Downlink Radio Resource Management for QoS Provisioning in OFDMA Systems:with emphasis on Admission Control and Packet Scheduling

Abstract

Orthogonal Frequency Division Multiple Access (OFDMA) is the preferred technology for future downlink mobile broadband access systems as the 3rd Generation Partnership Project Long Term Evolution (LTE) in downlink, where the diversification of the proposed services (Voice Over Internet Protocol, video streaming, gaming or simple web browsing...) and higher throughputs are key targets. Therefore, Quality of Service in OFDMA is a key issue for the success of next generation mobile systems. The present thesis aims at proposing a concrete Quality of Service awarepacket scheduling and Radio Admission Control solution for a realistic OFDMA based system indownlink where LTE is taken as a case study. In the frame of the thesis work, a detailed system model of LTE dedicated to Radio Resource Management study has been developed and implemented in a semi-static system level simulator.In a first phase, the study focuses on the dual time / frequency domain packet scheduling concept which allows a linear complexity. Fundamental design principles for throughput control are highlighted. Using those principles, the design of a complete Quality of Service aware packet scheduling algorithm based on the Required Activity Detection principle is proposed. The time domain Required Activity Detection algorithm shows to be among the best performing algorithmsin terms of Quality of Service outage. However, the study shows that it can be greatly improved by introducing delay awareness. In the frequency domain, Required Activity Detection applies weights to the frequency domain schedulers and when used, can decrease the outage of up to 50%.Packet scheduling also is studied in fractional load condition defined by a partial use of the frequency domain resource. The study shows that, fractional load cannot be used as a coverage enhancement technique with the packet scheduling algorithms of the thesis, furthermore, when fractional load occurs due to a lack of traffic, the block error rate can increase severely thus affecting the experienced Quality of Service. The thesis proposes various solutions to overcomethat problem, among which the simplest consists in using Wideband Interference Reporting in the Channel Quality Information reporting scheme.Finally, the thesis focuses on Radio Admission Control. New algorithms, namely the adaptive throughput and Required Activity Detection-based Radio Admission Control are tested and compared to a simple fixed throughput algorithm. It is shown that the Required Activity Detection based Radio Admission Control can track the channel and therefore keep the system in feasibility region