IN 519 – Enhanced performance standard for GPS

[Taken from IMO document NAV 48/18/1 issued 28 March 2002]

The Performance Standard for GPS in IMO Assembly Resolution A819(19) has, as members may be aware, been updated in the last few years.

The updated GPS standard includes a requirement that the receiver equipment should be capable of operating satisfactorily in typical interference conditions.

The International Electrotechnical Commission (IEC) has clarified this requirement and provided a corresponding text of results required.  This will be published soon in the second edition of IEC 61108-1 GPS.

While this work was progressing, further developments in the provision of the GPS service and in the understanding of its vulnerability have been announced, namely:

1. United States Department of Defense (DoD):  Global Positioning Systems – Standard Positioning Service – Performance Standard October 2001; and
   
   
2. John A Volpe, National Transportation Systems Center:  Vulnerability Assessment of the Transportation Infrastructure relying on the Global Positioning System August 2001.

There has also been the September 11^th terrorist attack and an increased awareness of the potential for not only natural and man-made but also deliberate interference to the GPS service.  The United States DoD has already scheduled a service update into the GPS programme in the coming years with, amongst others, the addition of commercial frequencies services on both L2 and L5 in addition to that established on L1.  These go some way to reducing the foreseen vulnerability to interference of receivers that can employ them.

The IEC thus believes that there are advantages in providing the mariner with option of having an enhanced performance standard for GPS receivers that employ these extra frequencies, to enable improved interference protection and some anti-jamming and anti-spoofing capability.

The IEC also sees this enhancement, particularly, as an essential extra aid in those waters and on those ships where an independent position fixing aid is absent or only infrequently available.  The enhanced GPS system could also provide more robust supplementary services such as timing (UTC) that can then be used, to advantage, in other navigational safety aids, such as AIS.  This would go some way to mitigate GPS dependency.

IEC has invited IMO to consider the implications of this development.