Hybrid Free Space Optical and RF Wireless Communication

Abstract

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. iii I gratefully appreciate the National Science Foundation for funding this research (under grant number ECCS-0636598). Finally, I want to thank to my wife and parents for their support. Without their help, this dissertation would not have been possible.

Performance Analysis of Multiuser FSO/RF Network Under Non-Equal Priority With $P$ -Persistence Protocol

“…RF is the probability of using the common backup RF link by the central RF will depend on the type of the protocol of assigning the RF link to the Jth remote node, either equal priority or non-equal priority with p-persistence protocol. In (5), ω is the data frame arrival probability defined as the probability that a new data frame arrives at the transmit buffer assigned for the Jth remote node within the time step T . Or in other words, ω is the probability that a time step T will have a new data frame.…”

“…In (4), γ(•, •) is the lower incomplete Gamma function defined in [24, Eq. (8.350.1)], γRF is the average SNR of the RF channel, given by γRF = E avg P RF G RF /σ 2 RF [6], where P RF , σ 2 RF , and G RF are respectively, transmitted RF power 5 , noise variance, assuming zero-mean circularly symmetric AWGN, and average power gain of the RF channel. The variance of the noise in the RF channel is given by σ 2 RF = W N 0 N F [14], where W is the RF bandwidth, N 0 is the noise power spectral density and N F is the noise figure of the RF receiver.…”

“…R ECENTLY free-space optical (FSO) technology has gained an increasing interest in data transmission [1] - [5] owing to their unique features including: 1) higher data rate, compared to radio frequency (RF) technology, 2) high transmission security, 3) large unregulated spectrum, and 4) faster and cheaper deployments, compared to fiber optics. Most of the current literature on FSO transmission systems are mainly limited to connecting two remote locations through a direct point-to-point FSO transmission link.…”

Topology Control Algorithm and Dynamic Management Scheme for Mobile FSO Networks

“…where RE i 0 is the residual energy of i; U andÛ are the average local standard deviation before and after the "help" process, respectively; and jE 1 jj is the number of links associated with j. Constraint (8) shows that the "help" process cannot worsen the uniformity. Constraint (9) indicates that all the links associated with j must remain connected during the movement of j.…”

“…The topology control algorithms aim to construct a minimum spanning tree (MST) or Delaunay triangulation (DT). The link allocation, routing, and scheduling proposed in [7,8] achieve a maximum throughput in hybrid FSO/RF wireless mesh networks. In [9], a bottom-up algorithm is proposed to bootstrap FSO networks, which is a distributed heuristic focusing on forming a spanning tree as fast as possible.…”