With small cell base stations (SBSs) densely deployed in addition toconventional macro base stations (MBSs), the heterogeneous cellular network(HCN) architecture can effectively boost network capacity. To support the hugepower demand of HCNs, renewable energy harvesting technologies can beleveraged. In this paper, we aim to make efficient use of the harvested energyfor on-grid power saving while satisfying the quality of service (QoS)requirement. To this end, energy-aware traffic offloading schemes are proposed,whereby user associations, ON-OFF states of SBSs, and power control are jointlyoptimized according to the statistical information of energy arrival andtraffic load. Specifically, for the single SBS case, the power saving gainachieved by activating the SBS is derived in closed form, based on which theSBS activation condition and optimal traffic offloading amount are obtained.Furthermore, a two-stage energy-aware traffic offloading (TEATO) scheme isproposed for the multiple-SBS case, considering various operatingcharacteristics of SBSs with different power sources. Simulation resultsdemonstrate that the proposed scheme can achieve more than 50% power savinggain for typical daily traffic and solar energy profiles, compared with theconventional traffic offloading schemes.
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