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Multi-Band Wavelet-Packet Spreading Codes with Intra-Code Subband Diversity for Communications in Multipath Fading Channels
IEICE TRANSACTIONS on Communications
Publication Date: 2001/07/01
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Wireless Communication Technology
CDMA, wavelet, diversity, frequency selective fading,
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Mobile communication channels always suffer serious frequency-selective fading due to multipath effect. Traditional spreading codes are characterized by the fact that their time-domain orthogonality is based on fixed chip width across a code period. They often fail to perform well under frequency-selective fading. This paper proposes a new class of CDMA codes, wavelet-packet orthogonal codes capable to retain time-domain orthogonality as well as to offer intra-code subband diversity to mitigate frequency-selective fading. The new codes are constructed by congregating several wavelets with various dilations and shifts. The combination of the wavelets in different nodes in a wavelet-packet full binary tree enables frequency diversity capability. Owing to the even code length, they can be easily used in mobile communications for multi-rate streaming and multi-code spreading. The performance study is carried out using correlation statistics distribution convolution algorithm and the results reveal that wavelet-packet codes, combined with RAKE receiver, perform better than traditional spreading codes in frequency-selective fading channels.