Approach to mitigate frequency-selective fading - design of multi-band wavelet packet spreading codes with intra-code subband diversity

Mobile communication always suffer serious frequency-selective fading due to multipath. Traditional spreading codes are characterized by the fact that the time-domain orthogonality is based on fixed chip width across code length. They may not perform satisfactorily under frequency-selective fading. This paper proposes a new class of CDMA code, wavelet-packet orthogonal codes capable to retain time-domain orthogonality as well as to provide intra-code subband 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 length of even chips, they can facilitate implementing multi-rate streaming and multi-bit spreading. The performance study is carried using statistics correlation distribution convolution (SCDC) algorithm and the results reveal that wavelet-packet codes with multi-band components, combined with RAKE, perform pretty well under frequency-selective fading.