CN105681245A - Continuous piecewise sliding window estimation frequency offset-based frequency tracking method - Google Patents

Abstract

The invention discloses a continuous piecewise sliding window estimation frequency offset-based frequency tracking method. The method includes the following steps that: modulated information is removed from unique code symbols; the unique code symbols are segmented according to fixed length; each segment of unique code symbols is accumulated in a grouped manner; frequency estimation is performed on the cumulative value of each segment of unique code symbols by using an M&M algorithm, the frequency offset estimation value of each segment of unique code symbols is obtained; the frequency offset estimation values are slid rightwards with a certain unique code window length, and the frequency estimation value of each segment of unique code symbols is calculated sequentially according to a fixed unique code length, and therefore, a series of continuous frequency estimation values can be obtained; and the continuous frequency estimation values are adopted to perform piecewise frequency offset compensation on continuous data frames. According to the method of the invention, based on a continuous frame structure, a carrier aided unique code symbol piecewise sliding window is adopted to estimate frequency offset, and frequency offset compensation is carried out piecewise, and therefore, fine frequency synchronization can be realized. With the method adopted, the influence of the dynamic change of frequency offset on carrier tracking performance can be decreased as far as possible, and demodulation performance can be improved.

Description

A kind of frequency tracking method estimating frequency deviation based on the sliding window of continuous segmentation

Technical field

The present invention relates to field of wireless communications systems, particularly relate to a kind of frequency tracking method estimating frequency deviation based on the sliding window of continuous segmentation.

Background technology

In satellite mobile communication system, baseband signal after demodulation down coversion is very easy to the impact by environment, crystal oscillator instability and Doppler frequency skew, thus the carrier frequency containing dynamic change offsets, this frequency shift can cause constellation point skew thus make receiving apparatus cannot correct demodulation source signal, therefore need before demodulation to carry out accurately carrier frequency synchronization and compensate. Usual carrier frequency synchronization divides two steps to complete, and namely first carries out carrier wave initial acquisition with synchronous, compensates major part frequency deviation; Complete catching and following the tracks of of residential frequency deviation and then. Catch accuracy and the impact of frequency deviation dynamic change in view of original frequency, accurately carry out residential frequency deviation tracking and just become particularly important. Generally adopt now unique code symbol auxiliary transmission technology; the existing multiple auxiliary frequency estimation algorithm of unique code under static or dynamic frequency offset change less situation; such as kay algorithm, fft algorithm etc.; but the Frequency Estimation performance of these algorithms under high dynamic frequency offset changing environment is very undesirable; usually can introduce bigger frequency error when carrying out frequency compensation, thus make frequency-tracking degradation.

Summary of the invention

It is an object of the invention to overcome the deficiencies in the prior art, it is provided that a kind of based on continuous frame structure, utilize the photocarrier method sliding window of unique code symbol segmentation to estimate frequency deviation, and the method that segmentation carries out compensate of frequency deviation realizes essence Frequency Synchronization.

It is an object of the invention to be achieved through the following technical solutions: a kind of frequency tracking method estimating frequency deviation based on the sliding window of continuous segmentation, comprises the following steps:

S1: ask conjugation relevant to the unique code symbol number extracted from Received signal strength unique code symbol number known for this locality, remove modulation information;

S2: to going the unique code symbol number after modulation information by regular length segmentation;

S3: every section of unique code grouping is cumulative;

S4: adopt frequency estimation algorithm to carry out Frequency Estimation every section of cumulative value, obtain the frequency deviation estimated value of each segmentation;

S5: slide to the right successively with certain unique code window length, then the frequency estimation of each segmentation is calculated successively by fixing unique code length degree, thus obtain a series of continuous print frequency estimation;

S6: continuous data frame is carried out segmentation compensate of frequency deviation by a series of continuous print frequency estimations adopting step S5 to obtain.

Described frequency estimation algorithm adopts M&M algorithm, and M&M algorithm carries out the workflow of Frequency Estimation and is:

SS1:N the cumulative value of unique code seeks auto-correlation;

SS2: the phase increment calculating autocorrelative function;

SS3: phase increment is multiplied by smoothing factor;

Frequency estimation is calculated after SS4:M level and smooth phase angle is cumulative.

The frequency deviation estimation formulas of described M&M algorithm is:

In formula, T_sFor symbol period, w (m) is smoothing factor, and R (m) is the autocorrelative function of definition, and arg{} is for seeking angle function, and unit is radian, has:

$w\left(m\right)=\frac{3(N-m)(N-m+1)-3M(N-M)}{M(4M^2-6MN+3N^2-1)}$

$R\left(m\right)=\frac{1}{N-m}\underset{k=m+1}{\overset{N}{\Σ}}\left(Z_k\right){\left(Z_{k-m}\right)}^{*},1\≤m\≤M$

Wherein M is algorithm design parameter, and value is M=N/2, N is the cumulative value length of unique code, Z_kRepresent the unique code cumulative signal gone after modulating.

The invention has the beneficial effects as follows: based on continuous frame structure, utilize the photocarrier method sliding window of unique code symbol segmentation to estimate frequency deviation, and the method that segmentation carries out compensate of frequency deviation achieves essence Frequency Synchronization. Solve the Frequency Estimation performance of existing algorithm under high dynamic frequency offset changing environment very undesirable, usually can introduce bigger frequency error when carrying out frequency compensation, thus make the problem of frequency-tracking degradation. The present invention can reduce frequency deviation dynamic change to the impact of carrier track performance as far as possible, promotes demodulation performance.

Accompanying drawing explanation

Fig. 1 is frequency-tracking schema of the present invention;

Fig. 2 is M&M Frequency Estimation schema;

Fig. 3 is segmentation compensate of frequency deviation schematic diagram.

Embodiment

The technical scheme of the present invention is described in further detail below in conjunction with accompanying drawing, but protection scope of the present invention is not limited to the following stated.

The present invention is by going uniqueness code symbol number after modulation information by regular length segmentation, again that every section of unique code grouping is cumulative, then M&M algorithm is adopted to carry out Frequency Estimation every section of cumulative value, obtain the frequency deviation estimated value of each segmentation, and then slide to the right successively with certain unique code window length, the frequency estimation of each segmentation is calculated again successively by fixing unique code length degree, thus can obtain a series of continuous print frequency estimation, finally adopt these continuous frequency deviation estimated values that continuous data frame is carried out segmentation compensate of frequency deviation.

Satellite communication system is transmitted usually frame by frame, every frame data are made up of unique code (UW), data block, assuming that the unique code number of every frame data is L, the data symbol numbers between each unique code is R, and the frequency-tracking flow process of continuous segmentation sliding window estimation essence frequency deviation is as shown in Figure 1.

According to Fig. 1, first local known unique code symbol number seeks conjugation relevant (i.e. conjugate multiplication) to the unique code symbol number extracted from Received signal strength, removes modulation information; Afterwards by its segmentation, if unique code regular length is 256, i.e. L=256, according to the roughly variation range of frame dynamic frequency offset every in practical application, can carry out segmentation by the unique code after conjugation, and as 256 UW are divided into 4 sections, every section then comprises 64 unique codes; Considering according to the dynamic frequency offset scope of data frame and the maximum frequency estimation range of M&M algorithm, can be divided into n group by every section of unique code again, often organizes m UW and adds up, then now the maximum frequency estimation range of M&M algorithm is {-F_d/(2*m*R),F_d/ (2*m*R) }, wherein F_dFor the symbol rate of channel frame, as long as the maximum dynamic frequency offset one ensureing data frame fixes within the Frequency Estimation scope of M&M algorithm;Assuming that n=16, m=4, next 16 groups of cumulative values employing M&M algorithms of every section being carried out Frequency Estimation, obtain 4 frequency estimations, the workflow of M&M algorithm is as shown in Figure 2.

As shown in Figure 2, by asking, the cumulative autocorrelative function of value and the phase increment of this auto-correlation sequence realize M&M Frequency Estimation, and its frequency deviation estimation formulas is:

In formula, T_sFor symbol period, w (m) is smoothing factor, and R (m) is the autocorrelative function of definition, and arg{}, for seeking angle function (unit is radian), has:

$w\left(m\right)=\frac{3(N-m)(N-m+1)-3M(N-M)}{M(4M^2-6MN+3N^2-1)}$

$R\left(m\right)=\frac{1}{N-m}\underset{k=m+1}{\overset{N}{\Σ}}\left(Z_k\right){\left(Z_{k-m}\right)}^{*},1\≤m\≤M$

Wherein M is algorithm design parameter, and optimum value is M=N/2, N is the cumulative value length of unique code, Z_kRepresent the unique code cumulative signal gone after modulating.

Next taking fixing unique code length degree as sliding window, slip R time to the right successively, then calculate R*4 frequency estimation successively by the fixing window length of L=256, wherein R is different with channel speed value according to different frame structure with sliding window length; Finally utilize (R+1) * 4 frequency estimations tried to achieve that these frame data are carried out segmentation compensate of frequency deviation. Here for L=256, R=1, concrete segmentation compensate of frequency deviation schematic diagram is as shown in Figure 3.

According to Fig. 3,256 UW being divided into 4 sections, every section of 64 UW, first can calculate with fixing window length 2564 frequency deviation estimated values, then sliding window once can calculate to the rightThus can form8 continuous print frequency deviation estimated values; As shown in Figure 3, then by dashed rectangle mark, these frame data being carried out segmentation, the data section of each mark adopts the frequency deviation estimated value of its correspondence to compensate respectively, it can be seen thatCorresponding data section crosses over two frames, namely this last frequency deviation value calculated of employing is carried out compensate of frequency deviation by front 16*R the data of next frame data, corresponding previous frequency is followed the tracks of and is returned last k frequency estimation in schema to following the tracks of next time, k is according to specific performance requirement, frame structure and channel speed is different and value is different, k=1 in this schematic diagram. If must be noted that in addition, present frame is the first frame, it can be seen thatAlso having 16*R data before first corresponding data section, owing to not having return of value when the first frame calculates, therefore this one piece of data can only be usedCarry out compensate of frequency deviation.

The above is only the preferred embodiment of the present invention, it is to be understood that the present invention is not limited to the form disclosed by this paper, should not regard the eliminating to other embodiments as, and can be used for other combinations various, amendment and environment, and in contemplated scope described herein, can be changed by technology or the knowledge in above-mentioned instruction or relevant field. And the change that those skilled in the art carry out and change do not depart from the spirit and scope of the present invention, then all should in the protection domain of claims of the present invention. M&M algorithm of the present invention, other communication specialities personnel can substitute by other frequency estimating methods, then all should in the protection domain of claims of the present invention.

Claims (3)

1. estimate the frequency tracking method of frequency deviation based on the sliding window of continuous segmentation for one kind, it is characterised in that, comprise the following steps:

S1: ask conjugation relevant to the unique code symbol number extracted from Received signal strength unique code symbol number known for this locality, remove modulation information;

S2: to going the unique code symbol number after modulation information by regular length segmentation;

S3: every section of unique code grouping is cumulative;

S4: adopt frequency estimation algorithm to carry out Frequency Estimation every section of cumulative value, obtain the frequency deviation estimated value of each segmentation;

S5: slide to the right successively with certain unique code window length, then the frequency estimation of each segmentation is calculated successively by fixing unique code length degree, thus obtain a series of continuous print frequency estimation;

S6: continuous data frame is carried out segmentation compensate of frequency deviation by a series of continuous print frequency estimations adopting step S5 to obtain.

2. a kind of frequency tracking method estimating frequency deviation based on the sliding window of continuous segmentation according to claim 1, it is characterised in that: described frequency estimation algorithm adopts M&M algorithm, and M&M algorithm carries out the workflow of Frequency Estimation and is:

SS1:N the cumulative value of unique code seeks auto-correlation;

SS2: the phase increment calculating autocorrelative function;

SS3: phase increment is multiplied by smoothing factor;

Frequency estimation is calculated after SS4:M level and smooth phase angle is cumulative.

3. a kind of frequency tracking method estimating frequency deviation based on the sliding window of continuous segmentation according to claim 1, it is characterised in that: the frequency deviation estimation formulas of described M&M algorithm is:

In formula, T_sFor symbol period, w (m) is smoothing factor, and R (m) is the autocorrelative function of definition, and arg{} is for seeking angle function, and unit is radian, has:

$w\left(m\right)=\frac{3(N-m)(N-m+1)-3M(N-M)}{M(4M^2-6MN+3N^2-1)}$

$R\left(m\right)=\frac{1}{N-m}\underset{k=m+1}{\overset{N}{\Σ}}\left(Z_k\right){\left(Z_{k-m}\right)}^{*},1\≤m\≤M$

Wherein M is algorithm design parameter, and value is M=N/2, N is the cumulative value length of unique code, Z_kRepresent the unique code cumulative signal gone after modulating.