MAC Layer

The IEEE 802.16 Working Group on Broadband Wireless Access is developing the standard for broadband wireless access networks in Metropolitan Area Network (MAN), also know as WiMAX. One of the features of the 802.16 MAC layer is that it is designed to differentiate service among traffic categories with different multimedia requirements. Based on these assumptions and considering that the standard does not specify a scheduling algorithm, an original analytical model was proposed based on Latency-Rate (LR) server theory and system characteristics specified by the standard for systems using the WirelessMAN-OFDM (Orthogonal Frequency Division Multiplexing) air interface. The proposed scheduling algorithm for the uplink traffic guarantees a bounded delay for the IEEE 802.16 and the Time Frame (TF) is calculated to maximize the number of allocated stations taking into account delay bound parameters. We show that it is possible to obtain worst-case performance guarantee on delay. Properties of the proposal are investigated theoretically. We present a set of simulation with both Constant Bit Rate (CBR) and Variable Bit Rate (VBR) flows and performance comparisons among different TFs. The results show that the delay upper bound can be achieved for a large range of networks load with bandwidth optimization.

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.

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.

5G Technology stands for the 5th Generation Mobile technology. 5G is a next major phase of mobile telecommunications standards beyond the 4G standards.5G is expected to provide speed upto 10Gbit/s, wider frequency band, high increased peak bit rate, high system spectral efficiency, ubiquitous connectivity and significant increase in QoS as compared to current 4G technology. Evolution of mobile communication technology to 5G is discussed in this review, followed by protocol stack and 5G architecture. A wide comparison is given between the various generations so as to compare why 5G technology is better and needed.

Wireless Local Area Networking standard (Wi-Fi) and the WPAN standard (Bluetooth and Zigbee) products utilize the same unlicensed 2.4 GHz ISM band. Co-existence between such wireless technologies within the same frequency spectrum is crucial to ensure that each wireless technology maintains and provides its desired performance requirements. This paper provides a brief description of the newly introduced Zigbee standards including the Physical (PHY) and media access control (MAC) layer. It focuses on developing MatLab/Simulink models for the Zigbee protocol and the performance evaluation of these models. Several simulations were run and the results were analyzed for the different scenarios. The results showed how the relationship between the signal Bit Error Rate (BER) and Signal to Noise Ratio (SNR) was affected when varying the data rate and power. Furthermore, this paper investigated the co-existence of WLAN (IEEE 802.11g) with Zigbee (IEEE 802.15.4 by quantifying potential interferences and examining the impact on the throughput performance of IEEE 802.11g and Zigbee devices when co-existing within a particular environment. The effect of Zigbee on IEEE 802.11g was compared with the effect of Bluetooth under the same operating conditions.

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.

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.

Wireless broadband technologies provide ubiquitous broadband access to wireless users, enabling services that were available only to wireline users. In this paper, we summarize emerging wireless broadband access technologies, ranging from WLANs to satellite communications.,We explain the latest standards,in the IEEE 802.11 and IEEE 802.16 families in detail. The MAC layer mechanisms of IEEE 802.11e, 802.11n, and 802.11s standards

The adoption of wireless sensor networks by applications that require complex operations, ranging from health care to industrial monitoring, has brought forward a new challenge of fulfilling the quality of service (QoS) requirements of these applications. However, providing QoS support is a challenging issue due to highly resource constrained nature of sensor nodes, unreliable wireless links and harsh operation environments.

A MAC (Medium Access Control) protocol has direct impact on the energy efficiency and traffic characteristics of any Wireless Sensor Network (WSN). Due to the inherent differences in WSN's requirements and application scenarios, different kinds of MAC protocols have so far been designed especially targeted to WSNs, though the primary mode of communications is wireless like any other wireless network. This is the subject topic of this survey work to analyze various aspects of the MAC protocols proposed for WSNs. To avoid collision and ensure reliability, before any data transmission between neighboring nodes in MAC layer, sensor nodes may need sampling channel and synchronizing. Based on these needs, we categorize the major MAC protocols into three classes, analyze each protocol's relative advantages and disadvantages, and finally present a comparative summary which could give a snapshot of the state-of-the-art to guide other researchers find appropriate areas to work on. In spite of various existing survey works, we have tried to cover all necessary aspects with the latest advancements considering the major works in this area.

Summary Wireless Local Area Networks (WLANs) are cost effective and desirable gateways to mobile computing. They allow computers to be mobile, cable less and communicate with speeds close to the speeds of wired LANs. These features came with expensive price to ...

In this paper, we propose a feasible beamforming (BF) scheme realized in media access control (MAC) layer following the guidelines of the IEEE 802.15.3c criteria for millimeterwave 60GHz wireless personal area networks (60GHz WPANs). The proposed BF targets to minimize the BF set-up time and mitigates the high path loss of 60GHz WPAN systems. It is based on designed multi-resolution codebooks, which generate three kinds of patterns of different half power beam widths (HPBWs): quasi-omni pattern, sector and beam. These three kinds of patterns are employed in the three stages of the BF protocol, namely device-to-device (DEV-to-DEV) linking, sectorlevel searching and beam-level searching. All the three stages can be completed within one superframe, which minimizes the potential interference to other systems during BF set-up period. In this paper, we show some example codebooks and provide the details of BF procedure. Simulation results show that the setup time of the proposed BF protocol is as small as 2% when compared to the exhaustive searching protocol. The proposed BF is a complete design, it re-uses commands specified in IEEE 802.15.3c, completely compliant to the standard; It has thus been adopted by IEEE 802.15.3c as an optional functionality to realize Giga-bit-per-second (Gbps) communication in WPAN Systems.

In this paper we conduct a feasibility study of delay-critical safety applications over vehicular ad hoc networks based on the emerging dedicated short range communications (DSRC) standard. In particular, we quantify the bit error rate, throughput and latency associated with vehicle collision avoidance applications running on top of mobile ad hoc networks employing the physical and MAC layers of DSRC. Towards this objective, the study goes through two phases. First, we conduct a detailed simulation study of the DSRC physical layer in order to judge the link bit error rate performance under a wide variety of vehicles speeds and multi-path delay spreads. We observe that the physical layer is highly immune to large delay spreads that might arise in the highway environment whereas performance degrades considerably at high speeds in a multi-path environment. Second, we develop a simulation testbed for a DSRC vehicular ad hoc network executing vehicle collision avoidance applications in an attempt to gauge the level of support the DSRC standard provides for this type of applications. Initial results reveal that DSRC achieves promising latency performance, yet, the throughput performance needs further improvement.

Summary Wireless Local Area Networks (WLANs) are cost effective and desirable gateways to mobile computing. They allow computers to be mobile, cable less and communicate with speeds close to the speeds of wired LANs. These features came with expensive price to ...

IEEE 802.16m amends the IEEE 802.16 Wireless MAN-OFDMA specification to provide an advanced air interface for operation in licenced bands. It will meet the cellular layer requirements of IMT-Advanced next generation mobile networks. It will be designed to provide significantly improved performance compared to other high rate broadband cellular network systems. For the next generation mobile networks, it is important to consider increasing peak, sustained data reates, corresponding spectral efficiencies, system capacity and cell coverage as well as decreasing latency and providing QoS while carefully considering overall system complexity. In this paper we provide an overview of the stateof-the-art mobile WiMAX technology and its development. We focus our discussion on Physical Layer, MAC Layer, Schedular,QoS provisioning and mobile WiMAX specification.

The aim of this thesis was to study the time synchronization in wireless sensor networks which are based on standards NTP and IEEE1588. Time synchronization is timekeeping which requires the coordination of events to operate a system in unison. This can be compared to the conductor of an orchestra keeping the orchestra in time. Another purpose was then to compare the differences of three synchronization protocols.

We introduce the TinyNode platform for wireless sensor networks. Supporting both research and industrial deployments, the platform offers communication ranges that exceed current platforms by a factor of 3 to 5, while consuming similar energy. It comes with a rich, practical set of hardware extensions and full TinyOS support. We describe the design choices of the TinyNode, the accompanying hardware modules, and the MAC layer implementation.

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, which bring the necessity to achieve an efficient medium access protocol subject to power constraints. Various MAC protocols with different objectives were proposed for wireless sensor networks. In this paper, 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 on MAC layer design.

IEEE 802.16m amends the IEEE 802.16 Wireless MAN-OFDMA specification to provide an advanced air interface for operation in licenced bands. It will meet the cellular layer requirements of IMT-Advanced next generation mobile networks. It will be designed to provide significantly improved performance compared to other high rate broadband cellular network systems. For the next generation mobile networks, it is important to consider increasing peak, sustained data reates, corresponding spectral efficiencies, system capacity and cell coverage as well as decreasing latency and providing QoS while carefully considering overall system complexity. In this paper we provide an overview of the stateof-the-art mobile WiMAX technology and its development. We focus our discussion on Physical Layer, MAC Layer, Schedular,QoS provisioning and mobile WiMAX specification.

IEEE 802.15.4 (Zigbee) is the new standard that has been developed for low cost, low data rate and low power consumption wireless network. This paper provides a brief description of this standard including the Physical (PHY) and medium access control (MAC) layer. It focuses on developing MatLab/Simulink models for the Zigbee protocol and the performance evaluation of these models. Simulation has been run using MatLab and the results have been analyzed. The results show how the relationship between the signal Bit Error Rate (BER) and Signal to Noise Ratio (SNR) is affected when varying the data rate and the input signal power to the noise channel.

Summary Wireless Local Area Networks (WLANs) are cost effective and desirable gateways to mobile computing. They allow computers to be mobile, cable less and communicate with speeds close to the speeds of wired LANs. These features came with expensive price to ...

In this paper, we use IEEE 802.11 standard for Wi-fi MAC transmitter and receiver module, for the wireless communication in radio frequency range. Wi-Fi wireless fidelity for LAN is designed for local area networks, which are private, local (short range), but where competing cable systems run at very high speeds. Wi-Fi MAC layer used various IEEE standards. Here we use IEEE 802.11 for VHDL modeling of Wi-Fi MAC layer. Here WI-Fi MAC transmitter and receiver used Probe request frame, association frame, RTS frame, CTS frame, modulation, signal processing filters and pulse shaping. In this paper we discuss about modulation, signal processing filters and pulse shaping.

An important problem for the WiMAX networks is how to provide a guaranteed quality of service for applications. A key aspect of this problem is how base stations should share bandwidth capacity between different classes of traffic. The decision needs to be made for each incoming packet and is known as the packet scheduling problem. A major challenge in packet scheduling is that the behavior of each traffic class may not be known in advance and can vary dynamically. this paper has described how the packet scheduling problem has been modeled as an application for reinforcement learning. We have demonstrated how our reinforcement learning approach could learn scheduling policies that satisfy the quality of service requirements of multiple traffic classes under a variety of conditions. The proposed solution has been designed to have an ability to accommodate integrated traffic in the networks with effective scheduling schemes. A series of simulation experiments have been carried out to evaluate the performance of the proposed scheduling algorithm. Results revealed that the proposed solution performs effectively to the integrated traffic composed of messages with or without time constraints and achieves proportional fairness among different types of traffic.

The requirements and solutions for industrial wireless mesh networks are much more challenging and complicated than those for the consumer mesh networks. This puts additional stress on existing hardware chips on the market for wireless mesh networks, which started as products marketed towards consumers. The reason why we talk about the IEEE 802.15.4 chips is because most of the industrial wireless mesh network standards converge on IEEE 802.15.4 as the physical and MAC layer standards. In this paper we selectively chronicle the challenges we faced with the IEEE 802.15.4 chips, the products targeted with ZigBee for the consumer market, to advance WirelessHART, the technology targeted for industrial process control. We also describe our resolution over the challenges and offer our wish list for the next generation IEEE 802.15.4 chips. I.

Keywords: IEEE 802.11p VANET MAC Mobility Relative speed a b s t r a c t Vehicular ad hoc networks (VANETs) are an extreme case of mobile ad hoc networks (MAN-ETs). High speed and frequent network topology changes are the main characteristics of vehicular networks. These characteristics lead to special issues and challenges in the network design, especially at the medium access control (MAC) layer. In this paper, we provide a comprehensive evaluation of mobility impact on the IEEE 802.11p MAC performance. The study evaluates basic performance metrics such as packet delivery ratio, throughput, and delay. An unfairness problem due to the relative speed is identified for both broadcast and unicast scenarios. We propose two dynamic contention window mechanisms to alleviate network performance degradation due to high mobility. The first scheme provides dynamic level of service priority via adaptation to the number of neighboring nodes, while the second scheme provides service priority based on node relative speed. Extensive simulation results demonstrate a significant impact of mobility on the IEEE 802.11p MAC performance, the unfairness problem in the vehicle-to-vehicle (V2V) communications, and the effectiveness of the proposed MAC schemes.

In this paper we are given concept of our WiMAX (Worldwide Interoperability for Microwave Access) network performance for QoS monitoring and optimization solution for BS (Base Station) with multimedia application. In the communication sector, the optimal objective is to equate quality and cost. Due to its large coverage area, low cost of deployment and high speed data rates. WiMAX is a promising technology for providing wireless lastmile connectivity. Physical and MAC layer of this technology refer to the IEEE 802.16e standard, which defines 5 different data delivery service classes that can be used in order to satisfy Quality of Service (QoS) requirements of different applications, such as VoIP, videoconference, FTP, Web, etc. In this paper we have made six scenarios. Here two types of MAC layer QoS are used and they are UGS and rtPS having application of Voice over IP (VoIP) and MPEG respectively. Also the traffic priority for UGS is high as compared to rtPS. In each scenario the number of fixed nodes (Fixed Subscriber Stations) and Mobile nodes (Mobile Subscriber Stations) are different. To cover more nodes or if nodes are outside the coverage area more than one BS are required. All the simulation results based on optimized networks and area we have considered between and Bhusaval and Jalgam.

This chapter provides a broad overview of the MAC protocols especially developed for sensor networks. These MAC protocols differ from typical WLAN access protocols in that they trade off performance (latency and throughput) for a reduction in energy consumption to maximize the lifetime of the network. This is in general achieved by duty cycling the radio, and it is the MAC layer that controls when the radio is switched on and off. An important consequence is that a MAC protocol needs to be aware of its neighbors' sleep/active schedules, since sending a message is only effective when the destination node is awake. An obvious solution is to have all nodes synchronize on one global schedule, so no separate neighbor state is required, which maps well onto the resource limitations of typical sensor nodes. However, grouping communication into small (active) periods increases the chance on collisions, hence, other forms of organization have been proposed. This chapter surveys, and details the historic development of, the three most common styles of medium access control for wireless sensor networks: random, slotted, and frame-based organization. and channel conditions at hand. In this chapter we will classify the major trends in MAC design for energy efficiency, and detail the historic advances within each class. We do not provide a thorough performance analysis, but include enough hints for end users to select an appropriate MAC for their (next) WSN deployment.

Mobile Ad-hoc Network (MANET) are a new paradigm of wireless wearable devices enabling instantaneous person-to-person, person-to-machine or machine-to-person communications immediately and easily .In this paper an overview and history of MANET is given .We discuss the issues which should keep in mind for designing of MAC layer and Routing protocols at Network layer. All these issues can be taken into consideration for the improvement of MANET performance. In mobile ad hoc networks, several interesting and difficult problems arises due to shared nature of the wireless medium, limited transmission power, limited transmission range, node mobility, and battery limitations, bandwidth limitation etc. The limited transmission range of wireless network coupled with the highly dynamic routing infrastructure need extra care. Mobility also create a lot of concerns. For communication, issues such as dynamic routing, efficient channel access and quality-of-service (QoS) support, bandwidth, synchronization, distributed nature, lack of central coordination should be considered. In this paper broadly we will discuss the above mentioned challenges at Network layer and MAC LAYER in mobile ad-hoc networks.

In 802.11 wireless links with disabled MAC retries, data and ACK packets within a TCP session collide resulting in packet losses. We show in this paper that in this situation, certain popular optimizations of TCP (fast-recovery) worsen the performance by causing ...

Wireless vehicular communications (WVC) has been identified as a key technology for intelligent transportation systems (ITS) for a few years ago. IEEE 802.11p is the proposed standard for physical and MAC layer of WVC devices. The main objective of the standard is to change the frame format and increase delay spread tolerance introduced by vehicle mobility, in which the channel bandwidth is scaled from 20 MHz i.e.802.11a to 10 MHz i.e. 802.11p. This paper proposes TDMA technique with fixed time slots and guard band between slots to ensure interoperability between wireless devices communicate in rapidly changing environment where transactions must be completed in small timeframe. The new TDMA sublayer is proposed to be on-top of the conventional 802.11p MAC. The simulation results present the performance analysis and validate the efficiency of the proposed scheme.

3G Long-Term Evolution (LTE) is a recent effort taken by cellular industries to step into wireless broadband market. The key enhancements target an introduction of new all-IP architecture, enhanced link layer and radio access with OFDM modulation and multiple antenna techniques.

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.

Wireless local area networks suffer from frequent bit-errors that result in Medium Access Control (MAC) layer packet drops. Bandwidth and media quality constraints of real-time applications necessitate analysis and modeling at the "MAC-to-MAC wireless channel". In this paper, we propose and evaluate stochastic models for the 802.11b MAC-to-MAC bit-error process. We propose an Entropy Normalized Kullback-Leibler (ENK) measure to accurately evaluate the performance of the models. We employ this measure to demonstrate that the traditional full-state Markov chains of order-10 and order-9 are required for accurate representation of the channel at 2 and 5.5 Mbps, respectively. However, the complexity of this modeling paradigm increases exponentially with respect to the order. For many real-time and non-real-time applications, which require (or could benefit significantly from) accurate modeling, the high complexity of full-state high-order Markov models makes them impractical or virtually ineffective. Thus, we propose two new linear-complexity models, which we refer to as the short-term energy model (SEM) and the zero-crossing model (ZCM). These models, which constitute the most important contribution of this paper, constrain the complexity to increase linearly with the model order. We illustrate that the linear-complexity models, while yielding orders of magnitude reduction in complexity, provide a performance comparable to that of the exponential complexity full-state models. Within the linear-complexity context, we illustrate that the zero-crossing model perform better than its short-term energy counterpart. Finally, for varying window sizes and due to its low complexity, we show that the zero-crossing model can be adapted in real-time. Such an adaptive model provides accurate channel modeling and characterization for rate adaptive applications.

IEEE 802.16m amends the IEEE 802.16 Wireless MAN-OFDMA specification to provide an advanced air interface for operation in licenced bands. It will meet the cellular layer requirements of IMT-Advanced next generation mobile networks. It will be designed to provide significantly improved performance compared to other high rate broadband cellular network systems. For the next generation mobile networks, it is important to consider increasing peak, sustained data reates, corresponding spectral efficiencies, system capacity and cell coverage as well as decreasing latency and providing QoS while carefully considering overall system complexity. In this paper we provide an overview of the state- of-the-art mobile WiMAX technology and its development. We focus our discussion on Physical Layer, MAC Layer, Schedular,QoS provisioning and mobile WiMAX specification.

Source-destination pairs in wireless sensor networks often have multiple shortest hop paths because the nodes are densely deployed. These multiple paths provide a great opportunity to reduce delay in an asynchronous duty-cycled network. In this paper, we exploit the redundancy available at the route layer using MAC-layer anycasting. We choose the next hop node that wakes up the soonest and thus reduce the delay incurred at each hop.

Dummynet is a widely used link emulator, developed long ago to run experiments in user-configurable network environments. Since its original design, our system has been extended in various ways, and has become very popular in the research community due to its features and to the ability to emulate even moderately complex network setups on unmodified operating systems.

t is common knowledge that over the last decade there has been a major boost in communication networks. In fact, the development of high-performance backbone networks was immediately followed by the rapid dissemination of broadband wired access technologies, such as leased lines based on fiber-optic links, cable modems using coaxial systems, and digital subscriber line (xDSL) access networks. This gave users a whole new class of services that exploit the increasing number of available network resources. Many new services are based on multimedia applications, such as voice over IP (VoIP), video conferencing, video on demand (VoD), massive online gaming, and peer-to-peer. Unlike traditional TCP/IP services, multimedia applications usually require strict network guarantees such as reserved bandwidth or bounded delays.

Security support is mandatory for any communication networks. For wireless systems, security support is even more important to protect the users as well as the network. Since wireless medium is available to all, the attackers can easily access the network and the network becomes more vulnerable for the user and the network service provider. Worldwide Interoperability for Microwave Access (WiMax) is going to be an emerging wireless technology nowadays. With the increasing popularity of Broadband internet, wireless networking market is thriving. In the IEEE 802.16e, security has been considered as the main issue during the design of the protocol. However, security mechanism of WiMax still remains an open research field. WiMax is relatively a new technology not deployed widely to justify the evidence of threats, risk and vulnerability in real situations. In this paper, a research is described three proposed chaos encryption techniques for multimedia transmission over Mobile WiMax physical and MAC layers. At first a global overview of the technology WiMax is given followed by an explanation of traditional encryption techniques used in WiMax. Then the proposed encryption techniques are presented with its chaos systems. Next, these techniques will be applied to different multimedia contents to compare between them and traditional techniques such as AES, IDEA, Blowfish and DES.

Understanding the performance of backoff algorithms in multihop ad hoc networks is a key feature to design efficient Medium Access Protocols for wireless networks. The 802.11 backoff algortihm, the Binary Exponential Backoff, and all the enhancement done to this algorithm are studied in depth in a single hop context. Very few analytical studies are done on 802.11 backoff algorithms in a multi-hop context due to the difficulty of modelling. In this paper we propose an analytical study, based on process algebra, of 4 backoff algorithms on 2 multi-hop scenarios. We evaluate the performance of each backoff algorithms from efficiency point of view and when possible from a fairness point of view.

Vehicular ad hoc networks (VANETs) have recently been considered as an attractive network architecture to provide various services ranging from road safety to entertainment applications. In this paper, we propose an IEEE-802.11-based multihop broadcast protocol to address the issue of emergency message dissemination in VANETs. The protocol adopts a binary-partition-based approach to repetitively divide the area inside the transmission range to obtain the furthest possible segment. The forwarding duty is then delegated to a vehicle chosen in that segment. Aside from accomplishing directional broadcast for highway scenario, the protocol also exhibits good adaptation to complex road structures. The main focus of the paper lies in reducing broadcast delay, which is an important factor for time-critical safety applications. Most importantly, the contention delay remains almost constant, irrespective of vehicle density. Mathematical analysis is performed to assess the effectiveness of the protocol. Simulation results demonstrate that the proposed protocol imparts greater performance in terms of latency and message progress when compared with contemporary multihop broadcast protocols for VANETs.

In this paper, we present an efficient MAC layer scheme using Dynamic Slot Assignment (DSA) in TDMA-based MAC protocols for cluster-based wireless sensor networks. The DSA scheme is presented to analyze the energy efficiency and channel utilization in a bursty traffic environment under low traffic conditions with a large number of sensor nodes in a single cluster. The DSA scheme will allow the network to adapt to the changing traffic load. Based on the network activity, the connection is established between the cluster-head node and those sensor nodes which have data to send, and a TDMA slot is assigned to each of them dynamically. We present the complete system model and model the data traffic by a correlated stochastic process (i.e. Markov chain) for a network where the second and subsequent connection arrival rate is dependent on the first arrival rate. We numerically compare our DSA with a traditionally proposed static TDMA model, the BMA model, and a variant of the BMA model (E...