Modulated Coding For Frequency-Selective Multipath Channels

本研究主要针对频率选择性衰落信道中多径干扰的抑制。随着人们对宽带数字无线通信（如无线图像/视频网络浏览和无线数据传输）的需求越来越大，技术挑战也呈指数级增长。其中一个挑战是，当信道的带宽变宽时，无线系统中存在更严重的多径。调制编码（Modulated Coding，MC）是一种定义在复数域上的卷积编码，它是PI最近提出的一种在收发双方都知道码间干扰（ISI）信道的情况下最佳地抑制ISI的方法。MC的优点在于，由于MC和ISI的运算都是在复数域上进行的，所以它们可以很自然地结合在一起，从而为针对给定ISI信道的最优MC研究提供了方便。由于MC的编码简单，也便于在MC之前进一步增加传统的纠错编码（ECC）。结果表明，在低信噪比下，ISI信道的MC和Turbo联合编码的性能可能优于AWGN信道的容量。例如，对于两抽头ISI信道[0.7071，0.7071]，在码率为1/4时，误码率为0.00001，信噪比E_B/N_0=-1.15 dB，超过了AWGN信道的容量。以前的MC研究的缺点是发射机需要知道ISI信道，这虽然对于某些应用是可能的，如存储信道和有线信道，但对于其他一些应用，如无线信道，可能是不实际的。该建议的目的是优化设计和更新MC没有充分的知识的ISI/多径信道的应用，特别是在无线通信系统中的发射机。由于MC结构简单，MC在发射端的更新是可能的，这不同于现有的编码方案。

This research involves the mitigation of multipath interferencesin a frequency-selective fading channel. As broadband digital wirelesscommunications is more demanded than ever, such as wireless image/videoweb browsing and wireless data transmission, the technical challengesare exponentially increasing. One of such challenges is that, when thebandwidth of a channel becomes wider, there are more severe multipathsin a wireless system. This implies that the multipath interferencemitigation becomes more important than ever.Modulated coding (MC), a convolutional coding defined on the complexfield, has been recently proposed by the PI to optimally mitigateintersymbol interferences (ISI) when the ISI channel is known at boththe transmitter and the receiver. The advantage of MC is that, sincethe arithmetic operations of both MC and ISI are over the complex field,they can be naturally combined together, which provides the convenienceof the optimal MC study for a given ISI channel. Since the encodingsimplicity of the MC, it is also convenient for further adding aconventional error correction coding (ECC) before the MC. It has beenshown that the combined MC and turbo coding of an ISI channel mayoutperform the AWGN channel capacity at low SNR. As an example, for thetwo tap ISI channel [0.7071,0.7071], the bit error rate is 0.00001 at thecode rate 1/4 and the SNR E_b/N_0=-1.15 dB, which is above the AWGNchannel capacity. The disadvantage of the previous MC study is that thetransmitter needs to know the ISI channel, which although may be possiblefor some applications, such as storage channels and wireline channels,may not be practical for some other applications, such as wirelesschannels. The aim of this proposal is to optimally design and update MCwithout the full knowledge of the ISI/multipath channel at thetransmitter with applications, in particular, in wireless communicationsystems. Due to the simple structure of MC, the MC update at thetransmitter is possible, which is unlike the existing coding schemes.