Access Mechanism in Wireless Powered Communication Networks With Harvesting Access Point

In this paper, we consider a relay-enabled wireless-powered communication network (WPCN), consisting of a relay-hybrid access point (RHAP), harvesting and transmitting nodes, and a base station (BS). Contrary to conventional networks, the nodes rely on the energy signal of the RHAP to harvest energy, and they transmit information to the BS via the RHAP. The nodes work on the principle of harvest-transmitto-cooperate protocol, in which a node harvests energy from a power source in the downlink and transfers information to a relay in the uplink to convey data to the BS. In this paper, we propose a new distributed medium access control (MAC) mechanism in a relay WPCN, based on carrier sense multiple access with collision avoidance, a binary exponential random backoff mechanism. In the proposed scheme, the nodes and the RHAP contend to access the channel with different contention window sizes. Furthermore, the RHAP is given more preference to access the channel by giving a smaller contention window size than the nodes. We propose a Markov chain model for the proposed-MAC and a Markov chain model for the energy states of the nodes. It models the behavior of changing states between energy harvesting and data transmission. The analysis and simulations show the effectiveness of the proposed MAC in terms of throughput and energy efficiency.