Abstract
The direct-sequence code-division multiple access ultra-wideband (DS-CDMA UWB) communication system is one of the solutions for the IEEE 802.15.3a standard. This system has some advantages, including low cost, low power spectral density, good resistance to the dense multipath environment, etc. However, multipath interference and multiple access interference (MAI) are two major problems of the DS-CDMA UWB system at high data rate multiple access indoor environments. In the first place, due to the fine channel resolution by using the pulse transmission, the RAKE receiver is an effective and primitive structure to mitigate this problem. On the other hand, multiuser detection is a general solution to resist MAI which degrades the system performance in the multiple access communication system. To improve the system performance, the partial parallel interference cancellation (PPIC) structure canceling the partial reconstructed MAI from the received signal has a small processing latency and simple structure in multiuser detection techniques. In this thesis, we investigate performance of the PPIC receiver with various RAKE combining schemes for high data rate DS-CDMA UWB systems over a realistic UWB multipath channel model with lognormal distributed multipath fading gain. Under a data rate condition of 100 Mbps, some performance comparisons between two RAKE receiver combining schemes, maximal ratio combining (MRC) and minimum mean-squared error combining (MMSEC), with the PPIC detector over the multipath channel are illustrated by computer simulations. For ease of implementation, we use an adaptive structure with the normalized least mean-squared (NLMS) algorithm to approach the MMSE solution. Using the NLMS algorithm, the channel fading gains which are required for MAI reconstruction in the PPIC detector can be estimated by the obtained MMSEC weights in the RAKE receiver. Simulation results show that the MRC RAKE receiver with PPIC and the MMSEC RAKE receiver with PPIC have better performance than the MRC RAKE receiver without PPIC and the MMSEC RAKE receiver without PPIC. As the results also indicate that, in high signal-to-noise ratio (SNR), the MMSEC RAKE receiver with PPIC and estimated channel fading gains has better performance than the MRC RAKE receiver with PPIC and accurate channel information.