Time-Slot Coding Scheme with Adaptive Loading Function for Multiple Access in Indoor Optical Wireless Communications

Optical wireless communications have been well studied as a potential technique to achieve data rates exceeding several gigabits/second transmission. However, a simple and effective multiuser access framework for such systems remains elusive to date. In this paper, the time-slot coding scheme is employed with 16-QAM modulation format to simultaneously provide high-speed wireless communications to multiple users. With the use of unique time slotted code for each user, we demonstrate an effective multiuser access framework and evaluate its performance. The code alignment tolerance is investigated and experimentally demonstrated as 27.6%, 28.1%, 28.4%, and 28.8% at a received optical power of -18, -16, -14, and -12 dBm, respectively. Furthermore, to provide flexible data rates and to improve the coverage in multiuser scenarios, the time-slot coding scheme is incorporated with the adaptive loading function allowing different users to deploy different modulation methods. Compared to conventional time-slot coding scheme, experimental results show that satisfactory coverage (BER <= 3.8 x 10(-3)) at 1 GBaud/s can be extended by up to 61.2%.