FCC ruling could cause satellite positioning failures, says u-blox
u-blox has spoken out against the use of parts of the L band for terrestrial cellular communications because this may interfere with positioning by satellite and reckons that FCC testing criteria are inappropriate. The company also reckons the ruling could disrupt the roll out of autonomous driving and 5G cellular communications in the US.
The FCC has granted a license to Ligado Networks LLC (Reston, Virginia) allowing the use of previously protected portion of the L band (1GHz to 2GHz) to be used for terrestrial communications. Prior to this the band was limited to satellite communication terminals and in operation had little impact on other satellite communications and global navigation satellite systems (GNSS) such as GPS.
u-blox said that following the FCC order Ligado will be free to use these frequencies, which are close to those used by GNSS receivers and could disrupt the operation of GNSS receivers from any manufacturer operating within a kilometer or so of a Ligado base station or near a compatible cellular handset.
u-blox said that FCC testing criteria are inappropriate and that operation by Ligado could disrupt the operation of millions of deployed GNSS receivers across the US. These are deployed in applications that include vehicle navigation, automated driver assistance, drone navigation, vehicle fleet tracking, asset tracking, wearable applications, machine control, base station synchronization and more. There are several generations of u-blox GNSS receivers in use in the millions of devices deployed in the USA.
They have been set up on the basis of a lack of GNSS interference based on the absence of high-powered signals in nearby frequency bands. The FCC has swept away that protection, leaving almost tens of millions of GNSS receiver applications at risk, u-blox said.
Next: Impact on automotive, 5G
The company went on to say that the presence of high-powered terrestrial signals in nearby sections of the L-band could cause the automotive industry to delay the deployment of autonomous vehicles in USA, while engineering solutions are found.
Similarly the latest ruling will have an impact on the roll out of 5G communications which requires many more basestations than previous generations. In urban areas and indoors, GNSS receivers will be required to keep these base stations in synch. But because these GNSS receivers will rely on fewer and even weaker signals than most GNSS receivers, their reliability and accuracy will be even more degraded by interference from strong cellular signals at frequencies close to the GNSS frequencies.
u-blox has conducted its own study on the susceptibility of u-blox GNSS receivers to interference resulting from such activity. These show that that GNSS receivers would suffer performance losses anywhere near a transmitting Ligado handset and when located up to one kilometer from a Ligado base station.
u-blox said it has recommendations on how to mitigate these disruptions but that implementation would be costly and inconvenient for customers and would also affect GNSS receiver performance.
The company added that the FCC should restore the original regime and prevent frequencies near the designated GNSS frequencies from being used for terrestrial wireless communications.
The FCC denied a request to stay its decision to authorize Ligado Networks to deploy a low-power terrestrial nationwide network using portions of its licensed spectrum back in January 2021. The request had come from the US Department of Commerce’s National Telecommunications and Information Administration (NTIA) the previous May.
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