共轭对称前导OFDM系统的定时偏移

Timing Offset in OFDM Systems Based on Conjugate-Symmetric Preamble

该文研究多径衰落信道中基于共轭对称结构前导的OFDM符号同步.通过分析共轭对称相关定时度量的统计特性,指出共轭对称前导经过多径信道时,在路径间相对延迟为偶数采样间隔的条件下会形成复合共轭对称结构.较强的复合共轭对称结构和第1径为非主径的情况下,依据定时度量的最大值进行符号同步估计时会产生定时偏移.定时偏移引起符号间干扰和子载波间干扰,偏移较大时将严重影响系统性能.仿真实验证实了上述分析的正确性.

This paper studies symbol synchronization methods based on the conjugate-symmetric preamble for OFDM systems in multipath fading channels.We analyze statistic properties of timing metric based on conjugate-symmetric correlation,and show that the compound-conjugate-symmetric structure is formed when two paths are separated by an even number of samples.The timing metric corresponding to the compound-conjugate -symmetric structure may be large under some conditions.We analyze the timing offset when the peak value of timing metric is used to detect the desired timing position,and show that the compound-conjugate-symmetric structure and the first path with small gain may result in backward shift in timing position.A large backward shift can cause inter-symbol and inter-channel interferences,seriously degrading the OFDM system performance.Simulation results confirm the analysis.