High sensitivity GPS receivers represent an attempt at seamless navigation in conditions that are not favourable for satellite reception. Reception of very weak signals is enabled through the special structure of these receivers and special signal processing techniques. Observation error sources, especially multipath, can cause large errors in position. The concept of high sensitivity GPS receivers operation is presented. The potential of signal processing using robust statistic methods and Doppler observables is discussed. The multipath error can be estimated using Doppler observables.

Key words: high sensitivity GNSS receivers, adverse conditions, multipath, robust statistics, Doppler observables