Zeyu Wu

January 2012
Free Space Optical Networking with Visible Light: A Multi-Hop Multi-Access Solution
Committee Members: Advisor: Thomas Little, SE/ECE

Abstract: Wireless communication is currently dominated by Radio Frequency (RF) technologies. However, constraints, such as limited bandwidth and electromagnetic interference, limit applications of RF technologies in certain scenarios. For example, RF signals can cause interference with aircraft communication or medical devices in airports or hospitals. Meanwhile, recent developments in solid-state Light-Emitting Diode (LED) materials and devices are driving a resurgence into the use of Free-Space Optical (FSO) wireless communication. Many opportunities exist to exploit low-cost nature of LEDs and lighting units for widespread deployment of optical communication. However, some characteristics of the optical medium, including directionality and susceptibility to visible light noise sources, must be managed.

In this dissertation, a model for indoor Visible Light Communication (VLC) applications is provided to analyze and predict the signal attenuation, Signal-to-Noise Ratio (SNR), Bit Error Rate (BER) and data rate. Discrete Multi-tone (DMT) modulation is discussed for optical signaling and analysis shows that although DMT requires good SNR, it can provide 4 to 5 times the channel capacity of simple modulation schemes such as On-Off Keying (00K). We propose an original solution for indoor applications that achieves continuous 10 Mb/s data rates while supporting multiple access under Non Line-of-Sight (LOS) condition. Analysis and simulation of the two protocols under the hexagonal transceiver configuration indicate suitability for high data rate communications between peers or multiple devices using the peer-to-host mode. Furthermore, a novel Medium Access Control (MAC) scheme is proposed in order to solve the contention among mobile receivers due to signal directionality, provide continuous connectivity and meet the expectation of low complexity and low cost. Performance analysis shows more than 50 % improvement on latency at the expense of a 6 % drop on system throughput.