Topology Control Schema for Better QoS in Hybrid RF/FSO Mesh Networks

Abstract

The practical limitations and challenges of radio frequency (RF) based communication networks have become increasingly apparent over the past decade, leading researchers to seek new hybrid communication approaches. One promising strategy that has been the subject of considerable interest is the augmentation of RF technology by Free Space Optics (FSO), using the strength of each communication technology to overcome the limitations of the other. In this article, we introduce a new scheme for controlling the topology in hybrid Radio-Frequency/Free Space Optics (RF/FSO) wireless mesh networks. Our scheme is based on adaptive adjustments to both transmission power (of RF and FSO transmitters) and the optical beam-width (of FSO transmitters) at individual nodes, with the objective of meeting specified Quality of Service (QoS) requirements, specifically end-to-end delay and throughput. We show how one can effectively encode the instantaneous objectives and constraints of the system as an instance of Integer Linear Programming (ILP). We demonstrate that the technique of Lagrangian Relaxation (LR), augmented with iterative repair heuristics, can be used to determine good (albeit sub-optimal) solutions for the ILP problem, making the approach feasible for mid-sized networks. We make the proposed scheme viable for large-scale networks in terms of number of nodes, number of transceivers, and number of source-destination pairs by solving the ILP problem using a Particle Swarm Optimization (PSO) implementation

On the design and optimization of a free space optical access network

“…Major FSO research has focused on the PHY so far, such as hardware architecture [31] and optical channel modeling [13]. Recently, there have been several work on the design [32][33][34] and (re)configuration [7,27,35,36] of FSO networks. As in the class of network planning work, ILPs are usually formulated and various heuristic algorithms are proposed to provide sub-optimal solutions.…”

“…FSO links and traditional RF links are complementary to each with respect to data rate, interference, robustness, and range. Several papers have investigated the hybrid RF/ FSO networks for enhanced performance [36][37][38]. In [37], genetic algorithms are used to improve the capacity performance with a minimum number of hybrid FSO/RF gateways.…”

“…In [37], genetic algorithms are used to improve the capacity performance with a minimum number of hybrid FSO/RF gateways. In [36], the authors propose to adaptively adjust both transmission power (of RF and FSO transmitters) and the optical beamwidth, to meet prescribed QoS requirements. In [38], the authors investigate radio signal transmission over terrestrial optical wireless channels under a WiMAX network setting, and provide an outage probability analysis.…”

On joint topology design and load balancing in free-space optical networks

“…Major FSO research has focused on the PHY, such as hardware architecture [3] and optical channel modeling [10,13]. There have been several work on the design [5,22] and configuration [4,7,21,23] of FSO networks. As in network planning, MILPs are usually formulated and various heuristic algorithms are proposed to provide sub-optimal solutions.…”

Hybrid Free Space Optical and RF Wireless Communication

“…The first algorithm aims minimize the number of clusters while the second one focuses on topology optimization. In [41], the authors present a topology control scheme based on RF and FSO transmitter power and optical beam-width adjustments to meet the QoS requirements, specifically end-to-end delay and throughput. The authors of [42] propose to the use FSO links in building hybrid FSO/RF gateway architecture to supplement the performance of existing wireline gateways.…”