Error Performance of Generalised Space Shift Keying for Indoor Visible Light Communications

In this paper the error performance analysis of a low complexity, multiple transmitter generalised space shift keying (GSSK) signalling technique for short range indoor visible light communications is presented. In an N_t transmitter system, this signalling technique is capable of achieving a spectral efficiency of N_t bits/s/Hz. The GSSK system has a higher spectral efficiency than the conventional on-off keying (OOK) and pulse position modulation (PPM) techniques. The GSSK transmitter is much simpler than that of an equivalent regular pulse amplitude modulation (PAM) system with similar spectral efficiency. An analytical expression for the symbol error rate (SER) is presented and verified using simulations. The receiver is based on the maximum likelihood criterion and using multiple photodetectors (PDs) in the receiver improves the error performance. Within the room and the transmitter-receiver configuration under consideration, with four PDs, a gain of 6 dB is attainable over the single PD system for the case of 2 and 3 bits/s/Hz. Considering a fixed link range with N_t = 2 and at a symbol error rate of 10^-6, using wide half angle LEDs with Φ_1/2= 60° requires about 12 dB less in electrical signal-to-noise ratio compared with Φ_1/2 = 30°. The beam directivity is however of much lower effect when the room under consideration is equiped with sufficient LEDs to provide full coverage. The GSSK technique can also support dimming control by using different pulse widths. This, however, is at a price of reduced spectral efficiency.