A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> Energy-efficient channel access <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> BIB001 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> Energy-efficient channel access <s> H-MAC is a novel Time Division Multiple Access (TDMA) based MAC protocol designed for Body Sensor Networks (BSNs). It improves energy efficiency by exploiting human heartbeat rhythm information to perform time synchronization for TDMA. Heartbeat rhythm is inherent in every human body and can be detected in a variety of biosignals. Therefore, biosensors in BSNs can extract the heartbeat rhythm from their sensory data. Moreover, all the rhythms represented by peak sequences are naturally synchronized since they are driven by the same source, the heartbeat. By following the rhythm, wireless biosensors can achieve time synchronization without having to turn on their radio to receive periodic timing information from a central controller, so that energy cost for time synchronization can be completely avoided and the lifetime of network can be prolonged. An active synchronization recovery scheme is also developed, in which two resynchronization procedures are implemented. The algorithms are verified using real world data from MIT-BIH multi-parameter database MIMIC. <s> BIB002 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> Energy-efficient channel access <s> Wireless body area networks (WBANs) form a new and interesting area in the world of remote health monitoring. An important concern in such networks is the communication between the sensors. This communication needs to be energy efficient and highly reliable while keeping delays low. Mobility also has to be supported as the nodes are positioned on different parts of the body that move with regard to each other. In this paper, we present a new cross-layer communication protocol for WBANs: CICADA or Cascading Information retrieval by Controlling Access with Distributed slot Assignment. The protocol sets up a network tree in a distributed manner. This tree structure is subsequently used to guarantee collision free access to the medium and to route data towards the sink. The paper analyzes CICADA and shows simulation results. The protocol offers low delay and good resilience to mobility. The energy usage is low as the nodes can sleep in slots where they are not transmitting or receiving. <s> BIB003 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> Energy-efficient channel access <s> This paper presents a novel energy-efficient MAC Protocol designed specifically for wireless body area sensor networks (WBASN) focused towards pervasive healthcare applications. Wireless body area networks consist of wireless sensor nodes attached to the human body to monitor vital signs such as body temperature, activity or heart-rate. The network adopts a master-slave architecture, where the body-worn slave node periodically sends sensor readings to a central master node. Unlike traditional peer-to-peer wireless sensor networks, the nodes in this biomedical WBASN are not deployed in an ad hoc fashion. Joining a network is centrally managed and all communications are single-hop. To reduce energy consumption, all the sensor nodes are in standby or sleep mode until the centrally assigned time slot. Once a node has joined a network, there is no possibility of collision within a cluster as all communication is initiated by the central node and is addressed uniquely to a slave node. To avoid collisions with nearby transmitters, a clear channel assessment algorithm based on standard listen-before-transmit (LBT) is used. To handle time slot overlaps, the novel concept of a wakeup fallback time is introduced. Using single-hop communication and centrally controlled sleep/wakeup times leads to significant energy reductions for this application compared to more ldquoflexiblerdquo network MAC protocols such as 802.11 or Zigbee. As duty cycle is reduced, the overall power consumption approaches the standby power. The protocol is implemented in hardware as part of the Sensiumtrade system-on-chip WBASN ASIC, in a 0.13- mum CMOS process. <s> BIB004 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> Energy-efficient channel access <s> This paper presents an energy-efficient medium access control protocol suitable for communication in a wireless body area network for remote monitoring of physiological signals such as EEG and ECG. The protocol takes advantage of the static nature of the body area network to implement the effective time-division multiple access (TDMA) strategy with very little amount of overhead and almost no idle listening (by static, we refer to the fixed topology of the network investigated). The main goal is to develop energy-efficient and reliable communication protocol to support streaming of large amount of data. TDMA synchronization problems are discussed and solutions are presented. Equations for duty cycle calculation are also derived for power consumption and battery life predictions. The power consumption model was also validated through measurements. Our results show that the protocol is energy efficient for streaming communication as well as sending short bursts of data, and thus can be used for different types of physiological signals with different sample rates. The protocol is implemented on the analog devices ADF7020 RF transceivers. <s> BIB005 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> Energy-efficient channel access <s> We propose the cross-layer based battery-aware time division multiple access (TDMA) medium access control (MAC) protocols for wireless body-area monitoring networks in wireless healthcare applications. By taking into account the joint effect of electrochemical properties of the battery, time-varying wireless fading channels, and packet queuing characteristics, our proposed schemes are designed to prolong the battery lifespan of the wireless sensor nodes while guaranteeing the reliable and timely message delivery, which is critically important for the patient monitoring networks. In addition, we develop a Markov chain model to analyze the performance of our proposed schemes. Both the obtained analytical and simulation results show that our proposed schemes can significantly increase the battery lifespan of sensor nodes while satisfying the reliability and delay-bound quality of service (QoS) requirements for wireless body-area monitoring networks. Furthermore, the case study of the electrocardiogram (ECG) monitoring application shows that besides meeting the delay requirements, our proposed schemes outperform the IEEE 802.15.4 and Bluetooth protocols in terms of battery lifespan. <s> BIB006 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> Energy-efficient channel access <s> Body Area Networks (BAN) are a specific type of Network structure. They are spread over a very small area and their available power is heavily constrained. Hence it is useful to have gateway points in the network, such as nodes carried around the belt, that are less power constrained and can be used for network coordination. This network structure can result in very low transmission power/range for the sensors and effective TDMA timing control. This paper presents an energy-efficient MAC protocol for communication within the Wireless Body Area Network. The protocol takes advantage of the fixed nature of the Body Area Network to implement a TDMA strategy with very little communication overhead, long sleep times for the sensor transceivers and robustness to communication errors. The protocol is implemented on the Analog Devices ADF7020 RF transceivers. <s> BIB007 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> Energy-efficient channel access <s> Wireless body sensor networks (BSNs) in healthcare systems operate under conflicting requirements. These are the maintenance of the desired reliability and message latency of data transmissions, while simultaneously maximizing battery lifetime of individual body sensors. In doing so, the characteristics of the entire system, including physical, medium access control (MAC), and application layers have to be considered. The aim of this paper is to develop a new MAC model for BSNs to fulfill all these specific rigorous requirements under realistic medical settings. For that purpose, a novel cross-layer fuzzy-rule scheduling algorithm and energy-aware radio activation policies are introduced. The main idea is to integrate a fuzzy-logic system in each body sensor to deal with multiple cross-layer input variables of diverse nature in an independent manner. By being autonomously aware of their current condition, body sensors are able to demand a "collision-free" time slot, whenever they consider it strictly required (e.g. high system packet delay or low body sensor residual battery lifetime). Similarly, they may refuse to transmit, if there is a bad channel link, thus permitting another body sensor to do so. This results in improving the system overall performance. The proposed MAC model is evaluated by computer simulations in terms of quality of service and energy consumption under specific healthcare scenarios. <s> BIB008 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> Energy-efficient channel access <s> This paper presents an energy-efficient implementation of a real-time on-demand MAC protocol for medical Wireless Body Sensor Network (WBSN). Medical WBSN is focused on pervasive healthcare and medical applications, such as monitoring vital signs, making basic drug delivery, etc. The sensor nodes in the heterogeneous WBSN generally require different data rates, due to their differing functions. Additionally, because of the strict resource constraints, the sensor nodes must be ultra-low-power. Thirdly, low-rate treatment-function nodes must also “work-on-demand” to prove proper activities in the slave nodes such as stimulus and drug delivery. These three requirements cannot currently be satisfied simultaneously in commonly-used single channel implementations because the channel monitoring consumes too much power for long-term use. In the proposed implementation, a secondary channel is introduced in, which is used for channel listening only. Benefiting from the secondary channel, the node can achieve both real-time “work-on-demand” and zero idle power, by means of recovering energy from the “demand token”. An elaborated energy-harvesting RF module achieves monitoring the secondary channel. The prototype system of sensor nodes is expected for the zero-idle-power and the response time of less than 2ms. <s> BIB009 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> Energy-efficient channel access <s> Wireless Body Area Network (WBAN) consists of low-power, miniaturized, and autonomous wireless sensor nodes that enable physicians to remotely monitor vital signs of patients and provide real-time feedback with medical diagnosis and consultations. It is the most reliable and cheaper way to take care of patients suffering from chronic diseases such as asthma, diabetes and cardiovascular diseases. Some of the most important attributes of WBAN is low-power consumption and delay. This can be achieved by introducing flexible duty cycling techniques on the energy constraint sensor nodes. Stated otherwise, low duty cycle nodes should not receive frequent synchronization and control packets if they have no data to send/receive. In this paper, we introduce a Traffic-adaptive MAC protocol (TaMAC) by taking into account the traffic information of the sensor nodes. The protocol dynamically adjusts the duty cycle of the sensor nodes according to their traffic-patterns, thus solving the idle listening and overhearing problems. The traffic-patterns of all sensor nodes are organized and maintained by the coordinator. The TaMAC protocol is supported by a wakeup radio that is used to accommodate emergency and on-demand events in a reliable manner. The wakeup radio uses a separate control channel along with the data channel and therefore it has considerably low power consumption requirements. Analytical expressions are derived to analyze and compare the performance of the TaMAC protocol with the well-known beacon-enabled IEEE 802.15.4 MAC, WiseMAC, and SMAC protocols. The analytical derivations are further validated by simulation results. It is shown that the TaMAC protocol outperforms all other protocols in terms of power consumption and delay. <s> BIB010 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> Energy-efficient channel access <s> In ultra-low data rate wireless sensor networks (WSNs) waking up just to listen to a beacon every superframe can be a major waste of energy. This study introduces MedMAC, a medium access protocol for ultra-low data rate WSNs that achieves significant energy efficiency through a novel synchronisation mechanism. The new draft IEEE 802.15.6 standard for body area networks includes a sub-class of applications such as medical implantable devices and long-term micro miniature sensors with ultra-low power requirements. It will be desirable for these devices to have 10 years or more of operation between battery changes, or to have average current requirements matched to energy harvesting technology. Simulation results are presented to show that the MedMAC allows nodes to maintain synchronisation to the network while sleeping through many beacons with a significant increase in energy efficiency during periods of particularly low data transfer. Results from a comparative analysis of MedMAC and IEEE 802.15.6 MAC show that MedMAC has superior efficiency with energy savings of between 25 and 87% for the presented scenarios. <s> BIB011 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> Energy-efficient channel access <s> This work outlines challenges and requirements of designing a Medium Access Control (MAC) protocol for Body Area Networks, where sensor nodes send their measurement data to a central gateway device (also known as sink or hub) regularly on TDMA basis. While a number of protocols has already been proposed specifically for BAN's, they fail to account for unique characteristics of wireless channel around the human body, namely the deep and long fades that hinder communication. As such, they can not provide reliability and latency guarantees that are essential for many BAN applications. This work proposes to employ variable TDMA scheduling that allows the order of transmissions within each TDMA round to be decided dynamically, rather than be fixed in advance. Accordingly, the hub is able to account for variations of the wireless channel when allocating TDMA slots, thus increasing the probability of successful transmissions. Initial evaluations based on extensive experimental measurements have shown that, under strict latency constraints, variable scheduling approach allows to reduce transmission losses by up to 15% without accounting for retransmissions, and achieve over 99.5% reliability when retransmissions are enabled. <s> BIB012 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> Energy-efficient channel access <s> Public m-health service will enable care-givers to continuously monitor patients' vital signals wherever they are, using Body Area Networks (BANs). To make this service available to a large number of people everywhere, public m-health service should be implemented in a license-free frequency band. However, the coexistence problem inherent in such a medium that may be shared by many co-located systems may cause disruption of BAN transmissions. This paper addresses the above problem by proposing a Centralized BAN Access Scheme (CBAS) to improve service availability and robustness of BANs. CBAS puts most of the complexities in the gateway, which has less energy and resource constraints than the body nodes. The gateway monitors all the available channels and assigns an interference-free channel to each scheduled node. Extensive simulation results show the effectiveness of CBAS in reducing durations of service interruption and thus improving service reliability of a BAN. <s> BIB013 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> Energy-efficient channel access <s> A wireless body area sensor network (WBASN) demands ultra low power and energy efficient protocols. Medium access control (MAC) layer plays a pivotal role for energy management in WBASN. Moreover, idle listening is the dominant energy waste in most of the MAC protocols. WBASN exhibits wide range of traffic variations based on different physiological data emanating from the monitored patient. For example, electrocardiogram data rate is multiple times more in comparison with body temperature rate. In this context, we propose a novel energy efficient traffic-aware dynamic (TAD) MAC protocol for WBASN. The protocol relies on dynamic adaptation of wake-up interval based on a traffic status register bank. The proposed technique allows the wake-up interval to converge to a steady state for fixed and variable traffic rates, which results in optimized energy consumption. A comparison with other energy efficient protocols for three different widely used radio chips i.e., cc2420, cc1000, and amis52100 is presented. The results show that TAD-MAC outperforms all the other protocols under fixed and variable traffic rates. Finally, life- time of a WBASN was estimated and found to be 3-6 times better than other protocols. <s> BIB014 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> Energy-efficient channel access <s> In this paper, we propose a hybrid polling Medium Access Control (MAC) protocol with Human Energy Harvesting capabilities, called HEH-BMAC, designed for Wireless Body Area Networks (WBANs). The proposed protocol uses a dynamic schedule algorithm to combine User Identification polling (ID) and Probabilistic Contention (PC) random access, adapting the network operation to the random, time-varying nature of the human energy harvesting sources. HEH-BMAC offers different levels of node priorities (high and normal), energy-awareness and flexibility. Extensive simulations have been conducted in order to evaluate the energy efficiency and throughput of our scheme compared to IEEE 802.15.6 standard in energy harvesting conditions. <s> BIB015
Collision-free access TDMA for periodic allocations BIB001 BIB005 BIB011 BIB002 BIB012 BIB006  BIB013 Tree-based distributed scheduling BIB003 Hybrid access Contention phase for access request BIB007 (contention-based/collision-free) Distributed queuing with collision-free data transmission BIB008 Energy-aware polling and probabilistic hybrid access BIB015  Preamble sampling, Polling at predefined wake-up times BIB004 BIB010 minimizing idle listening Polling with dynamic learning of wake-up times BIB014 Polling through secondary receiver BIB009 Synchronization 