The intensity modulation and direct detection (IM/DD) systems have been widely investigated and demonstrated to fulfil the requirement of short reach data communication links with simple implementation. DMLs are a low cost solution for IM/DD systems due to their low power dissipation, small footprint and high output optical power. However, for DMLs, the driving current can influence the optical density at its active region, hence the intrinsic chirp affects the generated optical carrier and results in distortions of the signals, which reduces transmission rates and signals decision accuracy. We propose a machine learning-based decision technique to mitigate nonlinear distortions of the DMLs without using any nonlinear processing, and demonstrate a 60-Gb/s PAM-8 IM/DD system using a DML. About 0.6-dB receiver sensitivity improvement is achieved after 2km transmission.
As light emitting diode (LED) based visible light communication (VLC) is getting increasingly widely used, amplitude jitter is still a common phenomenon in pulse amplitude modulation (PAM) VLC system, which deteriorates the system performance to a large extent. In this paper, we propose a novel signal decision method employing density-based spatial clustering of applications with noise (DBSCAN) of machine learning to distinguish different signal levels with jitter. Not only do we experimentally demonstrate that the Q factor of a PAM-4 VLC system employing DBSCAN is improved by up to 3.9dB, but also investigate the influence of jitter with different levels on PAM-4 system. As far as we know, this is the first time that DBSCAN has been successfully employed in PAM-4 VLC system.
We are seeing a growing use of light emitting diodes (LEDs) in a range of applications including lighting, TV and backlight board screen, display etc. In comparison with the traditional incandescent and fluorescent light bulbs, LEDs offer long life-space, much higher energy efficiency, high performance cost ratio and above all very fast switching capability. LED based Visible Light Communications (VLC) is an emerging field of optical communications that focuses on the part of the electromagnetic spectrum that humans can see. Depending on the transmission distance, we can divide the whole optical network into two categories, long haul and short haul. Visible light communication can be a promising candidate for short haul applications. In this paper, we outline the configuration of VLC, its unique benefits, and describe the state of the art research contributions consisting of advanced modulation formats including adaptive bit loading OFDM, carrierless amplitude and phase (CAP), pulse amplitude modulation (PAM) and single carrier Nyquist, linear equalization and nonlinear distortion mitigation based on machine learning, quasi-balanced coding and phase-shifted Manchester coding. These enabling technologies can support VLC up to 10Gb/s class free space transmission.
As a promising candidate technology for the next generation communication systems, visible light communication (VLC), combined with high modulation and coding schemes, can be used to achieve throughput much higher than the traditional RF wireless ones. We propose adopting multiple light-emitting diodes (LEDs) on the transmit side to form a multiple-input signal-output (MISO) VLC system. Through the maximum ratio transmit beamforming, the signals from the multiple LEDs can be added coherently at the receiver side, and, therefore, the signal-to-noise ratio of the system can be improved slightly. Meanwhile, a method of channel estimation with superposed signal is employed for better channel estimation. Extensive lab experiments demonstrate that a two-LED MISO-VLC system can achieve a data rate of 1.0 Gbit/s over a free-space link of 1.2 m.