Coded beam searching for bi-directional optical wireless communication system

In a communication system with steerable laser beams, the transmitter must find the direction towards the receiver. This requires a feedback loop such that the receiver can signal that the correct direction has been found. However, the receiver may not be able to instantly give high-resolution feedback if the beam hits its detector. At least during the acquisition phase, thus before transmitter and receiver are aligned in both directions, this feedback channel typically has a wider beam and a much lower bandwidth, thus a (possibly random) latency and a lower time resolution. It is often not practical to adaptively widen the optical beam during acquisition, but even if one designs for an adaptive beam width, it is not evident that this accelerates the search as we argue in this paper. The paper also describes a suitable address coding scheme based on maximum-length Linear Feedback Shift Register sequences, that accelerates the search significantly.