4. New radio interfaces for HSDPA and HSUPA

4.1 Radio interface evolution

The UMTS radio interface has evolved considerably since the first version of UMTS: TD-SCDMA appeared in Release 4, followed by HSDPA in Release 5 (valid for both FDD and TDD) and HSUPA in Release 6 (for FDD mode). At each stage, new digital wireless communications techniques were integrated. These include higher-order modulation (16-QAM), fast retransmission (HARQ), packet scheduling in Node B, and the introduction of short time intervals between data block transmissions on the radio interface.

4.2 HSDPA...