Evolution of High-Speed Downlink Packet Access in WCDMA by improved ARQ signalling

The fast physical-layer ARQ scheme adopted in the HSDPA feature of WCDMA depends on reliable uplink acknowledgement signalling. A significant enhancement to this signalling was introduced in "Release 6" of the UMTS specifications prepared by the 3rd Generation Partnership Project (3GPP). The enhancement was designed to maintain the reliability of the signalling, while reducing the overhead in transmission power. This allows more power to be allocated to data transmission, thus helping to increase the cell-edge data rate and the coverage of UMTS services, which is one of the key goals of WCDMA evolution. This paper explains the operation of the enhanced signalling and outlines a possible decoding technique for the base station. Simulation results are presented to illustrate the performance improvement delivered by the enhancement compared to the original "Release 5" version of HSDPA.