In-Band Coding for Power Reduction in Multiple-Subcarrier Modulated Wireless Optical Systems

In this work we apply techniques for power reduction in electrical multiple-subcarrier modulated (MSM) systems to wireless optical systems. The signal set is expanded by adding a zero amplitude constellation point to each frequency channel. A peak and average optical power gain are realized by coding over these increased degrees of freedom. We develop search techniques to find good mappings between transmitted symbols and trellis edges both at low and high bandwidth efficiencies. With a symbol-by-symbol bias, an average optical power reduction of 0.9 dB over uncoded systems is achieved with a simultaneous peak power reduction of 0.4 dB at the same bandwidth efficiency.