Channel Characteristics Analysis and Experimental Demonstration of a Diffuse Cellular Indoor Visible Light Communication System D. Wu, Z. Ghassemlooy, S. Rajbhandari and H. Le Minh, Optical Communication Research Group, School of CEIS, Northumbria University, Newcastle Upon Tyne, UK E-mail: dehao.wu@northumbria.ac.uk ABSTRACT This paper presents a spatial optical power distribution of a non-directed cellular indoor visible light communication (VLC) system using a light emitting diode (LED) and a holographic light shape diffuser (LSD). To realize a cellular system with a maximum coverage area and a minimum power consumption, both hexagonal and rectangular geometries are studied and analysed with and without the LSD. The simulation results show that more uniform optical power distribution can be achieved using the hexagonal geometry with a 30 o holographic LSD diffuser compared to the rectangular cellular shape with no LSD. In addition, a practical link for a single cell is designed, which operates at a date rate of 5 Mb/s using the on-off keying non-return-to-zero (OOK-NRZ) data format. The measured results for both the received optical power and the Q-factor distributions are shown and discussed. Keywords Visible light communication, light emitting diodes, power distribution, cellular optical wireless communications, bit error rate 1. INTRODUCTION LEDS are being widely used as sources in short -range indoor optical wireless communication (OWC) links for local area network (LAN). They promise numerous advantages compared with the conventional radio frequency (RF) systems, such as offering a potential huge bandwidth, a secure links as rays cannot penetrate walls or opaque objects, and freedom from spectrum regulation and licensing. Due to the fast dynamic response of most current available LEDs, they can be modulated with fast switches, enabling high transmission data rates. With the increasing popularity of high definition television and video over the internet, the indoor OWC access technology employing LEDs becomes one possible and economical solution to address the bandwidth congestion currently being experiencing in most access networks [1-3]. With the availability of highly efficient white LEDs(created by combining the prime colours: red, green, and blue or by using a blue emitter in combination with a phosphor), we are witnessing a surge in research and development in indoor VLC systems. Equalization has been employed for VLC systems in [4, 5] to improve the transmission data rate. In [6, 7], the application of orthogonal frequency division multiplexing (OFDM) over a VLC channel has been investigated with significantly reduced intersymbol interference (ISI) at high transmission data rates. [8, 9] has reported a novel diffused cellular indoor VLC system with the analyses of both power and Q-factor distributions. The common link configurations for indoor OWC systems are a line-of-sight (LOS), a diffuse and a hybrid LOS-diffuse [10- 12]. Normally, the diffuse system provides a lager coverage area and an excellent mobility [13, 14], but at the cost of lower data rates, higher path losses and multipath induces ISI caused by signal reflections from walls and other objects within the room. On the other hand, directed LOS links, where the beam is confined within a much narrower field of view (FOV), offers a much higher channel capacity, a higher data rate and a longer range [15, 16]. However, directed LOS links offers a reduced coverage area and in some applications it requires alignment and/or tracking systems to maintain the link availability. To achieve higher data rates as well as a wider coverage area, a cellular system would be the preferred option [17- 19]. In cellular systems, there should in principle be a minimum overlapping between coverage areas to achieve the optimum power efficiency. There are a number of cell shapes that could be adopted such as the circular, square, equilateral triangle, and the hexagonal. For a given distance between the center of a polygon and its farthest points, the hexagon has the largest area of the three [20, 21] with no un-covered regions between cells. In this paper, we analyse models for both rectangular and hexagonal shapes with and without LSD. We have adopted the hexagon shape to ensure a more uniform distribution of the optical radiation. We report a practical single cell cellular indoor VLC link employing a blue LED as the transmitter. In order to increase the cell coverage area with a uniform power distribution LSDs [22] of different angles are employed. The rest of the paper is organized as follow. In Section II, geometrics of transmitters, characteristics of LSD, the LOS channel, and receiver are described. In Section III, simulation results are shown and experimental work is outlined followed by the discussion. Finally, the conclusion is given in the last Section IV. 2. SYSTEM DESCRIPTION 2.1. System Overview The proposed indoor cellul ar VLC systems are shown in Figs. 1(a) and (b). To achieve a higher transmission