Constellation Design for a Multicarrier Optical Wireless Communication Channel

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 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. Designs are done for both flat-fading and frequency selective-fading scenarios, and following 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 minimize 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 MSM-Normal and MSM-SPSS. The short-term peak to average power ratio (PAPR) and long-term PAPR constraints are combined with the MSM-JDCM to mitigate the nonlinear distortion caused by high power amplifier and laser diode, which is another novelty of our scheme. To attain lower BER, a binary switching algorithm (BSA) is applied to find the improved constellation labeling.