Power-Efficient Constellation Design for a Multicarrier Optical Wireless System

A block-wise constellation design is presented for optical communication systems with multi-subcarrier modulation (MSM), intensity modulation (IM) and direct detection (DD). The DC-bias that is traditionally used only for compensating the negative peaks of the transmitter-side signals is treated as an information-carrying basis in our proposed scheme called MSM-JDCM (joint DC and multicarrier modulation). The design procedure follows a principle of high dimensional sphere packing. To simplify the problem, we apply the following methods. First, we use bounds on the waveform's maximum and minimum. Second, we use the maximum and minimum constraints on a set of sufficient samples of waveforms. Third, we relax non-convex distance constraints into convex ones by iterative linearizations. With the MSM-JDCM, we consider the minimization of electrical power, optical power, and peak power with a common target bit error rate (BER). Analysis shows that the MSM-JDCM offers significant power gains over its counterparts: MSM-Normal and MSM-SSPS (subcarrier signal point sequence).