HSDPA Official Site
High-Speed Downlink Packet Access (HSDPA) is an enhanced 3G (third generation) mobile telephony communications protocol in the High-Speed Packet Access (HSPA) family, also coined 3.5G, 3G+ or turbo 3G, which allows networks based on Universal Mobile Telecommunications System (UMTS) to have higher data transfer speeds and capacity. Current HSDPA deployments support down-link speeds of 1.8, 3.6, 7.2, 14.0 Mbit/s. Further speed increases are available with HSPA+, which provides speeds of up to 42 Mbit/s downlink.
The first phase of HSDPA has been specified in the 3rd Generation Partnership Project (3GPP) release 5. Phase one introduces new basic functions and is aimed to achieve peak data rates of 14.0 Mbit/s (see above). Newly introduced are the High Speed Downlink Shared Channels (HS-DSCH), the adaptive modulation QPSK and 16QAM and the High Speed Medium Access protocol (MAC-hs) in base station.
The second phase of HSDPA is specified in the upcoming 3GPP release 7 and has been named HSPA Evolved. It can achieve data rates of up to 42 Mbit/s. It will introduce antenna array technologies such as beamforming and Multiple-input multiple-output communications (MIMO). Beam forming focuses the transmitted power of an antenna in a beam towards the user’s direction. MIMO uses multiple antennas at the sending and receiving side. Deployments are scheduled to begin in the second half of 2008.
After HSPA Evolved, the roadmap leads to E-UTRA (Previously "HSOPA"), the technology specified in 3GPP Release 8. This project is called the Long Term Evolution initiative. The first release of LTE offers data rates of over 320 Mbit/s for downlink and over 170 Mbit/s for uplink using OFDMA modulation.