... Scintillation of a laser beam propagation through non-Kolmogorov strong turbulence. Peng Deng... more ... Scintillation of a laser beam propagation through non-Kolmogorov strong turbulence. Peng Deng a , Xiuhua Yuan Corresponding Author Contact Information , a , E-mail The Corresponding Author , Dexiu Huang a. a, Wuhan National ...
We propose a wide field-of-view optical receiver design based on a fisheye lens and an off-axis c... more We propose a wide field-of-view optical receiver design based on a fisheye lens and an off-axis catadioptric structure for free-space optical communications. The design utilizes a novel fisheye lens group to compress a wide field angle into a narrow field angle and produce the appropriately collimated light that can effectively be coupled into the following aperture of a catadioptric telescope. An off-axis catadioptric telescope with aspheric surface mirrors is designed to compress the incident beam spot size, compensate for the high order optical aberrations and eliminate light loss due to an obstruction. The parallel exit rays are reflected on a double-level tracking mechanism by feeding the position signal from a quadrant detector to correct the pointing error and optimize the coupling efficiency into an optical fiber. The final wide field-of-view optical receiver design is presented along with the evaluation of optical performance results and tracking characteristics. The proposed optical receiver not only can provide a 60-deg wide field-of-view to expand the tracking range, but also mitigates optical aberrations to improve the tracking accuracy for free space optical communication systems in a turbulent atmosphere.
The nonlinear dependence of the modulation bandwidth and electrical to optical conversion on the ... more The nonlinear dependence of the modulation bandwidth and electrical to optical conversion on the drive current of white LEDs were investigated by comparing novel analytical modeling and experimental measurement for visible light communications.
IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems
Security attacks may have disruptive consequences on cyber-physical systems, and lead to signific... more Security attacks may have disruptive consequences on cyber-physical systems, and lead to significant social and economic losses. Building secure cyber-physical systems is particularly challenging due to the variety of attack surfaces from the cyber and physical components, and often to limited computation and communication resources. In this paper, we propose a crosslayer design framework for resource-constrained cyber-physical systems. The framework combines control-theoretic methods at the functional layer and cybersecurity techniques at the embedded platform layer, and addresses security together with other design metrics such as control performance under resource and real-time constraints. We use the concept of interface variables to capture the interactions between control and platform layers, and quantitatively model the relation among system security, performance, and schedulability via interface variables. The general codesign framework is customized and refined to the automotive domain, and its effectiveness is demonstrated through an industrial case study and a set of synthetic examples.
Visible light communication (VLC) using lightemitting-diodes (LEDs) has been a popular research a... more Visible light communication (VLC) using lightemitting-diodes (LEDs) has been a popular research area recently. VLC can provide a practical solution for indoor positioning. In this paper, the impact of multipath reflections on a two-dimensional indoor VLC positioning is investigated, considering a complex indoor environment with walls, floor, and ceiling. For the proposed positioning system, an LED bulb is the transmitter and a photo-diode is the receiver to detect received signal strength information. Combined deterministic and modified Monte Carlo method is applied to compute the impulse response of the optical channel. Since power attenuation is applied to calculate the distance between the transmitter and receiver, the received power from each reflection order is analyzed. The positioning errors are further estimated for all the locations over the room and compared with the previous works where no reflections considered. Finally, calibration approaches are proposed to decrease the effect of multipath reflections.
Visible light communications (VLC) have recently attracted a growing interest and can be a potent... more Visible light communications (VLC) have recently attracted a growing interest and can be a potential solution to realize indoor wireless communication with high bandwidth capacity for RFrestricted environments such as airplanes and hospitals. Optical based orthogonal frequency division multiplexing (OFDM) systems have been proposed in the literature to combat multipath distortion and intersymbol interference (ISI) caused by multipath signal propagation. In this paper, we present a robust timing synchronization scheme suitable for asymmetrically clipped (AC) OFDM based optical intensity modulated direct detection (IM/DD) wireless systems. Our proposed method works perfectly for ACO-OFDM, Pulse amplitude modulated discrete multitone (PAM-DMT) and discrete Hartley transform (DHT) based optical OFDM systems. In contrast to existing OFDM timing synchronization methods which are either not suitable for AC OFDM techniques due to unipolar nature of output signal or perform poorly, our proposed method is suitable for AC OFDM schemes and outperforms all other available techniques. Both numerical and experimental results confirm the accuracy of the proposed method. Our technique is also computationally efficient as it requires very few computations as compared to conventional methods in order to achieve good accuracy.
Novel Optical Systems Design and Optimization XIV, 2011
ABSTRACT The free space optical communication systems should utilize optical antennas with beam t... more ABSTRACT The free space optical communication systems should utilize optical antennas with beam tracking mechanisms. However, the narrow field of view and optical aberration of antennas degrade the tracking performance of the system. In order to overcome the problems, we investigate the wide field of view optical antenna technology. The optical antenna consists of fisheye lens, compensating lens and a catadioptric telescope with off-axis aspheric surface mirrors. The structures and performances of the optical device elements are numerically analyzed so that their designs can make positive contribution in enlarging the field of view and reducing the optical aberration. The final optical antenna design is presented, along with the evaluation of optical performance and tracking characteristics. The proposed optical antenna could not only provide a wide field of view with approximately 60 degree and expand the range for tracking mechanism, but also mitigate the optical aberration and improve tracking accuracy of free space optical communication systems in turbulent atmosphere.
We propose a wide field-of-view optical receiver design based on a fisheye lens and an off-axis c... more We propose a wide field-of-view optical receiver design based on a fisheye lens and an off-axis catadioptric structure for free-space optical communications. The design utilizes a novel fisheye lens group to compress a wide field angle into a narrow field angle and produce the appropriately collimated light that can effectively be coupled into the following aperture of a catadioptric telescope. An off-axis catadioptric telescope with aspheric surface mirrors is designed to compress the incident beam spot size, compensate for the high order optical aberrations and eliminate light loss due to an obstruction. The parallel exit rays are reflected on a double-level tracking mechanism by feeding the position signal from a quadrant detector to correct the pointing error and optimize the coupling efficiency into an optical fiber. The final wide field-of-view optical receiver design is presented along with the evaluation of optical performance results and tracking characteristics. The proposed optical receiver not only can provide a 60-deg wide field-of-view to expand the tracking range, but also mitigates optical aberrations to improve the tracking accuracy for free space optical communication systems in a turbulent atmosphere.
Atmospheric turbulence causes strong irradiance fluctuations of propagating optical wave under th... more Atmospheric turbulence causes strong irradiance fluctuations of propagating optical wave under the severe weather conditions in long-distance free space optical communication. In this paper, the scintillation index for a Gaussian beam wave propagation through non-Kolmogorov turbulent atmosphere is derived in strong fluctuation regime, using non-Kolmogorov spectrum with a generalized power law exponent and the extended Rytov theory with a modified spatial filter function. The analytic expressions are obtained and then used to analyze the effect of power law, refractive-index structure parameter, propagation distance, phase radius of curvature, beam width and wavelength on scintillation index of Gaussian beam under the strong atmospheric turbulence. It shows that, with the increasing of structure parameter or propagation distance, scintillation index increases sharply up to the peak point and then decreases gradually toward unity at rates depending on power law. And there exist optimal value of radius of curvature and beam width for minimizing the value of scintillation index and long wavelength for mitigating the effect of non-Kolmogorov strong turbulence on link performance.
Visible light communications (VLC) based on light-emitting diodes (LEDs) combines lighting and da... more Visible light communications (VLC) based on light-emitting diodes (LEDs) combines lighting and data communications in applications of Internet-of-Things, ad-hoc networks and 5G networks, due to their high energy efficiency, spectral efficiency, security and reliability. We experimentally demonstrate a software-defined real-time multiple input multiple output (MIMO) visible light communication system using Single-Carrier Quadrature Amplitude Modulation (SC-QAM). The system uses two independent phosphorescent white LED transmitters with 10MHz bandwidth in the absence of blue filters, and two independent 150 MHz P-I-N photodiode optical receivers. Real-time MIMO signal processing is implemented by using the Field Programmable Gate Array (FPGA) based Universal Software Radio Peripheral (USRP) devices. Modulation formats and MIMO schemes are software-defined through USRP devices without changing the transceiver hardware. We measured and compared the constellation diagram, error vector magnitude (EVM) and bit error rate (BER) performance for single-carried M-QAM MIMO VLC using spatial diversity and spatial multiplexing. We demonstrate a real-time Single-Carrier 256-QAM 2x2 spatial multiplexing MIMO VLC link and achieve 1.81% averaged EVM, 2x10-5 BER and 12.3 b/s/Hz spectral efficiency over 2 m free space indoor transmission. The experimental results show that spatial diversity MIMO VLC improves error performance at the cost of spectral efficiency that spatial multiplexing should enhance.
In free-space optical communication links, atmospheric turbulence causes fluctuations in both the... more In free-space optical communication links, atmospheric turbulence causes fluctuations in both the intensity and the phase of the received signal, affecting link performance. Most theoretical treatments have been described by Kolmogorov's power spectral density model through weak turbulence with constant wind speed. However, several experiments showed that Kolmogorov theory is sometimes incomplete to describe atmospheric turbulence properly, especially through the strong turbulence with variable wind speed, which is known to contribute significantly to the turbulence in the atmosphere. We present an optical turbulence model that incorporates into variable wind speed instead of constant value, a non-Kolmogorov power spectrum that uses a generalized exponent instead of constant standard exponent value 11/3, and a generalized amplitude factor instead of constant value 0.033. The free space optical communication performance for a Gaussian beam wave of scintillation index, mean signal-to-noise ratio<SNR>, and mean bit error rate <BER>, have been derived by extended Rytov theory in non-Kolmogorov strong turbulence. And then the influence of wind speed variations on free space optical communication performance has been analyzed under different atmospheric turbulence intensities. The results suggest that the effects of wind speed variation through non-Kolmogorov turbulence on communication performance are more severe in many situations and need to be taken into account in free space optical communication. It is anticipated that this work is helpful to the investigations of free space optical communication performance considering wind speed under severe weather condition in the strong atmospheric turbulence.
We study the average capacity performance for multiple-input multiple-output (MIMO) free-space op... more We study the average capacity performance for multiple-input multiple-output (MIMO) free-space optical (FSO) communication systems using multiple partially coherent beams propagating through non-Kolmogorov strong turbulence, assuming equal gain combining diversity configuration and the sum of multiple gamma-gamma random variables for multiple independent partially coherent beams. The closed-form expressions of scintillation and average capacity are derived and then used to analyze the dependence on the number of independent diversity branches, power law α, refractive-index structure parameter, propagation distance and spatial coherence length of source beams. Obtained results show that, the average capacity increases more significantly with the increase in the rank of MIMO channel matrix compared with the diversity order. The effect of the diversity order on the average capacity is independent of the power law, turbulence strength parameter and spatial coherence length, whereas these effects on average capacity are gradually mitigated as the diversity order increases. The average capacity increases and saturates with the decreasing spatial coherence length, at rates depending on the diversity order, power law and turbulence strength. There exist optimal values of the spatial coherence length and diversity configuration for maximizing the average capacity of MIMO FSO links over a variety of atmospheric turbulence conditions.
... Scintillation of a laser beam propagation through non-Kolmogorov strong turbulence. Peng Deng... more ... Scintillation of a laser beam propagation through non-Kolmogorov strong turbulence. Peng Deng a , Xiuhua Yuan Corresponding Author Contact Information , a , E-mail The Corresponding Author , Dexiu Huang a. a, Wuhan National ...
We propose a wide field-of-view optical receiver design based on a fisheye lens and an off-axis c... more We propose a wide field-of-view optical receiver design based on a fisheye lens and an off-axis catadioptric structure for free-space optical communications. The design utilizes a novel fisheye lens group to compress a wide field angle into a narrow field angle and produce the appropriately collimated light that can effectively be coupled into the following aperture of a catadioptric telescope. An off-axis catadioptric telescope with aspheric surface mirrors is designed to compress the incident beam spot size, compensate for the high order optical aberrations and eliminate light loss due to an obstruction. The parallel exit rays are reflected on a double-level tracking mechanism by feeding the position signal from a quadrant detector to correct the pointing error and optimize the coupling efficiency into an optical fiber. The final wide field-of-view optical receiver design is presented along with the evaluation of optical performance results and tracking characteristics. The proposed optical receiver not only can provide a 60-deg wide field-of-view to expand the tracking range, but also mitigates optical aberrations to improve the tracking accuracy for free space optical communication systems in a turbulent atmosphere.
The nonlinear dependence of the modulation bandwidth and electrical to optical conversion on the ... more The nonlinear dependence of the modulation bandwidth and electrical to optical conversion on the drive current of white LEDs were investigated by comparing novel analytical modeling and experimental measurement for visible light communications.
IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems
Security attacks may have disruptive consequences on cyber-physical systems, and lead to signific... more Security attacks may have disruptive consequences on cyber-physical systems, and lead to significant social and economic losses. Building secure cyber-physical systems is particularly challenging due to the variety of attack surfaces from the cyber and physical components, and often to limited computation and communication resources. In this paper, we propose a crosslayer design framework for resource-constrained cyber-physical systems. The framework combines control-theoretic methods at the functional layer and cybersecurity techniques at the embedded platform layer, and addresses security together with other design metrics such as control performance under resource and real-time constraints. We use the concept of interface variables to capture the interactions between control and platform layers, and quantitatively model the relation among system security, performance, and schedulability via interface variables. The general codesign framework is customized and refined to the automotive domain, and its effectiveness is demonstrated through an industrial case study and a set of synthetic examples.
Visible light communication (VLC) using lightemitting-diodes (LEDs) has been a popular research a... more Visible light communication (VLC) using lightemitting-diodes (LEDs) has been a popular research area recently. VLC can provide a practical solution for indoor positioning. In this paper, the impact of multipath reflections on a two-dimensional indoor VLC positioning is investigated, considering a complex indoor environment with walls, floor, and ceiling. For the proposed positioning system, an LED bulb is the transmitter and a photo-diode is the receiver to detect received signal strength information. Combined deterministic and modified Monte Carlo method is applied to compute the impulse response of the optical channel. Since power attenuation is applied to calculate the distance between the transmitter and receiver, the received power from each reflection order is analyzed. The positioning errors are further estimated for all the locations over the room and compared with the previous works where no reflections considered. Finally, calibration approaches are proposed to decrease the effect of multipath reflections.
Visible light communications (VLC) have recently attracted a growing interest and can be a potent... more Visible light communications (VLC) have recently attracted a growing interest and can be a potential solution to realize indoor wireless communication with high bandwidth capacity for RFrestricted environments such as airplanes and hospitals. Optical based orthogonal frequency division multiplexing (OFDM) systems have been proposed in the literature to combat multipath distortion and intersymbol interference (ISI) caused by multipath signal propagation. In this paper, we present a robust timing synchronization scheme suitable for asymmetrically clipped (AC) OFDM based optical intensity modulated direct detection (IM/DD) wireless systems. Our proposed method works perfectly for ACO-OFDM, Pulse amplitude modulated discrete multitone (PAM-DMT) and discrete Hartley transform (DHT) based optical OFDM systems. In contrast to existing OFDM timing synchronization methods which are either not suitable for AC OFDM techniques due to unipolar nature of output signal or perform poorly, our proposed method is suitable for AC OFDM schemes and outperforms all other available techniques. Both numerical and experimental results confirm the accuracy of the proposed method. Our technique is also computationally efficient as it requires very few computations as compared to conventional methods in order to achieve good accuracy.
Novel Optical Systems Design and Optimization XIV, 2011
ABSTRACT The free space optical communication systems should utilize optical antennas with beam t... more ABSTRACT The free space optical communication systems should utilize optical antennas with beam tracking mechanisms. However, the narrow field of view and optical aberration of antennas degrade the tracking performance of the system. In order to overcome the problems, we investigate the wide field of view optical antenna technology. The optical antenna consists of fisheye lens, compensating lens and a catadioptric telescope with off-axis aspheric surface mirrors. The structures and performances of the optical device elements are numerically analyzed so that their designs can make positive contribution in enlarging the field of view and reducing the optical aberration. The final optical antenna design is presented, along with the evaluation of optical performance and tracking characteristics. The proposed optical antenna could not only provide a wide field of view with approximately 60 degree and expand the range for tracking mechanism, but also mitigate the optical aberration and improve tracking accuracy of free space optical communication systems in turbulent atmosphere.
We propose a wide field-of-view optical receiver design based on a fisheye lens and an off-axis c... more We propose a wide field-of-view optical receiver design based on a fisheye lens and an off-axis catadioptric structure for free-space optical communications. The design utilizes a novel fisheye lens group to compress a wide field angle into a narrow field angle and produce the appropriately collimated light that can effectively be coupled into the following aperture of a catadioptric telescope. An off-axis catadioptric telescope with aspheric surface mirrors is designed to compress the incident beam spot size, compensate for the high order optical aberrations and eliminate light loss due to an obstruction. The parallel exit rays are reflected on a double-level tracking mechanism by feeding the position signal from a quadrant detector to correct the pointing error and optimize the coupling efficiency into an optical fiber. The final wide field-of-view optical receiver design is presented along with the evaluation of optical performance results and tracking characteristics. The proposed optical receiver not only can provide a 60-deg wide field-of-view to expand the tracking range, but also mitigates optical aberrations to improve the tracking accuracy for free space optical communication systems in a turbulent atmosphere.
Atmospheric turbulence causes strong irradiance fluctuations of propagating optical wave under th... more Atmospheric turbulence causes strong irradiance fluctuations of propagating optical wave under the severe weather conditions in long-distance free space optical communication. In this paper, the scintillation index for a Gaussian beam wave propagation through non-Kolmogorov turbulent atmosphere is derived in strong fluctuation regime, using non-Kolmogorov spectrum with a generalized power law exponent and the extended Rytov theory with a modified spatial filter function. The analytic expressions are obtained and then used to analyze the effect of power law, refractive-index structure parameter, propagation distance, phase radius of curvature, beam width and wavelength on scintillation index of Gaussian beam under the strong atmospheric turbulence. It shows that, with the increasing of structure parameter or propagation distance, scintillation index increases sharply up to the peak point and then decreases gradually toward unity at rates depending on power law. And there exist optimal value of radius of curvature and beam width for minimizing the value of scintillation index and long wavelength for mitigating the effect of non-Kolmogorov strong turbulence on link performance.
Visible light communications (VLC) based on light-emitting diodes (LEDs) combines lighting and da... more Visible light communications (VLC) based on light-emitting diodes (LEDs) combines lighting and data communications in applications of Internet-of-Things, ad-hoc networks and 5G networks, due to their high energy efficiency, spectral efficiency, security and reliability. We experimentally demonstrate a software-defined real-time multiple input multiple output (MIMO) visible light communication system using Single-Carrier Quadrature Amplitude Modulation (SC-QAM). The system uses two independent phosphorescent white LED transmitters with 10MHz bandwidth in the absence of blue filters, and two independent 150 MHz P-I-N photodiode optical receivers. Real-time MIMO signal processing is implemented by using the Field Programmable Gate Array (FPGA) based Universal Software Radio Peripheral (USRP) devices. Modulation formats and MIMO schemes are software-defined through USRP devices without changing the transceiver hardware. We measured and compared the constellation diagram, error vector magnitude (EVM) and bit error rate (BER) performance for single-carried M-QAM MIMO VLC using spatial diversity and spatial multiplexing. We demonstrate a real-time Single-Carrier 256-QAM 2x2 spatial multiplexing MIMO VLC link and achieve 1.81% averaged EVM, 2x10-5 BER and 12.3 b/s/Hz spectral efficiency over 2 m free space indoor transmission. The experimental results show that spatial diversity MIMO VLC improves error performance at the cost of spectral efficiency that spatial multiplexing should enhance.
In free-space optical communication links, atmospheric turbulence causes fluctuations in both the... more In free-space optical communication links, atmospheric turbulence causes fluctuations in both the intensity and the phase of the received signal, affecting link performance. Most theoretical treatments have been described by Kolmogorov's power spectral density model through weak turbulence with constant wind speed. However, several experiments showed that Kolmogorov theory is sometimes incomplete to describe atmospheric turbulence properly, especially through the strong turbulence with variable wind speed, which is known to contribute significantly to the turbulence in the atmosphere. We present an optical turbulence model that incorporates into variable wind speed instead of constant value, a non-Kolmogorov power spectrum that uses a generalized exponent instead of constant standard exponent value 11/3, and a generalized amplitude factor instead of constant value 0.033. The free space optical communication performance for a Gaussian beam wave of scintillation index, mean signal-to-noise ratio<SNR>, and mean bit error rate <BER>, have been derived by extended Rytov theory in non-Kolmogorov strong turbulence. And then the influence of wind speed variations on free space optical communication performance has been analyzed under different atmospheric turbulence intensities. The results suggest that the effects of wind speed variation through non-Kolmogorov turbulence on communication performance are more severe in many situations and need to be taken into account in free space optical communication. It is anticipated that this work is helpful to the investigations of free space optical communication performance considering wind speed under severe weather condition in the strong atmospheric turbulence.
We study the average capacity performance for multiple-input multiple-output (MIMO) free-space op... more We study the average capacity performance for multiple-input multiple-output (MIMO) free-space optical (FSO) communication systems using multiple partially coherent beams propagating through non-Kolmogorov strong turbulence, assuming equal gain combining diversity configuration and the sum of multiple gamma-gamma random variables for multiple independent partially coherent beams. The closed-form expressions of scintillation and average capacity are derived and then used to analyze the dependence on the number of independent diversity branches, power law α, refractive-index structure parameter, propagation distance and spatial coherence length of source beams. Obtained results show that, the average capacity increases more significantly with the increase in the rank of MIMO channel matrix compared with the diversity order. The effect of the diversity order on the average capacity is independent of the power law, turbulence strength parameter and spatial coherence length, whereas these effects on average capacity are gradually mitigated as the diversity order increases. The average capacity increases and saturates with the decreasing spatial coherence length, at rates depending on the diversity order, power law and turbulence strength. There exist optimal values of the spatial coherence length and diversity configuration for maximizing the average capacity of MIMO FSO links over a variety of atmospheric turbulence conditions.
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