Ruowen Bai | McMaster University (original) (raw)

Papers by Ruowen Bai

Research paper thumbnail of Low-Complexity Layered ACO-OFDM for Power-Efficient Visible Light Communications

IEEE Transactions on Green Communications and Networking, 2022

Research paper thumbnail of Performance comparison of VLC MIMO techniques considering indoor illuminance with inclined LEDs

2016 IEEE International Conference on Wireless for Space and Extreme Environments (WiSEE), 2016

Visible light communication (VLC) is a promising complementary technology to radio frequency (RF)... more Visible light communication (VLC) is a promising complementary technology to radio frequency (RF) communication. In existing VLC multiple-input multiple-output (MIMO) system, light emitting diodes (LEDs) vertical MIMO (LVM) model is commonly used. However, in LVM model, illuminance distribution is not uniform enough for office and the optical channel is highly correlated, which degrade the system performance, especially in cases with small emitter separation. In this paper, LEDs inclined MIMO (LIM) model is proposed and the performance comparison of LIM and LVM model assuming line-of-sight (LOS) channel characteristics is presented. Theoretical analysis and simulation results show that LIM model outperforms LVM model in many respects. Firstly, LIM model provides more uniform office illuminance distribution than LVM model. In addition, LIM model with spatial modulation (SM) or spatial multiplexing (SMP) can achieve better bit error ratio (BER) performance when the receiver is in the center, especially with higher signal-to-noise ratio (SNR), because the inclined LEDs can reduce the MIMO channel correlation, which compensates the loss of received power. Besides, when the receiver is on the edge, LIM model with RC, SMP or SM all performs better than LVM model since more power is received and the channel correlation is lower. Furthermore, LIM model outperforms LVM model when considering receiver mobility since LIM model can provide a larger reliable communication area on the receiver plane.

Research paper thumbnail of High-Accuracy Three-Dimensional Visible Light Positioning Systems Using Image Sensor

2018 IEEE 87th Vehicular Technology Conference (VTC Spring), 2018

A 3D positioning method based on visible light communication is proposed. Compared to the previou... more A 3D positioning method based on visible light communication is proposed. Compared to the previous methods, we only need three light emitting diodes (LEDs) with known coordinates to obtain the object position without the priori knowledge of the receiver's height and tile angle. The gradient descent method and vector method are used to obtain the coordinate and inclination of the object (i.e., camera). To validate the effectiveness of our methods, the relation of mean positioning error caused by the discrete camera sensor pixel and the system parameters (i.e., focal length of the camera, pixel density and height of the receiver) is analyzed. Simulation results show the quantization error is about 5 cm.

Research paper thumbnail of Layered antisymmetry-constructed clipped optical OFDM for low-complexity VLC systems

Optics Express, 2021

In this paper, antisymmetry-constructed clipped optical orthogonal frequency division multiplexin... more In this paper, antisymmetry-constructed clipped optical orthogonal frequency division multiplexing (AC-OFDM) is proposed for visible light communication (VLC) systems, in which an antisymmetry property is imposed directly in time domain. AC-OFDM has nearly the same spectral efficiency and peak-to-average power ratio (PAPR) as traditional asymmetrically clipped optical OFDM (ACO-OFDM) but is less complex to implement. Layered AC-OFDM (LAC-OFDM) is then proposed as an extension to further improve spectral efficiency, where different layers of AC-OFDM signals are added in the time domain and transmitted simultaneously. Computational complexity analysis and numerical results show that LAC-OFDM has nearly the same spectral efficiency as layered asymmetrically clipped optical OFDM (LACO-OFDM) and enhanced unipolar OFDM (eU-OFDM) but is less complex. Specifically, LAC-OFDM requires less than half the multiplication and addition operations compared to the comparable LACO-OFDM scheme. Additionally, a pairwise iterative receiver for LAC-OFDM is proposed and its computational complexity is analysed. Monte Carlo simulation results show that LAC-OFDM requires nearly the same optical signal-to-noise ratio (OSNR) to achieve the same BER performance as LACO- and eU-OFDM.

Research paper thumbnail of Layered Antisymmetry-Constructed Clipped Optical OFDM for IM/DD Systems

2019 IEEE Global Communications Conference (GLOBECOM)

Research paper thumbnail of Kramers-Kronig Optical OFDM for Bandlimited Intensity Modulated Visible Light Communications

Journal of Lightwave Technology

Research paper thumbnail of Absolute Value Layered ACO-OFDM for Intensity-Modulated Optical Wireless Channels

ICC 2019 - 2019 IEEE International Conference on Communications (ICC)

Research paper thumbnail of Enhanced asymmetrically clipped DC biased optical OFDM for intensity-modulated direct-detection systems

Journal of Communications and Information Networks

In this paper, we propose an EADO-OFDM (Enhanced Asymmetrically Clipped DC Biased Optical Orthogo... more In this paper, we propose an EADO-OFDM (Enhanced Asymmetrically Clipped DC Biased Optical Orthogonal Frequency Division Multiplexing) method for IM/DD (Intensity-Modulated Direct-Detection) optical systems, in which the AV-DCO-OFDM (Absolute Valued DC Biased Optical OFDM) symbols on the even subcarriers and ACO-OFDM (Asymmetrically Clipped Optical OFDM) symbols on the odd subcarriers are combined for simultaneous transmission. Moreover, we discuss the PDF (Probability Density Function) and electrical SNR (Signal to Noise Ratio) of the symbols, which are utilized to estimate the BER (Bit Error Ratio) performance and overall performance of EADO-OFDM. The Monte Carlo simulation results have validated the theoretical analysis and have also confirmed the EADO-OFDM is attractive considering the following benefits. Firstly, EADO-OFDM is more energy efficient compared to the power-efficient DCO-OFDM (DC Biased Optical OFDM), since the required DC bias is smaller when appropriate constellation size combinations are chosen. In addition, EADO-OFDM performs better than the conventional ADO-OFDM (Asymmetrically Clipped DC Biased Optical OFDM), because the absolute value operation causes no clipping distortion.

Research paper thumbnail of Interleaved DFT-Spread Layered/Enhanced ACO-OFDM for Intensity-Modulated Direct-Detection Systems

Journal of Lightwave Technology

Research paper thumbnail of Iterative receiver for ADO-OFDM with near-optimal optical power allocation

Research paper thumbnail of Asymmetrically Clipped Absolute Value Optical OFDM for Intensity-Modulated Direct-Detection Systems

Journal of Lightwave Technology

Orthogonal frequency division multiplexing (OFD-M) is attracting increasing attention in optical ... more Orthogonal frequency division multiplexing (OFD-M) is attracting increasing attention in optical communication systems thanks to the inherent benefits such as high spectral efficiency and resistance to frequency-selective channels. In this paper, a novel energy and spectrally efficient scheme called asymmetrically clipped absolute value optical OFDM (AAO-OFDM) is proposed for intensity-modulated direct-detection (IM/DD) systems. In AAO-OFDM, absolute value optical OFDM (AVO-OFDM) signals on the even subcarriers and asymmetrically clipped optical OFDM (ACO-OFDM) signals on the odd subcarriers are combined for simultaneous transmission, which employs all the subcarriers requiring no DC biases. For AVO-OFDM scheme, the frequency symbols are firstly modulated on the even subcarriers, which are then fed into an inverse fast Fourier transform block. Afterwards, the absolute values of the bipolar time-domain signals are taken to guarantee nonnegativity, while their signs are mapped to the complex-valued symbols and modulated on the odd subcarriers. Since there remain unused odd subcarriers, other useful symbols can be modulated on them, which leads to the conventional ACO-OFDM scheme. At the receiver, the ACO-OFDM symbols on the odd subcarriers are demodulated firstly, which are reconstructed and removed from the received signals. Afterwards, the remaining signals are utilized to detect the AVO-OFDM symbols with the aid of the demodulated sign symbols on the odd subcarriers. Theoretical analysis and simulation results show that AAO-OFDM has lower peak-to-average power ratio than other optical OFDM schemes, which makes it less sensitive to the nonlinearity of the optical devices. Furthermore, it achieves better bit error rate performance compared to its counterparts for the same spectral efficiency.

Research paper thumbnail of Optical dual-mode index modulation aided OFDM for visible light communications

Research paper thumbnail of Asymmetrically Clipped Absolute Value Optical OFDM for Intensity-Modulated Direct-Detection Systems

Journal of Lightwave Technology

Orthogonal frequency division multiplexing (OFD-M) is attracting increasing attention in optical ... more Orthogonal frequency division multiplexing (OFD-M) is attracting increasing attention in optical communication systems thanks to the inherent benefits such as high spectral efficiency and resistance to frequency-selective channels. In this paper, a novel energy and spectrally efficient scheme called asymmetrically clipped absolute value optical OFDM (AAO-OFDM) is proposed for intensity-modulated direct-detection (IM/DD) systems. In AAO-OFDM, absolute value optical OFDM (AVO-OFDM) signals on the even subcarriers and asymmetrically clipped optical OFDM (ACO-OFDM) signals on the odd subcarriers are combined for simultaneous transmission, which employs all the subcarriers requiring no DC biases. For AVO-OFDM scheme, the frequency symbols are firstly modulated on the even subcarriers, which are then fed into an inverse fast Fourier transform block. Afterwards, the absolute values of the bipolar time-domain signals are taken to guarantee nonnegativity, while their signs are mapped to the complex-valued symbols and modulated on the odd subcarriers. Since there remain unused odd subcarriers, other useful symbols can be modulated on them, which leads to the conventional ACO-OFDM scheme. At the receiver, the ACO-OFDM symbols on the odd subcarriers are demodulated firstly, which are reconstructed and removed from the received signals. Afterwards, the remaining signals are utilized to detect the AVO-OFDM symbols with the aid of the demodulated sign symbols on the odd subcarriers. Theoretical analysis and simulation results show that AAO-OFDM has lower peak-to-average power ratio than other optical OFDM schemes, which makes it less sensitive to the nonlinearity of the optical devices. Furthermore, it achieves better bit error rate performance compared to its counterparts for the same spectral efficiency.

Research paper thumbnail of Low-Complexity Layered ACO-OFDM for Power-Efficient Visible Light Communications

IEEE Transactions on Green Communications and Networking, 2022

Research paper thumbnail of Performance comparison of VLC MIMO techniques considering indoor illuminance with inclined LEDs

2016 IEEE International Conference on Wireless for Space and Extreme Environments (WiSEE), 2016

Visible light communication (VLC) is a promising complementary technology to radio frequency (RF)... more Visible light communication (VLC) is a promising complementary technology to radio frequency (RF) communication. In existing VLC multiple-input multiple-output (MIMO) system, light emitting diodes (LEDs) vertical MIMO (LVM) model is commonly used. However, in LVM model, illuminance distribution is not uniform enough for office and the optical channel is highly correlated, which degrade the system performance, especially in cases with small emitter separation. In this paper, LEDs inclined MIMO (LIM) model is proposed and the performance comparison of LIM and LVM model assuming line-of-sight (LOS) channel characteristics is presented. Theoretical analysis and simulation results show that LIM model outperforms LVM model in many respects. Firstly, LIM model provides more uniform office illuminance distribution than LVM model. In addition, LIM model with spatial modulation (SM) or spatial multiplexing (SMP) can achieve better bit error ratio (BER) performance when the receiver is in the center, especially with higher signal-to-noise ratio (SNR), because the inclined LEDs can reduce the MIMO channel correlation, which compensates the loss of received power. Besides, when the receiver is on the edge, LIM model with RC, SMP or SM all performs better than LVM model since more power is received and the channel correlation is lower. Furthermore, LIM model outperforms LVM model when considering receiver mobility since LIM model can provide a larger reliable communication area on the receiver plane.

Research paper thumbnail of High-Accuracy Three-Dimensional Visible Light Positioning Systems Using Image Sensor

2018 IEEE 87th Vehicular Technology Conference (VTC Spring), 2018

A 3D positioning method based on visible light communication is proposed. Compared to the previou... more A 3D positioning method based on visible light communication is proposed. Compared to the previous methods, we only need three light emitting diodes (LEDs) with known coordinates to obtain the object position without the priori knowledge of the receiver's height and tile angle. The gradient descent method and vector method are used to obtain the coordinate and inclination of the object (i.e., camera). To validate the effectiveness of our methods, the relation of mean positioning error caused by the discrete camera sensor pixel and the system parameters (i.e., focal length of the camera, pixel density and height of the receiver) is analyzed. Simulation results show the quantization error is about 5 cm.

Research paper thumbnail of Layered antisymmetry-constructed clipped optical OFDM for low-complexity VLC systems

Optics Express, 2021

In this paper, antisymmetry-constructed clipped optical orthogonal frequency division multiplexin... more In this paper, antisymmetry-constructed clipped optical orthogonal frequency division multiplexing (AC-OFDM) is proposed for visible light communication (VLC) systems, in which an antisymmetry property is imposed directly in time domain. AC-OFDM has nearly the same spectral efficiency and peak-to-average power ratio (PAPR) as traditional asymmetrically clipped optical OFDM (ACO-OFDM) but is less complex to implement. Layered AC-OFDM (LAC-OFDM) is then proposed as an extension to further improve spectral efficiency, where different layers of AC-OFDM signals are added in the time domain and transmitted simultaneously. Computational complexity analysis and numerical results show that LAC-OFDM has nearly the same spectral efficiency as layered asymmetrically clipped optical OFDM (LACO-OFDM) and enhanced unipolar OFDM (eU-OFDM) but is less complex. Specifically, LAC-OFDM requires less than half the multiplication and addition operations compared to the comparable LACO-OFDM scheme. Additionally, a pairwise iterative receiver for LAC-OFDM is proposed and its computational complexity is analysed. Monte Carlo simulation results show that LAC-OFDM requires nearly the same optical signal-to-noise ratio (OSNR) to achieve the same BER performance as LACO- and eU-OFDM.

Research paper thumbnail of Layered Antisymmetry-Constructed Clipped Optical OFDM for IM/DD Systems

2019 IEEE Global Communications Conference (GLOBECOM)

Research paper thumbnail of Kramers-Kronig Optical OFDM for Bandlimited Intensity Modulated Visible Light Communications

Journal of Lightwave Technology

Research paper thumbnail of Absolute Value Layered ACO-OFDM for Intensity-Modulated Optical Wireless Channels

ICC 2019 - 2019 IEEE International Conference on Communications (ICC)

Research paper thumbnail of Enhanced asymmetrically clipped DC biased optical OFDM for intensity-modulated direct-detection systems

Journal of Communications and Information Networks

In this paper, we propose an EADO-OFDM (Enhanced Asymmetrically Clipped DC Biased Optical Orthogo... more In this paper, we propose an EADO-OFDM (Enhanced Asymmetrically Clipped DC Biased Optical Orthogonal Frequency Division Multiplexing) method for IM/DD (Intensity-Modulated Direct-Detection) optical systems, in which the AV-DCO-OFDM (Absolute Valued DC Biased Optical OFDM) symbols on the even subcarriers and ACO-OFDM (Asymmetrically Clipped Optical OFDM) symbols on the odd subcarriers are combined for simultaneous transmission. Moreover, we discuss the PDF (Probability Density Function) and electrical SNR (Signal to Noise Ratio) of the symbols, which are utilized to estimate the BER (Bit Error Ratio) performance and overall performance of EADO-OFDM. The Monte Carlo simulation results have validated the theoretical analysis and have also confirmed the EADO-OFDM is attractive considering the following benefits. Firstly, EADO-OFDM is more energy efficient compared to the power-efficient DCO-OFDM (DC Biased Optical OFDM), since the required DC bias is smaller when appropriate constellation size combinations are chosen. In addition, EADO-OFDM performs better than the conventional ADO-OFDM (Asymmetrically Clipped DC Biased Optical OFDM), because the absolute value operation causes no clipping distortion.

Research paper thumbnail of Interleaved DFT-Spread Layered/Enhanced ACO-OFDM for Intensity-Modulated Direct-Detection Systems

Journal of Lightwave Technology

Research paper thumbnail of Iterative receiver for ADO-OFDM with near-optimal optical power allocation

Research paper thumbnail of Asymmetrically Clipped Absolute Value Optical OFDM for Intensity-Modulated Direct-Detection Systems

Journal of Lightwave Technology

Orthogonal frequency division multiplexing (OFD-M) is attracting increasing attention in optical ... more Orthogonal frequency division multiplexing (OFD-M) is attracting increasing attention in optical communication systems thanks to the inherent benefits such as high spectral efficiency and resistance to frequency-selective channels. In this paper, a novel energy and spectrally efficient scheme called asymmetrically clipped absolute value optical OFDM (AAO-OFDM) is proposed for intensity-modulated direct-detection (IM/DD) systems. In AAO-OFDM, absolute value optical OFDM (AVO-OFDM) signals on the even subcarriers and asymmetrically clipped optical OFDM (ACO-OFDM) signals on the odd subcarriers are combined for simultaneous transmission, which employs all the subcarriers requiring no DC biases. For AVO-OFDM scheme, the frequency symbols are firstly modulated on the even subcarriers, which are then fed into an inverse fast Fourier transform block. Afterwards, the absolute values of the bipolar time-domain signals are taken to guarantee nonnegativity, while their signs are mapped to the complex-valued symbols and modulated on the odd subcarriers. Since there remain unused odd subcarriers, other useful symbols can be modulated on them, which leads to the conventional ACO-OFDM scheme. At the receiver, the ACO-OFDM symbols on the odd subcarriers are demodulated firstly, which are reconstructed and removed from the received signals. Afterwards, the remaining signals are utilized to detect the AVO-OFDM symbols with the aid of the demodulated sign symbols on the odd subcarriers. Theoretical analysis and simulation results show that AAO-OFDM has lower peak-to-average power ratio than other optical OFDM schemes, which makes it less sensitive to the nonlinearity of the optical devices. Furthermore, it achieves better bit error rate performance compared to its counterparts for the same spectral efficiency.

Research paper thumbnail of Optical dual-mode index modulation aided OFDM for visible light communications

Research paper thumbnail of Asymmetrically Clipped Absolute Value Optical OFDM for Intensity-Modulated Direct-Detection Systems

Journal of Lightwave Technology

Orthogonal frequency division multiplexing (OFD-M) is attracting increasing attention in optical ... more Orthogonal frequency division multiplexing (OFD-M) is attracting increasing attention in optical communication systems thanks to the inherent benefits such as high spectral efficiency and resistance to frequency-selective channels. In this paper, a novel energy and spectrally efficient scheme called asymmetrically clipped absolute value optical OFDM (AAO-OFDM) is proposed for intensity-modulated direct-detection (IM/DD) systems. In AAO-OFDM, absolute value optical OFDM (AVO-OFDM) signals on the even subcarriers and asymmetrically clipped optical OFDM (ACO-OFDM) signals on the odd subcarriers are combined for simultaneous transmission, which employs all the subcarriers requiring no DC biases. For AVO-OFDM scheme, the frequency symbols are firstly modulated on the even subcarriers, which are then fed into an inverse fast Fourier transform block. Afterwards, the absolute values of the bipolar time-domain signals are taken to guarantee nonnegativity, while their signs are mapped to the complex-valued symbols and modulated on the odd subcarriers. Since there remain unused odd subcarriers, other useful symbols can be modulated on them, which leads to the conventional ACO-OFDM scheme. At the receiver, the ACO-OFDM symbols on the odd subcarriers are demodulated firstly, which are reconstructed and removed from the received signals. Afterwards, the remaining signals are utilized to detect the AVO-OFDM symbols with the aid of the demodulated sign symbols on the odd subcarriers. Theoretical analysis and simulation results show that AAO-OFDM has lower peak-to-average power ratio than other optical OFDM schemes, which makes it less sensitive to the nonlinearity of the optical devices. Furthermore, it achieves better bit error rate performance compared to its counterparts for the same spectral efficiency.