Power control, transmission rate control and scheduling in cellular radio systems
Fredrik Berggren · KTH Publication Database DiVA (KTH Royal Institute of Technology) · 2001
Forthcoming broadband wireless systems are to provide a multitude of services, offering large amounts of data to be delivered within short periods of time. As the demand for wireless data is expected to increase, sustained by data communication networks and the Internet, strategies for managing the scarce radio resources become necessary. Emerging wireless services will require different quality of service (QoS), e.g., data rate, delay etc., making the objective of radio resource management extensive. Due to the necessity of sharing the radio resources, mutual interference among the users may limit system capacity. Transmitter power control based on signal-to-interference ratio (SIR), has shown to be an essential method for successfully balancing signal and interference powers and minimizing any unnecessary interference. In this work, transmission schemes based on power control, applicable for providing different QoS are developed. Rate of convergence and energy conservation constitute important properties of the schemes, reflecting their ability to rapidly find energy-efficient solutions. For that purpose, we first suggest a general iterative SIR based power control algorithm which can handle congested situations by removing radio links during power control updates. This algorithm is then extended with a greedy admission control procedure for a multi-rate CDMA system where the transmission rates are limited to a number of discrete levels. The scheme is used for maximizing throughput for a best effort type of service and this thesis includes its convergence properties and shows possible gains in throughput and energy saving. For supporting non-real time data services, where an average data rate is required, the possibility of joint power control and transmission scheduling is investigated for the CDMA downlink. A distributed power control algorithm which induces time division to avoid intra-cell interference is suggested. This thesis shows that the algorithm exhibits a fast rate of convergence and that a capacity gain as compared to pure CDMA transmission can be obtained. Finally, in a system where short data packets may arrive irregularly, SIR based power control is difficult to execute. Therefore, power control based on path gain is investigated as a means of increasing system throughput. This thesis shows a tradeoff between throughput, energy consumption and requirements on transmitter power dynamic range.