Effect of Diversity and Filtering on the Performance of Decorrelating Multiuser Detector Combining with Wavelet Packets Multicarrier CDMA system

Wavelet Packets (WPs), multiuser detection, diversity and suppression filters are very effective in reducing the interferences in Coded Division multiple access communication (CDMA) systems. In this paper, we analyzed a WP Multi-Carrier (MC)-CDMA system that employs decorrelating multiuser detector. This type of detector, supports a higher number of users, suppresses the multiple access interference (MAI), thus relaxes the power control requirements. Since the sinusoidal sub-carriers are replaced by WPs sub-carriers, the proposed system will have a higher immunity against multicarriers and multipath interferences compared with the system which employs a sinusoidal subcarrier. The CDMA system can suppress a given amount of interference, but if the interference signal is powerful enough, the receiver is ineffective in mitigating this problem. In this paper, the receiver employs suppression filter (SF) to mitigate the effect of narrow-band jammer interference. The performance of the system is investigated in slow fading Nakagami channel by means of three types of diversity, which are Selection Diversity, Equal Gain Combining and Maximum Ratio Combining. For these combining techniques, Bit Error Rate (BER) and outage probability performances are investigated using several fading models and diversity orders. Also, we investigate how the performance is influenced by various parameters, such as the number of taps of the SF, the ratio of narrow-band interference bandwidth to the spreadspectrum bandwidth. Finally, the system performance is compared with WP-MC/SU-CDMA system and Sinusoidal (Sin)-MC/MU-CDMA system. Results reveal considerable performance improvement of our proposed system over the other two systems.