Free-space optical multi-subcarrier communication employing power-efficient constellations

Multi-subcarrier modulation (MSM), known as a popular free-space optical (FSO) modulation technique, is preferred over the on-off keying (OOK) that typically requires an adaptive threshold and the pulse position modulation (PPM) that relies on accurate synchronisation. MSM is, however, criticized for its low power efficiency, and we thus focus on a power-efficient constellation design to increase its power efficiency with convex optimization tools. Our scheme, termed MSM-JDCM (joint DC and subcarrier modulation), takes advantage of the compactness of sphere packings in a high dimensional space and treats the DC-bias as part of the information basis. Our scheme is shown to greatly outperform previous schemes for most working SNRs with a small number of subcarriers, and the gain is expected to grow with the number of subcarriers. This paper focus on fading channel.