Search

A compact MIMO antenna with enhanced isolation and the ability to switch the frequency bands is an attractive candidate for the current multifunctional high-speed portable wireless devices. To achieve this objective, a simple and novel compact dual-mode 4-port MIMO configuration for WiMAX and WLAN standards has been introduced in this work. The compactness of the MIMO geometry (34 mm × 34 mm) is due to compact switchable curve-shaped monopoles arranged closely over a loop-shaped continuous ground plane. The ground plane is defected by etching open-ended slots to suppress the surface current flow between the elements. As antenna elements switch between mode-1 (WiMAX band) and mode-2 (WLAN band), the DGS slots are also switchable to enhance isolation across both bands. The switchable DGS slots function as bandstop filters and thus isolate the elements by 40 and 41 dB in the accomplished frequency bands. The intented MIMO antenna reports a − 10 dB return loss bandwidths of 400 MHz (3.3–3.7 GHz) and 1100 MHz (4.75–5.85 GHz) in mode-1 and mode-2, respectively. The diversity metrics of envelope correlation coefficient < 0.002, diversity gain ≈ 10 dB, total active reflection coefficient < − 10 dB, and channel capacity loss < 0.4 b/s/Hz, ensure excellent diversity/MIMO performance. The optimized 4-port MIMO configuration is fabricated, and measured results are compared with the simulated ones to validate the introduced technique. The MIMO antenna's compact form factor and excellent antenna/diversity characteristics confirm its potentiality for use in portable multifunctional wireless devices. [ABSTRACT FROM AUTHOR]

In the wireless cellular network, location management is one of the intricate dynamic issues that expend the available limited wireless resources in order to guarantee for delivering a call to the mobile device. Towards enhancing the Quality of Service and reducing the dilemma of location management, an improved location update scheme has been proposed in this paper to capture the daily behavioral pattern of the mobile users. Here a profile based LU scheme has been developed according to the mobility pattern of the individual users in a cellular network. Especially, mobile phone data is recorded in a Call Data Record (CDR) data base containing the spatial–temporal information of the millions of anonymized users for consecutive 2 months. In this paper, the proposed profile based LU technique takes into consideration of the individual user movement to optimize the location update characteristics in order to minimize the signaling cost of mobile network. The proposed algorithm shows an improvement of 17% in terms of bandwidth compared to the conventional technique. The use of CDR data for profiling the users, the mathematical formulation which has not yet been used by the other researchers and validation of the algorithm based on actual user data rather than theoretically predicted data are the novelty of this work. [ABSTRACT FROM AUTHOR]

Inverse artificial neural network (IANN) modeling is used to synthesize a metamaterial unit cell. The ANN approach is best suited to capture the mapping relation between inputs and outputs given a training dataset. In this work, the IANN method is applied to synthesize a metamaterial unit cell for which the inverse model is ill conditioned. A perfectly trained ANN is capable of generating the input data for a desired set of outputs for a fixed set of synaptic weights. In this work, a prior knowledge based input with difference (PKI-D) method is used to perform the inverse mapping. Although the split-ring resonator (SRR) is widely used to realize metamaterials for different applications, no closed-form formula is available to determine its design parameters. The goal of this work is to determine the dimensions of a SRR for a desired frequency and permeability value. The work is carried out in two phases. In the first phase, the inverse model is developed to estimate a single design parameter, then in the second phase, a multiple-parameter estimation model is developed. The average error for the PKI-D model is found to be 0.059. Backpropagation is used to train (solve) the input vector for unknown parameters. [ABSTRACT FROM AUTHOR]

We propose a computer-aided design (CAD) model for synthesis of the unit cell of a metamaterial with the aim of improving the performance of a microstrip antenna designed for use in a traffic collision avoidance system (TCAS). Synthesis of electromagnetic (EM) devices generally requires great computational resources because of their inherent properties, e.g., being complex, nonconvex, and continuous. However, techniques based on soft computing are much more convenient for problems related to such EM devices. In this work, CAD models based on a genetic algorithm and differential evolution are first developed to synthesize a rectangular patch antenna with a microstrip feed line. Transmission line method (TLM) analysis is then used to develop the proposed CAD model for a microstrip patch antenna. In the proposed CAD models, the input parameters are the design/operating frequency, the thickness of the substrate used, and the permeability (μ ) of the substrate material, whereas the outputs are the dimensions of the structural design of the radiating patch and the microstrip feed line. The CST MWS EM tool is also used to design the antenna and validate the parameters of the synthesized antenna. A comparison between the two CAD models is presented. After the successful design of the CAD model for the microstrip antenna, the metamaterial synthesis technique is applied. Then, a metamaterial lens is designed with the help of the proposed CAD model and used to improve the performance of an antenna for use in TCAS applications. A comparison of the performance improvement is given in tabular form towards the end of the paper, including both the simulated and measured results. [ABSTRACT FROM AUTHOR]

A new technique for the calculation of the permeability of an Omega unit cell is presented. In the proposed method, neuro-space mapping is used to transform the Omega unit cell structure to a split-ring resonator (SRR) structure using a functional link artificial neural network (FLANN), taking the dimensions of the Omega unit cell as the inputs and giving the dimensions of the equivalent SRR as the output. The permeability of the Omega-shaped SRR is then calculated using a formula derived by the Lorentz method with these mapped dimensions. The functional linked artificial neural network-space mapping technique is then used to find an SRR equivalent to the Omega unit cell. In the SM part, the FLANN is used as the coarse model and the CST engine as the fine model. The permeability of the Omega unit cell and the SRR match well over the range of 3.5 GHz to 6 GHz when using a learning rate of 0.002 and a tolerance value < 0.05. [ABSTRACT FROM AUTHOR]