Abstract
Three methods (transmit power adaptation, imaging reception, and Multicarrier Code Division Multiple Access (MC-CDMA)) are introduced to the optical wireless (OW) system and a significant improvement is achieved in the presence of very directive noise, multipath propagation, mobility, and shadowing typical in a real indoor environment. In the absence of shadowing, replacing a single non-imaging receiver by an imaging receiver with maximal ratio combining (MRC) improves the signal-to-noise ratio (SNR) by 20 dB in a conventional diffuse system (CDS) operating at 30 Mbit/s at a transmitter-receiver separation of 6m in agreement with previous results in the field. Further SNR improvement of 24 dB is achieved when a line strip multi-beam system (LSMS) replaces the CDS when both systems employ an imaging MRC receiver. Furthermore, our new adaptive LSMS (ALSMS) system coupled with the imaging MRC receiver offers an SNR improvement of 23 dB over the imaging MRC LSMS illustrating the gain achieved through adaptation. The results also show that combining transmit power adaptation with spot-diffusing (i.e. ALSMS) coupled with an imaging receiver based on select best (SB) increases the bandwidth from 46.5 MHz (non-imaging CDS) to 7.53 GHz thus enabling the OW system to achieve higher data rates and provide multi-user capabilities in our case by employing a MC-CDMA scheme. In a 10 user MC-CDMA OW system, a bit error rate (BER) improvement from 4.9 x 10(-1) to 2.1 x 10(-5) is achieved when the imaging MRC ALSMS system replaces the imaging CDS in a shadowed environment.