  Energy harvesting multi-hop networks allow for perpetual operation of low
cost, limited range wireless devices. Compared with their battery operated
counterparts, the coupling of energy and data causality constraints with half
duplex relay operation makes it challenging to operate such networks. In this
paper, a throughput maximization problem for energy harvesting two-hop networks
with decode-and-forward half-duplex relays is investigated. For a system with
two parallel relays, various combinations of the following four transmission
modes are considered: Broadcast from the source, multi-access from the relays,
and successive relaying phases I and II. Optimal transmission policies for one
and two parallel relays are studied under the assumption of non-causal
knowledge of energy arrivals and finite size relay data buffers. The problem is
formulated using a convex optimization framework, which allows for efficient
numerical solutions and helps identify important properties of optimal
policies. Numerical results are presented to provide throughput comparisons and
to investigate the impact of multiple relays, size of relay data buffers,
transmission modes, and energy harvesting on the throughput.
