UMTS data capacity improvements employing dynamic RRC timeouts

The management of radio and code resources of UMTS radio systems is a crucial issue in order to optimize the cell capacity, especially for packet-switched services. In UMTS the Radio Resource Control (RRC) protocol employs static timeouts to decide on the time when idle radio and code resources are released. Unfortunately, the optimal timeout values depend on many parameters, which are not necessarily under full control of the operator. Most important are the characteristics of packet traffic and the current system utilization. This paper presents detailed results for a new scheme based on the Simplex method initially introduced in Brosch and Mitschele-Thiel (2005). The scheme automatically adapts to the current situation. The scheme releases resources hold by inactive mobiles based on the demand and the current load situation instead of using static timeouts. In the paper we also propose an improvement of the initial Simplex method to minimize call setup delays. In addition we study the impact of the adaptive method on the signaling traffic. Simulation results show that the scheme allows for a reduction of the blocking and dropping rate by more than 31% without negative impacts on other parameters. Considering identical blocking and dropping rates, the system capacity can be improved by about 20%