Blocking probabilities for SDMA and transmit diversity in wireless networks using smart antenna technology

Recently, the demand of voice and data services over wireless network is growing rapidly. Smart antenna systems, which employ an antenna array coupled with adaptive signal processing techniques at the base station to improve capacity, coverage and trunking efficiency, have attracted much attention and have been treated as a core technology for future wireless communication systems.; Using smart antenna technology, a base station can spectrally separate signals by beam-forming within a cell. This means two or more mobile terminals can share the same channel resources such as time slot, frequency slot, and spreading code to communicate with the base station at the same time. Therefore, the spatial dimension can be exploited as a new multiple access scheme, which is so called space-division-multiple-access (SDMA).; SDMA is a promising approach to provide more channel capacity for future wireless communications. Many studies [13], [5] have shown that SDMA can effectively improve system capacity in a mobile communication environment. This dissertation first proposes a modified blocking probability formulation for two-fold SDMA. Secondly, in extending the two-fold SDMA blocking probability derivation, a new model for three-fold SDMA is proposed and a theoretical formulation is derived. In addition, a numerical algorithm [3], [4] is introduced for the three-fold SDMA model to avoid the numerical errors associated with large and sparse matrix inversion.; Simulations have been done to evaluate the probability of successfully creating two-fold and three-fold SDMA channels under different constraints. The analytical as well as simulation results show that SDMA can reduce the blocking probability of calls, resulting in more traffic loading than in traditional cellular systems.; Moreover, analytical and numerical results for blocking probability in hybrid CDMA and SDMA systems are presented in this dissertation. Simulation results show that SDMA can also provide capacity improvement for CDMA systems.; This dissertation also proposes an approach which fully utilizes multipath direction-of-arrival (DOA) estimation from mobile terminal to base station (uplink) measurements. The scheme combines the concept of transmit diversity and SDMA plus feedback from mobile terminals. Selective diversity is used for the mobile terminals to overcome unmatched channels conditions, with minimal feedback bandwidth requirements. Simulation results show that the new method can provide diversity gain to the system and result in greatly improvement of the system capacity.