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Enhanced performance of odd order square geometrical shaping QAM constellation in underwater and free space VLC system
摘要： Visible light communication(VLC) employing light-emitting diodes(LED) as light source has become a promising field for underwater wireless communication. However, due to the complex underwater environment and scattering, absorption and diffusion effects during optical transmission in water, the underwater VLC system will suffer from poor SNR and highly nonlinear distortion. In this paper, we proposed and experimentally demonstrated a novel Square Geometrical Shaping(SGS) odd order QAM discrete multitone(DMT) and carrier-less amplitude phase(CAP) modulation based VLC system. Unlike to traditional odd order QAM constellation aiming at the minimum Euclidean distance but without Gray coding at edge constellation points, the new SGS constellation boasts acceptable Euclidean distance and thoroughly Gray coding for every constellation point. Therefore, the system performance can be effectively enhanced by SGS constellation for low SNR and high nonlinearity cases. Both numerical and experimental results verify that SGS 32QAM and 128QAM constellations can outperform traditional QAM constellation by mitigating nonlinearity in a blue LED based underwater and free space VLC system using DMT modulation or CAP modulation. By employing SGS 128QAM, we successfully demonstrate 2.534Gb/s 1.2meter underwater transmission at the driving voltage of 1.1Vpp.
关键词： SGS constellation,nonlinearity,CAP,VLC underwater system,QAM-DMT
更新于2025-09-23 15:23:52
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Design of PAM-DMT-based Hybrid Optical OFDM for Visible Light Communications
摘要： In this letter, a pulse-amplitude-modulated based hybrid optical orthogonal frequency division multiplexing (PHO-OFDM) scheme is proposed. We use the high order quadrature-amplitude-modulation to replace the one-dimensional pulse-amplitude-modulated on the even subcarriers for compensating the data capacity weakness of the conventional pulse amplitude modulated discrete multitone (PAM-DMT). The combined time-domain PHO-OFDM signal has a larger amplitude range than the original PAM-DMT but with a reduced peak-to-average power ratio (PAPR). Besides that, a flexible power allocation method is introduced to the proposed PHO-OFDM systems to fully exploit the whole dynamic range of LEDs. The simulation results show that, under the same average bit rate, the proposed PHO-OFDM scheme has a better bit error rate performance compared with the conventional PAM-DMT scheme, thus demonstrating its application potential in visible light communications.
关键词： visible light communications (VLC),pulse-amplitude-modulated discrete multitone (PAM-DMT),optical orthogonal frequency division multiplexing (O-OFDM)
更新于2025-09-23 15:22:29
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Interplay of Bit Rate, Linewidth, Bandwidth, and Reach on Optical DMT and PAM with IMDD
摘要： We theoretically compare the performance of optical discrete multi-tone (DMT) and pulse amplitude modulation (PAM) using intensity modulated, direct detection (IMDD). PAM is a lower cost, lower complexity solution than DMT, however it is more vulnerable to chromatic dispersion on the C band. We compare DMT and PAM taking into consideration the interplay of laser linewidth, fiber length, transmission rate, and channel bandwidth. We use a semi-analytical model to examine bit error rates. We study how system parameters shift the performance advantages between DMT and PAM. Our model can also be used to find the best hardware solution and frequency band for a target modulation format and bit error rate.
关键词： PAM,O-band,C-band,chromatic dispersion,DMT,bandwidth,laser linewidth
更新于2025-09-23 15:22:29
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The spectral efficiency augmented HACO-OFDM based visible light communications
摘要： The conventional hybrid asymmetrically clipped optical orthogonal frequency division multiplexing (HACO-OFDM) has an obvious spectral efficiency loss due to the fact that the real part of the even subcarriers are not utilized. This paper proposes a scheme to augment the spectral efficiency of HACO-OFDM. In this scheme, more spectrum resources are exploited because the real part of selected even subcarrier group is utilized for data modulation at different depths. When the same modulation orders are used, the proposed scheme is able to achieve higher spectral efficiency than HACO-OFDM at the cost of acceptable increased computational complexity. When this scheme takes 5 depths, the joint modulation scheme uses 16QAM-4PAM and 64QAM-4PAM, the spectral efficiency of the proposed scheme can be increased by 31.33% and 23.48%, respectively. Moreover, compared with HACO-OFDM, the proposed scheme has advantages of lower PAPR and higher immunity to LED nonlinearity.
关键词： Visible light communications,HACO-OFDM,ASE-DMT
更新于2025-09-19 17:15:36
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[IEEE 2019 Global LIFI Congress (GLC) - Paris, France (2019.6.12-2019.6.13)] 2019 Global LIFI Congress (GLC) - A 5Gb/s $2\times 2$ MIMO Real-time Visible Light Communication System based on silicon substrate LEDs
摘要： In this paper, we propose and experimentally demonstrate a high-speed 2×2 MIMO real-time VLC system (64QAM-DMT) based 64QAM-Discrete Multi-Tone modulation. The system was achieved by utilizing field programmable gate arrays (FPGAs) and silicon substrate LEDs. The effect of attenuation of the attenuator in transmitter and receiver, the aperture diameter of the received signal, code rate and different modulation order have been investigated in our experiment. The experimental results show that our real-time VLC system can transmit over 2m distance for an overall 5Gb/s successfully.
关键词： Discrete Multi-Tone (DMT),Multiple-Input-Multiple-Output (MIMO),real-time Visible Light Communication (real-time VLC)
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - VCSEL Technologies for High-Capacity Dense WDM Networks
摘要： Long-wavelength vertical cavity surface emitting laser (VCSEL) technologies can represent an alternative solution for the development of transmitters with reduced cost, power consumption and footprint for very-high capacity metropolitan area systems. Exploiting direct modulation (DM) and advanced modulation formats, such as discrete multitone (DMT), and aggregating multiple DM-VCSELs emitting in the C-band with dense wavelength division multiplexers (WDM) in SOI chips allows to achieve multi-Tb/s transmitter module with 25 GHz granularity [1]. The interplay between the frequency chirp induced by VCSELs DM and the tight filtering of network WDM multiplexers plays a crucial role in the transmission performance. In this paper, we compare the adoption of two different long-wavelength InP VCSEL technologies: high-bandwidth short-cavity devices and MEMS-based widely-tuneable VCSELs [1]. We evaluate their performance in case of DM employing DMT modulation, providing more than 50-Gb/s capacity per wavelength; coherent detection (COH-D) is used to target hundreds of kilometres distances thanks to DSP chromatic dispersion (CD) compensation.
关键词： WDM,DMT,direct modulation,coherent detection,VCSEL
更新于2025-09-11 14:15:04
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Numerical Study of a Hybrid Optical DMT/DFT-S QAM Modulation
摘要： A hybrid modulation offers the peak-to-average power ratio (PAPR) robustness of discrete Fourier transform spread (DFT-S) QAM (quadrature amplitude modulation) with the bit rate optimization of discrete multi-tone (DMT) modulation. We examine via simulation under what circumstances this hybrid can increase achievable bit rate. Hybrid PAPR reduction allows us to increase the peak-to-peak voltage at the modulator electrical input to increase the signal mean power at the modulator output. We propose a methodology to identify the optimal driving strategy. We optimize the bit rate for the available spectrum, i.e., the spectral efficiency, taking into account the bandwidth limited nature of the transmitter. The final optimization we propose is the partition of the available spectrum into a lower frequency band for DFT-S QAM and a higher frequency band for DMT. The modulation level of the DFT-S QAM is also optimized. We compare the optimal hybrid performance versus DMT performance for a range of bit rates for a given modulation bandwidth. Improved performance comes at the cost of greater DSP complexity for the hybrid solution. We compare the number of complex multipliers required to implement hybrid versus DMT for both dispersive and non-dispersive systems.
关键词： simulation,DFT-spread,QAM,complexity comparison,frequency optimization,DMT,hybrid
更新于2025-09-10 09:29:36