Analysis and Performance Improvement of TCP during the Handover of LTE

Within the Third Generation Partnership Project (3GPP), the new project entitled Long Term Evolution (LTE) is going to be a new standard. LTE is characterized by a broadband optimized radio access network, which focuses on supporting a high throughput with low latency by an ip based transport network. During the handover, which is the procedure to disconnect a mobile user from a base station and connect it to another, LTE supports the inter-base station packet forwarding to achieve a seamless transition. However, given the mobility of the end users and the high bandwidth required, the handover may cause sudden degradation of the throughput of the TCP connection if the process is not correctly controlled. Moreover, during the handover, congestions in the transport network could lead to a poor utilization of the transport and radio resources available, and degrade significantly the user’s throughput. The aim of this thesis project is to study the impact on the user throughput and system performance when users with high bit rates tcp services are moving through cells of the network, and to propose enhancing solutions to counteract to possible throughput degradations.

First, we have implemented an accurate LTE simulator in the ns-2 . The simulator implements the tunneling mechanism of LTE for the end users ip packets. It allows us to switch the ip tunnel between the gateway and radio base station associated with the moving mobile in the gateway towards the target base station when the terminal arrives there. The simulator has then been used to investigate the performance of the handover event during a tcp connection with focus on the data forwarding and the router buffer dimension, and to propose two solutions to achieve a better end user throughput. The first solution is based on a prediction technique that avoid the data forwarding, whereas the second solution acts in the transport network with an active queue management. The simulation results show that the handover prediction could increase the tcp performance and, second, that the router buffer dimension does matter for the end user throughput in case of a congested transport network. The project has been performed at the Automatic Control Lab at KTH in Stockholm and in collaboration with Ericsson Research Lab.