Optical wireless communication system performance improvement by a decision feedback equalizer

Abstract

Summary form only given. We investigate the use of an adaptive decision feedback equalizer (DFE) in outdoor optical wireless communication systems using baseband non-return-to-zero (NRZ) on-off keying (OOK) modulation. We note that the intersymbol interference (ISI) induced by multi-path propagation of photons in optically thick clouds and fog impairs detection efficiency. Here, based upon theoretical analysis and Monte-Carlo simulation results of bit-error-rate (BER) with cloud and fog channel models, it is shown that using DFE, adapted according to the least-mean-squares algorithm improves the system's performance by more than 9.9 dB for a 1 Mbps, 300 m communication link. Some mathematical models of the communication characteristics of the optical wireless channel are developed. These are based on the temporal impulse response parameters of optical pulse propagation through clouds, transmission bandwidth and signal-to-noise ratio. The models include root-mean-square delay spread, BER and multi-path power penalty for unequalized and equalized optical channels. Several conclusions are obtained from this work. One is that analytical prediction models can be applied to optical wireless communication system parameters. Optical wireless communication system designers can use these models to evaluate system power budget and BER performance from the optical channel impulse response parameters. Using adaptive transmission bandwidth according to the BER model for the equalized channel, minimum BER can be achieved.