Turbo equalization over a frequency selective channel
Turbo equalization over a frequency selective channel
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发表时间：
1997
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通讯作者：
A. Glavieux;C. Laot;J. Labat
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作者：
A. Glavieux;C. Laot;J. Labat
本文提出了一种新的接收方案，该方案采用与涡轮码相同的原理，因此称为涡轮均衡器。该接收器通过迭代过程将均衡器和软输出信道解码器相关联。它非常适合在具有许多符号持续时间延迟扩展的信道上传输，并使用M-QAM调制。在某些情况下，涡轮均衡器可以完全克服信道频率选择性而不增加噪声水平，因此，该接收器可以实现与编码的非选择性高斯信道相同的性能。移动无线电通信和数字广播是许多关于受多普勒影响的频率选择性信道研究的起源。针对信道频率选择性，特别是信道编码和均衡，已经提出了不同的解决方案。在经典方法中，均衡器由解调器输出馈电，而不使用由信道编码引入的冗余来执行其处理。如果均衡器同时由解调器输出和信道解码器提供的软决定馈送，则有可能提高接收机的性能。使用这种方法，有必要考虑通过使用迭代过程执行的信道解码器引入的延迟。迭代p时的均衡器由迭代（p−1）时解码器提供的软决策馈送。在本文的其余部分，这种新的接收机方案将被称为涡轮均衡。让我们考虑图1所示的传输方案。
This paper deals with a new receiver scheme that uses the same principle as turbo-codes and called, for this reason a turbo-equalizer. This receiver associates an equalizer and a soft ouput channel decoder through an iterative process. It is well suited for transmissions over channels having a delay spread of many symbol durations and using M-QAM modulation. In certain cases, the turboequalizer can totally overcome the channel frequency selectivity without increasing the level of the noise and thus, this receiver can achieve the same performance as a non selective Gaussian channel with coding. I INTRODUCTION Mobile radio communications and digital broadcasting are at the origin of much research about frequency selectivity channels affected by Doppler. Different solutions have been proposed to combat the channel frequency selectivity, in particular channel coding and equalization. In a classical approach the equalizer is fed by the demodulator outputs and does not use the redundancy introduced by the channel coding to perform its processing. It is possible to improve the receiver performance if the equalizer is fed both by the demodulator ouputs and the soft decisions provided by the channel decoder. With this approach it is necessary to take into account the latency introduced by the channel decoder that is carried out by using an iterative process. The equalizer at iteration p is fed by soft decisions provided by the decoder at iteration ( p − 1). This new receiver scheme will be called turboequalization for the rest of this paper. II PRESENTATION OF THE TRANSMISSION SCHEME Let us consider the transmission scheme depicted in figure 1.