WAVELET TRANSFORM BASED MULTIUSER DETECTOR FOR ASYNCHRONOUS CDMA SYSTEMS

摘要

A new approach to implement the wavelet transform based multiuser detector (WTMUD) is proposed for asynchronous direct-sequence code division multiple access (DS-CDMA). In this approach, wavelet reconstruction is performed on the signal sequences that have been spread, and the reconstructed signals are sent to the pulse shaping filter. At the receiver, wavelet decomposition is performed on the sampled receive signals. Then, the existing multiuser strategies can be used to recover the transmitted bits from these decomposed sequences. In this way, a series of WTMUDs' can be implemented conveniently. So far as the WTMUDs' that need calculating the correlation matrix are concerned, the dimension of correlation matrix depends only on the number of users and has no relations with the packet length, even in asynchronous CDMA systems. This property not only reduces the computation complexity of inverting the correlation matrix, but also ensures the bit-by-bit detection of desired users. In addition, wavelet transform can mitigates the influence of noise to improve the signal-to-noise ratio (SNR) to achieve lower bit-error rate (BER). Simulation results show that WTMUDs' outperform their counterparts that do not incorporating wavelet transform on the aspects of BER performance, near-far resistance ability, and system capacity.