循环保护前缀不足的OFDM通信系统的频域均衡

Frequency-domain Equalizer for OF DM Systems with Insufficient CP

当循环保护前缀(CP)长度小于信道冲激响应长度时,正交频分复用(OFDM)通信系统的子载波间的正交性遭到破坏,接收信号存在符号间干扰(ISI)和子载波间干扰(ICI),频域单抽头均衡器不再适用。为解决这个问题,通常的方法是对接收信号先进行时域均衡,减少信道的有效冲激响应长度和恢复子载波间的正交性。但时域均衡器结构复杂,且其收敛性不能保证。为此,作者提出了一种频域均衡器,用来解决循环保护前缀不足的OFDM通信系统的频域均衡问题。频域均衡器的设计利用了OFDM系统的空闲子载波信息。该均衡器具有稀疏矩阵结构,因此计算量小。理论分析和计算机仿真表明:它能有效消除由于循环前缀不足引起的符号间干扰和子载波间干扰,从而较好地恢复传输信号。

In OFDM systems ,when the length of the cyclic prefix(CP)is shorter than the channel length,the orthogo-nality between sub-channels is lost because of the intersymbol interference(ISI )and interchannel interference(ICI ).In this case,the one-tap frequency domain equalizer can't be used any more.A time-domain equalizer(TEQ)is usually used in the receiver to reduce the duration of the overall response of the transmission system and recover the orthogo-nality.But the TEQ turns out to have a complex structure and may fall into divergence.In this paper,the authors pro-pose a frequency domain equalizer(FEQ)for OFDM systems with insufficient CP,by making use of the presence of null side sub-carriers.The equalizer has a sparse matrix structure and thus a low computational complexity.Theoretical analysis and simulation results show that it can efficiently remove ISI and ICI caused by insufficient CP and recover the transmitted data.