Reduction of mixed co-channel interference in microcellular STDD systems

STDD (shared time division duplexing) is an attractive candidate for high quality, low delay multiple access in microcellular systems. We show by means of theoretical analysis that STDD is superior to conventional TDMA as well as TDMA with slow speech activity detection (SAD) in terms of capacity. We demonstrate how a type of mixed co-channel interference particular to STDD can be eliminated by means of directional antennas at the base stations for both reception and transmission, combined with appropriate organization of the time burst. Numerical results are given for a frame length of 2 ms. Capacity gains of the order of 100% over TDMA are obtained with 40 speech slots per frame and a packet dropping rate of 0.1%.