—An undersampled color shift keying (UCSK) scheme is proposed to support non-flickering red, gree... more —An undersampled color shift keying (UCSK) scheme is proposed to support non-flickering red, green, and blue based optical camera communications (OCC). A dedicated framing structure is proposed to allow the receiver to obtain the camera's gamma curve and specify the phase error. A proof-of-concept experimental test-bed is developed to evaluate the bit error rate (BER) and error vector magnitude performance of the proposed OCC system. The experimental results show that the proposed system is able to achieve a data rate of 150 bps with a BER of 1.7×10-3 over a link span of up to 30 m, which is more than adequate for vehicle-to-vehicle communications. Keywords—Optical camera communications, undersampled color-shift keying (CSK) modulation, visible light communications
—Visible light communication (VLC) based localiza-tion is a potential candidate for indoor locali... more —Visible light communication (VLC) based localiza-tion is a potential candidate for indoor localization. However, since the field of view (FOV) of the photodiode (PD) is normally narrow, the PD might not be capable to detect enough LEDs to perform the triangulation algorithm. Furthermore, high direc-tionality is a significant character in VLC, and in practice, the direction of LED is commonly fixed and able to be known for once, but the direction of the PD is commonly random. In this paper, we exploit the direction of the LED in the lamp structure design and manage to mitigate the influence of the direction of the PD in the algorithm design. A localization algorithm based on received signal strength ratio (RSSR) with multi-directional LED array (MDLA) is proposed. In addition, we introduce the coverage ratio (CR) and the average angle acceptance ratio (AAAR) to evaluate the localization scheme's coverage in location and acceptance in direction, respectively. Simulation results show that when the tilt angle of LEDs is 15 • , the proposed scheme can attain the root-mean-square error (RMSE) of 0.04 m and 0.06 m in 2-D and 3-D localization, respectively, and it is more probably for it to obtain enough lamps compared to the conventional scheme using the triangulation algorithm with the lamp structure of a single LED.
A real-time bi-directional LED-to-LED VLC system is developed. The test results show that the pro... more A real-time bi-directional LED-to-LED VLC system is developed. The test results show that the proposed system can realize a downlink and uplink speed at 2.6Mbps and 2.55Mbps over a transmission range up to 2m.
—In visible light communication (VLC) systems, optical orthogonal frequency division multiplexing... more —In visible light communication (VLC) systems, optical orthogonal frequency division multiplexing (O-OFDM) is an appealing modulation. Among many proposed O-OFDM schemes, both direct current biased O-OFDM (DCO-OFDM) and asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) are widely used. Since VLC needs to take the dual requirements of illumination and communication into account, different dimming levels are often required. For high and low dimming level scenarios, system with ACO-OFDM normally has a better spectral efficiency performance than system with DCO-OFDM due to the smaller clipping noise. However, regarding the middle dimming level scenarios, the DCO-OFDM generally outperforms the ACO-OFDM. In order to improve system spectral efficiency within the wide dimming range, an asymmetrical and direct current biased optical orthogonal frequency division multiplexing (AAD-OFDM) is proposed in this paper. In AAD-OFDM based system, the modulation scheme is switched between ACO-OFDM and DCO-OFDM according to the required dimming level. Therefore, by adopting the proposed AAD-OFDM, the VLC system can fully utilize the dynamic range of LED at any dimming levels thus improving the performance. Simulation results show that the proposed scheme has high spectral efficiency within a wide dimming range.
In this paper, a real-time seven-direct-sequence spread-spectrum (7-DSSS) visible light communica... more In this paper, a real-time seven-direct-sequence spread-spectrum (7-DSSS) visible light communications (VLC) system based on field-programmable-gate-array (FPGA) is implemented and experimentally demonstrated. We add interference light in our field experiments to build the multipath environment. And then, we measure the bit error rate performance of both on and off keying (OOK) and 7-DSSS VLC systems for different bit rates over a transmission distance of 1.5 m. The results show that using the DSSS technique in VLC system the multipath induced interference is suppressed thus leading to improved performance.
In this paper a Direct Sequence Spread Spectrum (DSSS) based offline wireless white light communi... more In this paper a Direct Sequence Spread Spectrum (DSSS) based offline wireless white light communication system is established. Field measurements are conducted to compare the performance with and without DSSS. The experimental results show that the DSSS is able to improve performance obviously.
A support vector machine (SVM)-based data detection for 8-superposed pulse amplitude modulation a... more A support vector machine (SVM)-based data detection for 8-superposed pulse amplitude modulation and direct-current-biased optical orthogonal frequency division multiplexing in visible light communication is proposed and experimentally demonstrated. In this work, the SVM detector contains multiple binary classifiers with different classification strategies. The separating hyperplane of each SVM is constructed by means of the training data. The experiment results presented that the SVM detection offers improved bit error rate performance compared with the traditional direct decision method.
A support vector machine (SVM)-based data detection for 8-superposed pulse amplitude modulation i... more A support vector machine (SVM)-based data detection for 8-superposed pulse amplitude modulation in visible light communication is proposed and experimentally demonstrated. In this work, the SVM detector contains three binary classifiers with different classification strategies. And the separating hyperplane of each SVM is constructed by training data. The experiment results show that the SVM detection offers 35% higher data rates when compared with the traditional direct decision method. Keywords—support vector machine; superposed pulse amplitude modulation; visible light communiction; direct decision.
In this paper a comparison between a spiral and a strip shaped LED is presented in terms of the m... more In this paper a comparison between a spiral and a strip shaped LED is presented in terms of the maximum link distance achievable in visible light based car to car communications (VLC-C2C). The transmitted data is recovered from the frame brightness of the video signal. The intensity modulated LED is captured from two scenarios, using a focused and unfocused camera. A data rate of 180 bps with the bit error rate performance below the FEC limit of 10 −3 at a distance of 100 cm is successfully achieved, sufficient for transmitting road safety messages for VLC-C2C. It is shown that under the same conditions, the strip LED can effectively recover the data from a greater distance than its spiral counterpart.
In this letter, we experimentally demonstrate a 1024-quadrature-amplitude-modulation (QAM) optica... more In this letter, we experimentally demonstrate a 1024-quadrature-amplitude-modulation (QAM) optical camera communications (OCC) system using a dual light-emitting diode (LED) and a commercial digital single-lens reflex camera. An undersampled QAM subcarrier modulation (UQAMSM) is proposed to support a high-efficiency and non-flickering OCC system. Owing to the built-in gamma correction function of the camera, pre-and post-compensation techniques are successfully applied to compensate for the non-linear impairment. A dedicated framing structure is also designed to support the proposed UQAMSM and compensation techniques. The experimental results show that this system is able to achieve a data rate of 500 b/s using a dual LED and a 50 ft/s commercial camera over a transmission span of 1.5 m, which is suitable for the transmission and reception of location-based information. Index Terms— Compensation, optical camera communications, undersampled quadrature-amplitude-modulation subcarrier modulation, visible light communications.
—An undersampled color shift keying (UCSK) scheme is proposed to support non-flickering red, gree... more —An undersampled color shift keying (UCSK) scheme is proposed to support non-flickering red, green, and blue based optical camera communications (OCC). A dedicated framing structure is proposed to allow the receiver to obtain the camera's gamma curve and specify the phase error. A proof-of-concept experimental test-bed is developed to evaluate the bit error rate (BER) and error vector magnitude performance of the proposed OCC system. The experimental results show that the proposed system is able to achieve a data rate of 150 bps with a BER of 1.7×10-3 over a link span of up to 30 m, which is more than adequate for vehicle-to-vehicle communications. Keywords—Optical camera communications, undersampled color-shift keying (CSK) modulation, visible light communications
—Visible light communication (VLC) based localiza-tion is a potential candidate for indoor locali... more —Visible light communication (VLC) based localiza-tion is a potential candidate for indoor localization. However, since the field of view (FOV) of the photodiode (PD) is normally narrow, the PD might not be capable to detect enough LEDs to perform the triangulation algorithm. Furthermore, high direc-tionality is a significant character in VLC, and in practice, the direction of LED is commonly fixed and able to be known for once, but the direction of the PD is commonly random. In this paper, we exploit the direction of the LED in the lamp structure design and manage to mitigate the influence of the direction of the PD in the algorithm design. A localization algorithm based on received signal strength ratio (RSSR) with multi-directional LED array (MDLA) is proposed. In addition, we introduce the coverage ratio (CR) and the average angle acceptance ratio (AAAR) to evaluate the localization scheme's coverage in location and acceptance in direction, respectively. Simulation results show that when the tilt angle of LEDs is 15 • , the proposed scheme can attain the root-mean-square error (RMSE) of 0.04 m and 0.06 m in 2-D and 3-D localization, respectively, and it is more probably for it to obtain enough lamps compared to the conventional scheme using the triangulation algorithm with the lamp structure of a single LED.
A real-time bi-directional LED-to-LED VLC system is developed. The test results show that the pro... more A real-time bi-directional LED-to-LED VLC system is developed. The test results show that the proposed system can realize a downlink and uplink speed at 2.6Mbps and 2.55Mbps over a transmission range up to 2m.
—In visible light communication (VLC) systems, optical orthogonal frequency division multiplexing... more —In visible light communication (VLC) systems, optical orthogonal frequency division multiplexing (O-OFDM) is an appealing modulation. Among many proposed O-OFDM schemes, both direct current biased O-OFDM (DCO-OFDM) and asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) are widely used. Since VLC needs to take the dual requirements of illumination and communication into account, different dimming levels are often required. For high and low dimming level scenarios, system with ACO-OFDM normally has a better spectral efficiency performance than system with DCO-OFDM due to the smaller clipping noise. However, regarding the middle dimming level scenarios, the DCO-OFDM generally outperforms the ACO-OFDM. In order to improve system spectral efficiency within the wide dimming range, an asymmetrical and direct current biased optical orthogonal frequency division multiplexing (AAD-OFDM) is proposed in this paper. In AAD-OFDM based system, the modulation scheme is switched between ACO-OFDM and DCO-OFDM according to the required dimming level. Therefore, by adopting the proposed AAD-OFDM, the VLC system can fully utilize the dynamic range of LED at any dimming levels thus improving the performance. Simulation results show that the proposed scheme has high spectral efficiency within a wide dimming range.
In this paper, a real-time seven-direct-sequence spread-spectrum (7-DSSS) visible light communica... more In this paper, a real-time seven-direct-sequence spread-spectrum (7-DSSS) visible light communications (VLC) system based on field-programmable-gate-array (FPGA) is implemented and experimentally demonstrated. We add interference light in our field experiments to build the multipath environment. And then, we measure the bit error rate performance of both on and off keying (OOK) and 7-DSSS VLC systems for different bit rates over a transmission distance of 1.5 m. The results show that using the DSSS technique in VLC system the multipath induced interference is suppressed thus leading to improved performance.
In this paper a Direct Sequence Spread Spectrum (DSSS) based offline wireless white light communi... more In this paper a Direct Sequence Spread Spectrum (DSSS) based offline wireless white light communication system is established. Field measurements are conducted to compare the performance with and without DSSS. The experimental results show that the DSSS is able to improve performance obviously.
A support vector machine (SVM)-based data detection for 8-superposed pulse amplitude modulation a... more A support vector machine (SVM)-based data detection for 8-superposed pulse amplitude modulation and direct-current-biased optical orthogonal frequency division multiplexing in visible light communication is proposed and experimentally demonstrated. In this work, the SVM detector contains multiple binary classifiers with different classification strategies. The separating hyperplane of each SVM is constructed by means of the training data. The experiment results presented that the SVM detection offers improved bit error rate performance compared with the traditional direct decision method.
A support vector machine (SVM)-based data detection for 8-superposed pulse amplitude modulation i... more A support vector machine (SVM)-based data detection for 8-superposed pulse amplitude modulation in visible light communication is proposed and experimentally demonstrated. In this work, the SVM detector contains three binary classifiers with different classification strategies. And the separating hyperplane of each SVM is constructed by training data. The experiment results show that the SVM detection offers 35% higher data rates when compared with the traditional direct decision method. Keywords—support vector machine; superposed pulse amplitude modulation; visible light communiction; direct decision.
In this paper a comparison between a spiral and a strip shaped LED is presented in terms of the m... more In this paper a comparison between a spiral and a strip shaped LED is presented in terms of the maximum link distance achievable in visible light based car to car communications (VLC-C2C). The transmitted data is recovered from the frame brightness of the video signal. The intensity modulated LED is captured from two scenarios, using a focused and unfocused camera. A data rate of 180 bps with the bit error rate performance below the FEC limit of 10 −3 at a distance of 100 cm is successfully achieved, sufficient for transmitting road safety messages for VLC-C2C. It is shown that under the same conditions, the strip LED can effectively recover the data from a greater distance than its spiral counterpart.
In this letter, we experimentally demonstrate a 1024-quadrature-amplitude-modulation (QAM) optica... more In this letter, we experimentally demonstrate a 1024-quadrature-amplitude-modulation (QAM) optical camera communications (OCC) system using a dual light-emitting diode (LED) and a commercial digital single-lens reflex camera. An undersampled QAM subcarrier modulation (UQAMSM) is proposed to support a high-efficiency and non-flickering OCC system. Owing to the built-in gamma correction function of the camera, pre-and post-compensation techniques are successfully applied to compensate for the non-linear impairment. A dedicated framing structure is also designed to support the proposed UQAMSM and compensation techniques. The experimental results show that this system is able to achieve a data rate of 500 b/s using a dual LED and a 50 ft/s commercial camera over a transmission span of 1.5 m, which is suitable for the transmission and reception of location-based information. Index Terms— Compensation, optical camera communications, undersampled quadrature-amplitude-modulation subcarrier modulation, visible light communications.
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