The project "Robust Navigation" at FOI, Swedish Defence Research Agency, aims at developing cost effective and reliable navigation systems for tough environments when few weak or no GPS-satellite signals are available. The main issues are:

• Robustness - How to design a future robust and jamming resistant navigation system?
• Strategies - What navigation strategies should be used by collaborating autonomous in for example urban environments or during navigation warfare?
• Cost efficiency - When can simple and cheap navigation sensors be used?

The article  “Robust Navigation - Allowing other systems to support GPS renders increased robustness and precision” by FOI researcher Bengt Boberg (from "The Swedish Journal of Military Technology - Militärteknisk tidskrift") describes the problem associated with navigation in an urban environment. Three cases illustrate how few satellites a GPS receiver can use during a 12 hour period. Two different methods are described where small and cheap inertial navigation sensors (accelerometers and gyros) are integrated. One method, the tight integration, enables use of GPS even when the number of satellites is less than four.