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HSDPA tunes in

HSPA is about to see widespread deployment and, given our proclivity for ‘raw data’, it’s likely to be adopted more rapidly than person to person based 3G services. By Philip Ling.

It's easy to become disillusioned with wireless connectivity; it's now almost intrusive. Yet there's something 'magic' about wireless that will ensure its continued success, not least the perpetual improvements being made.

The latest is high speed packet access, the first incarnation of which will be for downloads, giving it the street name 'HSDPA'.

Third generation wireless networks use code division multiple access (CDMA), but HSDPA brings an interesting twist in the form of time multiplexing, giving it a TDMA feel as used in 2G. But, by making the best use of network bandwidth through bursting data on a channel shared by multiple users, much higher bit rates than the kbit/s of 2G are delivered – and to more users.

Peak rates of 14.4Mbit/s are specified, using a combination of 15 spreading codes and QPSK modulation with 16QAM. Helpfully, the rates are categorised by their modulation method (either with or without 16QAM on top of QPSK) and number of codes.

For instance, early live systems are delivering around 1.8Mbit/s (Cat 3 and 4 for QPSK with 16QAM, five codes), with 3.6Mbit/s (Cat 5, 6) possible. This rises to 7.2Mbit/s with 10 codes and 14.4Mbit/s with 15 codes.

Graham Pitcher

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