AT&T doubles 3G cell capacity but still faces backhaul challenges

T-Mobile (NYSE:DT) hasn’t been the only operator tinkering with its 3G network. AT&T (NYSE:T), too, announced today that it has completed upgrading its high-speed packet access (HSPA) network to double its network access capacity—fully two years earlier than it originally planned. But there’s a catch. While AT&T’s base stations can now handle up to 7.2 Mb/s on the downlink, it hasn’t yet completed the backhaul upgrades necessary to carry that increased bandwidth back into the network.

AT&T’s 3G cellsites are backhauled primarily through T1 lines, which, while adequate in the early days of UMTS, wind up becoming a choke point as AT&T upgrades to faster and faster network technologies. Even at the old 3.6 Mb/s iteration of HSPA, AT&T was reporting bottleneck problems. So while data from the subscriber device to the base station will now travel twice as fast, it will have apply the brakes as it wends its way through the transport network to the core.

AT&T, however, is planning to open up the bottleneck in several markets quickly. AT&T started deploying fiber-to-the-cell in Charlotte, Chicago, Dallas, Houston, Los Angeles and Miami last month, which allows the affected cell sites to take advantage of the full 7.2 Mb/s upgrade. AT&T will extend fiber to the majority of its 3G footprint in 2010 and complete a system wide upgrade by the end of 2011—just in time for its deployment of long-term evolution (LTE), which will need tremendous backhaul capacity.

T-Mobile likely faces many of the same transport bottlenecks as AT&T in its 3G network as fiber isn’t available to a majority of the country’s cell sites, though in urban areas—where both T-Mobile and AT&T’s 3G networks are concentrated its becoming easier to provision. T-Mobile hasn’t said how much of its 3G network is fiber-fed today, but it presumably has very aggressive backhaul plans. It plans to deploy HSPA+ across its network this year, which would beam 21 Mb/s of capacity in every cell. Without a fiber backhaul network, any upgrade beyond 7.2 Mb/s would be moot.

While customers outside of the initial six markets may have to wait to take advantage of the upgraded capacity, AT&T said the HSPA 7.2 provides some benefits on its own. The bigger channel capacities smooth out multiple subscriber sessions, providing more consistency for mobile data users if not increased overall capacity.