High-speed Indoor Optical Wireless Communications - Channel Modeling Methods and Applications

Open Access
Author:
Chowdhury, Mohammad
Graduate Program:
Electrical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
October 22, 2014
Committee Members:
  • Mohsen Kavehrad, Dissertation Advisor
  • Mohsen Kavehrad, Committee Chair
  • John Metzner, Committee Member
  • Aylin Yener, Committee Member
  • Kevin William Houser, Committee Member
Keywords:
  • indoor optical wireless
  • channel modeling algorithms
  • 10 Gbps bi-directional link
  • diffuse and line-of-sight optical links
Abstract:
Optical wireless communications (OWC) is an important research area that promises to mitigate some problems currently existing in radio frequency based systems, such as shortage of radio frequency spectrum, interference and necessity of transmission at very high data rates. Optical wireless communications can be both indoors and outdoors. The focus of this dissertation is on indoor optical wireless communication channels and systems. Indoor optical wireless channels pose some challenges to properly model and analyze propagation characteristics. Since light signals reflect from wall surfaces, receivers in an OWC system usually receive many reflections of the transmitted signals. This results in inter-symbol-interference (ISI) that has detrimental effects to the achievable performance of the system. Hence, it is necessary to understand reflection patterns and consequences of multiple bounces of light signals from reflecting surfaces by properly analyzing the channel impulse response. In this dissertation, methods of simulating indoor optical wireless channel impulse responses are discussed and an algorithm is elaborated that have been developed by combining two existing popular algorithms, namely Barry’s algorithm and Modified Monte Carlo method, thereby carrying the best features of both. Channel parameters that affect high speed data transmission such as rms delay spread is an important topic that has been discussed in details in this dissertation. Channel impulse responses of several channel conditions are simulated and associated rms delay spreads are found, thereby relating the results to the locations of the receiver and the source. Every data transfer communication system has to be duplex, i.e. requires both a downlink as well as an uplink channel. Hence, for establishing a high-speed communication system we have proposed a design of a duplex optical wireless system in this dissertation. Some considerations related to cost efficiency at the user side have been taken into account. The system is capable of working in full-duplex mode. Description of an experimental demonstration is also part of the dissertation where the demonstration was involved in establishing a bi-directional link that carries 10 Gbps data stream both ways and a uni-directional link that carries analog Cable Television transmission. The distance between the two ends of the system is 15 m. We have shown achievability of very low BER (approximately in the range of 10-20) by using off-the-shelf equipment and hence proposed a direct application of this system in datacenters to reduce the load of oversubscribed wired links connecting the top-of-the-rack or aggregate switches.