Medium Access Control

Underwater wireless sensor networks (UWSN) consist of a certain number of sensors that interact to send the sensed data to the sink node and perform collaborative task. Most UWSN choose acoustic as a communication medium for wireless transmission. However, electromagnetic waves are also offer a great merit in special underwater environment such as shallow water. UWSN is significantly different from terrestrial sensor networks in many aspects such as mobility of sensor nodes due to water current, propagation delay and propagation loss. These distinctions feature of underwater sensor network pose many new challenges for delivering information from sensor nodes to sink node effectively in UWSN. To achieve reliable data transfer in underwater sensor network scenarios, a new event MAC protocol need to be developed to provide energy efficient and reliable upstream data transfer.

Media Access Control (MAC) must be carefully considered in multi-hop Underwater Acoustic Sensor Networks (UASNs) due to limited bandwidth and large propagation delay. In particular, variable propagation delays in UASNs cause inaccurate time synchronization and therefore make reservation-based protocols less favorable. Large propagation delays limit the performance of carrier sense in predicting the status of the intended recipients, and therefore CSMA protocols show bad performance in UASNs too. Therefore, simple protocols, such as Aloha, show promise for UASNs. In this paper we consider the performance of a multi-hop ppersistent ALOHA protocol.

Considering the dynamic nature of portable computing devices with wireless communication capability, an extended model is introduced for worm spreading in the wireless ad hoc network, with a population of mobile agents in a planar distribution, starting from an initial infected seed. The effect of agents' mobility on worm spreading is investigated via extensive Monte Carlo simulations. The threshold behavior and the dynamics of worm epidemics in the wireless networks are greatly affected by both agents' mobility and spatial and temporal correlations. The medium access control mechanism for the wireless communication promotes the sensitivity of the spreading dynamics to agents' mobility.

Extensive studies have been carried out for reducing the handover time of wireless mobile network at medium access control (MAC) layer. However, none of them show the impact of reduced handover time on the overall performance of wireless mobile networks. This paper presents a quantitative analysis to show the impact of reduced handover time on the performance of wireless mobile networks. The proposed quantitative model incorporates many critical performance parameters involve in reducing the handover time for wireless mobile networks. In addition, we analyze the use of active scanning technique with comparatively shorter beacon interval time in a handoff process. Our experiments verify that the active scanning can reduce the overall handover time at MAC layer if comparatively shorter beacon intervals are utilized for packet transmission. The performance measures adopted in this paper for experimental verifications are network throughput under different network loads.

This paper proposes a general wireless sensor network architecture for monitoring horticultural crops that are distributed among small plots scattered at distances of up to 10 km from one another. The technology used for the real implementation of the architecture is based on the B-MAC (Berkeley Medium Access Control) medium access protocol to assure a high degree of sensor node power autonomy. To resolve this issue, a series of specialized sensor nodes (Soil-Mote, Environmental-Mote and Water-Mote) have been developed along with a gateway to interconnect them with the farm central offices. Before starting device development, simulations were conducted to ensure that acceptable performance would be achieved with the selected technology in terms of node autonomy, achieved throughput and delays. To that end, it was necessary to implement the selected B-MAC protocol in the ns-2 (Network Simulator-2) simulation framework. The final system was deployed on a real crop to check and validate the simulation results against experimental results.

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 lifetime of a WBASN was estimated and found to be 3 to 6 times better than other protocols.

We analyze an efficient Medium Access Control (MAC) protocol for use in a single cell of a wireless Local Area Network (LAN). A fixed frame structure with two periods is used; one period for making reservations using a Slotted Aloha protocol and a second period for data transmission. The MAC protocol operates in a centralized manner in which a single station, the base station, accepts reservations (transmission or data requests) that are made by the remote stations, and then schedules the times in which they will transmit or receive data. We consider two different types of client-server traffic models, an open-loop and a closed-loop model. In the open-loop model, a remote station can generate reservation requests for the base station whether or not it has received a response from the base station. In the closed-loop case, the remote station waits for a response before generating a new request. The performance of the MAC protocol was analyzed exactly for both the open and closed-loop traffic models and for cases in which transmission errors and a meanvalue type of radio capture model are included. In addition, different policies were considered for the transmission strategy that is used by the remote stations when they attempt to make reservations. We derive exact results for the mean throughput and waiting times as well as for the queue length distributions. We also derive an approximate Markov chain to treat a case in which a fixed-position capture model is used. Several types of behavior are illustrated through the use of numerical examples.

This article reviews the state-of-the-art energy-efficient contention-based and scheduledbased medium access control (MAC) protocols for mobile sensor networks (MSNs) by first examining access schemes for wireless sensor networks (WSNs). Efficient and proper mobility handling in sensor networks provides a window of opportunity for new applications. Protocols, such as S-MAC, reduce energy consumption by putting nodes to sleep after losing to channel contention or to prevent idling. Sleeping is a common method for energyefficient MAC protocols, but delay depends on sleep duration or frame time, and longer delays lead to higher packet lost rate when nodes are unsynchronized due to network mobility. MS-MAC extends S-MAC to include mobility-awareness by decreasing this sleep duration when mobility is detected. S-MAC with extended Kalman filter (EKF) reduces mobility-incurred losses by predicting the optimal data frame size for each transmission. MMAC utilizes a dynamic mobility-adaptive frame time to enhance TRAMA, a scheduled-based protocol, with mobility prediction. Likewise, G-MAC utilizes TDMA for cluster-based WSNs by combining the advantages of contention and contention-free MACs. Z-MAC also combines both methods but without clustering and allows time slot re-assignments during significant topology changes. All of the above MAC protocols are reviewed in detail.

In this paper, we provide a review of the benefits of employing multiple-input multiple-output (MIMO) processing techniques in vehicular ad hoc networks VANETs. These benefits include increasing the range of communication via beamforming, improving the reliability of communication via spatial diversity, increasing the throughput of the network via spatial multiplexing, and managing multiuser interference due to the presence of multiple transmitting terminals. We also present a number of key research challenges facing MIMO VANETs. The first one is deriving statistical MIMO-V2V channel models that take into account the spatial correlation between the transmit and receive antennas and validating them via extensive channel measurement campaigns. Deriving channel estimation and tracking algorithms for MIMO inter-vehicular channels is another challenging problem due to their non-stationary behavior and high Doppler spread. Further research is also needed to fully reap the benefits of multiple antennas in VANETs via space-time and space-frequency processing. In addition, cross layer optimization spanning the medium access control (MAC) and networking layers besides the physical layer is essential to satisfy the emerging applications of VANETS ranging from safety, convenience to infotainment.

In this paper, we propose a method for user selection and channel estimation for the multiple-input multiple-output (MIMO) broadcast channel for the downlink of a cellular mobile or local-area wireless communication system.A distributed self-selection procedure is combined with a code-division multiple access (CDMA) uplink signaling strategy to reduce the uplink signaling bandwidth, and the computational complexity of user selection at the base station. We exploit recent advances in sparse signal recovery, which we apply to the uplink multi-user detection and channel estimation problems to reduce the signaling bandwidth. We establish that full channel state information (and not just channel quality) for each self-selecting user can be obtained at the base station via a compressed-sensing technique with no increase in overhead for the uplink feedback channel. We demonstrate the new method as a medium access technique for MIMO downlink broadcast with transmitter precoding and linear receiver processing.

Studies of ad hoc wireless networks are a relatively new field gaining more popularity for various new applications. In these networks, the Medium Access Control (MAC) protocols are responsible for coordinating the access from active nodes. These protocols are of significant importance since the wireless communication channel is inherently prone to errors and unique problems such as the hidden-terminal problem, the exposed-terminal problem, and signal fading effects. Although a lot of research has been conducted on MAC protocols, the various issues involved have mostly been presented in isolation of each other. We therefore make an attempt to present a comprehensive survey of major schemes, integrating various related issues and challenges with a view to providing a big-picture outlook to this vast area. We present a classification of MAC protocols and their brief description, based on their operating principles and underlying features. In conclusion, we present a brief summary of key ideas and a general direction for future work.

An experimental investigation of the influence of the fiber distribution of wireless LAN (WLAN) signals on throughput performance is presented. Transmission using different mediumaccess-control mechanisms and IEEE 802.11b and 802.11g physical layers is considered, and results are compared with those from the corresponding simulations in a commercial event-driven network simulator (OPNET). Performance of the WLAN-overfiber network in the presence of multiple clients is also analyzed. This paper confirms that a fiber delay does not significantly affect the performance obtained by fragmentation mechanism. Furthermore, when multiple antenna units are fed by a single access point, it is demonstrated that the presence of hidden nodes can cause the performance of WLAN-over-fiber networks to deteriorate. Finally, it is shown that the request-to-send/clear-to-send mechanism can be utilized to mitigate the negative effects associated with the hidden node problem.

This paper describes the concept of sensor networks which has been made viable by the convergence of microelectro-mechanical systems technology, wireless communications and digital electronics. First, the sensing tasks and the potential sensor networks applications are explored, and a review of factors influencing the design of sensor networks is provided. Then, the communication architecture for sensor networks is outlined, and the algorithms and protocols developed for each layer in the literature are explored. Open research issues for the realization of sensor networks are also discussed. Ó 2002 Published by Elsevier Science B.V.

We analyze an efficient Medium Access Control (MAC) protocol for use in a single cell of a wireless Local Area Network (LAN). A fixed frame structure with two periods is used; one period for making reservations using a Slotted Aloha protocol and a second period for data transmission. The MAC protocol operates in a centralized manner in which a single station, the base station, accepts reservations (transmission or data requests) that are made by the remote stations, and then schedules the times in which they will transmit or receive data. We consider two different types of client-server traffic models, an open-loop and a closed-loop model. In the open-loop model, a remote station can generate reservation requests for the base station whether or not it has received a response from the base station. In the closed-loop case, the remote station waits for a response before generating a new request. The performance of the MAC protocol was analyzed exactly for both the open and closed-loop traffic models and for cases in which transmission errors and a meanvalue type of radio capture model are included. In addition, different policies were considered for the transmission strategy that is used by the remote stations when they attempt to make reservations. We derive exact results for the mean throughput and waiting times as well as for the queue length distributions. We also derive an approximate Markov chain to treat a case in which a fixed-position capture model is used. Several types of behavior are illustrated through the use of numerical examples.

Cognitive Radio plays a major part in communication technology by resolving the shortage of the spectrum through usage of dynamic spectrum access and artificial intelligence characteristics. The element of spectrum sharing in cognitive radio is a fundamental approach in utilising free channels. Cooperatively communicating cognitive radio devices use the common control channel of the cognitive radio medium access control to achieve spectrum sharing. Thus, the common control channel and consequently spectrum sharing security are vital to ensuring security in the subsequent data communication among cognitive radio nodes. In addition to well known security problems in wireless networks, cognitive radio networks introduce new classes of security threats and challenges, such as licensed user emulation attacks in spectrum sensing and misbehaviours in the common control channel transactions, which degrade the overall network operation and performance. This review paper briefly presents the known threats and attacks in wireless networks before it looks into the concept of cognitive radio and its main functionality. The paper then mainly focuses on spectrum sharing security and its related challenges. Since spectrum sharing is enabled through usage of the common control channel, more attention is paid to the security of the common control channel by looking into its security threats as well as protection and detection mechanisms. Finally, the pros and cons as well as the comparisons of different CR-specific security mechanisms are presented with some open research issues and challenges.

Wireless sensor networks have been used to gather data and information in many diverse application settings. The capacity of such networks remains a fundamental obstacle toward the adaptation of sensor network systems for advanced pplications
that require higher data rates and throughput. In this paper, we explore potential benefits of integrating directional antennas into wireless sensor networks. While the usage of directional antennas has been investigated in the past for ad hoc networks, their usage in sensor networks bring both opportunities as well as challenges. In this paper, Sectored-Antenna Medium Access Control (SAMAC), an integrated cross-layer protocol that provides the communication mechanisms for sensor network to fully utilize sectored antennas, is introduced. Simulation studies show that SAMAC delivers high energy efficiency and predictable delay performance with graceful degradation in performance with increased load.

This paper presents a distributed implementation of RAND, a randomized time slot scheduling algorithm, called DRAND. DRAND runs in O(δ) time and message complexity where δ is the maximum size of a two-hop neighborhood in a wireless network while message complexity remains O(δ), assuming that message delays can be bounded by an unknown constant. DRAND is the first fully distributed version of RAND. The algorithm is suitable for a wireless network where most nodes do not move, such as wireless mesh networks and wireless sensor networks. We implement the algorithm in TinyOS and demonstrate its performance in a real testbed of Mica2 nodes. The algorithm does not require any time synchronization and is shown to be effective in adapting to local topology changes without incurring global overhead in the scheduling. Because of these features, it can also be used even for other scheduling problems such as frequency or code scheduling (for FDMA or CDMA) or local identifier assignment for wireless networks where time synchronization is not enforced.

1 -DSRC (Dedicated Short Range Communications) is a well known widespread technology. One of the main applications of DSRC is RTTT (Road Transport and Traffic Telematics), especially EFC (Electronic Fee Collection) on tolled roads, bridges or tunnels. Other vehicle-related applications had been envisaged, such as car parking or fuel refilling automatic payment. These applications were successfully developed, deployed and are in current use in Portugal. Especially for EFC, medium access control is of utmost importance. In this paper we present a possible implementation scheme for the MAC-layer, suitable for low-cost microcontrollers, to operate between the two equipments (as in ), the RSE (Road Side Equipment) and the OBE (On Board Equipment). The result is interface software that controls the referred communication, embracing hardware and software into a join solution.

This article reviews the state-of-the-art energy-efficient contention-based and scheduledbased medium access control (MAC) protocols for mobile sensor networks (MSNs) by first examining access schemes for wireless sensor networks (WSNs). Efficient and proper mobility handling in sensor networks provides a window of opportunity for new applications. Protocols, such as S-MAC, reduce energy consumption by putting nodes to sleep after losing to channel contention or to prevent idling. Sleeping is a common method for energyefficient MAC protocols, but delay depends on sleep duration or frame time, and longer delays lead to higher packet lost rate when nodes are unsynchronized due to network mobility. MS-MAC extends S-MAC to include mobility-awareness by decreasing this sleep duration when mobility is detected. S-MAC with extended Kalman filter (EKF) reduces mobility-incurred losses by predicting the optimal data frame size for each transmission. MMAC utilizes a dynamic mobility-adaptive frame time to enhance TRAMA, a scheduled-based protocol, with mobility prediction. Likewise, G-MAC utilizes TDMA for cluster-based WSNs by combining the advantages of contention and contention-free MACs. Z-MAC also combines both methods but without clustering and allows time slot re-assignments during significant topology changes. All of the above MAC protocols are reviewed in detail.

~Ihsrruci-~rhe IEEE 802.1 I Medium Access Control (MAC) protucol provides a contention-based distributed channel access mechanism for mobile stations to share the wireless medium, which may introduce a lot of collisions in ease of overloaded active stations. Slow Contention Window (CW) decrease scheme is a simple and efficient solution for this problem. In this paper, we use an analytical model to compare the slow CW decrease scheme t u the IEEE 802.11 MAC protocol. Several parameters are invcrtigdted such as thc number of Svations, the initial CW size. the decrease factor value. the maximum bdckoff stage and the coexistence with the RequestToSend and ClearToSend (RlSICTS) mechanism. The results show that the slow CW decl-ease scheme can efficiently improve the throughput of IEEE 802.11. a n d that the throughput gain is higher when the -decrease hctor is larger. Moreover, the initial CW size and maximum backoff stage also affect tlie performance of slow CW decrease scheme. K q w i r d s -IEEE X02.11; DCF; slow CW decrease scheme; ~r s m s

Increasing deployment density and shrinking size of wireless sensor nodes requires small equipped battery size. This means emerging wireless sensor nodes must compete for efficient energy utilization. Medium Access Control (MAC) protocols play a vital role in energy consumption of sensor node as it controls the radio activities. Customized or open source simulators play an important role to measure the performance effectiveness of MAC protocols based on the fact that they are flexible, reduce experimental overhead and cost. Nevertheless, these benefits come at the cost of results accuracy. In this paper, we investigate differences of the behaviour of our agent based S-MAC protocols in real deployment compared to the results produced using our custom based simulator, which ignores the lower layers effects such as packet collision and overhearing. We use network simulator 2 (ns2), an open source simulator, which provides a complete protocol stack. We further try to find and explain the rationale of the variance of results produced by real deployment and that of simulators.

This paper investigates the challenges for developing the current local area network (LAN)-based Ethernet protocol into a technology for future network architectures that is capable of satisfying dynamic traffic demands with hard service guarantees using high-bit-rate channels (80. . .100 Gb/s). The objective is to combine high-speed optical transmission and physical interfaces (PHY) with a medium access control (MAC) protocol, designed to meet the service guarantees in future metropolitan-area networks (MANs). Ethernet is an ideal candidate for the extension into the MAN as it allows seamless compatibility with the majority of existing LANs. The proposed extension of the MAC protocol focuses on backward compatibility as well as on the exploitation of the wavelength domain for routing of variable traffic demands. The high bit rates envisaged will easily exhaust the capacity of a single optical fiber in the band and will require network algorithms optimizing the reuse of wavelength resources. To investigate this, four different static and dynamic optical architectures were studied that potentially offer advantages over current link-based designs. Both analytical and numerical modeling techniques were applied to quantify and compare the network performance for all architectures in terms of achievable throughput, delay, and the number of required wavelengths and to investigate the impact of nonuniform traffic demands. The results show that significant resource savings can be achieved by using end-to-end dynamic lightpath allocation, but at the expense of high delay.

Aiming at optimizing the use of a wireless sensor network (WSN) as a miniature components integrated on chip (according to SoC technology), the adoption of specific protocols in the fields of applications of such network type is crucial. WSNs differ largely from the traditional wireless networks, they consequently require the use of new variations of energy-preserving protocols to ensure a prolonged life span for a sensor and to allow autonomy for a mostly dynamic topology-characterized network. Indeed, several routing and medium access control (MAC) protocols were proposed, and often adapted to the targeted applicability (house automation, biology, security, rural…). In this paper, we put forward a layered model for WSNs, with reference to OSI, TCP/IP and IEEE802 models which guaranteed a simple design and an easy implementation, for computer networks on (LAN/Wi-LAN, WAN, PAN…), thanks to layer decomposition reducing complexity and outlining functionalities relating to layers/levels coordinating through specific interfaces. The suggested model defines the levels of abstraction features of a WSN nodes according to their types (sensor, base station "BS"…) and intelligence level so as to serve as a basic model for design and future implementations of WSNs protocols and applications. This layered model allows the interconnection of a WSN with any other type of computer network. .

Same as, radio-frequency-based wireless networks (RWNs) which used in terrestrial environments. The medium access control (MAC) protocol is a key element for underwater acoustic networks (UWANs). Due to peculiar features of underwater acoustic channels such as long propagation delay, very small channel capacity, low channel reliability, and high dynamics of channel quality, not only MAC protocols but also MAC design strategies originally developed for RWNs cannot work well in UWANs. This paper reviews these proposals with an enhanced MAC reference model. This model decomposes a MAC protocol into a couple of components that make up a common structure for various MAC protocols so that they can be more easily understood. The major remaining issues and possible research directions.

This paper surveys the design of embedded computer systems, which use software running on programmable computers to implement system functions. Creating an embedded computer system which meets its performance, cost, and design time goals is a hardware-software co-design p r o b l e w h e design of the hardware and software components influence each other. This paper emphasizes a historical approach to show the relationships between well-understood design problems and the as-yet unsolved problems in co-design. We describe the relationship between hardware and sofhvare architecture in the early stages of embedded system design. We describe analysis techniques for hardware and software relevant to the architectural choices required for hardware-software co-design. We also describe design and synthesis techniques for co-design and related problems.

The use of Unmanned Aerial Vehicles is growing increasingly across many civil benefits, including real-time monitoring, medical emergencies, surveillance, and defence. Many different types of UAVs are being developed to meet the demands of diverse users. Therefore, the research areas in the UAV domain are evolving as the types and number of UAVs increase. UAV's faces numerous problems in channel accessing, radio allotment, latency and most of these issues are because of the ineffective MAC protocols, moreover MAC is also important because it affects not only the system performance but also the energy efficiency in battery-powered sensor nodes. In this research article various Medium access control (MAC) protocols discussed and qualitatively compared on the basis of various Quality-of-Service (QoS) parameters.

This paper describes the concept of sensor networks which has been made viable by the convergence of microelectro-mechanical systems technology, wireless communications and digital electronics. First, the sensing tasks and the potential sensor networks applications are explored, and a review of factors influencing the design of sensor networks is provided. Then, the communication architecture for sensor networks is outlined, and the algorithms and protocols developed for each layer in the literature are explored. Open research issues for the realization of sensor networks are also discussed. Ó 2002 Published by Elsevier Science B.V.

Although IEEE 802.15.4 is being considered as a promising standard for low-cost low-power Wireless Sensor Networks (WSNs), several issues in the specification are still open. One of those open issues is how to build a synchronized multi-hop mesh network for power efficient, scalable, and robust networking. In fact, while the current specification supports multi-hop networking using peer-to-peer topology, it restricts its use to the beaconless mode. This paper presents an extension to the current IEEE 802.15.4 standard in which mesh networking in the low power beacon mode is enabled through the use of distributed beacon scheduling. The work presented in this paper has been implemented on top of the Open-ZB IEEE 802.15.4 implementation within the TinyOS operating system. The feasibility of our proposal is demonstrated and evaluated through both physical test-bed and computer based emulation.

Wireless mesh networks (WMNs) consist of mesh routers and mesh clients, where mesh routers have minimal mobility and form the backbone of WMNs. They provide network access for both mesh and conventional clients. The integration of WMNs with other networks such as the Internet, cellular, IEEE 802.11, IEEE 802.15, IEEE 802.16, sensor networks, etc., can be accomplished through the gateway and bridging functions in the mesh routers. Mesh clients can be either stationary or mobile, and can form a client mesh network among themselves and with mesh routers. WMNs are anticipated to resolve the limitations and to significantly improve the performance of ad hoc networks, wireless local area networks (WLANs), wireless personal area networks (WPANs), and wireless metropolitan area networks (WMANs). They are undergoing rapid progress and inspiring numerous deployments. WMNs will deliver wireless services for a large variety of applications in personal, local, campus, and metropolitan areas. Despite recent advances in wireless mesh networking, many research challenges remain in all protocol layers. This paper presents a detailed study on recent advances and open research issues in WMNs. System architectures and applications of WMNs are described, followed by discussing the critical factors influencing protocol design. Theoretical network capacity and the state-of-the-art protocols for WMNs are explored with an objective to point out a number of open research issues. Finally, testbeds, industrial practice, and current standard activities related to WMNs are highlighted.

In order to meet the requirements of 4G mobile networks targeted by the cellular layer of IMT-Advanced, Next Generation Mobile WiMAX devices based on IEEE 802.16m will incorporate sophisticated signal processing, seamless handover functionalities between heterogeneous technologies and advanced mobility mechanisms. This survey provides a description of key projected features of the physical (PHY) and medium access control (MAC) layers of 802.16m, as a major candidate for providing aggregate rates at the range of Gbps to high-speed mobile users. Moreover, a new unified method for simulation modeling, namely the Evaluation Methodology (EVM), introduced in 802.16m, is also presented.

A wireless sensor network (WSN) is a computer wireless network composed of spatially distributed and autonomous tiny nodes -smart dust sensors, motes -, which cooperatively monitor physical or environmental conditions. Nowadays these kinds of networks support a wide range of applications, such as target tracking, security, environmental control, habitat monitoring, source detection, source localization, vehicular and traffic monitoring, health monitoring, building and industrial monitoring, etc. Many of these applications have strong requirements for end-to-end delay and losses during data transmissions. In this work we have classified the main mechanisms that have been proposed to provide Quality of Service (QoS) in WSN at Medium Access Control (MAC) and network layers. Finally, taking into account some particularities of the studied MAC-and network-layer protocols, we have selected a real application scenario in order to show how to choose an appropriate approach for guaranteeing performance in a WSN deployed application.

Security in mobile ad hoc networks is difficult to achieve, notably because of the vulnerability of wireless links, the limited physical protection of nodes, the dynamically changing topology, the absence of a certification authority, and the lack of a centralized monitoring or management point. Earlier studies on mobile ad hoc networks (MANETs) aimed at proposing protocols for some fundamental problems, such as routing, and tried to cope with the challenges imposed by the new environment. These protocols, however, fully trust all nodes and do not consider the security aspect. They are consequently vulnerable to attacks and misbehavior.

We present a mathematical model to study decentralized detection in clustered wireless sensor networks (WSNs). Sensors and fusion centers (FCs) are distributed with the aim of detecting an event of interest. Sensors are organized in clusters, with FCs acting as cluster heads, and are supposed to observe the same common binary phenomenon. A query-based application is accounted for; FCs periodically send queries and wait for replies coming from sensors. After reception of data, FCs perform data fusion with a majority-like fusion rule and send their decisions to an access point (AP), where a final data fusion is carried out and an estimate of the phenomenon is obtained. We assume that sensors are IEEE 802.15.4-compliant devices and use the medium access control (MAC) protocol defined by the standard, based on carrier-sense multiple access with collision avoidance. Decentralized detection and MAC issues are jointly investigated through analytical modelling. The proposed framework allows the derivation of the probability of decision error at the AP, when accounting for packets' losses due to possible collisions. Our results show that MAC losses strongly affect system performance. The impact of different clustering configurations and of noisy communications is also investigated.

As more and more applications and services in our society now depend on the Internet, it is important that dynamically deployed wireless multi hop networks are able to gain access to the Internet and other infrastructure networks and services. This thesis proposes and evaluates solutions for providing multi hop Internet Access. It investigates how ad hoc networks can be combined with wireless and mesh networks in order to create wireless multi hop access networks. When several access points to the Internet are available, and the mobile node roams to a new access point, the node has to make a decision when and how to change its point of attachment. The thesis describes how to consider the rapid fluctuations of the wireless medium, how to handle the fact that other nodes on the path to the access point are also mobile which results in frequent link and route breaks, and the impact the change of attachment has on already existing connections.

Recently both ITU and IEEE have standardized solutions for passive optical networks (PONs) operating at gigabit per second line rates and optimized for the transport of packet-based traffic to improve the efficiency of previously standardized broadband PONs, which used the ATM cell as the data transport unit. The efficiency and performance of PON systems depend on the transmission convergence layer and mainly on the implemented medium access protocol. Although the latter is not part of the standards and left to the implementer, the standards describe a set of control fields that constitute the tool-set for the media access control (MAC) operation. Though starting from a common and quite obvious basis, the two standards present significant differences with the legacy of Ethernet marking the IEEE approach, while the emphasis of ITU is on demanding services. In this paper we compare the efficiency and performance of the two systems assuming the implementation of as close as possible MAC protocols. The target is twofold: assess and compare the traffic handling potential of each of the two standards and identify the range of applications they can support. Useful insight can also be gained to the MAC tools that could be designed into the next generation extra large WDM PONs. expensive optical links compared with the conventional point-to-point (P2P) transport solutions. In addition, they inherently concentrate traffic and greatly reduce the number of input ports in the access multiplexer, both important for the cost-sensitive residential access market. Owing to these advantages, PONs have generated during the last decade substantial commercial activity also reflected in the study of several standardization bodies. Since the initial standardization of ATM-based PONs (APONs or alternatively named in ITU-T G.983.1 standard [1] Broadband PONs-BPONs) newer standards support multi-gigabit rates and better adapt to the packet-based Internet applications. In January 2003, the GPON (Gigabit PON) standards were ratified by ITU-T and were included in the G.984.x series of ITU-T Recommendations [2, 3]. Driven by a closed group of worldwide system vendors and national telecom operators, they are designed to support a mix of TDM, ATM and packet-based services, reaching symmetrical transmission rates of up to 1.244 or 2.488 Gb/s. At the same time IEEE, through the activities of Ethernet in the first mile (EFM) 802.3ah group, has standardized a Gigabit Ethernet-friendly technology [4] called Ethernet PON (EPON) with the objective to leverage the great success of Ethernet as a LAN technology and exploit the economies of scale that the dominance of Ethernet has generated. The objective of EFM efforts has been to combine a minimal set of extensions to the IEEE 802.3 media access control (MAC) and MAC control sub-layers with a family of physical (PHY) layers. In addition, a mechanism for network operations, administration and maintenance (OAM) is included to facilitate network operation and troubleshooting.

Fifth generation (5G) vehicular systems support multiple services with strict Quality of Service (QoS) constraints. To fulfill the increased communication needs, 5G Vehicular Cloud Computing (5G-VCC) architectures with dense deployments of the access network infrastructures have been proposed. In such systems, the network resources manipulation is a critical task that could be addressed by the Medium Access Control (MAC) layer. MAC schemes that have been proposed for vehicular networks, can be applied to 5G-VCC systems in order optimal manipulation of communication resources to be accomplished. This paper makes an overview of available MAC schemes, while a comprehensive discussion about their implementation in 5GVCC systems is performed leading to useful conclusions.

Index Terms—5G Vehicular Cloud Computing (5G-VCC), Ultra Dense Networks (UDN), Medium Access Control (MAC), Vehicle to Vehicle (V2V), Vehicle to Infrastructure (V2I), Survey

Recent advances in microelectronics and integrated circuits, system-on-chip design, wireless communication and intelligent low-power sensors have allowed the realization of a Wireless Body Area Network (WBAN). A WBAN is a collection of low-power, miniaturized, invasive/non-invasive lightweight wireless sensor nodes that monitor the human body functions and the surrounding environment. In addition, it supports a number of innovative and interesting applications such as ubiquitous healthcare, entertainment, interactive gaming, and military applications. In this paper, the fundamental mechanisms of WBAN including architecture and topology, wireless implant communication, low-power Medium Access Control (MAC) and routing protocols are reviewed. A comprehensive study of the proposed technologies for WBAN at Physical (PHY), MAC, and Network layers is presented and many useful solutions are discussed for each layer. Finally, numerous WBAN applications are highlighted.

In this paper, a comprehensive overview of the new features of an upcoming new standard IEEE 802.11e to support Quality of Service (QoS) in Wireless Local Area Networks (WLANs) is presented. We address Medium Access Control (MAC) enhancements found in the current 802.11e draft specification by emphasizing the differences from the legacy 802.11 standard. New mechanisms for QoS support, namely Enhanced

Ultra-wideband (UWB) communication techniques have attracted a great interest in both academia and industry in the past few years for applications in short-range wireless mobile systems. This is due to the potential advantages of UWB transmissions such as low power, high rate, immunity to multipath propagation, less complex transceiver hardware, and low interference. However, tremendous R&D efforts are required to face various technical challenges in developing UWB wireless systems, including UWB channel characterization, transceiver design, coexistence and interworking with other narrowband wireless systems, design of the link and network layers to benefit from UWB transmission characteristics. This paper is to provide an overview of UWB communications, summarize the previous research results, and identify further research issues that need to be tackled. The emphasis is placed on the commercial wireless communications.

Studies of ad hoc wireless networks are a relatively new field gaining more popularity for various new applications. In these networks, the Medium Access Control (MAC) protocols are responsible for coordinating the access from active nodes. These protocols are of significant importance since the wireless communication channel is inherently prone to errors and unique problems such as the hidden-terminal problem, the exposed-terminal problem, and signal fading effects. Although a lot of research has been conducted on MAC protocols, the various issues involved have mostly been presented in isolation of each other. We therefore make an attempt to present a comprehensive survey of major schemes, integrating various related issues and challenges with a view to providing a big-picture outlook to this vast area. We present a classification of MAC protocols and their brief description, based on their operating principles and underlying features. In conclusion, we present a brief summary of key ideas and a general direction for future work.

Being a part of IEEE project 802, the 802.11 medium access control (MAC) is used to support asynchronous and time bounded delivery of radio data packets. It is proposed that a distributed coordination function (DCF), which uses carrier sense multiple access with collision avoidance (CSMA/CA) and binary slotted exponential backoff, be the basis of the IEEE 802.11 WLAN MAC protocols. This paper proposes a throughput enhancement mechanism for DCF by adjusting the contention window (CW) resetting scheme. Moreover, an analytical model based on Markov chain is introduced to compute the enhanced throughput of 802.11 DCF. The accuracy of the model and the enhancement of the proposed scheme are verified by elaborate simulations

Communication is usually the most energy-consuming event in Wireless Sensor Networks (WSNs). One way to significantly reduce energy consumption is applying transmission power control (TPC) techniques to dynamically adjust the transmission power. This article presents two new TPC techniques for WSNs. The experimental evaluation compares the performance of the TCP techniques with B-MAC, the standard MAC protocol of the Mica 2 platform. These experiments take into account different distances among nodes, concurrent transmissions and node mobility. The new transmission power control techniques decrease energy consumption by up to 57% over B-MAC while maintaining the reliability of the channel. Under a low mobility scenario, the proposed protocols delivered up to 95% of the packets, showing that such methods are able to cope with node movement. We also show that the contention caused by higher transmission levels might be lower than analytical models suggest, due to the action of the capture effect.