Information and Energy Cooperation in OFDM Relaying: Protocols and Optimization

Integrating power transfer into wireless communications to support simultaneous wireless information and power transfer (SWIPT) is a promising technique in energy-constrained wireless networks. While most existing work on SWIPT focuses on capacity-energy characterization, the benefits of cooperative transmission for SWIPT have been investigated far less. In this paper, we consider SWIPT in an orthogonal frequency-division multiplexing (OFDM) relaying system, where a source node transfers information and a fraction of power simultaneously to a relay node, and the relay node uses the harvested power from the source node to forward the source information to the destination. To support the simultaneous information and energy cooperation, we first propose a transmission protocol, assuming that the direct link between the source and destination does not exist, i.e., power-splitting (PS) relaying protocol, where the relay node splits the received signal power in the first hop into two separate parts: one for information decoding and the other for energy harvesting. Then, we consider the case that the direct link between the source and destination is available, and the transmission mode adaptation (TMA) protocol is proposed, where transmission can be completed by cooperative mode and direct mode simultaneously (over different subcarriers). In the direct mode, when the source transmits signal to the destination, the destination receives the signal as information, and the relay node concurrently receives the signal for energy harvesting. Joint resource-allocation problems are formulated to maximize the system throughput. By using the Lagrangian dual method, we develop efficient algorithms to solve the nonconvex optimization problems.