Vulnerability Assessment of the Transportation Infrastructure Relying on the Global Positioning System
The U.S. Department of Transportation was mandated by a Presidential Decision Directive to undertake a thorough evaluation of the national transportation infrastructure that relies on the Global Positioning System (GPS). The Volpe Center is supporting that effort by conducting an independent, integrated assessment of risks to civil users in the U.S. of GPS-based systems. A report on the project findings has recently been submitted to the Assistant Secretary for Transportation Policy at DOT.
A major finding of this report is that potential interference to the GPS L1 civil signal is a serious problem, in part because of increasing use of and reliance on GPS. Nevertheless, it is possible to mitigate the worst vulnerabilities.
A major element of GPS vulnerability lies in the very low power that makes it vulnerable to jamming. GPS also is vulnerable to spoofing, broadcast signals with deliberately misleading information, and to unintentional interference. The latter can be due to natural causes (for example, solar flares and ionospheric scintillation), but also to human sources (for example, TV broadcasts, Mobile Satellite Services, Ultra Wide-Band systems, military jamming/spoofing tests, and military communications systems). A peculiar but valid class of vulnerability is the degree of unrealistic expectations that can be produced in enthusiastic but unwary GPS users. If there is inadequate integrity monitoring, the ready willingness to accept a GPS-driven electronic display, for example, can magnify the effectiveness of jamming on the user. Loss of GPS is a threat not only to civil transportation users, but also to banking, communications, data processing and internet enterprises that rely increasingly on the GPS timing signal.
While disruptive technology is increasingly available, effective, and easy to hide, counter-measures, or mitigations, do provide reasonable expectation that the worst effects of GPS disruption can be mitigated by utilizing a combination of strengthening the GPS system and by integrating GPS with independent systems. An important part of ensuring sufficient robustness in GPS-based systems is to provide these systems with adequate integrity monitoring.
One key outcome of this analysis was the reinforcement of the vital need to implement backup systems to GPS in critical applications wherever possible.
For more information contact James Carroll at carrollj@volpe.dot.gov.
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