Amplitude-Coherent Detection for Optical Wireless Communications:
Opportunities and Limitations
Abstract
The proliferation of ubiquitous computing applications created a
multi-dimensional optimization problem that includes several conflicting
variables such as spectral efficiency, complexity, power consumption,
delay, and error probability. To relax the problem and provide efficient
solutions, it was necessary to augment the currently overutilized radio
spectrum with new frequency bands such as the optical spectrum, which
can be used to off-load some of the traffic of certain applications.
Therefore, this paper presents an efficient system design that uses
amplitude-coherent (AC) detection to reduce OWC system’s complexity,
improve its reliability and spectral efficiency. More specifically, we
use amplitude shift keying with orthogonal frequency division
multiplexing (OFDM) at the transmitter, and AC detection at the
receiver. The complexity reduction is achieved by using a low complexity
detector, channel estimator, and peak-to-average power ratio (PAPR)
reduction scheme. The spectral efficiency is achieved by using real data
symbols with discrete cosine transform (DCT), which requires a
subcarrier spacing that is 50% of the discrete Fourier transform (DFT),
and does not require Hermitian symmetry to generate real-valued OFDM
signals. Moreover, the derived channel estimator is blind, and the PAPR
reduction scheme does not require a feedback overhead between the
transmitter and receiver.