ALERT: FCC’s Auxiliary Station Proposal May Threaten Microwave Operation

FCC releases Part 101 Notice of Proposed Rulemaking (NPRM) introducing new “Auxiliary Stations” into the point-to-point microwave bands—Docket # 10-153

Part 101 NPRM—Comments are due October 25th

October 13, 2010


In the NPRM, the FCC has introduced a new type of operation into the Part 101 microwave bands called an “Auxiliary Station.” As proposed, these auxiliary stations will operate on a secondary basis in proximity to and in connection with a licensed primary link.

This secondary point-to-multipoint type of operation represents a radical departure from the existing Part 101 point-to-point microwave rules. The premise behind this proposal is that supposedly there are vast areas surrounding existing point-to-point links that cannot be used by others due to interference concerns and therefore auxiliary stations would make more efficient use of the fallow spectrum.

In fact, this premise is completely false and without merit. One need only look at congested areas such as Los Angeles (see map) to realize that thousands of licensed links are coexisting in close proximity to each other on a licensed interference free basis. Clearly, these sites are operating in the antenna sidelobes of other carriers and in many cases on the same frequency. Depending upon the specific interference geometry, a station can be placed exactly on the “main beam” of another path and still operate without interference.

The beauty of the Part 101 bands is that access to the spectrum is on a first-come first-served basis and through the prior frequency coordination process operates on a licensed non-interference basis. Unlike area-wide auctioned spectrum, licenses are granted on a site-by-site basis with everyone having an equal opportunity to the bands which are generally available when and where they are needed. An FCC license is relatively inexpensive, currently about $510 per transmitter for a 10 year license or $102 per year for a single link license with two transmitters. Licenses are free for State and Local Governments and non- profit entities.

To maintain the ready availability of channels for site-by-site licensing, the point-to-point microwave rules have always promoted spectrum efficiency by establishing certain operating requirements such as setting minimum antenna standards and data throughput, and specifying maximum transmit powers. Market forces have driven further efficiencies as evidenced by the typical antenna discrimination pattern that far exceeds FCC requirements.

The Commission for some inexplicable reason has decided that these time tested efficiency standards should no longer apply for auxiliary stations by eliminating the requirement that they meet any antenna standards, data throughput or power limitations. Because the Auxiliary Stations are subservient to a primary “mother” link in operation and interference protection, they create a perverse incentive for the licensee to operate as inefficiently as possible. In order to maximize the area around a mother link in which Auxiliary Stations could effectively operate (the necessary link budget to maintain and sustain link connection), the licensee has an incentive to maximize the power being transmitted from the mother link into the sidelobe area. This would be accomplished by using the maximum transmit power allowed (85 dBm) on the mother link and employing an antenna meeting only the minimum discrimination standards.

It’s worth noting that the FCC has another efficiency rule 101.113 (a) that requires licensees to use the minimum transmit power necessary to enable effective communication. Links typically use significantly less than the absolute maximum EIRP of 85 dBm. It appears that this is another well-intentioned rule that goes out the window for the sake of auxiliary sites.

The deployment of Auxiliary Stations also promotes the introduction of time-division duplexing (TDD) operation into the historically frequency-division duplexing (FDD) bands. Instead of each mother link transmitting on paired high and low frequencies in each direction as it is done today, each end of the link could operate with both high and low frequencies transmitting from both ends. This doubles the number of potential interference scenarios typically seen between two FDD links from 4 to 8, exacerbates the potential for reflective interference in urban markets by mixing high and low frequencies, all of which works to further sterilize the area around the mother link. The problems associated with mixing TDD and FDD have been well documented.

As evidenced by the large and growing number of terrestrial point-to-point frequencies and satellite earth stations licensed in the Part 101 bands, the existing coordination and licensing process has been extremely successful. The bands are used extensively by a wide variety of licensees including carriers, broadcasters, critical infrastructure, public safety, and state and local governments.

While the rules could always use improvement, the introduction of a point-to-multipoint secondary underlay into the point-to-point bands is not the answer. The Part 101 bands are not the place for an unproven science project which is based upon nothing more than hyperbole. The introduction of Auxiliary Stations would clearly disadvantage others from accessing the spectrum compared with the current environment and would significantly increase the potential for interference.

It appears that the Commission’s new definition of spectrum efficiency has changed from maximizing spectrum utilization for the benefit of everyone to what is in the best interest for one at the expense of all others.

If all of this is concerning to you, please get involved in the FCC proceeding and file your comments by October 25th.

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