Improved capacity in TDMA/SDMA using switched parasitic antennas

Parasitic antennas are much lower in cost and complexity than conventional smart antennas. For this reason, they may be considered for use at the portable station. In this paper we study the capacity of a space-division-multiple-access (SDMA) system when n-element switched parasitic antenna arrays (SPAA) are used for this purpose. Dynamic slot allocation (DSA) is used with a conventional smart antenna at the basestation. We first present analytic and simulation results which suggest the improvements in static capacity performance possible using this approach. Results show that the system capacity can be significantly improved with a small number of parasitic elements. We then then present results using measurements taken at McMaster University using an 8-element circular basestation antenna array and a 4-element switched-parasitic antenna array. The basestation array was used to collect spatial channel soundings in various indoor locations. We also propose several dynamic TDMA/SDMA slot allocation algorithms, which vary in their complexity and achieved performance. It is shown that significant improvements in capacity are possible using the proposed technique.