This proposal proposes a program of research and education in techniques for very high bit rate wireless infrared communications. In the context of wireless networks, the term "high bit rate system" refers to one that transmits tens or hundreds of megabits per second. The project lies in the intersection of the fields of photonics, communications, and networks. These fields are undergoing rapid growth and are becoming increasingly important components of an emerging information society. The research program involves both theoretical and experimental investigations into the nature and potential of the wireless infrared channel as a high-quality communications medium. The educational goals of the proposal are to develop and enhance the curriculum in the intersection between photonics, digital communications, and networks. The emphasis will be on developing interdisciplinary components to courses in these areas that will enhance students' ability to function effectively in these very different but linked fields.
Wireless Infrared Communications. Infrared radiation is a medium that can be used for high-speed wireless digital communication [1,2]. Since the infrared spectrum is blocked by typical surfaces, it is particularly well-suited to short-range applications, such as point-to-point links and local area networks. Infrared links can be classified as directed or non-directed. Directed links employ directional transmitters and receivers, which must be aimed to establish a link, whereas non-directed links employ wide-beam transmitters and wide-field-of-view receivers to remove the need for alignment. Line-of-sight (LOS) systems rely on a direct path between transmitter and receiver, whereas non-LOS links employ surface reflectivity to guide transmitted light to the receiver. The two extremes are directed LOS and non-directed non-LOS (or "diffuse"). Our focus is on diffuse links, which are the most suitable for use as the basis for a general purpose wireless local-area network. The most practical modulation technique is intensity modulation (IM), in which the trans-mitted signal is modulated onto the optical intensity of the transmitted beam. Down-conversion is most effectively done using direct detection (DD), where a photodetector produces a current proportional to the received optical power. The main challenges to achieving high speed communication over acceptable distances in IM/DD infrared systems are (1) the high path loss resulting from diffusing the signal energy, (2) the strong sources of background noise, including sunlight, incandescent lighting, and fluorescent lighting, and (3) the dispersion in the channel from multipath, photodetector capacitance, and photodetector transit-time. We also look at multiple access or medium access control issues. This can be achieved with multiplexing techniques, either optical or electrical, which are normally associated with the phys-ical layer of network architecture models. We also consider statistical multiplexing or contention-based sharing techniques, which are consider part of the data link layer. In the following sections, we describe both theoretical and experimental investigations into the nature and potential of the wireless infrared channel as a high-quality communications medium. ***
