An approximate model called metamodel or surrogate model is a mathematical model that numerically approximates response of a system during an engineering simulation process or test. The introduction of a metamodel makes it possible to express response defined in the design problem as a simple mathematical function of design variables. A metamodel can be built with response surface method (RSM), kriging, neural network, radial basis function, and so on. Each method has its advantages and disadvantages. A combined metamodel called hybrid model, ensemble model, or multiple surrogates has been developed to maximize each metamodel's strength. The hybrid model of this research includes RSM and kriging. Besides, a strategy to refine the hybrid metamodel is implemented by reducing design space. In this process, information related to Hessian is utilized for an unconstrained optimization problem, on the contrary feasibility for a constrained optimization problem. This research presents a new hybrid metamodel‐based optimization strategy called refined hybrid metamodel. Five mathematical test problems, two‐bar design, spring design, and propeller shaft design problems are solved with the suggested method, verifying its usefulness. Most of the optimal results with the proposed method are closer to exact solutions with smaller function evaluations than existing methods.

In wireless sensor network, two scenarios are combined which involve either short-range or long-range communications. IEEE 802.15.4g and IEEE 802.11 are considered in machine to machine environments, because they can utilize the identical frequency band. The performances of the physical modes of the IEEE 802.15.4g and the IEEE 802.11 standards are presented and are compared in terms of the bit error rate and throughput when additive white Gaussian noise, shadowing, and multipath fading channels are assumed. The numerical results show that IEEE 802.11 is more vulnerable than IEEE 802.15.4g in the shadowing channels when compared to the AWGN channel. For the multipath fading channel, IEEE 802.11 performs better than IEEE 802.15.4g. It is necessary that adequate communication is configured depending on the required performance characteristics, / 0 , service coverage, and channel environments.

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