Practical considerations for indoor wireless optical system implementation using OFDM

Abstract

This paper describes the implementation of OFDM (orthogonal frequency division multiplexing) for optical wireless systems using non-coherent light. In particular, light emitting diodes (LEDs) and photodiodes (PDs) are considered. The paper shows how classical OFDMis adapted to optical system constraints. Several key OFDM design issues are studied. In this context it is demonstrated that the impact of the cyclic prefix (CP) length on power and bandwidth efficiencies is negligible. Similarly, the effect of the Doppler frequency shift on intensity modulation with direct detection (IM/DD) optical transmission is discussed. The challenge of a high peak-to-average power ratio (PAPR) OFDM signal in the presence of LED nonlinear behavior is highlighted. An approach to estimate the overall signal-to-noise ratio (SNR) of the system and to determine the required analog-to-digital converter (ADC) resolution to achieve a target system SNR is introduced.