Cross-Layer Design for Ofdma Wireless System

This dissertation, "Cross-layer Design for OFDMA Wireless System" by Shui-wing, David, Hui, 許樹榮, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of the Thesis Entitled Cross-Layer Design for OFDMA Wireless Systems submitted by Hui Shui Wing David for the degree of Master of Philosophy at The University of Hong Kong in February 2007 High spectral efficiency support and Quality of Service (QoS) provision are two of the most important requirements in the next-generation wireless network design. Traditional layered network architecture has been unable to satisfy these wireless system requirements effectively due to its time varying characteristic. Cross-Layer Design has been proposed to enhance system spectral efficiency by considering multiuser diversity gain, and the QoS using the adaptive scheduler design over both the Physical (PHY) and Medium Access Control (MAC) layers. Orthogonal Frequency Division Multiple Access (OFDMA) with cross-layer scheduling further enhances the spectral efficiency by exploiting temporal diversity and spectral diversity while providing robust performance over frequency selective channels. This thesis focuses on Cross-Layer Scheduler Design for OFDMA wireless systems with heterogeneous delay requirements. Traditional Cross-Layer Design for OFDMA has neglected higher layer dynamics and delay requirements, assuming that perfect Channel State Information at the Transmitter (CSIT) is available. However, users may be delay sensitive with heterogeneous delay requirements and therefore CSIT can never be perfect, especially when the number of carriers is large. Without considering the CSIT imperfection, packet transmission outage occurs due to improper rate adaptation on imperfect CSIT, resulting in a significant degradation to the delay performance of heterogeneous users. This thesis focuses on combining information theory and queuing theory in modeling system dynamics, and proposes a novel analytical Cross-Layer Design framework for OFDMA systems with heterogeneous delay requirements and imperfect CSIT. The proposed cross-layer scheduling algorithm dynamically allocates the radio resource based on users' CSIT, source statistics and delay requirements. The delay-sensitive power allocation adopts the multilevel water-filling approach in which urgent users have higher water-filling levels. The delay-sensitive subcarrier allocation strategy has linear complexity with respect to the number of users and the number of subcarriers. Water-filling levels are obtained by an efficient Lagrange multiplier finding algorithms. The asymptotic multiuser diversity gain and the minimum power requirement saving of the proposed schedules are also obtained analytically. Simulation results show that substantial throughput gain is obtained while satisfying the delay constraints and target outage probability using the proposed scheduler regardless of the variation of traffic loadings and the CSIT imperfection. DOI: 10.5353/th_b3742717 Subjects: Orthogonal frequency division multiplexing Wireless communication systems - Design and construction