Heuristic Thresholds for Busy Burst Signalling in a Decentralised Coordinated Multipoint Network

In this paper, a novel decentralised coordinated beamforming technique for interference mitigation in multi-user multiple-input-multiple-output (MIMO) networks is proposed. When the available spectrum is fully reused in all cells, the base station (BS) can potentially activate a beam which causes detrimental co-channel interference (CCI) towards mobile stations (MSs) served by neighbouring cells. This problem is solved by requiring each active MS to transmit a busy burst (BB) in a time-multiplexed feedback channel using the spatial precoder utilised for receiving data. Likewise, the BS must scan the feedback channel using the same precoder which it intends to use for transmitting data in the next slot. Provided that channel reciprocity holds, the feedback channel and the data channel become reciprocal. This enables the BS to listen to the feedback channel and ascertain the amount of CCI it potentially causes towards the active MSs if it were to apply the particular spatial precoder. The BS is permitted to utilise only such precoders that cause CCI lower than a predetermined threshold. The impact of the threshold parameter for selecting spatial precoder in cellular networks is investigated and a novel heuristic for setting the thresholds in the downlink (DL) mode is proposed. It is demonstrated that the proposed heuristic achieves a 14% increase in spectral efficiency and a 6.3-fold increase in cell-edge user throughput compared to a transmit beamforming approach without interference awareness.