I Am Not Afraid of the GPS Jammer: Resilient Navigation Via Signals of Opportunity in GPS-Denied Environments Figure 15. Experiment 2 EKF results: SOP position error and 3s bounds. (A) GPS signals available, (B) GPS signals intermittent, and (C) GPS signals unavailable. Figure 14. Experiment 2 EKF results: receiver position error and associated 3s bounds for Scenario 2: assuming unknown SOP position. (A) GPS signals available, (B) GPS signals intermittent, and (C) GPS signals unavailable. lost was used to initialize the position states in both radio SLAM scenarios, and the receiver's and SOP's positions were expressed in an East-North-UP frame, centered at the receiver's initial position. The initial state estimate for Scenario 1 was ^x ¼ 081, while the initial state estimate for Scenario 2 was x^ ¼ ½016; 976:9; 3221:3; 58:9; 012 T. The initial estimation error covariance for Scenario 1 was P ¼ diag½1; 1; 1;