Power Efficient Ultra-Reliable Communication in Rician/Rayleigh Fading Environment using CC-HARQ

In this paper, we propose an efficient power allocation scheme for a communication system to achieve ultra-reliable communication. The system is considered to be located in a microcell which is considered to be a Rician channel due to the possibility of the transmitter and receiver arranging themselves in point-to-point contacts. Further, the system is considered to be interfered by a Rayleigh faded co-channel interferer signal which arises as a result of spectrum limitation. We formulate the power allocation problem as a minimization of the average retransmit power under the constraint of a given target outage probability. Then, we propose a numerical solution method for the optimization problem as the closed-form solution for the Karush-Kuhn-Tucker system is not feasible. We show through simulations that realizing ultra-reliable communication using an open-loop setup is much more power-consuming compared to the proposed power allocation scheme which provides high power gains. Further, we show that, even though the increase in the number of retransmissions will decrease the overall power requirement, this will also lead to a decrease in the throughput.