Due to their energy efficiency, many duty cycling-based MAC protocols have been proposed in WSNs. Although these protocols considerably reduce energy consumption by minimizing idle listening and ...overhearing, the energy efficiency comes at the cost of decreased packet delivery ratio and increased delay. In this paper, we present a multichannel asynchronous scheduled MAC protocol, called MCAS-MAC, which inherits the basic asynchronous scheduling operation from AS-MAC and adds back-to-back packet transmissions and multichannel support for high traffic dense WSN. Using RaPTEX, we evaluate the performance of MCAS-MAC by comparing it with existing duty cycling MAC protocols including BMAC, SMAC and AS-MAC.
The ongoing deployment of 5G networks is a key enabler for realizing upcoming services at scale, including the massive deployment of the Internet of Things, providing communications to support ...autonomous vehicles, and supporting the realization of smart cities. However, as the limitations of existing approaches become apparent, the need for next-generation technologies is growing, in terms of improving spectral efficiency, increasing network data rates and densification, supporting local/wide area wireless coordination, and more. In this Special Issue, we present some technologies to meet these demanding requirements and facilitate coordinating wireless networks to support future Beyond 5G networks.
Summary
A well‐optimized and well‐performed communication network protocol is necessary to build successful underwater acoustic sensor networks (UWASNs). But for wired and wireless communication, ...medium access control (MAC) has a great effect on network performance and optimization. But unlike land‐based MAC protocols, underwater MAC protocols come with various challenges and issues like high propagation delay, limited bandwidth for communication signals, large attenuation in network signals, and the high noise level in signals. It is very challenging to build a well‐optimized underwater MAC protocol. Also, in UWASN, sensor nodes are generally divided into sub‐network parts to reduce the propagation delay of data signals. But this creates the problem of non‐uniform traffic load in sensor nodes. So, considering these issues, dynamic hold time MAC (DHT‐MAC) protocol is proposed here. In this protocol, depending on the distance from the central node, sensor nodes are divided into two sub‐network zones (parent node and child node). Depending on the traffic load and propagation delay, the child nodes can change their respective parent nodes dynamically. Advantage of the proposed method is that, if any of the parent nodes stops working, the child node will connect to the nearest parent node. When collecting the data signals, it has been observed that child nodes have a light traffic load compared to parent nodes. So dynamic cooperative transmission MAC (DCT‐MAC) protocol which is a contention‐based MAC protocol has been used in child nodes and as parent nodes have high traffic load, reservation‐based MAC protocol has been used.
In this proposed communication network, all the sensor nodes are interconnected for data collection and transmission. This is a two‐stage communication network, which consists of all the surface and underwater sensor nodes in Stage 1 and interconnected wired/wireless network systems like Internet and network management systems, cloud storage and computing platforms, and sea‐shore control in Stage 2. Just below the central node (sink), sub‐surface sensor nodes are placed. And for deep‐sea monitoring system, nano ocean sensors are placed several hundreds of meters underwater or in sea bed (like acoustic or radio receive or transmit nodes, and hydrophone sensing nodes). The communication and network layer which collects data and needed information from the sensor layer and processes them for further works also controls the sensor nodes. AUVs or moving sensor nodes connect this communication network only if they have any data or information to transmit to the central node. The moving sensing nodes (AUVs) follow a pre‐determined and pre‐calculated underwater path to gather information and needed data and then transmit gathered information in data packets to a connected Stage 1 central node. And all of the other sensing nodes have very little movement, but with the ocean current, they have slight movement around a fixed position.
A close relationship between CM and CO chondrites has been suggested by previous petrologic and isotopic studies, leading to the suggestion that they may originate from similar precursor materials or ...even a common parent body. In this study, we evaluate the genetic relationship between CM and CO chondrites using Ti, Cr, and O isotopes. We first provide additional constraints on the ranges of ε50Ti and ε54Cr values of bulk CM and CO chondrites by reporting the isotopic compositions of CM2 chondrites Murchison, Murray, and Aguas Zarcas and the CO3.8 chondrite Isna. We then report the ε50Ti and ε54Cr values for several ungrouped and anomalous carbonaceous chondrites that have been previously reported to exhibit similarities to the CM and/or CO chondrite groups, including Elephant Moraine (EET) 83226, EET 83355, Grosvenor Mountains (GRO) 95566, MacAlpine Hills (MAC) 87300, MAC 87301, MAC 88107, and Northwest Africa (NWA) 5958, and the O-isotope compositions of a subset of these samples. We additionally report the Ti, Cr, and O isotopic compositions of additional ungrouped chondrites LaPaz Ice Field (LAP) 04757, LAP 04773, Lewis Cliff (LEW) 85332, and Coolidge to assess their potential relationships with known carbonaceous and ordinary chondrite groups. LAP 04757 and LAP 04773 exhibit isotopic compositions indicating they are low-FeO ordinary chondrites. The isotopic compositions of Murchison, Murray, Aguas Zarcas, and Isna extend the compositional ranges defined by the CM and CO chondrites in ε50Ti versus ε54Cr space. The majority of the ungrouped carbonaceous chondrites with documented similarities to the CM and/or CO chondrites plot outside the CM and CO group fields in plots of ε50Ti versus ε54Cr, Δ17O versus ε50Ti, and Δ17O versus ε54Cr. Therefore, based on differences in their Ti, Cr, and O isotopic compositions, we conclude that the CM, CO, and ungrouped carbonaceous chondrites likely represent samples of multiple distinct parent bodies. We also infer that these parent bodies formed from precursor materials that shared similar isotopic compositions, which may indicate formation in regions of the protoplanetary disk that were in close proximity to each other.
Traffic density around the globe is increasing on a day-to-day basis, resulting in more accidents, congestion, and pollution. The dynamic vehicular environment induces challenges in designing an ...efficient and reliable protocol for communication. Timely delivery of safety and non-safety messages is necessary for traffic congestion control and for avoiding road mishaps. For efficient resource sharing and optimized channel utilization, the media access control (MAC) protocol plays a vital role. An efficient MAC protocol design can provide fair channel access and can delay constraint safety message dissemination, improving road safety. This paper reviews the applications, characteristics, and challenges faced in the design of MAC protocols. A classification of the MAC protocol is presented based on contention mechanisms and channel access. The classification based on contention is oriented as contention-based, contention-free, and hybrid, whereas the classification based on channel access is categorized as distributed, centralized, cluster-based, cooperative, token-based, and random access. These are further sub-classified as single-channel and multi-channel, based on the type of channel resources they utilize. This paper gives an analysis of the objectives, mechanisms, advantages/disadvantages, and simulators used in specified protocols. Finally, the paper concludes with a discussion on the future scope and open challenges for improving the MAC protocol design.
Vehicular ad hoc network as an intelligent transportation system supports traffic management to facilitate navigation, safety, and services to end-users. Delivery of safety messages is prioritized to ...avoid hazards in the system. In this regard, this paper discusses the existing TDMA MAC protocols in vehicular ad hoc networks that efficiently coordinate and communicate with the vehicles and minimize the message collision. Vehicular movement and traffic density lead to link failures, collisions, and load imbalance in the network. MAC protocols with dynamic time slot synchronization, message priority, bandwidth, and frequency management techniques ensure safe message delivery, hazard prevention, and low message collision rates in VANETs. This article provides the classification of TDMA MAC protocols for distributed, centralized and hybrid protocols. Various types of collisions, two-way traffic load, multi-channel utilization, and access challenges are discussed in detail. Further, the working mechanism and performance attributes of TDMA MAC protocols are explained.
In underwater acoustic sensor networks (UASNs), medium access control (MAC) is an important issue because of its potentially significant effect on the network performance. However, designing a ...suitable MAC protocol for the UASN is challenging because of the specific characteristics of the underwater acoustic channel and network, such as limited available bandwidth, long propagation delay, high bit-error-rate, and sparse network topology. In addition, as the traffic load is non-uniformly distributed in a UASN for data collection, it is essential to consider the application feature for the MAC protocol. In this paper, we propose a MAC protocol in a data-collection-oriented UASN, abbreviated as the DCO-MAC protocol. In the proposed protocol, the network is partitioned into two kinds of sub-networks according to the traffic load. A contention-based MAC protocol is used in the sub-network with a light traffic load, while a reservation-based MAC protocol is used in the sub-network with a heavy traffic load. Meanwhile, the DCO-MAC protocol supports the access of mobile nodes. The theoretical analysis and simulation results demonstrate that, in a UASN for data collection, the proposed MAC protocol outperforms the other existing MAC protocols, in terms of the network throughput, end-to-end packet delay, energy overhead, and fairness.
Nontuberculous mycobacterial (NTM) infections are an emerging problem. Common organisms include Mycobacterium avium, M. intracellulare, and M. kansasii, along with the M. avium intracellulare complex ...(MAC), which includes both M. avium and M. intracellulare. Typically, NTM infections affect the lungs and subsequently demonstrate a chronic course. Therefore, persistent respiratory symptoms generally indicate of the presence of pulmonary NTM diseases, and chest radiography, along with a sputum examination, are essential for its diagnosis. Because NTM are ubiquitous environmental organisms, a positive culture from a minimum of two separate expectorated sputum samples are required to make a diagnosis. The repertoire of effective drugs for treatment is considerably limited, indicating the need for long-term management with multiple drugs. Establishing a treatment regimen with high therapeutic efficacy and safety is an important issue for the future.
The ongoing deployment of 5G networks is a key enabler for realizing upcoming services at scale, including the massive deployment of the Internet of Things, providing communications to support ...autonomous vehicles, and supporting the realization of smart cities. However, as the limitations of existing approaches become apparent, the need for next-generation technologies is growing, in terms of improving spectral efficiency, increasing network data rates and densification, supporting local/wide area wireless coordination, and more. In this Special Issue, we present some technologies to meet these demanding requirements and facilitate coordinating wireless networks to support future Beyond 5G networks.
•Studying MAC variability impact on eBC estimation.•Presenting spatial, seasonal and temporal MAC variability in Europe.•Proposing the site-specific MAC as the most effective approach to estimate ...eBC.•Long-term trend analysis links decreasing EC trends with method-dependent corrected eBC trends.
A reliable determination of equivalent black carbon (eBC) mass concentrations derived from filter absorption photometers (FAPs) measurements depends on the appropriate quantification of the mass absorption cross-section (MAC) for converting the absorption coefficient (babs) to eBC. This study investigates the spatial–temporal variability of the MAC obtained from simultaneous elemental carbon (EC) and babs measurements performed at 22 sites. We compared different methodologies for retrieving eBC integrating different options for calculating MAC including: locally derived, median value calculated from 22 sites, and site-specific rolling MAC. The eBC concentrations that underwent correction using these methods were identified as LeBC (local MAC), MeBC (median MAC), and ReBC (Rolling MAC) respectively. Pronounced differences (up to more than 50 %) were observed between eBC as directly provided by FAPs (NeBC; Nominal instrumental MAC) and ReBC due to the differences observed between the experimental and nominal MAC values. The median MAC was 7.8 ± 3.4 m2 g-1 from 12 aethalometers at 880 nm, and 10.6 ± 4.7 m2 g-1 from 10 MAAPs at 637 nm. The experimental MAC showed significant site and seasonal dependencies, with heterogeneous patterns between summer and winter in different regions. In addition, long-term trend analysis revealed statistically significant (s.s.) decreasing trends in EC. Interestingly, we showed that the corresponding corrected eBC trends are not independent of the way eBC is calculated due to the variability of MAC. NeBC and EC decreasing trends were consistent at sites with no significant trend in experimental MAC. Conversely, where MAC showed s.s. trend, the NeBC and EC trends were not consistent while ReBC concentration followed the same pattern as EC. These results underscore the importance of accounting for MAC variations when deriving eBC measurements from FAPs and emphasize the necessity of incorporating EC observations to constrain the uncertainty associated with eBC.
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