On transmit diversity and scheduling in wireless packet data

Downlink time division multiplexing is considered for cellular packet-switched systems, in conjunction with scheduling algorithms for fast packet switching across the served users. Additionally, open and closed loop transmit diversity techniques at the base station are considered to improve the spectral efficiency of the resulting system. A study is conducted on the effect of candidate transmit diversity techniques for packet data systems on the overall network data throughput in the presence of scheduling. Contrary to the circuit-switching paradigm, the presented results highlight the conflicting objectives of specific transmit diversity schemes and efficient scheduling and illustrate the impact of the medium access control layer functions on the physical layer performance. The open loop space time spreading technique is shown to offer inferior performance to no transmit diversity under greedy packet scheduling. An appropriate transmit diversity scheme is proposed for the downlink packet-data multiple access.