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In multispot-diffuse multiple-input-multiple-output (MSD-MIMO) system configuration, a communications channel can be considered virtually ideal at data rates of hundreds of megabits per second. Thus, the main concern is power efficiency. We propose a transceiver optical design that creates a reconfigurable transmitter output and independent communications channels. The transmitter employs multiple light sources that can be turned on and off, independently. In this way, an optical signal is provided only where it is needed. The receiver utilizes an imaging optical system and a segmented photodetector, thus performing direction diversity reception. We show that when maximum ratio combining is employed on the received electric signals and power-efficient modulation schemes such as L-level pulse-position modulation are used, significant power savings can be achieved. We also investigate the vulnerability of MSD-MIMO links to shadowing and blockage and their effects on communications cell size and required transmit power in a cellular configuration.
Date of Publication: May 2004