u-blox has been cautious towards the negative impacts of the US FCC’s recent approval of the use of a previously protected portion of the L‑band for terrestrial communication on global navigation satellite systems (GNSS) such as GPS and, subsequently, on their large US customer base.
Before the FCC’s decision, the license, granted to the American satellite communications company Ligado, was limited to use for satellite communication terminals. Such terminals transmit radio waves directionally toward satellites and receive weak satellite signals.
Following the recent FCC approval order, Ligado will be free to use these frequencies, which are very close to those used by GNSS receivers, to transmit downlink signals from cell towers and uplink signals from the user equipment. These signals are transmitted at dangerously high levels compared to those received by nearby GNSS receivers.
These signals threaten to disrupt the operation of GNSS receivers from any manufacturer operating in the vicinity of a Ligado base station or compatible cellular handset. In an internal study on the susceptibility of u-blox GNSS receivers to interference resulting from such activity, we confirmed that the transmissions would disrupt the operation of nearby GNSS receivers.
u-blox findings, outlined in an application note, show 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, a greater distance than the permitted separation between base stations.
Although we have developed recommendations to mitigate these disruptions, it is important to note that implementing these on millions of deployed products would involve a considerable cost and an inconvenience to our customers and would also affect GNSS receiver performance to some extent. The same would be true for receivers from any other manufacturer.
The FCC approval decision was justified based on supposed measurements of the levels of interference causing harm to GNSS receiver operation. Drawing on our extensive expertise in this area, u-blox completely rejects the criteria employed in this testing. As a wide range of other GNSS providers and technical experts have already attested, the only generally accepted criterion for harmful interference is a level of interference that results in a 1 dB reduction in the carrier-to-noise ratio measured by a GNSS receiver.
u-blox is also deeply involved in the development of products for future applications that will also be affected by this decision. One example is autonomous cars and trucks. Although these systems will use a range of sensors, GNSS is the only available source of absolute position information that most automotive manufacturers now recognize as being vital for high levels of autonomy. As this application is safety-critical, high integrity GNSS receivers are required. u-blox is involved in the development and deployment of such solutions.