Distributed DL/UL Asymmetry Synchronization for Adaptive-Tdd Wireless Access Networks

Adaptive time division duplex (ATDD) systems have the ability to efficiently utilize the radio spectrum and achieve higher capacity, when the traffic conditions are time-varying within a cell or diverse among different cells. However, severe co-channel interference conditions can occur when the movable TDD boundary is not synchronized amongst all frames in the base stations, compromising the spectral efficiency and the system´s robust operation. To reduce the interference outage probability, a distributed boundary synchronization (DBS) scheme is proposed that dynamically synchronizes the TDD boundaries amongst neighbouring sectors, thus avoiding sector-to-sector interference, whilst preserving the ATDD efficiency. Results show that DBS achieves an 8 dB improvement in the uplink SIR for the same interference outage, and a 27.5-60% increase in terms of capacity, subject to traffic asymmetry conditions. More importantly the proposed DBS scheme requires only simple modifications in the system