Chapter 8 – High-speed downlink packet access

The introduction of High-Speed Downlink Packet Access (HSDPA) in release 5 implied a major extension of the WCDMA radio interface, significantly enhancing the WCDMA downlink packet-data performance and capabilities in terms of higher peak data rate, reduced latency, and increased capacity. The enhancements were achieved through the introduction of several techniques, including higher-order modulation , rate control , channel-dependent scheduling , and hybrid-ARQ with soft combining . Some of the responsibility for managing radio resources was moved from the RNC to the Node B, in order to enable decisions relating to the air interface to be made closer to the interface and faster. HSDPA is the fundamental downlink building block of the subsequent HSPA evolution. Release 5 HSDPA is described in detail in this chapter, whereas enhancements that have followed in later releases are described in subsequent chapters.