Real Time Implementation of CAP Modulation With “Better-Than-Nyquist” Pulse Shaping in Visible Light

In this letter we experimentally verify a real-time implementation of the `better-than-Nyquist' pulse shape in carrier-less amplitude and phase (CAP) modulation in the context of a visible light communications system. We use two National Instruments universal software radio peripherals (USRPs) as a transmitter and receiver working independently. Previously reported experimental work on pulse shaping in CAP is also verified in real time, showing lower error vector magnitudes (EVM) can be obtained at shorter filter lengths using the better-than-Nyquist pulses in place of the conventionally used square-root raised cosine as the basis function of the signal. We show that a real time EVM penalty is an additional 3% EVM in the worst case and is a result of synchronisation offset at the receiver.