The proposed innovation is to use the comm-based measurements available from many advanced satellite cluster wireless networks to improve the flexibility and robustness of relative and absolute navigation systems without the additional expense, weight and power that a traditional navigation backup systems (like an extra GPS receiver) would require. This will be accomplished by comparing the range, range-rate or angle measurements predicted by GPS-based navigation solutions to the actual measurements obtained from the communication system. By monitoring these parity equations and the innovations of the GPS filters, FDIR can be significantly improved. These parity relations between redundant range measurements create a more sensitive residual than filter-based residuals because most filters naturally mask the faults. Recovery to GPS failure can be accomplished by relying on the comm measurements themselves to maintain relative state observability. Attempted recovery of GPS or other strategies can then be implemented without requiring the cluster to disperse. By building off of Carrier-phase Differential GPS (CDGPS) navigation filters and cluster flight simulations currently being built by Emergent under its DARPA System F6 contract, we will demonstrate the effectiveness of this FDIR technique in simulation.