Adaptive TDD Synchronisation for WIMAX Access Networks

In adaptive time division duplex (ATDD) wireless systems, severe co-channel interference conditions can occur if the movable downlink/uplink (UL) TDD boundary is not synchronised among all frames in base stations. To reduce interference outage and to improve a system's spectral efficiency, a new single frequency cell (SFC) network architecture is proposed, which allows for distributed boundary synchronisation (DBS) via inter-sector signalling. SFC-DBS dynamically synchronises TDD boundaries among neighbouring sectors for each frame, thus avoiding sector-to-sector interference, while preserving the ATDD radio resource assignment efficiency. Analysis shows that SFC-DBS achieves an additional 6-11 dB in the average UL signal-to-interference ratio, compared with existing channel assignment schemes, which corresponds to 25-50 % capacity gain subject to traffic asymmetry in different sectors. More importantly, the proposed SFC scheme does not incur any further cost in the frequency planning, whereas the DBS scheme requires only minor system modifications. Compared with interference cancellation via antenna arrays and beamforming, SFC-DBS achieves similar performance, albeit without the cost for complex radio transceivers and multiple antenna elements.