摘要
The dense deployment of low-power small-cell base stations (SBSs) can complement existing macro base stations (MBSs) to address the $1000 imes $ mobile data challenge. Considering the low power rating of SBSs, it may be possible to supply them with renewable energy, providing an appealing alternative for hyper-dense deployment of small cells. Since renewable energy is weak and intermittent, off-grid SBSs may not be always active. This raises the concern as to whether they can be a real solution. To assess the performance of a heterogeneous network (HetNet) with two tiers, including the traditional MBSs supplied by grid power and off-grid SBSs supplied by renewable energy, this paper develops an analytical framework based on the celebrated stochastic geometry. The proposed framework is versatile with numerous features included: non-uniform BS deployment, biased user association, flexible operation of off-grid SBSs, and resource allocation with minimum rate guarantee. We obtain important distance distributions, association probabilities, and coverage probabilities. Extensive numerical results validate the accuracy of theoretical analysis and show the impact of key system parameters on the performance of HetNet with off-grid SBSs.