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Energy harvesting and sleeping strategy are the important methods to deal with the increasing grid power consumption problem. However, power supply solely from energy harvesting modules would be more likely to cause energy outage of base station (BS), and the load of sleeping BS would lead to coverage hole problem, which directly affect user’s quality of service (QoS). In this paper, to achieve the trade-off between grid power consumption and user’s QoS for each tier, optimal joint of ON/OFF mode of a BS and power source switching strategies are designed for two-tier femtocell networks, which are powered by the cooperation of the harvested energy and grid power. Then, exploiting stochastic geometry and random walk theory, BS availability and availability region are characterized with the proposed strategies. Moreover, the relationships among BS availability, battery capacity of grid power and cut-off energy level are exploited to verify the proposed strategies. By numerical simulations, we find that when energy storage capacity achieves a certain value, the effect of grid power battery capacity on availability almost vanishes especially in femto tier. So these redundant grid power can be saved when the stored energy in battery meets current traffic requirement.

Considering that existing node coverage scheduling algorithms are mostly based on the accurate location information and have the problems of higher overlap in coverage and lower regional coverage quality, a location-independent energy balanced node-covered scheduling algorithm is proposed. First, the discrimination method for the redundant nodes is emphasized. On this basis, the procedure of the algorithm is given. The simulation results indicate that the proposed algorithm can effectively promote the coverage quality with less number of the active nodes compared with the Gao and the LDAS algorithm.

An executive v.p. and head of Americas at a solar independent power producer has left the company just over a year after he joined.