GPS World, December 2014

EXPERT ADVICE even consumer grade receivers used in automobiles tablets and smartphones will embrace all GNSS despite the added cost in chip size and power Setting aside the larger PNT discussion and considering only GPS what challenges must GPS address to remain the cornerstone of PNT services Here is my list of the top issues GPS faces today Signal Vulnerability Since the issue of GPS vulnerability was raised in the 2001 Volpe Report this issue has not changed but the stakes have risen much higher There is greater dependence on the GPS service than ever before with over a billion users It is generally conceded that for many applications reliance on GPS in its current form is insufficient and even risky Brad Parkinson espouses the mantra of protect toughen and augment GPS focusing on steps necessary to strengthen its service Numerous methods are being explored and implemented to protect and toughen GPS increased signal power on modernized satellites improved antennas and authentication of the signal against spoofing The U S Department of Transportation is actively seeking ways to protect GPS spectrum through public workshops on GPS adjacent band compatibility The GPS civil signal remains open to malignant spoofing by nefarious forces Various methods are being proposed to counter this threat It may seem that adding signal authentication is a bit too late since civil GPS signals have already been defined in interface specifications but it turns out this may not be the case At the Stanford Symposium Col Matt Smitham of the GPS Directorate stated that now is a good time to play with the civil navigation message implementations to explore features like authentication This is the time to do this change the message types he said Thus there is an opportunity to counter this threat Gaps in Service A low power service that has limited operation in many settings GPS does not provide full functionality at the Poles nor does it work indoors or underwater This issue is exacerbated by societys demands for PNT services anywhere The 2008 National PNT Architecture identified these gaps as a primary concern encouraging numerous actions to resolve them Split Leadership Although the Space Based PNT Executive Committee and its National Coordination Office provide a mechanism for establishing highlevel policy and providing outreach GPS World December 2014 www gpsworld com 44