Effects of parameter imbalances and PAR in multiple-antenna OFDM-CDMA systems

The peak-to-average ratio (PAR) reduction scheme employing a simple symbol transform in a OFDM-CDMA system is investigated. This approach is very simple because there is no additional complexity and it works with arbitrary numbers of subcarriers and without restriction on the allocation of spreading code, maintaining the original transmission efficiency. Simulation results show that the investigated scheme gives a PAR reduction gain of 2-3 dB compared to the original OFDM-CDMA signal and can provide a further PAR reduction by combining the selective mapping (SLM) and partial transmit sequence (PTS) schemes, which are less complex than the ordinary SLM and PTS approaches. The performance degradation due to imperfect parameters in the OFDM-CDMA system with multiple transmit antenna is also analysed. For the performance evaluation, an expression is derived for the average bit error rate (BER) in the presence of imperfect parameters such as channel estimation error, frequency offset, and erroneous side information introduced by the PAR reduction schemes. The results derived show that the multiple-antenna OFDM-CDMA system experiences a small performance loss from the erroneous side information, while a severe BER degradation due to parameter imbalances such as channel estimation error and frequency offset is observed.