Distributed channel allocation and rate control for hybrid FSO/RF vehicular ad hoc networks

We address joint channel allocation and rate control to maximize the network throughput in vehicular ad hoc networks (VANET). Considering the limited channel resources and quality of service (QoS) requirements of vehicular communication, a mixed-integer linear programming (MILP) problem is formulated. However, it is unrealistic and inefficient to choose a center node to perform global optimization in VANET. Hence, we propose a distributed channel allocation and rate control approach to solve the cross-layer design problem. Applying the carrier sense multiple access with collision avoidance protocol, the proposed channel allocation decides the channel usages by measuring the channel demands of links and transforms the MILP problem to a corresponding linear programming problem.We adopt the alternating direction method of multipliers (ADMM) to optimize the flow rates. Since imbalanced rates may be allocated to paths passing the same link, rate adjustment is proposed to ensure the throughput requirement of each path. Simulation results demonstrate the fast convergence of the proposed distributed algorithm and the improvement of ADMM with rate adjustment over the ADMM. While the performance is sensitive to the outage probability of the FSO link, increasing the single FSO link rate does not substantially improve the probability of finding a feasible solution. In addition, a small radio frequency communication range is desirable for a network with dense node distribution due to the dominated interference.