Achieving Covert Wireless Communications Using a Full-Duplex Receiver

Covert communications hide the transmission of a message from a watchful adversary while ensuring a certain decoding performance at the receiver. In this work, a wireless communication system under fading channels is considered where covertness is achieved by using a full-duplex (FD) receiver. More precisely, the receiver of covert information generates artificial noise with a varying power causing uncertainty at the adversary, Willie, regarding the statistics of the received signals. Given that Willie's optimal detector is a threshold test on the received power, we derive a closed-form expression for the optimal detection performance of Willie averaged over the fading channel realizations. Furthermore, we provide guidelines for the optimal choice of artificial noise power range, and the optimal transmission probability of covert information to maximize the detection errors at Willie. Our analysis shows that the transmission of artificial noise, although causes self-interference, provides the opportunity of achieving covertness but its transmit power levels need to be managed carefully. We also demonstrate that the prior transmission probability of 0.5 is not always the best choice for achieving the maximum possible covertness, when the covert transmission probability and artificial noise power can be jointly optimized.Comment: 13 pages, 11 figures, Accepted for publication in IEEE Transactions on Wireless Communication

Band structures of II-VI semiconductors using Gaussian basis functions with separable ab initio pseudopotentials: Application to prediction of band offsets

We describe the implementation of a separable pseudopotential into the dual space approach for ab initio density-functional calculations using Gaussian basis functions. We apply this Gaussian dual space method (GDS/DFT) to the study of II-VI semiconductors (II=Zn, Cd, Hg; VI=S, Se, Te, Po). The results compare well with experimental data and demonstrate the general transferability of the separable pseudopotential. We also introduce a band-consistent tight-binding (BC-TB) model for calculating the bulk contributions to the valence-band offsets (VBO’s). This BC-TB approach yields good agreement with all-electron ab initio GDS/DFT results. Comparisons between BC-TB results of VBO obtained with and without p-d coupling demonstrate quantitatively the importance of d electrons and cation-d–anion-p coupling in II-VI systems. Agreement between ab initio results and experimental results is excellent

First principles studies of band offsets at heterojunctions and of surface reconstruction using Gaussian dual-space density functional theory

The use of localized Gaussian basis functions for large scale first principles density functional calculations with periodic boundary conditions (PBC) in 2 dimensions and 3 dimensions has been made possible by using a dual space approach. This new method is applied to the study of electronic properties of II–VI (II=Zn, Cd, Hg; VI=S, Se, Te, Po) and III–V (III=Al, Ga; V=As, N) semiconductors. Valence band offsets of heterojunctions are calculated including both bulk contributions and interfacial contributions. The results agree very well with available experimental data. The p(2 × 1) cation terminated surface reconstructions of CdTe and HgTe (100) are calculated using the local density approximation (LDA) with two-dimensional PBC and also using the ab initio Hartree–Fock (HF) method with a finite cluster. The LDA and HF results do not agree very well

Dynamics simulation research on load vehicle of deep submergence rescue vehicle (LV-DSRV)

Submarine accidents can cause loss of human life and economy, as well as environment damage. Also submarine rescue is difficult for the complexity of rescue process and the uncertainty of the sea state. Success of rescue process is determined by reliability and safety of rescue device. Therefore, research on related device design is rather important. The existing knowledge always supplies some empirical formulas and generates a design scheme by general design rules. The scheme plan obtained may not be a good one due to simplicity of mechanical calculation analysis and particularity of design requirements. To improve design safety and reliability of shipborne device on submarine rescue system, dynamics simulation model of LV-DSRV based on sea state excitation was created in this paper. Wave excitation input at sea state 5 and 8 was considered as the extreme marine working conditions. Kinetic property of LV-DSRV was calculated making use of virtual prototype technology through ADAMS software, and mechanical characteristics of key parts were also analyzed. Optimization strategy was proposed and verified by increasing the number of horizontal wheels and adding gap between horizontal wheels and the track, providing with a case study for similar marine special mechanism design