We consider a carrier sense multiple access (CSMA) in an unslotted cognitive radio network with random residence time. In this system, if an arriving secondary user (SU) does not find any idle channels, then the SU ei...We consider a carrier sense multiple access (CSMA) in an unslotted cognitive radio network with random residence time. In this system, if an arriving secondary user (SU) does not find any idle channels, then the SU either enters the back-off group or gives up its service and leaves the system. SUs in the back-off group have random mobility, so may re-access the channel after random time or go to the other network after random residence time. We model the system by 3-demensional Continuous Time Markov Chain (CTMC) and obtain the steady state probability of the system by matrix analytic method. In numerical results, we compare the performance of two systems with and without residence time of SUs. It is shown that the random mobility of SUs has an impact on the performance of SUs in cognitive radio networks.展开更多
In the Internet of Things(IoT)scenario,many devices will communi-cate in the presence of the cellular network;the chances of availability of spec-trum will be very scary given the presence of large numbers of mobile u...In the Internet of Things(IoT)scenario,many devices will communi-cate in the presence of the cellular network;the chances of availability of spec-trum will be very scary given the presence of large numbers of mobile users and large amounts of applications.Spectrum prediction is very encouraging for high traffic next-generation wireless networks,where devices/machines which are part of the Cognitive Radio Network(CRN)can predict the spectrum state prior to transmission to save their limited energy by avoiding unnecessarily sen-sing radio spectrum.Long short-term memory(LSTM)is employed to simulta-neously predict the Radio Spectrum State(RSS)for two-time slots,thereby allowing the secondary node to use the prediction result to transmit its information to achieve lower waiting time hence,enhanced performance capacity.A frame-work of spectral transmission based on the LSTM prediction is formulated,named as positive prediction and sensing-based spectrum access.The proposed scheme provides an average maximum waiting time gain of 2.88 ms.The proposed scheme provides 0.096 bps more capacity than a conventional energy detector.展开更多
Cognitive radio (CR) is a technology that provides a promising new way to improve the efficiency of the use of the electromagnetic spectrum that available. Spectrum sensing helps in the detection of spectrum holes (un...Cognitive radio (CR) is a technology that provides a promising new way to improve the efficiency of the use of the electromagnetic spectrum that available. Spectrum sensing helps in the detection of spectrum holes (unused channels of the band), and instantly move into vacant channels while avoiding occupied ones. An energy detector with baseband sampling for CR is presented with mathematical analyses for an additive white Gaussian noise (AWGN) channels. A brief overview of the energy detection based spectrum sensing for CR technology is introduced. Practical implementation issues on Texas Instruments TMS320C6713 floating point DSP board are presented. Novelties of this work came from a derivation of probability of detection and probability of false alarm for the baseband energy detector without including the sampling theorems and the associated approximation.展开更多
In cognitive radio networks, the spectrum utilization can be improved by cognitive users opportunistically using the idle channels licensed to the primary users. However, the new arrived cognitive users may not be abl...In cognitive radio networks, the spectrum utilization can be improved by cognitive users opportunistically using the idle channels licensed to the primary users. However, the new arrived cognitive users may not be able to use the channel immediately since the channel usage state is random. This will impose additional time delay for the cognitive users. Excessive waiting delay can make cognitive users miss the spectrum access chances. In this paper, a discrete-time Markov queuing model from a macro point of view is provided. Through the matrix-geometric solution theory, the average sojourn time for cognitive users in the steady state before accessing the spectrum is obtained. Given the tolerant delay of cognitive users, the macro-based throughput is derived and an access control mechanism is proposed. The numerical results show the effects of service completion probability on average sojourn time and throughput. It is confirmed that the throughput can be obviously improved by using the proposed access control mechanism. Finally, the performance evaluations based on users are compared to that based on data packets.展开更多
随着空间卫星的广泛使用,射电天文望远镜受到高仰角的干扰越来越多,进一步确定整个天空中卫星干扰源的频率、位置和分布,是有效规划天文观测的重要手段。本文介绍了一种基于时频差对高仰角卫星干扰源定位的方法,即基于时频差信息,将干...随着空间卫星的广泛使用,射电天文望远镜受到高仰角的干扰越来越多,进一步确定整个天空中卫星干扰源的频率、位置和分布,是有效规划天文观测的重要手段。本文介绍了一种基于时频差对高仰角卫星干扰源定位的方法,即基于时频差信息,将干扰源定位解构为时频差联合估计与定位的问题。首先建立用于时频差联合估计的地面接收信号模型,基于四阶最大似然进行到达时间差(time difference of arrival,TDOA)与到达频率差(frequency difference of arrival,FDOA)的联合估计;然后建立干扰源定位模型,根据两步加权最小二乘算法对干扰源进行定位。经过仿真验证,实现了对高仰角快速运动干扰源的定位与轨迹估计,对于300 km高度干扰源的定位误差最小可达到78 m。利用基于联合时频差分析的卫星干扰源定位算法进行射电天文台址无线电环境测量可提升射电望远镜的科学产出,并保障其平稳运行。展开更多
针对射频指纹识别中单一特征无法全面表示信号的完整性,且类间特征差异较小从而限制识别准确率等问题,提出了一种基于时频和双谱特征融合的DA-ResNeXt50(ResNeXt50 with dense connection and ACBlock)射频指纹识别方法。首先,对采集到...针对射频指纹识别中单一特征无法全面表示信号的完整性,且类间特征差异较小从而限制识别准确率等问题,提出了一种基于时频和双谱特征融合的DA-ResNeXt50(ResNeXt50 with dense connection and ACBlock)射频指纹识别方法。首先,对采集到的不同设备的信号分别进行短时傅里叶变换(short-time Fourier transform,STFT)和双谱变换,将得到的图像二值化处理并拼接,综合利用两种变换分别在时频域和高阶统计特性上的优势,更全面地提取和表征不同设备的射频指纹特征;然后,提出了DA-ResNeXt50网络模型,借鉴密集连接思想,使四层残差单元每一层都与前面所有层直接相连,促进了特征的复用和传递,能更好地捕捉类间细微差异;最后,使用非对称卷积模块(asymmetric convolution block,ACBlock)替换模型最后一层残差单元的3×3卷积,可以有效地增加网络的感受野,增强卷积核的骨架部分,从而提高射频指纹识别性能。实验结果表明,相较于使用单一特征提取方法,提出的特征融合方法的性能有较大的提升,改进后的模型与多种经典模型相比,具有较高的识别精度。展开更多
文摘We consider a carrier sense multiple access (CSMA) in an unslotted cognitive radio network with random residence time. In this system, if an arriving secondary user (SU) does not find any idle channels, then the SU either enters the back-off group or gives up its service and leaves the system. SUs in the back-off group have random mobility, so may re-access the channel after random time or go to the other network after random residence time. We model the system by 3-demensional Continuous Time Markov Chain (CTMC) and obtain the steady state probability of the system by matrix analytic method. In numerical results, we compare the performance of two systems with and without residence time of SUs. It is shown that the random mobility of SUs has an impact on the performance of SUs in cognitive radio networks.
文摘In the Internet of Things(IoT)scenario,many devices will communi-cate in the presence of the cellular network;the chances of availability of spec-trum will be very scary given the presence of large numbers of mobile users and large amounts of applications.Spectrum prediction is very encouraging for high traffic next-generation wireless networks,where devices/machines which are part of the Cognitive Radio Network(CRN)can predict the spectrum state prior to transmission to save their limited energy by avoiding unnecessarily sen-sing radio spectrum.Long short-term memory(LSTM)is employed to simulta-neously predict the Radio Spectrum State(RSS)for two-time slots,thereby allowing the secondary node to use the prediction result to transmit its information to achieve lower waiting time hence,enhanced performance capacity.A frame-work of spectral transmission based on the LSTM prediction is formulated,named as positive prediction and sensing-based spectrum access.The proposed scheme provides an average maximum waiting time gain of 2.88 ms.The proposed scheme provides 0.096 bps more capacity than a conventional energy detector.
文摘Cognitive radio (CR) is a technology that provides a promising new way to improve the efficiency of the use of the electromagnetic spectrum that available. Spectrum sensing helps in the detection of spectrum holes (unused channels of the band), and instantly move into vacant channels while avoiding occupied ones. An energy detector with baseband sampling for CR is presented with mathematical analyses for an additive white Gaussian noise (AWGN) channels. A brief overview of the energy detection based spectrum sensing for CR technology is introduced. Practical implementation issues on Texas Instruments TMS320C6713 floating point DSP board are presented. Novelties of this work came from a derivation of probability of detection and probability of false alarm for the baseband energy detector without including the sampling theorems and the associated approximation.
文摘In cognitive radio networks, the spectrum utilization can be improved by cognitive users opportunistically using the idle channels licensed to the primary users. However, the new arrived cognitive users may not be able to use the channel immediately since the channel usage state is random. This will impose additional time delay for the cognitive users. Excessive waiting delay can make cognitive users miss the spectrum access chances. In this paper, a discrete-time Markov queuing model from a macro point of view is provided. Through the matrix-geometric solution theory, the average sojourn time for cognitive users in the steady state before accessing the spectrum is obtained. Given the tolerant delay of cognitive users, the macro-based throughput is derived and an access control mechanism is proposed. The numerical results show the effects of service completion probability on average sojourn time and throughput. It is confirmed that the throughput can be obviously improved by using the proposed access control mechanism. Finally, the performance evaluations based on users are compared to that based on data packets.
文摘随着空间卫星的广泛使用,射电天文望远镜受到高仰角的干扰越来越多,进一步确定整个天空中卫星干扰源的频率、位置和分布,是有效规划天文观测的重要手段。本文介绍了一种基于时频差对高仰角卫星干扰源定位的方法,即基于时频差信息,将干扰源定位解构为时频差联合估计与定位的问题。首先建立用于时频差联合估计的地面接收信号模型,基于四阶最大似然进行到达时间差(time difference of arrival,TDOA)与到达频率差(frequency difference of arrival,FDOA)的联合估计;然后建立干扰源定位模型,根据两步加权最小二乘算法对干扰源进行定位。经过仿真验证,实现了对高仰角快速运动干扰源的定位与轨迹估计,对于300 km高度干扰源的定位误差最小可达到78 m。利用基于联合时频差分析的卫星干扰源定位算法进行射电天文台址无线电环境测量可提升射电望远镜的科学产出,并保障其平稳运行。
文摘针对射频指纹识别中单一特征无法全面表示信号的完整性,且类间特征差异较小从而限制识别准确率等问题,提出了一种基于时频和双谱特征融合的DA-ResNeXt50(ResNeXt50 with dense connection and ACBlock)射频指纹识别方法。首先,对采集到的不同设备的信号分别进行短时傅里叶变换(short-time Fourier transform,STFT)和双谱变换,将得到的图像二值化处理并拼接,综合利用两种变换分别在时频域和高阶统计特性上的优势,更全面地提取和表征不同设备的射频指纹特征;然后,提出了DA-ResNeXt50网络模型,借鉴密集连接思想,使四层残差单元每一层都与前面所有层直接相连,促进了特征的复用和传递,能更好地捕捉类间细微差异;最后,使用非对称卷积模块(asymmetric convolution block,ACBlock)替换模型最后一层残差单元的3×3卷积,可以有效地增加网络的感受野,增强卷积核的骨架部分,从而提高射频指纹识别性能。实验结果表明,相较于使用单一特征提取方法,提出的特征融合方法的性能有较大的提升,改进后的模型与多种经典模型相比,具有较高的识别精度。
