Outage minimization in fading channels under energy harvesting constraints

This paper considers the use of energy harvesters in delay-constrained point-to-point wireless communications, where the source transmits with power drawn periodically from a device that harvests energy from the environment. In particular, the source is assumed to transmit over a block-fading channel with a constant transmission rate. It is also assumed that the channel state information (CSI) is unknown at the source but perfectly known at the destination, and the energy harvesting process is deterministic and known a priori at the source. The optimal power allocation is studied to minimize the receiver outage probability over a finite horizon of N energy-harvesting periods, each of which contains M communication blocks with independent channel fading coefficients. Although the outage minimization problem is shown to be non-convex, the optimal power allocation solution is obtained by the proposed forward search algorithm, which corresponds to an on-off transmission scheme. Moreover, a threshold-based sub-optimal low-complexity power allocation algorithm is proposed, which is shown to be asymptotically optimal as M goes to infinity. Finally, numerical results are provided to validate our analysis.