WO2021027591A1 - 基于重复序列的频偏估计方法及系统 - Google Patents

基于重复序列的频偏估计方法及系统 Download PDF

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WO2021027591A1
WO2021027591A1 PCT/CN2020/105990 CN2020105990W WO2021027591A1 WO 2021027591 A1 WO2021027591 A1 WO 2021027591A1 CN 2020105990 W CN2020105990 W CN 2020105990W WO 2021027591 A1 WO2021027591 A1 WO 2021027591A1
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frequency offset
value
relative frequency
relative
autocorrelation
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French (fr)
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赵东艳
唐晓柯
胡毅
李铮
赵亚红
赵旭
甘杰
张玉冰
闫发军
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State Grid Information and Telecommunication Group Co Ltd
Beijing Smartchip Microelectronics Technology Co Ltd
State Grid Corp of China SGCC
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State Grid Information and Telecommunication Group Co Ltd
Beijing Smartchip Microelectronics Technology Co Ltd
State Grid Corp of China SGCC
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0014—Carrier regulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2668—Details of algorithms
    • H04L27/2669—Details of algorithms characterised by the domain of operation
    • H04L27/2672—Frequency domain
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0014—Carrier regulation
    • H04L2027/0024—Carrier regulation at the receiver end
    • H04L2027/0026—Correction of carrier offset

Definitions

  • This application relates to the field of wireless communication, and particularly relates to a frequency offset estimation method and system based on repetitive sequences.
  • the initial synchronization acquisition in the receiver generally requires synchronization in the presence of frequency deviations between the transceivers.
  • repetitive sequences are often used in Orthogonal Frequency Division Multiplexing (OFDM) systems.
  • Synchronization schemes based on repetitive sequences often use sliding autocorrelation.
  • the autocorrelation amplitude reaches the maximum, and the angle of the autocorrelation value can be estimated at this time Frequency deviation.
  • the acquisition process is usually required to be able to combat large frequency deviations.
  • 802.11a and 802.15.4g respectively design the basic repetitive sequence length to be 1/4 of the OFDM useful symbol length (that is, the baseband FFT length)
  • the interval of the auto-correlation operation is usually designed to be a smaller length to achieve the maximum frequency offset that can be countered by the initial acquisition process is 2 times and 4 times the sub-carrier interval of the OFDM system.
  • the accuracy of frequency offset estimation under such a large frequency offset coverage is limited.
  • the frequency offset estimation accuracy obtained in the initial acquisition/coarse synchronization process based on the repeated sequence depends on the length of the total repeated sequence used, the signal-to-noise ratio and the size of the timing deviation. Obviously, the higher the accuracy of coarse frequency offset estimation, the smaller the impact on the subsequent fine synchronization detection probability based on autocorrelation characteristics, and the smaller the cumulative phase difference for the subsequent data demodulation process, which is more conducive to improving the subsequent data demodulation. performance. For 802.15.4g MR-OFDM with 1.2M bandwidth, the basic repetition of the short training sequence is 1/8 of the FFT length (Fourier transform length).
  • a frequency offset of 40 ppm corresponds to [-4, 4]
  • the frequency acquisition range of sub-carrier interval the receiver usually uses the autocorrelation accumulated value of the consecutive basic repeating segments (1/8 FFT length interval autocorrelation) to realize timing and frequency estimation. It can be analyzed that this large frequency offset coverage reduces the frequency offset estimation accuracy under the same data length and the same signal-to-noise ratio compared to the small frequency offset coverage scheme.
  • the purpose of this application is to provide a frequency offset estimation method and system based on a repetitive sequence, which can improve the frequency offset estimation accuracy under a large frequency offset coverage.
  • the present application provides a frequency offset estimation method based on a repetitive sequence, which includes: a receiver performs sliding autocorrelation operations on sampled signals at intervals of length N g and sums them to obtain an autocorrelation value.
  • the phase of the autocorrelation value obtains the first frequency offset estimation value, and the relative frequency offset of the first frequency offset estimation value with respect to the subcarrier spacing is recorded as the first relative frequency offset value, where, N is the length of the baseband Fourier transform, and G is an integer greater than 1.
  • the receiver performs sliding autocorrelation operations on the sampled signals at intervals of length N h and sums them to obtain another autocorrelation value, according to the autocorrelation value
  • calibrating the second relative frequency offset value through the first relative frequency offset value within the maximum integer frequency offset range, and obtaining the final frequency offset estimation value includes: The largest integer frequency offset range is expanded by h times, and then each integer in the expanded integer frequency offset range expanded by h times is divided by h to obtain multiple quotient values; and the second relative frequency offset value is compared with the multiple quotients. The values are respectively summed; each sum value is compared with the first relative frequency offset value, and the sum value closest to the first relative frequency offset value is used as the final frequency offset estimation value.
  • the present application also provides a frequency offset estimation system based on repeated sequences, which includes: a first relative frequency offset value calculation module, a second relative frequency offset value calculation module, and a calibration module.
  • the first relative frequency offset value calculation module is used to perform sliding autocorrelation operation on the sampled signal of the receiver at intervals of length N g and sum to obtain an autocorrelation value, and obtain the first frequency offset estimate according to the phase of the autocorrelation value Value, and record the relative frequency offset of the first frequency offset estimate with respect to the subcarrier spacing as the first relative frequency offset value, where, N is the length of the baseband Fourier transform, G is an integer greater than 1;
  • the calibration module is connected to both the first relative frequency offset value calculation module and the second relative frequency offset value calculation module, and is configured to compare the first relative frequency offset value to the first relative frequency offset value within the largest integer frequency offset range. Second, calibrate the relative frequency offset value to obtain the final frequency offset estimation value.
  • the calibration module includes: a quotient value obtaining module, a sum value obtaining module, and a comparison module.
  • the quotient evaluation module is used to expand the maximum integer frequency offset range by h times, and then divide each integer in the expanded integer frequency offset range by h times to obtain multiple quotients; and value evaluation The module is coupled with the quotient value evaluation module, and is used for summing the second relative frequency deviation value and the multiple quotient values respectively; the comparison module is coupled with the sum value evaluation module for summing Each sum value is compared with the first relative frequency offset value, and the sum value closest to the first relative frequency offset value is used as the final frequency offset estimation value.
  • the captured sampled signal is first performed at intervals of 1/G (G is an integer greater than 1) of the FFT length of the OFDM.
  • Autocorrelation calculation and accumulation calculation estimate a first relative frequency offset value without phase ambiguity, and perform autocorrelation calculation on the captured sample signal at intervals of h times the FFT length of OFDM (h is an integer greater than or equal to 1)
  • accumulate operation estimate a second relative frequency offset value with phase ambiguity but higher accuracy, within the maximum integer frequency offset range, pass the first relative frequency offset value without phase ambiguity to the phase ambiguity
  • the second relative frequency offset value with higher accuracy is calibrated to obtain a more accurate frequency offset estimation value.
  • This application is suitable for the frequency synchronization process at the receiving end of burst and continuous OFDM systems, and can improve the accuracy of frequency offset estimation under a large frequency offset coverage.
  • Fig. 1 is a flowchart of a frequency offset estimation method based on repeated sequences according to an embodiment of the present application
  • Fig. 2 is a block diagram of a frequency offset estimation system based on a repetitive sequence according to an embodiment of the present application.
  • the length is 1/G of the FFT length of OFDM (G is Integer greater than 1) is the interval to perform autocorrelation and accumulation operations on the captured sample signals to estimate a first relative frequency offset value without phase ambiguity, and at the same time as the interval of h times the FFT length of the OFDM (h is greater than or equal to 1) Carry out autocorrelation and accumulation operations on the captured sampled signal to estimate a second relative frequency offset value with phase ambiguity but higher accuracy. Within the maximum integer frequency offset range, pass the first relative frequency offset value.
  • the offset value calibrates the second relative frequency offset value to obtain a more accurate frequency offset estimation value.
  • This application is suitable for the frequency synchronization process at the receiving end of burst and continuous OFDM systems, and can improve the accuracy of frequency offset estimation under a large frequency offset coverage.
  • the frequency offset estimation method based on the repeated sequence includes steps S1 to S3.
  • step S1 the receiver performs a sliding autocorrelation operation on the sampled signals at intervals of length N g and sums them to obtain an autocorrelation value, obtains a first frequency offset estimation value according to the phase of the autocorrelation value, and combines the first
  • the relative frequency offset of the estimated frequency offset with respect to the subcarrier spacing is recorded as the first relative frequency offset value.
  • N is the length of the baseband Fourier transform
  • G is an integer greater than 1.
  • step S2 the receiver performs a sliding autocorrelation operation on the sampled signals at intervals of length N h and sums them to obtain another autocorrelation value, obtains the second frequency offset estimation value according to the phase of the autocorrelation value, and combines the first
  • the relative frequency offset of the estimated value of the two frequency offsets with respect to the subcarrier spacing is recorded as the second relative frequency offset value.
  • N h N*h
  • h is an integer greater than or equal to 1.
  • step S3 the second relative frequency offset value is calibrated through the first relative frequency offset value within the maximum integer frequency offset range to obtain the final frequency offset estimation value.
  • calibrating the second relative frequency offset value through the first relative frequency offset value within the maximum integer frequency offset range, and obtaining the final frequency offset estimation value includes: expanding the maximum integer frequency offset range by h times, and then Divide each integer in the integer frequency offset range expanded by h times by h to obtain multiple quotient values; respectively sum the second relative frequency offset value and the multiple quotient values; combine each sum value with the first A relative frequency offset value is compared, and the sum value closest to the first relative frequency offset value is used as the final frequency offset estimation value.
  • the air interface signal goes through the receiver antenna, radio frequency front end, carrier down-conversion, AD, digital filtering, etc., and then is sampled to baseband at 1 times the baseband rate.
  • G is 8) is the delay for sliding autocorrelation operation:
  • n 0 is the time index of the initial received data
  • s(i) is the symbol ⁇ +1, -1 ⁇ of the i-th basic repeat segment
  • l is the sampling interval, with a value range of 0 ⁇ N g -1
  • the above time resolution is 1 baseband sample.
  • This kind of operation can also be carried out using an iterative method to reduce the amount of calculation during each sliding sampling period.
  • the following cumulative operation can be done:
  • M is the number of times of autocorrelation accumulation.
  • the timing position can be determined.
  • the position is set to n C , and the first relative frequency deviation between the transceivers is calculated from the angle of A S (n C ) at the positioning time.
  • shift (Relative to the subcarrier spacing ⁇ f) is estimated as follows:
  • the relative frequency offset estimation range is [-G/2, G/2].
  • N h Nh, h is an integer greater than or equal to 1) as the interval autocorrelation operation and its accumulation during the sliding process:
  • the relative frequency offset estimation range is [-1/(2h), 1/(2h)].
  • G can be 2, 4 or 8
  • G can be 2, 4 or 8
  • this application also provides a frequency offset estimation system based on repeated sequences.
  • the frequency offset estimation system based on the repeated sequence includes: a first relative frequency offset value calculation module 10, a second relative frequency offset value calculation module 11, and a calibration module 12.
  • the first relative frequency offset value calculation module 10 is used to perform a sliding autocorrelation operation on the sampled signal of the receiver at intervals of length N g and sum to obtain an autocorrelation value, and obtain the first frequency offset estimate according to the phase of the autocorrelation value Value, and record the relative frequency offset of the first frequency offset estimate with respect to the subcarrier spacing as the first relative frequency offset value, where, N is the length of the baseband Fourier transform, and G is an integer greater than 1.
  • the calibration module 12 is connected to the first relative frequency offset value calculation module 10 and the second relative frequency offset value calculation module 11, and is used to compare the second relative frequency offset value with the first relative frequency offset value within the maximum integer frequency offset range. Perform calibration to obtain the final frequency offset estimate.
  • the calibration module 12 includes: a quotient value obtaining module 12a, a sum value obtaining module 12b, and a comparing module 12c.
  • the quotient evaluation module 12a is used to expand the maximum integer frequency offset range by h times, and then subtract 1 from the smallest number in the integer frequency offset range expanded by h times to obtain an integer, and expand the integer and h Each integer in the range of multiple integer frequency deviations is divided by h to obtain multiple quotient values; and the sum value obtaining module 12b is coupled with the quotient value obtaining module 12a, and is used to compare the second relative frequency deviation value with the multiple The quotient values are respectively summed; the comparison module 12c is coupled with the sum evaluation module 12b, and is used to compare each sum value with the first relative frequency deviation value, and compare the sum which is closest to the first relative frequency deviation value. The value is used as the final frequency offset estimate.
  • the autocorrelation operation is performed on the captured sampled signal at intervals of 1/G (G is an integer greater than 1) of the FFT length of the OFDM.
  • G is an integer greater than 1
  • accumulate operation estimate a first relative frequency offset value without phase ambiguity, and at the same time autocorrelate and accumulate the captured sampled signal at intervals of h times the FFT length of OFDM (h is an integer greater than or equal to 1)
  • Estimate a second relative frequency offset value with phase ambiguity but higher accuracy, within the maximum integer frequency offset range pass the first relative frequency offset value without phase ambiguity to the phase ambiguity but more accurate
  • the high second relative frequency offset value is calibrated to obtain a more accurate frequency offset estimation value.
  • This application is suitable for the frequency synchronization process at the receiving end of burst and continuous OFDM systems, and can improve the accuracy of frequency offset estimation under a large frequency offset coverage.
  • the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, this application may adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes.
  • a computer-usable storage media including but not limited to disk storage, CD-ROM, optical storage, etc.
  • These computer program instructions can also be stored in a computer-readable memory that can guide a computer or other programmable data processing equipment to work in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture including the instruction device.
  • the device implements the functions specified in one process or multiple processes in the flowchart and/or one block or multiple blocks in the block diagram.
  • These computer program instructions can also be loaded on a computer or other programmable data processing equipment, so that a series of operation steps are executed on the computer or other programmable equipment to produce computer-implemented processing, so as to execute on the computer or other programmable equipment.
  • the instructions provide steps for implementing functions specified in a flow or multiple flows in the flowchart and/or a block or multiple blocks in the block diagram.

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Abstract

本申请公开了一种基于重复序列的频偏估计方法及系统，该方法包括：以长度N g为间隔对采样信号作自相关运算并求和得到一个值，根据该值的相位获取第一频偏估计值并将该第一频偏估计值相对于子载波间隔的相对频偏记为第一相对频偏值，其中， Ng=N/G，N为基带傅里叶变换的长度，G为大于1的整数；以长度N h为间隔对采样信号作自相关运算并求和得到另一个值，根据该值的相位获取第二频偏估计值并将该第二频偏估计值相对于子载波间隔的相对频偏记为第二相对频偏值，其中Nh＝N*h，h为大于等于1的整数；通过第一相对频偏值对第二相对频偏值进行校准。该频偏估计方法及系统能够提高大频偏覆盖范围下的频偏估计精度。

Description

基于重复序列的频偏估计方法及系统
相关申请的交叉引用
本申请基于申请号为201910747864.2、申请日为2019年08月14日的中国专利申请提出，并要求该中国专利申请的优先权，该中国专利申请的全部内容在此引入本申请作为参考。
技术领域
本申请是关于无线通信领域，特别是关于一种基于重复序列的频偏估计方法及系统。
背景技术
接收机中的初始同步捕获一般要求在有收发信机之间的频率偏差情况下实现同步。为保证大频偏下的捕获以及同步，正交频分复用(Orthogonal Frequency Division Multiplexing，OFDM)系统中常使用重复序列。基于重复序列的同步方案常使用滑动自相关运算，在一定的初始频率偏差范围内，当接收窗滑动到重复信号的起始位置时，自相关幅度达到最大，此时自相关值的角度可以估计频偏。为降低对收发信机的晶振精确度的要求从而降低实现成本，通常要求捕获过程可以对抗较大的频偏，如802.11a和802.15.4g系统允许的频偏精度达20ppm，则接收机在初始捕获过程中需要克服40ppm的频偏，为此根据系统工作的射频信号中心频率范围，802.11a和802.15.4g分别设计了基本重复序列长度为OFDM有用符号长度(即基带FFT长度)的1/4和最低1/8，则自相关运算的间隔通常设计为一个较小的长度，以达到初始捕获过程可对抗的最大频偏为OFDM系统子载波间隔的2倍和4倍。但这种大的频偏覆盖范围下的频偏估计精度受限。
基于重复序列的初始捕获/粗同步过程中获得的频偏估计精度依赖于使 用的总重复序列的长度、信噪比及定时偏差的大小。显然粗频偏估计的精度越高，对后续的基于自相关特性的精同步检测概率影响越小，对后续的数据解调过程的累计相位差也越小，越有利于提高后续数据解调的性能。对1.2M带宽的802.15.4g MR-OFDM，其短训练序列的基本重复段为1/8的FFT长度(傅里叶变换长度)，当系统工作在870M频段时，40个ppm的频偏对应[-4，4]个子载波间隔的频率捕获范围，接收机中通常使用前后连续的基本重复段(1/8FFT长度间隔的自相关)的自相关累加值来实现定时和频率估计。可以分析这种大的频偏覆盖范围相比小频偏覆盖范围的方案降低了同数据长度和同信噪比下的频偏估计精度。
公开于该背景技术部分的信息仅仅旨在增加对本申请的总体背景的理解，而不应当被视为承认或以任何形式暗示该信息构成已为本领域一般技术人员所公知的现有技术。
发明内容
本申请的目的在于提供一种基于重复序列的频偏估计方法及系统，其能够提高大频偏覆盖范围下的频偏估计精度。
为实现上述目的，本申请提供了一种基于重复序列的频偏估计方法，其包括：接收机以长度N g为间隔对采样信号作滑动自相关运算并求和得到一个自相关值，根据该自相关值的相位获取第一频偏估计值，并将该第一频偏估计值相对于子载波间隔的相对频偏记为第一相对频偏值，其中，
Figure PCTCN2020105990-appb-000001
N为基带傅里叶变换的长度，G为大于1的整数；接收机以长度N h为间隔对所述采样信号作滑动自相关运算并求和得到另一个自相关值，根据该自相关值的相位获取第二频偏估计值，并将该第二频偏估计值相对于子载波间隔的相对频偏记为第二相对频偏值，其中，N h＝N*h，h为大于等于1的整数；在最大的整数频偏范围内通过所述第一相对频偏值对所述第 二相对频偏值进行校准，获得最终的频偏估计值。
在本申请的一实施方式中，在最大的整数频偏范围内通过所述第一相对频偏值对所述第二相对频偏值进行校准，获得最终的频偏估计值包括：将所述最大的整数频偏范围扩大h倍，然后将扩大了h倍的整数频偏范围中的每个整数分别除以h获得多个商值；将所述第二相对频偏值与该多个商值分别求和值；将每个和值与所述第一相对频偏值进行比较，将与该第一相对频偏值最接近的和值作为最终的频偏估计值。
本申请还提供了一种基于重复序列的频偏估计系统，其包括：第一相对频偏值计算模块、第二相对频偏值计算模块、校准模块。
第一相对频偏值计算模块，用于以长度N g为间隔对接收机的采样信号作滑动自相关运算并求和得到一个自相关值，根据该自相关值的相位获取第一频偏估计值，并将该第一频偏估计值相对于子载波间隔的相对频偏记为第一相对频偏值，其中，
Figure PCTCN2020105990-appb-000002
N为基带傅里叶变换的长度，G为大于1的整数；
第二相对频偏值计算模块，用于以长度N h为间隔对所述采样信号作滑动自相关运算并求和得到另一个自相关值，根据该自相关值的相位获取第二频偏估计值，并将该第二频偏估计值相对于子载波间隔的相对频偏记为第二相对频偏值，其中，N h＝N*h，h为大于等于1的整数；
校准模块与所述第一相对频偏值计算模块以及所述第二相对频偏值计算模块均相连，用于在最大的整数频偏范围内通过所述第一相对频偏值对所述第二相对频偏值进行校准，获得最终的频偏估计值。
在本申请的一实施方式中，所述校准模块包括：商值求取模块、和值求取模块、比较模块。商值求取模块用于将所述最大的整数频偏范围扩大h倍，然后将扩大了h倍的整数频偏范围中的每个整数分别除以h获得多个商值；和值求取模块与所述商值求取模块相耦合，用于将所述第二相对频 偏值与该多个商值分别求和值；比较模块与所述和值求取模块相耦合，用于将每个和值与所述第一相对频偏值进行比较，将与该第一相对频偏值最接近的和值作为最终的频偏估计值。
与现有技术相比，根据本申请的基于重复序列的频偏估计方法及系统，首先以长度为OFDM的FFT长度的1/G(G为大于1的整数)为间隔对捕获的采样信号进行自相关运算以及累加运算，估计一个没有相位模糊度的第一相对频偏值，同时以OFDM的FFT长度的h倍为间隔(h为大于等于1的整数)对捕获的采样信号进行自相关运算和累加运算，估计一个具有相位模糊度的但精度更高的第二相对频偏值，在最大的整数频偏范围内，通过没有相位模糊度的第一相对频偏值对具有相位模糊度的但精度更高的第二相对频偏值进行校准，从而获得更为精确的频偏估计值。本申请适用于突发和连续OFDM系统的接收端频率同步过程，可以在大的频偏覆盖范围下提高频偏估计的精度。
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此处的附图被并入说明书中并构成本说明书的一部分，示出了符合本公开的实施例，并与说明书一起用于解释本公开的原理。
图1是根据本申请一实施方式的基于重复序列的频偏估计方法的流程图；
图2是根据本申请一实施方式的基于重复序列的频偏估计系统的模块组成。
具体实施方式
下面结合附图，对本申请的具体实施方式进行详细描述，但应当理解本申请的保护范围并不受具体实施方式的限制。
除非另有其它明确表示，否则在整个说明书和权利要求书中，术语“包 括”或其变换如“包含”或“包括有”等等将被理解为包括所陈述的元件或组成部分，而并未排除其它元件或其它组成部分。
为了在大的频偏覆盖范围情况下能够提高频偏估计的精度，本申请提供了一种基于重复序列的频偏估计方法及系统，首先以长度为OFDM的FFT长度的1/G(G为大于1的整数)为间隔对捕获的采样信号进行自相关运算以及累加运算，估计一个没有相位模糊度的第一相对频偏值，同时以OFDM的FFT长度的h倍为间隔(h为大于等于1的整数)对捕获的采样信号进行自相关运算和累加运算，估计一个具有相位模糊度的但精度更高的第二相对频偏值，在最大的整数频偏范围内，通过第一相对频偏值对第二相对频偏值进行校准，获得更为精确的频偏估计值。本申请适用于突发和连续OFDM系统的接收端频率同步过程，可以在大的频偏覆盖范围下提高频偏估计的精度。
如图1所示，在一实施方式中，基于重复序列的频偏估计方法包括步骤S1～步骤S3。
在步骤S1中，接收机以长度N g为间隔对采样信号作滑动自相关运算并求和得到一个自相关值，根据该自相关值的相位获取第一频偏估计值，并将该第一频偏估计值相对于子载波间隔的相对频偏记为第一相对频偏值。其中，
Figure PCTCN2020105990-appb-000003
N为基带傅里叶变换的长度，G为大于1的整数。
在步骤S2中，接收机以长度N h为间隔对采样信号作滑动自相关运算并求和得到另一个自相关值，根据该自相关值的相位获取第二频偏估计值，并将该第二频偏估计值相对于子载波间隔的相对频偏记为第二相对频偏值。其中，N h＝N*h，h为大于等于1的整数。
在步骤S3中，在最大的整数频偏范围内通过第一相对频偏值对第二相对频偏值进行校准，获得最终的频偏估计值。
具体而言，在最大的整数频偏范围内通过第一相对频偏值对第二相对 频偏值进行校准，获得最终的频偏估计值包括：将最大的整数频偏范围扩大h倍，然后将扩大了h倍的整数频偏范围中的每个整数分别除以h获得多个商值；将第二相对频偏值与该多个商值分别求和值；将每个和值与第一相对频偏值进行比较，将与该第一相对频偏值最接近的和值作为最终的频偏估计值。
为了更清楚的说明，在另一实施例再次进行阐述，该实施例应用在宽带SUN-OFDM系统中，其中，FFT长度为N＝128，短训练序列为1/8周期的重复序列。
首先，空口信号经接收机天线、射频前端，载波下变频、AD、数字滤波等过程，然后在1倍于基带速率下被采样到基带，以y(n)来表示采样信号，n＝0，1，…，接收机对基带数据以N g(
Figure PCTCN2020105990-appb-000004
Figure PCTCN2020105990-appb-000005
G为大于1的整数，本实施例中，G取8)为延迟作滑动自相关运算：
Figure PCTCN2020105990-appb-000006
其中，n 0为起始接收数据的时间索引，s(i)为第i段基本重复段的符号{+1，-1}，l为采样间隔，取值范围为0～N g-1之间的整数，上面的时间分辨率为1个基带采样。
这种运算也可以使用迭代方法进行运算以减少每个滑动采样期间的计算量。为提高度量值的信噪比，可作如下累加运算：
Figure PCTCN2020105990-appb-000007
其中，M为自相关累加的次数。
使用滑动自相关的累加和其它相关运算，可以确定定时位置，设定时位置为n C，并由此定位时刻的A S(n C)的角度计算收发信机之间的第一相对频率偏移
Figure PCTCN2020105990-appb-000008
(相对于子载波间隔Δf)估计如下：
Figure PCTCN2020105990-appb-000009
该相对频偏估计范围为[-G/2，G/2]。
然后在滑动过程中增加N h(N h＝Nh，h为大于等于1的整数)为间隔的自相关运算及其累加：
Figure PCTCN2020105990-appb-000010
Figure PCTCN2020105990-appb-000011
其中
Figure PCTCN2020105990-appb-000012
根据定时同步算法确定的粗定时时刻n C，计算一个具有相位模糊度导致的偏离实际相对频偏整数个子载波间隔的高精度相对频偏如下：
Figure PCTCN2020105990-appb-000013
该相对频偏估计范围为[-1/(2h)，1/(2h)]。
然后，根据要求的最大相对频偏(相对于OFDM系统的子载波间隔)范围如[-G/2，G/2]，G可取2，4或者8，用估计的相对频偏
Figure PCTCN2020105990-appb-000014
对
Figure PCTCN2020105990-appb-000015
进行校准如下：
初始化：
Figure PCTCN2020105990-appb-000016
Figure PCTCN2020105990-appb-000017
校准尝试：
Figure PCTCN2020105990-appb-000018
Figure PCTCN2020105990-appb-000019
Figure PCTCN2020105990-appb-000020
Figure PCTCN2020105990-appb-000021
end end  (7)
校准结束时刻的
Figure PCTCN2020105990-appb-000022
即为原始最大相对频偏范围内的精度提高后的相对频偏估计。
基于同样的发明构思，本申请还提供了一种基于重复序列的频偏估计系统。如图1所示，在一实施方式中，基于重复序列的频偏估计系统包括：第一相对频偏值计算模块10、第二相对频偏值计算模块11、校准模块12。
第一相对频偏值计算模块10用于以长度N g为间隔对接收机的采样信号作滑动自相关运算并求和得到一个自相关值，根据该自相关值的相位获取第一频偏估计值，并将该第一频偏估计值相对于子载波间隔的相对频偏记为第一相对频偏值，其中，
Figure PCTCN2020105990-appb-000023
N为基带傅里叶变换的长度，G为大于1的整数。
第二相对频偏值计算模块11用于以长度N h为间隔对接收机的采样信号作滑动自相关运算并求和得到另一个自相关值，根据该自相关值的相位获取第二频偏估计值，并将该第二频偏估计值相对于子载波间隔的相对频偏记为第二相对频偏值，其中，N h＝N*h，h为大于等于1的整数。
校准模块12与第一相对频偏值计算模块10以及第二相对频偏值计算模块11均相连，用于在最大的整数频偏范围内通过第一相对频偏值对第二相对频偏值进行校准，获得最终的频偏估计值。
具体地，校准模块12包括：商值求取模块12a、和值求取模块12b、比较模块12c。商值求取模块12a用于将最大的整数频偏范围扩大h倍，然后将扩大了h倍的整数频偏范围中最小的数减去1后得到一整数，并将该整数以及扩大了h倍的整数频偏范围中的每个整数分别除以h获得多个商值；和值求取模块12b与商值求取模块12a相耦合，用于将第二相对频偏 值与该多个商值分别求和值；比较模块12c与和值求取模块12b相耦合，用于将每个和值与第一相对频偏值进行比较，将与该第一相对频偏值最接近的和值作为最终的频偏估计值。
综上，根据本实施方式的基于重复序列的频偏估计方法及系统，首先以长度为OFDM的FFT长度的1/G(G为大于1的整数)为间隔对捕获的采样信号进行自相关运算以及累加运算，估计一个没有相位模糊度的第一相对频偏值，同时以OFDM的FFT长度的h倍为间隔(h为大于等于1的整数)对捕获的采样信号进行自相关运算和累加运算，估计一个具有相位模糊度的但精度更高的第二相对频偏值，在最大的整数频偏范围内，通过没有相位模糊度的第一相对频偏值对具有相位模糊度的但精度更高的第二相对频偏值进行校准，从而获得更为精确的频偏估计值。本申请适用于突发和连续OFDM系统的接收端频率同步过程，可以在大的频偏覆盖范围下提高频偏估计的精度。
本领域内的技术人员应明白，本申请的实施例可提供为方法、系统、或计算机程序产品。因此，本申请可采用完全硬件实施例、完全软件实施例、或结合软件和硬件方面的实施例的形式。而且，本申请可采用在一个或多个其中包含有计算机可用程序代码的计算机可用存储介质(包括但不限于磁盘存储器、CD-ROM、光学存储器等)上实施的计算机程序产品的形式。
本申请是参照根据本申请实施例的方法、设备(系统)、和计算机程序产品的流程图和/或方框图来描述的。应理解可由计算机程序指令实现流程图和/或方框图中的每一流程和/或方框、以及流程图和/或方框图中的流程和/或方框的结合。可提供这些计算机程序指令到通用计算机、专用计算机、嵌入式处理机或其他可编程数据处理设备的处理器以产生一个机器，使得通过计算机或其他可编程数据处理设备的处理器执行的指令产生用于实现在流程图一个流程或多个流程和/或方框图一个方框或多个方 框中指定的功能的装置。
这些计算机程序指令也可存储在能引导计算机或其他可编程数据处理设备以特定方式工作的计算机可读存储器中，使得存储在该计算机可读存储器中的指令产生包括指令装置的制造品，该指令装置实现在流程图一个流程或多个流程和/或方框图一个方框或多个方框中指定的功能。
这些计算机程序指令也可装载到计算机或其他可编程数据处理设备上，使得在计算机或其他可编程设备上执行一系列操作步骤以产生计算机实现的处理，从而在计算机或其他可编程设备上执行的指令提供用于实现在流程图一个流程或多个流程和/或方框图一个方框或多个方框中指定的功能的步骤。
前述对本申请的具体示例性实施方案的描述是为了说明和例证的目的。这些描述并非想将本申请限定为所公开的精确形式，并且很显然，根据上述教导，可以进行很多改变和变化。对示例性实施例进行选择和描述的目的在于解释本申请的特定原理及其实际应用，从而使得本领域的技术人员能够实现并利用本申请的各种不同的示例性实施方案以及各种不同的选择和改变。本申请的范围意在由权利要求书及其等同形式所限定。

Claims (4)

  1. 一种基于重复序列的频偏估计方法，包括：
    接收机以长度N g为间隔对采样信号作滑动自相关运算并求和得到一个自相关值，根据该自相关值的相位获取第一频偏估计值，并将该第一频偏估计值相对于子载波间隔的相对频偏记为第一相对频偏值，其中，
    Figure PCTCN2020105990-appb-100001
    N为基带傅里叶变换的长度，G为大于1的整数；
    接收机以长度
    Figure PCTCN2020105990-appb-100002
    为间隔对所述采样信号作滑动自相关运算并求和得到另一个自相关值，根据该自相关值的相位获取第二频偏估计值，并将该第二频偏估计值相对于子载波间隔的相对频偏记为第二相对频偏值，其中，
    Figure PCTCN2020105990-appb-100003
    h为大于等于1的整数；
    在最大的整数频偏范围内通过所述第一相对频偏值对所述第二相对频偏值进行校准，获得最终的频偏估计值。
  2. 如权利要求1所述的基于重复序列的频偏估计方法，其中，在最大的整数频偏范围内通过所述第一相对频偏值对所述第二相对频偏值进行校准，获得最终的频偏估计值包括：
    将所述最大的整数频偏范围扩大h倍，然后将扩大了h倍的整数频偏范围中的每个整数分别除以h获得多个商值；
    将所述第二相对频偏值与该多个商值分别求和值；
    将每个和值与所述第一相对频偏值进行比较，将与该第一相对频偏值最接近的和值作为最终的频偏估计值。
  3. 一种基于重复序列的频偏估计系统，包括：
    第一相对频偏值计算模块，用于以长度N g为间隔对接收机的采样信号作滑动自相关运算并求和得到一个自相关值，根据该自相关值的相位获取第一频偏估计值，并将该第一频偏估计值相对于子载波间隔的相对 频偏记为第一相对频偏值，其中，
    Figure PCTCN2020105990-appb-100004
    N为基带傅里叶变换的长度，G为大于1的整数；
    第二相对频偏值计算模块，用于以长度
    Figure PCTCN2020105990-appb-100005
    为间隔对所述采样信号作滑动自相关运算并求和得到另一个自相关值，根据该自相关值的相位获取第二频偏估计值，并将该第二频偏估计值相对于子载波间隔的相对频偏记为第二相对频偏值，其中，
    Figure PCTCN2020105990-appb-100006
    h为大于等于1的整数；
    校准模块，与所述第一相对频偏值计算模块以及所述第二相对频偏值计算模块均相连，用于在最大的整数频偏范围内通过所述第一相对频偏值对所述第二相对频偏值进行校准，获得最终的频偏估计值。
  4. 如权利要求3所述的基于重复序列的频偏估计系统，其中，所述校准模块包括：
    商值求取模块，用于将所述最大的整数频偏范围扩大h倍，然后将扩大了h倍的整数频偏范围中的每个整数分别除以h获得多个商值；
    和值求取模块，与所述商值求取模块相耦合，用于将所述第二相对频偏值与该多个商值分别求和值；
    比较模块，与所述和值求取模块相耦合，用于将每个和值与所述第一相对频偏值进行比较，将与该第一相对频偏值最接近的和值作为最终的频偏估计值。
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