Bit Error Rate (BER) Performance of MIMO Systems in M-QAM with Nonlinear Effect

Out object in this paper it to study, the effect of nonlinearity on the bit error rate (BER) of MIMO systems in M-QAM modulation techniques. We consider Saleh’s model (power amplifier model) for the nonlinearity, and apply the nonlinear model on MIMO system with receiver diversity and transmitter diversity. For transmitter diversity, the Space-Time Block Coding (STBC) based on Alamouti scheme is used to provide transmits diversity for two transmitting antennas. The results show that, if there is a high variation in the amplitude of the M- QAM symbols, there will behigh effect of nonlinearity that causes high BER especially for high amplitude symbols at high SNR.

Space-time diversity signal processing employed by W-CDMA systems

Transmit diversity under transmission of signals from the base station to mobile station using the code-division multiple-access (CDMA) system allows us obtaining the performance gains close to the mobile station receiver diversity without complexity of the mobile station receiver antenna array. The multipath diversity can be achieved using the pre-RAKE precoding at the transmitter that could be employed and there is no need to install the RAKE receiver at the mobile station. We investigate several transmitter diversity techniques employed by wideband CDMA (W-CDMA) systems. We also study a possibility to combine transmitter diversity and precoding that achieves the gain of maximum ratio combining of all space and frequency diversity branches jointly with long-term prediction algorithm. It was demonstrated that the performance of the space-time pre-RAKE method approaches the performance of the maximum ratio combining for all space and frequency diversity branches. It is shown that all closed loop methods depend on the long range prediction to approximate the ideal performance in the fast fading environment.