Wavelet-based multicarrier CDMA system and its corresponding multi-user detection

A novel digital transmission system based on wavelet signalling has been proposed and analysed. The basic system consists of a bank of filters derived using the quadrature constrained least square (QCLS) algorithm and satisfying the perfect reconstructed quadrature mirror filter (PR-QMF) theory. A multicarrier CDMA system is constructed using this technique. where a user’s data is spread in the frequency domain and constraints are imposed to ensure channel orthogonality. The system exploits the localisation properties of the wavelets in time and frequency to develop data channels that have compact PSD characteristics and are resilient in an environment exposed to fading. Practical implementation of the wavelet transmission system using a bank of polyphase filters is considered. Simulation results are presented which show the wavelet system can better combat ISI and multiple access interference than an FF1-based multicarrier modulation system when both systems operate in identical fading environments. A wavelet detection scheme based on the MMSE criterion and then made adaptive using the LMS algorithm is theoretically analysed and software simulated. The proposed wavelet detector is near— far resistant and shows better BER performance compared with a decorrelator, but with higher computation costs.