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.
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.
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.
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.
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.
Digital signal processing algorithms, at times, necessitate the execution of a substantial quantity of mathematical operations to speed up and iterate upon a particular data set. Numerous digital ...signal processing (DSP) applications impose limitations on delay, necessitating the accomplishment of DSP operations within a predetermined timeframe, hence rendering deferred processing not feasible. Therefore, digital signal processing (DSP) necessitates a multiplier and accumulator (MAC) unit that exhibits fast speed, high throughput, and low power consumption. This research aims to develop and execute a low-power MAC unit utilising a hybrid logic technique to achieve power efficiency. A MAC unit has been purposefully designed with suitable geometries to provide optimised power, area, and delay characteristics. Estimating the delay in the MAC unit depends upon data flow analysis between the MAC blocks, explicitly focusing on low-power concerns. The developed hybrid adder cell possesses several advantageous characteristics, including a high operational speed, low power consumption, minimal transistor count. The MAC architecture uses a 45 nm CMOS technology with the Mentor Graphics tool. This research additionally examines different designs of multipliers and adders that are well-suited for the execution of high throughput signal processing while simultaneously achieving low power consumption. The registers in the MAC have been implemented in GDI logic using Multi Bit Flip flops technique to achieve low power operation. The entire MAC circuitry operates on a voltage supply of 1 V. The hybrid logic MAC architecture that has been developed demonstrates a significant decrease in area consumption, amounting to a reduction of 68 % when compared to the typical CMOS logic design. Hybrid logic demonstrates a power consumption that is 92 % better compared to CMOS logic.
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