Will your GPS Stiil Work?
by Roy Linker

GPS World

Civil P sunset 

The Office of Space Commercialization issued a Notice for Public Comment. In it, the U.S. Department of Defense (DoD) proposes to discontinue supporting P(Y) codeless/semi-codeless on both GPS L1 and L2 frequencies on modernized satellites (Block IIR-M, Block IIF, and Block IIIA/B/C) beginning December 31, 2020. After 2020, legacy dual-frequency receivers may still work, but the DoD would no longer assure that P(Y) power levels and the navigation message would remain the same.

Essentially, this means that every dual-frequency receiver designed in the 1980s, 1990s, and many in the early 2000s would become virtually obsolete. In the interest of disclosure, that includes my own legacy real-time kinematic (RTK) system.

All current post-processing and RTK algorithms are based on using codeless/ semi-codeless techniques of one sort or another. Those of us in the survey/engineering/construction/deformation monitoring/high-precision GIS industries would be most affected. We are going to get hit in the wallet--hard.

The DoD's proposal assumes that most organizations will have upgraded their GPS equipment by 2020 and will be using L2C and other modernized signals, so that L1/L2 P(Y) codeless/semi-codeless processing won't be needed. The DoD states that GPS manufacturers have indicated that the user community needs about 10 years to replace legacy GPS equipment with equipment capable of utilizing modernized GPS signals.

This means that any dual-frequency receiver not designed to use L2C could essentially become a paperweight after December 31, 2020. The receiver may still work after that date, but there is no assurance it will continue operating properly. The list of receivers affected is quite long and includes models from all major manufacturers, such as Trimble, Leica, Topcon, Magellan (Ashtech/ Thales), and NovAtel among others. One should not assume that all receivers sold today are capable of utilizing L2C. Ask before purchasing.

LI-only receivers such as handheld GPS units, car navigation systems, tracking devices, GPS-enabled mobile phones, Ll-only GPS mapping systems, and timing receivers are not affected by this proposal, nor are Ll-only RTK receivers. The exception is some newer receivers designed for GIS data collection at the decimeter level. Although not marketed as such, these are dual-frequency and might be affected.

ERIC GAKSTATTER is GPS World's contributing editor for Survey and Construction, writing a twic-monthly e-newsletter. He has spent 18 years in the GPS survey/mapping industry industry as a product manager, GPS user, consultant, and a non-partisan advocatet for the GPS user community.