RU2544178C1 - Device for receiving discrete signals transmitted through multibeam communication channel - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: device for receiving discrete signals transmitted through a multibeam communication channel comprises at least two first-stage correlators, at least one second-stage correlator and a decision device. The common input of the first-stage correlators is the input of the device; the first first-stage correlator calculates correlation between received and information signals; the output of the first first-stage correlator is connected to the first input of the second-stage correlator, the output of which is connected to the input of the decision device, and the output of the decision device is the output of the disclosed device. A unit for converting an estimate of pulsed channel reaction from the frequency band of the test signal into an estimate of pulsed channel reaction in the bandwidth of the information signal is connected between the output of the second first-stage correlator and the second input of the second-stage correlators, wherein the second first-stage correlator calculates correlation between the received and test signals.

EFFECT: accuracy of estimating pulsed channel reaction on a series of test pulses transmitted in a frequency band which does not match the frequency band of information pulses.

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Description

The invention relates to the field of transmission of discrete information and is intended for use in devices for receiving (decoding) communication signals transmitted, for example, in a KB radio channel or other channels with multipath propagation.

The main problems facing the developer of signal reception devices that have passed through the multipath communication channel are the dissipation of the signal energy over time, which (in the absence of technical measures to compensate for this effect) leads to a decrease in the signal-to-noise ratio on the solving device.

To overcome these problems, a priori knowledge of the instantaneous form of the channel impulse response (IRF) is necessary. Next, we use the following terminology: KFM — response of the propagation channel to the input action in the form of a δ-function (infinitely short pulse), KFM in the frequency band of some signal S (n) —convolution of the channel’s response to the δ-function with the autocorrelation function of this signal. With the known KFM, the entire alphabet of transmitted characters can be predicted, i.e. recounted to the point of reception. In this regard, most of the known solutions to these problems are one way or another based on radiation along with information (i.e., unknown at the receiving end of the communication system) symbols or signals of test (or test) signals that evaluate the instantaneous KFM or, more precisely, the KFM in the frequency band of the test pulse. Such a transmission principle is referred to as a “system with a test pulse and prediction” (or SIIP) (see, for example, [1], section 3.1, in particular, the footnote on p.109).

This principle underlies, in particular, objects [2-4].

The disadvantage of the principle of constructing a communication system for which well-known analogues are designed is the relatively low quality of reception (decoding) of messages, caused either by a loss of time during the transmission of test and information pulses separated in time (as is the case in [1]), or by the action of test pulses , which interferes with the reception of information pulses (and also vice versa, the action of information pulses, which interferes with the reception of test pulses), while transmitting both those and other pulses in one In the same frequency band. A disadvantage of the known analogues is that under the conditions of arrival (transmission) of test and information pulses in different frequency bands, they are inoperative.

The closest in technical essence to the claimed object is the device described in [5]. It is selected as a prototype. The prototype solves the following problem. One of two possible signals or connected symbols (binary communication system) is transmitted - S1 (t) or S2 (t), both symbols being located in the same frequency band. The shape of the transmitted signal (symbol) during propagation in the multipath channel was distorted, described as a convolution of this symbol with the KFM, the shape of which is a priori unknown. At the point of reception, a decision must be made as to which of the two characters was transmitted.

The block diagram of the prototype is shown in figure 1; explanations on it are given below when describing the principle of operation of the prototype.

The principle of operation of the prototype is as follows. For each possible moment of arrival of the connected signal, the mutual correlation between the received signal and each of the two possible symbols S1 (t) or S2 (t) is calculated. This action is performed by the correlators of the first stage (KPS) (positions 1-1 and 1-2 in figure 1). As a result of performing this function, temporary implementations are formed at the outputs of the KPS 1-1 and 1-2, and at the output of that KPS, the reference oscillation of which coincides with the actually transmitted symbol, this temporary implementation is an estimate of the KFM in the working frequency band, and at the output of another KPS - just noise. Due to the fact that the prototype information about which of the two possible characters was transmitted is unknown, it sums up (the same time samples) of temporary realizations formed at the outputs of both KPS (adder 2 in figure 1). This result of summing the estimate of the KFM in the working frequency band obviously contains. The adder 2 is also cumulative over a moving time interval, i.e. it accumulates arrays of KFM estimates, which are formed sequentially in time as a series of connected symbols arrives. Next, the calculation of the correlation between the estimate of the KFM (it is formed at the output of the adder 2) and each of the temporary realizations formed at the outputs of the KPS 1-1 and 1-2 is implemented. This function is performed in the correlators of the second stage (FAC) (position 3-1 and 3-2 in figure 1).

Note. Discrete correlation (and all of the above operations are discrete, i.e., performed in discrete time) is a scalar product of arrays of time samples of the signal and the reference wave (in our case, this takes place in the correlators of the first stage) or samples of two signals (in our case, takes place in the correlator of the second stage), calculated when updating the array of samples of the input signal (in the correlators of the first stage) or both signals (in the correlator of the second stage) with each update of the result of calculating the corre Relations, for example, to one or more samples. Convolution is the same correlation, but when it is calculated, one of the two arrays (this mainly concerns the array of samples of the reference oscillation) is read in the reverse order of the indices of the time argument. In the prototype, the concept of "correlator" appears, but in fact, we can talk about the calculation of convolutions. When performing all operations in discrete time, the time argument t is represented by its floppy disks t _n = n · f _d , where f _d is the sampling frequency. In this regard, further, all signals are recorded as discrete time signals S (n) = S (t _n ).

Further, for concreteness, we assume that the symbol S1 (n) is transmitted. Moreover, in FAC 3-1, a response is actually formed proportional to the energy of the transmitted multipath signal (i.e., distorted in the shape of the symbol S1 (n)), which corresponds to the effect of coherent addition of rays. This response is characterized by a high level. At the same time, the output of PIC 3-2 in this situation is only the realization of noise (it has a low level), which allows for comparing (in the resolver 4) the response levels generated at the outputs of PIC 3-1 and 3-2, with each other and / or with a threshold to decide on the actually transmitted character. So, in the case under consideration, as a rule, the level at the output of the PIC 3-1 will be large and / or exceeding the threshold, which will lead (also, as a rule) to the decision that the symbol S1 (n) is betrayed, which in the situation under consideration and is the right decision.

Thus, in the prototype, the problem of temporal dispersion of the energy of the communication signal is solved, because, as noted above, an effect is achieved that is equivalent to the coherent addition of all the rays. The disadvantage of the prototype, as well as the mentioned analogues, is that it is not applicable when transmitting test and information pulses in different frequency bands.

The purpose of the claimed device is to eliminate the specified disadvantage of the prototype, i.e. providing the possibility of receiving (decoding) messages when transmitting test and information pulses in different frequency bands. The goal is achieved in that in a device containing at least two correlators of the first stage, at least one correlator of the second stage, as well as a solving device, the common input of the correlators of the first stage being the input of the inventive device, the output of the first of the correlators of the first stage connected to the first input of the correlator the second stage, the output of which is connected to the input of the deciding device, and the output of the deciding device is the output of the inventive device, a conversion unit for evaluating the impulse response of the channel is introduced, including between the output of the second correlator of the first stage and the second input of the correlator of the second stage.

The inventive object can be used in a communication system in the general case with multi-position coding (while the number of correlators of the first and second steps accordingly increases in it). However, the minimum composition of its features occurs if it is used in a binary communication system, and with a passive pause. Moreover, the alphabet of transmitted characters consists of only two characters “0” and “1”, encoded during the transmission of a message, for example, as a zero level (ie, no radiation or passive pause) and S1 (n), respectively. Simultaneously with each information one, a test impulse Sи (n) is also emitted, the latter being emitted in a frequency band that does not coincide with the frequency band of information symbols (pulses). A variant of the system operation is also possible in which, in the case of transmitting the “0” symbol, the test pulse is not emitted.

The block diagram of the claimed object is shown in figure 2, where indicated:

- 1-1 and 1-2 - correlators of the first stage;

- 2 - correlator of the second stage;

- 3 - block conversion of the impulse response of the channel;

- 4 - decisive device.

Each correlator of the first stage (1-1 and 1-2) is implemented, for example, in accordance with [6], the block diagram in Fig.5.14, p.295. In this case, the signal input of the correlator is the lower input in the indicated Fig. 5.14, to which the received signal x (n) is supplied. The reference function of the correlator of the first stage (in the indicated Fig. 5.14 it is designated as h (n)) is stored in its long-term memory, which is not shown in Fig. 5.14 for simplicity. In the claimed device, the support functions of the correlators of the first stage h (n) are:

- correlator 1-1 - h1 (n) = S1 (n);

- correlator 1-2 - h1 (n) = Si and (n).

When the correlator of the first stage is implemented in the spectral region (i.e., based on the fast convolution procedure), the discrete Fourier transform (DFT) operation is performed in advance on the support function of each of these correlators, and the array of the DFT result (the result of its complex conjugation) is stored in long-term memory corresponding correlator of the first stage. DFT is also performed over the arrays of samples of the input signal x (n), then elementwise multiplication (i.e., multiplication of the same samples) of the arrays of DFT results over the reference function and input signal and the inverse DFT (DFT) from the array of the results of the specified multiplication are performed. The period of updating the array of samples of the input signal for adjacent time cycles of calculating the correlation in each of the correlators of the first stage is usually chosen equal to the duration of each of the signals (pulses) S1 (n) and Sи (n) (the durations of these signals coincide in the simplest case), while the length of the DFT window is the double duration of each of these signals. Two independently working correlators of the first stage are shown in FIG. 2 conditionally. When implemented in the spectral region, the DFT from the input signal that is part of these correlators can be common for two correlators of the first stage.

A variant of the block diagram of the correlator of the first stage in the time domain equivalent to the one considered is also possible; A description of this correlator option is given [6], Fig. 6.18b, p. 418, where (in accordance with the current state of the art), instead of a recirculating delay line that stores an array of time samples of the reference signal when it is strictly limited, a multi-bit shift register is stored that stores the samples represented by multi-bit code words. The dynamics of updating the input and output data of the correlator under consideration is illustrated, for example, in [7], pp. 76-78.

The correlator of the second stage 2 is implemented similarly to the correlator of the first stage (preferably in the time-domain variant), with the only difference being that it does not have a long-term memory that stores the reference oscillation. The duration of the signal update cycle at the output of the correlator of the second stage may be, for example, one sampling period of the input signals.

в полосе частот испытательного импульса Sи(n), сформированной на выходе второго коррелятора первой ступени (т.е. коррелятора 1-2), например, в оценку ИРК

в полосе частот информационного импульса S1(n). Блок-схема варианта реализации блока 3 приведена на фиг.3, где обозначены:The unit for recalculating the assessment of the KFM 3

in the frequency band of the test pulse Sи (n), formed at the output of the second correlator of the first stage (i.e., correlator 1-2), for example, in the estimation of the KFM

in the frequency band of the information pulse S1 (n). The block diagram of an embodiment of block 3 is shown in figure 3, where are indicated:

- 5-1, 5-2 - blocks of long-term memory;

- 6 - DFT calculator;

- 7 - block division;

- 8 - block multiplication;

- 9 - DFT calculator.

In the long-term memory blocks 5-1 and 5-2, the spectra of the signal S1 (n) and the test pulse Sи (n) are stored. These blocks are shown in Fig. 3 conditionally and can be combined with long-term memory blocks included in the composition of the correlators of the first stage 1-1 and 1-2 and storing the corresponding arrays of spectra of these signals (pulses). Block 9 performs the calculation of the inverse DFT (DFT) operation. The functions of the remaining blocks included in the block diagram of figure 3, are uniquely determined by their names. Thus, the output signal of block 3 (in the considered version of its implementation) calculates the specified recalculation according to the formula

where the entry of the FFT {M (k)} means the performance of the FFT operation on the array of samples of the discrete spectrum M (k) (k is the discrete argument of the frequency), defined as

- массивы спектров, являющиеся результатами выполнения операции ДПФ над массивами временных отсчетов соответственно информационного сигнала S1(n), испытательного сигнала Sи(n), а также оценки ИРК в полосе частот испытательного сигнала.where S1 (k), Sи (k) and

- arrays of spectra, which are the results of the DFT operation on arrays of time samples, respectively, of the information signal S1 (n), test signal Sи (n), as well as estimates of the KFM in the frequency band of the test signal.

формируется как промежуточный результат. При этом данный результат может быть использован для расчета по формуле (2) без дополнительной операции ДПФ (при этом вычислитель ДПФ 6, показанный на блок-схеме фиг.3, фактически заменяется оперативной памятью, хранящей поступающие в блок 3 из второго коррелятора первой ступени 1-2 текущие результаты вычисления массивов

).When implementing the correlator of the first stage 1-2 in the spectral region (i.e., based on the fast convolution procedure), the discrete spectrum used in relation (2)

formed as an intermediate result. Moreover, this result can be used to calculate according to the formula (2) without additional DFT operation (in this case, the DFT calculator 6 shown in the block diagram of Fig. 3 is actually replaced by the random access memory that stores incoming to block 3 from the second correlator of the first stage 1 -2 current array calculation results

)

The decisive device 4 is a comparison circuit of the current signal level at its input with a predetermined threshold stored in its long-term memory. In case the signal level exceeds the threshold, at the output of the deciding device 4, for example, code “1” is generated, and otherwise - code “0”. It should be noted that the procedure for calculating the correlation between the input and reference signals implemented by the correlators 1-1, 1-2, and 2 is linear (the reference signals (or their spectra) of the correlators 1-1 and 1-2 are stored in the long-term memory of these blocks, and the reference signal of the correlator 2 is operatively generated by the impulse response conversion unit of channel 3), and therefore the correlators 1-1 and 2 can be rearranged without changing the principle of operation of the claimed object. In this case, the connection between the output of the impulse response conversion unit of channel 3 and the reference input of the correlator 2 is maintained.

The principle of operation of the claimed device is as follows. When transmitting the symbol "1" (signal S1 (n)) at the output of the correlator of the first stage 1-1 (the reference oscillation of which coincides with the signal S1 (n)), a response is formed equal to the convolution of the KFM with the autocorrelation function of the signal S1 (n). At the same time, at the output of the correlator of the first stage 1-2 (whose reference oscillation coincides with the signal Si (n)), a response is formed equal to the convolution of the KFM with the autocorrelation function of the signal Si (n), i.e. an estimate of the KFM is formed in the frequency band of the test impulse Sи (n). The mentioned response of the correlator of the first stage 1-1 in the situation under consideration can be considered an estimate of the KFM in the frequency band of the information pulse S1 (n). Due to the mismatch of the frequency ranges occupied by the information and test pulses, the KFM estimates in the frequency ranges of these pulses are uncorrelated, regardless of which symbol was transmitted. As a result of recalculation of the estimate of the KFM in the frequency band of the test pulse to the estimate of the KFM in the frequency band of the information pulse carried out in the conversion unit 3, formed at the inputs of the correlator of the second stage 2 in the case of transmitting the symbol “1”, become correlated (coinciding to within at these noise inputs). As a result of this, when transmitting the symbol “1”, the response level of the correlator of the second stage 2 is high, and then the resolver 4 generates the code “1”. When transmitting the information symbol "0" at the output of the correlator of the first stage 1-1, a response is formed in the form of interference alone; in this case, regardless of whether a test pulse was emitted with this information symbol or not, the signals at the inputs of the correlator of the second stage 2 (despite the conversion in bol 3) remain uncorrelated, which determines the low level of response of the correlator of the second stage 2, and then the solving device 4 generates a code "0".

In cases of using the inventive device in communication systems of the SIIP type with multi-position (N-position) coding, the number of correlators of the first stage is N + 1 and the second stage is N. In cases of using the inventive device in communication systems operating with multi-position coding, without a special test pulse, when estimates of the KFM are generated using information pulses radiated in different frequency ranges, the number of correlators of the first and second steps is equal to N in each. x situations solver has N inputs.

As noted above, with the coincidence of the frequency ranges in which information and test signals are transmitted, there is an action (influence) that interferes with the reception of these signals, i.e. the information signal is an obstacle to the “branch” of receiving the test signal (ie, the corresponding correlator of the first stage) and vice versa. Frequency diversity of information and test signals provides improved reception (decoding) quality by eliminating this interfering effect. The inventive device, in contrast to the known analogues, provides the ability to receive (decode) signals when transmitting information and test pulses in different frequency ranges, i.e. its application allows you to realize the above effect of improving the quality of reception.

Literature

1. D.D. Klovsky. Transmission of discrete messages over the air. M.: Communication, 1969.

2. A device for receiving discrete signals in a multipath communication channel. Pat. RF №2048701.

3. Digital device for demodulating discrete signals in a multipath communication channel. Pat. RF 2267230.

4. Device for transmitting discrete signals in a multipath communication channel. Pat. RF №959291.

5. Sussman S.M. A matched filter communication system for multipath channels // IEEE Trans. IT - 6. N 3. June 1960.

6. "The use of digital signal processing." Ed. E. Oppenheim. M .: Mir, 1980.

7. L. Rabiner, B. Gould. Theory and application of digital signal processing. M .: Mir, 1978.

Claims (2)

1. A device for receiving discrete signals that have passed a multipath communication channel, containing at least two correlators of the first stage, at least one correlator of the second stage, and also a solving device, the general input of the correlators of the first stage being the input of the inventive device, the first correlator of the first stage calculates the correlation between the received and information signal, the output of the first of the correlators of the first stage is connected to the first input of the correlator of the second stage, the output of which is connected to the input of the decisive three, and the output of the deciding device is the output of the claimed device, characterized in that it includes a conversion unit for evaluating the impulse response of the channel (KFM) from the frequency band of the test signal to the KFM estimate in the frequency band of the information signal, included between the output of the second correlator of the first stage and the second the input of the correlator of the second stage, and the second correlator of the first stage calculates the correlation between the received and test signals. 2. The device for receiving discrete signals that have passed the multipath communication channel according to claim 1, characterized in that the conversion unit for estimating the KFM from the frequency band of the test signal to the KFM estimate in the frequency band of the information signal performs said recalculation according to the formula

where the entry of the ODPF {M (k)} means the operation of the ODPF on the array of samples of the discrete spectrum M (k) (k is the discrete argument of the frequency), defined as

where S1 (k), Sи (k) and

- arrays of spectra, which are the results of the DFT operation on arrays of time samples, respectively, of the information signal S1 (n), test signal Sи (n), as well as an array of samples generated at the output of the second correlator of the first stage, these arrays of spectra are stored in blocks of long-term memory, included in the recalculation unit of the estimate of the KFM from the frequency band of the test signal to the estimate of the KFM in the frequency band of the information signal.

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