CN100477655C

CN100477655C - A Method for Estimating OFDM Integer Multiple Frequency Offset

Info

Publication number: CN100477655C
Application number: CNB2006100252224A
Authority: CN
Inventors: 丁铭; 吴赟; 罗汉文; 张海滨; 浦索明
Original assignee: Shanghai Jiao Tong University; Sharp Corp
Current assignee: Shanghai Jiao Tong University; Sharp Corp
Priority date: 2006-03-30
Filing date: 2006-03-30
Publication date: 2009-04-08
Anticipated expiration: 2026-03-30
Also published as: CN1822584A; WO2007112681A1

Abstract

Present invention relates to a method for estimating integral times frequency offset in communication technology field. It is based on a L isotonic N point OFDM synchronizing training symbol, receiving end reorganization this N point symbol as M number L point OFDM symbol, then according to preceding stage module to obtain decimals times frequency offset estimated value, leading-in decimals times frequency offset corrective term in tradition FFT algorithm structure, thereby designing out FFT algorithm new structure capable of completing decimals times frequency offset compensating, for demodulating part OFDM reorganization symbol which is extracted from M number reorganization symbol through random, equal interval or continuous method, to proceed square merging above-mentioned demodulation result, the merged peak value corresponded frequently point being the unbiased estimate value of integral times frequency offset, in order to further reduce complexity of computation, adopting self-adaptive algorithm base on adjudicate reliability feedback. Said invention has advantage of lower calculation complexity and estimating error ratio, having very high application value in OFDM system.

Description

A Method for Estimating OFDM Integer Multiple Frequency Offset

技术领域 technical field

本发明涉及一种通信技术领域的方法，特别涉及一种估计OFDM整数倍频偏的方法。The invention relates to a method in the field of communication technology, in particular to a method for estimating OFDM integer multiple frequency offset.

背景技术 Background technique

目前，OFDM技术在越来越多的有线、无线通信领域得到应用，这主要由于OFDM技术具有许多优势：有效对抗多径干扰和窄带干扰，频谱利用率高，数据传输速率高等。然而，OFDM对于同步偏差，特别是对频率偏差非常敏感。频率偏差又分为子载波间隔的小数倍频率偏差和子载波间隔的整数倍频率偏差，在下面分别简称为小数倍频偏和整数倍频偏。其中，小数倍频偏会造成子载波间干扰(ICI)；整数倍频偏不会引起ICI，但会引起接收数据符号的循环移位，使得解调出来的信息符号的错误概率为50％。At present, OFDM technology has been applied in more and more wired and wireless communication fields, mainly because OFDM technology has many advantages: effective resistance to multipath interference and narrowband interference, high spectrum utilization rate, and high data transmission rate. However, OFDM is very sensitive to synchronization deviation, especially to frequency deviation. The frequency deviation is further divided into a fractional multiple frequency deviation of subcarrier spacing and an integer multiple frequency deviation of subcarrier spacing, which are referred to as fractional multiple frequency offset and integer multiple frequency offset respectively below. Among them, the fractional frequency offset will cause inter-subcarrier interference (ICI); the integer frequency offset will not cause ICI, but will cause the cyclic shift of the received data symbols, so that the error probability of the demodulated information symbols is 50% .

常见的估计OFDM整数倍频偏的方法有三种：There are three common methods for estimating OFDM integer frequency offset:

(1)基于特定频谱图样的同步训练序列，此方法需要对同步训练符号作快速傅里叶变换(FFT)，然后与已知频谱图样作循环移位相关，通过寻找相关峰来估计整数频偏。参见文献：Schmidl，T.M.等“Low-overhead，low-complexity[burst]synchronization for OFDM”，IEEE International Conference onCommunications，Volume 3，June 1996，Page(s)：1301-1306。(“低数据开销、低复杂度的OFDM同步方法”IEEE国际通信技术会议)(1) Based on the synchronization training sequence of a specific spectrum pattern, this method needs to perform Fast Fourier Transform (FFT) on the synchronization training symbol, and then perform cyclic shift correlation with the known spectrum pattern, and estimate the integer frequency offset by looking for the correlation peak . See literature: Schmidl, T.M. et al. "Low-overhead, low-complexity [burst] synchronization for OFDM", IEEE International Conference on Communications, Volume 3, June 1996, Page(s): 1301-1306. ("Low Data Overhead, Low Complexity OFDM Synchronization Method" IEEE International Communication Technology Conference)

(2)基于OFDM系统的虚拟子载波，OFDM信号在传输过程中只使用整个带宽的一部分子载波，在频带边缘一般预留一些子载波作为保护频带，称为虚拟子载波(virtual carriers)。由于OFDM的子载波间存在正交性，所以，虚拟子载波构成OFDM信号的“零子空间”，利用正交子载波间内积为零的性质，可以推算出整数倍频偏。参见文献：Liu，H.等，“A high-efficiency carrierestimator for OFDM communications，”IEEE Communications Letters，Volume2，Issue 4，April 1998，Page(s)：104-106。(“高效的OFDM频偏估计方法”IEEE通信技术通讯稿)(2) Based on the virtual subcarriers of the OFDM system, OFDM signals only use a part of the subcarriers of the entire bandwidth during transmission, and generally reserve some subcarriers at the edge of the frequency band as guard frequency bands, called virtual subcarriers (virtual carriers). Due to the orthogonality between OFDM subcarriers, virtual subcarriers constitute the "zero subspace" of OFDM signals, and the integer multiple frequency offset can be calculated by using the property that the inner product between orthogonal subcarriers is zero. See literature: Liu, H. et al., "A high-efficiency carrier estimator for OFDM communications," IEEE Communications Letters, Volume 2, Issue 4, April 1998, Page(s): 104-106. ("Efficient OFDM Frequency Offset Estimation Method" IEEE Communications Technology Newsletter)

(3)基于L等分的OFDM同步训练符号结构，此方法通过计算训练符号的特定延迟的自相关，再求相角来估计整数倍频偏。它的估计范围随着L的增加而变大，但估计精度随之变差，计算复杂度也相应增大。参见文献：Heiskala J等：OFDM Wireless LANs-A Theoretical and Practical Guide.[M].Indianapolis USA：Pearson Education Inc，2002.70-73.(《OFDM无线局域网--理论与实践的指导》)以下称该方法为传统方法。(3) Based on the L-divided OFDM synchronous training symbol structure, this method estimates the integer multiple frequency offset by calculating the autocorrelation of the specific delay of the training symbol, and then calculating the phase angle. Its estimation range becomes larger with the increase of L, but the estimation accuracy becomes worse, and the computational complexity increases accordingly. See literature: Heiskala J et al.: OFDM Wireless LANs-A Theoretical and Practical Guide. [M]. Indianapolis USA: Pearson Education Inc, 2002.70-73. ("OFDM Wireless LANs-A Theoretical and Practical Guide") hereinafter referred to as this method for the traditional method.

可是，上述三种方法都存在计算复杂度过高的缺点。设OFDM系统的子载波数为N，方法(1)需要计算N点FFT，至少需要

N次复数乘法；方法(2)需要计算信号之间的内积，至少需要N次复数乘法；方法(3)，需要计算延迟信号间的自相关，至少需要N-M次复数乘法。如今，N的一些典型值为512、1024或2048等，这使上述三种方法在实际应用中遇到很大困难。However, the above three methods all have the disadvantage of high computational complexity. Assuming that the number of subcarriers of the OFDM system is N, method (1) needs to calculate N-point FFT, at least

N times of complex multiplication; method (2) needs to calculate the inner product between signals, at least N times of complex number multiplication; method (3), needs to calculate the autocorrelation between delayed signals, at least NM times of complex number multiplication. Today, some typical values of N are 512, 1024, or 2048, etc., which makes the above three methods encounter great difficulties in practical applications.

发明内容 Contents of the invention

本发明的目的在于针对现有技术的不足，提供一种估计OFDM整数倍频偏的方法，使其通过重构符号的方法以及高效的FFT算法完成整数倍频偏的估计，充分利用OFDM系统，保证了频偏估计的性能，又具有较低的计算复杂度。The purpose of the present invention is to provide a method for estimating the OFDM integer multiple frequency offset for the deficiencies in the prior art, so that it can complete the estimation of the integer multiple frequency offset through the method of reconstructing symbols and an efficient FFT algorithm, and make full use of the OFDM system, The performance of the frequency offset estimation is guaranteed, and the calculation complexity is low.

本发明通过以下技术方案实现，具体包括如下步骤：The present invention is realized through the following technical solutions, specifically comprising the following steps:

步骤一：发送端产生一个L等分的N点OFDM同步训练符号，符号的每一个等分含M点(M＝N/L，且N、L、M均为整数)；Step 1: the transmitting end generates an L equally divided N-point OFDM synchronous training symbol, and each equal division of the symbol contains M points (M=N/L, and N, L, and M are all integers);

步骤二：对同步训练符号进行重构，即将步骤一中的符号，重构为M个L点OFDM信号符号；Step 2: reconstructing the synchronous training symbols, that is, reconstructing the symbols in step 1 into M L-point OFDM signal symbols;

步骤三：在步骤二所得的重构符号中，按随机、等间隔或连续的方法，抽取λM个重构符号(0＜λ≤1，且λM为整数)，根据系统前级获得的小数倍频偏估计值，在传统FFT算法结构中引入小数倍频偏修正项，从而设计出能完成小数倍频偏补偿的FFT算法新结构，用于解调上述λM个重构符号，得到λM个长度为L点的频域序列；Step 3: From the reconstructed symbols obtained in Step 2, extract λM reconstructed symbols (0<λ≤1, and λM is an integer) by random, equal interval or continuous method, according to the decimal number obtained in the previous stage of the system The estimated value of the multiplier frequency offset is introduced into the traditional FFT algorithm structure to introduce the correction item of the fractional multiplier frequency offset, so as to design a new structure of the FFT algorithm that can complete the compensation of the fractional multiplier frequency offset, which is used to demodulate the above λM reconstructed symbols, and obtain λM frequency domain sequences whose length is L points;

步骤四：对步骤三所得的频域序列，按照平方和进行合并，合并后的峰值所对应的频点就是整数倍频偏的估计值。Step 4: Merge the frequency domain sequences obtained in Step 3 according to the sum of squares, and the frequency points corresponding to the merged peaks are the estimated values of integer times frequency offsets.

完成步骤四后还可以进入基于判决可靠性反馈的自适应迭代算法，即计算步骤三所得频域序列的均值与峰值之比，作为步骤四所得估计值的可靠性指标，根据可靠性指标与某一门限值的比较结果，自适应地增加λ，重复步骤三与步骤四，最后得到较为可靠的整数倍频偏估计值。After completing step 4, you can also enter the adaptive iterative algorithm based on decision reliability feedback, that is, calculate the ratio of the mean value to the peak value of the frequency domain sequence obtained in step 3, and use it as the reliability index of the estimated value obtained in step 4. According to the reliability index and a certain According to the comparison result of a threshold value, λ is adaptively increased, and steps 3 and 4 are repeated to finally obtain a relatively reliable integer multiple frequency offset estimation value.

以下对本发明作进一步说明：The present invention is described further below:

(1)生成L等分的N点OFDM同步训练符号(1) Generate N-point OFDM synchronous training symbols of L equal division

L等分的OFDM同步训练符号是一种相当常见的训练序列结构，经常用于位同步算法和小数倍频偏估计算法中。其生成方法如下：L-divided OFDM synchronous training symbols are a fairly common training sequence structure, and are often used in bit synchronization algorithms and fractional frequency offset estimation algorithms. Its generation method is as follows:

设OFDM系统的子载波数目为N，有效符号周期为T，第k个子载波的频率为f_k＝k/T(0≤k≤N-1)，a_i，k是第i个符号，在第k个子载波上加载的频域数据；b_i，l第i个符号，第l个采样点的基带时域数据。如果设第i个符号是同步训练符号，则按照式(1)插入导频，就能生成L等分的OFDM同步训练符号。Assuming that the number of subcarriers in the OFDM system is N, the effective symbol period is T, the frequency of the kth subcarrier is f _k =k/T(0≤k≤N-1), a _{i, k} is the ith symbol, in The frequency domain data loaded on the kth subcarrier; b _{i, l} the ith symbol, the baseband time domain data of the lth sampling point. If it is assumed that the i-th symbol is a synchronous training symbol, then L equal-divided OFDM synchronous training symbols can be generated by inserting pilots according to formula (1).

$\{\begin{matrix} {a a}_{i i,, k k} &NotEqual; &NotEqual; 00 & k k = = 00 & ((mod mod L L)) \\ {a a}_{i i,, k k} = = 00 & k k &NotEqual; &NotEqual; 00 & ((mod mod L L)) \end{matrix} - - - - - - ((11))$

在L等分的情况下，每一个等分的训练符号所含的点数为M(M＝N/L)，如式(2)所示：In the case of L equal divisions, the number of points contained in the training symbols of each equal division is M (M=N/L), as shown in formula (2):

b_i，l＝b_i，l+nM(l＝0，1，2，…，M-1，n＝0，1，2，…，L-1) (2)b _i,l =bi _,l+nM (l=0,1,2,...,M-1,n=0,1,2,...,L-1) (2)

通常，由M点组成的一份信号称为一个slot。Usually, a signal composed of M points is called a slot.

(2)对同步训练符号进行重构(2) Reconstruct the synchronous training symbols

在(1)所述的同步训练符号中，每个slot含有M个点，把它们标记为1、2、3、……、M。本发明所指的OFDM符号重构，就是把每个slot中标号相同的时域点抽出，组成M个新的OFDM符号，每个重构OFDM符号含L个时域点，具体做法如下：In the synchronous training symbols described in (1), each slot contains M points, which are marked as 1, 2, 3, ..., M. The reconstruction of OFDM symbols referred to in the present invention is to extract identical time-domain points in each slot to form M new OFDM symbols, and each reconstructed OFDM symbol contains L time-domain points. The specific method is as follows:

设r_i，m(0≤m≤N-1)是接收端的第i个符号，第m个时域采样点，则M个重构符号可以表示成向量形式r_m(1≤m≤M)，见式(3)：Let r _{i, m} (0≤m≤N-1) be the i-th symbol at the receiving end, and the m-th time-domain sampling point, then the M reconstructed symbols can be expressed in the vector form r _m (1≤m≤M) , see formula (3):

$\{\begin{matrix} {r r}_{11} = = (({r r}_{i i,, 00},, {r r}_{i i,, M m},, {r r}_{i i,, 22 M m},, \cdot \cdot \cdot \cdot \cdot \cdot,, {r r}_{i i,, ((L L - - 11)) M m})) \\ {r r}_{22} = = (({r r}_{i i,, 11},, {r r}_{i i,, M m + + 11},, {r r}_{i i,, 22 M m + + 11},, \cdot &Center Dot; \cdot \cdot \cdot \cdot,, {r r}_{i i,, ((L L - - 11)) M m + + 11})) \\ {r r}_{33} = = (({r r}_{i i,, 22},, {r r}_{i i,, M m + + 22},, {r r}_{i i,, 22 M m + + 22},, \cdot \cdot \cdot &Center Dot; \cdot \cdot,, {r r}_{i i,, ((L L - - 11)) M m + + 22})) \\ \begin{matrix} . . & . . \end{matrix} \\ \begin{matrix} . . & . . \end{matrix} \\ \begin{matrix} . . & . . \end{matrix} \\ {r r}_{M m} = = (({r r}_{i i,, M m - - 11},, {r r}_{i i,, M m + + M m - - 11},, {r r}_{i i,, 22 M m + + M m - - 11},, \cdot \cdot \cdot \cdot \cdot \cdot,, {r r}_{i i,, ((L L - - 11)) M m + + M m - - 11})) \end{matrix} - - - - - - ((33))$

为论述简便起见，记：For the sake of brevity, remember:

r_m(n)＝r_i，nM+m (0≤m≤M-1，0≤n≤L-1) (4)r _m (n) = r _{i, nM+m} (0≤m≤M-1, 0≤n≤L-1) (4)

于是，r_m＝(r_m(0)，r_m(1)，…，r_m(n)，…，r_m(L-1))，以上的重构过程使得采样数据获得时间分集的优点，从而使估计算法更加鲁棒。Then, r _m = (r _m (0), r _m (1), ..., r _m (n), ..., r _m (L-1)), the above reconstruction process makes the sampling data obtain the advantage of time diversity , so that the estimation algorithm is more robust.

(3)解调重构符号，获得相应的频域序列(3) Demodulate and reconstruct symbols to obtain corresponding frequency domain sequences

在理想信道条件下，重构OFDM符号r_m中的时域点应该是完全相同的。然而，由于存在频率偏移，这些点的相位呈现出递增或是递减的趋势，如同被调制到某一频率上。于是，对于r_m而言，频偏的影响可以等效为含有L个子载波的OFDM系统的基带调制过程。因此，解调这些重构符号，寻找它们的频谱幅度峰值，就能对整数倍频偏做出估计。而解调OFDM重构符号的方法就是L点FFT算法，并且，L一般是比较小的数，比如4、8等等。较小点数的FFT算法正是本发明具有低计算复杂度的核心所在。Under ideal channel conditions, the time-domain points in the reconstructed OFDM symbol r _m should be exactly the same. However, due to the frequency offset, the phases of these points tend to increase or decrease, as if modulated to a certain frequency. Therefore, for _rm , the influence of the frequency offset can be equivalent to the baseband modulation process of an OFDM system containing L subcarriers. Therefore, by demodulating these reconstructed symbols and looking for their spectral magnitude peaks, integer multiple frequency offsets can be estimated. The method for demodulating OFDM and reconstructing symbols is the L-point FFT algorithm, and L is generally a relatively small number, such as 4, 8, and so on. The FFT algorithm with a smaller number of points is the core of the present invention with low computational complexity.

对r_m运用FFT算法，得：Using the FFT algorithm on _rm , we get:

${R R}_{m m} ((y the y)) = = DFT DFT (({r r}_{m m} | | y the y)) = = {Σ Σ}_{n no = = 00}^{L L - - 11} {r r}_{m m} ((n no)) {e e}^{- - j j 22 πny πny / / L L} - - - - - - ((55))$

于是，整数倍频偏的估计式表达为：Therefore, the estimating formula of integer multiple frequency offset is expressed as:

单纯的L点FFT算法还不足以完备地解决整数倍频偏的估计问题，特别当小数倍频偏在0.5附近时，R_m中会有两个频点的幅值都比较大，从而导致判决性能急剧下降。因此，本发明结合小数倍频偏估计值设计出新的FFT算法结构，在没有增加任何运算开销的前提下，保证本算法在正确的小数倍频偏估计的情况下，始终是无偏估计。The simple L-point FFT algorithm is not enough to completely solve the problem of integer multiple frequency offset estimation, especially when the fractional multiple frequency offset is around 0.5, there will be two frequency points in R _m with relatively large amplitudes, which will lead to judgment Performance drops drastically. Therefore, the present invention designs a new FFT algorithm structure in combination with the estimated value of the fractional frequency offset, and ensures that the algorithm is always unbiased under the correct estimation of the fractional frequency offset without increasing any calculation overhead. estimate.

采用现有技术可以轻易地实现小数倍频偏估计，比如基于对循环前缀相关求相角的方法、基于2等分符号相关求相角的方法、基于ML准则搜索的方法等。上述方法一般位于本发明方案的前级，本发明根据其给出的小数倍频偏估计值

能高效地实现整数倍频偏无偏估计的任务。Fractional frequency offset estimation can be easily realized using existing technologies, such as methods based on cyclic prefix correlation phase angle calculation, phase angle calculation based on bisection symbol correlation, and ML criterion search methods. The above-mentioned method is generally located at the front stage of the scheme of the present invention, and the present invention is based on the fractional multiple frequency offset estimation value given by it

The task of unbiased estimation of integer multiple frequency offset can be realized efficiently.

一般来讲，OFDM系统的子载波是2的整数次方，如：256、512、1024等。为了保证M为整数，L也只能是2的整数次方，设L＝2^β(β为正整数)。2^β点的FFT算法可以分为β级蝶形运算，第p级蝶形运算含有2^p-1个不同的复乘系数。原始2^β点FFT算法中的第p级，第q个复乘系数是：Generally speaking, the subcarriers of the OFDM system are integer powers of 2, such as: 256, 512, 1024, etc. In order to ensure that M is an integer, L can only be an integer power of 2, and L=2 ^β (β is a positive integer). The FFT algorithm of 2 ^β points can be divided into β-level butterfly operations, and the p-th level butterfly operation contains 2 ^p-1 different complex multiplication coefficients. The p-th stage, q-th complex multiplication coefficient in the original ^2β- point FFT algorithm is:

${W W}_{22^{β β}}^{q q,, p p} = = exp exp {{- - j j 22 π π \frac{{q q 22}^{β β - - p p}}{22^{β β}}}},, (\begin{matrix} p p = = 1,2 1,2,, . . . . . .,, β β \\ q q = = 0,1,2 0,1,2,, . . . . . .,, 22^{p p - - 11} - - 11 \end{matrix}) - - - - - - ((77))$

本发明中与之对应的第p级，第q个复乘系数是：In the present invention, corresponding to the p-level, the q-th complex multiplication coefficient is:

只要按照蝶形运算结构，将每一级的数学结果原样写出，就能证明本发明的正确性。对r_m运用修正的FFT算法，可得式(9)：As long as the mathematical results of each stage are written out as they are according to the butterfly operation structure, the correctness of the present invention can be proved. Applying the modified FFT algorithm to _rm , the formula (9) can be obtained:

式(9)表明，本发明提供的FFT算法结构，等效为先对重构符号作小数倍频偏为

的相位补偿，再作原始的FFT运算，达到了将频率观测点移动小数倍频偏的目的，从而使得本发明的整数倍频偏估计是无偏估计。只要小数倍频偏的估计比较准确，那么，新的FFT算法得到的将是无偏估计。而且，本发明提供的FFT算法中的修正项，只在复数的相位上进行加法运算，也没有破坏FFT算法的固有特点。需要指出的是，本发明的FFT算法的功能可以用如下的替代方法实现：根据小数倍频偏估计

先对r_m作时域相位补偿后，再作原始FFT运算。Equation (9) shows that the FFT algorithm structure provided by the present invention is equivalent to first making a fractional multiple frequency offset to the reconstructed symbol as

Phase compensation, and then the original FFT operation, achieves the purpose of moving the frequency observation point to a fractional multiple frequency offset, so that the integer multiple frequency offset estimation of the present invention is an unbiased estimate. As long as the estimation of fractional frequency offset is more accurate, the new FFT algorithm will obtain unbiased estimation. Moreover, the correction term in the FFT algorithm provided by the present invention only performs the addition operation on the phase of the complex number, and does not destroy the inherent characteristics of the FFT algorithm. It should be pointed out that the function of the FFT algorithm of the present invention can be realized by the following alternative method: according to the fractional multiple frequency offset estimation

After doing time-domain phase compensation to _rm first, do the original FFT operation.

替代方法虽然也达到了本发明设计新FFT算法结构的目的，但其计算复杂度高于本发明提供的算法。具体来讲，对于每个r_m，替代方法需要复乘次数为

而本发明只需

次复乘。Although the replacement method also achieves the purpose of designing a new FFT algorithm structure in the present invention, its computational complexity is higher than the algorithm provided by the present invention. Specifically, for each rm _m , the alternative method requires the number of complex multiplications to be

And the present invention only needs

multiple times.

基于式(9)，整数倍频偏的估计式表示为：Based on formula (9), the estimation formula of integer multiple frequency offset is expressed as:

(4)合并频域序列，通过寻找峰值，估计整数倍频偏(4) Merge the frequency domain sequence, and estimate the integer multiple frequency offset by finding the peak

理论上，本发明只需对1个r_m运用无偏估计的FFT算法，就能估计出整数倍频偏，但是，由于信道的多径衰落、噪声等影响，一般要采用多次联合判决的方法。具体操作方法如下：按随机、等间隔或连续的抽选方法，取出λM个r_m(0＜λ≤1，且λM为整数)。随机抽选方法是指从M个OFDM重构符号中，随机取出λM个不同的重构符号。等间隔抽选方法是指从M个OFDM重构符号中，先随机确定第一个重构符号，再等间隔地取出λM个不同的重构符号。连续抽选方法是指从M个OFDM重构符号中，先随机确定第一个重构符号，再连续地取出λM个不同的重构符号。Theoretically, the present invention only needs to use the FFT algorithm of unbiased estimation to 1 _rm , can estimate the frequency offset of integer times, but, because the multipath fading of the channel, noise etc. influence, generally need to adopt multiple joint judgments method. The specific operation method is as follows: λM r _m (0<λ≤1, and λM is an integer) are selected according to a random, equal interval or continuous selection method. The random selection method refers to randomly selecting λM different reconstructed symbols from the M OFDM reconstructed symbols. The equal-interval sampling method refers to randomly determining the first reconstructed symbol from the M OFDM reconstructed symbols, and then extracting λM different reconstructed symbols at equal intervals. The continuous selection method refers to randomly determining the first reconstructed symbol from M OFDM reconstructed symbols, and then continuously extracting λM different reconstructed symbols.

对λM个r_m运用无偏估计的FFT算法，得到一系列频域数据R_m，再按照平方和合并，合并后的峰值所对应的频点就是整数倍频偏的估计值。Use the FFT algorithm of unbiased estimation for λM r _m to obtain a series of frequency domain data R _m , and then combine them according to the sum of squares. The frequency point corresponding to the combined peak value is the estimated value of the integer multiple frequency offset.

其他合并方法有：模值合并，如式(12)所示，Other merging methods include: modular value merging, as shown in formula (12),

以及实部绝对值与虚部绝对值之和的合并，如式(13)所示。And the combination of the sum of the absolute value of the real part and the absolute value of the imaginary part, as shown in formula (13).

由于在1个OFDM符号内，信噪比可以认为不变，于是，式(11)等效为最大比合并，这是最优的合并方法。而式(12)及式(13)是次优的合并方式，用估计性能的下降换取了计算复杂度的下降。Since the signal-to-noise ratio can be considered unchanged within one OFDM symbol, formula (11) is equivalent to the maximum ratio combination, which is the optimal combination method. However, formula (12) and formula (13) are sub-optimal combining methods, and the decrease of computational complexity is exchanged for the decrease of estimation performance.

(5)基于判决可靠性反馈的自适应算法(5) Adaptive algorithm based on decision reliability feedback

当只取一个固定的λ时，前述方案比传统方法并不具有太大的优势，于是，本发明进一步提出基于判决可靠性反馈的自适应算法。When only a fixed λ is taken, the aforementioned scheme does not have much advantage over the traditional method. Therefore, the present invention further proposes an adaptive algorithm based on decision reliability feedback.

由于小数倍频偏估计的误差或非理想的信道条件，式(11)中的

相对于其他R(y)的数值优势会显著降低，导致式(11)的估计不可靠。将R(y)的平均值与

的比值作为式(11)可靠性指标V，根据V与某一门限值η的比较情况，采用多级联合判决的方法以提高本发明的估计性能。首先，按照式(3)进行符号重构，得到M个OFDM重构子符号r_m，记为集合S，设定门限值η，令n＝1(n表示第n级判决)。然后进入迭代次数为X的基于判决可靠性反馈的自适应算法：Due to errors in fractional frequency offset estimation or non-ideal channel conditions, the

The numerical advantage over other R(y) will be significantly reduced, making the estimation of Equation (11) unreliable. Compare the mean value of R(y) with

The ratio of is used as the reliability index V of formula (11), according to the comparative situation of V and a certain threshold value η, the method of multi-level joint decision is adopted to improve the estimation performance of the present invention. First, carry out symbol reconstruction according to formula (3) to obtain M OFDM reconstructed sub-symbols r _m , denoted as a set S, set a threshold value η, and set n=1 (n represents the nth level decision). Then enter the adaptive algorithm based on decision reliability feedback with the number of iterations X:

先从S中随机取出 $λ_{n} M (0 < λ_{n} \leq 1 - Σ_{j = 1}^{n - 1} λ_{j}$ 且λ_nM为整数)个r_m，形成集合S_n；S＝S-S_n。再对S_n中的每个r_m，用FFT算法计算式(9)，得到λ_nM个R_m。然后把λ_nM个R_m按式(11)进行合并，再与前级的结果相加，得U_n，其含有L个元素U_n(y)：First randomly take out from S $λ_{no} m (0 < λ_{no} \leq 1 - Σ_{j = 1}^{no - 1} λ_{j}$ And λ _n M is an integer) _rm , forming a set S _n ; S=SS _n . Then, for each _rm in S _n , use the FFT algorithm to calculate formula (9), and get λ _n M R _m . Then combine the λ _n M R _m according to formula (11), and add them to the result of the previous stage to get U _n , which contains L elements U _n (y):

${U u}_{n no} ((y the y)) = = {U u}_{n no - - 11} ((y the y)) + + \underset{{s the s}_{n no}}{Σ Σ} {| | {\overset{&OverBar; &OverBar;}{R R}}_{m m} ((y the y)) | |}^{22},, ((y the y &Element; &Element; [[- - L L / / 22,, L L / / 22)),, y the y &Element; &Element; Z Z)) - - - - - - ((1414))$

寻找式(14)的峰值对应的频点，对f_I做出估计：Find the frequency point corresponding to the peak value of formula (14), and estimate f _I :

${\overset{^^}{f f}}_{I I} = = \underset{y the y}{aeg aeg max max} {{{U u}_{n no} ((y the y))}} - - - - - - ((1515))$

将U_n(y)的平均值与的比值作为式(15)可靠性指标V_n：Compare the mean value of U _n (y) with The ratio of is used as the reliability index V _n of formula (15):

${V V}_{n no} = = \frac{\frac{11}{L L} \underset{y the y}{Σ Σ} {U u}_{n no} ((y the y))}{{U u}_{n no} (({\overset{^^}{f f}}_{I I}))} - - - - - - ((1616))$

当V_n小于等于门限η，或n＝X，算法结束；否则，令n＝n+1，重复上述过程。When V _n is less than or equal to the threshold η, or n=X, the algorithm ends; otherwise, set n=n+1 and repeat the above process.

由式(14)和式(15)可知，η的取值范围是[1/L，1)，η越小，调用后级判决的概率就越大，于是，计算复杂度上升，但估计性能得到提高。From formula (14) and formula (15), it can be seen that the value range of η is [1/L, 1), and the smaller η is, the greater the probability of invoking the judgment of the later stage, so the computational complexity increases, but the estimation performance get improved.

需要指出的是，式(16)并非可靠性指标的唯一表达，其他可靠性指标有：It should be pointed out that formula (16) is not the only expression of reliability index, and other reliability indexes are:

U_n(y)的第二大值与

之比作为可靠性指标V_n，如式(17)所示，The second largest value of U _n (y) and

The ratio of is used as the reliability index V _n , as shown in formula (17),

${V V}_{n no} = = \frac{{U u}_{n no} ((\underset{y the y}{arg arg max max} {{{U u}_{n no} ((y the y)) | | ((y the y &NotEqual; &NotEqual; {\overset{^^}{f f}}_{I I}))}}))}{{U u}_{n no} (({\overset{^^}{f f}}_{I I}))} - - - - - - ((1717))$

若V_n小于门限值α，则认为估计是可靠的，α的取值范围是(0，1)。If V _n is smaller than the threshold value α, the estimation is considered to be reliable, and the value range of α is (0, 1).

相邻两值的平均值与

的比值作为可靠性指标V_n，如式(18)所示，

The average of two adjacent values and

The ratio of is used as the reliability index V _n , as shown in formula (18),

${V V}_{n no} = = \frac{[[{U u}_{n no} (({\overset{^^}{f f}}_{I I} + + 11)) + + {U u}_{n no} (({\overset{^^}{f f}}_{I I} - - 11))]]}{22 {U u}_{n no} (({\overset{^^}{f f}}_{I I}))} - - - - - - ((1818))$

若V_n小于门限值β，则认为估计是可靠的，β的取值范围是(0，1)。If V _n is smaller than the threshold value β, the estimation is considered to be reliable, and the value range of β is (0, 1).

采用了基于判决可靠性反馈的自适应算法后，本发明的计算复杂度进一步降低，估计性能得到显著提高。After adopting the adaptive algorithm based on decision reliability feedback, the calculation complexity of the present invention is further reduced, and the estimation performance is significantly improved.

本发明的优点在于：通过OFDM符号重构，充分地利用接收数据，具有时间分集的特点；用FFT算法对整数倍频偏做估计，大大降低了系统的计算复杂度；结合小数倍频偏设计新的FFT算法，使本发明的估计成为无偏估计，提高了系统的可靠性。另外，本发明采用基于判决可靠性反馈的自适应合并算法，使得本发明兼有计算复杂度低和估计性能较优的特点。而且，仿真表明，本发明对小数倍频偏估计的误差不敏感，具有很好的鲁棒性。The advantages of the present invention are: through the reconstruction of OFDM symbols, the received data is fully utilized, and it has the characteristics of time diversity; the FFT algorithm is used to estimate the integer multiple frequency offset, which greatly reduces the computational complexity of the system; combined with the fractional multiple frequency offset A new FFT algorithm is designed to make the estimation of the present invention an unbiased estimation and improve the reliability of the system. In addition, the present invention adopts an adaptive merging algorithm based on decision reliability feedback, so that the present invention has the characteristics of low computational complexity and better estimation performance. Moreover, the simulation shows that the present invention is insensitive to errors in fractional multiple frequency offset estimation and has good robustness.

附图说明 Description of drawings

图1OFDM基带调制解调框图Figure 1 OFDM baseband modulation and demodulation block diagram

图2N＝1024，L＝8的OFDM同步训练符号的频域与时域对应关系示意图Figure 2N=1024, a schematic diagram of the corresponding relationship between the frequency domain and the time domain of OFDM synchronous training symbols of L=8

图3N＝1024，L＝8的OFDM同步训练符号重构示意图Figure 3 N=1024, L=8 OFDM synchronous training symbol reconstruction schematic diagram

图4本发明的实施框图The implementation block diagram of Fig. 4 the present invention

图5用于估计整数倍频偏的无偏估计8点FFT算法结构Figure 5. Unbiased estimation 8-point FFT algorithm structure for estimating integer multiple frequency offset

图6随机、等间隔或连续方法挑选OFDM重构符号时的系统性能图Figure 6 System performance diagram when selecting OFDM reconstruction symbols by random, equal interval or continuous method

图7本发明在采用等间隔方法挑选OFDM重构符号，存在小数倍频偏估计误差时的性能图Fig. 7 is the performance diagram of the present invention when the OFDM reconstruction symbol is selected by the equal interval method, and there is a fractional frequency offset estimation error

图8本发明在采用等间隔方法挑选OFDM重构符号，小数倍频偏估计完全正确时，迭代次数X＝0的基于判决可靠性反馈的自适应算法与传统方法的性能比较图Fig. 8 is a performance comparison diagram of the adaptive algorithm based on decision reliability feedback with the number of iterations X=0 and the traditional method when the present invention adopts the equal interval method to select OFDM reconstructed symbols and the fractional frequency offset estimation is completely correct

图9本发明在采用等间隔方法挑选OFDM重构符号，小数倍频偏估计完全正确时，迭代次数X＝1的基于判决可靠性反馈的自适应算法与传统方法的性能比较图Fig. 9 is a performance comparison diagram of the adaptive algorithm based on decision reliability feedback with the number of iterations X=1 and the traditional method when the present invention adopts the equal interval method to select OFDM reconstructed symbols and the fractional frequency offset estimation is completely correct

图10本发明在采用等间隔方法挑选OFDM重构符号，小数倍频偏估计完全正确时，迭代次数X＝2的基于判决可靠性反馈的自适应算法与传统方法的性能比较图Fig. 10 is a performance comparison diagram of the adaptive algorithm based on decision reliability feedback with the number of iterations X=2 and the traditional method when the present invention adopts the equal interval method to select OFDM reconstructed symbols and the fractional frequency offset estimation is completely correct

具体实施方式 Detailed ways

下面给出一个具体的OFDM参数配置，来阐述本发明的实现步骤。需要说明的是，下例中的参数并不影响本发明的一般性。A specific OFDM parameter configuration is given below to illustrate the implementation steps of the present invention. It should be noted that the parameters in the following examples do not affect the generality of the present invention.

3GPP组织的文档：TR 25.892 V6.0.0，“Feasibility Study for OrthogonalFrequency Division Multiplexing(OFDM)for UTRAN enhancement(Release6)”，给出的一组OFDM参数，如下：Documents organized by 3GPP: TR 25.892 V6.0.0, "Feasibility Study for Orthogonal Frequency Division Multiplexing (OFDM) for UTRAN enhancement (Release6)", a set of OFDM parameters given as follows:

系统带宽B 6.528MHzSystem bandwidth B 6.528MHz

子载波数N 1024Number of subcarriers N 1024

有效子载波数N_u 705Effective number of subcarriers N _u 705

有效带宽 4.495MHzEffective Bandwidth 4.495MHz

子载波间隔Δf 6.375kHzSubcarrier spacing Δf 6.375kHz

循环扩展CP 64(9.803us)Cyclic extension CP 64(9.803us)

符号周期T_s 156.85+9.81＝166.66usSymbol period T _s 156.85+9.81＝166.66us

在上述参数条件下，取L＝8，则M＝128，采用等间隔抽选方法以及式(11)的平方和合并方法，并采用式(16)作为估计可靠性指标，使用基于判决可靠性反馈的3级自适应算法，本发明的实现步骤如下：Under the above parameter conditions, take L=8, then M=128, adopt the equal interval sampling method and the square sum combination method of formula (11), and adopt formula (16) as the estimated reliability index, use the method based on the decision reliability The 3 grades of self-adaptive algorithm of feedback, the realization step of the present invention is as follows:

(1)依照式(1)，在子载波序号为160、168、176、184、192、200、208、216、224、232、240、248、256、264、272、280、288、296、304、312、320、328、336、344、352、360、368、376、384、392、400、408、416、424、432、440、448、456、464、472、480、488、496、504、520、528、536、544、552、560、568、576、584、592、600、608、616、624、632、640、648、656、664、672、680、688、696、704、712、720、728、736、744、752、760、768、776、784、792、800、808、816、824、832、840、848、856、864的频率上加载导频数据，其他子载波上放置零数据，将这样的频域数据通过图1的串并转换模块1、IDFT模块2、并串转换模块3，就能生成一个形如式(2)的8等分同步训练符号，图2是该同步训练符号的频域与时域对应关系的示意图。然后经过图1的模块插入循环前缀模块4、插入同步信息模块5、D/A转换模块6、发送滤波处理模块7，到达接收端。(1) According to formula (1), when the subcarrier numbers are 160, 168, 176, 184, 192, 200, 208, 216, 224, 232, 240, 248, 256, 264, 272, 280, 288, 296, 304, 312, 320, 328, 336, 344, 352, 360, 368, 376, 384, 392, 400, 408, 416, 424, 432, 440, 448, 456, 464, 472, 480, 488, 496, 504, 520, 528, 536, 544, 552, 560, 568, 576, 584, 592, 600, 608, 616, 624, 632, 640, 648, 656, 664, 672, 680, 688, 696, 704, Load pilot data on frequencies of 712, 720, 728, 736, 744, 752, 760, 768, 776, 784, 792, 800, 808, 816, 824, 832, 840, 848, 856, 864, other subcarriers Place zero data on the top, and pass such frequency domain data through serial-to-parallel conversion module 1, IDFT module 2, and parallel-to-serial conversion module 3 in Figure 1 to generate an 8-equalized synchronous training symbol in the form of formula (2), as shown in Figure 1 2 is a schematic diagram of the corresponding relationship between the frequency domain and the time domain of the synchronization training symbols. Then, through the modules in Fig. 1, insert the cyclic prefix module 4, insert the synchronous information module 5, the D/A conversion module 6, and the transmission filter processing module 7, and reach the receiving end.

(2)接收端经过图1中接收滤波处理模块8、A/D转换模块9的处理，结合图4中系统给出的位同步信息，将会获得完整的r_i，m(m＝0、1、……、1023)。依照式(3)，将r_i，m重构为128个8点OFDM符号r_m(m＝1、2、……、128)。图3是该重构过程的示意图。(2) the receiving end will obtain complete r _{i, m (m=0, m} (m=0, 1, ..., 1023). According to formula (3), r _{i, m} are reconstructed into 128 8-point OFDM symbols r _m (m=1, 2, ..., 128). Figure 3 is a schematic diagram of the reconstruction process.

(3)取λ₁＝0.25，λ₂＝0.25，λ₃＝0.5，X＝3。设定门限值η＝0.5，令n＝1(n表示第n级判决)。(3) Take λ ₁ =0.25, λ ₂ =0.25, λ ₃ =0.5, X=3. Set the threshold value η = 0.5, and set n = 1 (n represents the nth level decision).

(4)λ_nM取整数后为

因此，按等间隔的方法，取出

个r_m，结合前级给出的小数倍频偏估计值对上述

个r_m进行图5所示的运算，得到

个R_m。(4) After λ _n M is taken as an integer, it is

Therefore, according to the method of equal intervals, take out

r _m , combined with the fractional multiple frequency offset estimate given by the previous stage to the above

R _m performs the operation shown in Figure 5 to get

R _m .

(5)对上述

个R_m按式(14)进行合并，按式(15)作出整数倍频偏的估计值。按式(16)计算V_n。当V_n小于等于门限η，或n＝X，算法结束；否则，令n＝n+1，回到(4)。(5) For the above

The R _m are combined according to formula (14), and the estimated value of integer multiple frequency offset is made according to formula (15). Calculate V _n according to formula (16). When V _n is less than or equal to the threshold η, or n=X, the algorithm ends; otherwise, set n=n+1, and return to (4).

信道为8路瑞利衰落信道，如下：The channel is an 8-way Rayleigh fading channel, as follows:

延迟(ns) 相对功率(dB) Delay (ns) Relative Power (dB)

路径 10 0Path 10 0

路径2 153 -6.7Path 2 153 -6.7

路径3 306 -13.3Path 3 306 -13.3

路径4 459 -19.9Path 4 459 -19.9

路径5 612 -27.6Path 5 612 -27.6

路径6 765 -33.3Path 6 765 -33.3

路径7 919 -39.9Path 7 919 -39.9

路径8 1072 -46.6Path 8 1072 -46.6

图6是本发明采用随机、等间隔或连续方法挑选OFDM重构符号时的系统性能图，该图表明，当λ较小时(如0.1或0.2)，采用连续抽取方法的系统性能不如其他两种方法，当λ较大时，采用随机、等间隔或连续方法进行抽取时的系统性能趋于一致。总体来看，采用等间隔抽取方法的系统具有最好的性能。Fig. 6 is the system performance diagram when the present invention adopts random, equal interval or continuous method to select OFDM reconstruction symbols, and this figure shows that when λ is small (such as 0.1 or 0.2), the system performance of the continuous extraction method is not as good as the other two method, when λ is large, the system performance tends to be consistent when using random, equal interval or continuous method for extraction. Overall, the system with the equally spaced decimation method has the best performance.

图7是本发明在采用等间隔方法挑选OFDM重构符号，而且存在小数倍频偏估计误差时的性能图，该图显示，本发明对于小数倍频偏估计的误差并不敏感，这有利于提高整个系统的鲁棒性。Fig. 7 is the performance diagram of the present invention when the OFDM reconstruction symbols are selected by the equal interval method, and there is a fractional frequency offset estimation error. This figure shows that the present invention is not sensitive to the error of the fractional frequency offset estimation. It is beneficial to improve the robustness of the whole system.

图8是本发明在采用等间隔方法挑选OFDM重构符号时，小数倍频偏估计完全正确时，迭代次数X＝0的基于判决可靠性反馈的自适应算法与传统方法的性能比较图。在传统方法中，设定延时为一个slot，作相关，求相角，就能估计整数倍频偏，它需要(N-M)＝896次复乘。而在本发明中，λ＝0.2时，需要复乘约300次，这只相当于传统方法的1/3，但比传统方法取得0.5dB的信噪比增益；当λ＝0.6时，本发明需要复乘约900次，其计算复杂度与传统方法相等，但取得了3dB左右的信噪比增益。Fig. 8 is a performance comparison diagram of the adaptive algorithm based on decision reliability feedback with the number of iterations X = 0 and the traditional method when the present invention uses the equal interval method to select OFDM reconstructed symbols and the fractional frequency offset estimation is completely correct. In the traditional method, the delay is set as a slot, correlation is performed, and the phase angle is calculated to estimate the integer multiple frequency offset, which requires (N-M)=896 complex multiplications. And in the present invention, when λ=0.2, need complex multiplication about 300 times, this is only equivalent to 1/3 of traditional method, but obtains the signal-to-noise ratio gain of 0.5dB than traditional method; When λ=0.6, the present invention It needs about 900 times of complex multiplication, and its computational complexity is equal to that of the traditional method, but it achieves a signal-to-noise ratio gain of about 3dB.

图9是本发明在采用等间隔方法抽取时，小数倍频偏估计完全正确时，迭代次数X＝1的基于判决可靠性反馈的自适应算法与传统方法的性能比较图。该仿真中，设λ₁＝λ₂＝0.25，考察η的3种情况：0.5、0.75及0.875。当η＝0.5时，本发明比传统方法取得3dB的信噪比增益，并且，X＝1的自适应算法仿真表明，其需要的平均复乘次数只有传统方法的57％至64％；当η＝0.75时，本发明比传统方法取得2.2dB的信噪比增益，但其需要的平均复乘次数只有传统方法的57％至58％；当η＝0.875时，本发明比传统方法取得1.4dB的信噪比增益，但其需要的平均复乘次数只有传统方法的57％；Fig. 9 is a performance comparison chart of the adaptive algorithm based on decision reliability feedback with the number of iterations X = 1 and the traditional method when the fractional frequency offset estimation is completely correct when the equal interval method is used for extraction in the present invention. In this simulation, it is assumed that λ ₁ =λ ₂ =0.25, and three cases of η are examined: 0.5, 0.75 and 0.875. When η=0.5, the present invention obtains the signal-to-noise ratio gain of 3dB than traditional method, and, the self-adaptive algorithm emulation of X=1 shows, and the average times of multiplication that it needs has only 57% to 64% of traditional method; When η When =0.75, the present invention obtains the signal-to-noise ratio gain of 2.2dB than traditional method, but the average multiple times of its need only has 57% to 58% of traditional method; When η=0.875, the present invention obtains 1.4dB than traditional method The signal-to-noise ratio gain, but the average number of multiplications required is only 57% of the traditional method;

图10是本发明在采用等间隔方法抽取时，小数倍频偏估计完全正确时，迭代次数X＝2的基于判决可靠性反馈的自适应算法与传统方法的性能比较图。该仿真中，设λ₁＝λ₂＝0.25，λ₃＝0.5，考察η的3种情况：0.5、0.75及0.875。当η＝0.5时，本发明比传统方法取得4.7dB的信噪比增益，并且，X＝2的自适应算法仿真表明，其需要的平均复乘次数只有传统方法的57％至75％；当η＝0.75时，本发明比传统方法取得2.6dB的信噪比增益，但其需要的平均复乘次数只有传统方法的57％至58％；当η＝0.875时，本发明比传统方法取得1.3dB的信噪比增益，但其需要的平均复乘次数只有传统方法的57％。Fig. 10 is a performance comparison diagram of the adaptive algorithm based on decision reliability feedback with the number of iterations X = 2 and the traditional method when the fractional frequency offset estimation is completely correct when the method of equal intervals is used in the present invention. In this simulation, λ ₁ =λ ₂ =0.25, λ ₃ =0.5, and three cases of η are considered: 0.5, 0.75 and 0.875. When η=0.5, the present invention obtains the signal-to-noise ratio gain of 4.7dB than traditional method, and, the self-adaptive algorithm emulation of X=2 shows, and the average times of multiplication that it needs has only 57% to 75% of traditional method; When η=0.75, the present invention obtains the signal-to-noise ratio gain of 2.6dB than traditional method, but the average times of multiplication that it needs has only 57% to 58% of traditional method; When η=0.875, the present invention obtains 1.3 more than traditional method dB SNR gain, but the average number of complex multiplications required is only 57% of the traditional method.

仿真结果表明，本发明具有计算复杂度较低，且估计错误率较低的优点，在OFDM系统中具有很高的应用价值。Simulation results show that the present invention has the advantages of low computational complexity and low estimation error rate, and has high application value in OFDM systems.

Claims

1, a kind of method of estimating OFDM integral number frequency multiplication bias is characterized in that, comprises the steps:

Step 1: transmitting terminal produces the synchronous training symbol of N point OFDM of a L five equilibrium, and each five equilibrium of described symbol contains the M point;

Step 2: described synchronous training symbol is reconstructed, be about to the symbol in the step 1, be reconstructed into M L point ofdm signal symbol, the ofdm signal symbol sampler point that is about to each five equilibrium carries out the order number designation, again the identical time domain point of label is extracted out in order, formed new OFDM symbol;

Step 3: λ M the reconstruct symbol that receiving terminal uses the fft algorithm demodulation to pick out from M reconstruct symbol of step 2 gained, obtain the frequency-region signal sequence of a described λ M reconstruct symbol, it is the fractional part of frequency offset estimated value that coupling system prime synchronization module provides, in the multiple multiplying factor of traditional FFT algorithm structure, introduce the fractional part of frequency offset correction term, finish fractional part of frequency offset compensation and demodulating ofdm reconstruct symbol simultaneously; Perhaps, behind the fractional part of frequency offset of employing direct compensation OFDM reconstruct symbol, with the traditional FFT algorithm OFDM reconstruct symbol is carried out demodulation again;

Step 4: the frequency-region signal sequence to FFT computing gained in the step 3 merges, and the pairing frequency of the peak value after the merging is exactly the estimated value of integer frequency offset;

Described N, L, M are the integer greater than 0, M=N/L, and described λ M is an integer, 0＜λ≤1.

2, the method for estimating OFDM integral number frequency multiplication bias according to claim 1 is characterized in that, described step 3 from M L point ofdm signal symbol, is taken out λ M different reconstruct symbol at random; Perhaps from M L point ofdm signal symbol, determine first reconstruct symbol earlier at random, equally spaced take out λ M different reconstruct symbol again; Perhaps from M L point ofdm signal symbol, determine first reconstruct symbol earlier at random, take out λ M different reconstruct symbol more continuously.

3, the method for estimating OFDM integral number frequency multiplication bias according to claim 1, it is characterized in that described step 4, the merging method that merges the frequency-region signal sequence of OFDM reconstruct symbol are that quadratic sum merges, perhaps mould value and merging, the perhaps merging of real part absolute value and imaginary part absolute value sum.

4, the method for estimating OFDM integral number frequency multiplication bias according to claim 1, it is characterized in that, after described step 4, enter adaptive iteration algorithm based on the decision reliability feedback, promptly pass through the reliability of appraisal procedure four gained estimated values, increase the value of λ adaptively, repeating step three and step 4 obtain integer frequency offset estimated value comparatively reliably at last.

5, the method for estimating OFDM integral number frequency multiplication bias according to claim 4, it is characterized in that, the reliability of described appraisal procedure four gained estimated values, its method is the reliability index into step 4 gained estimated value of likening to of the mean value of the frequency-region signal sequence that obtains of calculation procedure four and maximum, if reliability index is less than threshold value η, think that then it is reliable estimating, otherwise, system will increase the value of λ, repeating step three and step 4, obtain integer frequency offset estimated value comparatively reliably at last, the span of described η is [1/L, 1].

6, the method for estimating OFDM integral number frequency multiplication bias according to claim 4, it is characterized in that, the reliability of described appraisal procedure four gained estimated values, the second largest value of the frequency-region signal sequence that obtains in calculation procedure four and maximum liken reliability index to into step 4 gained estimated value, if reliability index is less than threshold value α, think that then it is reliable estimating, otherwise, system will increase the value of λ, repeating step three and step 4, obtain integer frequency offset estimated value comparatively reliably at last, the span of described α is (0,1).

7, the method for estimating OFDM integral number frequency multiplication bias according to claim 4, it is characterized in that, the reliability of described appraisal procedure four gained estimated values, the mean value of adjacent two values of the frequency-region signal sequence that obtains in calculation procedure four and maximum liken reliability index to into step 4 gained estimated value, if reliability index is less than threshold value, think that then it is reliable estimating, otherwise, system will increase the value of λ, repeating step three and step 4, obtain integer frequency offset estimated value comparatively reliably at last, the span of described β is (0,1).