Time-frequency joint correction method and device

Abstract

The invention is suitable for the technical field of wireless transmission, and provides a time-frequency joint correction method and device, timing is estimated based on the phase of a frequency domain, different timing estimation ranges and precisions can be obtained by setting different subcarrier step lengths, and in addition, the time-frequency joint correction method and device can be applied to the field of wireless transmission. A high-precision timing position can be estimated by combining the phase deviation of the positive and negative frequency domains of the signal; for a frequency offset and timing joint estimation scheme of a signal with integer frequency offset, after the integer frequency offset is estimated in a frequency domain, subcarriers where the signal is located can be calculated again, and then timing estimation is obtained by using the phase difference of the subcarriers. Therefore, the timing and frequency offset estimation method can obtain high-precision timing and frequency offset estimation by adopting less calculation amount.

Description

Technical Field

[0001] The present invention relates to the field of wireless transmission technology, and in particular to a time-frequency joint correction method and device. Background Art

[0002] Orthogonal Frequency Division Multiplexing (OFDM) has the advantages of high-speed data transmission, efficient spectrum utilization and anti-multipath capability. In recent years, OFDM technology has been successfully applied in mobile and fixed data transmission, such as Asymmetric Digital Subscriber Line (ADSL), Digital Video Broadcasting (DVB-T and DVB-H), and Wireless LAN. Currently, OFDM has been regarded as the most competitive transmission technology for the fourth generation of mobile communications.

[0003] Since OFDM divides the channel into many orthogonal sub-channels in the frequency domain, the carriers of each sub-channel remain orthogonal, and the spectrum overlaps each other, which reduces the interference between sub-channels and improves the spectrum utilization. Therefore, the OFDM system is very sensitive to frequency offset. Even a small frequency offset may destroy the orthogonality between sub-carriers, thereby generating inter-carrier interference (ICI) and causing a serious degradation of system performance.

[0004] Another technical difficulty in implementing the OFDM system is that the system has high requirements for synchronization, because it is much more sensitive to timing errors than single-carrier technology. Symbol timing deviation refers to the advance or lag of the FFT window when demodulating OFDM symbols. If the symbol timing deviation is too large, the sum of the timing offset and the maximum delay extension length is less than the length of the cyclic prefix, which will cause inter-symbol interference, destroy the integrity of the OFDM symbol, and reduce the performance of the system. It can be said that accurate estimation of symbol timing deviation is the key to implementing the OFDM system.

[0005] Therefore, how to improve the efficiency and accuracy of OFDM receiver timing synchronization and carrier frequency offset estimation is the key to OFDM receiver design. At present, many methods for OFDM timing and carrier frequency offset joint synchronization have been proposed. Most algorithms use the received signal for correlation operation to obtain timing and carrier frequency offset estimation. In addition, in the article "OFDM symbol timing and integer frequency offset joint synchronization algorithm based on parallel FFT", a time-frequency two-dimensional symbol timing synchronization and carrier integer frequency offset joint estimation method based on parallel FFT structure suitable for OFDM system is proposed. The algorithm uses parallel FFT structure to simultaneously realize the cross-correlation operation and integer frequency offset compensation of the received pilot code and local pilot code of OFDM signal. The symbol timing of OFDM signal can be obtained through the cross-correlation of pilot code, and the cross-correlation is sensitive to the integer frequency offset of the carrier. Therefore, the parallel FFT unit can compensate for the frequency offset of the received signal, effectively eliminating the influence of integer frequency offset on cross-correlation performance, and at the same time, integer frequency offset estimation is given.

[0006] The disadvantage of the above method is that a large number of FFT operations are required, which is difficult to implement in actual products, and it is difficult to obtain high-precision timing, because high-precision timing requires increasing the sampling rate of the signal by several or dozens of times, which in turn increases the number of FFT transformation points, resulting in a sharp increase in the amount of processing operations. Therefore, it is necessary to provide a time-frequency joint correction method and device to solve the above problems. Summary of the invention

[0007] In view of the deficiencies in the prior art, the object of the present invention is to provide a time-frequency joint correction method and device to solve the problems existing in the above-mentioned background technology.

[0008] The present invention is implemented as follows: a time-frequency joint correction method, the method comprising the following steps:

[0009] S101, receiving a time domain signal y(n), and separating a pilot from the time domain signal y(n). p (n) means: y p (n), n = 1, ..., N, P (k) is the frequency domain signal of the sent pilot;

[0010] S102, transform the receiving end time domain pilot signal into the frequency domain by using FFT transformation:

[0011] Y p (k) = FFT(y p (n)), where n = 1, ..., N, k = 1, ..., N;

[0012] S103, the received frequency domain signal is correlated with the transmitted pilot signal, and the influence of the pilot signal is removed: the N frequency points of the received frequency domain signal are correlated with the frequency points corresponding to the pilot signal respectively: H(k)=Yp (k)*conj(P(k)), where k=1,…,N;

[0013] S104, coarse timing estimation: using a preset subcarrier step size Δm, divide the H values ​​of two frequency points at which the positive and negative frequency domain numbers differ by Δm: And n1~N-Δm; then find the average value of all tg(k): Calculate the timing estimate: Δt = atan(tg_ave) × N / (2π × Δm);

[0014] S105, perform timing compensation on the pilot: compensate the opposite linear phase of all N frequency points in the FFT processing frequency domain, H_comp(k) = H(k)×e -j×2π×Δt×k / N ,where,k=1,…,N;

[0015] S106, increase the subcarrier step length Δm, and repeat steps S104-S105;

[0016] S107, fine timing estimation: Assume Δm=n1-1, and divide the H values ​​of the two frequency points with a difference of Δm in the positive and negative frequency domains:

[0017]

[0018] S108, receive signal timing recovery: transform the receive end signal y(n) into the frequency domain using FFT transformation, Y(k)=FFT(y(n)), where n=1,…,N, k=1,…,N; perform frequency domain timing compensation, Y_comp(k)=Y(k)×e -j×2π×Δt×k / N , where k = 1,…,N; the compensated frequency domain signal is transformed into the time domain for subsequent receiving and processing.

[0019] As a further solution of the present invention: when the signal is only in the positive frequency domain or the negative frequency domain, or is asymmetrically distributed in the positive and negative frequency domains, the center frequency of the signal is first moved to zero frequency through spectrum shifting, and then timing estimation is performed.

[0020] As a further solution of the present invention: when the user signal occupies M subcarriers, the subcarriers are numbered m1 to m2 in the system bandwidth. M , then the center frequency is round((m1+m M ) / 2), the zero frequency within the system bandwidth is located at M all / 2; move the center frequency of the signal to zero frequency, the required frequency offset is: f_offset = round((m1+m M ) / 2)-M all / 2, then the signal obtained after spectrum shift is: y_shift(n)=y(n)×e -j×2π×f_offset×Δf / N,n=1,…,N, Δf is the subcarrier spacing in the OFDM system; timing estimation is performed based on y_shift(n), and y_shift(n) is used instead of y(n).

[0021] As a further solution of the present invention: the number of points of the signal processing FFT is N, and the frequency domain range of the FFT processing is 1 to N, where the zero frequency is at 1, 2 to N / 2+1 are positive frequency domain numbers, and N / 2+2 to N are negative frequency domain numbers.

[0022] As a further solution of the present invention: the number of useful subcarriers within the bandwidth is M all , M all <N, subcarrier number is 1~M all , where 1~M all / 2-1 is the subcarrier number in the negative frequency domain, M all / 2 is the number of the zero frequency point, M all / 2+1~M all is the subcarrier number in the positive frequency domain; all The subcarriers are mapped to the FFT processing frequency domain: system bandwidth zero frequency M all / 2 is mapped to the position of 1 in the frequency domain of FFT processing, and the system bandwidth is in the negative frequency domain from 1 to M all / 2-1 mapped to the frequency domain NM for FFT processing all / 2+2~N, the system bandwidth is in the positive frequency domain M all / 2+1~M all Mapped to the frequency domain of FFT processing 2~M all / 2+1 position.

[0023] As a further solution of the present invention: the user signal occupies M subcarriers, which are numbered m1 to m in the system bandwidth. M , m1 is the smallest number, located in the negative frequency domain, m M The maximum number is located in the positive frequency domain, and the corresponding FFT processing frequency domain number is n1 to N in the negative frequency domain and 1 to n in the zero frequency and positive frequency domain. M .

[0024] Another object of the present invention is to provide a time-frequency joint correction device, the device comprising:

[0025] The pilot separation module is used to receive the time domain signal y(n) and separate the pilot from the time domain signal y(n). p (n) means: y p (n), n = 1, ..., N, P (k) is the frequency domain signal of the sent pilot;

[0026] Frequency domain transformation module, used to transform the receiving end time domain pilot signal into frequency domain using FFT transformation: Yp (k) = FFT(y p (n)), where n = 1, ..., N, k = 1, ..., N;

[0027] The pilot removal module is used to receive the frequency domain signal and send the pilot signal to remove the influence of the pilot: the N frequency points of the received frequency domain signal are correlated with the frequency points corresponding to the pilot signal respectively:

[0028] H(k)=Y p (k)*conj(P(k)), where k=1,…,N;

[0029] The coarse timing estimation module is used to perform coarse timing estimation: using the preset subcarrier step size Δm, the H values ​​of two frequency points with a difference of Δm in the positive and negative frequency domain numbers are divided:

[0030] And n1~N-Δm; then find the average value of all tg(k): Calculate the timing estimate: Δt = atan(tg_ave) × N / (2π × Δm);

[0031] Timing compensation module, used to make timing compensation for pilot: compensate the opposite linear phase for all N frequency points in the FFT processing frequency domain, H_comp(k) = H(k)×e -j×2π×Δt×k / N ,where,k=1,…,N;

[0032] A step size increasing module, used for increasing the subcarrier step size Δm, and repeating the steps of removing the pilot influence and performing the coarse timing estimation;

[0033] The fine timing estimation module is used to perform fine timing estimation: Assume Δm = n1-1, and divide the H values ​​of the two frequency points with a difference of Δm in the positive and negative frequency domains:

[0034] Timing recovery module, used for receiving signal timing recovery: using FFT transform to transform the receiving end signal y(n) into the frequency domain, Y(k) = FFT(y(n)), where n = 1, ..., N, k = 1, ..., N; frequency domain timing compensation, Y_comp(k) = Y(k) × e -j×2π×Δt×k / N , where k = 1,…,N; the compensated frequency domain signal is transformed into the time domain for subsequent receiving and processing.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The present invention can obtain different timing estimation ranges and accuracies by setting different subcarrier step sizes, and can obtain high-precision timing. The present invention proposes a joint frequency offset and timing estimation scheme for signals with integer frequency offsets, which can accurately estimate the timing while obtaining integer frequency offset estimation through frequency domain processing; compared with existing methods, it uses very little computation and can obtain very high-precision timing and frequency offset estimation. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Flowchart of a time-frequency joint correction method.

[0038] Figure 2 A schematic diagram of FFT processing in the frequency domain in a time-frequency joint correction method.

[0039] Figure 3 A schematic diagram of subcarrier mapping to the FFT processing frequency domain in a time-frequency joint correction method.

[0040] Figure 4 The figure is a flow chart of a scheme for jointly estimating integer frequency offset and timing.

[0041] Figure 5 The figure is a schematic diagram of the structure of a time-frequency joint correction device. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0043] The specific implementation of the present invention is described in detail below in conjunction with specific embodiments.

[0044] like Figures 1 to 3 As shown, an embodiment of the present invention provides a time-frequency joint correction method, which is based on the principle that the time domain shift of the sequence corresponds to the phase rotation in the frequency domain. For a finite sequence x(n), 0≤n≤N-1, X(k) is the discrete Fourier transform of x(n): X(k)=DFT[x(n)]. If x m (n) = x((n+m)) N R N (n), where x((n+m)) N Represents x n The shift of the periodic extension sequence is multiplied by R N (n) represents the main value sequence of the periodic sequence after the extension sequence is shifted, so x m (n) is also a finite length sequence of N points. m The discrete Fourier transform of (n) is Xm (k), then in, Therefore, the shift m can be obtained based on the phase difference between frequency points k1 and k2. The formula for calculating the shift m is: m=atan(Δ) / (2π×(k2-k1) / N), where atan(·) represents a phase calculation operation.

[0045] In the embodiment of the present invention, the number of points of the signal processing FFT is assumed to be N, that is, the frequency domain range of the FFT processing is 1 to N, where the zero frequency is located at 1, 2 to N / 2+1 are positive frequency domain numbers, and N / 2+2 to N are negative frequency domain numbers. The number of useful subcarriers within the system bandwidth is M all , M all <N, subcarrier number is 1~M all , where 1~M all / 2-1 is the subcarrier number in the negative frequency domain, M all / 2 is the number of the zero frequency point, M all / 2+1~M all is the subcarrier number in the positive frequency domain; all The subcarriers are mapped to the FFT processing frequency domain (1 to N) with: system bandwidth zero frequency M all / 2 is mapped to the position of 1 in the frequency domain of FFT processing, and the system bandwidth is in the negative frequency domain from 1 to M all / 2-1 mapped to the frequency domain NM for FFT processing all / 2+2~N, the system bandwidth is in the positive frequency domain M all / 2+1~M all Mapped to the frequency domain of FFT processing 2~M all / 2+1. Assume that the subcarrier number of a subcarrier i in the system bandwidth is m i , the corresponding FFT processing frequency domain number is n i ,but:

[0046]

[0047] In the embodiment of the present invention, the user signal occupies M subcarriers, which are numbered m1 to m2 in the system bandwidth. M , m1 is the smallest number, located in the negative frequency domain, m M The maximum number is located in the positive frequency domain, and the corresponding FFT processing frequency domain number is n1 to N in the negative frequency domain and 1 to n in the zero frequency and positive frequency domain. M The method comprises the following steps:

[0048] S101, receiving a time domain signal y(n), and separating a pilot from the time domain signal y(n). p (n) means: y p(n), n = 1, ..., N, P (k) is the frequency domain signal of the sent pilot;

[0049] S102, transform the receiving end time domain pilot signal into the frequency domain by using FFT transformation:

[0050] Y p (k) = FFT(y p (n)), where n = 1, ..., N, k = 1, ..., N;

[0051] S103, the received frequency domain signal is correlated with the transmitted pilot signal, and the influence of the pilot signal is removed: the N frequency points of the received frequency domain signal are correlated with the frequency points corresponding to the pilot signal respectively: H(k)=Y p (k)*conj(P(k)), where k=1,…,N. The phase of the pilot itself is not a concern. Through the correlation operation, the influence of the pilot phase itself is removed, and the influence of the time-frequency offset is retained;

[0052] S104, coarse timing estimation: using a preset subcarrier step size Δm, divide the H values ​​of two frequency points at which the positive and negative frequency domain numbers differ by Δm: And n1~N-Δm; then find the average value of all tg(k): The timing estimate is obtained using the formula for calculating the shift m:

[0053] Δt=atan(tg_ave)×N / (2π×Δm), the two frequency points to be divided must be the frequency points where the user signal is located;

[0054] S105, perform timing compensation on the pilot: compensate the opposite linear phase of all N frequency points in the FFT processing frequency domain, H_comp(k) = H(k)×e -j×2π×Δt×k / N , where k = 1, ..., N. Here we introduce the frequency domain compensation algorithm. The timing offset in the frequency domain can be regarded as adding a linear phase e j×2π×Δt×k / N ;

[0055] S106, increase the subcarrier step size Δm, and repeat steps S104-S105, because the larger the subcarrier step size is set, the higher the estimated timing accuracy is, but the smaller the range is; the smaller the subcarrier step size is set, the larger the estimated timing range is, but the lower the accuracy is. Therefore, in order to take into account both the estimation range and accuracy, multiple estimates are required, and the subcarrier step size is increased from small to large. The specific Δm and the number of estimates need to be determined based on the actual system bandwidth, the subcarrier occupancy of the user signal and other factors;

[0056] S107, fine timing estimation: The subcarrier step size used in the above steps is limited to the positive frequency domain or the negative frequency domain, and the estimation accuracy is limited. In order to further improve the estimation accuracy, the phase of the positive frequency domain and the negative frequency domain can be considered jointly, and Δm=n1-1 can be set, and the H values ​​of the two frequency points with a difference of Δm in the positive and negative frequency domains are divided:

[0057] The remaining steps are the same as steps S102-S103, where Δm can also be set to other values, as long as it can ensure that the two H values ​​to be divided are located in the positive and negative frequency domains respectively;

[0058] S108, received signal timing recovery: Each time a timing estimate is obtained in the above steps, the entire received signal y(n) or the data part of y(n) can be compensated once, or all the results of the timing estimates can be accumulated and compensated uniformly. The specific compensation method can be performed in the time domain (existing technology) or in the frequency domain. Assuming that the timing deviation to be compensated is Δt, the frequency domain compensation method is: use FFT transformation to transform the receiving end signal y(n) to the frequency domain, Y(k) = FFT(y(n)), where n = 1, ..., N, k = 1, ..., N; frequency domain timing compensation,

[0059] Y_comp(k)=Y(k)×e -j×2π×Δt×k / N , where k = 1,…,N; the compensated frequency domain signal is transformed into the time domain for subsequent receiving and processing.

[0060] In the embodiment of the present invention, a scheme for optimizing the estimation of spectrally asymmetric signals is also provided: if the signal is in both the positive and negative frequency domains, the phases of the positive and negative frequency domains can be considered jointly, that is, Δm can be set very large, thereby greatly improving the accuracy; on the other hand, if the number of subcarriers in the positive and negative frequency domains is equivalent, then almost all H values ​​can be used to calculate the phase deviation, which can also improve the anti-noise performance. Therefore, when the signal is only in the positive or negative frequency domain, or when the positive and negative frequency domains are asymmetrically distributed, the center frequency of the signal is first moved to zero frequency through spectrum shifting, and then timing estimation is performed. Assume that the user signal occupies M subcarriers, numbered m1 to m in the system bandwidth. M , then the center frequency is round((m1+m M ) / 2), if (m1+m M ) / 2 is not an integer and can be rounded up, down or to the nearest integer, represented by round(·). The zero frequency within the system bandwidth is located at M all / 2; move the center frequency of the signal to zero frequency, the required frequency offset is: f_offset = round((m1+m M ) / 2)-M all / 2, then the signal obtained after spectrum shift is: y_shift(n)=y(n)×e -j×2π×f_offset×Δf / N ,n=1,…,N, Δf is the subcarrier spacing in the OFDM system, for example, Δf=15kHZ in the LTE system; then, timing estimation is performed based on y_shift(n), and a high-precision time offset estimation of the spectrum asymmetric signal can be obtained. y_shift(n) is used instead of y(n) in S101, and then starting from step S101 to step S108, it is the same as the above method.

[0061] like Figure 4 As shown, in the embodiment of the present invention, a scheme for jointly estimating integer frequency offset and timing is also provided: Further, if the received signal has integer frequency offset, the general method is to estimate the timing only after the integer frequency offset is estimated and compensated. Here, a scheme for estimating the timing without the integer frequency offset is proposed, which can effectively reduce the amount of calculation. The specific method is as follows:

[0062] S201, receiving a time domain signal y(n), and separating a pilot from the time domain signal y(n). p (n) means: y p (n), n = 1, ..., N, P (k) is the frequency domain signal of the sent pilot;

[0063] S202, transform the receiving end time domain pilot signal into the frequency domain by using FFT transformation:

[0064] Y p (k) = FFT(y p (n)), where n = 1, ..., N, k = 1, ..., N;

[0065] S203, directly estimating the integer frequency offset ΔF on the frequency spectrum (this is the prior art);

[0066] S204, recalculate the subcarriers occupied by the signal according to the integer frequency offset. The original user signal occupies M subcarriers, which are numbered m1 to m in the system bandwidth. M , after integer frequency offset, the subcarrier where the received signal is located becomes:

[0067] m1+ΔF~m M +ΔF;

[0068] S205, performing timing estimation in the frequency domain using the previous method;

[0069] S206, performing timing recovery on the entire received signal y(n) or the data portion of y(n) using the previous method;

[0070] S207, integer frequency offset compensation (existing technology).

[0071] In the embodiment of the present invention, the method for estimating timing based on the phase in the frequency domain obtains different timing estimation ranges and accuracies by setting different subcarrier step sizes; the method for estimating the phase deviation of the positive and negative frequency domains of the joint signal to obtain high-precision timing; the timing optimization method for the asymmetric distribution of the signal in the positive and negative frequency domains, that is, the center frequency of the signal is moved to zero frequency by spectrum shifting, and then the timing estimation is performed. For the frequency deviation and timing joint estimation scheme of the signal with integer frequency deviation, after estimating the integer frequency deviation in the frequency domain, the subcarrier where the signal is located is recalculated, and the phase difference of these subcarriers is used to obtain the timing estimate.

[0072] like Figure 5 As shown, the embodiment of the present invention further provides a time-frequency joint correction device, the device comprising:

[0073] The pilot separation module 100 is used to receive the time domain signal y(n) and separate the pilot from the time domain signal y(n). p (n) means: y p (n), n = 1, ..., N, P (k) is the frequency domain signal of the sent pilot;

[0074] The frequency domain transformation module 200 is used to transform the receiving end time domain pilot signal into the frequency domain by using FFT transformation: p (k) = FFT(y p (n)), where n = 1, ..., N, k = 1, ..., N;

[0075] The pilot removal module 300 is used to receive the frequency domain signal related to the sent pilot signal and remove the influence of the pilot: N frequency points of the received frequency domain signal are respectively related to the frequency points corresponding to the pilot signal:

[0076] H(k)=Y p (k)*conj(P(k)), where k=1,…,N;

[0077] The coarse timing estimation module 400 is used to perform coarse timing estimation: using a preset subcarrier step size Δm, the H values ​​of two frequency points at which the positive and negative frequency domain numbers differ by Δm are divided:

[0078] And n1~N-Δm; then find the average value of all tg(k): Calculate the timing estimate: Δt = atan(tg_ave) × N / (2π × Δm);

[0079] The timing compensation module 500 is used to perform timing compensation on the pilot: compensate the opposite linear phase of all N frequency points in the FFT processing frequency domain, H_comp(k) = H(k)×e -j×2π×Δt×k / N,where,k=1,…,N;

[0080] A step size increasing module 600 is used to increase the subcarrier step size Δm and repeat the steps of removing the pilot influence and performing coarse timing estimation;

[0081] The fine timing estimation module 700 is used to perform fine timing estimation: assuming Δm=n1-1, divide the H values ​​of two frequency points at a difference of Δm in the positive and negative frequency domains:

[0082] The timing recovery module 800 is used for receiving signal timing recovery: using FFT transformation to transform the receiving end signal y(n) into the frequency domain, Y(k) = FFT(y(n)), where n = 1, ..., N, k = 1, ..., N; frequency domain timing compensation, Y_comp(k) = Y(k) × e -j×2π×Δt×k / N , where k = 1,…,N; the compensated frequency domain signal is transformed into the time domain for subsequent receiving and processing.

[0083] The above only describes in detail the preferred embodiments of the present invention, which is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

[0084] It should be understood that, although each step in the flow chart of each embodiment of the present invention is shown in sequence according to the indication of the arrow, these steps are not necessarily performed in sequence according to the order indicated by the arrow. Unless there is a clear explanation in this article, the execution of these steps does not have a strict order restriction, and these steps can be performed in other orders. Moreover, at least a portion of the steps in each embodiment may include a plurality of sub-steps or a plurality of stages, and these sub-steps or stages are not necessarily performed at the same time, but can be performed at different times, and the execution order of these sub-steps or stages is not necessarily performed in sequence, but can be performed in turn or alternately with at least a portion of other steps or sub-steps or stages of other steps.

[0085] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the program can be stored in a non-volatile computer-readable storage medium. When the program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, storage, database or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory may include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM) or flash memory. Volatile memory may include random access memory (RAM) or external cache memory. As an illustration and not limitation, RAM is available in many forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link (Synchlink) DRAM (SLDRAM), memory bus (Rambus) direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM).

[0086] Those skilled in the art will readily appreciate other embodiments of the present disclosure after considering the disclosure in the specification and examples. This application is intended to cover any variations, uses or adaptations of the present disclosure, which follow the general principles of the present disclosure and include common knowledge or customary techniques in the art that are not disclosed in the present disclosure. The specification and examples are intended to be exemplary only, and the true scope and spirit of the present disclosure are indicated by the claims.

Claims

1. A time-frequency joint correction method, characterized in that: The method comprises the following steps: S101, receiving a time domain signal y(n), and separating a pilot from the time domain signal y(n). p (n) means: y p (n), n = 1, ..., N, P (k) is the frequency domain signal of the sent pilot; S102, transform the receiving end time domain pilot signal into the frequency domain by using FFT transformation: Y p y(k) = FFT(y p (n)), where n = 1, …, N, k = 1, …, N; S103, the received frequency domain signal is correlated with the transmitted pilot signal, and the influence of the pilot signal is removed: the N frequency points of the received frequency domain signal are correlated with the frequency points corresponding to the pilot signal respectively: H(k)=Y p (k)*conj(P(k)), where k=1,…,N; S104, coarse timing estimation: using a preset subcarrier step size Δm, divide the H values ​​of two frequency points at which the positive and negative frequency domain numbers differ by Δm: And n1~N-Δm; then find the average value of all tg(k): Calculate the timing estimate: Δt = atan(tg_ave) × N / (2π × Δm); S105, perform timing compensation on the pilot: compensate the opposite linear phase for all N frequency points in the FFT processing frequency domain, H_comp(k)=H(k)×e -j×2π×Δt×k / N ,where,k=1,…,N; S106, increase the subcarrier step length Δm, and repeat steps S104-S105; S107, fine timing estimation: Assume Δm=n1-1, and divide the H values ​​of the two frequency points with a difference of Δm in the positive and negative frequency domains: S108, receive signal timing recovery: transform the receive end signal y(n) into the frequency domain using FFT transformation, Y(k)=FFT(y(n)), where n=1,…,N, k=1,…,N; frequency domain timing compensation, Y_comp(k)=Y(k)×e -j×2π×Δt×k / N , where k = 1,…,N; the compensated frequency domain signal is transformed into the time domain for subsequent receiving and processing.

2. The time-frequency joint correction method according to claim 1, characterized in that: When the signal is only in the positive frequency domain or the negative frequency domain, or is asymmetrically distributed in the positive and negative frequency domains, the center frequency of the signal is first moved to zero frequency through spectrum shifting, and then timing estimation is performed.

3. The time-frequency joint correction method according to claim 2, characterized in that: When the user signal occupies M subcarriers, the subcarriers are numbered from m1 to m within the system bandwidth. M , then the center frequency is round((m1+m M ) / 2), the zero frequency within the system bandwidth is located at M all / 2; move the center frequency of the signal to zero frequency, the required frequency offset is: f_offset = round((m1+m M ) / 2)-M all / 2, then the signal obtained after spectrum shift is: y_shift(n)=y(n)×e -j×2π×f_offset×Δf / N ,n=1,…,N, Δf is the subcarrier spacing in the OFDM system; timing estimation is performed based on y_shift(n), and y_shift(n) is used instead of y(n).

4. The time-frequency joint correction method according to claim 1, characterized in that: The number of points of signal processing FFT is N, and the frequency domain range of FFT processing is 1 to N, where the zero frequency is at 1, 2 to N / 2+1 are positive frequency domain numbers, and N / 2+2 to N are negative frequency domain numbers.

5. The time-frequency joint correction method according to claim 4, characterized in that: The number of useful subcarriers within the bandwidth is M all , M all <N, subcarrier number is 1~M all , where 1~M all / 2-1 is the subcarrier number in the negative frequency domain, M all / 2 is the number of the zero frequency point, M all / 2+1~M all is the subcarrier number in the positive frequency domain; all The subcarriers are mapped to the FFT processing frequency domain: system bandwidth zero frequency M all / 2 is mapped to the position of 1 in the frequency domain of FFT processing, and the system bandwidth is in the negative frequency domain from 1 to M all / 2-1 mapped to the frequency domain NM for FFT processing all / 2+2~N, the system bandwidth is in the positive frequency domain M all / 2+1~M all Mapped to the frequency domain of FFT processing 2~M all / 2+1 position.

6. The time-frequency joint correction method according to claim 5, characterized in that: The user signal occupies M subcarriers, which are numbered from m1 to m within the system bandwidth. M , m1 is the smallest number, located in the negative frequency domain, m M The maximum number is in the positive frequency domain, and the corresponding FFT processing frequency domain number is n1 to N in the negative frequency domain and 1 to n in the zero frequency and positive frequency domain. M .

7. A time-frequency joint correction method, characterized in that: The method comprises the following steps: S201, receiving a time domain signal y(n), and separating a pilot from the time domain signal y(n). p (n) means: y p (n), n = 1, ..., N, P (k) is the frequency domain signal of the sent pilot; S202, transform the receiving end time domain pilot signal into the frequency domain by using FFT transformation: Y p y(k) = FFT(y p (n)), where n = 1, …, N, k = 1, …, N; S203, directly estimating the integer frequency offset ΔF on the frequency spectrum; S204, recalculate the subcarriers occupied by the signal according to the integer frequency offset. The original user signal occupies M subcarriers, which are numbered m1 to m in the system bandwidth. M , after integer frequency offset, the subcarrier where the received signal is located becomes: m1+ΔF~m M +ΔF; S205, performing timing estimation in the frequency domain; S206, performing timing recovery on the entire received signal y(n) or the data portion of y(n); S207, integer frequency offset compensation.

8. A time-frequency joint correction device, characterized in that: The device comprises: The pilot separation module is used to receive the time domain signal y(n) and separate the pilot from the time domain signal y(n). p (n) means: y p (n), n = 1, ..., N, P (k) is the frequency domain signal of the sent pilot; The frequency domain transformation module is used to transform the receiving end time domain pilot signal into the frequency domain using FFT transformation: Y p y(k) = FFT(y p (n)), where n = 1, …, N, k = 1, …, N; The pilot removal module is used to receive the frequency domain signal and send the pilot signal to remove the influence of the pilot: the N frequency points of the received frequency domain signal are correlated with the frequency points corresponding to the pilot signal respectively: H(k)=Y p (k)*conj(P(k)), where k=1,…,N; The coarse timing estimation module is used to perform coarse timing estimation: using the preset subcarrier step size Δm, the H values ​​of two frequency points with a difference of Δm in the positive and negative frequency domain numbers are divided: And n1~N-Δm; then find the average value of all tg(k): Calculate the timing estimate: Δt = atan(tg_ave) × N / (2π × Δm); Timing compensation module, used to make timing compensation for pilot: compensate the opposite linear phase for all N frequency points in the FFT processing frequency domain, H_comp(k) = H(k)×e -j×2π×Δt×k / N ,where,k=1,…,N; A step size increasing module, used for increasing the subcarrier step size Δm, and repeating the steps of removing the pilot influence and performing the coarse timing estimation; The fine timing estimation module is used to perform fine timing estimation: Assume Δm = n1-1, and divide the H values ​​of the two frequency points with a difference of Δm in the positive and negative frequency domains: Timing recovery module, used for receiving signal timing recovery: using FFT transform to transform the receiving end signal y(n) into the frequency domain, Y(k) = FFT(y(n)), where n = 1, ..., N, k = 1, ..., N; frequency domain timing compensation, Y_comp(k) = Y(k) × e -j×2π×Δt×k / N , where k = 1,…,N; the compensated frequency domain signal is transformed into the time domain for subsequent receiving and processing.

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