Cooperative Diamond Channel With Energy Harvesting Nodes

We consider the energy harvesting diamond channel, where the source and two relays harvest energy from nature and the physical layer is modeled as a concatenation of a broadcast and a multiple access channel. Since the broadcast channel is degraded, one of the relays has the message of the other relay and the multiple access channel can be modeled as a cooperative multiple access channel with common data. We find the optimal offline transmit power and rate allocations that maximize the end-to-end throughput. For the broadcast side, we show that there exists an optimal source power allocation, which is equal to the single-user optimal power allocation for the source energy arrivals. We then show that the fraction of the power spent on each broadcast link depends on the energy arrivals for the relays. For the multiple access side with no co-operation, with fixed source rates, we show that the problem can be cast as a multiple access channel with both data and energy arrivals and can be formulated in terms of data transmission rates only. We use a dual decomposition method to solve the overall problem efficiently. Finally, we focus on the diamond channel with co-operative multiple access capacity region and find the optimal rates and powers using a decomposition into inner and outer maximization problems.