On the Capacity Region of Optical Mobile Communication Systems With Spatial Light Modulation

Optical Mobile Communication (OMC) is a newly raised optical wireless communication system, where a novel device called Spatial Light Modulator (SLM) is applied. With the deploying of SLM units, OMC systems can split one light beam to multiple beams directing to different receivers, and hence bring in a new design freedom on the energy allocation for each sub-beam. In this paper, we study a general model of the OMC systems that the transmitter wants to broadcast multiple messages to multiple users, and some of the users may request a same message. We focus on characterizing the capacity region of such OMC systems, in order to assess the benefits on capacity by deploying SLM units. For the general cases, numerical solutions of the capacity region are raised, and for special cases that the system is symmetric or the signal to noise ratio (SNR) is rather low, closed form results of the capacity region are proposed. We also study the OMC system which broadcasts two different messages, and give out a partial closed form result of the capacity region. From this case, we can find that characterizing the capacity region for OMC systems is equivalent to optimizing high order polynomial, which is doable but impossible to find closed form results in general. Key words: Optical Mobile Communication, Spatial Light Modulator, capacity region.