低轨卫星通信中SCMA系统载波同步算法设计

为了提高低轨卫星通信频谱利用率及对抗存在的大多普勒频移, 考虑将稀疏码多址接入(sparse code multiple access, SCMA)技术应用于低轨卫星通信，提出一种针对SCMA系统的数据辅助载波同步方案。该同步方案的频偏、相偏估计算法分别采用分步相关法和最大似然法。同时, 根据所提分步相关算法的特点, 优化了导频和数据组成的分布图样。仿真结果表明, 以6个用户共享4个资源块的系统为例, 基于优化帧结构的载波同步方案可以利用较少的导频开销获得比使用经典帧结构的更高估计精度和更好误码性能。

Design of carrier synchronization algorithm for SCMA system in LEO satellite communication

To improve the spectral efficiency of low earth orbit(LEO)satellite communications and combat existing large Doppler frequency shifts,a sparse code multiple access(SCMA)technique is considered for LEO satellite communications,and a data-aided carrier synchronization scheme is proposed for the SCMA system.In this scheme,a stepwise correlation algorithm and a maximum-likelihood algorithm are used to estimate frequency offset and phase offset,respectively.Then,the distribution pattern of the pilot and data symbols is optimized according to the characteristic of the proposed stepwise correlation algorithm.Simulation results show that,taking an SCMA system with 6 users sharing 4 resources as an example,the proposed carrier synchronization scheme using the two optimized frame structures with less pilot overhead can achieve higher estimation accuracy and better error performance than that using the classical frame structure.