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Shen X.,University of Electronic Science and Technology of China | Huang J.,University of Electronic Science and Technology of China | Huang J.,Tong Fang Electronic Technology Company Ltd | Liu P.,The Academy of Satellite Application | And 3 more authors.
Radioengineering | Year: 2014

Collaborative beamforming has been widely used in wireless sensor networks to improve the directivity of signals in long-distance transmission. The performance of collaborative beamforming has been well analyzed for the case without phase offset in the literature. However, the phase ambiguity caused by carrier phase jitter or offset between the transmitter and receiver nodes always exists in a practical system. Although the effects of imperfect phase have been studied for uniform node distribution and Tikhonov phase noise model, the performance analysis of collaborative beamforming with arbitrary node distributions and any phase offset which may have various probability density functions (PDFs) depending on phaselocked loop circuits is still an open issue. This paper proposes a unified method to evaluate the performance of collaborative beamforming in the case of phase noise. Since non-parametric kernel method is used to build the PDFs of node and phase offset, the proposed non-parametric approach can provide accurate performance analysis for various node and phase noise distributions which may or may not be represented by explicit PDF functions. Computer simulation is conducted to verify validity of the proposed method. Source


Hu Y.,Nanjing University of Aeronautics and Astronautics | Song M.,Nanjing University of Aeronautics and Astronautics | Meng B.,The Academy of Satellite Application
Wireless Personal Communications | Year: 2015

In some special circumstance such as local conflict area or thick forests, the signal availability to the GPS receiver may greatly be decreased, and this will accordingly degrade the performance of the receiver. To improve this problem, we present a method to augment the GPS signal availability utilizing the navigation signal retransmission via the geosynchronous communications satellite (GEO comsat). The general implementation process of the proposed method is that at the transmitting side, we first upconvert the local-generated power-controlled GPS signal in the selected comsat frequency band, and then transmit it to the GEO comsat for its retransmission. While at the receiving side, we first downconvert the received GPS signal which may be overlapped with the strong communication signal to baseband. And then we make a cancellation on the strong communication signal with blind adaptive frequency-shift filtering to decrease its effect on the retransmitted GPS signal. Finally with the separated GPS signal, we can easily get the despreading and the demodulation results for the GPS receiver, and thus the goal of augmenting the signal availability for the GPS receiver is achieved. The final numerical results validate the effectiveness of the proposed method. © 2015, Springer Science+Business Media New York. Source


Zhou Y.,Beihang University | Zhou Y.,Xidian University | Zhou Y.,Chinese Academy of Sciences | Liu J.,Beihang University | And 5 more authors.
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2015

Revocation of access control on private e-healthcare records (EHRs) allows to revoke the access rights of valid users. Most existing solutions rely on a trusted third party too much to generate and update decryption keys, or require the computations of non-revoked users during the revocation, which make them impractical for some more complicated scenarios. In this paper, we propose a new revocation model, referred to as non-interactive revocable identity-based access control (NRIBAC) on EHRs. In NRIBAC, a trusted third party only needs to generate secret keys for group authorities and each group authority can generate decryption keys for the users in its domain. The NRIBAC distinguishes itself from other revocation schemes by the advantageous feature that it does not require any participation of non-revoked users in the revocation. We construct an NRIBAC scheme with short ciphertexts and decryption keys by leveraging hierarchical identity-based encryption and introducing the version information. We formally prove the security of the NRIBAC scheme and conduct thorough theoretical analysis to evaluate the performance. The results reveal that the scheme provides favorable revocation procedure without disturbing non-revoked users. © Springer International Publishing Switzerland 2015. Source


Sun Y.,Beihang University | Sun Y.,Xidian University | Sun Y.,Chinese Academy of Sciences | Wu Q.,Beihang University | And 6 more authors.
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2015

Blind signature is a fundamental tool in electronic cash. In most existing blind signature schemes, both the signer and the verifier need to take expensive modular exponentiations. This situation is deteriorated in significant monetary transactions in which a large number of (multi-)exponentiations need to be calculated. This paper proposes batch blind signature to reduce the computation overheads at both the signer and the verifier sides in blind signatures on elliptical curves. To this end, we first propose a batch multi-exponentiation algorithm that allows a batch of multi-base exponentiations on elliptic curves to be processed simultaneously. We next apply our batch multi-exponentiation algorithm to speed up the Okamoto-Schnorr blind signature scheme in both the signing and the verification procedures. Specifically, the proposed algorithm is exploited for generating blind signatures so that multiple messages can be signed in a batch for sake of saving computation costs. The algorithm is further employed in the verification process, which gives a different batch signature verification approach from the existing batch verification algorithm. An attracting feature of our approach is that, unlike existing batch verification signature approach, our approach does distinguish all valid signatures from a batch purported signatures (of correct and erroneous ones). This is desirable in e-cash systems where a signature represents certain value of e-cash and any valid signature should not passed up. The experimental results show that, compared with acceleration with existing simultaneous exponentiation algorithm, our batch approach is about 55% and 45% more efficient in generating and verifying blind signatures, respectively. © Springer International Publishing Switzerland 2015. Source


Wu X.-Y.,University of Electronic Science and Technology of China | Shen Y.,University of Electronic Science and Technology of China | Shen Y.,The Academy of Satellite Application | Tang Y.-X.,University of Electronic Science and Technology of China
Tien Tzu Hsueh Pao/Acta Electronica Sinica | Year: 2015

Measurements and characterizations are rarely conducted about indoor self-interference channel of CCFD(Co-time Co-frequency full-duplex). An extensive self-interference channel measurement is performed at 2.6GHz under typical indoor environment with channel sounder based on vector network analyzer. By analyzing the measurement data, the empirical channel characteristics such as path loss exponent, RMS(root-mean-square)delay spread have been extracted. Results show that path loss exponent and RMS delay statistics are different according to antenna separation of transmitter-receiver. When the separation is larger than 1m, the path loss exponent is 1.86, and the RMS delay statistics follow lognormal distribution.When the separation is less than 1m, the path loss exponent is 1.52, and the RMS delay statistics at different antenna separation follow lognormal distribution whose mean and variance are linear functions of antenna distance respectively. ©, 2015, Chinese Institute of Electronics. All right reserved. Source

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