基于QAM载波恢复算法的研究

Research on QAM-based carrier recovery method

针对高阶QAM调制解调系统对载波偏移的敏感性问题,采用一种基于导频、扫频环路和载波恢复环路的高阶QAM载波恢复方法。这里设计的扫频环路是由帧检测、扫频、频率校正三个模块组成,载波恢复环路由极性判决算法模块和判决导向模块组成。扫频和极性判决算法都具有较大的频偏捕获能力。两者联合用于载波频偏的捕获阶段,既克服了一般扫频算法残留频偏大的困难,也解决了极性算法可用角点少的问题。

In order to solve the sensitivity problem of high-order quadrature amplitude modulation（QAM）modulation and demodulation system for carrier offset,a new high-order QAM carrier recovery method based on pilot frequency,frequency sweep loop and carrier recovery loop is proposed. The frequency sweep loop is comprised of three modules of frame detection, frequency sweep and frequency correction. The carrier recovery loop contains the polarity decision algorithm module and decision-directed（DD）module. The frequency sweep and polarity decision algorithm both have large frequency offset acquisition ability. If They are applied jointly to the stage of frequency offset acquisition,the difficulty of larger residual frequency offset caused by general sweep algorithm can be overcome and the problem of polarity algorithm with little available corner can be solved.