Multi-level thresholding for reducing cascade yielding of FlahLinQ link scheduling

Qualcomm proposed a D2D (device-to-device) communication scheme called FLQ (FlashLinQ) which can achieve higher rate and more coverage than other D2D technology. In this paper, we propose a modified scheduling technique for FLQ to compensate the cascade yielding problem. In D2D link scheduling, some links should be selected to communicate in a data traffic period for efficiency frequency reuse. In FLQ, every link is assigned scheduling priority, and implements scheduling according to the priority and SIR (signal-to - interference ratio) which is computed from received local CSI (channel state information). The FLQ scheduling has two processes: Rx(receiver) yielding and Tx (transmitter) yielding. In the Rx yielding process, the links which are highly interfered by higher priority links give up communication. In the Tx yielding, the links which highly interfere to higher priority links yield for communication opportunity. Because the FLQ executes scheduling with only local CSI, the technique may suffer from cascade yielding problem that the links which have no interference with scheduled links are unnecessarily yielded by other yielded links. Especially, the cascade yielding is highly likely easy to occur in congested D2D network. Hence we propose a multi-thresholding to reduce the cascade yielding. The multi-thresholding is applied to the Rx yielding, and perform phased scheduling with multi-level threshold. The technique gradually reduces links with extremely low SIR by preemptive back off. Then, the proposed technique achieves better sum-rate and frequency reuse ratio by reducing incidence of the cascade.