Effective capacity evaluation of advanced wideband CDMA and UWB radio networks

Abstract

Abstract High radio capacity is one of the main targets in wireless network planning. The characteristics of the broadband radio channel pose serious challenges for achieving this goal. This thesis views the capacity problem from two frameworks. In the first, the effective user capacity in advanced direct sequence wideband code-division multiple-access (DS-CDMA) radio networks is evaluated. Sensitivity to various imperfections in key system parameters is studied. The analysis is based on a mathematical foundation that presents complex signal models and enables evaluation of the performance losses due to parameter estimation errors and multipath fading. The effective number of users supported in a cell is restricted by the multiple access interference (MAI) in the same cell (intracell interference) and overall background noise. The studied wideband CDMA receiver structures comprise conventional rake receivers with both the maximal ratio combining (MRC) and equal gain combining (EGC) schemes that can be supplemented with either linear decorrelating or nonlinear successive cancellation-based multiuser detectors and M-antenna spatial diversity. The second framework focuses on direct sequence spread spectrum-based ultra wideband (UWB) indoor communications. Cochannel interference limited capacity is evaluated against the outage probability criterion in exponentially decaying lognormal multipath fading channels. Distance-dependence and spatial distribution of users is taken into account at different spatial cell configurations. Only moderate complexity partial rake receivers with noncoherent combining are employed. Total interference is composed of interpath, multipath, intracell, and intercell interference contributions. Lognormal sum approximations and simulations are used to evaluate distributions of the desired and interfering signals. The impact of the timing errors at the receiver monopulse correlation is studied. The numerical results for the wideband CDMA framework show that effective user capacity and sensitivity depend critically on the joint impact of nonidealities in system parameters (e.g., channel profile, severity of fading, receiver algorithms). User capacities of the studied multiuser enhanced receivers were more prone to these impairments than those of the simpler single user receivers. The results should be used for network planning and optimization. The numerical results of the UWB framework suggest that, even in the multipath rich channel, the optimal number of rake fingers can be less than half of the significant multipaths. Differences between circular, square, and hexagonal cell models proved to be minor with respect to link distance distributions. The derived link distance statistics are useful tools in the analytic piconet dimensioning and optimization