3G HSDPA - High Speed Downlink Packet Access

- a tutorial, description or information about the basics of HSDPA, High Speed Downlink Packet Access, the enhancement to the UMTS / WCDMA standard for 3G cellular telecommunications

Improvements and enhancements are being made to the Wideband CDMA or UMTS 3G telecommunications system. Called High Speed Downlink Packet Access ( HSDPA ) the new technology promises to increase the download data rate five fold. In addition to this HSDPA also provides a two fold increase in base station capacity.

The introduction of HSDPA technology has come about as a result of the need to drive down costs as well as increasing the data rates possible. Current trends show the volume of IP / packet data rising and overtaking the more traditional circuit switched traffic. By adopting a packet based approach to the delivery of digital content as well as IP based person to person digitized voice, a single session can be used for multiple purposes and this can be used to drive revenues upwards. With this approach in mind the use of HSDPA is a key element in providing the user with a better 3G service as well as increasing revenues as a result of increased capacity and usage for the service providers.

HSDPA and standards
The new high speed technology part of the 3G UMTS evolution. Release 4 of the 3GPP W-CDMA standard provided the efficient IP support to enable provision of services through an all IP core network. Then Release 5 included HSDPA itself with support for the packet-based multimedia services. A further enhancement known as MIMO (Multiple Input Multiple Output) will then be contained within Release 6. As HSDPA needs to work alongside the original Release 99 systems, the new technology is completely backwards compatible.

Key HSDPA technologies
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.

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.

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.

A further channel known as the High Speed Downlink Shared Channel (HS-DSCH) has been introduced. W-CDMA normally carries data over dedicated transport channels (DCHs), several of which are multiplexed onto one RF carrier. This approach has been adopted because it provides the optimum performance with continuous user data. Under the new scheme the "bursty" nature of the data has been accounted for and more efficient use of the available spectrum has been made.

HSDPA performance
Using HSDPA scheme it will be possible to achieve peak user data rates of 10 Mbps within the 5 MHz channel bandwidth offered under 3G UMTS. The new scheme has a number of benefits. It improves the overall network packet data capacity, improves the spectral efficiency and will enable networks to achieve a lower delivery cost per bit. Users will see higher data speeds as well as shorter service response times and better availability of services. However new mobile designs will need to be able to handle the increased data throughput rates. Reports indicate that handsets will need to have at least double the memory currently contained within handsets. Nevertheless the advantages of 3G HSDPA mean that it will be widely used as networks are upgraded and new phones introduced.

Buy a book to read more about this topic ......

3G Evolution: HSPA and LTE for Mobile Broadband Erik Dahlman, Stefan Parkvall, Johan Skold, Per Beeming This comprehensive book describes the newest technolgies and standards selected by 3GPP to realise High Speed Packet Access and Long Term Evolution for mobile broadband. It includes clear explanations of OFDM and MIMO, some of the key technolgies required. An excellent book which is well ahead of the field.

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