高动态环境下联合导频与Viterbi的同步技术

Joint pilot and Viterbi decoding synchronization technology in high-dynamic environments

针对高动态环境下,移动目标的加速运动同时产生多普勒频偏和多普勒变化率,不易跟踪及消除,严重影响接收机性能的问题,提出了一种联合导频与Viterbi译码幸存处理的载波同步方法。该方法首先基于最小二次均方误差准则开环捕获,将频率偏移建模为泰勒级数展开的形式,利用已知序列辅助粗估多普勒频偏和变化率,将多普勒频偏和多普勒变化率限制到一个较小范围内;同时为了克服长时相位误差积累导致的性能恶化,采用幸存处理技术闭环跟踪载波,利用Viterbi逐符号判决的软信息输入到三阶锁相环路中,鉴相器输出相位误差调整频率合成器输出,实时迭代跟踪最小化鉴相器误差输出,实现载波同步和相干解调接收。仿真结果表明,当归一化频偏小0.1,归一化多普勒变化率小于10^(-3)时,所提方法能够准确跟踪载波;当误码率要求为10^(-5)时,这种译码同步级联跟踪的算法与理想不存在多普勒频偏和变化率的接收性能相比,信噪比仅有约0.8 dB的差距,而且明显优于传统的锁相环和最小均方误差算法。

Since the Doppler frequency offset and Doppler rate-of-change caused by the accelerated motion of the moving targets are hard to tract and eliminate in high-dynamic environment,which seriously affects the performance of the receiver,we propose a carrier synchronization method for joint pilot and Viterbi decoding per-survivor-processing(PSP).First,an open-loop acquisition is performed based on the minimum mean square error(MMSE)principle,and the frequency offset is modeled in the form of the Taylor series expansion.Then,a known sequence is used to estimate the Doppler frequency offset and Doppler rate-of-change,thereby limiting the frequency offset and rate-of-change to a small range.Meanwhile,to overcome the performance degradation caused by the accumulation of long-term phase errors,the closed-loop tracking is implemented by the PSP technology,and the soft information determined by Viterbi symbol-by-symbol is input to the third-order phase-locked loop(PLL).Moreover,the frequency synthesizer is adjusted according to the error of the phase detector.Then this action is iteratively performed to minimize the error of the phase detector and realize the carrier synchronization.Finally,coherent demodulation reception is achieved.Simulation results show that when the normalized frequency offset is less than 0.1 and the normalized rate-of-change is less than 10^(-3),the proposed method can track the carrier accurately.Furthermore,under the bit-to-error(BER)constraint of 10^(-5),there is only 0.8dB difference in S/N ratio between the proposed decoding synchronization cascade tracking algorithm and the ideal carrier synchronization without the Doppler frequency offset and rate-of-change.In addition,the propose algorithm is significantly superior to the traditional phase-locked loop and MMSE algorithm.