HSDPA, short for High-Speed Downlink Packet Access, is a new protocol for mobile telephone data transmission. It is known as a 3.5G (G stands for generation) technology. Essentially, the standard will provide download speeds on a mobile phone equivalent to an ADSL (Asymmetric Digital Subscriber Line) line in a home, removing any limitations placed on the use of your phone by a slow connection. It is an evolution and improvement on W-CDMA, or Wideband Code Division Multiple Access, a 3G protocol. HSPDA improves the data transfer rate by a factor of at least five over W-CDMA. HSDPA can achieve theoretical data transmission speeds of 8-10 (megabits per second). Though any data can be transmitted, applications with high data demands such as video and streaming music are the focus of HSDPA.
HSDPA improves on W-CD MA by using different techniques for modulation and coding. It creates a new channel within W-CDMA called HS-DSCH, or high-speed downlink shared channel. That channel performs differently than other channels and allows for faster downlink speeds. It is important to note that the channel is only used for downlink. That means that data is sent from the source to the phone. It isn't possible to send data from the phone to a source using HSDPA. The channel is shared between all users which lets the radio signals to be used most effectively for the fastest downloads.
