A new methodology that facilitates the control of the inherent dispersion error in the case of higher order finite-difference time-domain (FDTD) schemes is presented in this paper. The basic idea is to define suitable algebraic expressions that reflect numerical inaccuracies reliably. Then, finite-difference operators are determined via the minimization of the error estimators at selected frequencies. In order to apply this procedure, an error expansion in terms of cylindrical harmonic functions is performed, which also enables accuracy enhancement for all propagation angles. The design process produces a set of two-dimensional (2-D) FDTD algorithms with optimized frequency response. Contrary to conventional methodologies, the proposed techniques adjust their reliability range according to the requirements of the examined problem and can be, therefore, more efficient in computationally demanding simulations.

A site-specific numerical model, based on the finite-difference time-domain method, is developed in this paper for the indoor radio channel. The scenario of interest is concerned with wave propagation in a typical office environment, for which several simulations are performed considering different placements of the transmitting antenna. Both the 2- and 5-GHz bands are examined, where contemporary wireless local area networks operate. Important channel characteristics are evaluated via the estimation of received power levels, as well as the examination of small-scale fading and time dispersion

The latest new generation passive optical network (NG-PON) standard, known as 10-gigabit-capable passive optical network (XG-PON), enables a very promising architecture that offers 10 Gbps nominal data delivery ratio in the downstream direction. The optical line terminal (OLT) is located within the CO and constitutes the main decision-making tank of the PON. OLT applies a dynamic bandwidth allocation (DBA) scheme for coordinating the transmission opportunities, especially in the upstream direction. According to the standard, a differential fibre distance of 40 km, between ONUs and OLT, is allowed. This outspread deployment implies high propagation delays which should be taken into account of designing the bandwidth allocation. This work is focused on proposing a cognitive DBA scheme which is capable of forecasting the additional bandwidth, which arrives in ONUs, during the transmission coordination between OLT and ONUs. The k-nearest neighbors (k-NN) algorithm is applied for forecasting the additional bandwidth requests of each ONU. In addition, the adopted algorithm is enhanced with an adaptive learning-based method which efficiently selects the most appropriate k value based on the traffic dynamics.

A variety of electromagnetic (EM) problems present a high level of uncertainty in several aspects, which is interpreted as a variability in specific input variables. In many examples, certain stochastic parameters may exhibit a low or even a negligible contribution to the outputs of interest. However, neglecting a high number of random variables may result in computational errors of the examined quantities in a given problem. For this reason, we propose a hybrid algorithm, which is based on the combination of the polynomial-chaos (PC) approach and the method of moments (MoM). A dimensionality reduction of the PC technique is performed by considering the trivial random inputs as deterministic. The computational errors in the output values are mitigated through the utilization of the MoM. The numerical results, which present comparisons with the traditional PC approach, the MoM and the Monte Carlo technique, prove the validity of the proposed scheme.

The development of an accurate convolutional perfectly matched layer for the efficient termination of infinite graphene structures is introduced in this paper. Initially, the popular 2-D material receives the appropriate theoretical analysis, which reveals the necessity of a flexible terminating condition that can enhance the performance of existing absorbing schemes and offer sufficient truncation rates for the graphene's strongly confined surface waves. The consistency and behavior of the novel technique are substantiated via comprehensive comparisons with setups truncated by conventional absorbing boundary conditions. Finally, a graphene microribbon waveguide is addressed to indicate the capabilities of featured algorithm in complex structures.