| This dissertation introduces a successive interference cancellation (SIC) scheme for multicarrier (MC) DS/CDMA systems. In each subband, the SIC receiver successively reconstruct and remove the interfering signals from the user-of-interest without making any hard decisions. The performance of this system is compared to that of both a conventional MF receiver and a minimum mean-squared error (MMSE) receiver. Results will show that SIC outperforms MMSE when the number of users is small. The correlation among different subcarriers is also studied. Further, to make the system more realistic, we derive results for the performance degradation that a SIC scheme experiences due to phase and timing tracking errors. Simulations will again demonstrate the system improvement gained by SIC, which translates to increased capacity and better fading resistance.; The other focus of this dissertation is to investigate the proposed SIC system when combined with coding and interleaving, and we consider both convolutional coding and trellis coded modulation (TCM). It is shown that TCM outperforms convolutional coding in the presence of a severe multiple-access interference (MAI); also, TCM with a 16QAM constellation is better than TCM with an 8PSK constellation.; Note that the above SIC system is actually a soft SIC, where no hard decision is made. As an alternative approach, pilot symbol assisted SIC with hard decision feedback is presented. The latter system is shown to achieve better performance than soft SIC when the number of users is large, while soft SIC performs better during the initial cancellations. This result motivates the design of a combined SIC: soft SIC is employed during the initial cancellations, and the system changes to pilot symbol assisted SIC afterwards.; Finally, we combine a decision feedback interference cancellation (IC) and turbo coding to suppress MAI and improve near/far resistance. Simulations demonstrate the superior performance of the proposed decision feedback IC compared to both MMSE and MF receivers. A tradeoff between more powerful turbo codes by reducing the code rate and reduced frequency diversity is studied, and a comparison is made between the turbo coded system and convolutionally coded system. |
