600 MHz Band Plan Will Impact Future Network Efficiency

By Joan Engebretson April 28, 2014

The FCC is set to make some big decisions about the band plan for the upcoming auction of TV broadcast spectrum in the 600 MHz band – and those decisions involve other issues besides whether or not AT&T and Verizon should be restricted in the amount of spectrum they can acquire.

FCC officials said last week that Chairman Tom Wheeler is proposing limits on the nation’s two largest wireless network operators AT&T and Verizon but the officials declined to answer questions about other aspects of the band plan such as how many megahertz of spectrum would be included in each license or whether licenses would include paired or unpaired spectrum.

The officials did say the geographic areas used for licenses would be based on partial economic areas (PEAs). That’s a new approach that creates relatively large license areas for metro areas but relatively small license areas for rural areas, and it represents a compromise between the interests of large nationwide carriers who want metro areas and small rural carriers who want license areas that are small enough so that the carriers can afford to bid on them.

A few weeks back, FCC officials said Wheeler was aiming to divide 600 MHz spectrum into paired 5 x 5 MHz bands. But their refusal to discuss the band plan described in Wheeler’s latest proposal suggests either that Wheeler has rethought that issue or that he still wants to see paired 5 x 5 MHz bands but wants to downplay that aspect of his plan.

In either case, it suggests that there is some dissent about the idea of paired 5 x 5 MHz bands.

Paired or Unpaired

The paired versus unpaired issue is a straightforward one.

Paired spectrum lends itself well to the frequency division duplexed (FDD) form of 4G LTE wireless technology that separates upstream and downstream bandwidth by frequency, and that’s the type of LTE that major U.S. carriers primarily have deployed.

Unpaired spectrum is more suitable for the time division duplexed form of LTE that separates upstream from downstream bandwidth by timeslot. The only major carrier that has deployed TD-LTE is Sprint, which has argued that the technology is better suited for handling mobile data traffic because it enables operators to dedicate extra bandwidth to downstream traffic.

Sprint also has used FDD, which can interoperate with TD-LTE, and the company already has more spectrum than other U.S. network operators so I suspect the FCC will indeed specify only paired spectrum bands for the 600 MHz auction. But I also suspect the U.S. wireless industry ultimately may look wistfully at operators in other parts of the world that deployed TD-LTE from the start – and at their ability to easily support asymmetrical mobile data traffic.

Spectrum per License

The idea of allocating 5 x 5 MHz of spectrum per licensee also would not be surprising, as it would be a continuation of the approach the FCC recently adopted for the upcoming AWS-3 auction. And it’s not difficult to see why the commission would choose that approach over 10 MHz x 10 MHz or wider bands that have been offered in previous auctions. Narrower bands yield more total licenses, potentially enabling more operators to win spectrum in the auction.

But according to Roger Entner, founder of wireless consulting firm Recon Analytics, there is a downside to the narrower licenses.   In a recent blog post, Entner argues that wider channels provide higher mobile broadband speeds at lower cost.

According to a chart included in Entner’s post, a 20 MHz channel can provide 34 Mbps aggregate capacity per sector, supporting 6.8 Mbps per user with five concurrent users in a sector and yielding 100 percent efficiency.

In comparison, he argues that a 5 MHz channel is 95 percent efficient - supporting 8.5 Mbps aggregate capacity per sector or 1.6 Mbps per user with five concurrent users.

Potentially carriers could combine multiple channels to get more bandwidth, but Entner argues in his blog post that, “resources from a single larger channel can be more efficiently allocated than from separate independent channels.”

I doubt arguments such as these will sway the FCC, however, as Wheeler has made it clear that he’d like to see all operators having low-frequency spectrum in the sub-1 GHz range. Equipment operating in low-frequency spectrum including the 600 MHz band can do a better job of penetrating walls than higher-frequency spectrum – and Wheeler has argued that customers of every wireless company should be able to place a 911 call from an indoor location.

The industry shouldn’t have to wait long before details of the 600 MHz band plan are revealed. The commission is expected to adopt a report and order that will detail auction plans, including the band plan, in mid-May.




Edited by Stefania Viscusi

Contributing Editor

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