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Ding H.,Xidian University | Ding H.,Xian Communication Institute | Ge J.,Xidian University | Da Costa D.B.,Federal University of Ceara | Jiang Z.,Xidian University
IEEE Transactions on Vehicular Technology | Year: 2011

Three low-complexity relay-selection strategies, namely, selective amplify and forward (S-AF), selective decode and forward (S-DF), and amplify and forward with partial relay selection (PRS-AF) in a spectrum-sharing scenario are studied. First, we consider a scenario where perfect channel state information (CSI) is available. For these scenarios, the respective asymptotic outage behaviors of the secondary systems are analyzed, from which the diversity and coding gains are derived and compared. Unlike the coding gain, which is shown to be very sensitive with the position of the primary receiver, the diversity gain of the secondary system is the same as the nonspectrum-sharing system. In addition, depending on the cooperative strategy employed, an increase in the number of relays may lead to severe loss of the coding gain. Afterwards, the impacts of imperfect CSI regarding the interference and transmit channels on the outage behavior of the secondary systems are analyzed. On one hand, the imperfect CSI concerning the interference channels only affects the outage performance of the primary system, whereas it has no effect on the diversity gain of the secondary system. On the other hand, the imperfect CSI concerning the transmit channels of the secondary systems may reduce the diversity gain of the three relay-selection strategies to unity, which is validated by both theoretical and numerical results. © 2006 IEEE. Source


Ding H.,Xidian University | Ding H.,Xian Communication Institute | Ge J.,Xidian University | Da Costa D.B.,Federal University of Ceara | Jiang Z.,Xidian University
IEEE Transactions on Vehicular Technology | Year: 2011

This paper proposes a new efficient scheme for the combined use of cooperative diversity and multiuser diversity. Considering a decode-and-forward (DF) opportunistic relaying strategy, we first study the outage behavior of the joint sourcerelay-selection scheme with/without direct links, from which the significance of the direct links is recognized. Motivated by the crucial role of these links on the system performance, a two-step selection scheme is proposed, which first selects the best source node based on the channel quality of the direct links and then selects the best link from the selected source to the destination. The proposed scheme significantly reduces the amount of channel estimation while achieving comparable outage performance to that using the joint selection scheme. Most importantly, the achieved diversity order is the same as that using the joint selection scheme. In addition, assuming an amplify-and-forward (AF) opportunistic relaying strategy, the outage behavior of this two-step scheme is also analyzed, and its availability is confirmed as well. © 2006 IEEE. Source


Rao R.,Xian Jiaotong University | Rao R.,Xian Communication Institute | Tang T.,Xian Jiaotong University
Journal of the Optical Society of America B: Optical Physics | Year: 2011

We studied active lossless single-interface surface plasmon polariton (SPP) waveguides with extremely short guided wavelengths and optimally designed a nanometer-size active lossless single-mode dielectric-loaded SPP waveguide (DLSPPW). The sufficient condition, under which both lossless propagation and extremely short guided wavelength can be achieved simultaneously in active single-interface SPP waveguides, is presented. Underthe same condition, the gain coefficient of the active medium reaches its maximum. These maximum gain coefficients are calculated in cases when the metals Au, Ag, and Cu are used, respectively, operating in wavelengths ranging from 330 to 1600nm. From the above calculation results, the working wavelength and metal are selected for the active DLSPPW. A single-mode lossless DLSPPW is designed and optimized using the effective index and finite element methods in vacuum wavelength 450nm. In this waveguide, 95% of the energy flux is constrained within a core area with thickness of 20nm and width of 22nm. © 2011 Optical Society of America. Source


Zheng W.,Xian Communication Institute
Journal of Information and Computational Science | Year: 2015

Aiming at the sub-Nyquist sampled signal with several sub-bands, a Time-frequency Extremum Function (TFEF) is proposed to extract the Enhanced Typical Sparse Time-frequency Feature (ETSTF) of the signal in order to solve the imbalance problem of time-frequency feature extracting for various sub-bands with different SNR (Signal-to-Noise Ratio)s. And an evolutionary clustering algorithm is developed for the ETSTF data set wiping off the false classes' negative effect of idle sub-bands. Based on the clustering results, a novel strategy will be established subsequently for the wide-band spectrum sensing. Simulation experiments indicate the following. 1) The same share have the time-frequency points of various sub- bands with different SNRs extracted by TFEF, which means that TFEF enhances the time-frequency feature of the sub-band with lower SNR. 2) The time-frequency points of busy sub-bands have obvious clustering character. 3) The evolutionary clustering results neglect the idle sub-bands information and have clustering centers in the busy sub-bands. 1548-7741/Copyright © 2015 Binary Information Press Source


Ding H.,Xidian University | Ge J.,Xidian University | Jiang Z.,Xian Communication Institute
Electronics Letters | Year: 2010

Asymptotic average symbol error probabilities (ASEPs) using a range of modulation types are derived in closed-form for dual-hop amplify-and-forward wireless cooperative networks with partial relay selection in Rician fading. The joint impact of the Rician K-factor and the power imbalance on the ASEP of the network is investigated. As verified by simulation, the obtained ASEPs are tight bounds in medium and high signal-to-noise regions. © 2010 The Institution of Engineering and Technology. Source

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