Secure computation offloading assisted by intelligent reflection surface for mobile edge computing network

As an novel paradigm, computation offloading in the mobile edge computing (MEC) system can effectively support the resource-intensive applications for the mobile devices (MD) equipped with limited computing capability. However, the hostile radio transmission and data leakage during the offloading process may erode the MEC system’s potential. To tackle these hindrances, we investigate an IRS-assisted secure MEC system with eavesdroppers, where the intelligent reflecting surface (IRS) is deployed to enhance the communication between the MD and the AP equipped with edge servers and the malicious eavesdroppers may attack the wireless data offloaded by MD. The MD opt for offloading part of the tasks to the edge server for execution to support the computation-intensive applications. Moreover, the relevant latency minimization problem is formulated by optimizing the offloading ratio, the allocation of edge server computing capability, the multiple-user-detection (MUD) matrix and the IRS phase shift parameters, subject to the constraints of edge computation resource and practical IRS phase shifts. Then, the original problem is decouple into two subproblem, and the computing and communication subproblems are alternatively optimized by block coordinate descent (BCD) method with low complexity. Finally, simulation results demonstrate that the proposed scheme can significantly enhance the performance of secure offloading in the MEC system.     

The Setting Behaviour of α‐ and β‐CaSO4 · 0,5 H2O as a Function of Crystal Structure and Morphology

Calcium sulphate subhydrates (CaSO₄ · x H₂O, 0 < x ≤ 0.8) have a honeycomb‐shaped channel structure. The symmetry is either trigonal or a slight deviation thereof. Due to insufficient diffraction data and the high pseudosymmetry of the structure, it is not possible at this point to determine with certainty the specific arrangement of the water molecules in the channels. When the Fourier transformation method is used to calculate the growth form of the hemihydrate (x = 0.5), the calculated crystal form corresponds to the observed form only when the trigonal structural symmetry is largely retained. During dehydration of gypsum or, conversely, during the setting process of hemihydrate, heteroepitaxial growths of hemihydrate are observed on gypsum, or gypsum is grown heteroepitaxially on hemihydrate. The (100) faces of the hemihydrate and (010) of gypsum for the most part run parallel. Using diffraction and spectroscopic methods, it can be shown that a structural difference exists between α‐ and β‐hemihydrates, and that this difference probably accounts for the different setting behaviours. It is in this context that the presence of oxonium ions, particularly in β‐hemihydrate, found in NMR experiments is of interest. Textural studies indicated that the arrangement of gypsum crystals found in hardened gypsum is determined by the hemihydrate.