In order to solve the cross-channel signal problem caused by the uniform channelized wideband digital receiver when processing wideband signal and the problem that the sensitivity of the system greatly decreases when ...In order to solve the cross-channel signal problem caused by the uniform channelized wideband digital receiver when processing wideband signal and the problem that the sensitivity of the system greatly decreases when the bandwidth of wideband digital receiver increases,which both decrease the wideband radar signal detection performance,a new wideband digital receiver based on the modulated wideband converter(MWC)discrete compressed sampling structure and an energy detection method based on the new receiver are proposed.Firstly,the proposed receiver utilizes periodic pseudo-random sequences to mix wideband signals with baseband and other sub-bands.Then the mixed signals are low-pass filtered and downsampled to obtain the baseband compressed sampling data,which can increase the sensitivity of the system.Meanwhile,the cross-channel signal will all appear in any subbands,so the cross-channel signal problem can be solved easily by processing the baseband compressed sampling data.Secondly,we establish the signal detection model and formulate the criterion of the energy detection method.And we directly utilize the baseband compressed sampling data to carry out signal detection without signal reconstruction,which decreases the complexity of the algorithm and reduces the computational burden.Finally,simulation experiments demonstrate the effectiveness of the proposed receiver and show that the proposed signal detection method is effective in low signal-to-noise ratio(SNR)compared with the conventional energy detection and the probability of detection increases significantly when SNR increases.展开更多
认知无线网络与传统无线网络最大的区别在于频谱感知和信道切换功能。在认知网络中,认知用户需具备频谱感知的功能,当有授权用户接入时,可以实现动态频谱切换,从而不影响授权用户的通信。因此需要更改传统协议栈的传输层协议(Transmissi...认知无线网络与传统无线网络最大的区别在于频谱感知和信道切换功能。在认知网络中,认知用户需具备频谱感知的功能,当有授权用户接入时,可以实现动态频谱切换,从而不影响授权用户的通信。因此需要更改传统协议栈的传输层协议(Transmission Control Protocol,TCP)使其适应网络的频谱感知和信道切换。通过TCP-MAC跨层可以消除由于频谱感知带来的超时重传问题,改进的TCP-improved算法可解决信道切换带来的信道利用率不高或网络拥塞的问题。实验结果显示在认知环境下TCP-improved能很好的缓解由于频谱感知和信道切换对传输层的影响,实现了认知用户的传输层性能增强。展开更多
A series of numerical analyses have been performed to investigate the flow structures in a narrow confined channel with 12 staggered circular impingement holes and one bigger exit hole. The flow enters the channel thr...A series of numerical analyses have been performed to investigate the flow structures in a narrow confined channel with 12 staggered circular impingement holes and one bigger exit hole. The flow enters the channel through the impingement holes and exits through the far end outlet. The flow fields corresponding to two jet Reynolds numbers （25000 and 65000） and three channel con- figurations with different ratios of the channel height to the impingement hole diameter （Zr 1, 3, 5） are analyzed by solving the Reynolds averaged Navier-Stokes equations with the realizable k-e turbulence model. Detailed flow field information including the secondary flow, the interaction between the jets and the cross flow, and flow distribution along the channel has been obtained. Comparisons between the numerical and experimental results of the flow fields at the four planes along the channel are performed to validate the numerical method. The calculated impingement pattern, high velocity flow distribution, low velocity separation region and vortices are in good agreement with the experimental data, implying the validity and effectiveness of the employed numerical approach for analyzing relevant flow field.展开更多
基金supported by the National Natural Science Foundation of China(No.61571146)the Fundamental Research Funds for the Central Universities(HEUCF1608)
文摘In order to solve the cross-channel signal problem caused by the uniform channelized wideband digital receiver when processing wideband signal and the problem that the sensitivity of the system greatly decreases when the bandwidth of wideband digital receiver increases,which both decrease the wideband radar signal detection performance,a new wideband digital receiver based on the modulated wideband converter(MWC)discrete compressed sampling structure and an energy detection method based on the new receiver are proposed.Firstly,the proposed receiver utilizes periodic pseudo-random sequences to mix wideband signals with baseband and other sub-bands.Then the mixed signals are low-pass filtered and downsampled to obtain the baseband compressed sampling data,which can increase the sensitivity of the system.Meanwhile,the cross-channel signal will all appear in any subbands,so the cross-channel signal problem can be solved easily by processing the baseband compressed sampling data.Secondly,we establish the signal detection model and formulate the criterion of the energy detection method.And we directly utilize the baseband compressed sampling data to carry out signal detection without signal reconstruction,which decreases the complexity of the algorithm and reduces the computational burden.Finally,simulation experiments demonstrate the effectiveness of the proposed receiver and show that the proposed signal detection method is effective in low signal-to-noise ratio(SNR)compared with the conventional energy detection and the probability of detection increases significantly when SNR increases.
文摘认知无线网络与传统无线网络最大的区别在于频谱感知和信道切换功能。在认知网络中,认知用户需具备频谱感知的功能,当有授权用户接入时,可以实现动态频谱切换,从而不影响授权用户的通信。因此需要更改传统协议栈的传输层协议(Transmission Control Protocol,TCP)使其适应网络的频谱感知和信道切换。通过TCP-MAC跨层可以消除由于频谱感知带来的超时重传问题,改进的TCP-improved算法可解决信道切换带来的信道利用率不高或网络拥塞的问题。实验结果显示在认知环境下TCP-improved能很好的缓解由于频谱感知和信道切换对传输层的影响,实现了认知用户的传输层性能增强。
基金supported by the National Natural Science Foundation of China(No.51206180)the Natural Science Basic Research Plan in Shaanxi Province of China(No.2014JQ7276)
文摘A series of numerical analyses have been performed to investigate the flow structures in a narrow confined channel with 12 staggered circular impingement holes and one bigger exit hole. The flow enters the channel through the impingement holes and exits through the far end outlet. The flow fields corresponding to two jet Reynolds numbers （25000 and 65000） and three channel con- figurations with different ratios of the channel height to the impingement hole diameter （Zr 1, 3, 5） are analyzed by solving the Reynolds averaged Navier-Stokes equations with the realizable k-e turbulence model. Detailed flow field information including the secondary flow, the interaction between the jets and the cross flow, and flow distribution along the channel has been obtained. Comparisons between the numerical and experimental results of the flow fields at the four planes along the channel are performed to validate the numerical method. The calculated impingement pattern, high velocity flow distribution, low velocity separation region and vortices are in good agreement with the experimental data, implying the validity and effectiveness of the employed numerical approach for analyzing relevant flow field.
