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In cognitive radio applications, there are multiple different types of message queues. Existing queueing based works in underlay cognitive radio networks mainly focused on homogeneous packets. Therefore, we propose a new underlay scheme to deal with packets' heterogeneity by assuming high-priority packets have preemptive transmission opportunities over low-priority ones, and the former ones have impatient waiting time. We model the secondary user packets' behavior as a M/M/1+GI queueing system from the perspective of the whole system, which is represented by a two-dimensional state transition graph. The reneging probability of high-priority packets and the average waiting time in two-class priority queues are analyzed. Then we extend the single-channel model to multiple channels. Under this scenario, the closed form of low-priority packets' expected system delay is derived. Simulation results demonstrate that the average waiting time of high-priority packets decreases with the growing interference power threshold and the average waiting time of the low-priority packet is proportional to the arrival rate of high-priority packet and so on. This work may lay the foundation to design efficient Medium Access Control protocols and optimize long-term system performance by carefully choosing system parameters. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We consider the problem of bit error rate (BER) degradation because of the power gain imbalance between horizontal ( H)-polarization and vertical ( V)-polarization components in an orthogonal dual-polarization transmission system. To alleviate the aforementioned BER degradation problem, we propose a non-orthogonal polarization-domain rotation scheme where the axes of H-polarization and V-polarization components are rotated with different angles at the transmitter and de-rotated at the receiver. In addition, in order to assess the effectiveness of the polarization-domain rotation scheme, we derive the closed-form BER expression under a practical dual-polarized channel model, which is represented by cross-polarization ratio and co-polarization ratio (CPR). We also derive the approximated BER expressions for the two asymptotic values of CPR: balanced CPR and infinite CPR. With the derived BER expressions, we find the optimal rotation angles that jointly minimize the BER. According to the numerical results, it is shown that about 3dB E b/ N0 gain is obtained at the BER of 10−4 and the CPR of 10dB by the polarization-domain rotation scheme with optimal rotation angles compared with the conventional orthogonal dual-polarization transmission. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Two new demodulate-and-forward schemes of multi-relay cooperative diversity with switch-and-examine relaying (SER) are analyzed. To reduce relay usage and enhance bandwidth efficiency, the two new cooperative diversity schemes employ a switch-based relay selection. The proposed schemes consume less communication resource than regular relaying schemes, such as the selection combining (SC) or maximal ratio combining (MRC) schemes that always use all relays, and also achieve better performance than distributed switch-and-stay schemes. In the first scheme, the decision statistic for relay usage and selection is based on the signal-to-noise ratio (SNR). In the second scheme, the log-likelihood ratio (LLR) of received signals is used for the decision of relay usage and selection. With the two SER schemes, the bit error probability (BEP) of binary phase shift keying (BPSK) and the average number of used paths are derived and expressed in closed-form for the independent and identically distributed (i.i.d.) Rayleigh fading channels. Numerical and simulation results are presented for performance illustrations. According to the numerical results, the LLR-based SER not only achieves a lower BEP but also consumes less relay resource than the SNR-based SER. Furthermore, the LLR-based SER scheme even outperforms the corresponding SNR-based SC scheme for a range of average SNR. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Recently, Jiang et al. and He et al. independently found security problems in Chen et al.'s remote user authentication scheme for non-tamper-proof storage devices like Universal Serial Bus stick and proposed improvements. Nonetheless, we detect that the schemes proposed by Jiang et al. and He et al. overlook a user's privacy. We also observe that Jiang et al.'s scheme is vulnerable to insider attack and denial of service attacks and lacks forward secrecy. We point out that the password changing facility in He et al.'s scheme is equivalent to undergoing registration, whereas in Jiang et al.'s scheme, it is unsuitable. Moreover, the login phase of both the schemes is incapable to prevent the use of wrong password leading to the computation of an unworkable login request. Therefore, we design a new scheme with user anonymity to surmount the identified weaknesses. Without adding much in communication/computational cost, our scheme provides more security characteristics and keeps the merits of the original schemes. As compared with its predecessor schemes, the proposed scheme stands out as a more apt user authentication method for common storage devices. We have also presented a formal proof of security of the proposed scheme based on the logic proposed by Burrows, Abadi and Needham (BAN logic). Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Two-factor user authentication scheme allows a user to use a smart card and a password to achieve mutual authentication and establish a session key between a server and a user. In 2012, Chen et al. showed that the scheme of Sood et al. does not achieve mutual authentication and is vulnerable to off-line password guessing and smart card stolen attacks. They also found that another scheme proposed by Song is vulnerable to similar off-line password guessing and smart card stolen attacks. They further proposed an improved scheme. In this paper, we first show that the improved scheme of Chen et al. still suffers from off-line password guessing and smart card stolen attacks, does not support perfect forward secrecy, and lacks the fairness of session key establishment. We then propose a new security-enhanced scheme and show its security and authentication using the formal verification tool ProVerif, which is based on applied pi calculus. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper focuses on noncoherent detection scheme for multiple-input multiple-output two-way relay channel network with two two-antennas source nodes and one single-antenna relay node. An orthogonal differential space-time network coding (ODSTNC) scheme based on relay detection and forward protocol is proposed. The proposed scheme combines space-time coding with network coding, and the differential modulation and detection are used in both multiple access stage and broadcast stage. The multiple-symbol differential detection is employed at the relay. The maximum likelihood decision and its low-complexity sphere decoding decision are given. The upper and lower bounds on the average symbol error probability for this system under differential binary phase shift keying (DBPSK) are derived, and a diversity order of 2 is confirmed to be achieved. The simulation results show that the ODSTNC scheme has good performance, and it is available for the applications of far distance signal transmission between two terminals where channel state information is unknown. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Though the introduction of the new 4th Generation mobile access technologies promises to satisfy the increasing bandwidth demand of the end-users, it poses in parallel the need for novel resource management approaches at the side of the base station. To this end, schemes that try to predict the forthcoming bandwidth demand using supervised learning methods have been proposed in the literature. However, there are still open issues concerning the training phase of such methods. In the current work, the authors propose a novel scheme that dynamically selects a proper training set for artificial neural network prediction models, based on the statistical characteristics of the collected data. It is demonstrated that an initial statistical processing of the collected data and the subsequent selection of the training set can efficiently improve the performance of the prediction model. Finally, the proposed scheme is validated using network traffic collected by real, fully operational base stations. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

An indoor localization technology is increasingly critical as location-aware applications evolve. Researchers have proposed several indoor localization technologies. Because most of the proposed indoor localization technologies simply involve using the received signal strength indicator value of radio-frequency identification (RFID) for indoor localization, radio-frequency interference, and environmental factors often limit the accuracy of localization results. Therefore, this study proposes an accurate RFID localization based on the neural network (ARL-N2), a passive RFID indoor localization scheme for identifying tag positions in a room, combining a location identification based on dynamic active RFID calibration algorithm with a backpropagation neural network (BPN). The proposed scheme composed of two phases: in the training phase, an appropriate BPN architecture is constructed using the training data derived from the coordinates of reference tags and the coordinates obtained using the localization algorithm. By contrast, the online phase involves calculating the tracking tag coordinates and using these values as BPN inputs, thereby enhancing the estimated location. A performance evaluation of the ARL-N2 schemes confirms its high localization accuracy. The proposed method can be used to locate critical objects in difficult-to-find areas by creating minimal errors and applying and economical technique. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Anonymous receiver encryption is an important cryptographic primitive. It allows a sender to use the public identities of multiple receivers to encrypt messages so that only the authorized receivers or a privileged set of users can decrypt the messages, and the identities of the receivers are not revealed. Recently, Zhang et al. proposed a novel anonymous multi-receiver encryption scheme and claimed that their scheme could realize the receiver's identity privacy. Unfortunately, in this paper, we pointed out that the scheme by Zhang et al. did not achieve the anonymity of the receiver identity after analyzing the security of the scheme. At the same time, we give the corresponding attack. After analyzing the reason to produce such attacks, a novel anonymous multi-receiver encryption scheme is given to achieve the anonymity of the receiver's identities. And we formally prove that the proposed scheme is semantically secure for confidentiality and receiver identities' anonymity. The security of the scheme is based on decisional bilinear Diffie-Hellman problem. Compared with the scheme by Zhang et al., Fan et al., Wang et al., and Chien et al., our scheme is shown to be better performance and robust security. To the best of our knowledge, our scheme is most efficient in terms of computational cost and communication overhead. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

As users move around in wireless local area networks, they associate with different access points in succession to maintain connectivity. Without the carefully designed association control policy, it may lead to frequent handoffs and imbalanced load, which can potentially incur unacceptable delays and poor throughput. While existing works to this issue mainly focus on minimizing the number of handoffs over time, in this paper, we propose a new association control scheme with the goal of reducing the frequency of handoffs and balancing load among access points. The defined problem, handoff optimization and load balancing (HOLB,) is mathematically described as a minimum-maximum programming. Since the HOLB problem is a nondeterministic polynomial-time hard, two constant approximation algorithms are presented to resolve it. First, we propose an α-approximation( [ABSTRACT FROM AUTHOR]

Proxy signature allows an original signer to delegate her signing capability to a proxy signer. Recently, to provide lower communication cost and stronger security, Zhang and Yu proposed a short proxy signature scheme in the standard model. They claimed that their scheme simultaneously achieves several merits including strong unforgeability, shorter signature length, and lower computational cost. However, we show that Zhang and Yu's scheme is not as secure as they claimed, because anyone can obtain the actual signing key of proxy signer from three valid proxy signatures. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Multi-proxy signature is one of the useful primitives of the proxy signature. Till now, only a few schemes of identity-based multi-proxy signature (IBMPS) have been proposed using bilinear pairings, but most of the schemes are insecure or lack a formal security proof. Because of the important application of IBMPS scheme in distributed systems, grid computing, and so on, construction of an efficient and provable-secure IBMPS scheme is desired. In 2005, Li & Chen proposed an IBMPS scheme from bilinear pairings, but their paper lacks a formal model and proof of the security. Further, in 2009, Cao & Cao presented an IBMPS scheme with the first formal security model for it. Unfortunately, their scheme is not secure against the Xiong et al's attack. In this paper, first, we present an IBMPS scheme, then we formalize a security model for the IBMPS schemes and prove that the presented scheme is existential unforgeable against adaptive chosen message and identity attack in the random oracle model under the computational Diffie-Hellman assumption. Also, our scheme is not vulnerable for the Xiong et al's attack. The presented scheme is more efficient in the sense of computation and operation time than the existing IBMPS schemes. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper, we study joint resource allocation and adaptive modulation in single-carrier frequency-division multiple access systems, which is adopted as the multiple access scheme for the uplink in the 3GPP Long Term Evolution standard. We formulate an adaptive modulation and sum-cost minimization (JAMSCmin) problem. Unlike orthogonal frequency-division multiple access, in addition to the restriction of allocating a subchannel to one user at most, the multiple subchannels allocated to a user in single-carrier frequency-division multiple access systems should be consecutive as well. This renders the resource allocation problem prohibitively difficult and the standard optimization tools (e.g., Lagrange dual approach widely used for orthogonal frequency-division multiple access, etc.) cannot help towards its optimal solution. We propose a novel optimization framework for the solution of this problem that is inspired from the recently developed canonical duality theory. We first formulate the optimization problem as binary-integer programming (BIP) problem and then transform this BIP problem into continuous space canonical dual problem that is the concave maximization problem. Based on the solution of the canonical dual problem, we derive joint resource allocation and adaptive modulation algorithm, which has polynomial time complexity. We provide conditions under which the proposed algorithm is optimal. We compare the proposed algorithm with the existing algorithms in the literature. The results show a tremendous performance gain. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper proposes an ideal rateless codes model to comprehensively describe rateless codes and extends the definition of systematic linear block code to generalized systematic code. Under the proposed model, average delay, maximum disorder, and uniformity recovery entropy are introduced as performance indices to design efficient rateless codes. A novel coding scheme based on two-stage encoding and forward equal probability is proposed to optimize the proposed indices. In the first stage, the first k symbols are encoded, aiming to improve the performance of order recovery, uniformity recovery, and transmission efficiency as much as possible. In the second stage, the remaining infinite symbols are encoded, where the symbols with high degree are used to compensate the symbols loss in the first stage. Simulation results show that the proposed scheme can achieve generalized systematic rateless codes with high probability and also has less average delay and maximum disorder, better capacity achievability, and uniformity recovery performance than Luby trasform (LT) codes and rateless coded symbol sorting algorithm. Besides, the proposed scheme has the aforementioned advantages compared with expending window fountain codes except for uniformity recovery and maximum disorder performance when the erasure rate is higher than about 0.25. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]