Search

In this paper, a symbol cyclic shift-based discrete Fourier transform (SCS-DFT) precoding for orthogonal time frequency space (OTFS) is proposed and experimentally demonstrated in the visible light communication (VLC) system. The proposed scheme effectively mitigates the channel fading effect of edge subcarriers caused by inter-symbol interference (ISI) when there is no cyclic prefix (CP) in OTFS. In addition, only a training sequence (TS) symbol can realize channel estimation and equalization, and it can reduce the implementation complexity. The experimental results demonstrated that, compared with the conventional OTFS modulation, the proposed SCS-DFT OTFS can enhance the transmission performance while maintaining the high spectral efficiency of the VLC system. • We proposed a symbol cyclic shift-based DFT precoding scheme for OTFS-VLC systems. • This scheme can equalize the SNR and mitigate fading of edge subcarriers caused by ISI. • This scheme enhances performance while maintaining high spectral efficiency. [ABSTRACT FROM AUTHOR]

In this paper, to overcome the fading effect of the orthogonal frequency-division multiplexing-based visible light communication (OFDM-VLC) system, a joint preprocessing scheme based on orthogonal circulant matrix transform (OCT) pre-coding and pre-emphasis is proposed and experimentally demonstrated. Also, the experimental results show that compared with single OCT pre-coding or pre-emphasis method, the joint preprocessing scheme can efficiently improve the bit error rate (BER) performance of the OFDM-VLC system. To the best of our knowledge, the effectiveness of the joint pre-coding and pre-emphasis scheme is verified for the first time. [ABSTRACT FROM AUTHOR]

By controlling the on–off state of light emitting diode (LED), data can be modulated onto the visible light. By exploiting the rolling shutter effect (RSE) of camera image sensor, the data can be demodulated from the light correspondingly. Based on the principle, a kind of camera-based visible light communication (CVLC) system can be realized by using LED as transmitter and using mobile-phone camera as receiver. In this paper, to enhance the transmission performance and reduce the implementation complexity, a spaced color shift keying (SCSK) modulation scheme is proposed for RSE-based CVLC system. Meanwhile, a demodulation scheme based on HSB color space is proposed correspondingly. By using a commercial RGB-LED and a common smartphone, a CVLC system based on the SCSK scheme is experimentally demonstrated. The experiment results show that under the bit-error rate (BER) of 3.8e−3, the SCSK based VLC system can achieve a data capacity of up to 1.28 kbits per photo, although there are no clock recovery and blooming mitigation processes in the system. [ABSTRACT FROM AUTHOR]

In this paper, multi-band constant amplitude zero autocorrelation sequence (MB-CAZAC) precoding combined with the 128/64/32/16-quadrature amplitude modulation (QAM) technology is proposed and experimentally demonstrated in the orthogonal frequency-division multiplexing-based visible light communication (OFDM-VLC) system. By using the MB-CAZAC precoding, it can equalize the uneven signal-to-noise ratio (SNR) and reduce the PAPR compared with the traditional OFDM system. The experimental results show that the 128/64/32/16-QAM MB-CAZAC precoding outperforms the traditional scheme at different data rates for OFDM-VLC system. The spectral efficiency (SE) of the proposed scheme is up to 5.28 b/s/Hz. Meanwhile, it can be successfully transmitted 50-cm free-space at the bit error rate (BER) of 3 . 82 × 1 0 − 4 . [ABSTRACT FROM AUTHOR]

In this paper, dual-mode index modulation orthogonal frequency division multiplexing (DMIM-OFDM) enabled by orthogonal circulant matrix transform (OCT) precoding is proposed and experimentally demonstrated in visible light communication (VLC) systems. Since all available subcarriers are active to convey information bits, DMIM-OFDM can achieve higher spectral efficiency (SE) and energy efficiency (EE) than index modulation OFDM (IM-OFDM). In addition, to mitigate the uneven frequency-selective fading between different subblocks, channel-independent OCT precoding is applied to all subblocks to equalize the overall signal-to-noise ratio (SNR). The experimental results show that the DMIM-OFDM with OCT precoding outperforms the traditional IM-OFDM, DMIM-OFDM without precoding, and with DFT precoding at different SEs. For DMIM-OFDM VLC system with SE of 4.5 bit/s/Hz, by using OCT precoding, the receiver sensitivity improvement of 3 dB can be achieved at the bit error rate (BER) of 3.8e−3 after 3.5-m free-space transmission. • This paper proposes a novel DMIM-OFDM scheme enabled by OCT precoding and experimentally demonstrated in practical VLC systems. • Moreover, the OCT precoding is utilized to equalize the uneven SNR between different subcarriers, and further improve the BER performance of DMIM-OFDM. [ABSTRACT FROM AUTHOR]

Sampling frequency offset (SFO) between digital-to-analog converter (DAC) and analog-to-digital converter (ADC) will severely degrade the transmission performance of orthogonal frequency division multiplexing (OFDM) based visible light communication (VLC) system. In this paper, a novel SFO mitigation scheme based on rotated K-means clustering is proposed, which differs from traditional SFO compensation based on phase estimation and feedback. When SFO causes the constellation points to deviate from their original positions, this scheme can adaptively update the clustering centroids to achieve the correct symbol demapping without phase estimation and compensation. Experimental results indicate that after 3.5 m free-space transmission, the SFO tolerance of quadrature phase shift keying (QPSK) and 16-ary quadrature amplitude modulation (16-QAM) can reach ± 130 and ± 65 ppm with a bit error rate (BER) less than the hard-decision forward error correction (HD-FEC) threshold of 3.8e−3, respectively. • A novel scheme for SFO mitigation is proposed with clustering algorithm of machine learning. • Phase estimation and compensation is not required compared to conventional SFO mitigation schemes. • The proposed scheme is relatively robust to imperfect channel estimation. [ABSTRACT FROM AUTHOR]