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.