Comparison of modulation and detection techniques for CDMA cellular system
Michael Xiaolong Li · Summit (Simon Fraser University) · 1996
Direct Sequence Code Division Multiple Access is a modulation and multiple access technique currently being implemented in cellular mobile radio communication.Different coding, spreading and detection techniques are being investigated to improve the performance of cellular mobile systems.The channel in CDMA cellular mobile communication exhibits frequency-selective Rayleigh fading, where the RAKE receiver plays an important role in the system.In addition, the appearance of self-interference is a major concern in CDMA cellular mobile systems.Pilot Symbol Assisted Modulation can improve the performance of coherent detection without complex signal processing.This thesis studies the error performance of PSAM and differential detection of MPSK signals in a 3-ray frequency-selective Rayleigh fading channel with additive white Gaussian noise and self-interference.We investigate the effects of rate 112 and 1/3~convolutional codes with different constraint lengths in BPSK modulation, where different channel conditions are considered.We find the trade off between rate 112 code with larger processing gain and rate 113 code with smaller processing gain while the transmission bandwith is fixed.While keeping the information throughput unchanged, we compared the performance of rate 112 PSAM QPSK and rate 113 PSAM 8PSK modulation.Various constraint length convolutional code and channel conditions are also considered.It is found that rate 112 QPSK performs better than rate 113 8PSK modulation, and at lower fading rate ( f D T < 0.05), PSAM can improve the performance better than differential detection by 2dB.We also perform the uplink error performance simulation on a combined orthogonal/convolutional coding scheme for cellular CDMA.Closed loop power control and RAKE receiver are implemented, and the results are also compared with PSAM.Finally, special thanks to my wife, parents and sister for their support and encouragement during the past three years.