Slot Error Rate Performance of DH-PIM with Symbol Retransmission for Optical Wireless Links S. Rajbhandari, Z. Ghassemlooy, and N. M. Aldibbiat Optical Communications Research Group, NCRLab, School of Computing, Engineering and Information Sciences, Northumbria University, Newcastle upon Tyne, NE1 8ST, UK Email: fary.ghassemlooy@unn.ac.uk Abstract In this paper we introduce the dual-hear pulse interval modulation (DH-PIM) technique employing a simple retransmission coupled with a majority decision detection scheme at the receiver. We analytically investigate the slot error rate performance and compare results with simulated data for the symbol retransmissions rates of three, four and five, showing a good agreement. We demonstrate that the proposed scheme significantly reduces the slot error rate compared with the standard single symbol transmission system, with retransmission rate of five offering the highest code gain of ~5 dB. 1. Introduction The promise of a high-speed and unregulated bandwidth optical wireless link and the limitations of the available radio bandwidths have encouraged the research interest in optical wireless communication (OWC) systems [1-6]. OWC (both indoor and outdoor) is capable of providing a high data throughput (hundreds of MHz), flexible and secure links in a number of applications such as hospitals, museums, exhibition halls, trains and train stations, aircraft and airports etc. where RF based system may not be the most appropriate schemed to adopt because of security, safety and offered data rates [5-6]. In OWC systems (particularly in indoor application operating at 880-920 nm wavelength range) the allowable transmitter average power is limited mainly by the eye safety requirements, thus affecting the link length and system performance. Also to ensure a longer life span for the optical source in particular