AT&T is six markets away from completing a network upgrade that will give its 3G network broadband upload speeds to match its broadband download speeds. Called high-speed uplink packet access (HSUPA), the technology is an upstream complement to its already-deployed high-speed downlink packet access platform and supports uplink speeds of 500 kb/s or higher.

AT&T today said it will install the software upgrade in its final six markets next month, extending HSUPA to its entire 3G footprint of 275 markets. AT&T has been rolling out HSUPA quietly over the last year, simultaneously expanding its HSDPA footprint while upgrading previously launched markets with HSUPA. By year end, AT&T expects to have the bulk of its nationwide 3G network completed by year end, covering 350 markets.

The new uplink capacity will allow AT&T to launch peer-to-peer and real-time interactive services that require a hefty return channel. Like its CDMA counterpart, EV-DO Revision A, HSUPA adds both the upstream capacity and low latency necessary to support applications like VoIP, videoconferencing and multiplayer gaming. Sprint is using its Rev. A network to extend its Next Direct Connect service to its CDMA customers by turning the push-to-talk sessions into VoIP sessions. AT&T’s ambitions for HSUPA—at least for now—appear to be more modest. In its announcement, AT&T indicated it would initially position the service as a faster peer-to-peer and file-upload option for its laptop broadband users.

“The ability to quickly upload large files from a laptop is no longer a luxury — it's a necessity,” Kris Rinne, AT&T Mobility’s senior vice president of Architecture and Planning, said in a statement. “By fully deploying HSUPA across our 3G footprint, we not only meet the current needs of our customers but also lay the path for our continued evolution to even faster wireless broadband capabilities.”

AT&T has already begun seeding its network with HSUPA-embedded PC cards but doesn’t yet have HSUPA-capable handsets, limiting the scope of the technology to broadband access. As new handsets come online, though, AT&T may be able to use the uplink to supercharge some of its existing services as well as launch new ones like advanced push-to-talk. Last year AT&T launched Video Share, a service that allows 3G phones to send live video feeds between phones while in standard voice conversation. The service stops short of full videoconferencing, though, because of the upstream limitations of the UMTS network. Slow speeds required Video Share to buffer the multimedia stream, leaving the video out of synch with the voice conversation. Though AT&T hasn’t yet announced any plans to do so, it could use the HSUPA capabilities to send both Video Share’s voice and video streams over the same IP session, creating a true videoconferencing application.

Standard UMTS theoretically supports 384 kb/s over a 5-MHz return channel, but realistic network conditions can bite into that capacity considerably. When shared among several customers on the network, the average capacity allocated to individual users can be slower than dial-up-modem speeds. HSUPA pumps that theoretical channel capacity to 5.76 Mb/s, a 15-fold increase, but that capacity isn’t necessarily available to every customer. Like HSPA, HSUPA has a series of evolutionary iterations, called categories, which extend greater and greater capacity to individual handsets as silicon technologies improve. Category 1 doubles standard UMTS speeds to 730 kb/s, while category 6 would allow a device to take advantage of HSUPA’s full 5.76 Mb/s. AT&T said it expects average upload speeds to individual customers to range from 500 kb/s to 800 kb/s.

AT&T estimates it has now spent more than $20 billion on its 2G and 3G network upgrades since 2005. While capital spending on 3G is likely to fall off by the end of the year, it may not be too long before it starts investing in its next network. AT&T has committed to deploying both the next stage of UMTS--called HSPA+ or Evolved HSPA-- as well as a 4G network using long term evolution (LTE). AT&T has not made any timeline or capital commitments to either technology, but HSPA+ could come sooner rather than later. HSPA+ would require another upgrade to its current 3G radio access network, adding a higher order modulation and possibly smart antennas. The most radical change of HSPA+ would be transitioning from its current legacy core to a flat IP architecture.