Hybrid Free Space Optical and RF Wireless Communication

Hybrid free space optical/radio frequency (FSO/RF) technology has recently been proposed as a means of significantly increasing the throughput and reliability of wireless broadband communications. The motivation is to use parallel noninterfering communication channels to combat channel impairments. In order to implement and fully exploit hybrid FSO/RF technology, both point-to-point (P2P) communication system and network models need to be studied.

We develop physical-layer and network-layer models of hybrid FSO/RF networks. We address two topics: hybrid FSO/RF P2P systems and hybrid FSO/RF wireless mesh networks (WMN). Theoretical analyses are presented. In addition, we present practical implementations with performance that approaches the theoretical system performance derived. Numerical and simulation results are provided to show the advantages of hybrid FSO/RF systems.

For P2P communications, we model the hybrid FSO/RF system as an independent parallel channel system. We develop an information-theoretic analysis of the parallel channel model and implement an adaptive design resulting in a capacity-approaching and seamless joint system. Results show that this jointly optimized FSO/RF link significantly outperforms simple RF or FSO links.

In our research on hybrid FSO/RF WMN, we study both centralized and distributed routing algorithms. For centralized routing, we present network control algorithms based on both non-fading and fading communication channels using a physical interference model for the RF portion of the network. We study the throughput improvement achievable by augmenting the RF WMN with FSO links. In our distributed routing study, a hierarchical routing algorithm is developed for the hybrid FSO/RF network. The algorithm is optimized for the hybrid network so that the advantages of high-throughput FSO links and the reliability of RF links are highlighted. FSO links are able to relieve network congestion caused by the limited capacity and interference-limited nature of pure RF networks.