互补码在电离层探测中的应用

Application of Complementary Codes in Ionosphere Sounding

电离层探测仪一般采用m序列或Barker码序列调制的二相编码脉冲。但是这两种码元序列产生的编码脉冲信号经脉冲压缩后都存在较高的旁瓣。为降低脉冲压缩后信号的旁瓣,提出了在多普勒频移较低的电离层区域应用互补码作为二相编码脉冲的调制码元序列。互补码具有非常好的自相关特性,A序列和B码序自相关后相加,自相关和只有主瓣,不存在任何旁瓣。但是由于A,B相位编码脉冲并不同时发射,多普勒频移会降低互补码的脉冲压缩性能。仿真结果表明,当多普勒频移较低时,互补码相位编码脉冲回波脉压性能优越;但是当多普勒频移较高时,多普勒频移给A,B相位编码脉冲回波带来很大的相位差,使互补码脉冲压缩后指标严重恶化。

Ionosonde usually uses m-sequence or Barker codes to code the pulse,but what＇s undesirable is that high sidelobe peak level（PSL） exists after pulse compression.Using complementary codes as phase codes in areas where Doppler shift is weak is proposed.Complementary codes has superb autocorrelation characteristics as summation of autocorrelation of A,B code sequence has no sidelobe.But A,B coded pulses are not transmit simultaneously,Doppler shift degree the pulse compression capacity of complementary coded pulse.Simulation shows that： when Doppler shift is weak,complementary coded pulse has superior pulse compression capacity than m-sequence and Barker codes coded pulse,and when Doppler shift is severe,pulse compression capacity of complementary coded pulse degree seriously.