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Recent trends in the field of communication science show that most devices are built and governed by Visible Light Communication (VLC) and Light Emitting Diodes (LED). The communication process depends on source characteristics and bandwidth restriction, and effective methods of modulation and demodulation can enhance data rate. Attractive and practical Carrierless Amplitude-Phase (CAP) modulation is used for higher efficiency and easier implementation. However, the performance of the CAP-VLC system gets adversely affected by factors like jamming, scattering, and low sensitivity to receiver signal. Hence, this paper examines the mitigation of available system degrading factors, based on a high-speed, extreme learning machine algorithm (ELM). Prediction analysis and simulation are processed using trained raw dataset for CAP demodulation, to prove the level of performance in terms of accuracy as 92%, under various parametric conditions. This system that is proposed can achieve bit error rate (BER) of 40% to 50% of noise ratio and can be effectively used in sectors like medical health care, banking, and finance.

Visible light communications (VLCs) have attracted considerable interest in recent years owing to the potential to simultaneously achieve data transmission and illumination using low-cost light-emitting diodes (LEDs). However, the high-speed capability of such links is typically limited by the low bandwidth of LEDs. As a result, spectrally efficient advanced modulation formats have been considered for use in VLC links in order to mitigate this issue and enable higher data rates. Carrierless amplitude and phase (CAP) modulation is one such spectrally efficient scheme that has attracted significant interest in recent years owing to its good potential and practical implementation. In this paper, we introduce the basic features of CAP modulation and review its use in the context of indoor VLC systems. We describe some of its attributes and inherent limitations, present related advances aiming to improve its performance and potential and report on recent experimental demonstrations of LED-based VLC links employing CAP modulation. This article is part of the theme issue 'Optical wireless communication'. [ABSTRACT FROM AUTHOR]

Visible light communications (VLCs) have received extensive attention in the research community thanks to their advantages of high bandwidth, low cost, robustness to electromagnetic interference, operation in an unregulated spectrum, and high degree of spatial confinement in indoor scenarios. One of the main limitations for high data-rate transmission in VLC systems is the limited modulation bandwidth of commercial light emitting diodes. To circumvent this limitation, spectrally efficient modulation schemes should be used. Optical orthogonal frequency-division multiplexing (O-OFDM)-based schemes have become very popular and several proofs of concept have shown their ability to attain over gigabits per second transmission rates. We consider here the use of pulse amplitude modulation and carrier-less amplitude and phase modulation schemes together with frequency-domain equalization (FDE) at the receiver as interesting alternatives to O-OFDM. We show the advantages of the former schemes in terms of the peak-to-average-power ratio, and demonstrate through numerical results the merits of FDE-based signaling in attaining high data rates.

Abstract A Gray code mapping scheme is proposed to reduce coding penalty for probabilistically shaped 9QAM. The carrierless amplitude and phase modulation (CAP) probabilistically shaped 9QAM with the Gray code mapping scheme is experimentally investigated in a single carrier intensity modulation/direct detection (IM/DD) transmission system. The experiment results show that the proposed 9QAM with Gray coding has a gain of 0.034 bits/symbol and 0.111 bits/symbol over 9QAM without Gray coding and star-8QAM at a received optical power of -5.5 dBm, respectively. All of the three modulation formats have the same spectral efficiency (SE) equal to 3 bits/symbol. [ABSTRACT FROM AUTHOR]

40-Gb/s/λ multi-band carrierless amplitude and phase (CAP) modulation long-reach passive optical networks were demonstrated using 10-G class transceivers only. A major issue of multi-band CAP is that it is vulnerable to timing error, and this work has offered quantitative analysis about it in detail for the first time. A novel simple timing recovery approach, partial differential quadrature amplitude modulation constellation encoding and decoding schemes together with blind multimodulus algorithm equalization are proposed to address the issue efficiently, enabling zero-overhead signal recovery. Results show that it can offer excellent system tolerance to timing error of at least±0.1 symbol period even for the highest frequency CAP sub-band. The characteristics of the transceiver are measured, and optimization of critical system parameters is performed including the CAP sub-band count, 10-G Mach-Zehnder intensity modulator operation conditions, optical launch power, and wavelength offset asymmetrical optical filtering. For downlink using erbium-doped fiber amplifier preamplifiers, successful 40-Gb/s multi-band CAP signal transmission over an 80-km (90-km) single-mode fiber is achieved with a link power budget of 33 dB (29 dB) considering a forward error correction threshold bit error ratio of 3.8 × 10-3. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate a practical visible light communication (VLC) system of 3.2-m transmission using spectrally efficient discrete multitone (DMT) or carrierless amplitude phase (CAP) modulation. The transmitters consist of two light emitting diodes (LEDs) spaced 2 m apart, the arrangement of which corresponds to a common case for full-range illumination in indoor environments, and this work also investigates the influence of the difference in transmission path lengths from the LEDs to a single receiver. In the overlapped illumination area, the delay interference between the LEDs could result in up to about 40% capacity reduction using quaternary CAP or bit-loaded DMT signals, when two LEDs simply transmit the same signal. To mitigate the impact of the delay interference, Alamouti space-time block coding (STBC) is employed for both DMT and CAP signals, and the combination of CAP and STBC is proposed for the first time to the authors' best knowledge. Employing STBC, we successfully demonstrate interference-tolerant VLC over 3.2-m air transmission, and the maximum data rates for DMT and CAP signals are 220 and 150 Mbps, respectively. [ABSTRACT FROM PUBLISHER]

Hybrid multiband (HMB) CAP/QAM transmitter/receiver systems are proposed for the first time. Simulation results are provided to show the feasibility of 100 Gb Ethernet links employing a single-laser source transmitting HMB CAP-16/QAM-16, CAP-32/QAM-32, and CAP-64/QAM-64 signals. The proposed hybrid scheme has low sensitivity to directly modulated laser nonlinearities. We found that QAM receivers bring about identical jitter tolerance to ideally phase compensated CAP receivers, and QAM receivers are more practical since no phase tracking and compensation are required. Compared with the case of using a standard non phase compensated CAP receiver, the use of the modified QAM-16/32/64 receiver significantly lowers system timing jitter sensitivity in the multiband, as well as single-band case. Results also showthat the use of increasing number of bands causes increased system power margin. For practical jitter conditions of ±6 ps, three HMB CAP/QAM systems with optimum band counts are identified to be capable of supporting single-laser 100 Gb/s transmission over 15-km SMF. [ABSTRACT FROM AUTHOR]

Carrierless amplitude and phase (CAP) modulation is generating increasing interest for short reach optical communications. In this letter, we present the use of a decision-directed least mean square (DD-LMS) adaptive equalization algorithm for CAP128/256 transmission systems. A novel preconvergence scheme using aided threshold decision is proposed, called decision-assisted modified cascaded multimodulus algorithm. With the help of a DD-LMS-based equalizer, we demonstrate for the first time transmission of 10-Gb/s CAP128/256 signal over 40-km standard single mode fiber using low-cost directly modulated lasers. [ABSTRACT FROM PUBLISHER]