In multi-band carrier-less amplitude and phase modulation (m-CAP), the transmitter and receiver pulse shaping filters have a significant impact on the signal performance. Since m-CAP is an emerging and promising modulation format for visible light communications (VLC), it is necessary to balance the system performance and the filter length, due to limited integration density in field programmable gate arrays (FPGAs). In this paper we investigate the m-CAP VLC system performance for different number of sub-bands m = {2, 5, 10} under varying finite impulse response (FIR) filter parameters, such as the filter length Lf and the roll-off factor β. We show that increasing both β and Lf improves the bit error rate (BER) performance of the system substantially. We demonstrate that a BER target of 10-4 is achieved using Lf ≤ 12 symbols for m = 5 and 10 for low order subcarriers. Moreover, the BER limit is attained for β = 0.2 by all subcarriers, except the last two for m = 5 and 10, which is a significant improvement, even considering the slightly increased excess bandwidth in comparison to the literature.
In this paper, we investigate relay-assisted visible light communications (VLC) where a mobile user acts as a relay and forwards data from a transmitter to the end mobile user. We analyse the utilization of the amplify-and-forward (AF) and decode-and-forward (DF) relaying schemes. The focus of the paper is on analysis of the behavior of the mobile user acting as a relay while considering a realistic locations of the receivers and transmitters on a standard mobile phone, more specifically with two photodetectors on both sides of a mobile phone and a transmitting LED array located upright. We also investigate dependency of the bit error rate (BER) performance on the azimuth and elevation angles of the mobile relay device within a typical office environment. We provide a new analytical description of BER for AF and DF-based relays in VLC. In addition we compare AF and DF-based systems and show that DF offers a marginal improvement in the coverage area with a BER < 10–3 and a data rate of 100 Mb/s. Numerical results also illustrate that relay-based systems offer a significant improvement in terms of the coverage compared to direct non-line of sight VLC links.
In this Letter, we propose a new configuration for visible light communication systems, which results in doubling of the data rate due to the use of polarization division multiplexing. As light-emitting diodes are unpolarized incoherent light sources, we isolate both the perpendicular
s
and parallel
p
modes for independent modulation. For the first time, to the best of our knowledge, we show that it is possible to transmit and successfully recover two separate orthogonal frequency division multiplexing (OFDM) signals on each polarization (pol-OFDM). Furthermore, we compare the performance of the pol-OFDM system with the transmission of a single conventional OFDM signal without a polarizer over the same physical link. We show that similar bit error rates can be achieved while obtaining
∼
45
%
improvement in both the data rate and spectral efficiency due to polarization multiplexing.
This Letter presents original measurement results from an all-optical 10 Gbit/s free-space optics (FSO) relay link involving two FSO links and an all-optical switch. Considering the fact that reported analyses of relay links are dominated by analytical findings, the experimental results represent a vital resource for evaluating the performance of relay FSO links in the presence of atmospheric turbulence. Bit-error-rate (BER) performance of the relay system is tested for single and dual-hop links under several turbulence regimes. Furthermore, results from this measurement are used to ascertain real parameters of the outdoor links and to improve the accuracy of simulation results. Results show that using a dual-hop FSO link against a single FSO link could result in up to four orders of magnitude improvement in BER in the presence of atmospheric turbulence.
This paper describes the experimental verification of the utilization of long-term evolution radio over fiber (RoF) and radio over free space optics (RoFSO) systems using dual-polarization signals for cloud radio access network applications determining the specific utilization limits. A number of free space optics configurations are proposed and investigated under different atmospheric turbulence regimes in order to recommend the best setup configuration. We show that the performance of the proposed link, based on the combination of RoF and RoFSO for 64 QAM at 2.6 GHz, is more affected by the turbulence based on the measured difference error vector magnitude value of 5.5%. It is further demonstrated the proposed systems can offer higher noise immunity under particular scenarios with the signal-to-noise ratio reliability limit of 5 dB in the radio frequency domain for RoF and 19.3 dB in the optical domain for a combination of RoF and RoFSO links.
Abstract-This paper demonstrates a hybrid radio over multimode fibre and free space optics (RoMMF-FSO) system that can be used to extend the transmission range of the 4 th generation longterm evolution (4G-LTE) signal in access networks. A single mode filtering technique (SMFT) is used to enhance 4G-LTE performance. The proposed scheme is evaluated in terms of the system transfer function, laser beam profile, and error vector magnitude (EVM). We show that using SMFT increases the RoMMF-FSO system bandwidth by 2 GHz and improves the received optical power by 13.6 dB. Moreover, the proposed system enhances the EVM by 4%. The measured results show that using a 1 km MMF instead of a 1 km SMF will marginally increase the measured EVM from ~6.6% to ~7% with a 0.2 dB power penalty with respect to the LTE EVM limit of 12.5% as is specified for 16-quadrature amplitude modulation. The proposed system is validated practically under atmospheric turbulence conditions to mimic the outdoor environment. Measured EVM results are verified theoretically through transmitting LTE signals with turbulent using log-normal model. We also show that for a FSO link span of 500 m to meet the EVM target of 12.5% the SNR power penalties are ~2 dB and ~11 dB for σ R 2 of 1.2×10 -4 and 0.1, respectively compared with no turbulence.Index Terms-Free space optics, long term evolution, multimode optical fibres, radio-over-fibre.
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