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).