In order to obtain protection levels for PPP in multipath prone environments, we formulate a coarse threat model for urban and suburban environments. Based on this threat model, we determine analytically the limitations a of solution separation approach. In particular, we derive for which range of fault rates and fault lag this approach is likely to be feasible. We then describe a solution separation fault detection algorithm adapted to this threat model. Using data collected in urban and suburban environments, we evaluate the benefits of using up to 3 GNSS constellations and dual frequency in PPP combined with an FD algorithm based on solution separation, and in particular its ability to protect against measurement outliers.