical signals is used as a marker for the beginning of each frame, a marker is placed at the beginning of the first coding optical signal of each frame, frames with markers at the beginning each frame is transmitted along the optical fiber of the fiber-optic transmission path, at the receiving end of the fiber-optic path, the optical pulse of the marker is converted into an electrical pulse, which apuskaet N recovery processes digital data streams by decoding the electrical signals converted from optical signals encoding each frame into clusters, and their distribution over the parallel digital streams.

Consider the principle of operation of a fiber optic transmission line that implements the proposed method.

The figure 1 presents a diagram of the process of forming the aggregate stream of N structured digital streams with a speed of P bit / s, with bit intervals T _b ,

The structured digital streams are divided into clusters, which are blocks of K bits of information, the cluster period T _k is

Each cluster is encoded by an optical signal, representing Y groups of optical pulses following each other.

The number of pulses in a group can be from one to V, each optical pulse in a group has its own individual wavelength of optical radiation. Pulse wavelengths in one group are not repeated.

The optical signals encoding the first cluster of N component ¹ ( ¹ The original digital data streams are component, since an aggregate group data stream is formed from them) of the digital data streams are combined into a first frame encoding the second cluster into a second frame and so on. From frames accompanied by marker optical pulses, and following each other, an aggregate (group) data stream is formed. The wavelength of marker optical pulses of all frames is the same for all frames and is not used in the formation of coding optical signals.

The choice of the repetition period of the groups of pulses of the optical coding signals T _g depends on the priorities adopted during the design of the fiber-optic communication line.

.If the priority is the speed of the communication line, then the period of the groups is chosen equal to or less than the values of T _b (T _g ≤T _b ). Since the speed of the communication line depends on the number of coding optical signals placed in a frame of duration T _k , the maximum number of signals equal to the integer value of division is placed in the frame

.

If the priority is taken to reduce the requirements for the parameters of the fiber optic path and the reliability of message delivery, then clusters can be transmitted in frames consisting of only one coding signal. The period of the pulse groups in the coding signals can be found by the formula

будет превышать Т_б. Соответственно скорость волоконно-оптической линии передачи будет ниже скорости передаваемого информационного потока в

раз. При уменьшении скорости передаваемых оптических сигналов увеличивается отношение сигнал/шум, уменьшается значение параметра ошибок по битам и уменьшаются требования к параметрам оптического волокна волоконно-оптического тракта.In this case, the sequence of groups of pulses in

will exceed T _b . Accordingly, the speed of the fiber optic transmission line will be lower than the speed of the transmitted information stream in

time. By reducing the speed of the transmitted optical signals, the signal-to-noise ratio increases, the value of the bit error parameter decreases, and the requirements for the parameters of the optical fiber of the fiber optic path decrease.

The figure 2 presents a diagram of the process of decomposition of the aggregate flow. The process of restoring the original clusters of flows is started automatically by an optical marker pulse and begins at the end of the current cluster. The image of each cluster is stored in the resident program memory of the control microcontroller and uniquely corresponds to the composition of the encoding signal. That is, the number of coding signal variations should correspond to all possible cluster values.

The proposed method is implemented by the device, the structural diagram of the transmitting unit of which is shown in figure 3.

The transmitting unit contains the following nodes: nodes for extracting clock pulses from structured digital streams 1 and 2 (node 1 selects the synchronization signal of the 1st digital stream, and node 2 - the N-th digital stream), counter-dividers 3 and 4, counting clusters of size K bits, blocks of shift registers 5 and 6, converting serial K data bits to parallel K - bit code sent to the inputs of the microcontroller 7, the driver node 8, which controls the semiconductor optoelectronic transmitting modules 9, 10, 11 and associated with the outputs of the micro ntrollera 7, optical wavelength multiplexer 12 combines the output optical radiation modules 9, 10 and 11 into a single aggregate optical flow into the optical fiber path.

The transmitting unit of the device operates as follows.

The main nodes of the transmitting unit are controlled by a microcontroller 7. The microcontroller may be a multiprocessor system with parallel processing of information. The number of processors should correspond to the number of parallel digital streams.

The signals from the counters of frequency dividers 3 and 4 record and store in the resident memory the data of the clusters of transmitted digital streams, each cluster is assigned an individual number, which reflects its serial number and belonging to a specific digital stream. The controller also contains resident program memory, in which, in addition to the program code, individual codes of all possible clusters are entered (code table).

Using the resident data memory, which contains clusters of streams intended for transmission, and the resident program memory, which stores the code tables of the clusters, the microcontroller forms frames consisting of optical coding signals. First, sequences are formed from the marker electric pulse and parallel electrical signals in software (the number of parallel signals corresponds to the number of groups Y, the number of bits of parallel signals corresponds to the number of optical pulses in group V). Electrical signals are sent to drivers 8, which control transmitting optoelectronic modules that convert electrical signals into optical ones.

Frames are created from optical signals.

At the beginning of each frame, a marker optical pulse is generated (at the output of the optoelectronic module 9), then a sequence of Y groups of optical pulses is generated in accordance with the code table. Each group can consist of several optical pulses (from one to V) with different wavelengths of optical radiation generated by V transmitting optoelectronic modules (in the diagram, module 10 generates pulses at a wavelength of optical radiation λ ₁ , module 11 at a wavelength of optical radiation λ _V , other modules not shown).

As an example, we consider all possible states of pulse groups at V = 8.

State S ₁ = 1, the group consists of eight pulses with wavelengths λ ₁ , ... λ ₈ .

States S ₂ are characterized by the absence in the group of one pulse with one of the wavelengths from the set λ ₁ , ... λ ₈ . The number of such states can be determined by the formula

- число сочетаний из 8 по 1.Where

- the number of combinations of 8 to 1.

States S ₃ through S _{8 are} characterized by the absence in the group of two, three, and so on up to seven radiation pulses, the number of states is determined by the number of combinations of 8 in 2, 3, ... 7.

The total number of different states of a group of eight optical pulses S _Σ can be found by the formula

The number of states of any optical coding signal from Y groups of optical pulses S _c is determined by the number of arrangements from S _Σ in Y.

But the groups of pulses that make up the coding optical signals can be the same (contain the same sets of optical pulses). Different combinations of two, three, four, etc. can be identical. up to Y groups. The sequence of such groups may also differ; the number of possible states determined by the sequence is calculated by the number of movements from Y.

The full array of groups of states from which encoding optical signals are formed taking into account the comments made can be estimated by the formula

And the number of states of any encoding optical signal is determined by the number of arrangements from S _P in Y.

If the coding signal consists of eight groups (Y = 8, V = 8), then S _P = 255 · 8 = 2040, and the total number of states of such a coding signal S _KC can be found by the formula

- число возможных размещений из 2040 по 8.Where

- the number of possible placements from 2040 to 8.

The number obtained by formula (7) determines the maximum cluster size. The number of bits (bits) of a cluster is calculated based on its maximum size, and is determined by the binary number closest to it, consisting of only one logical unit.

The closest binary number, consisting of one unit, to the maximum cluster size calculated by formula (7) is a 22-bit hexadecimal number 7FFFFFFFFFFFFFFFFFFFFF h or a 87-bit binary number.

Thus, using eight bit intervals and eight wavelengths of optical radiation to form a coding optical signal, a 87-bit segment of the data stream can be transmitted over the transmission line.

As shown above, the encoding optical signals encapsulated in frames and accompanied by marker optical pulses using the optical multiplexer 12 are combined into a single aggregate stream directed to the receiving unit of the device through a fiber optic path.

The block diagram of the receiving unit is presented in figure 4.

The receiving unit contains the following nodes: a spectral optical demultiplexer 13, which extracts marker pulses (with an optical radiation wavelength λ _m ) from the optical aggregate signal and coding signal pulses (with optical radiation wavelengths λ ₁ , ... λ _V ), receiving optoelectronic modules (on the diagram shows the receiving optoelectronic modules of marker pulses 14, pulses with a wavelength of optical radiation λ ₁ , 15 and λ _V , 16, the rest are not shown), the microcontroller of the receiving unit 17 (multiprocessor, similar to micro to the controller of the transmitting unit), shift registers 18, which restore serial streams from the parallel output signals of the microcontroller (they perform the functions of a serializer).

The receiving unit operates as follows.

At the beginning of the frame, a marker pulse arrives, this pulse is first converted into an electrical pulse by the receiving optoelectronic module 14. The marker electric pulse starts the built-in timers of the microcontroller, which are configured to receive coding signals converted into electrical form.

The first Y code combinations of pulses are stored in the area of the resident data memory allocated for the first stream, the second Y code combinations are recorded in the memory area of the second stream and so on. After recording all the combinations, the microcontroller starts processing them. Processing is reduced to finding in the code tables the obtained image of the cluster, the code of which was transmitted over the transmission channel.

After finding the image of the cluster transmitted by the code signal, the microcontroller starts the recovery process of the cluster bit stream, for this, shift registers 18 are used.

After processing the first frame, subsequent frames are processed in the same sequence, so that the recovered streams are continuous.

Possible failures and errors in the transmission of information at the physical level by the receiving unit are not monitored; a higher transport level of the transmission system must be responsible for correcting possible errors.

The considered method of transmitting digital data streams over a fiber optic communication line has the following advantages compared to the prototype.

1. Greater noise immunity and reliability of the transmitted information.

2. Higher speed of information transfer.

3. Improved protection of transmitted information from unauthorized access at the physical level.

We show these advantages with specific examples.

The noise immunity and reliability of the transmitted information mainly depends on the signal-to-noise ratio of the transmission channel. In turn, this ratio is highly dependent on the data transfer rate. The requirements for the optical fiber of the fiber optic path also depend on the transmission speed.

If the priority in the design of the fiber-optic communication line is to reduce the requirements for the parameters of the fiber-optic path and the reliability of delivery, then it is necessary to reduce the speed in the transmission channel.

In the prototype method, a decrease in the data transfer rate in the transmission channel is provided by encoding the transmitted information bits by the optical wavelength. When using eight wavelengths to encode data in this way, no more than three bits of information can be encoded (possible variants of the encoded bits: 000; 001; 010; 011; 100; 101; 110, 111). In accordance with this, the speed in the transmission channel can be reduced by three times.

.The proposed method, as shown above, allows the use of optical signals from 8 groups of optical pulses with the number of pulses in the group up to 8 (the number of optical wavelengths used is eight) to encode 87 bits of information. Accordingly, a speed reduction of 10 times is possible.

.

For example, a data stream with a speed of 10 Gbit / s can be transmitted over a fiber optic line with a speed of 1 Gbit / s.

Consider the case when the priority in designing a fiber optic communication line is maximum performance.

As shown above, the fastest communication lines are those that use the method of spectral multiplexing of transmitted optical signals (WDM technology). When using nine wavelengths of optical radiation, the maximum aggregate flow rate can be no more than 9 · V, where B is the velocity of the component data streams.

If we use the proposed method, for eight wavelengths of optical radiation of optical coding signals (V = 8), one wavelength of optical radiation of a marker optical signal, eight groups of coding signal (Y = 8), the period of repetition of groups equal to the bit interval of information flows, then in the generated frames Q coding signals can be placed.

The value of Q can be found by the formula

where K (Y = 8, V = 8) is the number of bits of the encoded cluster at V = Y = 8.

Substituting the values of the parameters K (Y = 8, V = 8) = 87, Y = 8, we obtain Q = 10.7≈10.

That is, the maximum speed of the aggregate stream will be 10 V, where B is the speed of the component data streams. The gain compared to the WDM method is 10%. It can be shown that the gain will accelerate nonlinearly with increasing number of wavelengths of optical radiation.

The WDM method does not provide protection against unauthorized access at the physical level.

The method of transmitting data according to the prototype provides for encoding the transmitted data by the wavelength value. However, if we use the number of possible code combinations as a criterion for the quality of coding, then the proposed method is several orders of magnitude higher than the prototype method [4] (for 8 wavelengths by 84 orders of magnitude).

It should be noted that the code tables in the proposed method for each of the N data streams may be different.

The method provides for the possibility of changing the code tables at time intervals corresponding to the decoding time for the received fragment of the code sequence. This change can be incorporated into the control program algorithm of the microcontrollers of the transmitting and receiving units of the device that implements the proposed method.

References

1. Slepov N.N. Soliton networks. "Networks", No. 03, 1999.

2. Slepov N.N. Modern technologies of digital fiber-optic communication networks. M .: Radio and communications, 2000, 467 p.

3. Bufetov I.A., Dianov E.M. Optical discharge in optical fibers. Lightwave Russian edition, No. 4, 2004, pp. 50-51.

4. RF patent for the invention №2161374 "Method for the symbolic transmission of information on fiber-optic communication lines."

5. Bakharevsky A.L. New transponders for data transmission at 40 Gb / s based on CP-DQPSK modulation. Photon Express, No. 1 (89), February 2011, p. 28-29.

Claims (1)

A method of transmitting digital data streams over a fiber-optic communication line, which consists in forming a digital data stream, breaking it into clusters containing equal volumes of digital information, clustering with optical signals that transmit over the optical fiber of the fiber-optic transmission path, the receiving end of the transmission path, the optical signals are demultiplexed by the wavelength of the optical radiation, converted into electrical and decoded, characterized in that the number of generated digital data streams up to N, each of N streams is divided into clusters, and clusters are encoded with optical signals in the form of Y successive groups of optical pulses, in each group there can be from one to V optical pulses with different wavelengths of optical radiation, and the composition of each of the clusters is uniquely determined by the composition of the optical signal encoding it, which differs in sequence and the composition of the groups of optical pulses, encoding the optical signals are combined into frames of N signals, as the start markers of each frame use an optical pulse with a fixed wavelength of optical radiation different from the wavelengths of the pulses in the optical signals, place the marker at the beginning of the first coding optical signal of each frame, the frames with markers at the beginning of each frame are transmitted along the optical fiber of the optical fiber transmission path , at the receiving end of the fiber optic path, the optical pulse of the marker is converted into an electrical pulse, which starts the restoration of N digital data streams x by decoding the electrical signals converted from the optical coding signals of each frame into clusters, and their distribution in parallel digital streams.

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