中文摘要：

针对突发直扩系统在极低信噪比下载波估计精度和范围不能兼顾的问题,提出了一种联合导频辅助和解扩软输出的载波同步算法.基于导频和数据分插的帧结构,首先利用导频信息采用平均周期图法对载波频偏进行粗估计,通过最大似然算法得到相偏粗估计值,并对接收信号进行分段相位补偿;然后利用解扩软输出进行频偏细估计,进而得到相偏的细估值.理论分析和仿真结果表明：在极低信噪比和导频数目一定的条件下,算法的估计性能接近修正克拉美罗界,具有较高的频偏估计精度,且频偏和相偏估计范围大,能达到理想同步的误比特率性能.

英文摘要：

Current carrier synchronization algorithms at extremely low signal to noise ratios （SNRs） for burst direct sequence spread spectrum communication systems are not very good at achieving a high estimation precision and wide estimation range at the same time.A joint pilot assisted and despread soft-output carrier synchronization algorithm is proposed in this paper.Based on a frame structure in which the pilot symbols are separated with data symbols,a coarse frequency offset estimation is first performed based on the averaging periodogram method with the help of pilot symbols,and a coarse phase offset estimation is obtained with the maximum likelihood algorithm,and then the phase of the received signals is compensated for each segment of pilot and data symbols.Next,a fine frequency offset estimation is carried out using the despread soft output; then the fine phase offset estimation is obtained.Simulation results show that at extremely low SNRs and with a fixed number of pilots,the performance of the algorithm is near the modified Cramer-Rao bound with high frequency offset estimation precision and wide frequency offset and phase offset estimation ranges.The bit error rate of the algorithm is close to the ideal performance.