Performance enhancements of DS-CDMA system for fixed wireless access

by Ng, Benjamin Koon

Performance Enhancements of DS-CDMA System for Fixed Wùeless Access by Benjamin Koon Kei Ng Master of Applied Science, 1999. Department of Electrical and Cornputer Engineering, University of Toronto. In this thesis, performance enhancement of Fixed Wireless Access (FWA) system, employinghybrid Spatial Division Multiple Access (SDMA) and orthogonal CDMA with dynamic code docation, for both forward link and quasi-synchronous reverse link is inves tigated. The static characteristic of FWA's radio Channel eases the implementation of adaptive or highly directive antenna at the base station and directional antenna at the subscriber site. We analytically derive the capacity equations for vaxious antenna configurations combined with either orthogonal or non-orthogonal CDMA system. Using highly directive adaptive antenna in conjunction with orthogonal CDMA shows the most prornising performance. In such environment, dynamic sectorization is introduced and code allocation schemes axe proposed to assign codes for users in different areas. Simulation results demonstrate that the best code docation scheme proposed provides 60% increase in the number of users with code assigned, over conventional fixed alloca- tion. And with required SINR=6 dB, the outage probability is improved by 40%, when two antennas, having same directivity while one adopts the code allocation scheme and the other one does not, are compared. The concept of overlapping sectors is introduced and the corresponding code allo- cation schemes are presented. Simulation results show that this new concept increases the number of users with code assigned, without suffering fiom the high complexity associated with the dynamic sectors when using adaptive antennas. In particular, a 36-sectors system provides 45% improvement over conventional 6-sectors system.