HSDPA: High Speed Downlink Packet Access

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HSDPA (High Speed Downlink Packet Access) is an upgrade to UMTS/WCDMA and has become the leading global mobile broadband standard.. HSDPA increases the download speeds by up to 3.5 times, initially delivering typical user data rates of 550 to 800 kbps.  Improvements to the downlink, through HSDPA, were the first upgrade steps available to operators seeking to deploy mobile broadband services as a part of 3GPP Release 5. There is some confusion regarding the use of acronyms involving HSDPA, and its further evolution to High Speed Uplink Packet Access (HSUPA), as the terms are often used interchangeably along with the acronym HSPA which refers to the both HSDPA and HSUPA in their evolved state. 
HSDPA speeds are ideal for bandwidth-intensive applications, such as large file transfers, streaming multimedia and fast Web browsing. HSDPA also offers latency as low as 70 to 100 milliseconds (ms) making it ideal for real-time applications such as interactive gaming and delay-sensitive business applications such as Virtual Private Networks (VPNs).
High Speed Downlink Packet Access is predominately a software upgrade to Release 99 of the UMTS standard. HSDPA has been commercially available since December 2005, when Cingular Wireless – now AT&T – launched the world's first large scale HSDPA service. There are more than 475 HSDPA networks commercially deployed or in various stages of deployment. International roaming is available as the technology falls back on UMTS, EDGE and GPRS for the continuation of voice and data services.
HSDPA usually requires only new software and base station channel cards, instead of necessitating the replacement of major pieces of infrastructure from UMTS and does not require additional spectrum for deployment. As a result, UMTS operators can deploy HSDPA quickly and cost-effectively. In fact, most operators that deploy UMTS are deploying an HSDPA-ready network.
HSDPA technology significantly improves the UMTS downlink performance through techniques, such as adaptive modulation and coding, hybrid ARQ (HARQ) and fast scheduling. On the receiving side, initial HSDPA User Equipment (UE) solutions were based on single antenna CDMA rake receiver structures, similar to Release 99 UMTS receiver structures. The corresponding minimum performance requirement for HSDPA rake receivers was specified in Release 5. While the single antenna rake receivers worked very well for conventional UMTS and met initial system needs for HSDPA, advanced receiving technologies were later used to achieve even higher HSDPA throughputs. To achieve this goal, 3GPP studied two applicable techniques (receive diversity and advanced receiver architectures) as well as their minimum performance improvement and has specified them in Release 6.
HSDPA also benefits operators by making more efficient use of spectrum, up to three times more capacity than UMTS. This efficiency means that operators can easily and cost-effectively accommodate more users and services without having to buy additional spectrum just to keep up with growth. That efficiency also reduces operators' overhead costs, and thus, makes them better able to price their services at a point that is competitive yet profitable.
HSDPA is backward-compatible with UMTS, EDGE and GPRS. This design benefits customers when they travel to areas that have not yet been upgraded to HSDPA, as their HSDPA-enabled handsets and modems will still provide fast packet-data connections. This design also benefits operators and application developers because applications designed for UMTS also run on HSDPA networks and devices.
More than 40 percent of HSPA networks have been upgraded to HSPA+ and 4G Americas expects that nearly all will be upgraded due to the progressive roadmap available through 3GPP standards.