Massive MIMO systems for 5G: a systematic mapping study on antenna design challenges and channel estimation open issues

The next generation of mobile networks (5G) is expected to achieve high data rates, reduce latency, as well as improve the spectral and energy efficiency of wireless communication systems. Several technologies are being explored to be used in 5G systems. One of the main promising technologies that is seen to be the enabler of 5G is massive multiple-input multiple-output (mMIMO) systems. Numerous studies have indicated the utility of mMIMO in upcoming wireless networks. However, there are several challenges that needs to be unravelled. In this paper, the latest progress of research on challenges in mMIMO systems is tracked, in the context of mutual coupling, antenna selection, pilot contamination and feedback overhead. The results of a systematic mapping study performed on 63 selected primary studies, published between the year 2017 till the second quarter of 2020, are presented. The main objective of this secondary study is to identify the challenges regarding antenna design and channel estimation, give an overview on the state-of-the-art solutions proposed in the literature, and finally, discuss emerging open research issues that need to be considered before the implementation of mMIMO systems in 5G networks

UAV Communications in Integrated Terrestrial and Non-terrestrial Networks

With growing interest in integrating terrestrial networks (TNs) and non-terrestrial networks (NTNs) to connect the unconnected, a key question is whether this new paradigm could also be opportunistically exploited to augment service in urban areas. We assess this possibility in the context of an integrated TN-NTN, comprising a ground cellular deployment paired with a Low Earth Orbit (LEO) satellite constellation, providing sub-6 GHz connectivity to an urban area populated by ground users (GUEs) and uncrewed aerial vehicles (UAVs). Our study reveals that offloading UAV traffic to the NTN segment drastically reduces the downlink outage of UAVs from 70% to nearly zero, also boosting their uplink signal quality as long as the LEO satellite constellation is sufficiently dense to guarantee a minimum elevation angle. Offloading UAVs to the NTN also benefits coexisting GUEs, preventing uplink outages of around 12% that GUEs would otherwise incur. Despite the limited bandwidth available below 6 GHz, NTN-offloaded UAVs meet command and control rate requirements even across an area the size of Barcelona with as many as one active UAV per cell. Smaller UAV populations yield proportionally higher rates, potentially enabling aerial broadband applications

Integrating Terrestrial and Non-terrestrial Networks: 3D Opportunities and Challenges

peer reviewedIntegrating terrestrial and non-terrestrial networks has the potential of connecting the unconnected and enhancing the user experience for the already-connected, with technological and societal implications of the greatest long-term significance. A convergence of ground, air, and space wireless communications also represents a formidable endeavor for the mobile and satellite communications industries alike, as it entails defining and intelligently orchestrating a new 3D wireless network architecture. In this article, we present the key opportunities and challenges arising from this revolution by presenting some of its disruptive use cases and key building blocks, reviewing the relevant standardization activities, and pointing to open research problems. By considering two multi-operator paradigms, we also showcase how terrestrial networks could be efficiently re-engineered to cater for aerial services, or opportunistically complemented by nonterrestrial infrastructure to augment their current capabilitie

Evaporation reduction and prediction model for reservoirs

In this study, experiments were carried out at the Universiti Putra Malaysia, Fac-ulty of Engineering in order to investigate the performance of di®erent types of covers for evaporation reduction. The covers used were Mengkuang mat, pieces of plywood and galvanized iron corrugated sheet. The performance of the covers was tested using four PVC tanks. Measurement from the tanks revealed that evaporation reduction using Mengkuang mat was approximately 64% while it were about 50% and 36% for tanks covered with plywood and that shaded with a corrugated sheet respectively. The results obtained from experiments show that signi¯cant evaporation saving are possible if covers are used as barriers between water and atmosphere. Water samples were collected weekly from the four tanks to assess the impact of selected covers on water quality. The collected samples were taken to the laboratory and physical and chemical water quality analysis was conducted. The analysis included testing pH, EC, Tw, DO, BOD and COD. Test results were compared with the standards. The comparison revealed that there was a minor change in water quality of the covered tanks compared to the uncovered. These results confirmed the efectiveness of the covers in evaporation reduction with no harmful efects on water quality. In this study, models for predicting evaporation from reservoirs were proposed. The models were based on the concept of Neural Network. The proposed models were applied to predict the evaporation from two selected reservoirs. One of these reservoirs is Algardabyia Reservoir (located in Libya), while the second one is Batu Dam Reservoir (located in Malaysia). The meteorological data used to run the proposed models were air temperature (T), wind speed (W), relative humidity (RH), and solar radiation (Rs) for the period from 1997 to 2008. Data from 1997 to 2005 was used for models training and validation. Data from 2006 to 2008 was used for model testing. The proposed models simulating the evaporation from Algardabyia Reservoir was named (based on the number of input data) as EM4¡G, EM3¡G and EM2¡G. The same basis is used to name the models proposed for Batu Dam Reservoir. These models are EM4 ¡ B, EM3 ¡ B and EM2 ¡ B. Outputs from the proposed models were validated and it was found in agreement with the historical records. The validation process was based on computing selected statistical indices such as RMSE, MBA, MAE, R2, CE and d. The computed indices show that EM4¡G and EM4¡B models gave the most accurate predictions.Also, selected climate based models such as Penman (Pen) and Priestley-Taylor (P ¡T) were used to predict the evaporation from the Algardabyia Reservoir and Batu Dam Reservoir. The performance of P ¡ T model was found to be better than the Pen model

A Hybrid-Flipped Classroom Approach: Students’ Perception and Performance Assessment Un enfoque de aula invertida híbrida: evaluación de la opinión y el ren-dimiento de los estudiantes

This study presents an improved hybrid-flipped classroom (hybrid-FC) education method based on technology-enhanced learning (TEL) along with diluted classes for a course on probability and random processes in engineering. The proposed system was imple-mented with the participation of two student groups who alternated weekly between attending face-to-face activities and fully online classes as a sanitary measure during the pandemic. The education model was combined with the flipped classroom (FC) approach in order to improve the quality of learning and address the negative effects of remote education. Before the lessons, the students studied the course material, filled a question form, and then took a low-stake online quiz. Then, the students attended a session where the questions reported in the forms were discussed, and they took an online problem-solving session followed by an individual quiz. Class sessions were available to both online and face-to-face students, as well as in the form of video recordings for anyone who missed lessons. Qualitatively and quantitatively, the proposed education method proved to be more effective and comprehensive than conventional online methodologies. The students' performances were evaluated via quizzes and exams measuring the achievement of the course learning outcomes (CLOs). Weekly pre/post-tests were applied to examine the students’ progress in each topic. Midterm and final exams were planned to measure the level of success for all course topics. Additionally, the students' perception was assessed with questionnaires and face-to-face interviews. A performance assessment showed an apparent increase in the success rate, and the students' perception was found to be positive

SWOT analysis applications: An integrative literature review

A strengths, weaknesses, opportunities, and threats (SWOT) analysis has become a key tool used by businesses for strategic planning. Scholars have conducted SWOT research for over six decades. However, a collective understanding of SWOT analysis remains vague. This study accessed, analyzed, and synthesized the SWOT literature, allowing for new theoretical perspectives and frameworks to emerge. Using an integrative literature review, this study reviewed SWOT studies historically, providing a greater understanding of the SWOT analysis in different sectors and the different approaches used in SWOT studies. Furthermore, it fills the knowledge gap in the strategic planning context and indicates meaningful implications for managers that could help improve their strategic decisions