正交频分复用码分多址系统盲自适应频率同步算法

Blind Adaptive Frequency Synchronization Algorithm for OFDM-CDMA Systems over Frequency Selective Fading Channels

针对正交频分复用码分多址系统对载频偏移非常敏感的问题 ,在分析基于循环前缀的最大似然联合时间频率同步和基于虚拟子载波盲载频偏移估计的基础上 ,提出了一种用曲线拟合实现类MUSIC的快速算法 .考虑信号功率曲线随载频偏移的sinc函数形式 ,在曲线峰值点附近选取测试点 ,进行近似曲线拟合 ,通过对曲线参数估计 ,得到信号功率随载频偏移的解析表达式 ,闭式解得到载频偏移 ,解决了类MUSIC估计器多项式根搜索运算量大、收敛速度慢的问题 .仿真结果表明 ,在估计精度和载频偏移初值均相同的条件下 ,快速算法的运算量是类MUSIC算法的 1/8 5 ,而系统频谱利用率则提高了 2 5 % .

Orthogonal frequency division multiplexing code division multiple access (OFDM CDMA) scheme can sufficiently utilize the subcarrier diversity and meet the demand of diverse multimedia services;therefore it is broadly considered as an effective approach for future wireless multimedia communications. But it is very sensitive to carrier drifts, while the orthogonal property between the subcarriers is lost with carrier frequency offset. After analyzing the cyclic prefix (CP) based maximum likelihood (ML) joint time frequency synchronization and the blind carrier drift estimation with virtual subcarrier, a blind adaptive frequency offset estimation algorithm is proposed. It is the fast implementation of the MUSIC Like estimator with curve fitting to the signal power. With the original value of carrier drift, the testing points are selected to obtain the analytical formation of the curve,and the frequency offset is acquired in closed form. The fast algorithm reduces the computing burden of MUSIC Like method. The numerical simulations show that the complexity of the proposed algorithm is one eighth less than that of the MUSIC Like algorithm and has a 25% improvement of spectrum.