On/Off Sleep Scheduling in Energy Efficient Vehicular Roadside Infrastructure

Smart downlink scheduling can be used to reduce infrastructure-to-vehicle energy costs in delay tolerant roadside networks. In this paper we incorporate this type of scheduling into ON/OFF roadside unit sleep activity, to further reduce infrastructure power consumption. To achieve significant power savings however, the OFF-to-ON sleep transitions may be very lengthy, and this overhead must be taken into account when performing the ON state scheduling. We first incorporate the OFF/ON sleep transitions into a lower bound on energy usage that can be computed for given input sample functions. An online scheduling algorithm referred to as the Flow Graph Sleep Scheduler (FGS) is then introduced, which makes locally optimum decisions about when to initiate new ON/OFF cycles. This is done by computing an estimate of the energy needed to fulfill known vehicle communication requirements with and without the OFF period. This calculation is efficiently done using a novel minimum flow graph formulation. Results from a variety of experiments show that the proposed scheduling algorithm performs well when compared to the energy lower bound. It is especially attractive in situations where vehicle demands and arrival rates are such that the energy costs permit frequent ON/OFF cycling.