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Faster 3G Easier Said Than Done: Page 8 of 9

Future-Proofing
A flexible, software-based design will be vital for future improvements to the W-CDMA service offering. HSDPA is an unbalanced system, with a maximum of 14 Mbit/s on the downlink and 2 Mbit/s on the uplink, from the terminal to the network. That can be a concern, as TCP can easily be "uplink choked" if acknowledgments are slow, reducing the downlink rate.

Release 6 of the 3GPP specification will change that by introducing high-speed uplink packet access (HSUPA). This allows users to take advantage of faster uplinks with lower latency when sending large files or emails. That in turn improves the efficiency of the link, increasing effective throughput, even though the modulation has not changed. Indeed, without the improved efficiency of HSUPA, it is highly likely that HSDPA will be impaired in applications that have more balanced bandwidth needs.

HSUPA puts even more strenuous demands on the basestation design and will mean that the processing electronics will have to deal with a much more complex decode environment in the same way that HSDPA demands much more of the terminals in terms of decoding. HSUPA means moving further control functions from the RNC to the Node B. As is the case for HSDPA, these will likely break many installed architectures. Given the speed these changes are arriving, having a flexible or upgradeable platform is important.

Wrap Up
In summary, HSDPA significantly improves the quality and performance of wireless data for 3G " with a corresponding dramatic impact on the operator's profit. Changes to the modulation, architecture and networking control algorithm are all required. However, despite some claims, this upgrade is not simple and many basestations will require extensive new hardware if they are to deliver on the potential. Immediately following HSDPA is its counterpart for the upstream. This is too has great advantages but likely requires further hardware changes. Carriers should plan both for the major opportunity, but also to minimise the disruption.

About the Author
David Maidment is a product manager at picoChip Designs. David can be reached at [email protected].