High-Speed Downlink Packet Access (often abbreviated as HSDFPA) is one of the most recently released forms of protocol for sending mobile telephone data.
HSDPA is classified under 3.5G or generation technology. In a nutshell, it allows users to download data into their cell phones at the same speeds they would expect from an ADSL (or Asymmetric Digital Subscriber Line) internet connection. Of course, this assumes that the download speed has not been compromised by poor network connections.
Prior to HSDPA, the best users could expect was from the 3G protocol, W-CDMA, or Wideband Code Division Multiple Access. While W-CDMA was quite fast, it was not able to deliver the larger video files efficiently. HSDPA is five times faster than its predecessor, and under optimum conditions, can send data at an astonishing rate of eight to ten Mbps (megabits per second). This is more than enough for users to download video and even streaming applications.
HSDPA is able to operate at these speeds because of improvements in modulation and coding. It opens a separate channel specifically for large files, called HS-DSCH, or high-speed downlink shared channel. For greater efficiency the channel is one-way (from the source to the user) and shared between many users.
HSDPA is a breakthrough technology, but making it available is another matter altogether. Many countries have only recently upgraded to a 3G network, and providers are still studying whether the demand for 3.5G is worth the investment. It is also more realistic to assume that the networks will not immediately reach maximum speed. More likely, the HSDPA will initially operate at 1.8 Mbps and gradually upgraded.