Using One-Bit Sigma-Delta Modulator for DCO-OFDM and ACO-OFDM Visible Light Communication System

Abstract

Visible light communication based on white light emitting diodes provides optical wireless communication from 400 nm to 700 nm. Simple two-level on-off keying and pulse-position modulation are supported in IEEE standard 802.15.7 due to their compatibility with existing constant current light emitting diode drivers, but their low spectral efficiency have limited the achievable data rates in visible light communication. Orthogonal frequency division multiplexing has been applied to visible light communication due to its high spectral efficiency and ability to combat inter-symbol-interference. Direct current biased and asymmetrically-clipped are modified optical orthogonal frequency division multiplexing for visible light communication. The continuous magnitude of orthogonal frequency division multiplexed signals requires complicated mixed-signal digital-to-analog converter and modification of light emitting diode drivers. In this thesis, a one-bit sigma-delta modulator is introduced to the transmit signal generated by orthogonal frequency division multiplexing which produces two level output to drive the light emitting diodes. Such modification is compatible with the current light emitting diode lighting systems and drivers as the output of the one-bit sigma-delta modulator is equivalent to on-off keying signal, thus is immune to system nonlinearities. The use of sigma-delta modulator retains high spectral efficiency as the original input signal and improves the bit-error performance with respect to signal to noise ratio of the system as well.