1Renewables Powered Cellular Networks: Energy Field and Network Coverage

Abstract—Powering a radio access network using renewables such as wind and solar power promises dramatic reduction of the network operation cost and of the networks ’ carbon footprints. However, the spatial variation of the energy field can lead to fluctuation in power supplied to the network and thereby affects its coverage. This warrants research on quantifying this negative effect and techniques for countermeasure, motivating the current work. The paper considers a cellular downlink network with hexagonal cells and powered by harvesting energy. The network coverage of mobiles is specified by an outage constraint. A novel model of the energy field is developed using stochastic geometry. In the model, fixed maximum energy intensity occurs at Poisson distributed locations, called energy centers; the intensities fall off from the centers following an exponential-decay function of squared distance; the energy intensity at an arbitrary location is given by the decayed intensity from the nearest energy center. The effect of the energy field on the network performance depends on the harvester deployment. First, consider single harvesters deployed on the same sites as base stations (BSs). The mobile outage probability is shown to decrease exponentially with the product of the two parameters of the energy-field model, namely the energy-center density and exponential rate of the energy-decay function. Next, consider distributed harvesters whose generated energy is aggregated and then re-distributed to BSs. As the number of harvesters per aggregator increases, the power supplied to each BS is shown to converge to a constant proportional to the number of harvesters per BS, which counteracts the randomness of the energy field. Nevertheless, this requires regulating the energy loss in the aggregation process by increasing the harvester voltage for power transmission inversely with the aggregator density to the power of a quarter. In addition, it is shown that the above results hold whether or not BSs adapt their transmission powers to channels. I