Improved Downlink Capacity Of WiMAX Networks Based On Adaptive Cyclic Prefix And Relay Station

In recent years, there has been a considerable growth in demand for high-speedwireless internet access and this has caused the emergence of new long-range wirelesstechnology. In particular, IEEE802.16standards offer an alternative to the currentwired access networks such as cable modem and digital subscriber line (DSL) link.The Worldwide Interoperability for Microwave Access (WiMAX) has emerged asone of the most important4G wireless networks can provide high-speed wirelessinternet access to subscribers over large geographic regions in metropolitan areas.A relay station (RS) is a new enhancement that can increase the cell capacity andextend the coverage of base station. How to design802.16j relay-based WiMAXsystems and how the relay station architecture can lead to increase the capacity in thedownlink (DL).The capacity of802.16j systems is investigated taking into accountinformation pertaining to wireless channel condition, The design options include theheight of BS and relay station, the cell range, the topology of simulation, the relayposition, the transmit power at the relays, the number of relays deployed and the speedof terminal mobile. There are different challenges in designing the WiMAX networkingprotocols to provide high quality of service (QoS). How to efficiently estimate thecapacity of WiMAX networks over different channel characteristics and how toefficiently exploit the scarce bandwidth.This dissertation aims to solve these challenges to improve the performance ofWiMAX networks. First, we present an algorithm to calculate actual download (DL)capacity for mobile WiMAX, and take advantage to modify the configurable systemparameters in order to maximize the base station (BS) capacity. Second, analyze theeffect of overheads and different channel characteristics over capacity of downlink (DL)with and without overheads. The analyses focus in particular on the impact of AdaptiveModulation and Coding (AMC) and the factors influencing system bandwidth capacityin IEEE802.16e networks investigated. Due to the limited capacity of the cell, if allconnection requests have been approved, QoS requirement of each connection cannot besatisfied. We propose a simple CAC scheme based on adaptive cyclic prefix in order toenhance network performance and satisfy QoS requirements.Third, an analytical study of the WiMAX propagation channel by using Cost-231Hata Model is presented. This model, performance in different frequency band and theSNR achieved under different frequency band. Fourth, the system capacity ofIEEE802.16j standard is investigated and evaluated to understand how the relayarchitecture can lead to capacity and coverage increases in the downlink. To find the gain that can be achieved with relay systems varies significantly from position to otherpositions with different speed of mobile station relative to these deployment scenarioswill be study.Finally, the simulation of different system parameters and traffic cases to ease themobile WiMax planning estimated by using MATLAB.