HSUPA offers uplink system capacity improvements in a similar way to that provided by HSDPA in the downlink direction. This module, which is designed to supplement the UMTS Air Interface tutorial, explores the principles of HSUPA, as well as introducing the new HSUPA physical structure, channels and enhanced MAC-e and MAC-es functions. The processes of adaptive modulation and coding are also discussed, in addition to the techniques uses to maintained high uplink data rates. Finally, the modifications to the signalling procedures are detailed, along with the key changes to UMTS mobility.