Oscillating beam smart antenna systems with joint transmit diversity/directionality benefits

Abstract

This dissertation proposes a novel transmit diversity technique: By applying carefully-selected time-varying delays to the array elements of a smart antenna located at the base station (BS), small oscillations are generated in the beam pattern. Assuming a rich scattering environment (e.g., an urban area), these small oscillations create a time-varying channel demonstrating intra-symbol time variation characterized by coherence time Tc. At a single-antenna mobile, the time-varying channel (with coherence time Tc) creates a time diversity which is exploited to enhance the mobile’s performance. The mobile lies in the antenna pattern half power beam width (HPBW) at all times - in this way, directionality is supported to ensure high network capacity.In addition, a novel merger of multi-carrier code division multiple access (MC-CDMA) and the proposed smart antenna array is introduced at the base station (BS). We also introduce the merger of direct sequence CDMA (DS-CDMA) and the proposed oscillating-antenna-pattem smart antenna arrays. In both the MC-CDMA and DS-CDMA mergers, we observe: 1) very high capacity via the combining of space division multiple access (SDMA) (directionality of antenna array) and code division multiple access (inherent in MC-CDMA and DS-CDMA); and 2) very high performance via the construction of receivers that exploit both transmit diversity and frequency diversity.We establish both the probability of error performance and the network capacity (measured in terms of numbers of users) of wireless systems merging MC-CDMA and smart antennas with oscillating-beam-pattems.