RU2192094C1 - Method for coherent staggered signal transmission - Google Patents

Abstract

FIELD: radio engineering; radio communication systems. SUBSTANCE: method includes generation of N staggering channels and N pilot signals on sending end; data signal is transmitted through all staggering channels and pilot signal is passed through respective staggering channels; on receiving end transfer functions of staggering channels are estimated using transmitted pilot signals; using estimates obtained data signal transmitted through each staggering channel is pre-distorted on sending end. EFFECT: enhanced efficiency of signal transmission at frequency-selective signal fading. 7 cl, 6 dwg

Description

 The invention relates to the field of radio engineering, to a method for organizing diversity transmission of a signal in a radio communication system, in particular in a multiple access radio communication system.

 Radio communication in urban areas or rough terrain is characterized by multipath signal propagation, leading to fading of the signal on the receiving side, including frequency selective fading. Fading significantly degrades the quality of signal reception, while in information transfer systems, the likelihood of errors increases and the speed of information transfer decreases.

 Therefore, it is necessary to create such signal transmission methods that reduce the effect of fading on the quality of radio communications. The most effective way to combat fading is to organize diversity channels (in which the transmitted signal undergoes statistically independent distortion [1, Microwave Mobile Communications / Edited by William C. Jakes. IEEE Press. NY, 1994]) and transmit data on these diversity channels.

 Known methods for coherent diversity transmission of the signal, called Retransmission Diversity [1]. The signal transmission according to these methods is carried out with N spatially separated transmit antennas. At the same time, complex transmission coefficients of signals between the transmitting antennas and the receiving antenna are known on the transmitting side. This information is used to maximize the signal-to-noise ratio (SNR) in the receiving antenna by optimally setting the amplitude and phase of the transmitted signal in each transmitting antenna. Two main methods of obtaining the required information about the distribution channel are considered. In the first method, a time duplex is implemented in a communication system. Therefore, an estimate of the propagation channel is formed when a signal is received at said N antennas. The second method uses frequency duplex, but the frequency bands of the forward and reverse signal transmission channels are located close to each other so that the propagation channels in the forward and reverse directions are highly correlated. In this case, the return channel estimate is also taken as the forward channel estimate.

 In modern communication systems, frequency duplex is usually used and fairly wideband signals are used. Therefore, the elimination of the mutual influence of signals in the forward and reverse channels requires a significant frequency separation between these channels. These factors preclude the practical implementation of the Retransmission Diversity method [1].

 For multipath communication channels, a technical solution is known [2, "Pre-RAKE diversity combining in time division duplex CDMA mibile communications", IEEE, 1995, 0-7803-3002-1 / 95 431-435], namely, that The information signal intended for transmission is predistorted in such a way as to compensate for its distortion in the multipath channel. As a result, the received signal is single-beam and is processed by a simple single-beam receiver. This is especially true for the direct channel, because the subscriber station does not require the use of a complex multi-beam (Rake) receiver. To implement this method of signal transmission on the transmitting side, an estimate of the propagation channel is required. Therefore, the authors propose their own method for communication systems with temporary duplex, where obtaining such an estimate is not very difficult.

The closest technical solution to the claimed method of diversity signal transmission is the method described in the draft standard 3GPP [3; 3 rd Generation Partnership Project; Technical Specification Group Radio Access Network; Physical Layer procedures (FDD), 3G TS 25.214 v.3.3.0 (2000-06), pp 29-31, electronic version http://www.3gpp.org]. The prototype method is used in a direct channel (the direction of communication from the base station to the mobile station) of the 3GPP communication system is that:
two spatially separated signal transmission channels are formed on the transmitting side, a pilot signal corresponding to this channel is generated for each spatially separated signal transmission channel so that the generated pilot signals are mutually orthogonal, form an information signal orthogonal to the pilot signals, and transmit it through two spatially separated signal transmission channels simultaneously with the pilot signals;
on the receiving side, an estimate of the phase shift is formed, which must be introduced into the signal transmitted through the second spatially separated signal transmission channel in order to maximize the signal-to-noise ratio on the receiving side, or an estimate of the phase shift and amplitude factor (coefficient) to be introduced into the signal transmitted through the second spatially separated signal transmission channel in order to maximize the signal-to-noise ratio at the receiving side, the obtained estimates are reported to guide side;
on the transmitting side, the signal transmitted on the second spatially separated signal transmission channel is adjusted in accordance with the obtained estimates.

 This invention can be used in communication systems with frequency duplex due to the presence of feedback, which transfers the direct channel estimate from a mobile station (MS) to a base station (BS).

 The disadvantage of the prototype method is the low efficiency with frequency-selective fading of the signal. On the transmitting side, all components of the spectrum of the transmitted signal receive the same amplitude-phase corrections, while the amplitude-phase distortions of different parts of the spectrum of the received signal differ due to the frequency-selective nature of fading. Therefore, in the prototype method, it is impossible to ensure optimal coherent addition at the receiving point of copies of the information signal transmitted over the separated channels simultaneously for all spectral components of the information signal.

 The task to which the invention is directed is to increase the efficiency of signal transmission in a radio communication system with frequency selective fading of the signal.

 The problem is solved by using the proposed method of coherent diversity transmission of the signal.

The inventive method of coherent diversity transmission of a signal is that:
On the transmitting side, N diversity channels are formed,
generating N pilot signals and assigning each pilot signal to each diversity channel,
transmit an information signal through all diversity channels, and pilot signals through the corresponding diversity channels,
on the receiving side, the transfer functions of the diversity channels are estimated using the transmitted pilot signals, the results of the evaluation of the transfer functions of the diversity channels are transmitted to the transmitting side,
on the transmitting side, in accordance with the obtained evaluation results, the information signal transmitted through each diversity channel is pre-emphasized in such a way as to maximize the reception quality of the information signal on the receiving side.

 Moreover, the pilot signals of the diversity channels and the information signal are mutually orthogonal.

 Various methods for generating pilot signals are possible.

 The pilot signals of the diversity channels and the information signal may, for example, occupy the same frequency band.

 The pilot signal of each diversity channel may be a combination of narrowband pilot signals distributed over the frequency band occupied by the information signal.

 The pilot signal of each diversity channel may be a combination of narrowband pilot signals distributed over the frequency band allocated to the radio communication system, wherein the frequency band is divided between the narrowband pilot signals of the various diversity channels and the information signal.

 The predistortion operation of the information signal can be performed in various ways.

 For example, to pre-emphasize an information signal, divide the frequency band of the information signal into M adjacent frequency bands, filter the information signal in each frequency band to form M filtered information signals, adjust the phase and amplitude of each filtered information signal in accordance with the evaluation results of the transfer function of the corresponding channel diversity, forming adjusted filtered information signals, which then summarize .

 Or, for example, to carry out the predistortion of the information signal, a direct Fourier transform is performed on the information signal, the conversion result is multiplied with a function complex conjugate with the transfer function of the corresponding diversity channel, and the inverse Fourier transform is performed.

 Under the transfer function (or frequency transfer coefficient) of a linear system in the literature [4, I. Gonorovsky Radio circuits and signals. Moscow, "Soviet Radio". 1977, p. 176-177], [5, S. I. Baskakov. Radio engineering circuits and signals, M., "Higher School, 1988, pp. 211-212] refers to a complex function equal to the quotient of the spectral densities of the output and input signals of a linear system.

 A comparative analysis of the proposed method with the prototype shows that the inventive method is significantly different from the prototype.

 Common features of the proposed method and prototype is the formation of N diversity channels on the transmitting side and the presence of feedback from the receiving side, which serves to correct the parameters of the information signal transmitted through various diversity channels in order to improve the quality of reception of the information signal.

Distinctive features of the proposed method and prototype are the following features:
on the receiving side, the transfer functions of the diversity channels are estimated using the transmitted pilot signals,
transmit the results of the evaluation of the transfer functions of the diversity channels to the transmitting side,
on the transmitting side, in accordance with the obtained evaluation results, the information signal transmitted through each diversity channel is pre-emphasized in such a way as to maximize the reception quality of the information signal on the receiving side.

 The novelty and advantage of the proposed method of coherent diversity transmission of the signal is to take into account the frequency-selective nature of the fading of the signal by optimizing diversity transmission within the frequency band occupied by the information signal.

 These distinctive features provide the claimed method in comparison with the prototype compliance with the criterion of "novelty."

 Comparison of the claimed invention with other technical solutions known in the art, did not allow to identify signs that are defined as distinctive.

 The set of distinctive features when implementing in the present method, coherent diversity transmission of the signal can significantly increase the noise immunity and throughput of the radio communication system.

 Therefore, the claimed invention meets the criteria of the invention "significant differences", "non-obviousness" and meets the inventive step.

 The dependent claims provide examples of the basic operations of the proposed method, the disclosure of which allows you to better understand the practical implementation of the method.

 The description of the invention is illustrated by graphic materials.

Figure 1 illustrates the partitioning of the frequency band allocated in the radio communication system into frequency channels, where f ₁ , f ₂ , ..., f _M are the center frequencies of the frequency channels.

 In FIG. Figure 2 shows an example of the distribution of information and pilot symbols over frequency channels.

 Figure 3 illustrates an example implementation of the inventive method of coherent diversity transmission on the devices of the transmitting and receiving sides (example implementation of the inventive device for the OFDM system).

 FIG. 4 illustrates an example implementation of the inventive method of coherent diversity transmission on the devices of the transmitting and receiving sides (example implementation of the inventive device for the CDMA system).

 FIG. 5 shows an information signal predistortion unit for a CDMA system.

 In FIG. 6, position "a", the case is shown when the values of the transfer functions of two diversity channels corresponding to the same frequency are located in one half-plane on the plane of the complex variable; position “b” is the case when the values of the transfer functions of two diversity channels corresponding to the same frequency are located in different half-planes on the plane of the complex variable.

The device transmitting and receiving side (figure 3) contain:
on the transmitting side: M frequency channels 1 ₁ -1 _m , subcarrier frequency generator 2, first 3 and second 4 adders, correction unit 5, two transmit antennas 6 ₁ -6 ₂ and two receive antennas 7 ₁ -7 ₂ , first frequency inputs channels 1 ₁ -1 _m are information inputs and form the inputs of the device, their second inputs are connected to the corresponding outputs of the subcarrier frequency generator 2, the first outputs of the frequency channels l ₁ -1 _{m are} connected to the corresponding first inputs of the first 3 adder, the second outputs of the frequency channels l ₁ -1 _m are connected to a suitable E their second inputs of the second adder 4, the outputs of the first 3 and second 4 adders are connected respectively to the first 6 ₁ and the second June ₂ transmission antennas, the first July ₁ and second _{2 July} reception antennas are respectively connected to first and second inputs of the correction unit 5, the outputs of which connected to the third inputs of the M frequency channels l ₁ -1 _m ; each frequency channel contains the first 8, second 9 and third 10 multipliers, the first inputs of the first 8 and second 9 multipliers are combined to form the first input of the frequency channel, the second inputs of the first 8 and second 9 multipliers are combined to form the second input of the frequency channel, the output of the first 8 multiplier forms the first output of the frequency channel, the output of the second multiplier 9 is connected to the first input of the third multiplier 10, the second input of which forms the third input of the frequency channel, the output of the third multiplier 10 is the second output frequency channel;
on the receiving side: receiving antenna 11, demodulator 12, evaluation unit 13, feedback unit 14 and transmitting antenna 15, receiving antenna 11 is connected to the first input of the demodulator 12 and input of the evaluation unit 13, the first output of the evaluation unit 13 is connected to the second input of the demodulator 12 the output of which is the output of the device, the second output of the evaluation unit 13 is connected to the input of the feedback unit 14, the output of which is connected to the transmitting antenna 15.

Device transmitting and receiving side (figure 4) contain:
on the transmitting side: To the branches of the diversity transmission of the signal K users 15 ₁ -15 _k , each branch of the diversity transmission of the user signal contains N information predistortion blocks 16 ₁ -16 _k , the pilot signal generator 17, N adders 3 ₁ -3 _N , block correction 5, N transmit antennas 6 ₁ -6 _N and N receive antennas 7 ₁ -7 _N , the first inputs of the branches of the diversity transmission of the user signal 15 ₁ -15 _k are information inputs and form the inputs of the device, their second inputs are connected to the corresponding outputs of the block correction 5, branch outputs aznesennoy signal transmission members January ₁₅ -15 _to them are connected to respective first inputs of N adders March ₁ -3 _N, second inputs of adders March ₁ -3 _N connected to their respective outputs pilot signal generator 17, the output of each adder March ₁ -3 _N connected to the input of the corresponding transmitting antenna 6 ₁ -6 _N , receiving antennas 7 ₁ -7 _{N are} connected to the inputs of the correction unit 5,
moreover, the first inputs of the predistortion blocks of the information signal 16 ₁ -16 _N in each branch of the diversity transmission of the user signal are combined to form the first input of this branch, the second inputs of the predistortion blocks of the information signal 16 ₁ -16 _N form the second inputs in each branch, and the outputs of the predistortion blocks of the information the signal 16 ₁ -16 _N are the outputs of the corresponding branches of the diversity transmission of the user signal,
on the receiving side: receiving antenna 11, demodulator 12, evaluation unit 13, feedback unit 14 and transmitting antenna 15, receiving antenna 11 is connected to the first input of the demodulator 12 and input of the evaluation unit 13, the first output of the evaluation unit 13 is connected to the second input of the demodulator 12 the output of which is the output of the device, the second output of the evaluation unit 13 is connected to the input of the feedback unit 14, the output of which is connected to the transmitting antenna 15.

Figure 5 shows an example of the implementation of the block predistortion of the information signal 16, which contains M filters 18 ₁ -18 _m , M multipliers 19 ₁ -19 _m and the adder 20, and the inputs of the M filters are combined 18 ₁ -18 _m , forming the input of the block predistortion information signal 16, the output of each filter 18 ₁ -18 _{m is} connected to the first input of the corresponding multiplier 19 ₁ -19 _m , the second inputs of the multipliers 19 ₁ -19 _m receive the values of the transfer function of the predistortion block of the information signal corresponding to the central frequencies of the filters, the outputs are M per multipliers 19 ₁ -19 _{m are} connected to their respective inputs of the adder 20, the output of which is the output of the predistortion block of the information signal 16.

 Consider examples of the implementation of the claimed invention in communication systems using OFDM [6, Richard van Nee, Ramjee Prasad. OFDM for wireless Multimedia Communications] the principle of separation of channels in CDMA systems.

First, consider the application of the claimed invention in systems with OFDM. A multiple access radio communication system including at least one BS and one subscriber terminal (AT) is allocated a frequency band of width F. The allocated frequency band is divided into M frequency bands, as, for example, shown in FIG. 1, where f ₁ , f ₂ , ..., f _M are the center frequencies of the frequency bands. As can be seen from figure 1, the frequency bands intersect, which ensures the efficient use of the allocated frequency band.

 A stream of information symbols is formed on the BS, which is required to be transmitted to subscriber terminals. In this case, either the entire information stream can be transmitted to each subscriber station, or different parts of the stream can be transmitted to different subscriber terminals. The transmitted symbols in the general case are complex, which corresponds to quadrature types of modulation.

где Δf = f_i+1-f_i; i=1, 2, 3, ..,M-1; k∈Z.
В этом случае при приеме символов будут отсутствовать взаимные помехи между ними.During the duration of one T symbol, M symbols can be transmitted simultaneously through M frequency bands (frequency channels l ₁ -1 _m in FIG. 3). Symbol duration and frequency bandwidth must satisfy the condition

where Δf = f _{i + 1} -f _i ; i = 1, 2, 3, .., M-1; k∈Z.
In this case, when receiving characters, there will be no mutual interference between them.

To organize diversity in the forward channel, N diversity channels are formed on the transmitting side. Diversity channels may, for example, be formed by arranging signal transmission through N diversity transmit antennas. In this case, spatially separated antennas or antennas with different polarization can be used. For example, put N = 2. In the claimed invention, the information signal is coherently transmitted through N diversity channels (6 ₁ -6 ₂ in FIG. 3). To implement coherent transmission on the transmitting side, you need to know the transfer functions of the diversity channels. In communication systems with frequency duplex, the assessment of these transfer functions is possible only on the receiving side. In the claimed invention, this estimate is generated at the receiving side (at the subscriber terminal) using orthogonal pilot signals transmitted through various diversity channels, and then transmitted to the transmitting side (BS).

On the transmitting side, the information signal is pre-emphasized by phase or amplitude-phase correction of the information signal in the frequency channels 1 ₁ -1 _m in one of the diversity channels (for example, in the second) so as to maximize the signal-to-noise ratio on the receiving side.

 In this example implementation of the invention, the pilot signals are implemented by transmitting pilot symbols in part of the frequency bands. Moreover, half of the pilot symbols is transmitted through the first diversity channel, and the second half through the second diversity channel.

 On the receiving side, a direct estimation of the transfer functions of the diversity channels can only be carried out in those frequency bands over which the pilot symbols of the respective diversity channels are transmitted. An estimate of the entire transfer functions of both diversity channels can be obtained by interpolating these direct estimates, for example, using the Gaussian interpolation method, an example of which is given in [7, S. Sampei and T. Sunaga, "Rayleigh fading compensation for QAM in land mobile radio communications, "IEEE Trans. Veh. TechnoL, vol. 42, pp. 137-146, May 1993]. In this regard, the pilot symbols should be evenly distributed in the allocated frequency band with an interval that allows interpolation of direct estimates at the receiving side. An example of the distribution of information and pilot symbols over frequency channels is shown in FIG.

 Consider an example of processing the transmitted signal at the receiving side (figure 3).

We call the group symbol M symbols that are simultaneously transmitted through the M frequency bands and denote it by a. Some of the wildcard symbols are information symbols, the remaining symbols are pilot symbols of the first and second explode channels. The information and pilot parts of the wildcard symbol are denoted as a _d , and _p1 and a _p2, respectively (a _d , a _p1 , a _p2 ∈a).

где А_i, φ_i - амплитуда и фаза сигнала в i-ой частотной полосе;

помеха, например, аддитивный белый гауссовский шум с двусторонней спектральной плотностью мощности N₀/2;

символ, передаваемый в i-ой частотной полосе.After converting the input signal to a low frequency, the input quadrature (complex) signal in the duration interval of one wildcard ([0; T]) has the following form:

where A _i , φ _i - the amplitude and phase of the signal in the i-th frequency band;

interference, for example, additive white Gaussian noise with two-sided power spectral density N _0/2 ;

symbol transmitted in the i-th frequency band.

каждая из которых содержит информацию только об одном символе (который передавался в соответствующей частотной полосе)

Внутренняя структура решающих величин, соответствующих переданным информационным символам, имеет вид

где А_1i, φ_1i - амплитуда и фаза сигнала, пришедшего в точку приема через первый канал разнесения (от первой передающей антенны), в i-ой частотной полосе; А_2i, φ_2i - амплитуда и фаза сигнала, пришедшего в точку приема через второй канал разнесения (от второй передающей антенны), в i-ой частотной полосе;

комплексный весовой коэффициент, корректирующий фазу и амплитуду сигнала, передаваемого через вторую антенну, в i-ой частотной полосе;
внутренняя структура решающих величин, соответствующих переданным пилот-символам первого канала разнесения, имеет вид

внутренняя структура решающих величин, соответствующих пилот-символам второго канала разнесения, имеет вид

На приемной стороне осуществляется оценка передаточных функций первого и второго каналов разнесения. Для этого сначала формируются прямые оценки передаточных функций в тех частотных полосах, по которым передавались пилот-символы соответствующих каналов разнесения (выражения (5) и (6)). Затем посредством интерполяции полученных прямых оценок формируется оценка всей передаточной функции каждого канала разнесения. В результате амплитуды и фазы сигналов в частотных полосах А_1i, φ_1i и А_2i, φ_2i являются известными.On the receiving side, the input signal is divided into signals of different frequency bands. As a result, M critical quantities are formed

each of which contains information about only one symbol (which was transmitted in the corresponding frequency band)

The internal structure of the critical quantities corresponding to the transmitted information symbols has the form

where A _1i , φ _1i is the amplitude and phase of the signal that arrived at the receiving point through the first diversity channel (from the first transmitting antenna) in the i-th frequency band; And _2i , φ _2i - the amplitude and phase of the signal that arrived at the receiving point through the second diversity channel (from the second transmitting antenna), in the i-th frequency band;

complex weighting factor, which corrects the phase and amplitude of the signal transmitted through the second antenna in the i-th frequency band;
the internal structure of the decision values corresponding to the transmitted pilot symbols of the first diversity channel has the form

the internal structure of the decision values corresponding to the pilot symbols of the second diversity channel has the form

On the receiving side, the transfer functions of the first and second diversity channels are evaluated. To do this, first direct estimates of the transfer functions are formed in those frequency bands along which the pilot symbols of the respective diversity channels were transmitted (expressions (5) and (6)). Then, by interpolating the obtained direct estimates, an estimate of the entire transfer function of each diversity channel is formed. As a result, the amplitudes and phases of the signals in the frequency bands A _1i , φ _1i and A _2i , φ _2i are known.

Таким образом, цель фазовой коррекции информационного сигнала, передаваемого через вторую антенну, заключается в обеспечении когерентного суммирования информационного сигнала, пришедшего по двум каналам разнесения, в точке приема. Амплитудная коррекция обеспечивает передачу большей части энергии информационного сигнала по каналу разнесения с меньшим затуханием сигнала и меньшей части по каналу разнесения с большим затуханием сигнала. В результате указанной амплитудно-фазовой коррекции максимизируется отношение сигнал-шум на входе приемника.The values of the coefficients used to correct the phase Δφ _i and amplitude ΔA _{i of the} information signal (information signal pre-emphasis) in different frequency bands in the second antenna are transmitted to the transmitting side on the reverse channel (see Fig. 2). In general, these coefficients are equal

Thus, the purpose of the phase correction of the information signal transmitted through the second antenna is to provide coherent summation of the information signal received via the two diversity channels at the receiving point. Amplitude correction provides the transfer of most of the energy of the information signal through the diversity channel with less signal attenuation and a smaller part through the diversity channel with greater signal attenuation. As a result of the specified amplitude-phase correction, the signal-to-noise ratio at the receiver input is maximized.

 Note that it is not necessary to transmit the value of the correction factor for each frequency band. This value can only be transmitted for part of the frequency bands, and correction factors for the remaining frequency bands can be obtained by interpolating the available coefficients.

где

решающее правило, в соответствии с которым по решающей статистике (аргументу) выносится решение в пользу того или иного переданного символа, принадлежащего алфавиту символов Ω на передающей стороне (например, для двоичной фазовой манипуляции анализируется только знак решающей статистики).Estimates of information symbols on the receiving side are formed in accordance with the expression

Where

a decisive rule, according to which a decisive statistic (argument) is made in favor of a given symbol belonging to the symbol alphabet Ω on the transmitting side (for example, only the decisive statistic sign is analyzed for binary phase manipulation).

 Consider another example implementation of the claimed invention in relation to communication systems with code division multiplexing (CDMA). The corresponding structural diagram of the claimed invention is shown in figure 4. In CDMA systems, all users simultaneously use the same frequency band to transmit information. Separation of user signals on the receiving side is due to the fact that these signals are phase-shifted code sequences having low cross-correlation. A correlator is used as a receiver, which calculates the correlation of the input signal, in which the signals of all simultaneously working users are present, and the user signal. As a result, the signal of the received user is amplified by the correlator to a much greater extent than the signals of other users. The direct channel of CDMA systems is synchronous (the beginning of the code sequences of all users is aligned), which makes it possible to use orthogonal code sequences produced for example from an ensemble of orthogonal Walsh codes to separate users.

 Some of the signals transmitted over the forward channel are official and apply to all users. An example of an overhead signal is a pilot signal, which is used, in particular, to estimate the parameters (frequency, time position, complex envelope) of the received signal.

In the claimed invention, the transmission of the signal of each user is carried out simultaneously through N diversity channels, for example, through N diversity transmit antennas (6 ₁ -6 _N ). Therefore, copies of the information signal are distributed through N different diversity channels before arriving at the receiving point and forming a total information signal. In order to ensure at the receiver input close to optimal addition of copies of the information signal that have passed through various diversity channels, it is required to have estimates of said diversity channels on the transmitting side. In the claimed invention, these estimates are formed on the receiving side and then transmitted to the transmitting side. In order for the required estimates to be generated at the receiving side, an orthogonal pilot signal must be transmitted through each diversity channel.

 Thus, in the claimed invention, N orthogonal pilot signals (in block 17) are formed on the transmitting side according to the number of diversity channels. For this, in the CDMA system, from the ensemble of code sequences assigned to different transmission channels, N code sequences must be allocated for the pilot signals of N diversity channels. The number of orthogonal code sequences of a given length Q on the BS is limited. Typically, only Q orthogonal code sequences of length Q can be generated. The length of the code sequence affects the transmission rate of information using this sequence. In general, the shorter the code sequence, the faster the information can be transmitted and vice versa. Therefore, on BS short orthogonal sequences are deficient in comparison with long ones. In order not to reduce the data rates in the forward channel as pilot signals, long code sequences can be used. The only restriction on the length of the code sequence in this case is the requirement of stationarity of the propagation channel during the orthogonality interval.

 In the case where orthogonal sequences are insufficient, quasi-orthogonal sequences can be used to expand the ensemble of signals, as is provided for in some modern CDMA communication standards [8, 3GPP2 C. S0002-A Physical Layer Standard for cdma 2000 Spred Spectrum Systems, June, 2000]. Quasi-orthogonal sequences have non-zero, but rather low cross-correlation and at the same time have a significantly larger ensemble size than orthogonal sequences.

 Based on the transmitted pilot signals, estimates of the transfer functions of the respective diversity channels are generated at the receiving side (evaluation block 13). The specified assessment can be carried out using known methods. For example, the impulse responses of diversity channels can be first evaluated [9, A. Hewitt, W. Lau, J. Austin, and E. Wilar, "An autoregressive approach to the identification of multipath ray parameters from field measurements," IEEE Trans. on Comm., vol. 37, pp. 1136-1143, Nov. 1989], [10, J. Ehrenberg, T. Ewart, and R. Morris, "Signal processing techniques for resolving individual pulses in a multipath signal," J. Acoust. Soc. Amer., Vol. 63, pp. 1861-1865, Jun. 1978], [11, Zoran kostic, M. Ibrahim Sezan, and Edward L. Titlebaum, "Estimation of the parameters of a multipath channel using set-theoritic deconvolution," IEEE Trans. on Comm., vol. 40, No. 6, June 1992]. The transfer functions can then be obtained by calculating the inverse Fourier transform of the impulse response estimates.

 The evaluation results of the transfer functions of the diversity channels are then transmitted to the transmitting side (block 14).

 Let us now consider an example of how the received information can be used on the transmitting side to improve the quality of reception in the direct channel.

On the transmitting side, N blocks of information signal predistortion (16 ₁ -16 _N ) are formed according to the number of diversity channels. In each predistortion block of the information signal (16 ₁ -16 _N ), predistortions are introduced into the spectrum of the information signal transmitted through the corresponding diversity channel in such a way as to maximize the reception quality in the forward channel.

где

- СП информационного сигнала на входе приемника;

- СП передаваемого информационного сигнала;

- передаточные функции блоков предыскажения информационного сигнала;

- суммарная энергия информационного сигнала пользователя ограничена некоторым значением Е_s.To understand the nature of the pre-emphasis introduced into the spectrum of the information signal in each pre-emphasis block of the information signal, we analyze the structure of the information signal at the input of the receiver. The spectral density (SP) of the equivalent video frequency information signal on the transmission interval of one information symbol [0; T] can be represented as follows:

Where

- SP information signal at the input of the receiver;

- SP of the transmitted information signal;

- transfer functions of the predistortion blocks of the information signal;

- the total energy of the user's information signal is limited to a certain value of E _s .

Since the information signal is received against the background of additive interference (additive white Gaussian noise with two-sided power spectral density N _0/2 ), to maximize the reception quality it is necessary to maximize the signal-to-noise ratio (SNR) at the output of the receiver. The optimal receiver in this case is a matched filter [4].

где ΔF - полоса частот, занимаемая информационным сигналом.We write the expression for the SNR at the output of the filter, consistent with the signal (9)

where ΔF is the frequency band occupied by the information signal.

Согласно неравенству Шварца

максимум (11) обеспечивается тогда, когда

где А - постоянное число.Expression (10) is converted to the form

According to Schwartz inequality

maximum (11) is provided when

where A is a constant number.

 Condition (13) determines the transfer functions of the predistortion blocks of the information signal. The physical meaning of (13) is as follows. The phase-frequency characteristics (PFC) of the transfer functions of the information signal predistortion blocks provide a coherent summation of the spectral densities of the information signal transmitted through various diversity channels at the receiver input. The amplitude-frequency characteristics (AFC) of the information signal predistortion blocks provide the emission of most of the energy of the information signal at those frequencies of its spectrum where the transmission coefficient of the propagation channel is greater, and the smaller part of the signal energy is where the transmission coefficient of the propagation channel is less. This ensures the optimal use of the energy of the transmitted information signal.

Thus, the energy of each transmitted information symbol E _s must be distributed over the spectra of copies of the information signal transmitted through various diversity channels, in proportion to the frequency response of the corresponding information signal predistortion blocks.

 When implementing the inventive method of coherent diversity transmission, it is important to find a compromise between the amount of control information transmitted from the reception to the transmitting side and the noise immunity of the diversity transmission. This compromise is due to the fact that, on the one hand, the more complete information about the transfer functions of the diversity channels is available on the transmitting side, the higher the noise immunity of the claimed method of coherent diversity transmission. On the other hand, the transmission of a large amount of control information reduces the throughput of the reverse channel. Thus, it is important to minimize the amount of control information transmitted while maintaining high quality diversity signal transmission.

 In this regard, various private technical solutions are possible within the framework of the claimed general method of coherent diversity transmission.

где g_i - вектор отсчетов передаточной функции i-го канала разнесения;

- передаточная функция i-го канала разнесения; f_k - значение частоты, при котором берется k-ый отсчет передаточной функции; М - количество отсчетов передаточной функции.To reduce the amount of information transmitted, you can use the following approach. The transfer functions are discretized, as a result of which the transfer function of each diversity channel is replaced by an equivalent vector of samples of the transfer function, taken at a certain interval

where g _i is the sample vector of the transfer function of the i-th diversity channel;

- transfer function of the i-th diversity channel; f _k is the frequency value at which the kth sample of the transfer function is taken; M is the number of samples of the transfer function.

вместо самих передаточных функций.The selection of the sampling interval is carried out taking into account the usual requirements arising from the Kotelnikov theorem [4]. Thus, on the transmitting side, it is sufficient to transmit the sample vectors of the transfer functions of the diversity channels g _i ,

instead of the transfer functions themselves.

arg(•)- функция взятия аргумента комплексного числа.A significant reduction in the transmitted amount of information can be achieved if you notice that the phase response and frequency response of the transfer functions of the signal spectrum correction channels are independent. In this case, the phase response is especially significant, since they affect the nature of the summation of the spectral densities of the useful signal transmitted through various diversity channels. By controlling only the phase response of the signal spectrum correction channels, a significant gain in the SNR at the receiving side can be obtained. Thus, a technical solution is possible in which only samples of the phase response of the transfer functions of the diversity channels are transmitted to the transmitting side. Moreover, it is sufficient to transmit the phase response with respect to the phase response of the diversity channel selected as the reference. This allows you to transfer N-1 vectors of phase response samples instead of N vectors. Suppose, for example, the first diversity channel is a reference. Then, for the transmitting side, it is necessary to transmit the vectors of samples of the phase-frequency characteristics of the diversity channels from the second to the Nth
Φ $\genfrac{}{}{0ex}{}{\text{T}}{\text{i}}$ = [φ _i1 , φ _i2 , ..., φ _iM ], (15)
Where

arg (•) is the function of taking the argument of a complex number.

 The amount of information transmitted can be further reduced by reducing the bit depth of the digital representation of the transmitted samples of the phase response of the diversity channels. To do this, we note that in order to obtain a gain in the SNR, it is sufficient to ensure such an accuracy in the phase response of the information signal predistortion blocks, which still ensures the addition (and not subtraction) of the spectral densities of the useful signal of the various diversity channels at the receiving point. It is easy to verify that in this case, the allowable mismatches at the point of reception of the phase spectra of the useful signal transmitted through any two different diversity channels can lie in the range from 90 to 120 degrees, depending on the ratio of the amplitudes of the spectral components.

 With that said, it is sufficient to transmit the following information. For the first (selected as the reference) diversity channel, nothing is transmitted. For the remaining diversity channels, the sample vectors of the phase response of the diversity channels are transmitted, but each sample is represented by a single-bit number ("0" or "1"). This number shows that the corresponding phase-frequency reference is located either in one phase half-plane with the reference phase-frequency reference of the same name (Fig.6a), or in another phase half-plane (Fig.6b), i.e.

На передающей стороне полученная информация используется для расчета передаточных функций блоков предыскажения информационного сигнала (в блоке 5) в соответствии с выражениями
Т₁=[1,1,...,1] - (17)
- передаточная функция блока предыскажения информационного сигнала, соответствующего опорному каналу разнесения;

Если позволяют условия, то следует передавать и информацию об АЧХ каналов разнесения, поскольку ее использование позволяет существенно увеличить помехоустойчивость когерентной разнесенной передачи. В этом случае для каждого канала разнесения, включая и опорный, следует передавать вектор отсчетов его АЧХ
A_i ^T=[A_i1, A_i2, ..., A_iM]. (19)
При этом для представления каждого отсчета АЧХ достаточно использовать несколько разрядов, например 2-4 разряда. Выражения для передаточных функций блоков предыскажения информационного сигнала тогда должны быть модифицированы

- передаточная функция блока предыскажения информационного сигнала, соответствующего опорному каналу разнесения;

где q(b_im) - функция преобразования принятого двоичного числа в фазовый сдвиг; данная функция может быть задана в виде таблицы соответствия передаваемого n разрядного числа определенному фазовому сдвигу.Φ $\genfrac{}{}{0ex}{}{\text{T}}{\text{i}}$ = [b _i1 , b _i2 , ..., b _iM ], (16)
Where

On the transmitting side, the obtained information is used to calculate the transfer functions of the information signal predistortion blocks (in block 5) in accordance with the expressions
T ₁ = [1,1, ..., 1] - (17)
- the transfer function of the predistortion block of the information signal corresponding to the reference diversity channel;

If conditions allow, information about the frequency response of the diversity channels should also be transmitted, since its use can significantly increase the noise immunity of coherent diversity transmission. In this case, for each diversity channel, including the reference one, a vector of samples of its frequency response should be transmitted
A _i ^T = [A _i1 , A _i2 , ..., A _iM ]. (19)
In this case, to represent each reference of the frequency response, it is sufficient to use several bits, for example, 2-4 bits. The expressions for the transfer functions of the predistortion blocks of the information signal should then be modified

- the transfer function of the predistortion block of the information signal corresponding to the reference diversity channel;

where q (b _im ) is the conversion function of the received binary number into a phase shift; this function can be specified in the form of a table of correspondence of the transmitted n bit number to a certain phase shift.

 The methods described above for reducing the amount of transmitted control information from the receiving to the transmitting side are general in nature and, in particular, can also be applied in the previously considered example of the application of the claimed invention in a communication system with OFDM.

An example of a hardware implementation of an information signal predistortion unit is illustrated in FIG. 5. The information signal is first filtered out using a set of M filters (18 ₁ -18 _m ) on M adjacent frequency bands. The signal of each frequency band is multiplied with the value of the transfer function of the information signal predistortion block at the center frequency of this frequency band (this operation is performed using multipliers 19 ₁ -19 _m ), and the results are summed in adder 20. The required pre-distorted information signal is taken from the output of adder 20 .

 There are other possible ways of implementing blocks pre-emphasis information signal. For example, an information signal predistortion block can be implemented as a filter, the impulse response of which can be obtained using the inverse.

 There are other possible ways of implementing blocks pre-emphasis information signal. For example, the information signal predistortion block can be implemented as a filter, the impulse response of which can be obtained using the inverse Fourier transform of the transfer function of the information signal predistortion block. Obtaining the transfer function of the predistortion block of the information signal was discussed in detail above.

 In other words, the predistortion of the information signal can be carried out in the time and in the spectral regions, while the achieved effect of improving the noise immunity of the reception will be the same. Since there is a one-to-one correspondence between the temporal and spectral representation of the signal, the form of signal representation during the implementation of the invention on the transmitting and receiving sides does not matter.

 Note that although the spatial or polarization diversity is used in the examples of implementation of the invention described in the description, any known types of diversity (for example, temporal or frequency) can be used in the claimed invention. The invention, which consists in predistorting the information signal in accordance with the transfer functions of the diversity channels to maximize the reception quality of the information signal, remains unchanged.

 The claimed invention in comparison with the known technical solutions in this technical field allows to increase the noise immunity of signal transmission in a radio communication system with frequency selective fading of the signal.

Claims (7)

 1. The method of coherent diversity transmission of the signal, which consists in the fact that N transmit diversity channels are generated on the transmitting side, N pilot signals are generated and each pilot diversity channel is assigned its own pilot signal, an information signal is transmitted through all the diversity channels, and the pilot signals according to the corresponding diversity channels, on the receiving side, the transfer functions of the diversity channels are evaluated using the transmitted pilot signals, the results of the evaluation of the transfer functions of the diversity channels are transmitted to the transmitting side, on the ne edayuschey side in accordance with the results obtained estimates performed predistortion information signal transmitted through each channel separation so as to maximize the reception quality of the information signal on the reception side.  2. The method according to claim 1, characterized in that the pilot signals of the diversity channels and the information signal are mutually orthogonal.  3. The method according to claim 1 or 2, characterized in that the pilot signals of the diversity channels and the information signal occupy the same frequency band.  4. The method according to claim 1 or 2, characterized in that the pilot signal of each diversity channel is a collection of narrow-band pilot signals distributed over the frequency band occupied by the information signal.  5. The method according to claim 1, or 2, or 4, characterized in that the pilot signal of each diversity channel is a combination of narrow-band pilot signals distributed over the frequency band allocated to the radio communication system, while the frequency band is divided between the narrow-band pilot signals of various diversity channels and an information signal.  6. The method according to claim 1, characterized in that to carry out the predistortion of the information signal, divide the frequency band of the information signal into M adjacent frequency bands, filter the information signal in each frequency band, forming M filtered information signals, adjust the phase and amplitude of each filtered information signal in accordance with the results of evaluating the transfer function of the corresponding diversity channel, forming the corrected filtered information signal s, which are then summed.  7. The method according to claim 1, characterized in that for the predistortion of the information signal, a direct Fourier transform is performed on the information signal, the conversion result is multiplied with a function complex conjugate with the transfer function of the corresponding diversity channel, and the inverse Fourier transform is performed.

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