Abstract: This paper researches the carrier frequency sychronization for downlink of LTE system and analyzes two traditional Carrier Frequency Offset（CFO） estimation algorithms which are the estimation based PSS correlation and the Max-Likelihood（ML）estimation based on Cycle Prefix（CP）. Aiming at the latter algorithm has the shortcomings that are a poor ability to resist multipath and polarity reversion and a smaller estimation scale, this paper proposes an improved algorithm. This improved algorithm reduces the influence of multi-path through substracting a part of interferenced data from the CP when using the CP to estimate the CFO. To expand the estimation scale and enhance the ability of resisting the polarity reversion, this improved algorithm uses the polarity information of the estimated result of algorithm based on PSS correlation. The simulations show that, the improved algorithm has a better performance in the multi-path condition compared to the original algorithm, when [|εF|] approach to 0.5, the original algorithm can resit the polarity information effectively and has good robust ability to the changement of [|εF|] nearby 0.5, when [|εF|>0.5], the original algorithm is invalid but the improved algorithm still can estimate the [εF] and keep a higher estimation performance.

Key words: Long Term Evolution（LTE）, Carrier Frequency Offset（CFO） estimation, reducing influence of multi-path, resisting polarity reversion, expanding estimation scale

摘要： 主要研究了LTE系统下行链路中的载波同步，分析了基于PSS相关估计和基于CP的ML估计两类传统频偏估计算法。针对后者抗多径能力不足、抗极性反转能力差和估计范围较小的缺陷，提出了一种改进频偏估计算法。该算法在利用CP数据进行ML频偏估计时去掉一部分受符号干扰的数据，以减少多径影响;利用PSS相关估计结果的极性信息，对算法估计结果进行修正，扩大频偏估计范围和提高抗极性反转能力。仿真结果表明：改进算法相对于原算法在多径环境下具有更好的估计性能;当频偏[|εF|]接近0.5时能够抵抗极性反转具有较高的鲁棒性，当[|εF|>0.5]时原算法失效而改进算法仍能够保持较高的估计性能。

关键词: 长期演进（LTE）, 频偏估计, 减小多径影响, 抗极性反转, 扩大频偏估计范围