1. Welcome to
GPS.gov
. Available at:
http://www.gps.gov/
. Accessed 21 Apr 2016
2. The Qualcomm/SnapTrack Wireless-Assisted GPS Hybrid Positioning System and Results from Initial Commercial Deployments,. Available at:
https://www.ion.org/publications/abstract.cfm?articleID=2037
. Accessed 21 Apr 2016
3. Glonass. Available at:
http://www.glonass.it/eng/
. Accessed 21 Apr 2016
4. Galileo | European GNSS Agency. Available at:
http://www.gsa.europa.eu/galileo
. Accessed 21 Apr 2016
5. BeiDou Navigation Satellite System — Home. Available at:
http://en.beidou.gov.cn
/. Accessed 21 Apr 2016