RU2232474C2 - Method and device for synchronizing communication system signals and eliminating their phase ambiguity - Google Patents

Abstract

FIELD: digital engineering; synchronizing communication system signals and eliminating their ambiguity.

SUBSTANCE: method involves signal demodulation and differential decoding, addition of cophasal- and quadrature-channel signals, correlation of signal with unique sync signal word followed by differential coding to ensure synchronization of receiving end and elimination of ambiguity for absolute phase keyed signals and differential coding for relatively phase keyed signals. Device implementing this method has series-connected coherent phase-keyed signal demodulator, differential decoder, cophasal and quadrature channel adder, shift register, correlator whose output functions as device output, and differential coder whose inputs are connected to decoder outputs, differential coder outputs being used as device outputs.

EFFECT: optimized processing of absolute and relative phase-keyed signals, simplified hardware design.

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Description

The invention relates to the field of digital technology and can be used in the processing of signals of communication systems with phase modulation.

Digital transmission of information is becoming increasingly common in communication systems. Currently, special attention is paid to the development of communication systems with multiple access based on time division of channels (TDMA). As a rule, phase modulation methods are used in these systems. In this case, both absolute phase shift keying (AFM) and relative phase shift keying (OFM) are used. Sometimes in one communication system one and another type of manipulation is used. So, in the “Spade” system, four-phase AFM is used in the information channels, and two-phase OFM in the common signaling channel [1, pp. 201 and 202]. Each of these methods of manipulation has its advantages and disadvantages.

For communication systems with AFMs, the main disadvantage is the "reverse operation" mode, when instead of the original transmitted information at the receiving side, distorted information is obtained due to the ambiguous phase of the restored reference carrier oscillation in the demodulating device. An advantage of communication systems with AFM as compared to OFM is higher noise immunity (occurrence of single errors on the receiving side during single failures in the communication line).

For communication systems with OFM, the main drawback is the occurrence of pair errors on the receiving side during single failures in the communication line, which is explained by the principle of organization of the OFM signal when the value of the subsequent symbol is determined relative to the state of the previous symbol. The main advantage is the lack of a “reverse operation” mode due to preliminary differential encoding of information on the transmitting side and differential decoding of it on the receiving side.

,

А и В

, где А, В и

,

- соответственно прямые и инверсные значения символов в подканалах.To synchronize and eliminate the “reverse work” in communication systems with AFM, special code messages are used, which, although they reduce the efficiency of the communication system, provide an unambiguous subsequent restoration of the initial information [5 - prototype]. If a four-phase AFM is used in a communication system, then after a demodulating device the following combinations of information in subchannels are possible: AB,

,

A and b

where A, B and

,

- respectively, direct and inverse symbol values in subchannels.

According to the prototype method, synchronization and disambiguation are performed by performing the following operations:

- the received signal is demodulated (converted to digital form);

,

А, В

- для четырехфазного сигнала);- correlate the resulting digital stream with possible code combinations of unique synchronization words (AB,

,

A, B

- for a four-phase signal);

- determine, according to the results of the correlation, the type of the unique word of the clock signal and form its response on the time axis, thereby ensuring synchronization on the receiving side;

- according to the results of determining the type of a unique synchronization word (type of phase ambiguity) in the signal, the information part is brought to the form AB, i.e. eliminate phase ambiguity.

The disadvantage of the prototype method is the complexity of the hardware implementation of the personnel, packet synchronization and phase ambiguity elimination devices.

,

А, В

трансформируются к исходной комбинации АВ.The ambiguity (“reverse work”) is currently eliminated by the use of correlators for each of the possible states of the sync tag combination. The response of one or another correlator is used to generate control signals for disambiguation. As a result, possible combinations of AB,

,

A, B

are transformed to the original combination AB.

One of the possible synchronization and disambiguation schemes, which is used in modern equipment for four-position AFM, is shown in figure 2 [5 - prototype]. The device includes two N-bit shift registers 4, four correlators 5, four threshold circuits 7 and four digital adders 8, a decoder 9 and a data decoder 10.

The disadvantage of the prototype device is the complexity of the hardware implementation (especially correlators with triggering on unique words of the error signal) and the bulkiness of the device. In communication systems with TDMA, as a rule, packet, frame, and superframe signals are transmitted, i.e. on the receiving side should be installed three sets of prototype devices.

The aim of the invention is to optimize the method of processing signals from AFM and OFM and simplify the hardware implementation.

To achieve this goal, a method is proposed in which the signal is demodulated and correlated with a unique clock signal. According to the invention, after demodulating the signal, the operation of differential decoding and summing of the signals of the in-phase and quadrature channels is introduced, and after the correlation, the operation of differential encoding is introduced, which eliminates phase ambiguity during AFM; for signals with OFM, the operation of differential encoding is excluded (transit mode).

A device that implements the proposed method contains a coherent phase demodulator of signals and series-connected shift register and correlator. According to the invention, a differential decoder and an adder of the in-phase and quadrature channels, as well as a differential encoder, the second input of which is connected to the output of the correlator, and the first inputs to the outputs of the decoder, the outputs of the demodulator connected to the inputs of the differential decoder and the register inputs are introduced into it shift - to the outputs of the adder. The outputs of the device are the outputs of the differential encoder and correlator.

The proposed method and device that implements it are not described in the literature, obviously do not follow from the achievements of science and technology, therefore they meet the criteria of novelty and inventive step.

Figure 1 shows the structural diagram of the device according to the proposed method, figure 2 is a structural diagram of a prototype device.

The proposed method performs the following sequence of operations:

- the signal is demodulated;

- the signal is differentially decoded;

- summarize the signals of the in-phase and quadrature channels;

- the signal is correlated with a unique sync word;

- the signal is differentially encoded, which ensures synchronization of the receiving side and elimination of phase ambiguity for signals with AFM;

- exclude differential coding for signals with OFM.

The device according to the proposed method contains (Fig. 1) a coherent demodulator of phase-shifted signals 1, a differential decoder 2, an in-phase and quadrature channel adder 3, a shift register 4 and a correlator 5, and a differential encoder 6. The outputs of the decoder 2 are connected to the inputs of the encoder 6, the outputs of which and the output of the correlator 5 are the outputs of the device.

The device operates as follows.

, для четырехфазной АВ,

,

А, В

). Далее сигнал АФМ поступает на дифференциальный декодер 2, где сигнал трансформируется в сигнал а' - для двухфазного сигнала и а'в' для четырехфазного сигнала, при этом только уникальные слова синхронизации трансформируются в постоянные кодовые комбинации независимо от неоднозначности демодулятора 1. Одновременно трансформируется и информация после декодера 2.The input signal of the intermediate frequency F _{IF is} fed to the demodulator 1, where it is converted into a digital stream accompanied by a clock frequency (for two-phase modulation A or

, for four-phase AB,

,

A, B

) Next, the AFM signal is fed to differential decoder 2, where the signal is transformed into signal a 'for a two-phase signal and a'b' for a four-phase signal, while only unique synchronization words are transformed into constant code combinations regardless of the ambiguity of demodulator 1. At the same time, information is also transformed. after decoder 2.

The constant unique words of synchronization of the subchannels a 'and b' are summed in adder 3 into the stream a'b ', fed to shift register 4 and then allocated by one correlator 5, by the response of which the initial bits are set in encoder 6 to restore the original (transmitted) information. When processing signals from the OFM differential encoder 6 is placed in transit mode.

Differential encoding / decoding procedures for 2FM and 4FM signals are well known [1, p.201 and 202], for TRELLIS signals <8FM and 16FM are given in the Appendix, for KAM16, ..., KAM256 signals, the differential encoding / decoding procedures are adequate to the procedures for 4FM, since the manipulation codes are selected so that during phase jumps of the reconstructed demodulator carrier by 90 and 180 °, only the highest bits in the in-phase and quadrature channels change, they are subjected to differential coding / decoding procedures anija algorithms for four-phase modulation (4FM).

Consider the essence of the procedure for processing AFM signals using a specific example for a single AFM. Let the original sequence be transmitted

Then after demodulator 1 we get

We expose one and the other sequence of differential decoding operation according to the rule

we get

Distortions of the preceding characters before the sync pattern after demodulator 1 cause a single error in the code combination after differential decoder 2, and a character distortion in the code combination causes a pair error, which is caused by high bit depth (from 30 to 40 characters) of code words in TDMA communication systems insignificantly in the operation of extracting sync signs if the codeword is considered as a noise-like signal with a large base. Next, using only one correlator, we select the sync sign transformed as a result of the differential decoding operation to one code combination, we collapse it in duration to an elementary symbol and use it for the initial installation of the memory element (A _i-1 ) of the differential encoder. We set A _i-1 = 0 and subject the information sequence to the differential encoding operation according to the rule

,

,

where A _i is the initial value of the characters at the current time;

A _i-1 is the value of the symbol at the previous moment;

and _i is the currently encoded symbol value.

Then after the encoder we get the original sequence of characters

for any ambiguity in the information sequence after demodulator 1.

Setting the symbol A _i-1 = I for the differential encoding operation based on the results of highlighting the sync sign will give an inverse combination of the original sequence of characters, that is, it is necessary to have a priori information about the true value of the last character in the code pattern of the sync sign and use this value as A _{i- 1} character in differential encoding operation.

The table shows the results of processing AFM signals in case of single failures in the communication line.

The table shows that when single faults occur in the communication line on the receiving side after the decoding operation, pair errors occur (see expression (1) and the table), which during the encoding operation are reduced to one error. It would seem that in the case of a differential coding operation for single failures in the communication line with a two-position AFM, an inverse information sequence should be obtained, however, this does not happen precisely because paired errors occur during the previous decoding operation. The first error would give an inverse information sequence, but the second error following it gives the original combination, and the second error after the decoder is corrected in the encoder. The obtained data can be extended to the processing of signals with AFM of higher multiplicity.

Thus, as a result of the considered procedure for processing AFM signals by using OFM signal processing devices, it was possible to optimize the processing process, significantly simplify the technical implementation of the device while maintaining high noise immunity and operability of the device both for AFM signals and for OFM signals.

Literature

1. Spilker J. Digital satellite communications. - M.: Communication, 1979.

2. Kindleman P.D. and Kuner E.B. Fast correlator. “Instruments for scientific research”, 1968, No. 6.

3. Express information VINITI, a series of PI, 1974, No. 29, p.8-12.

4. Single-chip correlator 64 bit words. Electronics, 1980, No. 23, p. 123 and 124.

5. Shunvoku Sasaki, Hiroshi Kurihara, Burst Codeword with arbitrary Length for Four-Phase CPSK / TDMA System. Fourth International Conference on Digital Satellite Communications, 23 - 25 October 1978, Montreal, p. 327-332.

Claims (2)

1. A method for synchronizing and eliminating phase ambiguity of signals of communication systems, in which the signal is demodulated and correlated with a unique sync signal word, characterized in that after demodulation the signal is differentially decoded and summed in-phase and quadrature channel signals, and after correlation with a unique word, the signal is differentially encoded, This ensures synchronization of the receiving side and eliminates phase ambiguity for signals with absolute phase modulation, while for signals with relative base card modulated differential encoding operation rule (transit mode). 2. A device containing a demodulator and a series-connected shift register and correlator, characterized in that a series-connected differential decoder and an adder in-phase and quadrature channels are inserted into it, the outputs of which are connected to the inputs of the shift register, as well as a differential encoder, while the outputs of the demodulator are connected to the inputs of the decoder, the outputs of which are connected to the first inputs of the encoder, to the second input of which the output of the correlator is connected, the outputs of the device are the outputs of the encoder and correl ora.

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