**2. Algorithm Design**

The proposed tightly-coupled algorithm is illustrated in Figure 1 and comprises two parts. In the first part, a dual w-test-based FDE model is designed for multiple failure detection in urban areas. In the second part, a scoring strategy is used to exclude faulty measurements. The remaining satellites are then fused with IMU sensor measurements to compute the final state.

**Figure 1.** System Framework.

*2.1. Dual w-Test*
