Optical Wireless Communications Adopting Delay-Tolerant Repetition-Coding With Orthogonal-Filters and On-Demand Equalization

Transmitter diversity schemes, such as repetition coding (RC), can tackle the optical channel blockage issue in high-speed line-of-sight link based optical wireless communication (OWC) systems, and channel synchronization is required to realize the benefit. In this article, an orthogonal-filters-based repetition coding (OF-RC) transmitter diversity scheme with on-demand equalization is proposed to address time delays amongst multiple optical wireless channels in the indoor OWC systems. The OF is used for the separation and recovery of the overlapped multipath signals from the single received data stream, and hence, the proposed novel OF-RC scheme can relax the channel synchronization requirement without frequent channel state feedback. The proposed OF-RC principle is firstly investigated via both numerical analysis and experimental demonstration in the two-transmitters scenario, where the OF is constructed using the square root RC filter with orthogonal sine/cosine function sets. Results show that a bit-error-rate (BER) performance within the 7% forward-error-correction (FEC) limit is achieved using the proposed OF-RC scheme together with on-demand fast recursive-least-squares (RLS) equalization. Furthermore, both fractional and integer OF length delays can be handled by the proposed OF-RC scheme. In addition to the two-transmitters scenario, the generalized OF-RC scheme supporting more transmitters is also theoretically investigated, and multidimensional OFs are constructed via the multiband approach. The performance and feasibility of OWC system with the generalized OF-RC scheme is numerically simulated in the three-transmitters scenario, and results demonstrate the capability of the generalized OF-RC scheme. The proposed OF-RC scheme with on-demand equalization provides a promising solution to tackle the fundamental time delay limitation in high-speed indoor OWC systems.