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Lei C.,Beihang University | Lei C.,National Key Laboratory of CNS ATM | Zhang J.,Beihang University | Zhang J.,National Key Laboratory of CNS ATM
Chinese Journal of Aeronautics | Year: 2012

The detection of sparse signals against background noise is considered. Detecting signals of such kind is difficult since only a small portion of the signal carries information. Prior knowledge is usually assumed to ease detection. In this paper, we consider the general unknown and arbitrary sparse signal detection problem when no prior knowledge is available. Under a Neyman-Pearson hypothesis-testing framework, a new detection scheme is proposed by combining a generalized likelihood ratio test (GLRT)-like test statistic and convex programming methods which directly exploit sparsity in an underdetermined system of linear equations. We characterize large sample behavior of the proposed method by analyzing its asymptotic performance. Specifically, we give the condition for the Chernoff-consistent detection which shows that the proposed method is very sensitive to the ℓ 2 norm energy of the sparse signals. Both the false alarm rate and the miss rate tend to zero at vanishing signal-to-noise ratio (SNR), as long as the signal energy grows at least logarithmically with the problem dimension. Next we give a large deviation analysis to characterize the error exponent for the Neyman-Pearson detection. We derive the oracle error exponent assuming signal knowledge. Then we explicitly derive the error exponent of the proposed scheme and compare it with the oracle exponent. We complement our study with numerical experiments, showing that the proposed method performs in the vicinity of the likelihood ratio test (LRT) method in the finite sample scenario and the error probability degrades exponentially with the number of observations. © 2012 Elsevier Ltd. All rights reserved. Source

Zhang X.-J.,Beihang University | Zhang X.-J.,National Key Laboratory of CNS ATM | Guan X.-M.,Beihang University | Guan X.-M.,National Key Laboratory of CNS ATM | And 3 more authors.
Communications in Theoretical Physics | Year: 2013

In recent years, the transportation system has been faced by increasing challenge in congestion and inefficiency, and research in traffic network has become a significant area of interest. In this paper, we introduce a dynamic-information-based (DIB) queueing strategy into network traffic model under the efficient routing strategy. DIB makes a packet with higher priority to be delivered if there are less packets travelling along its path from the current node to the destination. It is found that, compared with the traditional first-in-first-out (FIFO) queueing strategy, DIB can effectively balance the traffic load of the system via delaying packets to be delivered to congested nodes. Although the network capacity has no obvious changes, some other indexes which reflect transportation efficiency are efficiently improved in the congestion state. Besides, extensive simulation results and discussions are provided to explain the phenomena. The results may provide novel insights for research on traffic systems. © 2013 Chinese Physical Society and IOP Publishing Ltd. Source

Wang Y.,National Key Laboratory of CNS ATM | Feng Y.,Queensland University of Technology | Li R.,National Key Laboratory of CNS ATM
24th International Technical Meeting of the Satellite Division of the Institute of Navigation 2011, ION GNSS 2011 | Year: 2011

The paper explores methods and algorithms used to generate, apply and validate covariance matrices of GPS orbits in the context of position solution. In general, the research of satellite orbit error is threefold. The first is covariance matrix generation of satellite orbit error which may include systematic orbit biases or sudden changes in the orbit solution. The next is to determine and test "Bad" satellites which have large orbit error with the highest probability. The third is to validate what integrity benefit can be obtained if orbit covariance matrices are considered in estimation of user positioning solutions. However, the existing integrity studies have not addressed these issues directly yet. The paper starts with a general description of a satellite integrity orbit monitoring problem and computing orbital covariance matrices from different orbital solutions in real time. Next the paper describes covariance propagations in the least square navigation solutions. The method to determine 'bad' satellites is then analyzed preliminarily. Experimental analysis with GPS orbits of several hours and several widely distributed ground GNSS stations are performed to demonstrate the proposed integrity concepts and determination algorithms. The results have shown that the effects of large broadcast orbital errors on the user solutions can indeed be effectively reduced by considering the orbital covariance matrices estimated. Source

Huaxian L.,Beihang University | Huaxian L.,National Key Laboratory of CNS ATM | Yanbo Z.,Beihang University | Yanbo Z.,National Key Laboratory of CNS ATM | And 3 more authors.
Proceedings of the 2011 IEEE 5th International Conference on Cybernetics and Intelligent Systems, CIS 2011 | Year: 2011

Instead of assigning 3D trajectories of the flights in some sectors under traditional Air Traffic Management (ATM), the Route Network Flow Assignment (RNFA) problem is redefined in the new generation of aviation. It needs to properly assign both the 3D trajectories and the time slots (4D trajectories) for all the flights in the whole airspace, aiming at maximizing the use of airspace and alleviating the air traffic congestion. It is an optimization problem in essence and has to optimize all the flights' 4D trajectories. This problem is challenging because of the large scale of the flights and the relativity among them. To deal with it, this paper puts forward an effective method. The main idea is to introduce a divide-and-conquer strategy to divide this large scale problem into small ones. During which, a dynamic grouping operator is adopted, while considering the relativity among the flights. For the optimization of the subcomponents, a dual coding Differential Evolution (DE) method is proposed to adapt the high efficiency DE to this discrete optimization problem. The experimental results show that our method can solve the RNFA problem both effectively and efficiently and outperforms the current approaches. Moreover, the application of the proposed methodology can also be served as a benchmark application in the fields of the large scale problems' optimization. © 2011 IEEE. Source

Zhang J.,Beihang University | Zhang J.,National Key Laboratory of CNS ATM | Hu Z.,Beihang University | Hu Z.,National Key Laboratory of CNS ATM | And 2 more authors.
Chinese Journal of Aeronautics | Year: 2011

This paper presents a novel approach for checking route oscillation of border gateway protocol (BGP) quickly, by which the privacy of routing policies of autonomous system (AS) can be respected. Firstly, route update chain tag (RUCT) is constructed to track the forwarding of update report, and local routing library is made to record the changing history of update report. Then route oscillation can be identified by analyzing correlative state of RUCT and local routing library. The characteristic of this approach is that an arbitrary AS can check route oscillation alone only by sharing its network ID, which greatly respects the privacy of routing policies for each AS. This paper shows that both looping in RUCT and consecutive positive-negative report in local record are sufficient conditions for route oscillation. Comparative experiments demonstrate the availability and efficiency of the proposed approach. © 2011 Chinese Journal of Aeronautics. All rights reserved. Source

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