A secure network coding based modify-and-forward scheme for cooperative wireless relay networks

This paper investigates the security at the physical layer of cooperative relay communications. Inspired by the principle of physical-layer network coding (PNC), we propose a new secure relaying scheme, namely secure PNC-based modify-and-forward (SPMF). In the proposed scheme, the relay node linearly combines the decoded data from the source node with an encrypted key before conveying the mixed data to the destination node. As both the linear PNC operation and encrypted key at the relay are unknown to the eavesdropper, the SPMF scheme provides a double security level in the system. Particularly, taking into account the practical scenario of the imperfect knowledge shared between the relay and destination, the secrecy outage probability (SOP) of the proposed SPMF scheme is analysed and evaluated in comparison with modify-and-forward, cooperative jamming, decode-and-forward and direct transmission schemes. The proposed scheme is shown to achieve a performance improvement of up to 3 dB when compared to the conventional schemes under imperfect knowledge of shared information between the nodes

Beamforming in coexisting wireless systems with uncertain channel state information

This paper considers an underlay access strategy for coexisting wireless networks where the secondary system utilizes the primary spectrum to serve its users. We focus on the practical cases where there is uncertainty in the estimation of channel state information (CSI). Here the throughput performance of each system is limited by the interference imposed by the other, resulting in conflicting objectives. We first analyze the fundamental tradeoff between the tolerance interference level at the primary system and the total achievable throughput of the secondary users. We then introduce a beamforming design problem as a multiobjective optimization to minimize the interference imposed on each of the primary users while maximizing the intended signal received at every secondary user, taking into account the CSI uncertainty. We then map the proposed optimization problem to a robust counterpart under the maximum CSI estimation error. The robust counterpart is then transformed into a standard convex semi-definite programming. Simulation results confirm the effectiveness of the proposed scheme against various levels of CSI estimation error. We further show that in the proposed approach, the trade-off in the two systems modelled by Pareto frontier can be engineered by adjusting system parameters. For instance, the simulations show that at the primary system interference thresholds of -10 dBm (-5 dBm) by increasing number of antennas from 4 to 12, the secondary system throughput is increased by 3.3 bits/s/channel-use (5.3 bits/s/channel-use

Parameter optimization of tuned mass damper for three-degree-of-freedom vibration systems

There are problems in mechanical, structural and aerospace engineering that can be formulated as Nonlinear Programming. In this paper, the problem of parameters optimization of tuned mass damper for three-degree-of-freedom vibration systems is investigated using sequential quadratic programming method. The objective is to minimize the extreme vibration amplitude of vibration models. It is shown that the constrained formulation, that includes lower and upper bounds on the updating parameters in the form of inequality constraints, is important for obtaining a correct updated model

Mechanism of Inverse Magnetoresistance in High-TaT_{a} Annealed MnNi/Co/Ag(Cu)/Py Spin Valves

The magnetic transport properties -- magnetoresistive (MR) effects of MnNi/Co/Ag(Cu)/\break Py pinned spin valve structures (SVs) prepared by rf sputtering method and annealed at $T_{a} = 100$°C - 500°C for 30 minutes in high vacuum ($\sim 10^{ - 5}$ torr) are investigated. The received results show a change in the observed MR behaviors from a normal giant magnetoresistance effect to an inverse magnetoresistance effect after annealing at high temperatures, 300°C and 400°C, for these SVs. The origin and mechanism of the IMR behavior are analyzed and discussed. These results will suggest an ability to manufacture SV devices used the IMR effect for enhancing the application capacities for SV-sensor systems

APPLICATION OF THE FLUX BENDING EFFECT IN AN ACTIVE FLUX-GUIDE FOR LOW-NOISE PLANAR VECTOR TMR MAGNETIC SENSORS

A concept of a planar vector magnetic sensor comprising in-plane tunnel magnetoresistive (TMR) sensors and an active flux-guide (AFG) was introduced in this work. The AFG redirected the magnetic flux at high-frequency benefiting the vertical detection capability and lessening the noise of the TMR at low-frequency measurement. The vertical sensitivity of 19.5 V/T was almost the similar the in-plane sensitivity of 19.2 V/T. In addition, the 1-Hz field noise was suppressed from 6 nT/sqrt-Hz down to 0.4 nT/sqrt-Hz. The flux bending effect of the AFG was also verified by the angular measurements with the deflected angle was found to be about 50º. It revealed that the vertical field component was certainly detected by the in-plane sensor and the proposed method was a feasible technique for the development of the low-noise planar three-dimensional magnetic sensor