Performance Analysis of Hybrid-ARQ Characteristics in HSDPA

This paper describes network level simulation results for Enhanced UMTS. High-Speed Downlink Packet Access (HSDPA) enhances both the capacity and the peak rate of WCDMA-based systems. Link adaptation and Hybrid-Automatic Repeat reQuest (H-ARQ) are two key functions creating these enhancements. This paper considers the results of different aspects of the H-ARQ process. This process is considered from two viewpoints. The results are mainly gathered from the ns-2 based network level simulator Enhanced UMTS Radio Access Networks Extension (EURANE). This is a network level simulator with realistic traffic and user scenarios. Also results from a more fundamental analysis of H-ARQ characteristics based on link-level results will be included. In this more fundamental point of view, only the underlying channel conditions are used for a preliminary study of new ideas. The rounding down and delaying of the CQI reporting both have a significant impact on throughput and transfer delay of the HSDPA channel. The analysis of the link-level results provides a first insight how different parts of the WCDMA system interact with each other and impact the end-to-end performance as experienced by the user. Both viewpoints show that the H-ARQ functionality indeed enhances the capacity and peak rate of the WCDMA system.