Wireless broadband access: WiMAX and beyond - Investigation of bandwidth request mechanisms under point-to-multipoint mode of WiMAX networks

The WiMAX standard specifies a metropolitan area broadband wireless access air interface. In order to support QoS for multimedia applications, various bandwidth request and scheduling mechanisms are suggested in WiMAX, in which a subscriber station can send request messages to a base station, and the base station can grant or reject the request according to the available radio resources. This article first compares two fundamental bandwidth request mechanisms specified in the standard, random access vs. polling under the point-to-multipoint mode, a mandatory transmission mode. Our results demonstrate that random access outperforms polling when the request rate is low. However, its performance degrades significantly when the channel is congested. Adaptive switching between random access and polling according to load can improve system performance. We also investigate the impact of channel noise on the random access request mechanism

Investigation of efficient resource allocation schemes for WiMAX networks

This thesis was submitted for the degree of Master of Philosophy and was awarded by Brunel University on 9 July 2008.WiMax (Worldwide Interoperability for Microwave Access) is a promising wireless technology with the aim of providing the last mile wireless broadband access designed for both fixed and mobile consumers as an alternative solution to the wired DSL and cable access schemes. The purpose of this research project is to investigate efficient resource allocation algorithms for WiMax. To achieve this goal, we investigate efficient PHY layer Partial Usage of SubCarriers (PUSC) allocation as well as MAC layer piggyback bandwidth request mechanisms. At the PHY layer we proposed improvements on the Uplink and Downlink PUSC subcarrier allocation scheme. For the Uplink PUSC we suggested a method by allocating different frequencies to neighbouring cells in combination with the Integer Frequency Reuse (IFR) and Fractional Frequency Reuse (FFR) in order to reduce interferences and collisions. The simulation results exhibit that collision rates can be reduced to zero for both IFR and FFR patterns with the proposed improvement by assuming that perfect power control is used in the system. In addition, there is no collision at cell edges. The results also show that FFR patterns achieve lower inter-cell interference and higher capacities as compared to the IFR patterns. For the Downlink PUSC we introduced an offset scheme with the purpose of increasing the number of users in the system. At the MAC layer we propose an improvement on the piggyback bandwidth request mechanism by increasing the size of the piggyback bandwidth request in order to reduce the number of bandwidth requests and hence improve the resource utilisation. The simulation results demonstrate that our improved scheme achieves higher throughput, less delay and packet loss rates as compared to the standardised piggyback bandwidth request mechanism

Mobile Networks

The growth in the use of mobile networks has come mainly with the third generation systems and voice traffic. With the current third generation and the arrival of the 4G, the number of mobile users in the world will exceed the number of landlines users. Audio and video streaming have had a significant increase, parallel to the requirements of bandwidth and quality of service demanded by those applications. Mobile networks require that the applications and protocols that have worked successfully in fixed networks can be used with the same level of quality in mobile scenarios. Until the third generation of mobile networks, the need to ensure reliable handovers was still an important issue. On the eve of a new generation of access networks (4G) and increased connectivity between networks of different characteristics commonly called hybrid (satellite, ad-hoc, sensors, wired, WIMAX, LAN, etc.), it is necessary to transfer mechanisms of mobility to future generations of networks. In order to achieve this, it is essential to carry out a comprehensive evaluation of the performance of current protocols and the diverse topologies to suit the new mobility conditions

Call Admission Control Scheme for Improved Quality of Service in WiMAX Communication at Vehicular Speeds

The IEEE 802.16e standard, also known as mobile WiMAX, has emerged as an exciting mobile wireless communication technology that promises to offer both high throughput and guaranteed quality of service (QoS). Call admission control (CAC) scheme serves as a useful tool for WiMAX, which ensures that resources are not overcommitted and thereby, all existing connections enjoy guaranteed QoS. Existing CAC schemes largely depend on readily available information like currently available resources and bandwidth demand of the new call while making an acceptance or rejection decision once a new request arrives. Since wireless channels are not as reliable as wired communication, CAC scheme in WiMAX communication faces a serious challenge of making a right estimate of the usable channel capacity (i.e., effective throughput capacity) while computing the available resources in various communication scenarios. Existing CAC schemes do not consider the impact of mobility at vehicular speeds when computing the usable link capacity and available resources. In this paper, we propose a new CAC scheme that estimates the usable link capacity for WiMAX communication at various vehicular speeds and uses this information while making a CAC decision. The proposed CAC scheme takes the speed distribution model of a mobile node into account during the CAC decision making process. Simulation results confirm that the proposed scheme achieves lower dropping rate and improved QoS compared to existing schemes

Interoperability Among Heterogeneous Networks for Future Aeronautical Communications

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Enhancing Scheduling for IEEE 802.16 Networks

The IEEE 802.16 standard defines the specifications of the Worldwide Interoperability for Microwave Access (WiMAX) technology as a Broadband Wireless Access network. This type of networks supports multiservice traffic (data, voice and video) and guarantees the Quality of Service at the MAC layer level. However, the IEEE 802.16 standard specifies three QoS components that reside in the MAC layer such as scheduler and call admission control. Although, the IEEE 802.16 defined the function of each component but left the implementation open for vendors and operators. In this thesis, we aim to design two new scheduling algorithms that guarantee QoS in WiMAX network. The new algorithms will consider application traffic requirements, channel condition states and compliant with the standard. The first algorithm is Deadline maximum Signal to Interference Ratio (DmSIR) scheduling algorithm and it is a modified version from maximum Signal to Interference Ratio (mSIR) scheduling algorithm. The DmSIR scheduling algorithm makes scheduling decision based on two factors: the packets deadline and signal to noise ratio. The second algorithm which we named the Priority based Deficit Round Robin (PbDRR) solves the problem of long delay for non real-time traffic with low signal to noise ratio as well as giving priority to real-time traffic that approach to deadline. The PbDRR scheduling algorithm makes scheduling decision based on three factors: packets deadline, signal to noise ratio and backlog traffic. We used the NS2 network simulation to evaluate the performance of the new algorithms and three performance metrics are evaluated for this purpose. The simulation results for DmSIR shows enhancement in the performance compared to the mSIR scheduling algorithm but the non real-time traffic with low signal to noise ratio suffers from long delay. On the other hand, the simulation results for the PbDRR scheduling algorithm shows better performance than the DmSIR and Deficit Round Robin + Fragmentation (DRR+F) scheduling algorithms

Energy efficiency in next generation wireless networks: methodologies, solutions and algorithms

Mobile Broadband Wireless Access (BWA) networks will offer in the forthcoming years multiple and differentiated services to users with high mobility requirements, connecting via portable or wearable devices which rely on the use of batteries by necessity. Since such devices consume a relatively large fraction of energy for transmitting/receiving data over-the-air, mechanisms are needed to reduce power consumption, in order to increase the lifetime of devices and hence improve user’s satisfaction. Next generation wireless network standards define power saving functions at the Medium Access Control (MAC) layer, which allow user terminals to switch off the radio transceiver during open traffic sessions for greatest energy consumption reduction. However, enabling power saving usually increases the transmission latency, which can negatively affect the Quality of Service (QoS) experienced by users. On the other hand, imposing stringent QoS requirements may limit the amount of energy that can be saved. The IEEE 802.16e standard defines the sleep mode is power saving mechanism with the purpose of reducing energy consumption. Three different operation classes are provided, each one to serve different class of traffic: class I, best effort traffic, class II real time traffic and class III multicast traffic. Several aspects of the sleep mode are left unspecified, as it is usually done in standards, allowing manufacturers to implement their own proprietary solutions, thus gaining a competitive advantage over the rivals. The work of this thesis is aimed at verifying, the effectiveness of the power saving mechanism proposed into IEEE 802.16e standard, focusing on the mutual interaction between power saving and QoS support. Two types of delay constrained applications with different requirements are considered, i.e., Web and Voice over IP (VoIP). The performance is assessed via detailed packet-level simulation, with respect to several system parameters. To capture the relative contribution of all the factors on the energy- and QoS-related metrics, part of the evaluation is carried out by means of 2k · r! analysis. Our study shows that the sleep mode can achieve significant power consumption reduction, however, when real time traffic is considered a wise configuration of the parameters is mandatory in order to avoid unacceptable degradation of the QoS. Finally, based on the guidelines drawn through the analysis, we extend our contribution beyond a simple evaluation, proposing a power saving aware scheduling framework aimed at reducing further the energy consumption. Our framework integrates with existing scheduling policies that can pursue their original goals, e.g. maximizing throughput or fairness, while improving the energy efficiency of the user terminals. Its effectiveness is assessed through an extensive packet level simulation campaign