Dynamic Slot Allocation (DSA) in Indoor SDMA/TDMA Using a Smart Antenna Basestation

In this paper, we introduce and study the use of dynamic slot allocation (DSA) in packet-switched space-division-multiple-access (SDMA) systems. In conventional SDMA, a smart antenna is used at the basestation to simultaneously communicate with multiple stations on the same frequency channel. When dynamic slot allocation is added, the basestation uses uplink channel measurements to intelligently construct future SDMA/TDMA frames. It is shown that under a simple minimum signal-to-interference-plus-noise ratio (SINR) constraint, the problem of performing optimal dynamic slot allocation is NP-complete. Heuristic slot allocation algorithms are introduced which are capable of greatly increasing SDMA/TDMA frame capacity compared with a random allocation of stations. The paper uses both theoretical results and measured data from an experimental testbed to characterize the performance of dynamic slot allocation. The experimental system operates at a carrier frequency of 1.86 GHz and uses an eight-element circular antenna array. It is demonstrated that significant increases in system capacity are possible using DSA in the indoor situations that were tested. Dynamic slot allocation requires the channel to be essentially constant from the time that channel measurements are made until the SDMA/TDMA frame is transmitted. We also present channel measurements which show the effects of channel time coherence in the presence of indoor pedestrian movement. This and other results we have taken suggest that dynamic slot allocation is possible at the frequency considered, provided turnaround times are in the low-to-mid tens of milliseconds.