Microsoft, Google and the Wireless Internet Service Providers Association (WISPA) are urging the FCC to allow co-channel spectrum sharing in the C-band. The proposal would allow fixed wireless operators to use the same spectrum band as incumbent users, who are comprised largely of satellite operators that use the spectrum for their earth stations. The commission is currently pondering how it might best make a portion of the C-band, comprised of spectrum between 3700 and 4200 MHz, available for wireless services.

While spectrum sharing and spectrum sharing proposals are becoming increasingly common, the C-band proposal is unlike some other approaches in that it calls for the same channel to be used by new and incumbent users in different geographic areas. This is different from some other spectrum sharing options, such as the TV white spaces system already in use that allows fixed wireless providers to share spectrum with incumbent TV broadcasters within a geographic area by assigning operators’ equipment to channels within a band that are different from those already in use by the broadcasters.

To support their recommendation, Microsoft, Google and WISPA commissioned research, conducted by wireless expert and Virginia Tech professor Jeff Reed, which has been filed with the FCC.

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C-band Co-channel Sharing
The Microsoft, Google, WISPA proposal calls for exclusion zones of approximately 10 kilometers around satellite earth stations operating in the C-band to protect the earth stations from harmful interference caused by fixed wireless network operators, also known as point-to-multipoint or P2MP operators. This approach would leave more than 80 million Americans, or 78% of the geographic area of the U.S., outside the protection zones and potentially able to receive fixed wireless service at speeds that could exceed a gigabit per second, the backers said.

Co-channel Sharing (Source: Reed Engineering)

The proposal is based on repacking earth stations in the upper 300 MHz of the C-band, with that spectrum shared between satellite operators and fixed wireless providers. The remaining 200 MHz of the band could be made available for use by mobile operators.

According to the Microsoft, Google and WISPA report, mobile operators would not be able to share spectrum with satellite operators on a co-channel basis because mobile network infrastructure typically uses omnidirectional antennas, potentially interfering with radio altimeters for aeronautical navigation that are used in the adjacent 4200-4400 MHz band. Fixed wireless operators would be able to avoid this because they use narrow vertical beams, according to researchers.

A Resolution to Fixed Vs. Mobile Issues?
If the proposal that Microsoft, Google and WISPA have made passes the scrutiny of wireless experts and gains traction with the FCC, it could help to ensure that fixed wireless providers gain a foothold in the C-band. A coalition of fixed wireless stakeholders known as the Broadband Access Coalition previously asked the commission to make the entire C-band available for fixed wireless use on a shared basis with satellite operators, but the commission now seems to be leaning toward repacking the satellite operators into a portion of the band and making the remainder of the band available to mobile and fixed wireless operators through an auction.

An open issue is whether the FCC or the C-Band Alliance of satellite operators would conduct the auction. And although fixed wireless operators potentially could participate in that auction, those operators argue that it is difficult for them to outbid mobile operators.

If co-channel sharing with satellite operators is indeed impractical for mobile operators but is feasible for fixed operators, the solution could help ensure that both types of operators have a seat at the C-band table.

Of course, even if the proposal withstands expert scrutiny, there is still likely to be disagreement over how much spectrum the satellite operators need. Although the C-Band Alliance has offered to free up about 200 MHz of spectrum, some stakeholders say that amount can and should be higher. If more spectrum is freed up for auction, however, that would likely reduce the speeds that the fixed operators would be able to deliver using the remaining spectrum shared with the satellite operators.

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