While UMTS mobile wireless systems have had considerable success in uptakes of high-quality circuit-switch applications, they failed to achieve the all pervasive mobile data due to the lack of an efficient data transmission platform. Broadband HSDPA changes the game considerably though. It provides high-speed data downlink channels (HS-DSCH), can be shared between multiple users efficiently and offers improved error control handling.
HSDPA uses high-speed downlink shared channels that can switch between users every 2 ms to offer packet-switch data services to several users at once. It uses three physical channels to enable HS-DSCH transmission. A downlink control channel called high-speed shared control channel (HS-SCCH), an uplink control channel called high-speed dedicated physical control channel (HS-DPCCH) and a downlink physical channel to carry the HS-DSCH user data called the high-speed physical downlink shared channel (HS-PDSCH).
HSDPA doubles the rate of data transmissions through the use of 16-QAM modulation on HS-PDSCH when the channel conditions are favorable. An HSDPA system can vary the number of physical channels, the modulation scheme and the code rate to make the best possible use of conditions by taking measurements from handsets.
Another unique and important feature of broadband HSDPA is the Hybrid automatic repeat request (HARQ) functionality. It requests a retransmission of any data blocks that were not correctly received and then combines the two transmissions to increase the likelihood of decoding the transport block, resulting in reduced data latency and increased channel utilization.
A higher performance terminal will receive higher data rates as compared to lower performance terminals according to the 3GPP standards and HSDPA applications that require higher data rates benefit from these rate increases in data transmission. Higher performance terminals are, therefore, more desirable to both network operators and users as they perform better than average on any given HSDPA network.
Smart phones with HSDPA enabled should be able to take advantage of higher data rates in UMTS cells with HSDPA transmit capability and should be backward compatible with 2.5G/3G systems. There are twelve categories of HSDPA capable mobile device as defined in UMTS standards release 5 which support different peak data rates and allow for various levels of implementation complexity.
When HSDPA is deployed on a network in combination with High-Speed Uplink Packet Access (HSUPA), they form the High-Speed Packet Access (HSPA) technology. HSPA is the leading mobile broadband technology for the near future, and also the most widely deployed worldwide. HSDPA's popularity saw a huge increase during 2007 when telecommunication companies globally started selling HSDPA USB modems for mobile broadband connections, and landline replacement boxes providing HSDPA for data via Ethernet and WiFi along with ports to connect traditional landlines.
HSDPA allows operators to accommodate more users cost-effectively, without having to buy additional spectrum, by making more efficient use of the available spectrum to reduce operator overhead costs to make them more competitive while still remaining profitable.