Differential Signalling in Free-Space Optical Communication Systems

In this paper, we review the differential signalling technique and investigate its implementation of in free-space optical (FSO) communication systems. The paper is an extended version of our previous works, where the effects of background noise, weak turbulence and pointing errors (PEs) were investigated separately. Here, for the first time, we present a thorough description of the differential signalling scheme including for combined effects. At first, we present an extension of the analysis of differential signalling to the case of moderate to strong atmospheric turbulence. Next, we investigate a more general case where both channel turbulence and PEs are taken into consideration. We provide closed-form expressions for the optimal detection threshold and the average bit-error-rate, and present a set of numerical results to illustrate the performance improvement offered by the proposed differential signalling under various turbulence and PEs conditions

Implementation and Evaluation of a Gigabit Ethernet FSO Link for 'The Last Metre and Last Mile Access Network'

In this paper, we propose a simple and a low cost 1 Gbps Ethernet free-space optical (FSO) communications link, which can be used both for the last meter and last mile access networks. In the emerging fifth generation wireless systems, which require at least an order of magnitude increase in the peak data rates and three orders of magnitude increase in network capacity with reduced latency, deploying multiple technologies will play a crucial role to meet these requirements. One possible complementary wireless technology to the radio frequency is the unlicensed FSO, which can bridge the gap between the existing RF wireless and optical fibre communication networks by providing high data rates, low installation costs and high energy efficiency. In this work, we propose a high-speed FSO system, which can be readily implemented using off the shelf components, and assess its performance experimentally under turbulence and fog conditions using the dedicated indoor atmospheric chamber. We show that, the proposed system under the turbulence condition with a scintillation index of 0.43 offers almost the same data rate (i.e., ∼99%) as the link under a clear channel, while the packeterror-rate reduces from 10−3 to 2 × 10−2

Communication characteristics of high-brightness light sources based on luminescence concentration

Communication characteristics of high-brightness solid-state light sources based on luminescence concentration generated using blue emitting InGaN light emitting diode arrays are demonstrated here for the first time. The proposed device is used as a transmitter in visible light communications, and its performance is evaluated

A Head/Taillight Featuring Hybrid Planar Visible Light Communications/Millimetre Wave Antenna for Vehicular Communications

With the emergence of the fifth generation and beyond mobile networks, both visible light communications (VLC) and radio frequency (RF) or millimetre wave (mmW) systems are expected to maintain the connectivity in various environments. In outdoor environments the link (VLC or RF) availability is paramount, which is affected by channel conditions. In particular, in vehicular communications other vehicles, harsh environment, and road geometry and structure will have the impact on the link connectivity and availability. In such cases, a front-end antenna solution, which benefits both optical and RF communication links, can be seen as an attractive option that can be fitted in future vehicles. In this paper, we present the design and practical implementation of a planar hybrid VLC/mmW antenna operating at 20.8 GHz and show measured results for characterization of RF and VLC links as well as communications performance. We have used the widely adopted on-off keying and quadrature amplitude modulation schemes with different orders to demonstrate data rates of 5 Mb/s and up to 100 Mb/s for the VLC and mmW links, respectively. By measuring the bit error rate and the error vector magnitude for VLC and Rf links, respectively for each modulation we have shown that the proposed hybrid planar antenna is suitable for example in a typical vehicle -to-vehicle communications

Impact of Link Parameters and Channel Correlation on the Performance of FSO Systems With the Differential Signaling Technique

We investigate the effects of link parameters and the channel correlation coefficient on the detection threshold, Q-factor, and bit-error-rate (BER) of a free-space optical system employing a differential signaling scheme. In systems employing differential signaling schemes, the mean value of the signal is used as the detection threshold level, provided that differential links are identical or highly correlated. However, in reality, the underlying links are not essentially identical and have a low level of correlation. To show the significance of the link parameters as well as the correlation coefficient, we derive analytical relations describing the effect of weak turbulence and we determine the improvement of Q-factor with the channel correlation. Further, for the same signal-to-noise ratio, we demonstrate that a link with a higher extinction ratio offers improved performance. We also propose a closed-form expression of the system BER. We present experimental results showing improved Q-factor for the correlated channel case compared to the uncorrelated channel

Performance of Vehicular Visible Light Communications under the Effects of Atmospheric Turbulence with Aperture Averaging

In this paper, we investigate the performance of a vehicular visible light communications (VVLC) link with a non-collimated and incoherent light source (a light-emitting diode) as the transmitter (Tx), and two different optical receiver (Rx) types (a camera and photodiode (PD)) under atmospheric turbulence (AT) conditions with aperture averaging (AA). First, we present simulation results indicating performance improvements in the signal-to-noise ratio (SNR) under AT with AA with increasing size of the optical concentrator. Experimental investigations demonstrate the potency of AA in mitigating the induced signal fading due to the weak to moderate AT regimes in a VVLC system. The experimental results obtained with AA show that the link’s performance was stable in terms of the average SNR and the peak SNR for the PD and camera-based Rx links, respectively with <1 dB SNR penalty for both Rxs, as the strength of AT increases compared with the link with no AT

Performance Analysis and Software-Defined Implementation of Real-Time MIMO FSO with Adaptive Switching in GNU Radio Platform

In this paper, we provide the first software-based implementation of multiple-input multiple-output (MIMO) free space optical (FSO) link with the adaptive switching based on the software defined radio developed by GNU Radio software system, which emulates the real-time capability of the proposed scheme. We propose a switching mechanism to independently configure each transmitter and receiver, based on the channel state information provided at the transmitter via a feedback link and evaluate the link performance under atmospheric conditions such as fog and turbulence. We also validate the advantages of mitigating both the turbulence and fog in the proposed MIMO FSO system by means of numerical simulations and the developed GNU Radio software platform

Implementation and Evaluation of a 10 Gbps Real-time FSO Link

In this paper, we present and experimentally evaluate a real-time 10 Gbps free-space optical (FSO) link under varying atmospheric conditions. In bandwidth-craving wireless technologies due to the ubiquitous consumption by internet of things devices and requiring high data rate online services, unlicensed FSO systems can be a promising candidate to satisfy the network capacity of the existing data communications technologies. In this work, we verify the experiment using small form-factor pluggable transceivers mounted FPGA as a FSO transmitter and receiver. Here, a high-speed single FSO link is proposed and its performance under turbulence and fog conditions using the dedicated indoor atmospheric chamber is evaluated. We show that the proposed system under the turbulence condition with a scintillation index of 0.35 offers the same data rate as the link under a clear channel, while the bit error rate increases from 10-12 to 5 × 10-4

Relayed FSO Links for Ground-to-Train Communications

Relay assisted FSO, which is primarily used as a fading mitigation technique, can be employed to reduce the impact of network layer handover in the context of HST communications. In this paper, we propose a relay-based FSO system to provide ground to train communications and relays the information to the next base stations. Two schemes are analyzed via numerical simulations namely (i) all optical amplify and forward (AOAF); and (ii) AOAF with optical and optical-electronical-optical regeneration schemes in terms of the bit error rate performance and transmission range attained