Electronic tracking for wireless infrared communications

Abstract

A high-speed wireless system (>or=100 Mb/s) for indoor infrared (IR) communications via the line of sight is described and feasibility is shown in an experimental demonstrator. A diffuse link is used for connectivity, and tracked directed links are used for high-speed communications. The transmitter is made of a laser diode array in combination with multiple-beam forming optics. For the receiver (Rx), a wide-angle lens, and an avalanche photodiode array are used. For the diffuse link, the signals from all pixels in the array are combined. Pixels are selectively addressed to realize directed links. Fast electronic tracking of a directed link is possible by switching the signal path onto the right pixel in the array. Diffuse link, directed link, position detection, and tracking can be realized with one and the same transceiver hardware. A favorite system design is derived from constraints due to the IR channel, eye safety, lenses, photodetectors, and the overall system complexity. The experimental system shows some key features, namely 155-Mb/s wireless transmission over a distance of nearly 2 m with electronic tracking at an imaging IR Rx. Electronic tracking of IR links, thus, allows both high data rates and high capacity for wireless access in small office and home environments

A review of communication-oriented optical wireless systems

“…In [114], system issues for a 100 Mb/s MSD link were also presented. A 140 Mb/s MSD system with a single receiver [120] and a 155 Mb/s using a multi-element imaging receiver are presented in [65]. Following the above, MSD links maintain the high bandwidth and low path losses of point-to-point links and at the same time achieve mobility that is comparable with those in diffuse links at the expense of slightly more complicated transmitters and receivers [112].…”

“…Although such systems are ideal for high-speed data distribution, they are of high complexity and do not permit motion of terminals. High-speed electronic tracking was reported in [65] to support mobility at a rate of 155 Mb/s over ranges of nearly 2 m. Tracking was accomplished by using a transmitter that had an array of laser diodes combined with optics and a receiver with a wide FOV and detection array. Tracking involved the selection and switching of paths onto the appropriate receive element.…”

Recent developments in indoor optical wireless systems

“…In [43], the development of a combined directed (for high-speed) and diffuse link (for connectivity) system was demonstrated. In this approach, the diffuse link was provided by a high-power laser directed at a diffusely radiating surface, and the directed link was implemented with a vertical cavity surface emitting laser diode array with focusing lens.…”

Beam shaping with tip-tilt varifocal mirror for indoor optical wireless communication

“…The device shown here is a practical, low cost way of doing this. There are, however, some situations when having a larger beam could be beneficial, such as when the transmitter is first locating the receiver, or when it is tracking a receiver as it moves [14,15]. Varifocal capability provides dynamic control of the beam size to continuously optimize the beam for the specific scenario.…”