While GNSS can provide reliable PNT services for most of our daily applications they present several vulnerabilities. They are vulnerable to unintentional interference, intentional jamming, and malicious spoofing, especially for DoD-related applications. On the battlefield, PNT utilizing any single GNSS service becomes unreliable. Therefore, to overcome this shortcoming, a family of more robust methods was proposed. This proposal enhances the reliability of PNT services by exploiting multiple sources for navigation.