分布式光纤传感技术具有大检测范围、长距离传输、高灵敏度等特点,在油气管道泄漏检测、周界入侵以及地球物理科学等中有着极为广泛的应用。研究了直接探测型相敏光时域反射仪中探测器检测带宽对空间分辨率和噪声基底的影响,采用不同检...分布式光纤传感技术具有大检测范围、长距离传输、高灵敏度等特点,在油气管道泄漏检测、周界入侵以及地球物理科学等中有着极为广泛的应用。研究了直接探测型相敏光时域反射仪中探测器检测带宽对空间分辨率和噪声基底的影响,采用不同检测带宽的探测器对原始信号进行采集,绘制了外部扰动事件响应的强度图。结果表明,光电探测器检测带宽为12.5 MHz的相敏光时域反射系统中,噪声基底低至-61 dB rad2/Hz,且对空间分辨率的影响小于3 m。该研究为进一步发展高灵敏度的基于直接探测型相敏光时域反射仪的分布式光纤传感系统提供了重要参考。展开更多
针对视频在网络传输过程中的时延、拥塞和丢包率高等问题,提出了一种基于非平衡多描述编码的视频网络传输质量保证算法,在检测网络链路可用带宽的基础上,通过马尔科夫模型预判网络链路的拥塞状态并据此调整视频传输路径。实验表明,与RED...针对视频在网络传输过程中的时延、拥塞和丢包率高等问题,提出了一种基于非平衡多描述编码的视频网络传输质量保证算法,在检测网络链路可用带宽的基础上,通过马尔科夫模型预判网络链路的拥塞状态并据此调整视频传输路径。实验表明,与RED(random early detection)算法相比,该算法更能有效地估计网络拥塞状况、降低视频丢包率和减少网络延迟,从而更有效地保证视频网络传输质量。展开更多
This paper firstly analyzes the property of the low frequency electromagnetic wave, which can penetrate many types of non-metallic materials, and the ability of Ultra-Wide Band (UWB) impulse signal which has high rang...This paper firstly analyzes the property of the low frequency electromagnetic wave, which can penetrate many types of non-metallic materials, and the ability of Ultra-Wide Band (UWB) impulse signal which has high range resolution. Then the methods are discussed for conducting surveillance through walls, detecting and locating the moving persons behind the partitions. The schematic diagram of Through-Wall Detecting Radar (TWDR) and the models of moving target are shown and the principle of detecting the moving target is also provided with coherent superimposing technique on a range gate. Finally an algorithm for estimating the location of targets is given. The performance of TWDR is validated by the experiments of penetrating a wood block, a red brick wall and a reinforced concrete wall.展开更多
Cognitive Radio （CR） can use the fre- quency band allocated to a Primary User （PU） on the premise that it will prevent significant of avoiding causing great interference to the PU. In this paper, we consider a wid...Cognitive Radio （CR） can use the fre- quency band allocated to a Primary User （PU） on the premise that it will prevent significant of avoiding causing great interference to the PU. In this paper, we consider a wideband CR system where the Secondary User （SU） mini- raises its interference to the PU by jointly al- locating the optimal sensing threshold and sub- carrier power. A multi-parameter optimization problem is formulated to obtain the joint opt- imal allocation by alternating direction opti- mization, which minimises the total interfer- ence to the PU over all of the subcarriers sub- ject to the constraints on the throughput, Bit Error Rate （BER） and maximal total power of the SU, the subcarrier rate and interference power of the PU, and the false alarm and mis- detection probabilities of each subcarrier. The simulation results show that the proposed joint allocation algorithm can achieve the desired mitigation on the interference to the PU at the different subcarrier gains.展开更多
Chromatic Dispersion （CD） monitoring technique based on narrow-band electrical power detecting is one of the cost-effective and simple CD monitoring techniques, while the performance of this method is debased by fac...Chromatic Dispersion （CD） monitoring technique based on narrow-band electrical power detecting is one of the cost-effective and simple CD monitoring techniques, while the performance of this method is debased by factors such as bandwidth and center frequency of the detected frequency band, self-phase modulation （SPM） ,light source chirps and optical fiber losses. The CD-electrical power curve is simulated to investigate the effects of the factors above mentioned. Theoretical analysis shows that in single-channeled fiber link,the effect of SPM is small enough （≤0. 003% ） to be ignored,while the chirps and the losses must be taken into account ; the bandwidth of the detected frequency band would better be less than 2π× GHz;the selected central frequency is related to the shape of the original pulse,a central frequency of 12 GHz is chosen in a 4.0 Gbit/s system,and 5GHz is chosen in a 10 Gbit/s system. A testing system is established. The experimental results agree well with the theoretical analysis.展开更多
To solve the slow congestion detection and rate convergence problems in the existing rate control based fair data collection schemes, a new fair data collection scheme is proposed, which is named the improved scheme w...To solve the slow congestion detection and rate convergence problems in the existing rate control based fair data collection schemes, a new fair data collection scheme is proposed, which is named the improved scheme with fairness or ISWF for short. In ISWF, a quick congestion detection method, which combines the queue length with traffic changes of a node, is used to solve the slow congestion detection problem, and a new solution, which adjusts the rate of sending data of a node by monitoring the channel utilization rate, is used to solve the slow convergence problem. At the same time, the probability selection method is used in ISWF to achieve the fairness of channel bandwidth utilization. Experiment and simulation results show that ISWF can effectively reduce the reaction time in detecting congestion and shorten the rate convergence process. Compared with the existing tree-based fair data collection schemes, ISWF can achieve better fairness in data collection and reduce the transmission delay effectively, and at the same time, it can increase the average network throughput by 9.1% or more.展开更多
The detection performance is evaluated for our proposed analog multiuser receiver in Ultra-WideBand (UWB) transmitted-reference system. In the presence of dense multipath and multi-access signals,the performance analy...The detection performance is evaluated for our proposed analog multiuser receiver in Ultra-WideBand (UWB) transmitted-reference system. In the presence of dense multipath and multi-access signals,the performance analysis is difficult due to the complicated waveform of received impulse. We develop an approach to analyze the steady-state Signal-to-Interference-plus-Noise (SINR) of the detector output. The multipath-spread impulse is fitted to an exponentially decaying profile in the analysis. A closed-form expression of steady-state SINR is further deduced for the proposed Least Minimum Square (LMS) detector. The analysis is validated by simulations in Line-Of-Sight (LOS) and Non-Line-Of-Sight (NLOS) channel respectively. Based on the theoretical results,the multipath delay spread is employed to determine the optimal width of the integration window of the detector.展开更多
A novel scheme for photonic envelope detection and fiber transmission of 24 GHz impulse radio ultra-wideband(IRUWB) signal is proposed based on phase modulator(PM). In the system, an optics assisted envelope detection...A novel scheme for photonic envelope detection and fiber transmission of 24 GHz impulse radio ultra-wideband(IRUWB) signal is proposed based on phase modulator(PM). In the system, an optics assisted envelope detection unit(OAEDU) is used for filtering one of the first sidebands at the output of PM, then this narrow band optical signal transfers over single-mode fiber(SMF), and the envelope of 24 GHz IR-UWB signal is obtained after photodetection(PD) and low pass filter(LPF). The numerical simulation results show that the combination of PM and OAEDU can alleviate the fiber chromatic dispersion(CD) effectively. The proposed system may provide a simple and cost-effective solution for IR-UWB receiver.展开更多
文摘分布式光纤传感技术具有大检测范围、长距离传输、高灵敏度等特点,在油气管道泄漏检测、周界入侵以及地球物理科学等中有着极为广泛的应用。研究了直接探测型相敏光时域反射仪中探测器检测带宽对空间分辨率和噪声基底的影响,采用不同检测带宽的探测器对原始信号进行采集,绘制了外部扰动事件响应的强度图。结果表明,光电探测器检测带宽为12.5 MHz的相敏光时域反射系统中,噪声基底低至-61 dB rad2/Hz,且对空间分辨率的影响小于3 m。该研究为进一步发展高灵敏度的基于直接探测型相敏光时域反射仪的分布式光纤传感系统提供了重要参考。
文摘针对视频在网络传输过程中的时延、拥塞和丢包率高等问题,提出了一种基于非平衡多描述编码的视频网络传输质量保证算法,在检测网络链路可用带宽的基础上,通过马尔科夫模型预判网络链路的拥塞状态并据此调整视频传输路径。实验表明,与RED(random early detection)算法相比,该算法更能有效地估计网络拥塞状况、降低视频丢包率和减少网络延迟,从而更有效地保证视频网络传输质量。
基金Supported by the National 863 Program (No.2001AA132020).
文摘This paper firstly analyzes the property of the low frequency electromagnetic wave, which can penetrate many types of non-metallic materials, and the ability of Ultra-Wide Band (UWB) impulse signal which has high range resolution. Then the methods are discussed for conducting surveillance through walls, detecting and locating the moving persons behind the partitions. The schematic diagram of Through-Wall Detecting Radar (TWDR) and the models of moving target are shown and the principle of detecting the moving target is also provided with coherent superimposing technique on a range gate. Finally an algorithm for estimating the location of targets is given. The performance of TWDR is validated by the experiments of penetrating a wood block, a red brick wall and a reinforced concrete wall.
基金supported by the National Natural Science Foundation of China under Grant No. 61201143the Scientific Research Foundation for Introduced Talent of Nanjing University of Aeronautics and Astronautics under Grant No. 56YAH13029
文摘Cognitive Radio （CR） can use the fre- quency band allocated to a Primary User （PU） on the premise that it will prevent significant of avoiding causing great interference to the PU. In this paper, we consider a wideband CR system where the Secondary User （SU） mini- raises its interference to the PU by jointly al- locating the optimal sensing threshold and sub- carrier power. A multi-parameter optimization problem is formulated to obtain the joint opt- imal allocation by alternating direction opti- mization, which minimises the total interfer- ence to the PU over all of the subcarriers sub- ject to the constraints on the throughput, Bit Error Rate （BER） and maximal total power of the SU, the subcarrier rate and interference power of the PU, and the false alarm and mis- detection probabilities of each subcarrier. The simulation results show that the proposed joint allocation algorithm can achieve the desired mitigation on the interference to the PU at the different subcarrier gains.
基金Supported by the National Natural Science Fund of China undercontact No.60377031 and No.60577013 ,National Basic Research Program of China under contact No.2003CB314907 .
文摘Chromatic Dispersion （CD） monitoring technique based on narrow-band electrical power detecting is one of the cost-effective and simple CD monitoring techniques, while the performance of this method is debased by factors such as bandwidth and center frequency of the detected frequency band, self-phase modulation （SPM） ,light source chirps and optical fiber losses. The CD-electrical power curve is simulated to investigate the effects of the factors above mentioned. Theoretical analysis shows that in single-channeled fiber link,the effect of SPM is small enough （≤0. 003% ） to be ignored,while the chirps and the losses must be taken into account ; the bandwidth of the detected frequency band would better be less than 2π× GHz;the selected central frequency is related to the shape of the original pulse,a central frequency of 12 GHz is chosen in a 4.0 Gbit/s system,and 5GHz is chosen in a 10 Gbit/s system. A testing system is established. The experimental results agree well with the theoretical analysis.
基金supported in part by the National Natural Science Foundation of China under Grants No. 61103178, No. 60803151the Research Fund for the Doctoral Program of Higher Education of China under Grant No. 20096102120045
文摘To solve the slow congestion detection and rate convergence problems in the existing rate control based fair data collection schemes, a new fair data collection scheme is proposed, which is named the improved scheme with fairness or ISWF for short. In ISWF, a quick congestion detection method, which combines the queue length with traffic changes of a node, is used to solve the slow congestion detection problem, and a new solution, which adjusts the rate of sending data of a node by monitoring the channel utilization rate, is used to solve the slow convergence problem. At the same time, the probability selection method is used in ISWF to achieve the fairness of channel bandwidth utilization. Experiment and simulation results show that ISWF can effectively reduce the reaction time in detecting congestion and shorten the rate convergence process. Compared with the existing tree-based fair data collection schemes, ISWF can achieve better fairness in data collection and reduce the transmission delay effectively, and at the same time, it can increase the average network throughput by 9.1% or more.
基金Supported by the Guangxi Natural Science Foundation (No.0731025, No.0731026)the Established Project by Guangxi Education Department (No.200808LX117)
文摘The detection performance is evaluated for our proposed analog multiuser receiver in Ultra-WideBand (UWB) transmitted-reference system. In the presence of dense multipath and multi-access signals,the performance analysis is difficult due to the complicated waveform of received impulse. We develop an approach to analyze the steady-state Signal-to-Interference-plus-Noise (SINR) of the detector output. The multipath-spread impulse is fitted to an exponentially decaying profile in the analysis. A closed-form expression of steady-state SINR is further deduced for the proposed Least Minimum Square (LMS) detector. The analysis is validated by simulations in Line-Of-Sight (LOS) and Non-Line-Of-Sight (NLOS) channel respectively. Based on the theoretical results,the multipath delay spread is employed to determine the optimal width of the integration window of the detector.
基金supported by the National High Technology Research and Development Program of China(Nos.2013AA013303,2013AA013301 and 2013AA013403)
文摘A novel scheme for photonic envelope detection and fiber transmission of 24 GHz impulse radio ultra-wideband(IRUWB) signal is proposed based on phase modulator(PM). In the system, an optics assisted envelope detection unit(OAEDU) is used for filtering one of the first sidebands at the output of PM, then this narrow band optical signal transfers over single-mode fiber(SMF), and the envelope of 24 GHz IR-UWB signal is obtained after photodetection(PD) and low pass filter(LPF). The numerical simulation results show that the combination of PM and OAEDU can alleviate the fiber chromatic dispersion(CD) effectively. The proposed system may provide a simple and cost-effective solution for IR-UWB receiver.
