US Patent 7375683 Use of geo-stationary satellites to augment wide

The present invention improves WAMLAT Timing Availability by using timing from one or more of a variety of sources. These sources include unaugmented SATNAV timing, from GPS or/and GALILEO, GEO timing from pseudo SATNAV signals, additional GEO timing for non SATNAV applications, timing derived from both terrestrial and satellite television and radio transmissions, and stable on board oscillators to withstand short term interruptions in satellite timing. The use of one or more of these multiple sources of timing improves accuracy and reliability of wide area multilateration systems.