OFDM系统在短波宽带信道上均衡方法

Equalization Technique for OFDM Systems in Wideband HF Channel

由于短波宽带信道的时变和多径 ,使正交频分复用 (OFDM)信号的正交性受到损失 (产生子载波间干扰 ICI) ,从而导致了码间串扰 (ISI) ,误码底板上升 ,并且随着信道的多普勒频移的增加而增加。针对这种情况 ,提出了一种简单的频域均衡方法。这种均衡方法假设 :在一个 OFDM块期间 ,信道的冲激响应 (CIR)是线性变化的 ,而常规的单抽头频域均衡器对频率选择性多径衰落信道的补偿是假定在一个快速傅里叶变换 (FFT)块期间信道是静态的。当相对多普勒频移在范围 (0 .0 0 5 <Δf D<0 .1 )以内时 ,均衡器可以有效地补偿由信道的多径时变造成的正交性损失。通过对 ICI的均衡 ,极大地改善了比特误码率 (BER)

A loss of subchannel orthogonality due to Wideband HF channels in orthogonal frequency division multiplexing(OFDM) systems leads to interchannel interference(ICI) which increases the error floor in proportion to the Dopller frequency. A simple frequency domain equalization technique is proposed. In this technique, the equalization of the received OFDM signal is achieved by using the assumption that the channel impulse response(CIR) varies in a linear fashion during a block period, while normal single tap frequency equalization assumes that the channel is static in a FFT block. The loss of orthogonality caused by the time variation of a multipath fading channel can be compensated effectively by the proposed equalizer if the relative Doppler frequency change is in the range of (0.005<Δ f D <0.1). It is also shown that improved BER results can be obtained with the proposed approach by compensating for the multiplicative distortion and for the ICI.