Transceiver Design Concept for Cellular and Multispot Diffusing Regimes of Transmission
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Transceiver Design Concept for Cellular and Multispot Diffusing Regimes of Transmission S. Jivkova Central Laboratory of Optical Storage and Processing of Information, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria Email: [email protected]
M. Kavehrad Center for Information and Communications Technology Research (CICTR), Department of Electrical Engineering, The Pennsylvania State University, University Park, PA 16802, USA Email: [email protected] Received 25 March 2004; Revised 23 August 2004 A number of attempts have been made in an effort to combine the advantages of line-of-sight and diffuse configurations for indoor optical wireless communications via sophisticated combinations of elements that are characteristic for these architectures. A different approach has been followed in the present investigation, namely, developing a transceiver capable of operating in both configurations. It is proposed that the transceiver design be based on the utilization of two-dimensional arrays of infrared lightemitting devices and photodetectors. Basic design parameters of transceiver optics are derived from considerations about link blockage and system compliance with the unique features of line-of-sight and diffuse methods of transmission. Keywords and phrases: optical communications, wireless communications, local area networks.
1.
INTRODUCTION
It has been more than two decades now since Gfeller and Bapst [1] suggested that diffusely scattered infrared light could be utilized as a medium for wireless communications indoors. Various system configurations for optical wireless local area networks have been investigated since then. They differ in the degree of directionality of the transmitter and receiver and the orientation of the units. The latter factor underlies the development of two major classes of link topology: line-of-sight (LOS) links, in which an LOS path between receiver and transmitter exists, and nonLOS or diffuse links, which rely on diffuse signal reflections off the room surfaces. In this paper, the term “diffuse” is used for a link architecture that prohibits the existence of an LOS between receiver and transmitter regardless of the transmitter radiation pattern. This is in distinction from other investigations that apply this term to links that employ a transmitter with a Lambertian radiation pattern, even when an unobstructed LOS signal path exists (see, e.g., [2]). This is an open-access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Line-of-sight architectures LOS links exhibit low power requirements when transmitted optical power is concentrated in a narrow beam thus creating a high power flux density at the receiver. Furthermore, such links do not suffer from multipath signal distortion. If additionally a narrow field-of-view (FOV) receiver is used, an efficient optical noise rejection and a high optical signal gain are achievable [3]. Generally speaking, nar
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