Pseudoranges, the four-unknown nonlinear least-squares fix (three position components plus receiver clock bias), Dilution of Precision, and the principal error sources (ionosphere, troposphere, multipath).
## What you'll learn 1. Describe the GPS constellation and signal architecture. 2. Explain how a pseudorange is formed and why it is "pseudo". 3. Formulate GPS positioning as a nonlinear least-squares problem. 4. Explain how satellite geometry amplifies pseudorange noise into position error. 5. Identify the four dominant GPS error sources and their typical magnitudes. 6. Interpret GPS accuracy specifications (CEP, $1\sigma$, 2DRMS). ## In this block