HSDPA technology has its limits and to further enhance its performance, the DC-HSDPA technology was introduced.

An advanced HSDPA+ network can theoretically support up to 28 Mbit/s and 42 Mbit/s with a single 5 MHz carrier. Doubling the bandwidth to 10MHz results in theoretically, double the sustained data rate.


3G HSDPA High Speed Downlink Packet Access provides additional capability to the basic 3G UMTS cellular telecommunications system.

HSDPA was the first upgrade along the path to HSPA which enabled high speed data to be carried in both directions. However as much more data was carried in the downlink direction, HSDPA was standardised and implemented first to provide the maximum benefit as soon as possible.




HSDPA technologies

The 3G HSDPA upgrade includes several changes that are built onto the basic 3GPP UMTS standard. While some are common to the companion HSUPA technologies added to the uplink, others are specific to HSDPA High Speed Downlink Packet Access, because the requirements for the each direction differ.

  • Additional channels:   In order to be able to transport the data in the required fashion, and to provide the additional responsiveness of the system, additional channels have been added which are described in further detail below.
  • Modulation:   One of the keys to the operation of HSDPA is the use of an additional form of modulation. Originally W-CDMA had used only QPSK as the modulation scheme, however under the new system16-QAM which can carry a higher data rate, but is less resilient to noise is also used when the link is sufficiently robust. The robustness of the channel and its suitability to use 16-QAM instead of QPSK is determined by analyzing information fed back about a variety of parameters. These include details of the channel physical layer conditions, power control, Quality of Service (QoS), and information specific to HSDPA.
  • Improved scheduling:   Further advances have been made in the area of scheduling. By moving more intelligence into the base station, data traffic scheduling can be achieved in a more dynamic fashion. This enables variations arising from fast fading can be accommodated and the cell is even able to allocate much of the cell capacity for a short period of time to a particular user. In this way the user is able to receive the data as fast as conditions allow.
  • Fast HARQ:   Fast HARQ (hybrid automatic repeat request), has also been implemented along with multi-code operation and this eliminates the need for a variable spreading factor. By using these approaches all users, whether near or far from the base station are able to receive the optimum available data rate.