Quality of Packet Services in UMTS and Heterogeneous Networks

In this thesis, the performance investigation of packet services in both a standalone UMTS network and a UMTS network coexisting with other networks is undertaken. The investigations are concerned with the performance of a single link. Apart from objective performance metrics such as goodput and delay, subjective measures of user perceived QoS are also used. A real time emulation platform that uses a combination of simulated and real network protocols has been developed to enable both subjective and objective investigations from the user’s perspective. With regard to a standalone UMTS network, detailed emulation results are given concerning the performance enhancements due to the several mechanisms that control UMTS link layer retransmissions. The results show that the maximum number of retransmissions is the most determinant factor, and setting it to three or more eliminates TCP retransmissions and gives optimal performance (up to 85% improvement in the goodput). The impact of TCP spurious retransmissions and the improvements due to several proposed TCP extensions such as Eifel are also investigated. Eifel leads to 33% improvement in the goodput while DSACK improves the performance by only 14% when out of order delivery is employed at the RLC layer. However, for the delay spike cases, the improvements are less than 9%. The impact of inter-system handover and associated buffering techniques, including a new technique called intermediate buffering, on different TCP extensions when UMTS coexists with other networks are investigated. Full buffering during handover can lead to the worst performance, as compared with no buffering at all, and intermediate buffering gives the best result. Eifel improves the performance when the handover delay is small and full buffering is employed, but it causes up to 34% degradation in the goodput when