Merits and limitations of spatial modulation for optical wireless communications

In this paper an optical wireless communication system that uses spatial modulation (SM), a concept of encoding information on the spatial location in space of an optical source to increase data rate, is discussed with the view to highlighting its merits and limitations. The SM technique represents a low complexity, alternative method of increasing the number of bits transmitted per symbol. The technique depends on the natural disparity in the channel parameters of optical sources that occupy different positions in space. As a result, the error performance of an SM technique is heavily influenced by the receiver location with respect to the optical sources as well as how similar or dissimilar the channel gain values are. Simulation results for three transmitting LED sources in a room show that for a mobile receiver to ensure wireless communication at a symbol error rate of 10-6, up to 109 dB of signal-to-noise ratio (SNR) is required. This high SNR requirement will undoubtedly impose limitations on the system particularly when the receiver is mobile and the available optical power is limited.