A high-precision frequency offset estimation method and device

Abstract

The application provides a high-precision frequency offset estimation method and device, which receives a data frame sequence at a current time, the data frame sequence comprises a plurality of continuous data frames, each data frame comprises a preamble sequence and a plurality of data, and each preamble sequence comprises a plurality of sub-sequences; coarse estimation is performed on the preamble sequence in a first frequency offset range to obtain a coarse frequency offset; coarse frequency offset compensation is performed on each preamble sequence by using the coarse frequency offset to obtain a coarse-compensated preamble sequence; fine estimation is performed on the coarse-compensated preamble sequence in a second frequency offset range to obtain a fine frequency offset; fine frequency offset compensation is performed on each coarse-compensated preamble sequence by using the fine frequency offset to obtain a fine-compensated preamble sequence. The application jointly estimates several adjacent preambles, adopts a phased approximation in the joint estimation process, first compresses the possible frequency offset, and then adjusts the autocorrelation interval and accumulates the autocorrelation of adjacent preambles, so that the estimation precision is improved under the premise of ensuring the frequency offset estimation range.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of signal detection, and particularly relates to a high-precision frequency offset estimation method and device. BACKGROUND

[0002] The frequency offset is the sum of the crystal oscillator frequency offset and the Doppler frequency offset: f offset = f LO + f Doppler The crystal oscillator frequency offset f LO is considered constant in a short time, and is determined by the crystal oscillator stability e PPM and the carrier frequency f c , that is, f LO = f c · e PPM . The frequency offset causes the constellation diagram to rotate and produce a decision error, so effective frequency offset compensation of the received signal is a prerequisite for reliable reception.

[0003] The preamble structure is shown in Figure Figure 1 , which is composed of two identical sequences (Seq) and a cyclic prefix (CP, Cycle Prefix). The length of the preamble sequence is not more than the coherence time of the wireless channel, and the channel experiences a single quasi-static time-domain fading. After the preamble sequence experiences the quasi-static channel, the preamble structure is still maintained, so it has good estimation performance under the condition that the quasi-static assumption is established. The existing frequency offset estimation algorithm first performs frequency offset blind compensation. If the compensation direction is correct and the compensation value is large enough, the existing technical solution can be used to compensate the residual frequency offset. The disadvantage of this method is that the possibility of one-step success is low, and multiple attempts are required, and the number of attempts is uncertain, so the algorithm time delay fluctuates greatly. The existing frequency offset estimation algorithm is represented as:

[0004]

[0005] Where f s represents the sampling rate, L is the preamble sequence length, T is the preamble interval, and s(m), m=0, 1,..., L-1 represents the nth preamble sequence.

[0006] Therefore, the existing frequency offset estimation algorithm has low estimation accuracy in complex scenarios such as low preamble overhead, low signal-to-noise ratio, and high-speed movement, which leads to a significant decline in system performance. SUMMARY

[0007] In order to solve the above problems existing in the prior art, the application provides a high-precision frequency offset estimation method and device. The technical problems to be solved by the application are solved by the following technical solutions:

[0008] The application provides a high-precision frequency offset estimation method, which comprises:

[0009] S100, receiving a data frame sequence at a current time, the data frame sequence comprising a plurality of continuous data frames, each data frame comprising a preamble sequence and a plurality of data, each preamble sequence comprising a plurality of sub-sequences;

[0010] S200, performing coarse estimation on the preamble sequence within the first frequency offset range to obtain a coarse frequency offset;

[0011] S300, performing coarse frequency offset compensation on each preamble sequence by using the coarse frequency offset to obtain a coarse-compensated preamble sequence;

[0012] S400, performing fine estimation on the coarse-compensated preamble sequence within the second frequency offset range to obtain a fine frequency offset;

[0013] The first frequency offset range is smaller than the second frequency offset range.

[0014] S500, performing fine frequency offset compensation on each coarse-compensated preamble sequence by using the fine frequency offset to obtain a fine-compensated preamble sequence.

[0015] Beneficial effects:

[0016] The application provides a high-precision frequency offset estimation method and device, which comprises the following steps: receiving a data frame sequence at a current time, the data frame sequence comprising a plurality of continuous data frames, each data frame comprising a preamble sequence and a plurality of data, each preamble sequence comprising a plurality of sub-sequences; performing coarse estimation on the preamble sequence within the first frequency offset range to obtain a coarse frequency offset; performing coarse frequency offset compensation on each preamble sequence by using the coarse frequency offset to obtain a coarse-compensated preamble sequence; performing fine estimation on the coarse-compensated preamble sequence within the second frequency offset range to obtain a fine frequency offset; and performing fine frequency offset compensation on each coarse-compensated preamble sequence by using the fine frequency offset to obtain a fine-compensated preamble sequence. The application jointly estimates a plurality of adjacent preambles, adopts a phased approximation in the joint estimation process, first compresses the possible frequency offset, and then adjusts the autocorrelation interval and accumulates the autocorrelation of adjacent preambles, thereby improving the estimation precision under the premise of ensuring the frequency offset estimation range.

[0017] The application will be further described in detail below with reference to the drawings and embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a preamble structure diagram disclosed by the prior art;

[0019] Figure 2 is a data frame structure diagram provided by the application;

[0020] Figure 3 is a preamble structure detail diagram provided by the application;

[0021] Figure 4is a flowchart of a high-precision frequency offset estimation method provided by the present application.

[0022] Figure 5 is a trend chart of the frequency offset estimation precision with the number of preambles. DETAILED DESCRIPTION

[0023] The present application will be further described in detail below with specific examples, but the embodiments of the present application are not limited thereto.

[0024] In combination Figures 2 to 5 , the present application provides a high-precision frequency offset estimation method comprising:

[0025] S100, receiving a data frame sequence at a current time, the data frame sequence comprising a plurality of continuous data frames, each data frame comprising a preamble sequence and a plurality of data, and each preamble sequence comprising a plurality of sub-sequences;

[0026] The present application determines a first frequency offset range for coarse estimation and a second frequency offset range for fine estimation according to the number of preamble sequences in the data frame sequence.

[0027] Reference Figure 2 and Figure 3 , the present application is applicable to preambles with multi-segment repetition structure characteristics, such as Figure 3 , which is composed of a cyclic prefix (CP) and Q identical sub-sequences. If the length of such a preamble sequence is N, denoted as {s(n), n=0, 1,..., N}, then:

[0028] s(n)=s(n+D i ), n=0, 1,..., N-D i (1);

[0029] wherein , parameters i and Q are both configurable positive integers, satisfying: 2≤Q≤N, 1≤i<Q.

[0030] The present application uses a plurality of consecutive preambles for frequency offset estimation, and it is necessary to introduce subscript k to label the preambles. The kth transmitted preamble sequence is denoted as {s k (n), n=0, 1,..., N-1}, so formula (1) can be expressed as

[0031] s k (n)=s k (n+D i ), n=0, 1,..., N-D i (2);

[0032] To facilitate the understanding of how such preamble performs the coarse frequency offset estimation, the received preamble sequence can be expressed as

[0033]

[0034] where f err represents the frequency offset, with unit of Hertz (Hz); represents the initial phase, with unit of radian (rad), T s represents the sampling interval, with unit of second (s); w(n) is the Gaussian white noise. According to (2) and (3), the autocorrelation function of the 1st received preamble with interval D i can be expressed as

[0035]

[0036] If (4) satisfies two conditions:

[0037] ① the useful signal term is much larger than the noise term w′,

[0038] ② |2πf err D i T s |≤π, i.e.

[0039] then the frequency offset estimation value can be uniquely solved as where |·| represents the absolute value and arg{.} represents the phase angle operation.

[0040] Condition ① indicates that increasing the energy of the useful signal term helps to improve the estimation accuracy, thus the latest K autocorrelation functions with interval D i are accumulated, i.e.

[0041]

[0042]

[0043]

[0044] where K is a configurable positive integer, and particularly, K=1, Γ1(i)=γ1(i). The initial value of index p in (6) is expressed as max{k-K+1,1} instead of k-K to adapt to the special case that the number of received preambles is less than K. It is worth mentioning that the K noise terms are added, which does not mean that the noise increases linearly, and in fact, the mean of the noise is still zero. It is not difficult to verify that the calculation amount can be reduced by using the following recursive formula to calculate (6).

[0045] Γ k+1 (i)=Γ k ​(i) - γ max{k-D+1,1} (i) + γ k+1 (i), k≥1 (7);

[0046] Accordingly, the frequency offset estimation formula is given by formula (6)

[0047]

[0048] where D i The value has a significant impact on the performance of the frequency offset estimation. If D i is too large, the frequency offset estimation range is small according to condition ②, and the preamble sequence used is short, and the energy of the useful signal term is insufficient; if D i is too small, the phase difference caused by the frequency offset is too small, which is easily submerged by noise, and the estimation accuracy is not high. In summary, the value of D i is selected according to the size of the frequency offset. Qualitatively, when the frequency offset range is large, a smaller D i is selected, and when the frequency offset range is small, a larger D i is selected.

[0049] In reality, the specific size of the frequency offset is unknown, and can be performed in two steps. The first step covers a large frequency offset range by using a smaller D i , and the second step improves the estimation accuracy by increasing D i to obtain a larger phase difference. Because increasing D i causes the available preamble sequence to be shortened, thereby causing the problem of insufficient energy of the useful signal term, this problem can be improved by combining multiple adjacent preambles, and the processing flow is shown in Figure 4 .

[0050] S200, coarse estimation is performed on the preamble sequence in the first frequency offset range to obtain a coarse frequency offset

[0051] This step uses the frequency offset estimation formula to perform coarse estimation on the preamble sequence in the first frequency offset range to obtain a coarse frequency offset.

[0052] S300, using the coarse frequency offset, coarse frequency offset compensation is performed on each preamble sequence to obtain a coarse compensation preamble sequence

[0053] This step substitutes the coarse frequency offset into the frequency offset compensation formula, and performs coarse frequency offset compensation on each preamble sequence using the frequency offset compensation formula to obtain a coarse compensation preamble sequence.

[0054] S400, fine estimation is performed on the coarse compensation preamble sequence in the second frequency offset range to obtain a fine frequency offset

[0055] Referring to Figure 4 , this step uses the frequency offset estimation formula Fine frequency offset is obtained by fine estimation on the preamble sequence after coarse compensation and within the second frequency offset range.

[0056] The first frequency offset range is smaller than the second frequency offset range; the first frequency offset range is a range from the first preamble sequence to a preamble sequence with a first preset number; and the second frequency offset range is a range from the first preamble sequence to a preamble sequence with a second preset number.

[0057] S500, fine frequency compensation is performed on each preamble sequence after coarse compensation by using the fine frequency offset to obtain a fine-compensated preamble sequence.

[0058] Reference Figure 4 The fine frequency offset is substituted into the frequency offset compensation formula and fine frequency compensation is performed on each preamble sequence by using the frequency offset compensation formula to obtain a fine-compensated preamble sequence.

[0059] The estimation method of the present application has a long correlation time at a low moving speed, so that the estimation accuracy can be improved by increasing the length of the preamble. Although the transmission efficiency is reduced due to the increased overhead of the preamble, the accuracy can be greatly improved with time.

[0060] The present application provides a high-precision frequency offset estimation device for performing the following steps:

[0061] S100, a data frame sequence is received at a current time, the data frame sequence includes a plurality of continuous data frames, each data frame includes a preamble sequence and a plurality of data, and each preamble sequence includes a plurality of sub-sequences;

[0062] S200, coarse frequency offset is obtained by coarse estimation on the preamble sequence within the first frequency offset range;

[0063] S300, coarse frequency compensation is performed on each preamble sequence by using the coarse frequency offset to obtain a coarse-compensated preamble sequence;

[0064] S400, fine frequency offset is obtained by fine estimation on the preamble sequence after coarse compensation and within the second frequency offset range;

[0065] The first frequency offset range is smaller than the second frequency offset range;

[0066] S500, fine frequency compensation is performed on each preamble sequence after coarse compensation by using the fine frequency offset to obtain a fine-compensated preamble sequence.

[0067] The device of the present application has the same implementation process as the method, which will not be described here.

[0068] The estimation effect of the application is illustrated by simulation analysis with given parameters.

[0069] The parameters used in this example are: EPA channel model, SNR=0dB, OFDM system, N=512, Q=4, D i =2, K=1~100.

[0070] The trend of the frequency offset estimation accuracy with the number of pilots is shown in Figure 4 When the number of joint pilots is greater than 32, the residual frequency offset of the application is not more than 20Hz.

[0071] The application provides a high-precision frequency offset estimation method and device. The method comprises the following steps: receiving a data frame sequence at a current time, the data frame sequence comprising a plurality of continuous data frames, each data frame comprising a pilot sequence and a plurality of data, and each pilot sequence comprising a plurality of sub-sequences; performing coarse estimation on the pilot sequence in a first frequency offset range to obtain a coarse frequency offset; performing coarse frequency offset compensation on each pilot sequence by using the coarse frequency offset to obtain a pilot sequence after coarse compensation; performing fine estimation on the pilot sequence after coarse compensation and in a second frequency offset range to obtain a fine frequency offset; and performing fine frequency offset compensation on each pilot sequence after coarse compensation by using the fine frequency offset to obtain a pilot sequence after fine compensation. The application performs joint estimation on a plurality of adjacent pilots, adopts a phased approximation in the joint estimation process, first reduces the possible frequency offset, and then adjusts the autocorrelation interval and accumulates the autocorrelation of adjacent pilots, thereby improving the estimation accuracy under the premise of ensuring the frequency offset estimation range.

[0072] In addition, the terms "first", "second", "third", "fourth", "fifth", "sixth", "seventh" and "eighth" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first", "second", "third", "fourth", "fifth", "sixth", "seventh" and "eighth" can explicitly or implicitly include one or more of the features. In the description of the application, the meaning of "a plurality of" is two or more, unless otherwise explicitly specified.

[0073] Although the application is described herein in conjunction with various embodiments, other variations of the disclosed embodiments can be understood and implemented by those skilled in the art with reference to the attached drawings, disclosure, and appended claims in the process of implementing the claimed application. In the claims, the word "comprising" does not exclude other components or steps, and "a" or "one" does not exclude a plurality.

[0074] The above is a further detailed description of the application in conjunction with specific preferred embodiments, and the specific implementation of the application cannot be limited to these descriptions. For those skilled in the art to which the application belongs, without departing from the concept of the application, a number of simple deductions or substitutions can be made, which should be regarded as falling within the protection scope of the application.

Claims

1. A high-precision frequency offset estimation method, characterized in that: include: S100, receiving a data frame sequence at the current moment, wherein the data frame sequence includes a plurality of consecutive data frames, each data frame includes a preamble sequence and a plurality of data, and each preamble sequence includes a plurality of subsequences; the number of preamble sequences included in the data frame sequence is K, and if the length of each preamble sequence is N, the preamble sequence is recorded as {s(n), n = 0, 1, ..., N}, then s(n)=s(n+D i ),n=0,1,...,N-D i ; The kth transmitted preamble sequence is represented as {s k (n), n=0,1,...,N-1}, then the leading sequence is expressed as: s k (n)=s k (n+D i ),n=0,1,...,N-D i ; in, Parameters i and Q are both configurable positive integers, satisfying: 2≤Q≤N, 1≤i <Q; The received preamble sequence only considers the effects of frequency offset, initial phase and noise, and is expressed as: Among them, f err Indicates frequency deviation, represents the initial phase, T s represents the sampling interval, w(n) is Gaussian white noise; The first received preamble begins with D i The autocorrelation function of the interval can be expressed as The latest K received preambles are i The autocorrelation function of the interval is expressed as: S200, performing a coarse estimation on a preamble sequence within a first frequency offset range to obtain a coarse frequency offset; S200 includes: using the frequency deviation estimation formula A coarse frequency offset is obtained by roughly estimating the preamble sequence within the first frequency offset range. Indicates the offset frequency, T s represents the sampling interval, γ p (i) indicates the latest p received preambles with D i is the autocorrelation function of the interval, the initial value of the index p is expressed as max{k-K+1,1}, K is a configurable positive integer, |·| means taking the absolute value, and arg{.} means taking the phase angle operation; S300, using the coarse offset frequency to perform coarse offset compensation on each preamble sequence to obtain a coarsely compensated preamble sequence; S300 includes: substituting the coarse offset frequency into the offset frequency compensation formula And use the frequency offset compensation formula to perform frequency offset coarse compensation on each leading sequence to obtain the coarse compensated leading sequence r k (n) represents the preamble sequence before coarse frequency offset compensation; S400, performing fine estimation on the preamble sequence after coarse compensation and within the second frequency offset range to obtain a fine frequency offset; S400 includes: using the frequency offset estimation formula A fine frequency offset is obtained by performing a fine estimation on the preamble sequence after coarse compensation and within the second frequency offset range. The first frequency offset range is smaller than the second frequency offset range; the first frequency offset range is a range formed by counting from the first preamble sequence until the number of preamble sequences reaches a first preset number; the second frequency offset range is a range formed by counting from the first preamble sequence until the number of preamble sequences reaches a second preset number; S500, using the fine frequency offset to perform fine frequency offset compensation on each coarsely compensated preamble sequence to obtain a finely compensated preamble sequence; S500 includes: substituting the fine frequency offset into the frequency offset compensation formula The frequency offset compensation formula is used to perform fine frequency offset compensation on each preamble sequence to obtain a finely compensated preamble sequence.

2. The high-precision frequency offset estimation method according to claim 1, wherein: Before S200, the high-precision frequency offset estimation method further includes: A coarsely estimated first frequency offset range and a finely estimated second frequency offset range are determined according to the number of preamble sequences in the data frame sequence.

3. A high-precision frequency offset estimation device, characterized in that: Used to perform the following steps: S100, receiving a data frame sequence at the current moment, wherein the data frame sequence includes a plurality of consecutive data frames, each data frame includes a preamble sequence and a plurality of data, and each preamble sequence includes a plurality of subsequences; the number of preamble sequences included in the data frame sequence is K, and if the length of each preamble sequence is N, the preamble sequence is recorded as {s(n), n = 0, 1, ..., N}, then s(n)=s(n+D i ),n=0,1,...,N-D i ; The kth transmitted preamble sequence is represented as {s k (n), n=0,1,...,N-1}, then the leading sequence is expressed as: s k (n)=s k (n+D i ),n=0,1,...,N-D i ; in, Parameters i and Q are both configurable positive integers, satisfying: 2≤Q≤N, 1≤i <Q; The received preamble sequence only considers the effects of frequency offset, initial phase and noise, and is expressed as: Among them, f err Indicates frequency deviation, represents the initial phase, T s represents the sampling interval, w(n) is Gaussian white noise; The first received preamble begins with D i The autocorrelation function of the interval can be expressed as The latest K received preambles are i The autocorrelation function of the interval is expressed as: S200, performing a rough estimation on the preamble sequence within the first frequency offset range to obtain a rough offset frequency; S200 includes: using the frequency offset estimation formula A coarse frequency offset is obtained by roughly estimating the preamble sequence within the first frequency offset range. Indicates the offset frequency, T s represents the sampling interval, γ p (i) indicates the latest p received preambles with D i is the autocorrelation function of the interval, the initial value of the index p is expressed as max{k-K+1,1}, K is a configurable positive integer, |·| means taking the absolute value, and arg{.} means taking the phase angle operation; S300, using the coarse offset frequency to perform coarse offset compensation on each preamble sequence to obtain a coarsely compensated preamble sequence; S300 includes: substituting the coarse offset frequency into the offset frequency compensation formula And use the frequency offset compensation formula to perform frequency offset coarse compensation on each leading sequence to obtain the coarse compensated leading sequence r k (n) represents the preamble sequence before coarse frequency offset compensation; S400, performing fine estimation on the preamble sequence after coarse compensation and within the second frequency offset range to obtain a fine frequency offset; S400 includes: using the frequency offset estimation formula A fine frequency offset is obtained by performing a fine estimation on the preamble sequence after coarse compensation and within the second frequency offset range. The first frequency offset range is smaller than the second frequency offset range; the first frequency offset range is a range formed by counting from the first preamble sequence until the number of preamble sequences reaches a first preset number; the second frequency offset range is a range formed by counting from the first preamble sequence until the number of preamble sequences reaches a second preset number; S500, performing fine frequency offset compensation on each coarsely compensated preamble sequence using the fine frequency offset to obtain a finely compensated preamble sequence; S500 includes: substituting the fine frequency offset into the frequency offset compensation formula The frequency offset compensation formula is used to perform fine frequency offset compensation on each preamble sequence to obtain a finely compensated preamble sequence.

Images