1. http://www.unoosa.org/oosa/en/ourwork/icg/icg.html
2. http://www.unoosa.org/documents/pdf/icg/activities/2007/WG‐A‐2007.pdf
3. http://www.unoosa.org/oosa/en/ourwork/icg/working‐groups.html
4. GNSS Integrity and Receiver Autonomous Integrity Monitoring (RAIM)