Critical transmission ranges (or radii) in wireless ad-hoc and sensor networks have been extensively investigated for various performance metrics such as connectivity, coverage, power assignment and energy consumption. However, the regions on which the networks are distributed are typically either squares or disks in existing works, which seriously limits the usage in applications. In this article, we consider a convex region (i.e., a generalisation of squares and disks) on which wireless nodes are uniformly distributed. We have investigated two types of critical transmission radii, defined in terms of$k-$connectivity and the minimum vertex degree, respectively, and have also established their precise asymptotic distributions. These make the previous results obtained under the circumstance of squares or disks special cases of this work. More importantly, our results reveal how the region shape impacts the critical transmission ranges: it is the length of the boundary of the (fixed-area) region that completely determines the transmission ranges. Furthermore, by isodiametric inequality, the smallest critical transmission ranges are achieved when regions are disks only.

Commercialized 5G technology will provide reliable and efficient connectivity of motor vehicles that could support the dissemination of information under an intelligent transportation system. However, such service still suffers from risks or threats due to malicious content producers. The traditional public key infrastructure (PKI) cannot restrain such untrusted but legitimate publishers. Therefore, a trust-based service management mechanism is required to secure information dissemination. The issue of how to achieve a trust management model becomes a key problem in the situation. This paper proposes a novel prototype of the decentralized trust management system (DTMS) based on blockchain technologies. Compared with the conventional and centralized trust management system, DTMS adopts a decentralized consensus-based trust evaluation model and a blockchain-based trust storage system, which provide a transparent evaluation procedure and irreversible storage of trust credits. Moreover, the proposed trust model improves blockchain efficiency by only allowing trusted nodes participating in the validation and consensus process. Additionally, the designed system creatively applies a trusted execution environment (TEE) to secure the trust evaluation process together with an incentive model that is used to stimulate more participation and penalize malicious behaviours. Finally, to evaluate our new design prototype, both numerical analysis and practical experiments are implemented for performance evaluation.

Infrastructure as a Service (IaaS) is a service mode of cloud, which provides Virtual Machines (VMs) to customers. With the increasingly fierce competition in market, cloud providers pay more attention to Quality of service (Qos). As the practical measurement costs a large amount of resource, deriving performance metrics from analytical model is a good choice. Recently, Stochastic Petri Net (SPN) has been used to construct analytical models, but they lack the ability to exhibit hierarchies of IaaS cloud. Compare to SPN, Performance Evaluation Process Algebra (PEPA) has the feature of compositionality, which imports the hierarchial strategy into the semantics. So, PEPA models of IaaS cloud are closed to actual architecture and can be more easily accepted by engineers. This paper provides a PEPA model of IaaS cloud and gives some numerical results.

As product of the combination of Internet technology and sensor network, Internet of things (IoT) greatly facilitates the mutual interaction of the information world and physical world. Furthermore, with the rapid development of modern transportation systems, as a typical successful application of IoT in the real life, intelligent traffic system (ITS) has a great significance on management of the traffic information and transport infrastructure. Therefore, in order to achieve the efficient use of transportation resources, it is particularly important to evaluate and analyze the performance of ITS. In this paper, an advanced high level formalization — Performance Evaluation Process algebra (PEPA), a kind of stochastic process algebra (SPA), is adopted to model the process of real-time traffic status query in ITS. Meanwhile, by using fluid approximation approach to analyze performance of the model and then the performance parameters of the system in practical application can be achieved accurately.

We study the secrecy outage performance of a dual-hop multiple relay decode-and-forward (DF) cognitive relay network under the interference constraints in this paper, where all relays and the destination are equipped with K antennas. All channels we considered in the proposed system experience the Nakagami-m fading, and the selection combining technique is employed at the antennas of all the main link receiving nodes. An eavesdropper with single antenna could wiretap the information at each hop, and the transmit power at the main link is limited by the interference constraints of the primary user receiver. We derive the exact system secrecy outage probability to evaluate the system secrecy performance, and the Monte-Carlo simulation results are also given to validate the veracity of the numerical analytical results.

In this paper, we investigate the secrecy outage probability in a dual-hop decode-and-forward (DF) secondary cognitive radio network, which is equipped with one source, one destination, multiple eavesdroppers (EAVs) and multirelay. The direct links from the source to the destination and the EAVs are considered because of the moderate shadowing environment. All channels experience the Rayleigh fading. To analyse the system performance, we consider the minimum relay selection, where the most annoying eavesdropper is selected first according to the maximum signal-to-noise ratio (SNR) of the direct links from the source to the EAVs. Then, the best relay is selected according to the minimum SNR from the selected EAV to relays. The selection combining (SC) technique is also employed in our system. The circumstance that the relays can or not deliver the information is considered. We evaluate the system performance through the closed- form accurate and asymptotic secrecy outage probability. The simulation results are also derived by Monte Carlo Simulations to verify the numerical results.

In this paper, we study the physical-layer security of amplify-and-forward relaying networks under a spectrum-sharing mechanism over independent non-identically distributed Rayleigh fading channels. Relay selection is presented to select the best relay, which can guarantee the security performance by minimizing the received signal-to-noise ratio at the eavesdropper. In order to guarantee the quality-of-service of primary networks, both the maximum tolerable peak interference power at the primary users and maximum allowable transmit power at secondary users are considered. Closed-form lower and upper bounds as well as asymptotic expressions for the intercept outage probability (OP) are derived. From the asymptotic expressions, it can be observed that the diversity order of intercept OP equals to two. Our analysis results are validated by Monte-Carlo simulation.

This paper investigates a massive MIMO multi-pair two-way relay system, where K-pair users exchange information within communication pair, with the help of a shared amplify- and-forward (AF) relay station (RS). Large scale antenna array is equipped at the RS and each user has a signal antenna. The RS adopts the zero-forcing reception/zero-forcing transmission (ZFR/ZFT) beamforming. The imperfect channel state information (CSI) is considered, and the impact of channel estimation errors on system performances is investigated. Based on two power scaling schemes, we obtain the asymptotic spectral efficiency and asymptotic energy efficiency of the considered system. Our results reveal that when the number of RS antennas grows without bound, the small-fading can be averaged out; the additional noise and residual self-interference generated by channel estimation errors will completely disappear; and inter-pair interference will also vanish. Consequently, the simulation results will be confirmed by Monte-Carlo simulation method.

A multi-pair two-way amplify-and-forward relaying system is considered in this paper, where the K-pair users exchange information within pairs, with the help of a shared relay station. Each user is equipped with a single antenna while the relay station is equipped with a very large number of antennas N, where N≫2K. The impact of imperfect channel state information (CSI) due to the channel estimation errors on spectral efficiency (SE) and energy efficiency (EE) is investigated. Asymptotic expressions for EE and SE are obtained in this paper for three power-scaling schemes when maximum-ratio combining/maximum-ratio transmission (MRC/MRT) is adopted. Our analytical results reveal that when the number of relay station antennas N→∞, the effect of the small-scale fading can be averaged out; the residual self-interference and additional noise generated by channel estimation errors will completely vanish, and the inter-pair interference will disappear. However, the imperfect CSI deteriorates EE and SE. When there are no estimation errors, our analytical results reduce to the existing results. Simulation results confirm the validity of our analysis.

A novel quantization watermarking method is presented in this paper, which is developed following the established feature modulation watermarking model. In this method, a feature signal is obtained by computing the normalized correlation (NC) between the host signal and a random signal. Information modulation is carried out on the generated NC by selecting a codeword from the codebook associated with the embedded information. In a simple case, the structured codebooks are designed using uniform quantizers for modulation. The watermarked signal is produced to provide the modulated NC in the sense of minimizing the embedding distortion. The performance of the NC-based quantization modulation (NCQM) is analytically investigated, in terms of the embedding distortion and the decoding error probability in the presence of valumetric scaling and additive noise attacks. Numerical simulations on artificial signals confirm the validity of our analyses and exhibit the performance advantage of NCQM over other modulation techniques. The proposed method is also simulated on real images by using the wavelet-based implementations, where the host signal is constructed by the detail coefficients of wavelet decomposition at the third level and transformed into the NC feature signal for the information modulation. Experimental results show that the proposed NCQM not only achieves the improved watermark imperceptibility and a higher embedding capacity in high-noise regimes, but also is more robust to a wide range of attacks, e.g., valumetric scaling, Gaussian filtering, additive noise, Gamma correction, and Gray-level transformations, as compared with the state-of-the-art watermarking methods.