Accelerated beam searching for optical wireless communication system with slow feedback channel

In Optical Wireless Communication (OWC), the use of narrow beams can enhance the achievable bit rates and reduces interference. However, this requires a mechanism to find the direction in which the transmitter must send its beam towards the receiver. It turns out that it may be counterproductive to widen the beam during the direction search phase. This paper analyzes a system with a feedback loop that allows the receiver to report back, once it sees an incoming signal. However, this feedback channel may not have a high time resolution and may have a relatively long and random delay. This paper studies the appropriate beam width adaptation during direction search and acquisition, taking into account the received (electrical) energy per bit, and noise limitations of the transimpedance amplifier. The paper also introduces a new address coding scheme. It uses continuous addressing, thereby eliminating overhead from packet headers, error correction coding or synchronisation words, by adopting maximum-length Linear Feedback Shift Register sequences. This accelerates the beam direction search.