Design and analysis of MAC protocols for wireless networks

During the last few years, wireless networking has attracted much of the research and industry interest. In addition, almost all current wireless devices are based on the IEEE 802.11 and IEEE 802.16 standards for the local and metropolitan area networks (LAN/MAN) respectively. Both of these standards define the medium access control layer (MAC) and physical layer (PHY) parts of a wireless user. In a wireless network, the MAC protocol plays a significant role in determining the performance of the whole network and individual users. Accordingly, many challenges are addressed by research to improve the performance of MAC operations in IEEE 802.11 and IEEE 802.16 standards. Such performance is measured using different metrics like the throughput, fairness, delay, utilization, and drop rate. We propose new protocols and solutions to enhance the performance of an IEEE 802.11 WLAN (wireless LAN) network, and to enhance the utilization of an IEEE 802.16e WMAN (wireless MAN). First, we propose a new protocol called HDCF (High-performance Distributed Coordination Function), to address the problem of wasted time, or idle slots and collided frames, in contention resolution of the IEEE 802.11 DCF. Second, we propose a simple protocol that enhances the performance of DCF in the existence of the hidden terminal problem. Opposite to other approaches, the proposed protocol attempts to benefit from the hidden terminal problem. Third, we propose two variants of a simple though effective distributed scheme, called NZ-ACK (Non Zero-Acknowledgement), to address the effects of coexisting IEEE 802.11e EDCA and IEEE 802.11 DCF devices. Finally, we investigate encouraging ertPS (enhanced real time Polling Service) connections, in an IEEE 802.16e, network to benefit from contention, and we aim at improving the network performance without violating any delay requirements of voice applications

Performance Analysis of Concurrent Transmission with Reducing Handshakes in Multi-Hop Wireless Mesh Networks (WMNS)

The IEEE 802.11 Distributed Coordination Function (DCF) Medium Access Control (MAC) protocol continues to suffer from throughput degradation when directly applied in multi-hop Wireless Mesh Network (WMN). The Request-to-Send/Clear-to-Send (RTS/ CTS) signaling partially solved hidden node problems however the exposed node problems remain unaddressed. These exposed nodes lead to throughput degradation especially when the transmission in multi-hop networks is considered. The major reason for this poor performance is the restricted nature of the IEEE 802.11 MAC, which does not allow exposed nodes to initiates its transmission for the entire duration of ongoing transmission. Moreover, since multi-hop communication such as wireless mesh network transfer the data packet via intermediate nodes, the amount of control handshakes that take place at each intermediate node significantly reduce the throughput. This project proposes a set of enhancement to the existing IEEE 802.11 DCF MAC by enabling concurrent transmission by the exposed nodes and reduces the amount of handshakes required at every hop until the data packet reaches its destination. Analytical models are developed for analytical study of MAC protocols operating in multi-hop mesh networks and simulated over quasi-static Rayleigh fading channel. The multi-hop network performances are evaluated in terms of throughput and delay. The protocol outperforms the existing IEEE DCF MAC with more than 260% increase in overall throughput of multi-hop WM

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

Medium access control mechanisms for quality of service in wireless computer networks.

The fast growth and development of wireless computer networks and multimedia applications means it is essential that these applications can be transmitted over the standard IEEE 802.11 Medium Access Control (MAC) protocol with high Quality of Service (QoS). The lack of QoS in the standard IEEE 802.11 Distributed Coordination Function (DCF) results in applications with considerably different QoS requirements receiving similar network services. This means, the performance of time-sensitive applications with stringent delay, jitter, and packet loss requirements will not be met. Even time-insensitive applications will be treated unfairly because access to the medium is on a random basis. Therefore, the main aims of this thesis are: (i) to investigate the limitations and performance of the IEEE 802.11 DCF, (ii) to develop a comprehensive solution that provides effective and efficient QoS provisioning in IEEE 802.11 DCF scheme in a fair, scalable, and robust manner. The latter is achieved by developing novel MAC mechanisms for providing QoS in the IEEE 802.11 DCF for multimedia transmission.The scarcity of channel capacity, unfairness and hidden terminal problems, multiple hops, and other conditions and parameters that affect QoS in a wireless network are issues which require in depth investigations and analysis. In this thesis, extensive investigations using the network simulator 2 (NS-2) package were carried out to examine the impact of these issues on the main QoS parameters (throughput, delay, jitter, packet loss and collision). The findings revealed that the IEEE 802.11 DCF protocol performed inadequately when transmitting various applications due to the limitations inherent in its operation. The performance of the IEEE 802.11 DCF protocol was also investigated by studying the impact of varying the values of minimum Contention Window (CW[min]) and the Distributed Inter Frame Space (DIFS). The study shows that inappropriate values of CW[min] and DIFS resulted in significant network performance degradations and demonstrated that it was important to select an appropriate set of MAC protocol transmission parameters in order to provide improved QoS.Artificial Intelligence (AI) techniques using fuzzy logic and Genetic Algorithms (GAs) for assessing and optimising MAC protocol transmission parameters were developed and their effectiveness evaluated. The study confirmed that the application of AI techniques significantly improved the QoS for audio and video applications by more than 50% and fairly shared the channel access among the contending stations as compared to the standard IEEE 802.11 DCF scheme. Ratio based and Collision Rate Variation (CRV) schemes were developed to dynamically adjust the CW and DIFS values according to the current and past network conditions. Using these schemes significant improvements with service differentiation were achieved in an Independent Basic Service Set (IBSS). A queue status monitoring technique was devised for the intermediate stations. This provided QoS differentiation at the MAC layer for multi-hop networks. Autoregressive (AR) models that accurately predicted the network parameters were also developed. These enabled the MAC protocol transmission parameters to be adjusted in an improved manner. Using these models, average QoS was improved by more than 60%; average delay, packet loss and collision were reduced by more than 50% compared to IEEE 802.11 DCF scheme.This led to the development of novel MAC mechanisms to provide QoS in IEEE 802.11 MAC protocol. The mechanisms support multiple QoS metrics and consider traffic history and predict future network conditions. The schemes also are characterised by the simplicity, robustness, and ease of implementation. The contribution of this thesis is the development of a comprehensive solution to provide effective and efficient QoS differentiation in IEEE 802.11 DCF scheme for multimedia transmission in a distributed, fair, scalable, and robust manner. Furthermore, through the use of these approaches, the findings of this study provide a framework that also contributes to the knowledge concerning the QoS over the IEEE 802.11 MAC protocol

Study of distributed coordination function (DCF) and enhanced dcf (EDCF) in IEEE 802.11 MAC protocols for multimedia applications

IEEE 802.11e Medium Access Control (MAC) is an enhancement to the legacy IEEE 802.11 standard’s Wireless Local Area Network (WLAN) ideally to support Quality-ofService (QOS). The 802.11e MAC is both centrally-controlled and contention-based channel accesses based. This project covers evaluation of the contention-based channel access mechanism, called Enhanced Distributed Coordination Function (EDCF), in comparison with the 802.11 legacy MAC, Distributed Coordination Function. Three different types of multimedia traffic are considered namely, voice, video and data. The evaluation was performed using ns-2 simulator (version 2.34) on Linux Ubuntu. The metrics used in the evaluation are throughput, delay, jitters and packet loss. The graphs from the metrics benchmarked the performance of EDCF and DCF evaluation. Through this simulation study, EDCF conclusively provides differentiated channel access for various multimedia traffic types. Simulation results proved that comparatively EDCF performs better performance than legacy DCF

Improved IEEE 802.11 point coordination function considering fiber-delay difference in distributed antenna systems

In this paper, we present an improved IEEE 802.11 wireless local-area network (WLAN) medium access control (MAC) mechanism for simulcast radio-over-fiber-based distributed antenna systems where multiple remote antenna units (RAUs) are connected to one access point (AP). In the improved mechanism, the fiber delay between RAUs and central unit is taken into account in a modification to the conventional point coordination function (PCF) that achieves coordination by a centralized algorithm. Simulation results show that the improved PCF outperforms the distributed coordination function (DCF) in both the basic-access and request/clear-to-send modes in terms of the total throughput and the fairness among RAU

A distributed wireless MAC scheme for service differentiation in WLANs.

Mobile communications is evolving due to the recent technological achievements in wireless networking. Today, wireless networks exist in many forms, providing different types of services in a range of local, wide area and global coverage. The most widely used WLAN standard today is IEEE 802.11. However, it still has problems with providing the QoS required for multimedia services using distributed methods. In this thesis, a new distributed MAC scheme is proposed to support QoS in wireless LANs. In the scheme, stations use CSMA for channel access, with collisions between stations being resolved by sending a set of beacons in a predefined manner, and virtual collisions being resolved by schedulers at the stations. The proposed MAC scheme is analyzed mathematically, for two-priority case, and the results obtained are validated by simulation. The mathematical model estimates the average delay experienced by data packets of priority one and two under different conditions. A performance evaluation study of the proposed MAC scheme as well as the IEEE 802.11 DCF, and IEEE 802.11e EDCF MAC schemes is also done by means of stochastic simulation. It is found that the results obtained by simulation are in very good agreement with the analytical results, thereby validating them. Moreover, the simulation study evaluated different performance measures of these MAC schemes. The results showed that the IEEE 802.11 DCF scheme does not support QoS, but the proposed MAC scheme and the upcoming IEEE 802.11 EDCF both do. In general, the results show that the proposed MAC scheme performs equally or better than the current IEEE 802.11 DCF scheme in every case considered. It is also found that the proposed MAC scheme performs equally well as the upcoming IEEE 802.11e EDCF scheme, in every case considered in this thesis

An automatic cooperative retransmission MAC protocol in wireless local area networks

Existing solutions for cooperation in wireless networks either require simultaneous transmission of source and relay nodes or impose major modifications to original MAC protocols. In this paper, a new efficient retransmission MAC protocol is proposed for IEEE 802.11 based cooperation communications, with minimum modifications to the DCF scheme. Throughput and access delay performance of the proposed protocols is analyzed in error-prone and highly temporally correlated channels. Numerical results show that significant benefits can be achieved with our cooperative protocol, compared with the legacy schemes