对于高时间分辨率的超宽带(ultra wideband,UWB)信号来说,在测距应用中主要通过估计信号到达时间(time of arrival,TOA)来计算距离。文章提出了一种基于动态阈值检测的TOA估计算法以提高测距精度并降低算法复杂度。对接收方收到的匹配...对于高时间分辨率的超宽带(ultra wideband,UWB)信号来说,在测距应用中主要通过估计信号到达时间(time of arrival,TOA)来计算距离。文章提出了一种基于动态阈值检测的TOA估计算法以提高测距精度并降低算法复杂度。对接收方收到的匹配滤波输出脉冲进行峰值检测,确定直达单径(direct path,DP)的检测区间;设定一个能够反映出信号和信道特性的联合度量参数,根据该参数的不同设置相应的最佳阈值因子,在检测区间中通过阈值检测搜索DP精确位置对应的时刻,得到TOA的估计值。仿真采用IEEE802.15.4a标准信道,其结果表明所提算法适用于不同信噪比和延时特性的信道,并兼顾运算复杂度与算法精度。展开更多
Vehicular ad hoc networks （VANETs） that use the IEEE 802.11p communication standard face a number of challenges, not least when it comes to safety messages on the VANET control channel （CCH） where short delay time...Vehicular ad hoc networks （VANETs） that use the IEEE 802.11p communication standard face a number of challenges, not least when it comes to safety messages on the VANET control channel （CCH） where short delay times and reliable delivery are of pri- mary importance. In this paper we propose a vehicular machine-to-machine （VM2M） overlay network that uses Long Term Evolu- tion （LTE） physical random access channel （PRACH） to emulate VANET CCH. The overlay network uses dedicated preambles to separate vehicular traffic from regular LTE traffic and a cartier sense multiple access with collision avoidance （CSMA-CA） layer similar to the one used in IEEE 802.15.4 to avoid the four step handshake and the overhead it incurs. The performance of the pro- posed overlay is evaluated under a wide range of PRACH parameters which conform to the scenarios with high vehicle velocities and large distances between roadside units （RSUs） that may be encountered in rural areas and on highways.展开更多
The IEEE 802.15.4 standard utilizes the CSMA-CA mechanism to control nodes’ access to the shared wireless communication medium. CSMA-CA implements the Binary Exponential Backoff (BEB) algorithm by which a node refrai...The IEEE 802.15.4 standard utilizes the CSMA-CA mechanism to control nodes’ access to the shared wireless communication medium. CSMA-CA implements the Binary Exponential Backoff (BEB) algorithm by which a node refrains from sending any packet before the expiry of its backoff period. After that, the node is required to sense the medium for two successive time slots to assert that the medium is clear from any ongoing transmissions (this is referred to as Clear Channel Assessment (CCA)). Upon finding the medium busy, the node doubles its backoff period and repeats that process. While effective in reducing the likelihood of collisions, this approach takes no measures to preserve the priorities among the nodes contending to access the medium. In this paper we propose the Priority-Based BEB (PB-BEB) algorithm in which we enhance BEB such that nodes’ priority is preserved. We provide a simulation study to examine the performance of PB-BEB. Our simulations show that the latter not only outperforms BEB in terms of fairness, but also show promising results in terms other parameters like channel utilization, reliability, and power conservation.展开更多
This paper presents a CMOS G;-C complex filter for a low-IF receiver of the IEEE802.15.4 standard.A pseudo differential OTA with reconfigurable common mode feedback and common mode feed-forward is proposed as well as ...This paper presents a CMOS G;-C complex filter for a low-IF receiver of the IEEE802.15.4 standard.A pseudo differential OTA with reconfigurable common mode feedback and common mode feed-forward is proposed as well as the frequency tuning method based on a relaxation oscillator.A detailed analysis of non-ideality of the OTA and the frequency tuning method is elaborated.The analysis and measurement results have shown that the center frequency of the complex filter could be tuned accurately.The chip was fabricated in a standard 0.35μm CMOS process,with a single 3.3 V power supply.The filter consumes 2.1 mA current,has a measured in-band group delay ripple of less than 0.16μs and an IRR larger than 28 dB at 2 MHz apart,which could meet the requirements of the IEEE802.15.4 standard.展开更多
文摘对于高时间分辨率的超宽带(ultra wideband,UWB)信号来说,在测距应用中主要通过估计信号到达时间(time of arrival,TOA)来计算距离。文章提出了一种基于动态阈值检测的TOA估计算法以提高测距精度并降低算法复杂度。对接收方收到的匹配滤波输出脉冲进行峰值检测,确定直达单径(direct path,DP)的检测区间;设定一个能够反映出信号和信道特性的联合度量参数,根据该参数的不同设置相应的最佳阈值因子,在检测区间中通过阈值检测搜索DP精确位置对应的时刻,得到TOA的估计值。仿真采用IEEE802.15.4a标准信道,其结果表明所提算法适用于不同信噪比和延时特性的信道,并兼顾运算复杂度与算法精度。
文摘Vehicular ad hoc networks （VANETs） that use the IEEE 802.11p communication standard face a number of challenges, not least when it comes to safety messages on the VANET control channel （CCH） where short delay times and reliable delivery are of pri- mary importance. In this paper we propose a vehicular machine-to-machine （VM2M） overlay network that uses Long Term Evolu- tion （LTE） physical random access channel （PRACH） to emulate VANET CCH. The overlay network uses dedicated preambles to separate vehicular traffic from regular LTE traffic and a cartier sense multiple access with collision avoidance （CSMA-CA） layer similar to the one used in IEEE 802.15.4 to avoid the four step handshake and the overhead it incurs. The performance of the pro- posed overlay is evaluated under a wide range of PRACH parameters which conform to the scenarios with high vehicle velocities and large distances between roadside units （RSUs） that may be encountered in rural areas and on highways.
文摘The IEEE 802.15.4 standard utilizes the CSMA-CA mechanism to control nodes’ access to the shared wireless communication medium. CSMA-CA implements the Binary Exponential Backoff (BEB) algorithm by which a node refrains from sending any packet before the expiry of its backoff period. After that, the node is required to sense the medium for two successive time slots to assert that the medium is clear from any ongoing transmissions (this is referred to as Clear Channel Assessment (CCA)). Upon finding the medium busy, the node doubles its backoff period and repeats that process. While effective in reducing the likelihood of collisions, this approach takes no measures to preserve the priorities among the nodes contending to access the medium. In this paper we propose the Priority-Based BEB (PB-BEB) algorithm in which we enhance BEB such that nodes’ priority is preserved. We provide a simulation study to examine the performance of PB-BEB. Our simulations show that the latter not only outperforms BEB in terms of fairness, but also show promising results in terms other parameters like channel utilization, reliability, and power conservation.
基金Project supported by the National High Technology Research and Development Program of China(No.2008AA010701)
文摘This paper presents a CMOS G;-C complex filter for a low-IF receiver of the IEEE802.15.4 standard.A pseudo differential OTA with reconfigurable common mode feedback and common mode feed-forward is proposed as well as the frequency tuning method based on a relaxation oscillator.A detailed analysis of non-ideality of the OTA and the frequency tuning method is elaborated.The analysis and measurement results have shown that the center frequency of the complex filter could be tuned accurately.The chip was fabricated in a standard 0.35μm CMOS process,with a single 3.3 V power supply.The filter consumes 2.1 mA current,has a measured in-band group delay ripple of less than 0.16μs and an IRR larger than 28 dB at 2 MHz apart,which could meet the requirements of the IEEE802.15.4 standard.
