Quality of Service-Based Medium Access Control Mechanism for Multimedia Traffic in Mobile Ad Hoc Networks

This thesis describes an investigation on the problem of quality of service (QoS) support in mobile ad hoc networks (MANETs). The decentralized nature of wireless ad hoc networks makes them suitable for a variety of applications where central nodes cannot be relied on. This thesis presents a medium access control (MAC) QoS mechanism for multimedia applications in IEEE 802.11e based MANETs. IEEE 802.11e standard draft includes new features to facilitate and promote the provision of QoS guarantees in wireless networks with a long-term solution based on QoS-architectures. The motivation is driven by the need to support increasing demand of time-sensitive applications such as Voice over IP (VoIP) and video conferencing applications. IEEE 802.11e enhances the Distributed Coordination Function (DCF) and the Point Coordination Function (PCF) of the legacy IEEE 802.11, through a new coordination function: the Hybrid Coordination Function (HCF). Within the HCF, there are two methods of channel access: HCF Controlled Channel Access (HCCA) and Enhanced Distributed Channel Access (EDCA). EDCA operates in infrastructure-less ad hoc mode and is widely used in MANETs, unlike HCCA, which further assures QoS provisioning operates in infrastructure mode in the presence of access points (AP). Recent researches showed that EDCA lacks QoS support of real-time traffic in MANETs due to its contention based medium access method. This thesis takes HCCA QoS provisioning potentials to MANETs by implementing a MAC mechanism in which HCCA is employed on top of EDCA to work in infrastructure-less environment like MANET with the help of multiple channels. The mechanism dedicates a unique receiver-based channel to every mobile node. It will act as virtual hybrid coordinator (VHC) to exercise control over the channel in contention-free manner while maintaining a common channel in which all mobile nodes can exchange broadcast and routing related messages. The mechanism can be easily integrated with existing 802.11 systems without modification to existing protocols while ensuring a level of admission control and resource reservation over the medium. Simulation results indicate that the mechanism significantly improves the overall network throughput by 20% at the saturation point and improves average delay by 20% at the saturation point compared to pure EDCA with or without multiple channels. Even with multi-channel EDCA, our mechanism guarantees better performance in terms of throughput and MAC delay for high priority traffic in MANET. The research contribution on MAC layer can be integrated into a larger framework for QoS support in MANETs, which opens a wide range of further research in QoS provisioning in MANETs and solve QoS multi-layer design and implementation issues

Adaptive EDCF: Enhanced service differentiation for IEEE 802.11 wireless ad-hoc networks

This paper describes an adaptive service differentiation scheme for QoS enhancement in IEEE 802.11 wireless ad-hoc networks. Our approach, called adaptive enhanced distributed coordination function (AEDCF), is derived from the new EDCF introduced in the upcoming IEEE 802.11e standard. Our scheme aims to share the transmission channel efficiently. Relative priorities are provisioned by adjusting the size of the contention window (CW) of each traffic class taking into account both applications requirements and network conditions. We evaluate through simulations the performance of AEDCF and compare it with the EDCF scheme proposed in the 802.11e. Results show that AEDCF outperforms the basic EDCF, especially at high traffic load conditions. Indeed, our scheme increases the medium utilization ratio and reduces for more than 50% the collision rate. While achieving delay differentiation, the overall goodput obtained is up to 25% higher than EDCF. Moreover, the complexity of AEDCF remains similar to the EDCF scheme, enabling the design of cheap implementations

Adaptive medium access control for VoIP services in IEEE 802.11 WLANs

Abstract- Voice over Internet Protocol (VoIP) is an important service with strict Quality-of-Service (QoS) requirements in Wireless Local Area Networks (WLANs). The popular Distributed Coordination Function (DCF) of IEEE 802.11 Medium Access Control (MAC) protocol adopts a Binary Exponential Back-off (BEB) procedure to reduce the packet collision probability in WLANs. In DCF, the size of contention window is doubled upon a collision regardless of the network loads. This paper presents an adaptive MAC scheme to improve the QoS of VoIP in WLANs. This scheme applies a threshold of the collision rate to switch between two different functions for increasing the size of contention window based on the status of network loads. The performance of this scheme is investigated and compared to the original DCF using the network simulator NS-2. The performance results reveal that the adaptive scheme is able to achieve the higher throughput and medium utilization as well as lower access delay and packet loss probability than the original DCF

Improving multiple broadcasting of multimedia traffic in wireless ad-hoc networks

The increasing use of multimedia streaming applications in addition with advent of internet television and radio, demands from today's wireless networks to handle with reliability multiple broadcasting and multicasting sources. However, the way that 802.11 standard, which is the primary technology in wireless networking, handle this type of traffic raises a series of problems mainly related to the lack of an effective feedback mechanism. This lack in turn, limits the capability of random backoff process to eliminate collisions and reduce reliability and fairness. This inherited drawback of the standard is affecting the way broadcast and multicast traffic is transmitted as well as the overall performance of the network. In this paper initially we are highlighting the drawback of the IEEE 802.11 MAC algorithm in handling multiple stations “media type” data broadcasting in an ad-hoc wireless network. Then, we propose two different approaches in alleviating these problems. The first approach is the simple linear increase of the contention window (CW) while the second propose a linear increase of the CW implementing an exclusive backoff number allocation (EBNA) algorithm. In addition we are modifying the 802.11 medium access control (MAC) algorithm to use the clear to send to self (CTS-to-Self) protection mechanism prior to every transmission. Both the above techniques are simulated and compared with the classic 802.11 MAC. The results show that the overall performance of the network can be improved using these alternative MAC methods

Model checking medium access control for sensor networks

We describe verification of S-MAC, a medium access control protocol designed for wireless sensor networks, by means of the PRISM model checker. The S-MAC protocol is built on top of the IEEE 802.11 standard for wireless ad hoc networks and, as such, it uses the same randomised backoff procedure as a means to avoid collision. In order to minimise energy consumption, in S-MAC, nodes are periodically put into a sleep state. Synchronisation of the sleeping schedules is necessary for the nodes to be able to communicate. Intuitively, energy saving obtained through a periodic sleep mechanism will be at the expense of performance. In previous work on S-MAC verification, a combination of analytical techniques and simulation has been used to confirm the correctness of this intuition for a simplified (abstract) version of the protocol in which the initial schedules coordination phase is assumed correct. We show how we have used the PRISM model checker to verify the behaviour of S-MAC and compare it to that of IEEE 802.11

A cross layer multi hop network architecture for wireless Ad Hoc networks

In this paper, a novel decentralized cross-layer multi-hop cooperative network architecture is presented. Our architecture involves the design of a simple yet efficient cooperative flooding scheme,two decentralized opportunistic cooperative forwarding mechanisms as well as the design of Routing Enabled Cooperative Medium Access Control (RECOMAC) protocol that spans and incorporates the physical, medium access control (MAC) and routing layers for improving the performance of multihop communication. The proposed architecture exploits randomized coding at the physical layer to realize cooperative diversity. Randomized coding alleviates relay selection and actuation mechanisms,and therefore reduces the coordination among the relays. The coded packets are forwarded via opportunistically formed cooperative sets within a region, without communication among the relays and without establishing a prior route. In our architecture, routing layer functionality is submerged into the MAC layer to provide seamless cooperative communication while the messaging overhead to set up routes, select and actuate relays is minimized. RECOMAC is shown to provide dramatic performance improvements, such as eight times higher throughput and ten times lower end-to-end delay as well as reduced overhead, as compared to networks based on well-known IEEE 802.11 and Ad hoc On Demand Distance Vector (AODV) protocols