多径衰落信道下QOTDM系统的盲均衡算法

Blind equalization algorithm for the QOTDM system in multi-path fading channels

提出准正交时分复用系统的一种高效盲均衡算法.在发送端将一路准正交时分复用样点序列移频后与另外一路叠加,得到频谱白化的发送信号,接收机用梳状滤波器对接收信号和移频后的接收信号滤波得到两路样点序列.通过改进的恒模算法对两路样点序列初步均衡,下采样后再通过恒模算法处理,当输出误差低于门限后切换到结合判决反馈的最小均方误差算法均衡,可消除多径衰落带来的符号间干扰.Monte Carlo仿真表明,在地空通信的多径衰落信道下,新算法可以明显消除准正交时分复用系统存在的"地板效应";当信道的莱斯因子为10 dB、误符号率为10-3时,新算法比正交频分复用有4 dB左右的性能改善.

An efficient blind equalization scheme for the Quasi-Orthogonal Time Division Multiplexed （QOTDM） system is presented. At the transmitter, the transmitted signal with a white frequency spectrum can be obtained by adding one group of QTODM sample sequences with a frequency shift to the other group, and the receiver can get two group sample sequences by filtering the received signal and the received signal with a frequency shift using a comb filter. Firstly, two groups of sample sequences are equalized blindly by the modified constant modulus algorithm （MCMA）, then the output of the primary equalizer is equalized by MCMA before the deferent error is larger than the gate, and finally the equalizer adopts the algorithm of lease mean square combined with the decision feedback technique. After equalization, the inter symbol interference （ISI） can be cancelled. It is shown by Monte Carlo simulation that the new scheme can cancel the ＂ground effect＂ of the QOTDM system in the ground-air multi-path fading channel. When the Rice fading factor is 10 dB, the signal-to-noise ratio of 4 dB or so for SER of 10^-3 can be achieved by the scheme proposed compared with OFDM.