Generalized Spatial Multiplexing for Optical Wireless Communication Systems

Spatial Multiplexing (SMP) is one of the most commonly used multiple-input multiple-output (MIMO) techniques in optical wireless communication (OWC) systems. Although SMP can achieve high spectral efficiency, it suffers from severe inter-channel interference (ICI). In this paper, we for the first time propose a novel MIMO technique, i.e., generalized SMP (GSMP), for intensity modulation/direct detection (IM/DD) OWC systems. Differing from conventional SMP which activates all the transmitters to transmit signals, GSMP selects a variable number of transmitters for signal transmission. The information bits of GSMP can be carried by both the spatial index symbols via variable-number transmitter selection and the constellation symbols transmitted by the activated transmitters. Compared with SMP, GSMP has the advantages of reduced ICI and enhanced spectral efficiency. The obtained analytical and simulation results show that GSMP can achieve greatly improved bit error rate performance than conventional SMP to achieve the same spectral efficiency in indoor 2 × 2 and 4 × 4 MIMO-OWC systems.