Kablosuz çoğulortam yayınında eniyileme üzerine

This dissertation is concerned with the development of a cross-layer framework for wireless broadcasting systems. Both cellular and ad hoc networks are considered. It has been well-established that cross-layer designs provide significant gains in the performance of point-to-point wireless communication systems. However, the point-to-multipoint nature of the broadcast system has so far eluded most researchers into thinking that a cross-layer solution is not feasible. This dissertation aims to dispell this reasoning. Indeed, throughout the thesis, we show that practical cross-layer solutions for wireless broadcast systems exist and they provide significant performance gains.First, we consider a CDMA-based cellular broadcast system where the video content to be broadcast is SVC encoded prior to transmission. For this scenario, we develop a solution where we aim to simultaneously maximize the number of users receiving the video broadcasting service and the average successfully decoded video data rate. The proposed broadcast system aims to optimally divide the code space amongst the multiple layers of the SVC content using multiple-objective optimization. This framework finds the best compromise between the objectives of maximizing the average decodable video data rate and minimizing the basic quality video outage probability. Simulations conducted for the ITU Pedestrian A and Vehicular B channels show that high data rates with low outages are possible when a 3G system such as 1xEV-DO is used for video broadcasting, however, it may not be desirable to use scalable video coding for this purpose.Second, we consider a cellular broadcast system where the video encoding is conducted using the state-of-the-art video codec, H.264/AVC. In this scenario, we optimize the number of users receiving the broadcasting service and the average video quality of the received stream. To solve this problem optimally, we adjust the physical and the application layer parameters in a cross-layer fashion while utilizing the characteristics of the video that is being transmitted as well as the wireless channel. We propose a content-adaptive, multi-objective optimized, cross-layer video broadcasting framework for a wireless system capable of supporting a multitude of transmission data rates using H.264/AVC. The optimization problem aims to find H.264/AVC as well as physical layer system parameters jointly to reach the optimal compromise between the objectives of maximizing the average received video PSNR and minimizing the video broadcast service outage probability. Simulations conducted for the ITU Pedestrian A and Vehicular B channels show that significant gains in system performance can be achieved for video broadcasting using such a cross-layer design is used.Third, we consider a wireless ad hoc system where any of the participating nodes may cooperate in the broadcast initiated by the source node. In such a scenario, significant difficulties exist in terms of the selection of participating relay nodes if the aim is to achieve the optimal capacity for a given total energy constraint. For a given number of active users and the CSI between each user, finding the optimal broadcast capacity achieving subset of cooperating nodes satisfying the energy constraint is an NP-complete problem. To alleviate the problem, we consider the case of a circular ad hoc network where there are infinitely many nodes. In this scenario, we find critical points that determine the optimal broadcast capacity for a given total energy constraint. Following this analysis, we propose two algorithms, one distributed and one centralized, both based on heuristics computed by the theoretical model. Not only the proposed methods present a practical solution to the optimal broadcast capacity achieving relay selection problem but they also provide a significant increase in the overall system performance. We discuss the behaviors of the broadcast capacity for the two proposed models under a variety of system settings based on realistic assumptions. The results show that using a randomized and distributed relay selection in broadcasting yields significant gains in the system performance, even in the worst case scenario.