Uplink bidirectional efficient multiuser visible light communications using TDD and diversity techniques

In an indoor multiuser bidirectional visible light communications (VLC) system, the performance of uplink VLC transmission degrades significantly due to design constraints and limited power available at uplink devices. In this paper, we propose an efficient uplink transmission scheme based on an orthogonal code division multiple access (OrCDMA) technique in a multiuser uplink transmission environment. While achieving minimal multiple user interference with the OrCDMA, the uplink performance is further enhanced with selection combining at the receiver, exploiting OrCDMA benefits. For bidirectional data transmission, we also employ time division duplexing (TDD). Performance evaluation was conducted for uplink transmission in an indoor VLC environment. It is found that with 5 uplink receivers installed, the bit-error rate (BER) is better than 10-5 over most locations and a BER of 10-5 is achieved at a signal-to-noise ratio (SNR) value of 5.5 dB for 16 users while maintaining a data rate of 58.18 Mbps.