January 17, 2017–Ligado Networks LLC has asked the FCC to reject a technical analysis submitted to the agency last month that concluded Ligado’s network would cause interference to Iridium’s aviation services (TRDaily, Dec. 14, 2016). “The Commission should reject the analysis set out by Iridium in its recent filing in the above referenced dockets not only because Iridium’s technical analysis relies on a flawed model, but also because (i) Iridium has a secondary license and thus lacks a basis to assert interference claims, (ii) Ligado’s revised proposal makes Iridium better off than the status quo, and thus Ligado’s proposal would accommodate Iridium’s legitimate spectrum concerns and (iii) Iridium’s analysis is divorced from the spectrum reality it exists in today,” Ligado said in a redacted filing yesterday in IB dockets 11-109 and 12-340.
“To emphasize the final point, if the Commission were to use Iridium’s proposed interference framework then five million mobile earth-station terminals (METs) already authorized and operating currently would be destroying Iridium’s service,” Ligado complained. “But everyday observation indicates that Iridium’s service functions perfectly well. For this reason if none other, the Commission must disregard Iridium’s analysis and reject the Iridium assertions.”
More specifically, Ligado said that the Hata-Okumura propagation model used in the Iridium technical analysis “is inapplicable to Ligado’s proposal. Hata-Okumura is designed for a base station height of 30-200 meters, but Iridium applies it to transmitter and receiver heights of just two (2) meters. In addition, Hata-Okumura is designed for distances of 1-20 kilometers, yet Iridium extrapolates losses in the range of 100-200 meters by combining Hata-Okumura and Free-Space Path Loss models. And finally, Hata-Okumura applies to frequencies in the range of 150-1500 MHz, but Iridium relies on it for the spectrum at issue, 1626.5 MHz.”
Ligado also said that “Iridium asserts that Ligado has chosen the wrong propagation models; yet, it has used those same types of propagation models in other submissions before the Commission to evaluate analogous circumstances. In those submissions, Iridium’s path loss values align closely with Ligado’s calculations.”
In addition, “Iridium incorrectly relies on analysis from [Commerce Spectrum Management Advisory Committee] WG-1 to assess the Iridium-Ligado case. This analysis does not hold force in the current circumstances. WG-1 focused on protecting federal meteorological fixed earth stations from spectrum sharing (not adjacent band operations) in the 1695-1710 MHz band, and its analysis does not apply to potential interference to Iridium’s satellite transmissions from LTE at 1626.5 MHz,” Ligado maintained. – Paul Kirby, firstname.lastname@example.org