Energy Efficient Spectrum Access in Wireless Cognitive Radio Ad Hoc Networks

In this paper, the resource allocation problem is considered for energy efficient spectrum access in a wireless cognitive radio ad hoc network, where each node is equipped with cognitive radio and has limited battery energy. The network is an OFDMA system operating on time slots. In each slot, the users with new traffic demand will sense the entire spectrum and locate the available subcarrier set. By assuming that a central coordinator has the link gain information of all the new simultaneous transmitting receiving pairs (say through a rendezvous channel), an energy efficient subcarrier selection and power allocation scheme is derived by minimizing energy per bit across the network while considering all the interference from co-channel users, together with QoS requirements and maximal power limit. An -optimal solution for the unconstrained optimization problem is attained in the first part of the paper by the proposed efficient one-dimensional sub-gradient search algorithm. Then a near-optimal solution for the constrained resource allocation problem is derived by combining the optimal solution and distributed power control. The solution provides insights on the properties of energy efficient resource allocation in an ad hoc network which differ from the case of cellular networks, and it can be served as a benchmark for the design of distributed resource allocation schemes for such networks. The results could also be directly applied to networks with certain infrastructure support (such as a cluster based network).