Modulated Coding For Frequency-Selective Multipath Channels

University Of Delaware, Newark DE

Investigators

Abstract

This research involves the mitigation of multipath interferences in a frequency-selective fading channel. As broadband digital wireless communications is more demanded than ever, such as wireless image/video web browsing and wireless data transmission, the technical challenges are exponentially increasing. One of such challenges is that, when the bandwidth of a channel becomes wider, there are more severe multipaths in a wireless system. This implies that the multipath interference mitigation becomes more important than ever. Modulated coding (MC), a convolutional coding defined on the complex field, has been recently proposed by the PI to optimally mitigate intersymbol interferences (ISI) when the ISI channel is known at both the transmitter and the receiver. The advantage of MC is that, since the arithmetic operations of both MC and ISI are over the complex field, they can be naturally combined together, which provides the convenience of the optimal MC study for a given ISI channel. Since the encoding simplicity of the MC, it is also convenient for further adding a conventional error correction coding (ECC) before the MC. It has been shown that the combined MC and turbo coding of an ISI channel may outperform the AWGN channel capacity at low SNR. As an example, for the two tap ISI channel [0.7071,0.7071], the bit error rate is 0.00001 at the code rate 1/4 and the SNR E_b/N_0=-1.15 dB, which is above the AWGN channel capacity. The disadvantage of the previous MC study is that the transmitter needs to know the ISI channel, which although may be possible for some applications, such as storage channels and wireline channels, may not be practical for some other applications, such as wireless channels. The aim of this proposal is to optimally design and update MC without the full knowledge of the ISI/multipath channel at the transmitter with applications, in particular, in wireless communication systems. Due to the simple structure of MC, the MC update at the transmitter is possible, which is unlike the existing coding schemes.