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Chen X.,Peking University | Zhang J.,Peking University | Lu J.,Peking University | Lu X.,Peking University | And 6 more authors.
Optics Letters | Year: 2015

We demonstrate precise microwave frequency dissemination of a hydrogen maser synchronized frequency comb over a 120 km commercial fiber link. The phase noise was compensated by a feed-forward digital compensation scheme, where the value of locally detected phase noise was first transmitted to the remote user end via a wavelength division multiplexing channel in the same fiber link and then compensated directly at the user end. The fractional frequency instability was measured to be at 5.28 × 10-16/s. © 2015 Optical Society of America.

Sun W.-L.,Henan Institute of Science and Technology | Sun W.-L.,Beijing Satellite Navigation Center | Guan J.,China Institute of Technology
ETRI Journal | Year: 2015

In this paper, we focus on a novel technique called the cube-linear attack, which is formed by combining cube attacks with linear attacks. It is designed to recover the secret information in a probabilistic polynomial and can reduce the data complexity required for a successful attack in specific circumstances. In addition to the different combination strategies of the two attacks, two cube-linear schemes are discussed. Applying our method of a cube-linear attack to a reduced-round Trivium, as an example, we get better linear cryptanalysis results. More importantly, we believe that the improved linear cryptanalysis technique introduced in this paper can be extended to other ciphers. © 2015 ETRI.

Wu Z.,Beijing Satellite Navigation Center | Wu Z.,Wuhan Naval University of Engineering | Bian S.,Wuhan Naval University of Engineering
Journal of Geodesy | Year: 2015

GNSS integer ambiguity validation is considered to be a challenge task for decades. Several kinds of validation tests are developed and widely used in these years, but theoretical basis is their weakness. Ambiguity validation theoretically is an issue of hypothesis test. In the frame of Bayesian hypothesis testing, posterior probability is the canonical standard that statistical decision should be based on. In this contribution, (i) we derive the posterior probability of the fixed ambiguity based on the Bayesian principle and modify it for practice ambiguity validation. (ii) The optimal property of the posterior probability test is proved based on an extended Neyman–Pearson lemma. Since validation failure rate is the issue users most concerned about, (iii) we derive the failure rate upper bound of the posterior probability test, so the user can use the posterior probability test either in the fixed posterior probability or in the fixed failure rate way. Simulated as well as real observed data are used for experimental validations. The results show that (i) the posterior probability test is the most effective within the R-ratio test, difference test, ellipsoidal integer aperture test and posterior probability test, (ii) the posterior probability test is computational efficient and (iii) the failure rate estimation for posterior probability test is useful. © 2015, Springer-Verlag Berlin Heidelberg.

Han C.,Beijing Satellite Navigation Center
2014 31th URSI General Assembly and Scientific Symposium, URSI GASS 2014 | Year: 2014

The BeiDou Navigation Satellite System (BDS) is a global navigation satellite system to be developed independently by China. It will provide positioning, navigation, and timing services with a global coverage by 2020. It can be used for transport, weather forecast, fishing, forestry, telecommunications, hydrological monitoring, and mapping. The service modes are the open service (OS) and the authorized service (AS). The open service is provided free of charge with positioning accuracy of 10 meters, velocity accuracy of 0.2 m/s, and timing accuracy of 50 nanoseconds. The authorized service is provided with a more secure and higher level of integrity. Beside that AS also provides communication services. © 2014 IEEE.

Sun L.,Beijing Satellite Navigation Center | Chen J.,Beijing Satellite Navigation Center | Tan S.,Beijing Satellite Navigation Center | Chai Z.,Beijing Institute of Environmental Features
GPS Solutions | Year: 2015

As the Compass satellite system is under construction, various applications are emerging. Multipath mitigation is still a critical problem that must be resolved, especially short delay multipath. Research on multipath mitigation is reported and a multipath limiting antenna array including the algorithm is discussed. The carrier phase data of the receiver are subjected to forward–backward spatial smoothing to decorrelate the signals. The multiple signal classification (MUSIC) algorithm estimates the direction of the satellite signal and the direction of the multipath. Based on the direction of arrival (DOA), the beamforming maximizes the gain in the satellite signal direction and places nulls in the multipath directions. Compared to other beamforming algorithms, the method presented places nulls in the multipath directions and obtains high gain in the satellite direction. At the same time, the phase is not changed during the vector weighting method. The multipath limiting antenna array discussed resolves the problem that the short delay multipath cannot be reduced in signal processing multipath mitigation technology and that in the process, the phase in the direction of the satellite signal is not changed. An extra carrier phase measurement error of the receiver is not introduced, and a phase correction after beamforming is not necessary. The multipath limiting antenna array and the algorithm can provide support for the high-performance satellite navigation system. © 2014, Springer-Verlag Berlin Heidelberg.

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