Modulated Coding For Frequency-Selective Multipath Channels

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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.