 HSDPA is based on shared channel transmission, and its key features are shared channel and multi-code transmission, higher-order modulation, short transmission time interval (TTI), fast link adaptation and scheduling, and fast hybrid automatic repeat request (HARQ).Further new features are the High Speed Downlink Shared Channels (HS-DSCH), quadrature phase shift keying, 16-quadrature amplitude modulation, and the High Speed Medium Access protocol (MAC-hs) in base station.The upgrade to HSDPA is often just a software update for WCDMA networks.