Correction: Green communication for cognitive radio networks based on game and utility-pricing theories.

[This corrects the article DOI: 10.1371/journal.pone.0235953.]

Design and characterization of a compact single-layer multibeam array antenna using an 8×8 Butler matrix for 5G base station applications

A multibeam array antenna employing a Butler matrix is a promising solution for fifth generation (5G) base stations. Due to inaccurate phase differences between output ports in the Butler matrix, the radiation characteristics could show incorrect main beam directions. In addition, the literature has also reported the issue of high amplitude imbalance in the Butler matrix. This paper presents a single-layer multibeam array antenna fed by an 8×8 Butler matrix operating at 28 GHz for 5G base station applications-a more cost-effective solution for large-scale production. The Butler matrix consists of twelve quadrature hybrids, sixteen crossovers, and eight phase shifters. This circuit was integrated with eight antenna elements at the output ports of the Butler matrix. The proposed multibeam array antenna was fabricated using a low dielectric constant and a low loss tangent substrate. The dimensions of the multibeam array antenna were 88×106×0.254 mm3 . The Butler matrix achieved low insertion losses and low phase error with average values of 2.5 dB and less than ±10 ° at 28 GHz, respectively. The measured return losses were less than -10 dB at 28 GHz. The measured radiation patterns were obtained and eight main beams were pointed at ±6 ° , ±18 ° , ±30 ° , and ±44 ° with measured gains between 9 dBi and 14 dBi

Design of quadrifilar helix antenna with parasitic element and channel characterisation for small cell network.

Small cell networks (SCN) have emerged as a viable solution for improving the spectral efficiency in order to satisfy the growing demand for high data rate mobile network. SCNs consist of multiple short range base station (BS) to cover small areas. The BS is typically known as femtocell BS. Polarisation mismatch loss between the BS and mobile station (MS), and inter-cell interference between BSs can be the performance limiting factors for SCN deployment in non-cluttered open space. This work covers the antenna design for the femtocell BS and channel characterisations within a SCN environment. Two designs for quadrifilar helix antenna (QHA) gain improvement using parasitic loop have been proposed. The designs are based on parasitic meandered loop (PML) and parasitic quadrifilar helix loop (PQHL). These parasitic loops are able to improve the boresight gain by up to 1.8 dB. Another design that is evaluated in this work is the switched parasitic QHA (SPQHA). By using parasitic elements at the side of the QHA, it gives a low complexity beam steering capability with up to 35° beam tilt. This feature is useful in cooperative SCNs to improve coverage and minimise interference. The performance of BS antennas with different polarisations against mobile station (MS) under random human handling in a real environment has been evaluated. Results show that polarisation mismatch between the BS and MS can be severe due to lack of signal depolarisation in short range communication. Results also show that a circular polarised BS antenna can be a good compromise to minimise polarisation mismatch loss in a SCN environment. A second field measurement has been conducted to evaluate the performance of the SPQHA in a real environment. Results have shown that SPQHAs are able to provide a high diversity gain. With local parasitic switching on one BS, 8 dB diversity gain can be achieved. With global parasitic switching on two BSs, 13 dB diversity gain is obtained. Furthermore, MIMO antenna selection using SPQHAs has also been shown to be able to match the performance of a 8-elements QHA-based MIMO setup. As a result, MIMO SPQHA can reduce the number of RF-chains required as compared to a full MIMO setup

No-reference quality assessment for image-based assessment of economically important tropical woods.

Image Quality Assessment (IQA) is essential for the accuracy of systems for automatic recognition of tree species for wood samples. In this study, a No-Reference IQA (NR-IQA), wood NR-IQA (WNR-IQA) metric was proposed to assess the quality of wood images. Support Vector Regression (SVR) was trained using Generalized Gaussian Distribution (GGD) and Asymmetric Generalized Gaussian Distribution (AGGD) features, which were measured for wood images. Meanwhile, the Mean Opinion Score (MOS) was obtained from the subjective evaluation. This was followed by a comparison between the proposed IQA metric, WNR-IQA, and three established NR-IQA metrics, namely Blind/Referenceless Image Spatial Quality Evaluator (BRISQUE), deepIQA, Deep Bilinear Convolutional Neural Networks (DB-CNN), and five Full Reference-IQA (FR-IQA) metrics known as MSSIM, SSIM, FSIM, IWSSIM, and GMSD. The proposed WNR-IQA metric, BRISQUE, deepIQA, DB-CNN, and FR-IQAs were then compared with MOS values to evaluate the performance of the automatic IQA metrics. As a result, the WNR-IQA metric exhibited a higher performance compared to BRISQUE, deepIQA, DB-CNN, and FR-IQA metrics. Highest quality images may not be routinely available due to logistic factors, such as dust, poor illumination, and hot environment present in the timber industry. Moreover, motion blur could occur due to the relative motion between the camera and the wood slice. Therefore, the advantage of WNR-IQA could be seen from its independency from a "perfect" reference image for the image quality evaluation

EMBLR: A High-Performance Optimal Routing Approach for D2D Communications in Large-scale IoT 5G Network

Coping with the skyrocketing needs for massive amounts of data for the future Fifth Generation (5G) network, Device-to-Device (D2D) communications technology will provide seamless connectivity, high data rates, extended network coverage, and spectral efficiency. The D2D communications are a prevalent emerging technology to achieve the vision of symmetry in the Internet of Things (IoT) services. However, energy resource constraints, network stability, traffic congestion, and link failure of the devices are the crucial impediments to establish an optimal route in the D2D communications based IoT 5G network. These obstacles induced packet drop, rapid energy depletion, higher end-to-end delay, and unfairness across the network, leading to significant route and network performance degradation. Therefore, in this paper, an energy, mobility, queue length, and link quality-aware routing (EMBLR) approach is proposed to overcome the challenges and boost network performance. Moreover, a multicriteria decision making (MCDM) technique is utilized for the selection of the intermediate device in an optimal route. Extensive simulation has been conducted and proven that the proposed routing approach significantly enhances network performance. Overall, results have been carried out in Quality of Service (QoS) performance metrics and compared with other well-known routing approaches. © 2020 by the authors. Licensee MDPI, Basel, Switzerland

Joint Optimization Scheme of User Association and Channel Allocation in 6G HetNets

The sixth-generation (6G) wireless cellular network integrates several wireless bands and modes with the objectives of improving quality of service (QoS) and increasing network connectivity. The 6G environment includes asymmetrical heterogeneous networks (HetNets) with the intention of making effective use of the available frequencies. However, selecting a suitable gNB and a communication channel that works for users in the network is an enormous challenge in 6G HetNets. This paper investigates a joint user association (UA) and channel allocation (CA) problem in two-tier HetNets by considering the downlink scenario to improve QoS. Our study presents an innovative scheme for user association and channel allocation, wherein the user can be connected to either the macro base station (MBS) or a possible small base station (SBS) in a direct or relay-assisted link. Furthermore, the proposed scheme identifies the optimal channel to be allocated to each user so that the overall network QoS can be maximized. A symmetric matching game-based user association is proposed to find the optimal association for users. Moreover, a modified auction game is applied to allocate the optimal channel by considering the quota of each gNB. Regarding connection probability, throughput, energy efficiency (EE), and spectrum efficiency (SE), the simulation results show that the proposed approach performs well over the state-of-the-art techniques

Improvement of electrical conductivity of PEMA film by incorporating EMITFSI and carbon based nanofiller

The electrical conductivity of dual inclusion of 1-ethyl-3-methyl imidazolium bis(trifluorosulfonyl) imide ionic liquid and three allotropes of carbon based nanofillers (multiwalled carbon nanotube, graphene and graphite) in poly (ethyl methacrylate) films with thickness ranging from 100 to 250 μm has been investigated in the temperature range of 300–380 K. It is found that the electrical conductivity of film with 0.5 wt % multiwalled carbon nanotube has the highest ambient electrical conductivity of 4.9 × 10−6 Scm−1 which is five order of magnitude higher than pure poly (ethyl methacrylate) film. Moreover, the stability of the highest electrical conductivity is also found to be significantly improved for a longer period. From the investigated physicochemical properties, these improvements are likely can be explained by the aggregation of multiwalled carbon nanotubes, the increase in electronic transport and the reduction in glass transition temperature which likely effect its ionic mobility. Consequently, these enhancements may lead to a promising improvement of its electrical properties for a stable near room temperature application. © 2019 Elsevier B.V

Mutual Coupling Reduction of a Wideband Circularly Polarized Microstrip MIMO Antenna

Mutual coupling (MC) between elements in an antenna array could significantly affect antenna performance, but this effect has rarely been reported for circularly polarized (CP) antennas. Therefore, this paper investigates a wideband CP multiple-input-multiple-output (MIMO) antenna operating between 1.8 and 2.6 GHz. A line patch was introduced between closely placed radiating elements ( 0.3\lambda ) to produce a high isolation between elements in the proposed antenna. The designed MIMO antenna has a wide impedance bandwidth, a wide axial ratio (AR) bandwidth, a very low MC ( \text{S}-{{21}} < -25 dB), a low envelop correlation coefficient (ECC < 0.01), a high diversity gain (DG 10 dB), and a realized gain of above 2 dB over the entire frequencies. The prototype of the proposed antenna geometry was fabricated and measured. A good agreement between the simulated and measured results was observed. © 2013 IEEE

Q‐switching pulses generation with samarium oxide film saturable absorber

Q-switching pulses generation in an erbium-doped fiber laser (EDFL) was demonstrated by using a samarium oxide (Sm2O3) film as a saturable absorber (SA) for the first time. The passively Q-switched EDFL operated stably at 1567 nm with tunable repetition rates, ranging from 47 to 66 kHz with the increase in pump power from 51.0 to 88.1 mW. At 88.1 mW pump power, the maximum pulse energy and the minimum pulse width were obtained at 26 nJ and 5.6 μs, respectively. These results demonstrated that the proposed Sm2O3 SA is viable for the construction of a flexible and reliably stable Q-switched pulsed fiber laser in the 1.5 μm region. © 2019 Wiley Periodicals, Inc