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A special issue of Electronics (ISSN 2079-9292). This special issue belongs to the section "Computer Science & Engineering".

Deadline for manuscript submissions: closed (28 February 2022) | Viewed by 27751

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Special Issue Editors

Prof. Dr. Agustín Zaballos

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Guest Editor

Computer Engineering Department of the La Salle, Universitat Ramon Llull, 08022 Barcelona, Spain
Interests: internet technologies; smart grids; ubiquitous sensor networks; internet of things communications
Special Issues, Collections and Topics in MDPI journals

Dr. Joan Navarro

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Guest Editor

GRITS—Research Group in Internet Technologies and Storage, La Salle-Ramon Llull University, 08022 Barcelona, Spain
Interests: cloud computing; big data; concurrency control in large-scale distributed systems and replication policies in cloud-based databases
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The advent of low-cost devices committed to easily sensing multiple environment variables—and actuate over them—has recently boosted the interest and feasibility for researchers in conceiving ubiquitous sensor networks (USNs). Modern improvements in communications for heterogeneous networks, such as next-generation networks, have facilitated the adoption of USNs in several domains (e.g., engineering, education, healthcare, agriculture and environmental monitoring). New middleware architectures for USNs take advantage of the latest advances in fog, edge, and cloud computing to address the scalability, storage, computing, and integration challenges typically found in these distributed architectures. Furthermore, large efforts are being made to come up with new communication protocols and strategies to make USNs a reality in electromagnetically harsh environments.

This Special Issue seeks high-quality contributions that address latent challenges in USNs and contribute to advance on the state-of-the-art in this field. Survey and research papers detailing theoretical and experimental developments are welcome. The topics of interest include, but are not limited to the following:

Middleware for ubiquitous sensing and computing;
Robust communication protocols for electromagnetically harsh environments;
Lightweight distributed architectures for sensing and acting;
Methods for assessing and improving the performance of USNs;
Data management and analytics in ubiquitous computing;
Emerging applications of USNs;
Solutions to cybersecurity issues in USNs;
Low-power consumption electronics to enable USNs.

Prof. Dr. Agustín Zaballos
Dr. Joan Navarro
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Electronics is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

ubiquitous sensor networks
distributed storage and computing systems
wireless sensor networks
ubiquitous computing
communication protocols

Published Papers (9 papers)

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Research

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14 pages, 5715 KiB

Open AccessArticle

On the Reuse of a Matching Network for IoT Devices Operating at 900 MHz Embedding Antenna Boosters

by Jaime Gui, Aurora Andújar and Jaume Anguera

Electronics 2022, 11(8), 1267; https://doi.org/10.3390/electronics11081267 - 17 Apr 2022

Cited by 1 | Viewed by 2376

Abstract

The Internet of Things (IoT) is evolving rapidly, enabling more new applications than ever before. Some radio systems in the IoT space used to connect things with things operate at the 863–928 MHz frequency band (e.g., LoRa, ISM). IoT wireless devices at 900 MHz need an efficient antenna to send data into the cloud, and ensure range and long battery life. Moreover, the antenna should be easy to use across different device sizes. In this regard, antenna booster technology is proposed, which relies on a tiny element called an antenna booster, able to excite radiation currents on the ground plane of the IoT device. The antenna booster in this paper is only 12 mm × 3 mm × 2.4 mm (height), representing only ~λ/30 at 863 MHz. Such an antenna booster is reactive across the 863–928 MHz frequency range and, thus, a matching network is needed. The paper first proposes a matching network on a 120 mm × 60 mm ground plane. Afterward, an analysis is carried out to find the set of different ground plane sizes where the same matching network as the one used for the 120 mm × 60 mm ground plane can be reused, ensuring an S₁₁ < −6 dB. The goal is to find a map representing a cluster of ground planes where the same antenna system can be used (the same antenna booster and the same matching network) to simplify the design of IoT devices embedding antenna boosters. The analysis is addressed using MoM (Method of Moments) electromagnetic software (IE3D) and validated through measurements. Results indicate that a broad set of device sizes can reuse the same matching network with the same antenna booster, thus, simplifying and accelerating the design of IoT devices since no adjustment is needed on the antenna system. Full article

(This article belongs to the Special Issue Ubiquitous Sensor Networks)

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16 pages, 3404 KiB

Open AccessArticle

SC-FDE Layer for Sensor Networks in Remote Areas Using NVIS Communications

by Tomas Gonzalez, Joaquim Porte, Jordi Male, Joan Navarro, Josep M. Maso, Agustín Zaballos, Joan L. Pijoan and David Badia

Electronics 2021, 10(14), 1636; https://doi.org/10.3390/electronics10141636 - 09 Jul 2021

Cited by 3 | Viewed by 1976

Abstract

Despite high costs and lengthy deployments, satellite communications have traditionally been used to provide coverage in remote areas. However, given the fact that there is no radio infrastructure available in these areas, Near Vertical Incidence Skywave (NVIS) technology has positioned itself as an attractive alternative to communicate with low-power nodes in remote areas. This type of communication works in the HF frequency range complying with STANAG and MIL-STD standards, which define a physical layer for scenarios that differ from NVIS and low-power communication. The purpose of this paper was to present the definition of a new communication physical layer based on single-carrier frequency-domain equalization (SC-FDE) based on these standards but adapted to the ionospheric communication channel. This physical layer was compared to an OFDM-based layer from a previous study. The experiments performed show that this new approach achieves better results than OFDM in terms of a higher signal quality with a higher specific BER probability. Finally, this layer was also used in the theoretical design of an NVIS gateway to link sensor network devices spanning large-scale remote areas in a secure manner in the context of ubiquitous sensor networks (USN). Full article

(This article belongs to the Special Issue Ubiquitous Sensor Networks)

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25 pages, 6412 KiB

Open AccessArticle

Low-Cost Distributed Acoustic Sensor Network for Real-Time Urban Sound Monitoring

by Ester Vidaña-Vila, Joan Navarro, Cristina Borda-Fortuny, Dan Stowell and Rosa Ma Alsina-Pagès

Electronics 2020, 9(12), 2119; https://doi.org/10.3390/electronics9122119 - 11 Dec 2020

Cited by 15 | Viewed by 3825

Abstract

Continuous exposure to urban noise has been found to be one of the major threats to citizens’ health. In this regard, several organizations are devoting huge efforts to designing new in-field systems to identify the acoustic sources of these threats to protect those citizens at risk. Typically, these prototype systems are composed of expensive components that limit their large-scale deployment and thus reduce the scope of their measurements. This paper aims to present a highly scalable low-cost distributed infrastructure that features a ubiquitous acoustic sensor network to monitor urban sounds. It takes advantage of (1) low-cost microphones deployed in a redundant topology to improve their individual performance when identifying the sound source, (2) a deep-learning algorithm for sound recognition, (3) a distributed data-processing middleware to reach consensus on the sound identification, and (4) a custom planar antenna with an almost isotropic radiation pattern for the proper node communication. This enables practitioners to acoustically populate urban spaces and provide a reliable view of noises occurring in real time. The city of Barcelona (Spain) and the UrbanSound8K dataset have been selected to analytically validate the proposed approach. Results obtained in laboratory tests endorse the feasibility of this proposal. Full article

(This article belongs to the Special Issue Ubiquitous Sensor Networks)

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21 pages, 673 KiB

Open AccessArticle

Intra-Network Interference Robustness: An Empirical Evaluation of IEEE 802.15.4-2015 SUN-OFDM

by Robbe Elsas, Jeroen Hoebeke, Dries Van Leemput, Adnan Shahid, Glenn Daneels, Jeroen Famaey and Eli De Poorter

Electronics 2020, 9(10), 1691; https://doi.org/10.3390/electronics9101691 - 15 Oct 2020

Cited by 3 | Viewed by 2257

Abstract

While IEEE 802.15.4 and its Time Slotted Channel Hopping (TSCH) medium access mode were developed as a wireless substitute for reliable process monitoring in industrial environments, most deployments use a single/static physical layer (PHY) configuration. Instead of limiting all links to the throughput and reliability of a single Modulation and Coding Scheme (MCS), you can dynamically re-configure the PHY of link endpoints according to the context. However, such modulation diversity causes links to coincide in time/frequency space, resulting in poor reliability if left unchecked. Nonetheless, to some level, intentional spatial overlap improves resource efficiency while partially preserving the benefits of modulation diversity. Hence, we measured the mutual interference robustness of certain Smart Utility Network (SUN) Orthogonal Frequency Division Multiplexing (OFDM) configurations, as a first step towards combining spatial re-use and modulation diversity. This paper discusses the packet reception performance of those PHY configurations in terms of Signal to Interference Ratio (SIR) and time-overlap percentage between interference and targeted parts of useful transmissions. In summary, we found SUN-OFDM O3 MCS1 and O4 MCS2 performed best. Consequently, one should consider them when developing TSCH scheduling mechanisms in the search for resource efficient ubiquitous connectivity through modulation diversity and spatial re-use. Full article

(This article belongs to the Special Issue Ubiquitous Sensor Networks)

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18 pages, 4584 KiB

Open AccessArticle

Sensing-HH: A Deep Hybrid Attention Model for Footwear Recognition

by Yumin Yao, Ya Wen and Jianxin Wang

Electronics 2020, 9(9), 1552; https://doi.org/10.3390/electronics9091552 - 22 Sep 2020

Cited by 1 | Viewed by 2378

Abstract

The human gait pattern is an emerging biometric trait for user identification of smart devices. However, one of the challenges in this biometric domain is the gait pattern change caused by footwear, especially if the users are wearing high heels (HH). Wearing HH puts extra stress and pressure on various parts of the human body and it alters the wearer’s common gait pattern, which may cause difficulties in gait recognition. In this paper, we propose the Sensing-HH, a deep hybrid attention model for recognizing the subject’s shoes, flat or different types of HH, using smartphone’s motion sensors. In this model, two streams of convolutional and bidirectional long short-term memory (LSTM) networks are designed as the backbone, which extract the hierarchical spatial and temporal representations of accelerometer and gyroscope individually. We also introduce a spatio attention mechanism into the stacked convolutional layers to scan the crucial structure of the data. This mechanism enables the hybrid neural networks to capture extra information from the signal and thus it is able to significantly improve the discriminative power of the classifier for the footwear recognition task. To evaluate Sensing-HH, we built a dataset with 35 young females, each of whom walked for 4 min wearing shoes with varied heights of the heels. We conducted extensive experiments and the results demonstrated that the Sensing-HH outperformed the baseline models on leave-one-subject-out cross-validation (LOSO-CV). The Sensing-HH achieved the best

F_{m}

score, which was 0.827 when the smartphone was attached to the waist. This outperformed all the baseline methods at least by more than 14%. Meanwhile, the

F_{1}

Score of the Ultra HH was as high as 0.91. The results suggest the proposed model has made the footwear recognition more efficient and automated. We hope the findings from this study paves the way for a more sophisticated application using data from motion sensors, as well as lead to a path to a more robust biometric system based on gait pattern. Full article

(This article belongs to the Special Issue Ubiquitous Sensor Networks)

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16 pages, 4511 KiB

Open AccessArticle

High-Performance Long Range-Based Medium Access Control Layer Protocol

by Yang Liu, Lei Liu, Jiacheng Liang, Jin Chai, Xuemei Lei and Hui Zhang

Electronics 2020, 9(8), 1273; https://doi.org/10.3390/electronics9081273 - 07 Aug 2020

Cited by 6 | Viewed by 3050

Abstract

Long Range (LoRa) has become one of the most promising physical layer technologies for the Internet of Things (IoT) ecosystem. Although it manifests low-power consumption and long-distance communication, LoRa encounters a large number of collisions in the IoT environment, which severely affects the system’s throughput and delay performance. In this paper, a code division carrier sense multiple access (CD/CSMA) protocol that resolves the traditional channel collision problem and implements multi-channel transmission is proposed for the LoRa medium access control (MAC) layer. To reduce data transmission delay and maximize the throughput of the system, the adaptive p-persistent CSMA protocol divides the channel load into four states and dynamically adjusts the data transmission probability. Then, to reduce channel collisions significantly, the code division multiple access (CDMA) protocol is performed on different channel states. Moreover, the combination of the proposed adaptive p-persistent CSMA protocol and the CDMA successfully reduces the number of data retransmissions and makes LoRa more stable. The simulation results demonstrate that the proposed adaptive p-persistent CD/CSMA protocol can achieve near-optimal and occasionally even better performance than some conventional MAC protocols, especially in a heavy load channel. Full article

(This article belongs to the Special Issue Ubiquitous Sensor Networks)

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21 pages, 7472 KiB

Open AccessArticle

Study of NVIS Channel for USN Protocol Definition in Antarctica

by Josep M. Maso, Joaquim Porte, Joan L. Pijoan and David Badia

Electronics 2020, 9(6), 1037; https://doi.org/10.3390/electronics9061037 - 23 Jun 2020

Cited by 3 | Viewed by 2957

Abstract

Every year, the number of ubiquitous sensor networks (USN) is increasing and the need for remote USN communications is emerging in some scenarios. As an alternative to satellite communications, more interests are focused on high frequencies (HF) communications as a low-cost option to reach links of more than 250 km without a line of sight. The HF standards are designed for generic communication channels being not robust for near vertical incidence skywave (NVIS) USN. In this article, we propose a new protocol for USN in remote places based on NVIS communications. For that purpose, we study the main characteristics of the NVIS channel with the presence of groundwaves, particularly in Antarctica. We analyze the availability of the channel, the height of the layers, the delay spread, and the Doppler spread. On the basis of the results obtained, we propose two protocols based on an OFDM (orthogonal frequency division multiplexing) modulation depending on the presence of the groundwave at the receiver. Finally, we make a simulation of the two OFDM configurations and we compare it with real tested standard modulations. The results show a better performance of the new protocol compared to the current HF standards. Full article

(This article belongs to the Special Issue Ubiquitous Sensor Networks)

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15 pages, 2895 KiB

Open AccessArticle

A New Intra-Cluster Scheduling Scheme for Real-Time Flows in Wireless Sensor Networks

by Gohar Ali, Fernando Moreira, Omar Alfandi, Babar Shah and Mohammed Ilyas

Electronics 2020, 9(4), 683; https://doi.org/10.3390/electronics9040683 - 23 Apr 2020

Cited by 1 | Viewed by 2363

Abstract

Real-time flows using time division multiple access (TDMA) scheduling in cluster-based wireless sensor networks try to schedule more flows per time frame to minimize the schedule length to meet the deadline. The problem with the previously used cluster-based scheduling algorithm is that intra-cluster scheduling does not consider that the clusters may have internal or outgoing flows. Thus, intra-cluster scheduling algorithms do not utilize their empty time-slots and thus increase schedule length. In this paper, we propose a new intra-cluster scheduling algorithm by considering that clusters may have having internal or outgoing flows. Thus, intra-cluster scheduling algorithms do not differentiate the intra-cluster time slots and utilize their empty time slots. The objective is to schedule more flows per time frame, to reduce schedule length and improve the acceptance rate of flows. Simulation results show that the acceptance rate of the proposed scheme has a higher performance than the previous scheme. Full article

(This article belongs to the Special Issue Ubiquitous Sensor Networks)

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Review

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31 pages, 992 KiB

Open AccessReview

Communication Technologies in Emergency Situations

by Anna Carreras-Coch, Joan Navarro, Carles Sans and Agustín Zaballos

Electronics 2022, 11(7), 1155; https://doi.org/10.3390/electronics11071155 - 06 Apr 2022

Cited by 7 | Viewed by 5129

Abstract

Emergency situations such as wildfires, water floods, or even terrorist attacks require continuous communication between the coordination centres, the several on-the-field teams, and their respective devices to properly address the adverse circumstances. From a technological point of view, this can be best seen as a live Ubiquitous Sensor Network—composed of human beings (e.g., first responders, victims) and devices (e.g., drones, environmental sensors, radios)—with stringent and special communication requirements in terms of flexibility, mobility, reliability, bandwidth, heterogeneity, and speed of deployment. However, for this specific use case, most of the already deployed and well-known communication technologies (e.g., satellite, 4G/5G) might become unusable and hard to repair due to the associated effects of the disaster itself. The purpose of this paper is (1) to review the emergency communications challenges, (2) to analyse the existing surveys on technologies for emergency situations, (3) to conduct a more updated, extensive, and systematic review of the emergency communications’ technologies, and (4) to propose a heterogeneous communication architecture able to communicate between moving agents in harsh conditions. The proposed approach is conceived to link the relocating agents that constitute a Ubiquitous Sensor Network spanning a large-scale area (i.e., hundreds of square kilometres) by combining Near Vertical Incidence Skywave technologies with Drone-Based Wireless Mesh Networks. The conclusions derived from this research aim to set up the fundamentals of a rapidly deployable Emergency Communications System inspired by the Ubiquitous Sensor Network paradigm. Full article

(This article belongs to the Special Issue Ubiquitous Sensor Networks)

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