Design, characterisation and performance assessment issues of multi-carrier CDMA exploiting higher order PSK/QAM formats for future wireless systems

This thesis presents research that has addressed various design issues related to multicarrier Code Division Multiple Access (CDMA) communication systems. The combination of multi-carrier CDMA with higher order Phase Shift Keying (PSK) and Quadrature Amplitude Modulation (QAM) mapping has been considered. The investigation has been carried out for two different multi-carrier CDMA schemes, namely, Multi-Carrier CDMA (MC-CDMA) and Multi- Carrier Direct Sequence CDMA (MC-DS-CDMA). Different architectures for combining multicarrier CDMA with higher order PSK/QAM mapping have been developed. Their performance has been studied in terms of power efficiency, spectral efficiency and implementation complexity. As for all multi-carrier arrangements, the Peak-to-Average Power Ratio (PAPR) is of special significance and accordingly the implications for PAPR has also been investigated. Multi-carrier CDMA signals are vulnerable to the non-linear distortion caused by nonlinear elements and system components (such as High Power Amplifier (HPA)). The degradation due to non-linear effects is expected to be even more significant when higher order constellations are used. Hence, the degradation caused by HPA non-linearities on higher order PSK/QAM multi-carrier CDMA signals has been studied in terms of Bit Error Rate (BER) degradation and spectral spreading. The high PAPR of the multi-carrier CDMA signal results in reduced system efficiency (in the presence of non-linearities). Controlling the PAPR of the multi-carrier CDMA signal is one way of improving system performance. In this work the variation of the PAPR of multi-carrier CDMA (MC-CDMA and MC-DS-CDMA) with allocation of the spreading codes has been investigated. Overall, the theoretical, design and simulation issues addressed in this thesis provide an insight into the performance of PSK/QAM multi-carrier CDMA systems in the presence of Additive White Gaussian Noise (AWGN) and HPA non-linearities. The results obtained can be used by receiver designers, as well as system and network developers of future wireless systems