Exclusive: Testing shows AT&T 3G network outperforming VZW

Dicklin said the discrepancy most likely lies in resources allocated to 3G in both networks. Verizon’s CDMA network runs 2G and 3G off of the same infrastructure, and though EV-DO has separate channels from CDMA 1X voice, the processing resources of the base stations are shared between the two. Since VZW prioritizes voice over data, Dicklin said, 3G data quality likely falls as a the number of voice calls on a cell site increase, leading to bigger peaks and valley in overall data coverage and capacity.

Meanwhile AT&T’s HSPA network is a dedicated 3G network, running independently of the GSM 2G infrastructure. As voice usage increases that traffic is merely shifted to the 2G network, leaving all of the 3G network’s resources available for data and resulting in a much more consistent experience, Dicklin said.

AT&T—much more than Verizon—has fielded numerous complaints about lack of coverage, not just in areas where it doesn’t offer 3G, but in large markets where its 3G coverage is supposedly ubiquitous. Evidence of those coverage holes were found in Root’s data. While AT&T has very strong signals in large swathes of its 3G footprint, signal strength fell off rapidly outside of the hot zones. In six of the seven markets, 30% to 50% of its footprint had signal strengths of less than half of full power. The consistency of Verizon’s network fared slightly better in many markets, but of the top four, Sprint beat everyone hands down. Less than 10% of its footprint had half-strength or less signals.

As a result, more than other operators, AT&T has a network with areas of intense capacity separated by gaps of low signal strength. The reason for this is likely a result of how AT&T planned the network, Dicklin said. While AT&T installed new infrastructure for 3G, it used the same towers occupied by its 2G network. But much of AT&T’s 2G network runs over the 850 MHz cellular frequency, while its 3G network is built on the 1900 MHz PCS band. Cellular has higher propagation characteristics than PCS and therefore longer cell radii. That means in many areas, AT&T’s 3G cells are much more dispersed than they would be in a network that was designed solely for the PCS band.

“To AT&T’s benefit, they’ve managed to get enough people off of the older 2G technology, so they can move 3G into the lower frequencies,” Dicklin said, referring to 850 MHz carriers AT&T has launched in several markets, including San Francisco. “That will reduce the gaps in between cells.”

Verizon technically has an advantage in 3G network planning as it could upgrade 1X carriers at all of its sites to EV-DO whether they were PCS or cellular. AT&T’s network may not be planned as well as Verizon, creating sizable coverage gaps in cities, but Verizon’s advantage has probably been mitigated by by the constant fight on its networks between voice and data resources, Dicklin said. “I’ve been carrying around a Droid and I’ve been carrying around an iPhone for the last few weeks, and the data experience has been far more consistent on the iPhone,” Dicklin said.

AT&T’s planned expansion of 3G into the cellular bands will help fill in some of those coverage holes, just as planned upgrades to the existing HSPA and backhaul networks will add more capacity, but Dicklin said he doesn’t expect those improvements to make too much of an impact on AT&T’s overall network performance. AT&T’s network is under extremely close scrutiny from hordes of iPhone users who are all placing enormous expectations on the network, Dicklin said, but Verizon will probably face the same scrutiny if the Droid or some other data-intensive device proves popular.

“The carriers have all done a pretty good job managing the capacity issue,” Dicklin said. “All of the heavy marketing directed against AT&T is much more of problem for AT&T than its actual network performance.”
Root Wireless was started by several former engineers in the US wireless industry with the aim of providing an independent source of wireless performance metrics for third parties to evaluate the carrier’s networks. It currently sells its data and maps to CNET, which uses it to power a service called Root Coverage.

For details on Root’s data in the seven 3G markets tested see the related Unfiltered post: 3G vs. 3G: Whose mobile data network is best?