Design of Media Access Control Schemes for Performance Enhancement of Future Generation Wireless Systems

Wireless Local Area Networks (WLANs) now provide connectivity to many businesses, homes and educational institutions. The wireless channel itself is plagued with numerous problems, such as it does not natively allow sharing of the wireless resource. WLAN devices utilize a complex medium access control (MAC) mechanism to allow multiple users to share the wireless resource. The distributed coordination function (DCF) is the most commonly used multiple access scheme in WLANs and a member of the 802.11 standard [1]. In this thesis, two major roles of MAC protocols are examined: maximizing network throughput and service differentiation. Firstly, a novel MAC scheme is proposed that makes use of Multiple-Input, Multiple-Output (MIMO) antenna technology to improve overall network throughput. The proposed MIMO-Aware MAC (MA-MAC) scheme utilizes the beamforming feature available in MIMO systems to allow two simultaneous transmissions of the wireless channel overlapped in time. This results in increased aggregate network throughput. This proposed scheme is shown to offer better throughput and delay performance versus existing MAC schemes proposed for simultaneous transmission. In addition, this MAC scheme is able to achieve this performance in a manner compatible with the existing standard. The latter part of this thesis proposes a new Time Division Multiple Access (TDMA) based scheme for providing video, voice and data services (also known as the Triple-Play services) in a point-to-multipoint network. By dynamically allocating transmission slots, the proposed Television TDMA (TV-TDMA) scheme is shown to better meet delay requirements for video and voice traffic, and is able to achieve higher overall saturation throughput for best-effort traffic than existing Quality of Service enabled protocols

Design of Media Access Control Schemes for Performance Enhancement of Future Generation Wireless Systems

Wireless Local Area Networks (WLANs) now provide connectivity to many businesses, homes and educational institutions. The wireless channel itself is plagued with numerous problems, such as it does not natively allow sharing of the wireless resource. WLAN devices utilize a complex medium access control (MAC) mechanism to allow multiple users to share the wireless resource. The distributed coordination function (DCF) is the most commonly used multiple access scheme in WLANs and a member of the 802.11 standard [1]. In this thesis, two major roles of MAC protocols are examined: maximizing network throughput and service differentiation. Firstly, a novel MAC scheme is proposed that makes use of Multiple-Input, Multiple-Output (MIMO) antenna technology to improve overall network throughput. The proposed MIMO-A ware MAC (MA-MAC) scheme utilizes the beamforming feature available in MIMO systems to allow two simultaneous transmissions of the wireless channel overlapped in time. This results in increased aggregate network throughput. This proposed scheme is shown to offer better throughput and delay performance versus existing MAC schemes proposed for simultaneous transmission. In addition, this MAC scheme is able to achieve this performance in a manner compatible with the existing standard. The latter part of this thesis proposes a new Time Division Multiple Access (TDMA) based scheme for providing video, voice and data services (also known as the Triple-Play services) in a point-to-multipoint network. By dynamically allocating transmission slots, the proposed Television TDMA (TV-TDMA) scheme is shown to better meet delay requirements for video and voice traffic, and is able to achieve higher overall saturation throughput for best-effort traffic than existing Quality of Service enabled protocols

Multimedia computer networks quality of service techniques evaluation and development.

The growth in the transmission of time-sensitive applications over computer networks means that Quality of Service (QoS) needs to be managed in an efficient manner. Network QoS management in this thesis refers to evaluation and improvement of QoS provided by integrated wired and wireless computer networks. Evaluation of QoS aims to analyse and quantify network performance with respect of meeting multimedia applications' transmission requirements. QoS improvement involves the ability to take actions to change network performance toward improved operation. Therefore, the main aims of this thesis are: (i) to develop techniques for evaluation QoS in multimedia computer networks, (ii) to develop techniques that uses the information from (i) to manage and improve network performance. Multimedia traffic generates a large amount of data. Collecting this information poses a challenge as it needs to be sufficiently fast and accurate. A contribution of this thesis is that adaptive statistical sampling techniques to sample multimedia traffic were developed and their effectiveness was evaluated. Three different adjustment mechanisms were incorporated into statistical sampling techniques to adjust the traffic sampling rate: simple linear adjustment, quarter adjustment, and Fuzzy Inference System (FIS). The findings indicated that the developed methods outperformed the conventional non-adaptive sampling methods of systematic, stratified and random. The data collected included important QoS parameters, i.e. delay, jitter, throughput, and packet loss that indicated network performance in delivering real-time applications. An issue is that QoS needs evaluation in an informative manner. Therefore, the second contribution of this thesis is that statistical and Artificial Intelligent (AI) techniques were developed to evaluate QoS for multimedia applications. The application's QoS parameters were initially analysed either by Fuzzy C-Means (FCM) clustering algorithm or by Kohonen neural network. The analysed QoS parameters were then used as inputs to a regression model or Multi-Layer Perceptron (MLP) neural network in order to quantify the overall QoS. The proposed QoS evaluation system differentiated the network's QoS into a number of levels (Poor to Good QoS) and based on this information, the overall network's QoS was successfully quantified. In order to facilitate QoS assessment, a portable hand-held device for assessing the QoS in multimedia networks was designed, regression model was implemented on the microcontroller board and its performance was successfully demonstrated.Multimedia applications transmitted over computer networks require a large bandwidth that is a critical issue especially in wireless networks. The challenge is to enable end-to-end QoS by providing different treatments for different classes of traffic and efficient use of network resources. In this thesis, a new QoS enhancement scheme for wireless-wired networks is developed. This scheme consisted of an adaptive traffic allocation algorithm that is incorporated into the network's wireless side to improve the performance of IEEE 802.11e Enhanced Distributed Channel Access (EDCA) protocol, and a Weighted Round Robin (WRR) queuing scheduling mechanism that was incorporated into the wired side. The proposed scheme improved the QoS for Multimedia applications. The average QoS for voice, and video applications were increased from their original values by 72.5%, and 70.3% respectively

Performance analysis of vehicular networks for motorway scenario.

Abstract Not Provided

Adaptation of the IEEE 802.11 protocol for inter-satellite links in LEO satellite networks

Knowledge of the coefficient of thermal expansion (CTE) of a ceramic material is important in many application areas. Whilst the CTE can be measured, it would be useful to be able to predict the expansion behaviour of multiphase materials.. There are several models for the CTE, however, most require a knowledge of the elastic properties of the constituent phases and do not take account ofthe microstructural features of the material. If the CTE could be predicted on the basis of microstructural information, this would then lead to the ability to engineer the microstructure of multiphase ceramic materials to produce acceptable thermal expansion behaviour. To investigate this possibility, magnesia-magnesium aluminate sp~el (MMAS) composites, consisting of a magnesia matrix and magnesium aluminate s~ne'l (MAS) particles, were studied. Having determined a procedure to produce MAS fr alumina and magnesia, via solid state sintering, magnesia-rich compositions wit ~ various magnesia contents were prepared to make the MMAS composites. Further, the l\.1MAS composites prepared from different powders (i.e. from an alumina-magnesia mixture ahd from a magnesia-spinel powder) were compared. Com starch was added into the powder mixtures before sintering to make porous microstructures. Microstructural development and thermal expansion behaviour ofthe MMAS composites were investigated. Microstructures of the MAS and the MMAS composites as well as their porous bodies were quaritified from backscattered electron micrographs in terms of the connectivity of solids i.e. solid contiguity by means of linear intercept counting. Solid contiguity decreased with increasing pore content and varied with pore size, pore shape and pore distribution whereas the phase contiguity depended strongly on the chemical composition and was less influenced by porosity. ' The thermal expansion behaviour of the MAS and the MMAS composites between 100 and 1000 °C was determined experimentally. Variation in the CTE ofthe MAS relates to the degree of spinel formation while the thermal expansion of the MMAS composites depends strongly on phase content. However, the MMAS composites with similar phase compositions but made from different manufacturing processes showed differences in microstructural features and thermal expansion behaviour. Predictions of the CTE values for composites based on a simple rule-of-mixtures (ROM) using volume fraction were compared with the measured data. A conventional ROM accurately predicted the effective CTE of a range of dense alumina-silicon carbide particulate composites but was not very accurate for porous multiphase structures. It provided an upper bound prediction as all experimental values were lower. Hence, the conventional ROM was modified to take account of quantitative microstructural parameters obtained from solid contiguity. The modified ROM predicted lower values and gave a good agreement with the experimental data. Thus, it has been shown that quantitative microstructural information can be used to predict the CTE of multiphase ceramic materials with complex microstructures.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Multipass communication systems for tiled processor architectures

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.Includes bibliographical references (p. 191-202).Multipass communication systems utilize multiple sets of parallel baseband receiver functions to balance communication data rates and available computation capabilities. This is achieved by spatially pipelining baseband functions across parallel resources to perform multiple processing passes on the same set of received values, thus allowing the system to simultaneously convey multiple sequences of data using a single wireless link. The use of multiple passes mitigates the effects of data rate on receiver processing bottlenecks, making the use of general-purpose processing elements for high data rate communication functions viable. The flexibility of general-purpose processing, in turn, allows the receiver composition to trade-off resource usage and required processing rate. For instance, a communication system could be distributed across 2 passes using 2x the overall area, but reducing the data rate for each pass and the resultant overall required processing rate, and hence clock speed, by 1/2. Lowering the clock speed can also be leveraged to reduce power through voltage scaling and/or the use of higher Vt devices. The characteristics of general-purpose parallel processors for communications processing are explored, as well as the applicability of specific parallel designs to communications processing.(Cont.) In particular, an in depth look is taken of the Raw processor's tiled architecture as a general-purpose parallel processor particularly well suited to portable communications processing. An example of a multipass system, based on the 802.11a baseband, implemented on the Raw processor along with the accompanying hardware implementation is presented as both a proof-of-concept, as well as a means to explore some of the advantages and trade-offs of such a system. A bit-error rate study is presented which shows this multipass system to be within a small fraction of dB of the performance of an equivalent data rate single pass system, thus demonstrating the viability of the multipass algorithm. In addition, the capability of tiled processors to maximize processing capabilities at the system block level, as well as the system architectural level, is shown. Parallel implementations of two processing intensive functions: the FFT and the Viterbi decoder are shown. A parallelized assembly language FFT utilizing 16 tiles is shown to have a 1,000x improvement , and a parallelized 48-tile assembly language Viterbi decoder is shown to have a 10, 000x improvement over corresponding serial C implementations.by Nathan Robert Shnidman.Ph.D

Bandwidth management and quality of service

With the advent of bandwidth-hungry video and audio applications, demand for bandwidth is expected to exceed supply. Users will require more bandwidth and, as always, there are likely to be more users. As the Internet user base becomes more diverse, there is an increasing perception that Internet Service Providers (ISPs) should be able to differentiate between users, so that the specific needs of different types of users can be met. Differentiated services is seen as a possible solution to the bandwidth problem. Currently, however, the technology used on the Internet differentiates neither between users, nor between applications. The thesis focuses on current and anticipated bandwidth shortages on the Internet, and on the lack of a differentiated service. The aim is to identify methods of managing bandwidth and to investigate how these bandwidth management methods can be used to provide a differentiated service. The scope of the study is limited to networks using both Ethernet technology and the Internet Protocol (IP). Tile study is significant because it addresses current problems confronted by network managers. The key terms, Quality of Service (QoS) and bandwidth management, are defined. “QoS” is equated to a differentiating system. Bandwidth management is defined as any method of controlling and allocating bandwidth. Installing more capacity is taken to be a method of bandwidth management. The review of literature concentrates on Ethernet/IP networks. It begins with a detailed examination of definitions and interpretations of the term Quality of Service and shows how the meaning changed over the last decade. The review then examines congestion control, including a survey of queuing methods. Priority queuing implemented in hardware is examined in detail, followed by a review of the ReSource reserVation Protocol (RSVP) and a new version of IP (lPv6). Finally, the new standards IEEE 802.1p and IEEE 802.1Q are outlined, and parts of ISO/IEC 15802-3 are analysed. The Integrated Services Architecture (ISA), Differentiated Services (DiffServ) and MultiProtocol Label Switching (MPLS) are seen as providing a theoretical framework for QoS development. The Open Systems Interconnection Reference Model (OSI model) is chosen as the preferred framework for investigating bandwidth management because it is more comprehensive than the alternative US Department of Defence Model (DoD model). A case study of the Edith Cowan University (ECU) data network illustrates current practice in network management. It provides concrete examples of some of the problems, methods and solutions identified in the literary review. Bandwidth management methods are identified and categorised based on the OSI layers in which they operate. Suggestions are given as to how some of these bandwidth management methods are, or can be used within current QoS architectures. The experimental work consists of two series of tests on small, experimental LANs. The tests are aimed at evaluating the effectiveness of IEEE 802.1 p prioritisation. The results suggest that in small Local Area Networks (LANs) prioritisation provides no benefit when Ethernet switches are lightly loaded

Quality of service differentiation for multimedia delivery in wireless LANs

Delivering multimedia content to heterogeneous devices over a variable networking environment while maintaining high quality levels involves many technical challenges. The research reported in this thesis presents a solution for Quality of Service (QoS)-based service differentiation when delivering multimedia content over the wireless LANs. This thesis has three major contributions outlined below: 1. A Model-based Bandwidth Estimation algorithm (MBE), which estimates the available bandwidth based on novel TCP and UDP throughput models over IEEE 802.11 WLANs. MBE has been modelled, implemented, and tested through simulations and real life testing. In comparison with other bandwidth estimation techniques, MBE shows better performance in terms of error rate, overhead, and loss. 2. An intelligent Prioritized Adaptive Scheme (iPAS), which provides QoS service differentiation for multimedia delivery in wireless networks. iPAS assigns dynamic priorities to various streams and determines their bandwidth share by employing a probabilistic approach-which makes use of stereotypes. The total bandwidth to be allocated is estimated using MBE. The priority level of individual stream is variable and dependent on stream-related characteristics and delivery QoS parameters. iPAS can be deployed seamlessly over the original IEEE 802.11 protocols and can be included in the IEEE 802.21 framework in order to optimize the control signal communication. iPAS has been modelled, implemented, and evaluated via simulations. The results demonstrate that iPAS achieves better performance than the equal channel access mechanism over IEEE 802.11 DCF and a service differentiation scheme on top of IEEE 802.11e EDCA, in terms of fairness, throughput, delay, loss, and estimated PSNR. Additionally, both objective and subjective video quality assessment have been performed using a prototype system. 3. A QoS-based Downlink/Uplink Fairness Scheme, which uses the stereotypes-based structure to balance the QoS parameters (i.e. throughput, delay, and loss) between downlink and uplink VoIP traffic. The proposed scheme has been modelled and tested through simulations. The results show that, in comparison with other downlink/uplink fairness-oriented solutions, the proposed scheme performs better in terms of VoIP capacity and fairness level between downlink and uplink traffic