QoS- and Energy-Aware Optimal Resource Allocations in DF Relay-Assisted FSO Networks

Abstract

Due to the growing demand for high quality of service (QoS) in the already congested radio spectrum, there is a need to design energy-efficient free-space optical (FSO) networks. In this regard, this paper investigates the joint optimization of resources like power allocation (PA) on transmitting nodes and placement of relay node in QoS and energy-aware FSO networks. The performances of the optimizations are measured in a realistic channel incorporating the fading due to three impairments: atmospheric turbulence, pointing error, and angle-of-arrival (AOA) at the receiver. For QoS-aware network, the outage probability based on bit error probability (BEP) is minimized for the error-free transmission, whereas energy-efficiency (EE) is maximized in the energy-aware network. Performances in both the networks are investigated by optimizing the resources using three optimization schemes: (i) optimal PA for a fixed relay placement (RP), (ii) optimal RP for a fixed PA, and (iii) joint optimization of PA and RP. It is shown that the problems for individual optimization of PA and RP are conditionally pseudoconvex which is used to obtain the jointly global solution using joint optimization algorithm. In case of EE maximization, the optimal solutions are obtained through fast converging multi-dimensional golden search algorithms. Numerical results validate the proposed analysis as well as compare the different optimization schemes along with their computational complexities. The investigation demonstrates that an outage enhancement and EE improvement of around 37% and 10% respectively can be achieved over the benchmark schemes. Lastly using the obtained results, we observe the various design insights on optimization of PA and RP in the dual-hop FSO network.