Reversed Time Slot Configuration in TDD-CDMA Overlay Systems for Enhanced Downlink Throughput

Recently, the demand for downlink (DL) high-speed data access has been increasing. For a DL-centered data service, time division duplex-code division multiple access (TDD-CDMA) and adaptive modulation and coding (AMC) are promising techniques. Furthermore, overlay systems not only expand the coverage, but enhance the network and user throughputs. Specifically with TDD-CDMA, each overlay system can re-use the same frequency band, and therefore an efficient frequency usage is achievable while overlay networks interfere with each other. In this paper, we propose a novel time slot configuration over the TDD-CDMA overlay system for high-speed DL access. In our system, micro base stations (microBSs) are equipped with directional antennas to alleviate the strong BS-microBS interference and AMC is also used to gain the synergy effect between the proposed slot configuration and AMC. In the computer simulation results, we show largely increased DL network and user throughputs but slightly decreased uplink throughputs dependent on the probability of LOS between BS and microBS