CN108471391B - Channel compensation method and device - Google Patents

Channel compensation method and device Download PDF

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CN108471391B
CN108471391B CN201710100255.9A CN201710100255A CN108471391B CN 108471391 B CN108471391 B CN 108471391B CN 201710100255 A CN201710100255 A CN 201710100255A CN 108471391 B CN108471391 B CN 108471391B
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channel
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CN108471391A (en
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程晨
陶想林
张炜
李彧
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Sanechips Technology Co Ltd
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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00Modulated-carrier systems
    • H04L27/0014Carrier regulation
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00Modulated-carrier systems
    • H04L27/26Systems using multi-frequency codes
    • H04L27/2601Multicarrier modulation systems
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00Modulated-carrier systems
    • H04L27/26Systems using multi-frequency codes
    • H04L27/2601Multicarrier modulation systems
    • H04L27/2647Arrangements specific to the receiver only
    • H04L27/2655Synchronisation arrangements
    • H04L27/2668Details of algorithms
    • H04L27/2669Details of algorithms characterised by the domain of operation
    • H04L27/2672Frequency domain
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00Modulated-carrier systems
    • H04L27/26Systems using multi-frequency codes
    • H04L27/2601Multicarrier modulation systems
    • H04L27/2647Arrangements specific to the receiver only
    • H04L27/2655Synchronisation arrangements
    • H04L27/2689Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation
    • H04L27/2691Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation involving interference determination or cancellation
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00Modulated-carrier systems
    • H04L27/26Systems using multi-frequency codes
    • H04L27/2601Multicarrier modulation systems
    • H04L27/2647Arrangements specific to the receiver only
    • H04L27/2655Synchronisation arrangements
    • H04L27/2689Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation
    • H04L27/2695Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation with channel estimation, e.g. determination of delay spread, derivative or peak tracking
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00Modulated-carrier systems
    • H04L27/0014Carrier regulation
    • H04L2027/0024Carrier regulation at the receiver end
    • H04L2027/0026Correction of carrier offset

Abstract

The invention discloses a channel compensation method, which comprises the following steps: acquiring a first frequency domain signal value of each frequency point and a channel frequency domain response value corresponding to the first frequency domain signal value; carrying out normalization processing on the channel frequency domain response value to obtain a result after the normalization processing; performing conjugation operation on the result after the normalization processing to obtain a result of the conjugation operation; and outputting a second frequency domain signal value corresponding to the first frequency domain signal value, wherein the second frequency domain signal value is a complex multiplication result of the conjugate operation result and the corresponding first frequency domain signal value. The invention also discloses a channel compensation device.

Description

Channel compensation method and device
Technical Field
The present invention relates to channel processing technologies, and in particular, to a channel compensation method and apparatus.
Background
In a digital communication system, due to the influence of poor channel characteristics such as multipath transmission, channel fading and the like, signals can be seriously interfered at a receiving terminal; the channel compensation technology mainly compensates for channel characteristics of a channel or the entire transmission system, thereby improving the channel fading resistance of the communication system.
In wireless communication systems and power line carrier communication systems, currently, a commonly used modulation technique is mainly an Orthogonal Frequency Division Multiplexing (OFDM) technique, and since the technique adds a Cyclic Prefix (CP) to each OFDM Symbol, Inter Symbol Interference (ISI) introduced by multipath transmission can be easily avoided. Accordingly, in a communication system employing the OFDM technique, a relatively simple frequency domain channel compensation technique can be used to compensate for channel characteristics. In the prior art, frequency domain channel compensation algorithms mainly include a zero forcing (LS) algorithm, a Minimum Mean Square Error (MMSE) algorithm and a Maximum Likelihood estimation (ML) algorithm; among them, the LS algorithm is the least complex but the worst performance; although the ML algorithm has the best performance, the ML algorithm has high complexity and very high hardware realization cost; in addition, because the performance of the MMSE algorithm is better than that of the LS algorithm and the complexity is lower than that of the ML algorithm, the MMSE algorithm is the most commonly used frequency domain channel compensation algorithm in the wireless communication and power line carrier communication systems at present.
The reason why the MMSE algorithm is widely applied in wireless communication and power line carrier communication systems is analyzed above, and in order to further illustrate the MMSE algorithm, the principle of the MMSE algorithm is derived in detail below.
Let the weight matrix of MMSE be:
Figure BDA0001231520870000011
wherein the content of the first and second substances,
Figure BDA0001231520870000012
h is a channel frequency domain response matrix, and I is a unit matrix; the channel compensated frequency domain signal may be represented as:
Figure BDA0001231520870000021
wherein, XMMSEFor the frequency domain signal after channel compensation, and Y is the frequency domain receiving signal with noise(ii) a Further, the above formula can be decomposed into:
Figure BDA0001231520870000022
wherein X is the frequency domain signal after ideal channel compensation, Z is the noise signal in the frequency domain receiving signal, and Z isMMSEThe noise is superposed after MMSE channel compensation; the mean square error of the noise can be further derived as:
Figure BDA0001231520870000023
wherein the content of the first and second substances,
Figure BDA0001231520870000024
is the smallest estimate of the statistical information of the noise signal z. The above detailed derivation obtains the mean square error of the noise after channel compensation, so that the signal-to-noise ratio after channel compensation can be maximized according to the mean square error. However, the snr is a parameter related to the actual environment, and different snrs may be caused by different application scenarios and different time noises, so that a separate detection and calculation module is required to monitor the snr in real time. In addition, the signal-to-noise ratio can be estimated by using an auxiliary data estimation method, which is to perform correlation operation by using transmitted known data (such as a preamble or a training sequence) to obtain the signal-to-noise ratio; in the existing methods using auxiliary data estimation, the more mature methods include a BOUMARD signal-to-noise ratio estimation method, a signal-to-noise ratio estimation method based on a correlation function, and an MMSE signal-to-noise ratio estimation method. Due to the fact that training sequences are designed in the power line carrier communication and wireless communication technologies, a signal-to-noise ratio can be monitored by adopting an auxiliary data estimation method; however, the method needs to perform cross-correlation operation on the received signal or the result of channel estimation, and as the number of frequency points increases and the time domain period length increases, the resource cost and power consumption overhead of the cross-correlation operation are both increased significantly, which is not favorable for controlling the power consumption and cost of the low-cost chip.
Disclosure of Invention
In order to solve the existing problems, embodiments of the present invention provide a channel compensation method and apparatus, which do not need to detect and estimate the snr during channel compensation, thereby reducing power consumption.
In order to achieve the purpose, the technical scheme of the invention is realized as follows:
the embodiment of the invention provides a channel compensation method, which comprises the following steps:
acquiring a first frequency domain signal value of each frequency point and a channel frequency domain response value corresponding to the first frequency domain signal value;
carrying out normalization processing on the channel frequency domain response value to obtain a result after the normalization processing;
performing conjugation operation on the result after the normalization processing to obtain a result of the conjugation operation;
and outputting a second frequency domain signal value corresponding to the first frequency domain signal value, wherein the second frequency domain signal value is a complex multiplication result of the conjugate operation result and the corresponding first frequency domain signal value.
In the foregoing solution, the normalizing the channel frequency domain response value to obtain a result after the normalization includes:
calculating a modulus of the channel frequency domain response value to obtain a result after modulus calculation;
and dividing the channel frequency domain response value by the result after the modulus calculation to obtain the result after the normalization processing.
In the foregoing solution, the normalizing the channel frequency domain response value to obtain a result after the normalization includes:
performing phase calculation on the channel frequency domain response value to obtain a phase compensation angle value of the corresponding first frequency domain signal value;
calculating sine values and cosine values of the phase compensation angle values;
and obtaining the result after the normalization processing according to the sine value and the cosine value.
In the foregoing solution, the obtaining the result after the normalization processing according to the sine value and the cosine value includes:
and setting the cosine value as a real part of the result after the normalization processing, and setting a negative value of the sine value as an imaginary part of the result after the normalization processing.
An embodiment of the present invention further provides a channel compensation apparatus, where the apparatus includes: the device comprises an acquisition module, a normalization processing module, a conjugate operation module and an output module; wherein the content of the first and second substances,
the acquisition module is used for acquiring a first frequency domain signal value of each frequency point and a channel frequency domain response value corresponding to the first frequency domain signal value;
the normalization processing module is used for performing normalization processing on the channel frequency domain response value to obtain a result after the normalization processing;
the conjugation operation module is used for performing conjugation operation on the result after the normalization processing to obtain a result of the conjugation operation;
the output module is configured to output a second frequency-domain signal value corresponding to the first frequency-domain signal value, where the second frequency-domain signal value is a result of complex multiplication of the result of the conjugate operation and the corresponding first frequency-domain signal value.
In the foregoing solution, the normalization processing module includes: a first calculation unit and a division unit; wherein the content of the first and second substances,
the first calculating unit is configured to calculate a modulus of the channel frequency domain response value, and obtain a result after the modulus calculation;
the division unit is configured to divide the channel frequency domain response value and the result obtained after the modulo calculation to obtain the result obtained after the normalization processing.
In the foregoing solution, the normalization processing module includes: a second calculating unit, a third calculating unit and an obtaining unit; wherein the content of the first and second substances,
the second calculating unit is configured to perform phase calculation on the channel frequency domain response value to obtain a phase compensation angle value of the corresponding first frequency domain signal value;
the third calculating unit is configured to calculate a sine value and a cosine value of the phase compensation angle value;
and the acquisition unit is used for acquiring the result after the normalization processing according to the sine value and the cosine value.
In the foregoing solution, the obtaining unit is specifically configured to set the cosine value as a real part of the result after the normalization processing, and set a negative value of the sine value as an imaginary part of the result after the normalization processing.
The channel compensation method and the device provided by the embodiment of the invention firstly acquire a first frequency domain signal value of each frequency point and a channel frequency domain response value corresponding to the first frequency domain signal value; then, carrying out normalization processing on the channel frequency domain response value to obtain a result after the normalization processing; performing conjugation operation on the result after the normalization processing to obtain a result of the conjugation operation; and outputting a second frequency domain signal value corresponding to the first frequency domain signal value, wherein the second frequency domain signal value is a complex multiplication result of the conjugate operation result and the corresponding first frequency domain signal value. As can be seen, in the embodiments of the present invention, a second frequency domain signal value obtained by performing channel compensation on a first frequency domain signal value is output by performing mathematical operation on the first frequency domain signal value and a channel frequency domain response value; in the embodiment of the invention, the signal-to-noise ratio is not required to be detected and estimated during channel compensation, so that the cross-correlation operation of the first frequency domain signal value or the channel frequency domain response value is not required, thereby saving the resource cost and the power consumption expense generated during the cross-correlation operation, greatly reducing the power consumption, saving the area of a chip and reducing the cost.
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Fig. 1 is a schematic flow chart of a first implementation of the channel compensation method according to the present invention;
FIG. 2 is a schematic flow chart of a digital receiver;
FIG. 3 is a schematic diagram illustrating a detailed flow of normalization in the implementation flow of FIG. 2;
FIG. 4 is a second schematic flow chart of the normalization process in the implementation flow chart shown in FIG. 2;
FIG. 5 is a schematic flow chart of a second implementation of the channel compensation method according to the present invention;
FIG. 6 is a diagram illustrating the performance comparison of the channel compensation method of the present invention with the zero-forcing channel compensation method and the MMSE channel compensation method;
FIG. 7 is a schematic diagram of a first embodiment of a channel compensation apparatus according to the present invention;
FIG. 8 is a schematic diagram of a detailed structure of a normalization processing module in the apparatus shown in FIG. 7;
FIG. 9 is a second schematic diagram of a detailed structure of a normalization processing module in the apparatus shown in FIG. 7;
fig. 10 is a schematic structural diagram of a second embodiment of the channel compensation device according to the present invention.
Detailed Description
The channel compensation method provided by the embodiment of the invention is applied to a receiver system based on a Phase Shift Keying (PSK) power line carrier OFDM communication system, and outputs a second frequency domain signal value after channel compensation is carried out on a first frequency domain signal value by carrying out mathematical operation on the first frequency domain signal value and a channel frequency domain response value; in the embodiment of the invention, the signal-to-noise ratio is not required to be detected and estimated during channel compensation, so that the cross-correlation operation of the first frequency domain signal value or the channel frequency domain response value is not required, the resource cost and the power consumption cost generated during the cross-correlation operation can be saved, and the power consumption is greatly reduced.
The implementation, functional features and advantages of the objects of the present invention will be further explained with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The principles of the channel compensation method of the present invention are explained in detail below in order to illustrate that the snr does not need to be detected and estimated during channel compensation.
In a receiver system of a PSK-based power line carrier OFDM communication system, a frequency domain received signal matrix is as follows:
Y=HX+Z (1)
in formula (1), Y ═ Y1,...,yk,...,yn]K is the number of frequency points, ykIs the frequency domain signal value of frequency point k; h ═ H1,...,hk,...,hn]A channel frequency domain response matrix for the signal, containing amplitude and phase response information, hkThe channel frequency domain response value is the frequency point k; z ═ Z1,...,zk,...,zn]The signal is noise, and because the signal adopts PSK modulation, X only contains phase information; it can be seen that the signal-to-noise ratio of the frequency point k is represented by hkAnd zkIt was determined that assuming Z is uniformly distributed additive white Gaussian noise, the SNR at frequency point k is proportional to
Figure BDA0001231520870000061
Meanwhile, considering that in a receiver system of a PSK-based power line carrier OFDM communication system, information amplitude only affects the confidence of information, and the signal-to-noise ratio determines the confidence of data, the signal-to-noise ratio of a corresponding frequency point can be multiplied on each information data to represent the confidence, so that a signal matrix after channel compensation is deduced to be:
Figure BDA0001231520870000062
since the decoded log-likelihood ratio input is concerned only with the relative magnitude of the values, not the absolute magnitude, Z in equation (2) can be omitted; meanwhile, since H itself has a certain amplification and reduction amplitude, calculation of a dynamic range in a digital system is affected, and in order to keep the dynamic range of Y unchanged as much as possible, formula (2) after Z is omitted may be divided by a modulus | H | of a channel frequency domain response matrix, and a signal matrix after channel compensation is further derived as follows:
Figure BDA0001231520870000063
as can be seen from equation (3), the channel compensation of the signal X is independent of the noise Z, so that the signal-to-noise ratio does not need to be detected and estimated during the channel compensation.
Fig. 1 is a schematic flow chart of an implementation of a first embodiment of the channel compensation method of the present invention, and referring to fig. 1, the channel compensation method of the present embodiment includes the following steps:
step 101: acquiring a first frequency domain signal value of each frequency point and a channel frequency domain response value corresponding to the first frequency domain signal value;
the channel compensation method of the embodiment is mainly applied to the channel equalization process of processing the received signal by the digital receiver and is used for carrying out channel compensation on the received signal; fig. 2 is a schematic flow chart of a digital receiver, and referring to fig. 2, the flow of processing a received signal by the digital receiver includes a channel equalization process, where the channel equalization process has two input data paths: one path is a channel frequency domain response value obtained after channel estimation, and the other path is a frequency domain signal value obtained after Fourier transform.
Generally, because the OFDM multi-carrier modulation divides a channel into a plurality of orthogonal sub-channels, converts a high-speed data signal into parallel low-speed sub-data streams, and modulates the parallel low-speed sub-data streams onto each sub-channel for transmission, a receiver system can receive first frequency domain signal values of a plurality of frequency points; in addition, under the multipath channel model, each path has a channel frequency domain response value in transmission, and the channel frequency domain response value corresponds to the first frequency domain signal value. It should be noted that the frequency point number may be set according to actual needs, and the specific frequency point number needs to refer to the type of OFDM multi-carrier modulation; in this embodiment, the number of frequency points can be described in detail by taking 1024 as an example.
Further, since the channel frequency domain response value of each frequency point is calculated in the preamble portion of each data packet and is used only 1 time, and each data packet generally includes a plurality of data OFDM symbols, the channel frequency domain response value and the first frequency domain signal value of each data OFDM symbol generally arrive at the channel compensation module sequentially. In this embodiment, the first frequency domain signal value is obtained through fourier transform, and the corresponding channel frequency domain response value is obtained through channel estimation; since the first frequency domain signal value and the corresponding channel frequency domain response value are obtained by different processing, the detailed description will be given by taking the example of non-simultaneously obtaining the first frequency domain signal value and the corresponding channel frequency domain response value of each frequency point.
Step 102, carrying out normalization processing on the channel frequency domain response value to obtain a result after the normalization processing;
fig. 3 is a schematic diagram of a refinement flow of the normalization process in the implementation flow shown in fig. 2, and referring to fig. 3, step 102 specifically includes the following steps:
step 1021, calculating a modulus of the channel frequency domain response value, and obtaining a result after modulus calculation;
here, a Coordinate Rotation Digital Computer (Cordic) method may be employed to calculate a modulus of the channel frequency domain response value.
Step 1022, dividing the channel frequency domain response value by the result after the modulo calculation to obtain the result after the normalization processing.
Here, the division calculation may be implemented by calculating an inverse of the modulo-calculated result and multiplying the inverse of the modulo-calculated result by the channel frequency domain response value.
Further, the channel compensation method of the present embodiment actually performs phase compensation only on the first frequency domain signal value, and therefore, the channel compensation may also be performed from the phase perspective; in this way, the normalization of the channel frequency domain response value can be achieved by calculating the phase of the channel frequency domain response value. Compared with the method for realizing the normalization processing by adopting the division operation, the normalization processing method has the advantages that the cost for realizing the normalization processing by adopting the normalization processing method is lower than the cost for realizing the normalization processing by adopting the division operation; however, in terms of accuracy, the method for implementing the normalization processing by the division operation does not additionally introduce a phase error, and the normalization processing method introduces a phase error, so that the accuracy of implementing the normalization processing by the normalization processing method is lower than that of implementing the normalization processing by the division operation. Therefore, when normalization processing is performed, the normalization processing method needs to be selected by comprehensively considering the cost and the precision of the normalization processing.
Fig. 4 is a second schematic view of a detailed flow of the normalization process in the implementation flow shown in fig. 2, and referring to fig. 4, step 102 specifically includes the following steps:
step 1023, phase calculation is carried out on the channel frequency domain response value to obtain a phase compensation angle value of the corresponding first frequency domain signal value;
here, a Cordic method may be adopted to perform phase calculation on the channel frequency domain response value, so as to obtain a phase compensation angle value of the corresponding first frequency domain signal value.
Step 1024, calculating a sine value and a cosine value of the phase compensation angle value;
here, the sine value and the cosine value of the phase compensation angle value may be calculated using a Cordic method.
And 1025, obtaining the result after the normalization processing according to the sine value and the cosine value.
Here, the cosine value may be set as a real part of the result after the normalization processing, and a negative value of the sine value may be set as an imaginary part of the result after the normalization processing.
103, performing conjugate operation on the result after the normalization processing to obtain a conjugate operation result;
and 104, outputting a second frequency domain signal value corresponding to the first frequency domain signal value, wherein the second frequency domain signal value is a complex multiplication result of the conjugate operation result and the corresponding first frequency domain signal value.
Specifically, when normalization processing is realized by adopting division operation, a first frequency domain signal value of each frequency point is obtained after Fourier transform, and a channel frequency domain response value corresponding to the first frequency domain signal value is obtained after channel estimation;
calculating a modulus of the channel frequency domain response value by adopting a Cordic method to obtain a result after modulus calculation;
calculating the reciprocal of the result after the modulo calculation; multiplying the reciprocal of the result after the modulus calculation by the channel frequency domain response value to obtain a result after normalization processing;
performing conjugation operation on the result after the normalization processing to obtain a result of the conjugation operation;
and outputting a second frequency domain signal value corresponding to the first frequency domain signal value, wherein the second frequency domain signal value is a complex multiplication result of the conjugate operation result and the corresponding first frequency domain signal value.
When the channel frequency domain response value is normalized by calculating the phase of the channel frequency domain response value, obtaining a first frequency domain signal value of each frequency point after Fourier transform, and obtaining a channel frequency domain response value corresponding to the first frequency domain signal value after channel estimation;
performing phase calculation on the channel frequency domain response value by adopting a Cordic method to obtain a phase compensation angle value of a corresponding first frequency domain signal value;
calculating a sine value and a cosine value of the phase compensation angle value by adopting a Cordic method;
setting the cosine value as a real part of the result after normalization processing, and setting a negative value of the sine value as an imaginary part of the result after normalization processing;
performing conjugation operation on the result after the normalization processing to obtain a result of the conjugation operation;
and outputting a second frequency domain signal value corresponding to the first frequency domain signal value, wherein the second frequency domain signal value is a complex multiplication result of the conjugate operation result and the corresponding first frequency domain signal value.
It can be understood that the channel compensation method of the present invention can reduce power consumption because: in a PSK modulated OFDM system, the signal-to-noise ratio of a corresponding frequency point can be multiplied on each information data to represent confidence, and the input of the decoded log-likelihood ratio only cares about the relative size of a numerical value and does not care about the absolute size, so that the influence of noise can be ignored during channel compensation, the detection and estimation of the signal-to-noise ratio are not needed, and the cross-correlation operation of a first frequency domain signal value or a channel frequency domain response value is also not needed, thereby saving the resource cost and the power consumption cost generated during the cross-correlation operation, and realizing the great reduction of the power consumption.
Further, before outputting a second frequency domain signal value corresponding to the first frequency domain signal value, a result of complex multiplication between the result of the conjugate operation and the corresponding first frequency domain signal value is calculated according to a preset formula; fig. 5 is a schematic flow chart of an implementation of the second embodiment of the channel compensation method of the present invention, and referring to fig. 5, the channel compensation method of the present embodiment further includes, before step 104 of the first embodiment of the method:
step 103a, calculating a result D of complex multiplication between the result of the conjugate operation and the corresponding first frequency domain signal value according to a preset formula.
The preset formula is as follows:
D=c(a+b)-b(c+d)+j(c(a+b)+a(d-c)) (4)
in equation (4), a denotes a real part of a result of the conjugation operation, b denotes an imaginary part of the result of the conjugation operation, c denotes a real part of the first frequency-domain signal value, d denotes an imaginary part of the first frequency-domain signal value, and j denotes an imaginary unit.
Calculating a result D of complex multiplication of the result of the conjugate operation and the corresponding first frequency domain signal value by using formula (4), wherein the complex multiplication can be realized by three real multiplication times and five real addition times; compared with the traditional complex multiplication which is realized by four real multiplication and two real addition, the real multiplication is replaced by three real addition, and the multiplier resource can be saved.
In this embodiment, a specific implementation example of the channel compensation method of the present invention is described in detail.
Specifically, a first frequency domain signal value of the frequency point k is obtained after Fourier transform, and a channel frequency domain response value corresponding to the first frequency domain signal value of the frequency point k is obtained after channel estimation;
calculating a modulus of the channel frequency domain response value by adopting a Cordic method to obtain a result after modulus calculation;
calculating the reciprocal of the result after the modulo calculation; multiplying the reciprocal of the result after the modulus calculation by the channel frequency domain response value to obtain a result after the normalization processing;
performing conjugation operation on the result after the normalization processing to obtain a result of the conjugation operation;
calculating a result D of complex multiplication of the result of the conjugate operation with the corresponding first frequency domain signal value, based on D ═ c (a + b) -b (c + D) + j (c (a + b) + a (D-c));
determining the result D as a second frequency-domain signal value corresponding to the first frequency-domain signal value and outputting the result D;
and acquiring a first frequency domain signal value of the frequency point n different from the frequency point k and a corresponding channel frequency domain response value, and calculating a second frequency domain signal value corresponding to the first frequency domain signal value of the frequency point n until channel compensation of the first frequency domain signal value of each frequency point is completed.
Fig. 6 is a schematic diagram showing performance comparison between the channel compensation method of the present invention and the zero-forcing channel compensation method and the MMSE channel compensation method, and the diagram compares BER performance of an OFDM system using the channel compensation method of the present invention, the zero-forcing channel compensation method and the MMSE channel compensation method in QPSK modulation and a 16-path multipath channel model, respectively; referring to fig. 6, a curve with squares identifies the bit error rate BER of the signal-to-noise ratio of the OFDM system obtained by the MMSE channel compensation method; the signal-to-noise ratio of the OFDM system is identified by a curve with a circle, and the BER is obtained by adopting a zero-forcing channel compensation method; the signal-to-noise ratio of the curve identification OFDM system with the triangle is the bit error rate BER obtained by the channel compensation method; it can be seen that the performance of the OFDM system using the zero-forcing channel compensation method is the worst, and the performance of the OFDM system using the channel compensation method of the present invention and the MMSE channel compensation method is similar, and the difference is within 0.2dB, which are all superior to the zero-forcing channel compensation method by about 3 dB.
The invention also provides a channel compensation device, which is used for realizing the specific details of the channel compensation method of the invention and achieving the same effect.
Fig. 7 is a schematic structural diagram of a first embodiment of a channel compensation apparatus according to the present invention, and referring to fig. 7, the apparatus includes: the device comprises an acquisition module 21, a normalization processing module 22, a conjugate operation module 23 and an output module 24; wherein the content of the first and second substances,
the acquiring module 21 is configured to acquire a first frequency domain signal value of each frequency point and a channel frequency domain response value corresponding to the first frequency domain signal value;
the channel compensation device of the embodiment is mainly applied to the channel equalization process of the digital receiver for processing the received signal, and is used for performing channel compensation on the received signal.
Generally, because the OFDM multi-carrier modulation divides a channel into a plurality of orthogonal sub-channels, converts a high-speed data signal into parallel low-speed sub-data streams, and modulates the parallel low-speed sub-data streams onto each sub-channel for transmission, a receiver system can receive first frequency domain signal values of a plurality of frequency points; in addition, under the multipath channel model, each path has a channel frequency domain response value in transmission, and the channel frequency domain response value corresponds to the first frequency domain signal value. It should be noted that the frequency point number may be set according to actual needs, and the specific frequency point number needs to refer to the type of OFDM multi-carrier modulation; in this embodiment, the number of frequency points can be described in detail by taking 1024 as an example.
Further, since the channel frequency domain response value of each frequency point is calculated in the preamble portion of each data packet and is used only 1 time, and each data packet generally includes a plurality of data OFDM symbols, the channel frequency domain response value and the first frequency domain signal value of each data OFDM symbol generally arrive at the channel compensation module sequentially. In this embodiment, the first frequency domain signal value is obtained through fourier transform, and the corresponding channel frequency domain response value is obtained through channel estimation; since the first frequency domain signal value and the corresponding channel frequency domain response value are obtained by different processing, the detailed description will be given by taking the example of non-simultaneously obtaining the first frequency domain signal value and the corresponding channel frequency domain response value of each frequency point.
The normalization processing module 22 is configured to perform normalization processing on the channel frequency domain response value to obtain a result after the normalization processing;
fig. 8 is a schematic diagram of a detailed structure of the normalization processing module in the apparatus shown in fig. 7, and referring to fig. 8, the normalization processing module 22 includes: a first calculation unit 221 and a division unit 222; wherein the content of the first and second substances,
the first calculating unit 221 is configured to calculate a modulus of the channel frequency domain response value, and obtain a result after the modulus calculation;
here, the first Cordic unit may be adapted to calculate a modulus of the channel frequency domain response value using a Cordic method.
The division unit 222 is configured to divide the channel frequency domain response value and the result obtained after the modulo calculation to obtain the result obtained after the normalization processing.
Here, the division unit 222 may implement a division calculation by calculating an inverse of the modulo result and multiplying the inverse of the modulo result by the channel frequency domain response value using an anderson divider.
Further, the channel compensation apparatus of the present embodiment actually performs phase compensation only on the first frequency domain signal value, and therefore, channel compensation may also be performed from the phase perspective; in this way, the normalization of the channel frequency domain response value can be achieved by calculating the phase of the channel frequency domain response value. Compared with the normalization processing implemented by the division unit 222, in terms of cost, the normalization processing implemented by the normalization processing module 22 is lower than the normalization processing implemented by the division unit 222; however, in terms of accuracy, the normalization processing performed by the division unit 222 does not introduce a phase error, and the normalization processing module 22 introduces a phase error, so that the accuracy of the normalization processing performed by the normalization processing module 22 is lower than that of the normalization processing performed by the division unit 222. It can be seen that, when performing the normalization process, the normalization processing module 22 needs to be selected by comprehensively considering the cost and precision of the normalization process.
Fig. 9 is a schematic diagram of a second refined structure of the normalization processing module in the apparatus shown in fig. 7, and referring to fig. 9, the normalization processing module 22 includes: a second calculation unit 223, a third calculation unit 224, and an acquisition unit 225; wherein the content of the first and second substances,
the second calculating unit 223 is configured to perform phase calculation on the channel frequency domain response value to obtain a phase compensation angle value of the corresponding first frequency domain signal value;
here, a second Cordic unit may be used to perform a phase calculation on the channel frequency domain response value by using a Cordic method to obtain a phase compensation angle value of the corresponding first frequency domain signal value.
The third calculating unit 224 is configured to calculate a sine value and a cosine value of the phase compensation angle value;
here, a third Cordic unit may be used to calculate sine and cosine values of the phase compensation angle values using a Cordic method.
The obtaining unit 225 is configured to obtain the result after the normalization processing according to the sine value and the cosine value.
Here, the cosine value may be set as a real part of the result after the normalization processing, and a negative value of the sine value may be set as an imaginary part of the result after the normalization processing.
The conjugation operation module 23 is configured to perform conjugation operation on the result after the normalization processing to obtain a result of conjugation operation;
the output module 24 is configured to output a second frequency-domain signal value corresponding to the first frequency-domain signal value, where the second frequency-domain signal value is a result of complex multiplication between the result of the conjugate operation and the corresponding first frequency-domain signal value.
Specifically, when the division unit 222 is used to implement normalization processing, a first frequency domain signal value of each frequency point is obtained after fourier transform, and a channel frequency domain response value corresponding to the first frequency domain signal value is obtained after channel estimation;
calculating a modulus of the channel frequency domain response value by using a first Cordic unit through a Cordic method to obtain a modulus calculated result;
adopting an anderson divider to realize division calculation by calculating the reciprocal of the result after the modulus calculation and multiplying the reciprocal of the result after the modulus calculation by the channel frequency domain response value to obtain a result after normalization processing;
performing conjugation operation on the result after the normalization processing to obtain a result of the conjugation operation;
and outputting a second frequency domain signal value corresponding to the first frequency domain signal value, wherein the second frequency domain signal value is a complex multiplication result of the conjugate operation result and the corresponding first frequency domain signal value.
When the channel frequency domain response value is normalized by calculating the phase of the channel frequency domain response value, obtaining a first frequency domain signal value of each frequency point after Fourier transform, and obtaining a channel frequency domain response value corresponding to the first frequency domain signal value after channel estimation;
performing phase calculation on the channel frequency domain response value by using a second Cordic unit by using a Cordic method to obtain a phase compensation angle value of the corresponding first frequency domain signal value;
calculating a sine value and a cosine value of the phase compensation angle value by using a third Cordic unit and a Cordic method;
setting the cosine value as a real part of the result after normalization processing, and setting a negative value of the sine value as an imaginary part of the result after normalization processing;
performing conjugation operation on the result after the normalization processing to obtain a result of the conjugation operation;
and outputting a second frequency domain signal value corresponding to the first frequency domain signal value, wherein the second frequency domain signal value is a complex multiplication result of the conjugate operation result and the corresponding first frequency domain signal value.
It is understood that the channel compensation device of the present invention can reduce power consumption because: in PSK modulated OFDM system, can multiply the signal-to-noise ratio of the corresponding frequency point on each information data, come to characterize the confidence, and the logarithmic likelihood ratio input of the decoding only cares about the relative size of the numerical value, does not care about the absolute size, therefore adopt the influence that the signal channel compensating device of the invention can ignore the noise while realizing the channel compensation, does not need to detect and estimate the signal-to-noise ratio, therefore does not need signal-to-noise ratio to detect and estimate the module either, thus can save the area of the chip, realize the great reduction of the power consumption.
Further, before outputting a second frequency domain signal value corresponding to the first frequency domain signal value, a result of complex multiplication between the result of the conjugate operation and the corresponding first frequency domain signal value is calculated according to a preset formula; fig. 10 is a schematic diagram of a second embodiment of the channel compensation apparatus of the present invention, and referring to fig. 10, the channel compensation apparatus of the present embodiment includes, in addition to the obtaining module 21, the normalization processing module 22, the conjugate operation module 23, and the output module 24:
a calculating module 23a, configured to calculate a result D of complex multiplication of the result of the conjugate operation and the corresponding first frequency domain signal value according to D ═ c (a + b) -b (c + D) + j (c (a + b) + a (D-c)).
Wherein a denotes a real part of a result of the conjugate operation, b denotes an imaginary part of the result of the conjugate operation, c denotes a real part of the first frequency-domain signal value, d denotes an imaginary part of the first frequency-domain signal value, and j denotes an imaginary unit.
Calculating a result D of complex multiplication of the result of the conjugate operation and the corresponding first frequency-domain signal value by using a formula D ═ c (a + b) -b (c + D) + j (c (a + b) + a (D-c)), wherein the complex multiplication can be realized by three real multiplications and five real additions; compared with the traditional complex multiplication which is realized by four real multiplication and two real addition, the real multiplication is replaced by three real addition, and the multiplier resource can be saved.
In this embodiment, a specific implementation example of the channel compensation apparatus of the present invention is described in detail.
Specifically, a first frequency domain signal value of the frequency point k is obtained after Fourier transform, and a channel frequency domain response value corresponding to the first frequency domain signal value of the frequency point k is obtained after channel estimation;
calculating a modulus of the channel frequency domain response value by using a first Cordic unit through a Cordic method to obtain a modulus calculated result;
adopting an anderson divider to realize division calculation by calculating the reciprocal of the result after the modulus calculation and multiplying the reciprocal of the result after the modulus calculation by the channel frequency domain response value to obtain a result after normalization processing;
performing conjugation operation on the result after the normalization processing to obtain a result of the conjugation operation;
calculating a result D of complex multiplication of the result of the conjugate operation with the corresponding first frequency domain signal value, based on D ═ c (a + b) -b (c + D) + j (c (a + b) + a (D-c));
determining the result D as a second frequency-domain signal value corresponding to the first frequency-domain signal value and outputting the result D;
and acquiring a first frequency domain signal value of the frequency point n different from the frequency point k and a corresponding channel frequency domain response value, and calculating a second frequency domain signal value corresponding to the first frequency domain signal value of the frequency point n until channel compensation of the first frequency domain signal value of each frequency point is completed.
In practical applications, the obtaining module 21, the normalization Processing module 22, the conjugate operation module 23, the output module 24, the calculating module 23a, the first calculating Unit 221, the dividing Unit 222, the second calculating Unit 223, the third calculating Unit 224, and the obtaining Unit 225 may be implemented by a Central Processing Unit (CPU), a microprocessor Unit (MPU), a Digital Signal Processor (DSP), a Field Programmable Gate Array (FPGA), or the like in the mobile terminal.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, and improvement made within the spirit and scope of the present invention are included in the protection scope of the present invention.

Claims (8)

1. A channel compensation method, for use in a receiver of a communication system having the following characteristics: multiplying each information data by the signal-to-noise ratio of the corresponding frequency point to represent the confidence coefficient; the decoded log-likelihood ratio input only concerns the relative magnitude of the values, not the absolute magnitude;
the method comprises the following steps:
acquiring a first frequency domain signal value of each frequency point and a channel frequency domain response value corresponding to the first frequency domain signal value;
carrying out normalization processing on the channel frequency domain response value to obtain a result after the normalization processing;
performing conjugation operation on the result after the normalization processing to obtain a result of the conjugation operation;
and outputting a second frequency domain signal value corresponding to the first frequency domain signal value, wherein the second frequency domain signal value is a complex multiplication result of the conjugate operation result and the corresponding first frequency domain signal value.
2. The method of claim 1, wherein the normalizing the channel frequency domain response value to obtain a normalized result comprises:
calculating a modulus of the channel frequency domain response value to obtain a result after modulus calculation;
and dividing the channel frequency domain response value by the result after the modulus calculation to obtain the result after the normalization processing.
3. The method of claim 1, wherein the normalizing the channel frequency domain response value to obtain a normalized result comprises:
performing phase calculation on the channel frequency domain response value to obtain a phase compensation angle value of the corresponding first frequency domain signal value;
calculating sine values and cosine values of the phase compensation angle values;
and obtaining the result after the normalization processing according to the sine value and the cosine value.
4. The method of claim 3, wherein obtaining the normalized result from the sine and cosine values comprises:
and setting the cosine value as a real part of the result after the normalization processing, and setting a negative value of the sine value as an imaginary part of the result after the normalization processing.
5. A channel compensation apparatus, for use in a receiver of a communication system having the following characteristics: multiplying each information data by the signal-to-noise ratio of the corresponding frequency point to represent the confidence coefficient; the decoded log-likelihood ratio input only concerns the relative magnitude of the values, not the absolute magnitude;
the device comprises: the device comprises an acquisition module, a normalization processing module, a conjugate operation module and an output module; wherein the content of the first and second substances,
the acquisition module is used for acquiring a first frequency domain signal value of each frequency point and a channel frequency domain response value corresponding to the first frequency domain signal value;
the normalization processing module is used for performing normalization processing on the channel frequency domain response value to obtain a result after the normalization processing;
the conjugation operation module is used for performing conjugation operation on the result after the normalization processing to obtain a result of the conjugation operation;
the output module is configured to output a second frequency-domain signal value corresponding to the first frequency-domain signal value, where the second frequency-domain signal value is a result of complex multiplication of the result of the conjugate operation and the corresponding first frequency-domain signal value.
6. The apparatus of claim 5, wherein the normalization processing module comprises: a first calculation unit and a division unit; wherein the content of the first and second substances,
the first calculating unit is configured to calculate a modulus of the channel frequency domain response value, and obtain a result after the modulus calculation;
the division unit is configured to divide the channel frequency domain response value and the result obtained after the modulo calculation to obtain the result obtained after the normalization processing.
7. The apparatus of claim 5, wherein the normalization processing module comprises: a second calculating unit, a third calculating unit and an obtaining unit; wherein the content of the first and second substances,
the second calculating unit is configured to perform phase calculation on the channel frequency domain response value to obtain a phase compensation angle value of the corresponding first frequency domain signal value;
the third calculating unit is configured to calculate a sine value and a cosine value of the phase compensation angle value;
and the acquisition unit is used for acquiring the result after the normalization processing according to the sine value and the cosine value.
8. The apparatus according to claim 7, wherein the obtaining unit is specifically configured to set the cosine value as a real part of the result after the normalization processing, and set a negative value of the sine value as an imaginary part of the result after the normalization processing.
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