Adaptive mobile multicarrier code division multiple access optical wireless systems employing a beam clustering method and diversity detection

The authors consider a mobile optical wireless system that employs an adaptive beam clustering method (ABCM) to improve system performance. Our new ABCM system offers a significant signal-to-noise ratio (SNR) improvement of 22 dB over a line strip multibeam system (LSMS) at a 6 m transmitter-receiver horizontal separation when both systems employ an 8 degrees diversity receiver and operate at 50 Mbit/s. At the worst communication path in the 50 Mbit/s on-off keying (OOK) system, the combination of beam power adaptation, beam clustering and diversity reception can reduce the transmit power by almost 7 dB while achieving 10(-9) bit error rate (BER). An increase in the channel bandwidth from 26.8 MHz (a conventional diffuse system (CDS)) to almost 8 GHz can be achieved when an 8 degrees angle diversity ABCM system is implemented at the worst communication path. The increase in the channel bandwidth and SNR can be used to enable multiuser capabilities, in our case, by employing a multicarrier code division multiple access (MC-CDMA) scheme. At transmitter and receiver locations of (2 m, 4 m, 1 m) and (1 m, 1 m, 1 m), the MC-CDMA ABCM system achieves a BER of 5 x 10(-10) in a four-user scenario compared to a BER of 5 x 10(-1) when MC-CDMA CDS is considered. Furthermore, a zero forcing equalisation technique was employed to reduce multiple access interference and improve the BER performance. The results confirm that while the CDS and the LSMS systems benefit, the equalisation scheme, which increases receiver complexity, is not necessary when the ABCM replaces CDS or LSMS at the data rate considered.