In this study, we propose a new Amplify-and-Forward (AF) amplification factor to improve the error performances of the current AF schemes and thus enhance the total capacity at the destination terminal. The proposed scheme has two degrees of freedom, meaning that it contains two variable parameters that can simultaneously vary the amplification factor instead of one as in traditional variable-gain or semi-blind relaying. The numerical results show that the proposed AF scheme outperforms some current ones with which it is compared in terms of average capacity and probability of outage and thus brings AF relaying performances closer to that of Decode-and Forward (DF) strategy which hitherto outperforms it. The results also show that by increasing or decreasing the power share of the relay, the optimal location of the relay is not only moved closer to or farther away from the destination, the total average capacity at that location is also correspondingly increased or decreased.

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This paper proposes a utility-based scheduling framework for efficient differentiation of users' Quality-of-Service (QoS) in a broadband wireless access system involving heterogeneous mixed traffic flows. The utility-based scheduling framework, called Maximum QoS Satisfaction (MQS), is based on three novel Radio Resource Allocation (RRA) techniques; delay-based scheduling policy for Real-Time (RT), minimumrate-based scheduling policy for Non-Real-Time (NRT) and a throughputbased scheduling policy for Best-Effort (BE) services. Simulation study shows that MQS achieves superior performances in terms of average system throughput and user satisfaction both in single and heterogeneous mixed traffic scenarios, when compared to some existing ones.

The needs of high speed broadband wireless access at lower cost and easy deployment to meet the modern mobile services leads in the emergence of an another IEEE standard called Worldwide Interoperability for Microwave Access (WiMAX). The limitations of con ventional Broadband wireless access have been overcomewith the scalable features of WiMAX. The main purpose of this paper is to evaluate, analyze and compare the performance of a WiMAX under different data rate and coding techniques. For this purpose a simulation model of WiMAX PHY layer transmitter and Receiver has been designed using MATLAB. The model was implemented at the Physical Layer using ConvolutionalEncoding Rate of 3/416-QAM modulations and transmitted with 256 OFDM symbols in both the AWGN and Rayleigh fading channels. In this thesis, the performance analysis is being done by studying the bit loss and Packet losses that occurred during transmission over channel. It is found that the performance of transmitted data not only depends on parameters like Signal to noise ratio (SNR) and Signal power but also on the effect of transmission channel.

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