Multi-Band Wavelet Packet Spreading Codes with Intra-Code Subband Diversity for Communications in Frequency-Selective Fading Channels

摘要

Mobile communication channels always suffer from serious frequency-selective fading due to multipath. Traditional spreading codes are characterized by the common feature that their time-domain orthogonality is based on fixed chip width across the code length. They often fail to perform satisfactorily under frequency-selective fading. This paper proposes a new class of CDMA codes, wavelet-packet orthogonal codes that are capable to retain time-domain orthogonality as well as to provide intra-code subband (frequency) diversity to mitigate frequency-selective fading. The new codes are constructed by congregating several wavelet waveforms with various dilations and shifts. The combination of the wavelet waveforms in different nodes in a wavelet-packet full binary tree enables frequency diversity capability. Owing to the even code length, they can be readily applied to mobile communication systems for multi-rate streaming and multi-bit spreading. The performance study is carried out using correlation statistics distribution convolution algorithm and the results reveal that the proposed wavelet-packet codes,combined with RAKE receiver, perform comfortably better than many traditional time-domain orthogonal codes, such as Gold codes and msequences in frequency-selective fading channels.