RU2459359C1 - Method to generate channel signals and device that implements it - Google Patents

Abstract

FIELD: information technologies.

SUBSTANCE: device that implements the Method to generate channel OFDM signals comprises a source of information, a unit comprising a converter of serial symbols into parallel ones and an expander, a unit to insert a protective interval and a quadrature modulator comprising two digital-to-analog converters, two multipliers, a bearing oscillation generator, a device of phase shift by π/2, a summator, a unit of signal generation on the basis of internal vectors of subband matrices, which includes a generator of internal vectors of subpolar matrices, a device to control the generator of the internal vectors of subband matrices, J multipliers to multiply n arriving parallel information symbols to internal vectors of subpolar matrices and the summator.

EFFECT: increased number of channels simultaneously transferring data in a dedicated frequency range and reduction of interference noise of radio communication systems.

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Description

The invention relates to the field of radio communications, namely to wireless communication with frequency division, and can be used for digital generation of channel signals.

A known method of generating channel signals [1], in systems with frequency separation, implemented by sampling with a frequency f _d = 8 kHz, input voice messages (having a frequency f _in = 4 kHz), received from M subscribers to the corresponding input of one of them from M parallel-connected channels, the subsequent presentation of each quantized value of the count of the voice message, in each of M parallel-connected channels, into an 8-bit PCM signal that modulates in the phase modulator different for each of M channels carrier frequencies using the FM-4 method, from the output of each of the M channels the phase-shifted signals, after passing through the channel combining circuit, are fed to the input of the terminal stage of the transmitting device.

The specified method does not allow the best use of the allocated frequency resources in the formation of channel signals in systems with frequency separation, since in order to reduce the mutual influence between adjacent channels, it is necessary to introduce guard intervals, which is a disadvantage of this device.

The closest technical solution (prototype) is a method of generating channel signals using orthogonal frequency division multiplexing OFDM and a device that implements it [2].

The known method is carried out by converting information symbols, where the symbol is a signal of a multi-position modulation system containing information about the number of bits combined in groups and their combinations, which, depending on the bit combination, is assigned a specific symbol value, and they are transmitted on orthogonal subcarrier frequencies. The method is as follows.

Present on the transmitting side information in the form of a set of n consecutive information symbols of length n * τ, where τ is the duration of one symbol, they are converted into a set of n parallel information symbols of length τ each, which are then converted into parallel information symbols of duration T _S = n * τ each. Next, the resulting set is processed by the inverse fast Fourier transform (IFFT) algorithm. The IFFT procedure allows calculating the values of the channel signal at time instants [0 T _S ], i.e. summation of harmonic components arranged in series with a step Δf in the frequency domain, with Δf = 1 / T _S , where T _S is the signal duration, and modulated by information symbols, and the entire frequency band allocated for transmission is divided into n frequency intervals of width V = [-ν _i , -ν _i-1 ) ∪ [ν _i-1 , ν _i ) each, and thus, each information symbol is transmitted in its subchannel. The use of the IFFT procedure allows each of the n information symbols of increased duration to be multiplied by the corresponding subcarrier frequency with a fixed frequency step Δf without using n multipliers and n subcarrier generators, which greatly simplifies the circuitry of the transmitter and receiver of the communication system using OFDM. Next, the insertion of the guard interval and processing of the quadrature modulator.

However, the use of signal-code constructions in the form of an orthogonal Fourier basis with a rectangular shape of the modulating pulse does not allow minimizing the time-frequency localization of the generated channel signals and, as a result, their level of out-of-band emissions, thereby making it impossible to ensure minimal sensitivity to interchannel and intersymbol interference.

A device [3] is known that implements the technical implementation of this method, which includes a series-connected information source 1, block 2, which includes a series-connected converter of consecutive symbols in parallel and an expander, n outputs of the latter are connected to the corresponding inputs of block 3 of the inverse fast Fourier transform ( OBPF), the first and second outputs of which are connected to the corresponding inputs of the block 4 inserts the protective interval. The first and second outputs of block 4 are connected to the corresponding inputs of the quadrature modulator, which includes two digital-to-analog converters 5 and 6, two multipliers 7 and 8, a carrier oscillator 9, a phase shift device 10 by π / 2, an adder 11, and the first output unit 4 is connected to the input of the digital-to-analog converter 5, the output of which is connected to the first input of the multiplier 7, and the second input of the multiplier 7 is connected to the output of the generator 9. The second output of the protective interval insert unit 4 is connected to the input of the second digital-to-analog converter 6, the output of which is connected to the first input of the second multiplier 8, and the second input of the multiplier 8 is connected to the output of the device 10 phase shift by π / 2, the input of which is connected to the output of the generator 9. The outputs of the multipliers 7 and 8 are connected to the corresponding inputs of the adder 11, the output of which finally forms a channel signal at a given carrier frequency.

The disadvantages of this device correspond to the disadvantages of the method that is implemented on it, and are confirmed by the energy spectra in figure 4.

The objective of the invention is the creation of a method and device for its implementation, providing the formation of OFDM channel signals with an out-of-band emission level not higher than minus 65-70 dB in communication systems with frequency multiplexing.

The technical result of using the proposed inventions is to increase the number of channels simultaneously transmitting information in the selected frequency range by about 20% and reducing interference interference from radio communication systems.

The problem is achieved in that the formation of channel signals during the transmission of information in the frequency compression mode is implemented using a new orthogonal signal basis of the eigenvectors of the subband matrices, i.e. taking into account the characteristic feature of the concentration of energy of the eigenvector in a given frequency range.

To do this, into a known method of generating OFDM channel signals, which includes representing on the transmitting side information in the form of a set of n consecutive information symbols of duration n * τ, where τ is the duration of one symbol, converting them into a set of N parallel information symbols with a duration of τ each, the subsequent transformation each symbol of duration τ to a symbol of duration n * τ, each subject to N = n, insertion of the guard interval, processing with a quadrature modulator, the following new Signs of:

- instead of the IFFT procedure, before inserting the guard interval, a set of eigenvectors of the subband matrix is formed, from which J vectors are selected whose eigenvalues are λ _i ≈1, moreover, J = N;

- multiply each of the J received eigenvectors by the corresponding information symbol for transmission over the communication channel and then summarize the resulting set of modulated eigenvectors.

The device that implements the proposed method, instead of the inverse fast Fourier transform (OBPF) block, contains a signal generation block based on eigenvectors of subband matrices, which includes:

- shaper of the eigenvectors of the subband matrices, which ensures noise immunity of the generated channel signals no lower than in the prototype, due to the orthogonality property of the generated eigenvectors;

- a control device for the eigenvector of the subband matrices, which provides the choice of J eigenvectors with the eigenvalue λ _i ≈1, which reduces the level of out-of-band emissions of the channel signal to minus 65-70 dB;

- J multipliers for multiplying the incoming information symbols by eigenvectors of subband matrices, allowing the use of generated eigenvectors for transmitting information by modulating them with data;

- adder combining a set of modulated eigenvectors into real Re and imaginary Im signals.

The invention is illustrated by the images presented in the figures:

Figure 1 - Scheme of the prototype;

Figure 2 - Scheme of the proposed device;

Figure 3 - Block diagram of the signal generation based on the eigenvectors of the subband matrices;

Figure 4 - Energy spectrum of the channel signal generated using the prototype;

Figure 5 - The energy spectrum of the channel signal generated using the proposed device.

The method is as follows.

1. Information is represented as a set of n consecutive information symbols of duration n * τ, where τ is the duration of one symbol,

2. A set of n consecutive information symbols of length n * τ is converted into a set of n parallel characters of duration τ each;

3. The resulting n parallel information symbols of duration τ each are converted into n parallel information symbols of duration n * τ each;

4. Divide the frequency band allocated for transmission into n frequency intervals of width V = [- ν _i , -ν _i-1 ) ∪ [ν _i-1 , ν _i ) each;

где

- собственные векторы субполосных матриц вида

, m,n=1,…,L c элементами вида;

5. Produce the formation of eigenvectors of subband matrices for given frequency intervals according to the following expressions

Where

- eigenvectors of subband matrices of the form

, m, n = 1, ..., L with elements of the form;

6. I select eigenvectors according to the criterion of the maximum eigenvalue λ _i = 1, ie leave J vectors whose eigenvalues λ _i ≈1. Moreover, J = n,

ванных собственных векторов согласно следующему выражению:1. The multiplication intended for the transmission of n information symbols over the communication channel by the received J eigenvectors and the subsequent summation of the resulting set are modulated

eigenvectors according to the following expression:

, где:

- сформированный канальный сигнал;

where:

- formed channel signal;

- последовательность информационных символов; [4]

- a sequence of information symbols; [four]

8. Insert the guard interval at the beginning of the generated signal, i.e. insert a copy of the terminal fragment of the signal at its beginning;

9. Process in a quadrature modulator and transmit to the communication channel. The criteria of "novelty" and "inventive step" the proposed method meets due to the presence of the following features:

где- the formation of eigenvectors of subband matrices Q for given frequency intervals, according to the following expressions

Where

- собственные векторы субполоспых матриц вида

, m, n=1,…,L с элементами вида:

- eigenvectors of sub-half-matrix matrices of the form

, m, n = 1, ..., L with elements of the form:

- a sample of eigenvectors according to the criterion of the maximum eigenvalue λ _i = 1, i.e. for information transfer, J eigenvectors are used, the eigenvalue X of which satisfies the condition λ _i ≈1, moreover, J = n;

- the multiplication of n information symbols intended for transmission over the communication channel by the received J eigenvectors and the subsequent summation of the resulting set of modulated eigenvectors according to the following expression:

, где: - сформированный канальный сигнал;

where: - formed channel signal;

- последовательность информационных символов.

- a sequence of information symbols.

The above-mentioned features make it possible to form channel signals during information transmission in the frequency compression mode, with a minimum level of out-of-band emissions due to the use of eigenvectors of sub-band matrices with eigenvalue λ _i ≈ 1 as basic functions, which is confirmed by the energy spectra shown in Fig. 5.

To implement this method, a device is proposed for generating channel signals OFDM with a minimum level of out-of-band emissions of a channel signal outside the allocated frequency range (Figure 2), including an information source 1, the output of which is connected to the input of block 2, including a serial to parallel converter and an extender, the outputs of the latter are connected to the corresponding inputs of the signal generating unit 12 based on the eigenvectors of the subband matrices, the first and second outputs of which connected to the corresponding inputs of the guard interval insert unit 4, the first and second outputs of which are connected to the corresponding inputs of the quadrature modulator, which includes two digital-to-analog converters 5 and 6, two multipliers 7 and 8, a carrier oscillator 9, and a phase shift device 10 by π / 2, adder 11. The first output of block 4 is connected to the input of the digital-to-analog converter 5, the output of which is connected to the first input of the multiplier 7, and the second input of the multiplier 7 is connected to the output of the oscillating carrier, 9. Second the output of the guard interval insertion unit 4 is connected to the input of the second digital-to-analog converter 6, the output of which is connected to the first input of the second multiplier 8, and the second input of the multiplier 8 is connected to the output of the phase shift device 10 by π / 2, the input of which is connected to the output of the generator 9. The outputs of the multipliers 7 and 8 are connected to the corresponding inputs of the adder 11, the output of which finally forms a channel signal at a given carrier frequency.

This scheme differs from the prototype in the presence of a block 12 for generating a signal based on eigenvectors of subband matrices, which includes:

- shaper 13 eigenvectors of subband matrices, which ensures noise immunity of generated channel signals no lower than in the prototype, due to the orthogonality property of generated eigenvectors;

- device 14 for controlling the generator of eigenvectors of subband arrays, which reduces the level of out-of-band emissions of the channel signal to minus 65-70 dB by selecting eigenvectors with an eigenvalue λ _i ≈1;

- J multipliers 15 for multiplying incoming n parallel information symbols of duration n * τ each by eigenvectors of subband matrices, allowing the use of generated eigenvectors to transmit information by modulating them with data;

- adder 16, combining a set of modulated eigenvectors into real Re and imaginary Im signals.

These features together allow you to get the claimed technical result and are not known from the prior art as well as the influence of the presence of these signs on the increase in the number of channels simultaneously transmitting information in the selected frequency range by about 20% and the reduction of interference interference of radio communication systems by reducing the level of out-of-band signal emissions, which makes it possible to recognize them as meeting the criteria of “novelty” and “inventive step”.

The proposed method is implemented on this device as follows. The information to be transmitted through the communication channel is represented on the transmitting side as a set of n consecutive information symbols of duration n * τ, where τ is the duration of one symbol. Then, in block 2, which contains the converter of consecutive characters into parallel characters and an expander, the set of n consecutive information characters is converted into a set of n parallel information characters of duration τ each, followed by the conversion of each n parallel information character of duration τ into a character of duration n * τ each. Next, each of N parallel information symbols of duration n * τ is supplied to the corresponding output of block 2, and the number of outputs of block 2 is equal to the number of N parallel information symbols. From each output of block 2, parallel information symbols of duration n * τ simultaneously arrive at the corresponding inputs of signal generation block 12 based on their own subband matrices, i.e., at the first inputs of the multipliers 15, signals from the corresponding outputs of the block 13 of the own shaper are sent to the second inputs of the multipliers 15 vectors of subband matrices, which is controlled by the device 14 for controlling their own subband matrices, the purpose of which is to set the parameters of the generated eigenvectors their selection. From the outputs of the multipliers 15, the modulated eigenvectors are fed to the corresponding inputs of the adder 16, and then from the first output of the adder 16, the real component of the combined signal Re goes to the first input of the guard interval insert unit 4. From the second output of the adder 16, the imaginary component of the combined signal Im is fed to the second input of the guard interval insert unit 4. Next, the signals from the outputs of block 4 simultaneously arrive at the corresponding inputs of the quadrature modulator, which includes two digital-to-analog converters 5 and 8, two multipliers 6 and 9, a carrier oscillator 7, a device 10 for phase shift by π / 2, an adder 11. Moreover, the signal Re from the first output of block 4 goes to the input of the digital-to-analog converter 5, and the signal Im from the second output of block 4 to the input of the digital-to-analog converter 6, where they are converted to analog form. From the outputs of the digital-to-analog converter 5 and the digital-to-analog converter 6, the signals are supplied to the inputs of the corresponding multipliers 7 and 8, in which the input signal is multiplied by the carrier oscillation of a given frequency, which respectively comes to the multiplier 7 from the carrier oscillator 9, and to the multiplier 8 from the shift device 10 phase at π / 2. From the outputs of the multipliers 7 and 8, the received signals simultaneously arrive at the corresponding inputs of the adder 11, thus, at the output of the quadrature modulator, the channel signal OFDM is finally generated at the carrier frequency for transmission over the communication channel.

As a result of using the proposed technical solutions through the use of a new orthogonal signal basis of eigenvectors of subband arrays, it is possible to generate channel signals with a minimum level of out-of-band emissions outside the allocated frequency band, which allows to increase by approximately 20% the number of channels simultaneously transmitting information in the provided frequency range, and as a result, reduce interference interference of radio communication systems.

References

1. Thomasi W. Electronic Communication Systems [Text]. M .: Technosphere, 2007 .-- 1360 p.

2. IEEE Std P802.16-2004, IEEE Standart for Local and metropolitan area networks - Part 16: Air Interface for Fixed BWA Systems.

3. Shakhnovich I.V. Modern technologies of wireless communication [Text] - M .: Technosphere, 2004.

4. Zhilyakov E.G. Variational methods of analysis and construction of functions according to empirical data [Text]: monograph. - Belgorod: BelSU Publishing House, 2007.

Claims (2)

1. A method of generating OFDM channel signals, including representing on the transmitting side information in the form of a set of n consecutive information symbols of length n · τ, where τ is the duration of one symbol, converting it into a set of n parallel information symbols with a duration of τ each, and then each the symbol n of duration τ is converted into symbols of duration n · τ each; divide the frequency band allocated for transmission into n frequency intervals of width V = [- ν _i , -ν _i-1 ) ∪ [ν _i-1 , ν _i ) each, insert the guard interval and process the quadrature modulator, characterized in that before inserting the guard interval, a set of eigenvectors is formed for the given frequency intervals according to the following expressions

where

- eigenvectors of subband matrices of the form

, m, n = 1, ..., L with elements of the form;

from which J such eigenvectors are sampled, the eigenvalues of which λ _i = 1, provided J = n, then the multiplication of n information symbols intended for transmission through the communication channel n of duration n · τ by the received J eigenvectors and subsequent summation of the resulting modulated set eigenvectors according to the following expression

where

- formed channel signal;

- a sequence of information symbols. 2. An OFDM channel signal generating apparatus including an information source whose output is connected to a block containing a serial to parallel converter and an expander, a guard interval insert and a quadrature modulator, including two digital-to-analog converters, two multipliers, a carrier oscillator, a phase shift device on π / 2, the adder, while the first output of the protective interval insertion unit is connected to the input of the digital-to-analog converter, the output of which is connected to the first input the house of the first multiplier, the second input of which is connected to the output of the carrier oscillator, and the second output of the guard interval insert is connected to the input of the second digital-to-analog converter, the output of which is connected to the first input of the second multiplier, the second input of which is connected to the output of the phase shift device by π / 2 , the input of which is connected to the output of the carrier oscillator, and the outputs of the multipliers are connected to the corresponding inputs of the adder, the output of which finally forms a channel signal carrier frequency, characterized in that the n outputs of the block containing the serial to parallel converter and the expander are connected to the corresponding inputs of the signal conditioning block based on the eigenvectors of the subband matrices, the first and second outputs of which are connected to the corresponding inputs of the guard interval insert at the same time, the signal generation unit based on the eigenvectors of the subband matrices includes an eigenvector of the subband matrices, a control device eniya subband generator eigenvectors of matrices, J multipliers for multiplying the n parallel information symbols received on subband eigenvectors of matrices adder.

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