  Renewable energy assisted heterogeneous networks can improve system capacity
and reduce conventional energy consumption. In this paper, we propose a
semi-Markov decision process (SMDP)-based downlink packet scheduling scheme for
solar energy assisted heterogeneous networks (HetNets), where solar radiation
is modeled as a continuous-time Markov chain (CTMC) and the arrivals of
multi-class downlink packets are modeled as Poisson processes. The proposed
downlink packet scheduling scheme can be compatible with the mainstream
wireless packet networks such as long-term evolution (LTE) networks and the
fifth-generation (5G) networks because the SMDP is a real-time admission
control model. To obtain an asymptotically optimal downlink packet scheduling
policy, we solve the semi-Markov decision problem using the relative value
iteration algorithm under average criterion and the value iteration algorithm
under discounted criterion, respectively. The simulation results show that the
average cost of the SMDP-based packet scheduling scheme is less than that of
the greedy packet scheduling scheme.
