CN102316062A

CN102316062A - Algorithm for synchronizing carrier wave based on prior probability assistance

Info

Publication number: CN102316062A
Application number: CN2010102209920A
Authority: CN
Inventors: 徐俊辉; 高中杰; 张忠培
Original assignee: University of Electronic Science and Technology of China
Current assignee: University of Electronic Science and Technology of China
Priority date: 2010-07-07
Filing date: 2010-07-07
Publication date: 2012-01-11

Abstract

A priori probability-based assisted carrier synchronization calculation belongs to the technical field of wireless communication, and particularly relates to carrier synchronization with residual frequency offset in a low signal-to-noise ratio environment. This method achieves the following purposes: use the prior probability auxiliary algorithm to calculate the phase error information of each symbol, so that the algorithm can realize synchronization under the condition of low signal-to-noise ratio and residual frequency offset; improve the performance of the system, and reduce the computational complexity A good compromise between performance and system performance.

Description

Auxiliary Carrier Synchronization Algorithm Based on Prior Probability

技术领域 technical field

本发明属于无线通信技术领域，特别涉及低信噪比环境下，残留频偏的载波同步。 The invention belongs to the technical field of wireless communication, and in particular relates to carrier synchronization with residual frequency offset in a low signal-to-noise ratio environment. the

背景技术 Background technique

在低信噪比条件下，Turbo码和LDPC码系统对载波频率和相位的同步要求很严格，即使存在小的频偏和相偏也会使系统的性能恶化。因此数据在进入译码器前必须采用适当的技术使其能够精确地同步。然而，在极低信噪比环境下，精确的载波同步是一个很困难的问题，比如，采用BPSK调制，Turbo码编码器的码率为1/6，当SNR＜-7.8dB时，很少的无线接收机能实现同步。 Under the condition of low signal-to-noise ratio, Turbo code and LDPC code system have very strict requirements on the synchronization of carrier frequency and phase, even if there is a small frequency deviation and phase deviation, the performance of the system will be deteriorated. So the data must adopt appropriate technology to make it can be accurately synchronized before entering the decoder. However, in the environment of extremely low signal-to-noise ratio, precise carrier synchronization is a very difficult problem. For example, using BPSK modulation, the code rate of the Turbo code encoder is 1/6, and when SNR<-7.8dB, rarely The wireless receiver can achieve synchronization. the

发明内容 Contents of the invention

本发明提出了一种基于先验概率辅助载波同步算法，采用本算法可以实现在残余频偏下的载波同步，并且系统性能可以更接近译码器的性能。 The invention proposes an auxiliary carrier synchronization algorithm based on a priori probability, which can realize the carrier synchronization under the residual frequency offset, and the system performance can be closer to the performance of the decoder. the

本发明的创新之处在于：采用极大似然估计的方法估计出每个符号的载波信息，然后将误差信息输入到滤波器，之后得到待估计的相偏信息。 The innovation of the present invention lies in: the carrier information of each symbol is estimated by the method of maximum likelihood estimation, then the error information is input into the filter, and then the phase offset information to be estimated is obtained. the

本发明在先验概率辅助载波同步算法的基础上对载波相位估计算法做了改进，提出了基于逐个符号的先验概率辅助载波同步算法。 The present invention improves the carrier phase estimation algorithm on the basis of the prior probability assisted carrier synchronization algorithm, and proposes the prior probability assisted carrier synchronization algorithm based on each symbol. the

1、系统结构 1. System structure

基于先验概率辅助载波同步算法如图1所示，[r_i]_k表示接收到的第k帧数据的第i个符号，[y_i]_k表示解旋后的第k帧数据的第i个符号。接收端将数据缓存，译码器输出的外信息用于码辅助迭代载波相位误差估计，环路滤波器将相位误差信号转换成控制信号，该控制信号控制数控振荡器的输出，得到待估计的相位误差，然后对r_i进行相位补偿得到y_i，最后解调并译码再进行下一次的相位误差估计。 The auxiliary carrier synchronization algorithm based on prior probability is shown in Figure 1, [r _i ] _k represents the i-th symbol of the received k-th frame data, and [y _i ] _k represents the i-th symbol of the k-th frame data after derotation symbols. The receiving end caches the data, and the external information output by the decoder is used for code-assisted iterative carrier phase error estimation. The loop filter converts the phase error signal into a control signal, and the control signal controls the output of the numerically controlled oscillator to obtain the estimated phase error, and then perform phase compensation on _ri to obtain y _i , and finally demodulate and decode the next phase error estimation.

2、基于先验概率辅助载波同步算法 2. Auxiliary carrier synchronization algorithm based on prior probability

2.1基于先验概率辅助载波同步算法简介 2.1 Brief introduction of auxiliary carrier synchronization algorithm based on prior probability

基于先验概率辅助载波同步算法主重点在于载波相位误差的估计。本发明采用的相位误差估计表达式可以写成： The main focus of carrier synchronization algorithm based on prior probability is the estimation of carrier phase error. The phase error estimation expression that the present invention adopts can be written as:

${\overset{~ ~}{φ φ}}_{ML ML} = = \frac{{ω ω}_{11} {θ θ}_{11} + + 22 {ω ω}_{22} {θ θ}_{22}}{{ω ω}_{11} + + 44 {ω ω}_{22}}$

其中，ω_k为第k次谐波的幅度，θ_k为第k次谐波的相位，ω_k和θ_k可以由下面的式子得到。 Among them, ω _k is the magnitude of the kth harmonic, θ _k is the phase of the kth harmonic, and ω _k and θ _k can be obtained by the following formula.

${ω ω}_{11} cos cos (({θ θ}_{11})) = = {a a}_{11}^{i i} cos cos (({φ φ}_{i i}))$

${ω ω}_{11} sin sin (({θ θ}_{11})) = = {a a}_{11}^{i i} sin sin (({φ φ}_{i i}))$

${ω ω}_{22} cos cos (({θ θ}_{22})) = = {a a}_{22}^{i i} cos cos ((22 {φ φ}_{i i}))$

${ω ω}_{22} sin sin (({θ θ}_{22})) = = {a a}_{22}^{i i} sin sin ((22 {φ φ}_{i i}))$

其中，φ_i是[r_i]_k的相位，

是第i个符号的第n次谐波，定义为： where φ _i is the phase of [r _i ] _k ,

is the nth harmonic of the i-th symbol, defined as:

${a a}_{n no}^{i i} = = \frac{11}{π π} {&Integral; &Integral;}_{- - π π}^{π π} {Λ Λ}_{L L,, BPSK BPSK}^{i i} ((φ φ)) cos cos ((nφ nφ)) dφ dφ$

对于Turbo系统，在第一次迭代之前是没有先验信息可以利用的，但是可以用传输的符号概率来代替，用P_i(m)表示，利用这些概率值对似然函数求平均值，这样可以求得第i个符号的对数似然函数(LLF)，对于BPSK而言，第i个符号的对数似然函数可以写成， For Turbo systems, there is no prior information available before the first iteration, but the transmitted symbol probabilities can be used instead, denoted by P _i (m), and these probability values are used to average the likelihood function, such that The log-likelihood function (LLF) of the i-th symbol can be obtained. For BPSK, the log-likelihood function of the i-th symbol can be written as,

${Λ Λ}_{L L,, BPSK BPSK}^{i i} ((φ φ)) = = log log {{sech sech ((\frac{L L ((i i))}{22})) \cdot \cdot cosh cosh [[\frac{L L ((i i))}{22} + + \frac{{A A}_{i i} cos cos ((φ φ - - {φ φ}_{i i}))}{{σ σ}^{22}}]]}}$

环路滤波器表达式可以写成， The loop filter expression can be written as,

$θ θ ((i i)) = = θ θ ((i i - - 11)) + + γ γ {\overset{~ ~}{φ φ}}_{ML ML} ((i i))$

其中，γ是环路滤波器的系数。 where γ is the coefficient of the loop filter. the

2.2基于先验概率辅助载波同步算法步骤 2.2 Auxiliary carrier synchronization algorithm steps based on prior probability

基于先验概率码辅助载波同步算法是基于逐个符号的同步算法，具体的工作流程如下： The code-assisted carrier synchronization algorithm based on prior probability is a symbol-by-symbol synchronization algorithm. The specific workflow is as follows:

第一步：参数初始化，设置最大迭代次数为M，且

The first step: parameter initialization, set the maximum number of iterations to M, and

[y_i]_k＝[r_i]_kexp(-jθ(0)) [y _i ] _k ＝[r _i ] _k exp(-jθ(0))

第二步：计算第k帧第i个符号的误差信息 Step 2: Calculate the error information of the i-th symbol in the k-th frame

第三步：经过滤波器得到

Step 3: get through the filter

第四步：频偏补偿[y_i]_k＝[r_i]_kexp(-jθ(i))。 Step 4: Frequency offset compensation [y _i ] _k =[r _i ] _k exp(-jθ(i)).

第五步：BPSK解调。 Step 5: BPSK demodulation. the

第六步：Turbo译码。 Step 6: Turbo decoding. the

第七步：返回步骤二进行下一次迭代。 Step 7: Return to Step 2 for the next iteration. the

附图说明 Description of drawings

图1基于先验概率辅助载波同步算法框图。 Fig. 1 is a block diagram of an auxiliary carrier synchronization algorithm based on prior probability. the

Claims

1. based on the auxiliary Carrier Synchronization Algorithm of prior probability; Receiving terminal is with metadata cache; The external information of decoder output is used for the auxiliary iteration carrier phase error of sign indicating number and estimates that loop filter converts phase error signal to control signal, the output of this control signal control digital controlled oscillator; Obtain phase error to be estimated, then to r _iCarry out phase compensation and obtain y _i, phase error estimation and phase error is next time carried out in last demodulation and decoding again.

2. said based on the auxiliary Carrier Synchronization Algorithm of prior probability according to claim 1, comprise following step:

Be based on the synchronized algorithm of symbol one by one based on prior probability sign indicating number subcarrier synchronized algorithm, concrete workflow is following:

The first step: parameter initialization, it is M that maximum iteration time is set, and θ (0)=0,

[y _i] _k＝[r _i] _kexp(-jθ(0))

Second step: the control information

of calculating i symbol of k frame

The 3rd step: obtain

through wave filter

The 4th step: compensate of frequency deviation [y _i] _k=[r _i] _kExp (j θ (i)).

The 5th step: BPSK demodulation.

The 6th step: Turbo decoding.

The 7th step: return step 2 and carry out next iteration.