Dropping L1 – Yes You Can
A pure L5-band GNSS receiver in a mobile phone faces no U.S. regulatory, public safety,
3GPP, or satellite adequacy blocks
Sunnyvale, California, 23 February 2023
– One of the questions frequently asked of oneNav is, “don’t phones have to have L1 to comply with E911?” A close second is, “won’t Public Safety insist that phones have L1?” The answer to both questions is NO. With that out of the way, we next hear, “can you drop L1 and still comply with 3GPP standards?” Followed by, “are there enough L5-band satellites available to get good performance?” YES and ABSOLUTELY YES are the answers to the last two questions.
E911 and Public Safety
The first FCC order concerning the location of wireless calls to 9-1-1 (referred to as E911) was issued in 1996 and specifically amended in 1999 to ensure technological neutrality between network-based and handset-based location solutions. As the Commission originally assumed that location information could only be provided by technologies based in or overlaid on wireless carrier networks, nothing in its compliance rules refers to the operation of a handset solution, to any GNSS, or to an L1 signal at all. Thus, by definition, no L1 signal is required to be present for E911 compliance.
As for Public Safety, their primary concern is the speed with which emergency services can be provided to wireless customers. Public Safety Answering Points (PSAPs) neither require nor receive any information about specific satellite signals used in calculating wireless 9-1-1 calls: they care about dispatching assistance expeditiously and accurately and are agnostic with respect to L1, L5, network- based, or any other location determination methods. Emergency response in deep urban environments especially benefits from single-frequency L5, the accuracy of which outshines both L1 and current L1/L5 hybrid solutions.
3GPP and Satellite Availability
The relevant 3GPP standards are written to support whatever combination of bands (L1, L2, or L5) and constellations (GPS, GLONASS, Galileo, or BDS) are present in a mobile phone GNSS receiver. Conversely, if a specific band or constellation is
not supported, no test is required.
L5-band signals were designed specifically to support high performance applications. With 18 GPS satellites and at least 24 Galileo satellites broadcasting in the L5 band today, a solution without the measurement errors from L1 is more accurate than a solution which includes L1. Including BDS (40+) and QZSS (4), more than 80 L5-band satellites are available globally.
Yes, you can drop L1. Your GNSS receiver performance, cost, and complexity will be better for it. Less is more.
oneNav is powering high performance positioning for location-dependent mobile services. The oneNav team comprises top GNSS experts from Qualcomm, Apple, Intel, SnapTrack, SiRF, Trimble and eRide with decades of GNSS and mobile industry experience. The team has expertise in GNSS system architecture, multipath mitigation, signal processing, ASIC design and AI/machine learning, and collectively has filed over 300 career GNSS patents. Investors include Google Ventures, Norwest Venture Partners and GSR Ventures. To learn more, please visit www.onenav.ai.
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