Design and implementation of a maximal-ratio angle-diversity receiver for optical wireless communication systems

A maximal-ratio angle-diversity receiver is composed of multiple sectors with relatively small field-of-views. Each sector estimates the signal-to-noise ratio (SNR) of the collected signal and its gain made proportional to the relation i/(sigma) 2, where i and (sigma) represent the average signal and the shot noise root mean square (rms) values, respectively. The output signals of all sectors are then combined through an adder circuit. This paper presents the design and implementation of a maximal-ratio receiver using discrete components. A major challenge is the design of the variable gain amplifier (VGA) which requires a large dynamic range because of the large fluctuations of both signal and noise in a typical office room environment. This problem was overcome through the utilization of a cascade of two VGAs where the assignment of gains to each VGA minimizes dynamic range requirements through an innovative topology. The first one provides a gain inversely proportional to the rms shot noise and the second one a gain proportional to the SNR referred to the input of the front-end. Measurements on an implemented prototype show results close to the ideal gain of a maximal-ratio receiver making the proposed techniques suitable for maximal-ratio angle-diversity receivers.