基于OFDM技术的数字AM广播系统时间同步算法研究

A Study of the Timing Recovery Method for OFDM on the Digital AM Broadcasting System

针对基于OFDM调制技术的数字AM广播系统,研究适合中短波信道(<30MHz)的时间同步算法.首先建立一个可以同时估计符号偏差和时钟相位偏差的两级时间同步模型.对符号偏差估计,给出一种改进的最大似然算法;对时钟相位偏差估计,给出一种利用梳状导频的估计算法.仿真和实际测试表明,这种两级同步方案能够满足OFDM系统对时间同步精度要求.

OFDM is an effective modulation technique for high-rate and high-speed transmission over the frequency selective fading channel. However, the OFDM system can be extremely sensitive and vulnerable to timing synchronization errors. In this paper, a low-complexity two-stage timing recovery scheme is proposed. The timing recovery process can be divided into symbol synchronization and sample clock synchronization. In the former process, an improved ML algorithm is proposed. Its performance can approach the optimal ML algorithm without estimating SNR and therefore can have lower complexity. In the latter process, an simple synchronization algorithm is proposed using scatter pilots to estimate sample clock phase errors, and a low pass loop filter is used to track the symbol timing drift caused by sample clock frequency offset. Simulations are carried out on DAMB channels, and the results indicate that our proposed scheme can achieved good performance and are robust to multipath fading channels. Its low complexity enables the scheme to operate easily run on the DSP chip.