Analysing uplink scheduling in mobile networks : a flow perspective

Abstract

The main purpose of mobile networks is to enable customers that are located at arbitrary geographical locations to communicate with each other without the need of a physical connection. Within only two centuries mobile technology has evolved from analogue networks providing telephony services towards digital networks supporting larger variety of mobile services, enhanced coverage and higher data rates. A key element of providing wireless connectivity is the management of the radio spectrum to be shared by the mobile users. The challenge in the spectrum management is to nd a trade-o between eciently using the network and at the same time providing the quality of service (QoS) requested by the users. In this task operators are strongly assisted by the radio resource management (RRM) mechanisms and scheduling in particular. Scheduling is responsible for the distribution of the available radio resource over the users that have requested service. This thesis focuses on the performance of uplink scheduling schemes in mobile networks. We have dedicated special attention to the impact of ow-level dynamics, i.e. the random user behaviour regarding the initiation and completion of data ow transfers. Additionally, we investigate the possibilities to adopt relaying as a technique to boost performance and how it interacts with the scheduling mechanism. In order to evaluate the impact of the ow-level dynamics on the scheduling performance we propose a novel hybrid analysis approach, which we consider to be an overall contribution of this thesis. The approach is a combination of analytical methods and simulation. Packet level details, playing on a small time scale, are captured by analytical methods, while the ow-level behaviour, playing on a larger time scale, is simulated. This combination enables fast evaluation and comparison of the performance of dierent schedulers expressed in terms of ow throughputs and mean ow transfer times. Our general conclusion is that ow dynamics can have signicant impact on performance. For example, we show that some changes (benets) in performance exhibit only during the interaction of ow transfers. Therefore, analysis of the system at ow level should be included in the analysis of mobile systems. The proposed hybrid analytical/simulation approach, which captures both packetand ow-level behaviour, is very exible and can be easily adapted to reect changes in factors such as environmental conditions or technological specications. These features make the approach very appropriate for application in other studies as well. In our studies we have investigated the impact of various factors, e.g. intercell interference and individual user channel conditions, on the scheduling scheme. Based on our ndings we conclude that a scheduling scheme should be carefully designed to consider, among others, requirements towards utilisation eciency, user's QoS demands and the wireless environment. Furthermore, we also show that relaying leads to improved service provided, not only to users that directly make use of a relay station but also to users that communicate directly to the network.