Low-timing-sensitivity waveform design for carrierless amplitude and phase modulation in visible light communications

The carrierless amplitude and phase (CAP) modulation is a promising candidate for visible light communication (VLC) because of its high frequency efficiency and low implementation complexity. However, the CAP receiver is highly sensitive to timing errors because of the bad eye diagram performance and requires a complex synchronisation circuit. In this study, the conventional CAP pulse is extended to a generalised CAP pulse. The zero inter-symbol interference (zero-ISI) and the zero cross-channel interference (zero-CCI) constraints are assumed for the generalised CAP pulses. Two new sets of wider eye opened two-dimensional (2D) CAP pulses and a set of frequency efficient 3D CAP pulses are proposed to meet the zero-ISI and zero-CCI constraints for VLC. Simulation results show that the proposed new 2D CAP pulses are more tolerant to the timing offset than the existing CAP pulses in VLC systems, but the corresponding bit error rate performances are poorer when the accurate timing synchronisation is obtained. Moreover, the proposed new 3D CAP pulses are more sensitive to the timing offset than the existing CAP pulses.