Does AT&T really have the spectrum it needs?

Reading through the very positive story in Telephony about how AT&T is “doubling” its network capacity, and wondering where reporter Kevin Fitchard — usually pretty solid in things telecom — gets the numbers to back up his assertation that AT&T “has reams of cellular and PCS spectrum” that it could throw at digital data should its 3G networks clog up more than they already are now.

For one, I don’t believe that AT&T has “reams” of spectrum, at any bandwidth that can quickly be reassigned (or tailored for new uses with equipment to match). What I wish Fitchard had asked AT&T is how big are AT&T’s channel sizes per cell site, and how many cell sites does it really have in its 3G/4G network?

(Without getting too technical, the “channel” we are talking about is the size of the wireless “pipe” being sent from tower to user; the bigger the channel, the more data and capacity that can be sent per site. Current cellular implementations typically use 1.25 MHz channels, which accounts in part for their limited capacity. So-called “4G” technologies like Clearwire’s WiMax implementations use 5 MHz and 10 MHz channels, for example, to help support faster download speeds. But even AT&T’s “reams” of 700 MHz spectrum only have around 20 MHz of depth in any market — limiting the channel size to 5 MHz in most implementations, which means even LTE deployments won’t be as fast as they are often advertised.)

It’s all well and good to talk about increasing the download-speed capacity on AT&T’s high-speed packet access (HSPA) network to a theoretical number of 7.2 Mbps, but that number is useless if it’s not backed up by spectrum depth, which is the thing that matters when it comes to whether or not a network delivers as promised. Unless AT&T comes through with some real numbers, reporters like Fitchard and his readers would do well to question why those “reams” of cellular spectrum aren’t already being used to ease the pain of frustrated iPhone users.

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About Paul Kapustka

Paul Kapustka is a longtime journalist who has spent more than two decades covering the information technology business, Paul most recently has been focusing on mobility and how it has changed the computing and collaborative landscape. His newest project outside Mobile Enterprise 360 is a research and analysis operation called WiFi Journal. He is also editor in chief of Mobile Sports Report, which covers the intersection of mobile technology and sports business. Paul is also the founder of Sidecut Reports, a research firm that covered the emergence of 4G technology in the cellular marketplace.

Comments

  1. This should be required data at FCC level, what they have and how much they use at any time or place. This is public spectrum? Backhaul seems to be bigger issue?

  2. At a recent conference in Silicon Valley, AT&T admitted that the backhaul for many of its cellular base stations is DSL. Unbelievable.

  3. UMTS/HSPA currently uses only 5 MHz FDD channels. So the discussion about spectrum “depth” isn’t pertinent. In future 3GPP standards “Multi-Carrier” HSPA will be possible – putting together 2 or more 5 MHz channels, but is not currently available. A 5 MHz HSPA carrier has a capacity of 14.4 Mbit/s (7.2 is the single user peak bit rate that AT&T’s particular network will support.) What’s more, concerning LTE, which is based on OFDMA, even if an operator only has 20 MHz of spectrum available, he could still dedicate that to one channel, using PUSC to mitigate interference.

  4. AT&T has 12Mhz (Lower Band Block B)in most markets (CMA) of the new 700Mhz spectrum. Verizon Wireless has the 22Mhz (Upper Band C Block)capacity Nationwide