By Katie Marsal

Published: 02:00 PM EST

An AT&T executive has confirmed in a new interview that the US iPhone service provider is currently performing a variety of upgrades on its 3G network that should combine to double capacity in the coming months.

AT&T Mobility vice president of technology realization Scott McElroy tells TelephonyOnline that his team plans to upgrade "the downlink capacity on its high-speed packet access (HSPA) from 3.6 megabits per second to 7.2 Mb/s through software upgrades at the base station."

Although McElroy doesn't provide a timetable for completing the upgrade, he says the carrier is in the process of field certifying the faster network in two test markets, adding that AT&T plans to eventually migrate its 3G networks to evolved-HSPA (or HSPA+), which would increase top speeds threefold.

AT&T could then theoretically upgrade its HSPA network to 14.4 Mb/s but is expected to forgo that option due to a technical problem and its ability to migrate directly to 21 Mb/s HSPA+, McElroy said. He told TelephonyOnline that AT&T will focus "on upgrades to the baseband, which will dramatically increase capacity without having to fiddle with the elements on the tower or in the core."

Interestingly, McElroy also noted that AT&T is simultaneously upgrading its network backbone to handle the increased data traffic resulting from its network upgrades, confirming an AppleInsider report from earlier this month. However, he refused to reveal the exact extent of those upgrades.

It was reported on April 3rd that AT&T was rushing to rollout a major upgrade to its 3G mobile data service in anticipation of a tenfold increase in network traffic from new iPhone hardware expected to go on sale in June, according to a vendor source.

AppleInsider noted that the network rollout was tied to a "massive" order of new Juniper routers that can handle higher data throughputs optimized for video streaming and related features targeted toward video stream broadcasts. Apple has reportedly been evaluating a portion of the network upgrade already accessible to its engineers for testing purposes and is said to be genuinely impressed, with one engineer telling AT&T reps that the iPhone maker has "never gotten pages to load as fast as they were loading on the new routers."

People familiar with the matter say Apple has set a strict deadline that asks AT&T to complete the upgrade, quality test it, and have it ready to go live no later than May 31st. The Cupertino-based company's third-generation iPhone is expected to be unveiled a few weeks later.

Meanwhile, McElroy says AT&T is also looking further ahead, selecting vendors for its 4G (or long-term evolution (LTE)) network expected to go live in test markets by 2010 ahead of widespread commercial availability the following year.

The carrier will reportedly use both its 700 MHz and advanced wireless services (AWS) spectrum to facilitate the LTE launch, with other spectrums on reserve should 4G usage take off. It could also repurpose its 2G and 3G channels for LTE once users begin migrating off those channels to the 4th-gen network.

"We feel very good about our spectrum position," McElroy said. "And we say that with full understanding of what the data demands will be."