A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> MAC Layer Design for WBANs <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> BIB001 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> MAC Layer Design for WBANs <s> The wireless medium being inherently broadcast in nature and hence prone to interferences requires highly optimized medium access control (MAC) protocols. This holds particularly true for wireless sensor networks (WSNs) consisting of a large amount of miniaturized battery-powered wireless networked sensors required to operate for years with no human intervention. There has hence been a growing interest on understanding and optimizing WSN MAC protocols in recent years, where the limited and constrained resources have driven research towards primarily reducing energy consumption of MAC functionalities. In this paper, we provide a comprehensive state-of-the-art study in which we thoroughly expose the prime focus of WSN MAC protocols, design guidelines that inspired these protocols, as well as drawbacks and shortcomings of the existing solutions and how existing and emerging technology will influence future solutions. In contrast to previous surveys that focused on classifying MAC protocols according to the technique being used, we provide a thematic taxonomy in which protocols are classified according to the problems dealt with. We also show that a key element in selecting a suitable solution for a particular situation is mainly driven by the statistical properties of the generated traffic. <s> BIB002 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> MAC Layer Design for WBANs <s> The seamless integration of low-power, miniaturised, invasive/non-invasive lightweight sensor nodes have contributed to the development of a proactive and unobtrusive Wireless Body Area Network (WBAN). A WBAN provides long-term health monitoring of a patient without any constraint on his/her normal dailylife activities. This monitoring requires low-power operation of invasive/non-invasive sensor nodes. In other words, a power-efficient Medium Access Control (MAC) protocol is required to satisfy the stringent WBAN requirements including low-power consumption. In this paper, we first outline the WBAN requirements that are important for the design of a low-power MAC protocol. Then we study low-power MAC protocols proposed/investigated for WBAN with emphasis on their strengths and weaknesses. We also review different power-efficient mechanisms for WBAN. In addition, useful suggestions are given to help the MAC designers to develop a low-power MAC protocol that will satisfy the stringent WBAN requirements. <s> BIB003 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> MAC Layer Design for WBANs <s> Design of power-efficient medium access control (MAC) protocols in wireless body area networks (WBANs) is important as it helps to prolong the network lifetime. This paper attempts to survey recent works of power efficient MAC protocols for WBANs and presents a comparison of the approaches pursued. We investigate a few MAC protocols devised for WBAN by highlighting their salient features. Finally, a number of open research issues are discussed. <s> BIB004 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> MAC Layer Design for WBANs <s> Advances in wireless communication technologies, such as wearable and implantable biosensors, along with recent developments in the embedded computing area are enabling the design, development, and implementation of body area networks. This class of networks is paving the way for the deployment of innovative healthcare monitoring applications. In the past few years, much of the research in the area of body area networks has focused on issues related to wireless sensor designs, sensor miniaturization, low-power sensor circuitry, signal processing, and communications protocols. In this paper, we present an overview of body area networks, and a discussion of BAN communications types and their related issues. We provide a detailed investigation of sensor devices, physical layer, data link layer, and radio technology aspects of BAN research. We also present a taxonomy of BAN projects that have been introduced/proposed to date. Finally, we highlight some of the design challenges and open issues that still need to be addressed to make BANs truly ubiquitous for a wide range of applications. <s> BIB005 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> MAC Layer Design for WBANs <s> The increasing use of wireless networks and the constant miniaturization of electrical devices has empowered the development of Wireless Body Area Networks (WBANs). In these networks various sensors are attached on clothing or on the body or even implanted under the skin. The wireless nature of the network and the wide variety of sensors offer numerous new, practical and innovative applications to improve health care and the Quality of Life. The sensors of a WBAN measure for example the heartbeat, the body temperature or record a prolonged electrocardiogram. Using a WBAN, the patient experiences a greater physical mobility and is no longer compelled to stay in the hospital. This paper offers a survey of the concept of Wireless Body Area Networks. First, we focus on some applications with special interest in patient monitoring. Then the communication in a WBAN and its positioning between the different technologies is discussed. An overview of the current research on the physical layer, existing MAC and network protocols is given. Further, cross layer and quality of service is discussed. As WBANs are placed on the human body and often transport private data, security is also considered. An overview of current and past projects is given. Finally, the open research issues and challenges are pointed out. <s> BIB006 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> MAC Layer Design for WBANs <s> Recent developments and technological advancements in wireless communication, MicroElectroMechanical Systems (MEMS) technology and integrated circuits has enabled low-power, intelligent, miniaturized, invasive/non-invasive micro and nano-technology sensor nodes strategically placed in or around the human body to be used in various applications, such as personal health monitoring. This exciting new area of research is called Wireless Body Area Networks (WBANs) and leverages the emerging IEEE 802.15.6 and IEEE 802.15.4j standards, specifically standardized for medical WBANs. The aim of WBANs is to simplify and improve speed, accuracy, and reliability of communication of sensors/actuators within, on, and in the immediate proximity of a human body. The vast scope of challenges associated with WBANs has led to numerous publications. In this paper, we survey the current state-of-art of WBANs based on the latest standards and publications. Open issues and challenges within each area are also explored as a source of inspiration towards future developments in WBANs. <s> BIB007 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> MAC Layer Design for WBANs <s> Interest in Wireless Body Area Networks (WBANs) has increased significantly in recent years thanks to the advances in microelectronics and wireless communications. Owing to the very stringent application requirements in terms of reliability, energy efficiency, and low device complexity, the design of these networks requires the definition of new protocols with respect to those used in general purpose wireless sensor networks. This motivates the effort in research activities and in standardisation process of the last years. This survey paper aims at reporting an overview of WBAN main applications, technologies and standards, issues in WBANs design, and evolutions. Some case studies are reported, based on both real implementation and experimentation on the field, and on simulations. These results have the aim of providing useful insights for WBAN designers and of highlighting the main issues affecting the performance of these kind of networks. <s> BIB008
The main functions of the MAC layer include: (i) the access regulation to the shared wireless medium among the system nodes; and (ii) the scheduling of transmissions to achieve desired performance goals, such as throughput guarantees, time-delay constraints and QoS provisioning. In addition to these functionalities that are common to all systems, a MAC protocol suitable for WBANs must handle specific challenges, associated with the WBAN topology and the node constraints. Furthermore, the MAC protocol design has a significant impact on energy efficiency, QoS provisioning, reliability and interference, which, as mentioned in Section 3, are some key requirements of mHealth applications. Several extensive surveys and comprehensive guidelines on MAC layer design for the wider category of sensor networks are available in the literature, such as the works in BIB001  and more recently in BIB002 . Even though these works can provide helpful insights for many of the challenges also faced in WBANs, especially in the design of low-energy MAC protocols, they are not specifically addressed to healthcare applications. Two overviews on WBAN-oriented MAC protocols have been published in 2010 BIB003 BIB004 , but are missing later advancements in this rapidly growing research field. Finally, more recent surveys on WBANs that include discussions on the MAC layer challenges can be found in BIB005 BIB006 BIB007 BIB008 . In this section, we update and complement the existing surveys by identifying the main challenges and design approaches to tackle the aforementioned requirements of mHealth applications in WBANs. After a thorough study of the proposed MAC protocols in the literature, we provide a survey of the representative mechanisms employed for (i) energy-efficient channel access and synchronization; (ii) QoS provisioning; (iii) reliability; and (iv) interference mitigation and coexistence.