SDMA/TDMA dynamic slot assignment using a smart antenna basestation

by Shad, Faisal

There is an increasing demand today for the deployment of wireless services such as cellular telephony, paging, wireless locd area networks, digital broadcast television, and wireless Internet. The demand for bandwidth from these services continues to increase as more people adopt the technology and the applications become more sophisticated. In the recent years, researchers have demonstrated that smart antennas are capable of improving wireless link quality and increasing coverage area. In addition to this, it has also been demonstrated that smart antennas can permit the reuse of the frequency spectrum in the same wireless coverage area using space division multiple access (SDMA). SDMA has the potential to provide a tremendous increase in system capacity over conventional wireless systems. In this thesis we consider the application of smart antemas for packet switched SDMA networks. The system considered is an infrastructure network employing a smart antenna baseatation which communicates with portable stations that have omnidirectional antemas. A time division multiple access (TDMA) packet switched system that incorporates SDMA is considered. Several heuristic dynamic slot assignment (DSA) strategies are proposed. DSA is the name given to the process of allocating packets to the time slots in rd-time on a frame by frame basis. The pnmary objective of DSA is to maximize the frame capacity. Both a theoretical Rayleigh fading channel mode1 and experimental data collected using an 8 element circular antema array built at the Communications Research Laboratory at McMaster University is used to measure the frame capacity of the heuristics. Analytic, simulated, and experimental results demonstrate that the SDMAITMDA frame capacity is several times higher than the single omnidirectional basestation antenna case. The results also iii provide insight into how the protocol performance is dected by parameters such as wireless channel model, slot assignrnent cornplexity, power control, pedestrian motion in the channel, and signal to noise ratio (SNR). The weLl known slotted ALOHA protocol which is best suited for bursty data communication between a large population of portable stations is adapted for operation with a smart antenna basestation. Versions of this protocol are considered where contention takes place in the data slot directly and when a reservation channel feeds a contention free data channel. The DSA heuristics developed earlier are applied to the contention free data channe1 to improve system capacity. An SDMA version of the slotted ALOHA protocol is modified for operation in a multicell situation. Simulation and analytic results show that the single ceLl slotted ALOHA system can achieve a many-fold increase in system capacity, especially when intelligent slot scheduling is done at the basestation. The sensitivity of the protocol capacity to factors such as the hardware complexity, packet six, SNR, and protocol complexity is examined. An analysis of the multicell slotted ALOHA protocol reveals that it is possible to reuse the frequency in every ceU and still achieve a per cell capaxity similar to ordinary single-cell slotted ALOHA with only a modest degree of srnart antenna beamforming hardware at the basestations. The DSA heuristics are then extended to multicell situations. Several DSA techniques requiring various degrees of coordination between the basestations are examined. DSA enhancements are also proposed for systems with variable length packets.