Reference symbol assisted multistage successive interference cancelling receiver for code division multiple access wireless communication systems

This thesis investigates the performance of the reference symbol assisted successive interference cancelling (RAMSIC) receiver for CDMA wireless communication systems. The reverse link of a CDMA system with binary antipodal modulation and coherent detection is considered. The results with biphase spreading of the modulated signal show that the initial capacity improvement is relatively small. This is because interference from symbols not yet detected by the receiver signifcantly corrupts the channel estimates. Therefore, the transmitted signal structure has been modified to include guard intervals around the reference symbols to minimize this interference. Single cell analysis shows that the proposed technique results in a system with capacity approaching 80% that of the system with successive interference cancellation operating with perfect channel estimates. Multi-cell performance results demonstrate that without any forward error correction, the capacity of the proposed system with the RAMSIC receiver compares very favourably with that of comparable CDMA systems employing conventional detection and coding even when the path loss exponent is two. Further analysis shows that the RAMSIC receiver with quadriphase spreading performs significantly better than that with biphase spreading which in turn is superior to the conventional matched filter receiver. Performance analysis with imperfect parameter estimation shows that chip synchronization errors of the order to be expected in a properly designed conventional CDMA system have only minimal effect on performance but power control error, on the other hand, significantly affects performance. Hence, additional diversity should be employed to minimize the power control error. Consequently, the application of antenna diversity is then investigated. The results show that with a realistic feedback power control algorithm and in fast fading the capacity of the system with dual receive antenna diversity can be increased 1.6 times over that of the IS-95 system. It is also demonstrated that the capacity of the system in slow fading environment increases dramatically over that under fast fading. Therefore, the 1.6 fold advantage of the RAMSIC receiver may be interpreted as the worst case performance advantage. Investigation of transmitter antenna diversity shows that in systems requiring lower BER (10{dollar}sp{lcub}-4{rcub}{dollar} or less), such as in image and video communication, artificial multipath created by two transmitting antennas should also be considered as one possible way to increase capacity.