无线光通信脉冲位置调制的符号同步技术

讨论了PPM序列的符号同步原理；在分析随机PPM序列的精确符号同步概率上限的基础上，给出了一种在PPM序列中插入同步信号来实现PPM精确符号同步的方案及其数字逻辑电路实现。该方案通过改变PPM调制序列结构，按照一定的间隔在PPM序列中插入脉冲时隙肩并肩的2个相邻符号作为同步符号，通过对同步符号的检测来提取同步信号。理论及仿真实验表明，该方案能实现PPM精确符号同步。
关 键 词 无线光通信; PPM序列; 脉冲位置调制; 符号同步

Abstract One of the most important issues of pulse position modulation (PPM) for optical wireless communications is the receiver symbol synchronization subsystem, in this paper, the basic principle of symbol synchronization for PPM sequence is discussed, and the upper limit of exact synchronization probability for random PPM sequence is analyzed. To solve this problem a new scheme of inserting synchronous back-to-back PPM symbols to the PPM sequence at intervals of certain symbols is presented, the synchronization signal is obtained by searching for the synchronous symbols, and the corresponding digital logic circuit is presented too. Theory and experiment results show that the exact PPM symbol synchronization can be obtained by this scheme with more credibility compared to the scheme proposed by Ref.[8].
Key words optical wireless communications; PPM sequence; pulse position modulation; symbol synchronization