JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 30, NO. 12, JUNE 15, 2012 1843 10 Gb/s Indoor Optical Wireless Systems Employing Beam Delay, Power, and Angle Adaptation Methods With Imaging Detection Mohammed T. Alresheedi and Jaafar M. H. Elmirghani Abstract—In this paper, we propose a mobile optical wireless system that employs beam delay adaptation, and makes use of our previously introduced beam angle and power adaptation multi- beam spot diffusing configuration in conjunction with an imaging receiver. Our ultimate goal is to improve the bandwidth, reduce the effect of intersymbol-interference, and increase the signal-to- noise ratio (SNR) when the transmitter operates at a higher data rate under the impact of multipath dispersion, background noise, and mobility. A significant reduction in the delay spread can be achieved compared to a conventional diffuse system (CDS) when an imaging receiver replaces a nonimaging receiver at the room’s corner, where the delay spread is reduced from 2.4 ns to about 0.35 ns. Our proposed system, beam delay, angle, and power adapta- tion in a line strip multibeam spot diffusing configuration (BDAPA- LSMS), offers a reduction in delay spread by a factor of more than 10 compared with only the beam angle and power adaptation LSMS. An increase in channel bandwidth from 36 MHz (CDS) to about 9.8 GHz can be achieved when our methods of beam delay, angle, and power adaptation coupled with an imaging receiver are employed. These improvements enhance our system and enable it to operate at a higher data rate of 10 Gb/s. At a bit rate of 30 Mb/s, our proposed BDAPA-LSMS achieves about 50 dB SNR gain over conventional diffuse systems that employ a nonimaging receiver (CDS). Moreover, our simulation results show that the proposed BDAPA-LSMS at a bit rate of 10 Gb/s achieves about 32.3 dB SNR at the worst communication path under the presence of back- ground noise and mobility while achieving a bit error rate below . Index Terms—Angle and power adaptation, beam delay, gigabit mobile optical wireless systems, imaging receivers, signal-to-noise ratio (SNR). I. INTRODUCTION R ECENTLY, optical wireless (OW) communication has gained increasing attention as a potential technology for the implementation of LANs. The use of the optical medium as a means for indoor wireless communication was proposed al- most three decades ago. Gfeller and Bapst first proposed and investigated indoor OW using IR radiation [1]. IR communica- tions refer to the use of free space propagation of light waves in Manuscript received June 17, 2011; revised December 05, 2011, January 30, 2012; accepted March 05, 2012. Date of current version April 09, 2012. The work of M. T. Alresheedi was supported by a scholarship from King Saud Uni- versity, Riyadh, Saudi Arabia. The authors are with the School of Electronic and Electrical Engi- neering, University of Leeds, Leeds, LS2 9JT, U.K. (ml07mta@leeds.ac.uk; j.m.h.elmirghani@leeds.ac.uk). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JLT.2012.2190970 the near infrared band as a transmission medium for communi- cations. The behavior of IR signals is similar to that of signals in the visible spectrum which are absorbed by dark objects and directionally reflected by shiny surfaces. One of the prime mo- tivators for reconsidering the use of IR radiation in the wireless context is the demand for greater transmission bandwidths. Be- cause of the nature of light, free space IR links offer numerous advantages over their RF counterparts including an abundant unregulated spectrum, freedom from fading [1], [2], and a de- gree of privacy at the physical layer as optical signals are con- fined to the room in which they originate (hence, the possibility of frequency reuse). Despite these advantages, there are some limitations including: eye safety considerations which restrict the maximum transmit power [3], [4], multipath propagation which leads to an increased delay spread, and directive noise sources (background noise) which reduce the signal-to-noise ratio (SNR). In addition to these limitations, OW networks rely on a fiber (or some other) distributed network that feeds access points since optical signals are blocked by walls and other ob- jects. Recently, many researchers have suggested and studied the use of visible light (white-light emitting diodes (LEDs)) for indoor communications [5]. Compared with conventional IR wireless communications, white LED OW can use higher power levels and also can minimize the shadowing as the white LED lights are distributed within a room. Achieving high data rates is challenging due to the low modulation bandwidth of white LEDs which is few megahertz [6]. There are, however, some approaches to improve the modulation bandwidth of white LEDs using different equalization schemes including the use of simple ON–OFF keying (OOK) predistortion to- gether with a simple first-order RC equalization circuits [7] or postequalization at the receiver [8]. Another approach has also been proposed to achieve high-speed transmission rates, up to 513 Mb/s by utilizing discrete multitone modulation in combination with quadrature amplitude modulation [9]. Such a complex modulation scheme will complicate the transmitter’s and receiver’s designs. Transmission of OOK over an equal- ized channel is simpler compared to the advanced modulation scheme considered, since the latter requires extensive signal processing at the transmitting and receiving ends. IR optical communications can offer much higher transmission rates than visible light communication (up to Gb/s). This is due to the wider modulation bandwidth of laser sources used in IR OW instead of white LEDs. OW transmission links can be classified into two categories: direct line of sight (DLOS) and non-LOS (diffuse systems). DLOS can only be established by having a direct path between 0733-8724/$31.00 © 2012 IEEE