高阶QAM的载波恢复方法研究

Research on high-order QAM carrier recovery method

文章针对高阶正交幅度调制(QAM)的调制解调系统对载波偏移的敏感性,采用一种基于扫频环路、极性判决算法、直接判决(DD)和导频相结合的载波恢复方法。扫频和极性判决算法的频偏捕获范围大,相位抖动也较大,DD算法捕获范围较小,一般只达到系统符号率的±3%,相位抖动也较小。系统将扫频和极性判决算法联合用于载波频偏的捕获阶段,将DD算法用于频偏的跟踪阶段来纠正捕获阶段的残留频偏,同时加入导频加快了载波环路的同步速度。Matlab仿真结果表明,该算法性能可靠,频偏捕获范围大,可达系统符号率的±10%且捕获时间短,相位抖动小,稳定度高,能够快速准确地恢复载波。

Aiming at the sensitivity of the modulation and demodulation system of high-order quadrature amplitude modulation（QAM） on carrier offset, a carrier recovery method based on the frequency sweeping loop, polarity decision algorithm, decision-directed（DD） algorithm and pilot is used. Frequency sweeping and polarity decision algorithm both have large frequency offset capture range and large phase jitter, while DD algorithm has smaller phase jitter and smaller range of frequency offset capture that usually reaches only -＋-3~//00 of symbol rate. In the system, frequency sweeping and polari- ty decision algorithm are used in the capturing stage of frequency offset, while DD algorithm is used in tracking stage to correct the residual frequency offset of the capturing stage, and the pilot is also add- ed to accelerate the synchronization speed of the carrier loop. The Matlab simulation results show that the system has reliable performance, and it has a large range of frequency offset capture, which is up to ±10% of symbol rate. The capturing time is short, the phase jitter is small, the stability is high, and the carrier is recovered quickly and accurately.