QoS-aware MAC protocols for wireless sensor networks: A survey <s> Introduction <s> We provide an in-depth study of applying wireless sensor networks to real-world habitat monitoring. A set of system design requirements are developed that cover the hardware design of the nodes, the design of the sensor network, and the capabilities for remote data access and management. A system architecture is proposed to address these requirements for habitat monitoring in general, and an instance of the architecture for monitoring seabird nesting environment and behavior is presented. The currently deployed network consists of 32 nodes on a small island off the coast of Maine streaming useful live data onto the web. The application-driven design exercise serves to identify important areas of further work in data sampling, communications, network retasking, and health monitoring. <s> BIB001 </s> QoS-aware MAC protocols for wireless sensor networks: A survey <s> Introduction <s> The literature on cross-layer protocols, protocol improvements, and design methodologies for wireless sensor networks (WSNs) is reviewed and a taxonomy is proposed. The communication protocols devised for WSNs that focus on cross-layer design techniques are reviewed and classified, based on the network layers they aim at replacing in the classical open system interconnection (OSI) network stack. Furthermore, systematic methodologies for the design of cross-layer solution for sensor networks as resource allocation problems in the framework of non-linear optimization are discussed. Open research issues in the development of cross-layer design methodologies for sensor networks are discussed and possible research directions are indicated. Finally, possible shortcomings of cross-layer design techniques such as lack of modularity, decreased robustness, and instability are discussed, and precautionary guidelines are presented. <s> BIB002 </s> QoS-aware MAC protocols for wireless sensor networks: A survey <s> Introduction <s> Recent technological advances in sensors, low-power integrated circuits, and wireless communications have enabled the design of low-cost, miniature, lightweight, and intelligent physiological sensor nodes. These nodes, capable of sensing, processing, and communicating one or more vital signs, can be seamlessly integrated into wireless personal or body networks (WPANs or WBANs) for health monitoring. These networks promise to revolutionize health care by allowing inexpensive, non-invasive, continuous, ambulatory health monitoring with almost real-time updates of medical records via the Internet. Though a number of ongoing research efforts are focusing on various technical, economic, and social issues, many technical hurdles still need to be resolved in order to have flexible, reliable, secure, and power-efficient WBANs suitable for medical applications. This paper discusses implementation issues and describes the authors' prototype sensor network for health monitoring that utilizes off-the-shelf 802.15.4 compliant network nodes and custom-built motion and heart activity sensors. The paper presents system architecture and hardware and software organization, as well as the authors' solutions for time synchronization, power management, and on-chip signal processing. <s> BIB003 </s> QoS-aware MAC protocols for wireless sensor networks: A survey <s> Introduction <s> In this paper, we assess the state of the art of Quality of Services (QoS) support in wireless sensor networks (WSNs). Unlike traditional end-to-end multimedia applications, many non-end-to-end mission-critical applications envisioned for WSNs have brought forward new QoS requirements on the network. Further, unique characteristics of WSNs, such as extremely resource-constrained sensors, large-scale random deployment, and novel data-centric communication protocols, pose unprecedented challenges in the area of QoS support in WSNs. Thus, we first review the techniques for QoS support in traditional networks, analyze new QoS requirements in WSNs from a wide variety of applications classified by data delivery models, and propose some non-end-to-end collective QoS parameters. Next, the challenges of QoS support in this new paradigm are presented. Finally, we comment on current research efforts and identify many exciting open issues in order to stimulate more research interest in this largely unexplored area. Keywords— Wireless networks, wireless sensor networks, QoS, collective QoS <s> BIB004 </s> QoS-aware MAC protocols for wireless sensor networks: A survey <s> Introduction <s> Wireless sensor networks are appealing to researchers due to their wide range of application potential in areas such as target detection and tracking, environmental monitoring, industrial process monitoring, and tactical systems. However, low sensing ranges result in dense networks and thus it becomes necessary to achieve an efficient medium-access protocol subject to power constraints. Various medium-access control (MAC) protocols with different objectives have been proposed for wireless sensor networks. In this article, we first outline the sensor network properties that are crucial for the design of MAC layer protocols. Then, we describe several MAC protocols proposed for sensor networks, emphasizing their strengths and weaknesses. Finally, we point out open research issues with regard to MAC layer design. <s> BIB005 </s> QoS-aware MAC protocols for wireless sensor networks: A survey <s> Introduction <s> The availability of low-cost hardware such as CMOS cameras and microphones has fostered the development of Wireless Multimedia Sensor Networks (WMSNs), i.e., networks of wirelessly interconnected devices that are able to ubiquitously retrieve multimedia content such as video and audio streams, still images, and scalar sensor data from the environment. In this paper, the state of the art in algorithms, protocols, and hardware for wireless multimedia sensor networks is surveyed, and open research issues are discussed in detail. Architectures for WMSNs are explored, along with their advantages and drawbacks. Currently off-the-shelf hardware as well as available research prototypes for WMSNs are listed and classified. Existing solutions and open research issues at the application, transport, network, link, and physical layers of the communication protocol stack are investigated, along with possible cross-layer synergies and optimizations. <s> BIB006 </s> QoS-aware MAC protocols for wireless sensor networks: A survey <s> Introduction <s> In today's competitive industry marketplace, the companies face growing demands to improve process efficiencies, comply with environmental regulations, and meet corporate financial objectives. Given the increasing age of many industrial systems and the dynamic industrial manufacturing market, intelligent and low-cost industrial automation systems are required to improve the productivity and efficiency of such systems. The collaborative nature of industrial wireless sensor networks (IWSNs) brings several advantages over traditional wired industrial monitoring and control systems, including self-organization, rapid deployment, flexibility, and inherent intelligent-processing capability. In this regard, IWSN plays a vital role in creating a highly reliable and self-healing industrial system that rapidly responds to real-time events with appropriate actions. In this paper, first, technical challenges and design principles are introduced in terms of hardware development, system architectures and protocols, and software development. Specifically, radio technologies, energy-harvesting techniques, and cross-layer design for IWSNs have been discussed. In addition, IWSN standards are presented for the system owners, who plan to utilize new IWSN technologies for industrial automation applications. In this paper, our aim is to provide a contemporary look at the current state of the art in IWSNs and discuss the still-open research issues in this field and, hence, to make the decision-making process more effective and direct. <s> BIB007 </s> QoS-aware MAC protocols for wireless sensor networks: A survey <s> Introduction <s> Visual sensor networks have emerged as an important ::: class of sensor-based distributed intelligent systems, ::: with unique performance, complexity, and quality of service ::: challenges. Consisting of a large number of low-power camera nodes, ::: visual sensor networks support a great number of novel ::: vision-based applications. The camera nodes provide information ::: from a monitored site, performing distributed and collaborative ::: processing of their collected data. Using multiple cameras in the ::: network provides different views of the scene, which enhances ::: the reliability of the captured events. However, the large amount ::: of image data produced by the cameras combined with the ::: network's resource constraints require exploring new means ::: for data processing, communication, and sensor management. ::: Meeting these challenges of visual sensor networks requires ::: interdisciplinary approaches, utilizing vision processing, communications ::: and networking, and embedded processing. In this ::: paper, we provide an overview of the current state-of-the-art in ::: the field of visual sensor networks, by exploring several relevant ::: research directions. Our goal is to provide a better understanding ::: of current research problems in the different research fields of ::: visual sensor networks, and to show how these different research ::: fields should interact to solve the many challenges of visual sensor ::: networks. <s> BIB008
Wireless sensor networks (WSNs) have appeared as one of the emerging technologies that combine automated sensing, embedded computing and wireless networking into tiny embedded devices. While the early research on WSNs has mainly focused on monitoring applications, such as agriculture  and environmental monitoring BIB001 , based on low-rate data collection, current WSN applications can support more complex operations ranging from health care BIB003 to industrial monitoring and automation BIB007 . Besides these, the availability of low-cost hardware and rapid development of tiny cameras and microphones have enabled a new class of WSNs: multimedia or visual wireless sensor networks BIB006 BIB008 and this new class has contributed to new potential WSN applications, such as surveillance. What is common in these emerging application domains is that performance and quality of service (QoS) assurances are becoming crucial as opposed to the best-effort performance in traditional monitoring applications. The term QoS is widely used in the area of all kinds of networks but still there is no consensus on its exact meaning. International Telecommunication Union (ITU) Recommendation E.800 (09/08) has defined QoS as: ''Totality of characteristics of a telecommunications service that bear on its ability to satisfy stated and implied needs of the user of the service''. Traditionally it refers to the control mechanisms that orchestrate the resource reservation rather than the provided service quality itself. Simply or practically, QoS brings the ability of giving different priorities to various users, applications, and data flows, frames or packets based on their requirements by controlling the resource sharing. Hence higher level of performance over others can be provided through a set of measurable service parameters such as delay, jitter, available bandwidth, and packet loss. QoS requirements in traditional data networks fundamentally stem from the end-to-end bandwidth-hungry multimedia applications BIB004 . In this context, reservationbased approaches, such as Integrated Services or IntServ  , are widely used in providing QoS guarantees. However, guaranteeing a certain QoS is a challenging issue due to the unpredictable nature of the wireless links, unstable topology (due to node failure or link failure) and severe resource constraints in WSNs. These constraints make it harder to adopt the existing solutions in wired and other wireless networks. Besides these constraints, while recent applications, especially real-time, multimedia and mission-critical applications, call for Qos support, the inherent characteristic of WSNs, ''energy efficiency'' makes the QoS provision a challenging task. Parallel to recent advancements, WSN applications have become more and more bandwidth-hungry and delaysensitive. In order to meet these requirements, WSNs need novel and well-designed QoS support in each layer of the communication protocol stack since envisioned applications are dissimilar to traditional end-to-end applications. Especially real-time multimedia and mission-critical applications brought forward new QoS requirements since they need delay-bounded and reliable data delivery. This variety of the applications and requirements of these applications make implementation of a ''one-size-for-all'' QoS-support mechanism impossible. However, well-defined requirements and QoS parameters can be a guide to develop QoS-support for effective and efficient delivery of sensor data. In this work, we focus on the QoS support at the MAC layer and survey the existing protocols in the literature. Although centralized MAC schemes exist for other types of networks, such as point coordination function (PCF) in IEEE 802.11, where nodes request the right for medium access from a coordinator, these schemes are hardly applied to WSNs due to the large number of sensor nodes, multihop nature of the networks and scalability issues. Therefore, our focus is on distributed QoS support at the MAC layer. The reason why we focus on the MAC layer is that, all other upper-layer components are dependent on the MAC layer and this makes it a primary decisive factor for the overall performance of the network. Nowadays, cross-layer solutions for WSNs where functionalities of multiple traditional layers are melted into a functional module, are widely adopted BIB002 . By the cross-layer approach, a single module can obtain every necessary information regardless of the layer abstraction and has chance to optimize the overall performance of the sensor network. However, interoperability or interchangeability between layers cannot be mentioned in this case since there is no layer abstraction within the protocol stack. In case of QoS support, there is no distinction between layered and cross-layer protocols. QoS awareness can be adopted with the same goals and challenges by both concepts. In this paper, our aim is to survey the existing QoSaware MAC protocols for WSNs including mobile, underground and underwater sensor networks. To the best of our knowledge, although there exist surveys on QoS support in WSNs BIB004 and on MAC protocols for WSNs BIB005  , there is no extensive survey paper on the QoSaware MAC protocols, including their comparative evaluation. Although, Zogovic et al.  briefly summarize QoS Provisioning at MAC and physical layers for WSNs, they neither provide an extensive survey, nor discuss the comparisons and provide a classification together with future research directions. Our contribution is to present a detailed survey on the topic and discuss the open issues in this domain which, we believe, is going to receive a lot of attention in the coming years. We start with a background information in the context of QoS provision in wired and wireless networks. We summarize different types of QoS approaches and discuss which can be applied to WSNs. Additionally, we mention the QoS perspectives, namely application-specific QoS and network-specific QoS, and discuss the requirements of different types of applications. Then, we elaborate on the challenges of QoS provisioning in WSNs and discuss the QoS metrics, such as bounded delay, guaranteed throughput, together with the tunable parameters at the MAC layer, such as duty cycle, contention window size. After explaining the metrics and parameters, we discuss the QoS mechanisms that can be applied in the context of WSNs. We then continue explaining the details of existing QoS-aware MAC protocols for WSNs including their QoS metrics, parameters, mechanisms and present an extensive comparison of them. We conclude the paper with open research issues and possible future research directions. The rest of the paper is organized as follows: in Section 2, we provide background information on QoS support in wired and wireless networks. In Section 3, we discuss the QoS challenges and continue with the QoS metrics in WSNs in Section 4. We present the QoS mechanisms in Section 5 and explain the details of the existing QoS-aware MAC protocols in WSNs and give comparisons in Section 6. Section 7 discusses the MAC layer tradeoffs and Section 8 elaborates on the properties of a well-defined MAC protocol. In Section 9 we discuss the open issues and give possible directions for the future research. Finally, in Section 10, we draw the conclusions.