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Beijing, China

Gao Z.,Beijing University of Posts and Telecommunications | Gao Z.,Chinese Academy of Sciences | Shi Y.,Beijing University of Posts and Telecommunications | Chen S.,Datang Telecom Technology | Li Q.,University of Southern California
IEICE Transactions on Communications

Routing is a challenging issue in mobile social networks (MSNs) because of time-varying links and intermittent connectivity. In order to enable nodes to make right decisions while forwarding messages, exploiting social relationship has become an important method for designing efficient routing protocols in MSNs. In this paper, we first use the temporal evolution graph model to accurately capture the dynamic topology of the MSN. Based on the model, we introduce the social relationship metric for detecting the quality of human social relationship from contact history records. Utilizing this metric, we propose social relationship based betweenness centrality metric to identify influential nodes to ensure messages forwarded by the nodes with stronger social relationship and higher likelihood of contacting other nodes. Then, we present SR Bet, a novel social-based forwarding algorithm, which utilizes the aforementioned metric to enhance routing performance. Simulations have been conducted on two real world data sets and results demonstrate that the proposed forwarding algorithm achieves better performances than the existing algorithms. Copyright © 2015 The Institute of Electronics, Information and Communication Engineers. Source

Peng L.,Beihang University | Liu D.,Datang Telecom Technology
Proceedings - 2013 7th International Conference on Image and Graphics, ICIG 2013

The depth of field (DoF) in photography is limited by the aperture size and focal length. When the focal length is definite, large aperture size leads to small DoF. In dark scene, we use a large aperture at the cost of deep DoF. The paper gives a detailed analysis of the focused plenoptic camera mode presented by Georgiev and Lumsdaine, and proposes a novel reconstruction algorithm. It recovers the image from radiance samples captured on the sensor and can get images of extended DoF to all-in-focus even with large aperture size. Beside, it can change the angle of view after the exposure. Depth of field of the rendered photo in this algorithm is also studied. The simulation result shows that under the assist of new algorithm, the DoF can be extended greatly. © 2013 IEEE. Source

Liu P.,Beihang University | Zhang R.M.,Beihang University | Liu D.J.,Datang Telecom Technology
Applied Mechanics and Materials

Plenoptic camera provides us with the capability of refocusing photographs after exposure and extended depth of field. But the registration error for the micro lens array and image sensor influences on the quality of extracted 4D light field and thus leads to a degradation of the reconstructed image. The paper discusses two type of registration errors based on the structure of focused plenoptic camera and proposes a correction algorithm to acquire accurate light field from the sensor data. The simulation shows that registration errors deteriorate the reconstructed image and the artifact will be reduced significantly after using the algorithm. © (2014) Trans Tech Publications, Switzerland. Source

Huo Q.,Peking University | Liu T.,Datang Telecom Technology | Sun S.,Peking University | Song L.,Peking University | Jiao B.,Peking University
IET Communications

In this study, we consider the selective combining in hybrid cooperative networks (SCHCNs scheme) with one source node, one destination node and N relay nodes. In the SCHCN scheme, each relay first adaptively chooses between amplify-andforward protocol and decode-and-forward protocol on a per frame basis by examining the error-detecting code result, and Nc(1 ≤ Nc ≤ N) relays will be selected to forward their received signals to the destination. We first develop a signal-to-noise ratio (SNR) threshold-based frame error rate (FER) approximation model. Then, the theoretical FER expressions for the SCHCN scheme are derived by utilising the proposed SNR threshold-based FER approximation model. The analytical FER expressions are validated through simulation results. © The Institution of Engineering and Technology 2014. Source

Zhu X.,Datang Telecom Technology | Chen S.,Datang Telecom Technology | Hu H.,Datang Telecom Technology | Su X.,China Mobile | Shi Y.,Beijing University of Posts and Telecommunications
IEEE Wireless Communications

Mobile communication solutions for highspeed railway scenarios aim at providing seamless coverage, high system capacity and a high data rate for end users, which in turn face the challenges of Doppler frequency shift, penetration loss, mobility management and system capacity planning. Because the scarcity of frequency resources and increasing wireless broadband requirements have become very serious problems worldwide, increasing attention has been focused on time-division duplexing based technology, on which we focus in this article. Time-division synchronous code-division multiple access based and time-division Long Term Evolution based solutions are introduced with appropriate technology analysis. The experimental results of TD-SCDMA-based solutions in the Shanghai maglev high-speed network environment and the simulation results of TD-LTEbased solutions are presented. Finally, to improve performance, we discuss an enhanced solution based on mobile relays with performance evaluation, which is considered as a more comprehensive solution for high-speed railway scenarios. © 2002-2012 IEEE. Source

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