HSDPA is a mouthful for speed

New HSDPA technology brings higher download speeds to 3G.
  • John Blau (IDG News Service)
  • 17 February, 2005 08:33

If the acronym HSDPA means nothing to you, read on because the technology behind this string of letters could soon significantly change the way you work and play on your mobile device.

High Speed Downlink Packet Access (HSDPA) is one of the new technologies being talked up and even demonstrated at the 3GMS World Congress in Cannes.

The technology, a rival to the EV-DO (evolution data optimized) standard in CDMA (Code Division Multiple Access) found in the U.S. and parts of Asia, promises something surprisingly missing in early 3G (third-generation) mobile broadband networks -- high data speeds similar to those of fixed-line ADSL (asymmetrical digital subscriber line) services.

Remember all the talk about 3G offering data downloads at speeds up to 2M bps (bits per second)? Well, yes, those speeds are achievable -- in a lab with a handset held next to the base station. It's a theoretical speed that looks good in promotional brochures but is nearly impossible to achieve for the ordinary Joe Blow subscriber.

The first wave of 3G technology, Release 99 (R99), offers a maximum speed of 384K bps. Even that's a peak rate, or something you might reach if you're alone in a mobile cell at 5 a.m. Most likely, you're going to have speeds between 150K bps and 250K bps, according to John Leonard, vice president business strategy at Lucent Technologies.

With HSDPA, expect initial throughput rates of between 400K bps and 600K bps, with a peak rate of 14.4M bps.

HSDPA technology is the key feature of the Release 5 specification approved in 1999 by the 3GPP (Third Generation Partnership Project). The technology offers several significant improvements over R99 networks.

Unlike R99, HSDPA introduces an additional transport channel, called the high-speed downlink share channel. Up to 15 of these channels can operate in the WCDMA (Wideband CDMA) radio channel, allowing multiple users to share the entire downlink channel.

The additional channel is designed to take advantage of bursty data traffic, typical in data networks, through multiplexing. For example, once your data has been dispatched, other users can gain access to the network in much the same way they do with DSL technology.

Another feature is adaptive modulation and coding (AMC), a technique used to compensate for variations in radio conditions. With this technique, a network node schedules the transmission of data packets to a user by matching the user's priority and estimated channel operating environment with the appropriate coding and modulation scheme, thus increasing throughput under favorable conditions.

In addition, HSDPA offers a retransmission mechanism for quick error correction. In spread-spectrum networks such as WCDMA, handsets confirm when they receive data and communicate key information such as channel condition and power back to the network. While this process is handled by the Radio Network Control (RNC) system in R99 networks, with HSDPA, it is processed directly in the base station, enabling a much faster response.

Several operators have already begun HSDPA tests, including Vodafone Group PLC in Japan and New Zealand, and mm02 PLC on the Isle of Man in the U.K. Many others, such as T-Mobile International are in the starting blocks.

"This is a first big step to give users of mobile devices an ADSL experience," said T-Mobile Chief Technology Officer Hamid Akhavan. "We're very excited."

For those still undecided, several vendors, including Telefonaktiebolaget LM Ericsson, Nortel Networks and Siemens, have been conducting live demonstrations in Cannes. You have to be blind not to see the improvement.

Lucent, for instance, showed video clips in both R99 and HSDPA. While the images transmitted over R99 were a bit fuzzy, those over HSDPA were DVD-quality, with latency speeds of just over 70 milliseconds.

Nine video clips can be transmitted with HSDPA in the same time required to send one with R99, according to Lucent.

So when can you expect HSDPA? In Cannes, several vendors including Siemens and Motorola unveiled HSDPA PC cards, with initial peak speed rates of 3.6M bps.

The first HSDPA handsets will be available on the market early next year, with the technology to be integrated into PCs a year later, according to Mikael Back, vice president of WCDMA radio networks at Ericsson.

New HSDPA handsets, according to John Leonard, vice president business strategy at Lucent, will need to manage higher power consumption and heat dissipation requirements in addition to integrating new algorithms in their chipsets.

Now if you're wonder whether the industry is tinkering with technology to upload data faster, the answer is yes. Another standard is in the pipeline: HSUPA (High Speed Uplink Access). The technology is to deliver a maximum speed of 5.8M bps. In addition to speed, the technology will enable VOIP (voice of Internet Protocol) over the radio link. "You need to have a symmetric link, and HSUPA will provide this," Leonard said.

But, like its download cousin, HSUPA will also require operators to make some software and even possibly hardware changes in their networks, and handsets manufacturers will need to deliver new phones -- all of which will require time and, above all, money.

And if you think the innovation stops there, come back to this show next year when the focus most likely will turn to "super 3G," or what some in the industry are calling 4G (fourth generation).

The technology, a further evolution of 3G, will target download speeds of up to 100M bps and upload speeds of up to 50M bps with low 50 millisecond latency rates, according to Ericsson Chief Technology Officer Hakan Eriksson. It could be standardized by 2007, with the first products available by 2009, he said.

The 3GSM World Congress runs through Thursday.