Iridium Sees Intolerably High OOBE Interference From Ligado Plans

Iridium's current system and forthcoming Next constellation face much higher out-of-band-emissions (OOBE) than they can tolerate from Ligado's planned LTE deployment, the first company said in a filing Friday in FCC docket 11-109. Iridium said the job of dealing with interference to mobile satellite service operators falls on the ancillary terrestrial component provider -- a policy that "makes sense as the ATC provider is seeking a deviation from the original allocation (from satellite to terrestrial) and reaping the corresponding financial windfall." The company also said that beyond Ligado's plans for using 1627.5-1637.5 MHz for commercial mobile radio service and the interference threat it raises, it had taken no position on the remaining spectrum Ligado wants to employ. In an accompanying, redacted technical analysis in the filing, Iridium said Ligado user terminals would create interference for Iridium operations in the1617.775-1626.5 MHz band, but its user terminals at 1646.5-1656.5 MHz don't raise worries. Iridium said the Ligado concerns are that Ligado OOBE would inhibit Iridium communications and that the wider the Ligado user terminal deployment the greater the risk of one operating near an Iridium terminal. It also said the OOBE mask Ligado proposed to protect GPS receivers wouldn't sufficiently protect immediately adjacent Iridium receivers. Iridium said its user terminal interference concerns arose from signal propagation modeling, and one Ligado user terminal at various line-of-sight distances would result in emission levels close to 50 dB higher than the Iridium receiver noise floor, and still produce excessive interference as far away as a kilometer. Iridium repeatedly voiced concerns about interference from Ligado's proposed use of the 16275-1637.5 MHz band (see 1606220041 and 1607070010). Ligado didn't comment.