The US 3.65 GHz Band: What Does it Mean for WiMAX?

The FCC recently blessed WiMAX gear in the bottom 25 MHz of the 50 MHz available in the 3.65 GHz range.
 
In almost all respects, the FCC made no changes whatsoever to its prior rulings on the 3.65 GHz spectrum. What it did, however, was clarify the rules around its "contention protocol" requirement, which are extremely important for both WiMAX equipment vendors and carriers potentially using this spectrum. The spectrum is still non-exclusive, but does require base station registration and a filing fee for the spectrum by each provider, of which there could be many. This is close to the unlicensed-band approach, aside from the registration and fee. One operator described it to me as a "lightly regulated" band, which seems a very apt characterization.

This band is potentially very important, with a solid block of spectrum (50 MHz) that would carry even more bandwidth per MHz than the 2.5 GHz range. It also boasts a mid-range blend of power allotment (higher than unlicensed spectrum and lower than licensed spectrum) that has a lot of utility, especially for rural providers. Specifically, this is 25 watts per 25 MHz of spectrum for fixed/portable use and 1 watt per 25 MHz of spectrum for mobile use (a much lower power allotment – likely indicating a more commonly fixed/portable approach in the band early on). Non Line of Sight (NLOS) service at modest ranges should be possible with this power allotment.

This would free smaller companies in many locales from competing in a hugely expensive licensed spectrum auction. It should significantly help the deployment of broadband access in underserved areas, at least once equipment is available. Several operators have written me that they are already asking their providers when gear will be available.

What the FCC did was to redefine the contention protocol to include two main sub-classes. These fall into "unrestricted" and "restricted." Unrestricted gear could be used across all 50 MHz, and restricted gear could be used only in the lower 25 MHz of the band. WiMAX falls into the restricted category. An example of an unrestricted protocol would be the CSMA/CA (carrier sense multiple access / collision avoidance) approach that Wi-Fi currently uses. This is very similar to the typical Ethernet computer network method, whereby each device is constantly talking and looking for an opportunity to transmit. Although the polling methods used by WiMAX are much more efficient, they only work within the context of WiMAX-to-WiMAX gear (at least at this time – some vendors are working on protocols that could be extended across both definitions). Thus, the restriction to the lower 25 MHz is designed to prevent WiMAX gear from interfering with unrestricted protocols in the upper 25 MHz.

Certainly other unrestricted contention-avoidance protocols are in development for the 3.65 GHz spectrum. However, the FCC wanted to speed the deployment of currently-available gear to the market for the 3.65 GHz range, specifically the retuning and use of currently available 802.16d fixed WiMAX radios. These are already being shipped internationally for the 3.5 GHz licensed spectrum range, for which 802.16e mobile WiMAX technology should ultimately be deployed also. Shifting to this new frequency will be relatively trivial for vendors.

The FCC declared the entire 50 MHz of spectrum available to be served by unrestricted-type gear, perhaps in part because unrestricted systems would not interfere with the WiMAX or restricted-protocol systems in the bottom 25 MHz, as they incorporate some type of “Listen Before Transmit” approach. However, the restricted systems would probably interfere with the unrestricted ones. So in my view, the FCC essentially segmented the band into WiMAX (or WiMAX-type gear) and Others.

Is this a good thing? Yes, especially in terms of time-to-market. Also, there were few, if any, gear types that were ready for the unrestricted protocol previously defined. This is a huge WiMAX win. We could potentially have gear certified by the FCC for this band next year.

By Tim Sanders, Senior Analyst – US Market, Maravedis - CEO – the Final Mile

Friday, July 06, 2007 in Archives | Business | Equipment  | Permalink |  Comments (2)