Statistical characterisation of the indoor sseudorange error using low cost receivers

The Global Positioning System (GPS) has made outdoor localization broadly available and is commonly employed for automotive navigation by a very large number of users. Low cost devices available on the mass market are currently able to track satellite signals down to a signal power of -159 dBm. With these high sensitivity devices, receiving (i.e. acquiring) GNSS signals indoor becomes possible. However, the building material used and the kind of construction greatly influence the signal propagation. For instance, European houses are more affected by attenuation as they are now mostly built of concrete compared to many American houses that are often built of wood and brick work. Typical wave propagation mechanism into most European buildings is through windows as ordinary glass attenuates electromagnetic waves less compared to thick concrete walls. Bearing this in mind, diffraction at window frames, as well as outdoor and indoor reflections play an important role in indoor GNSS positioning through the effects on the propagation channel. In the paper we report on both the temporal and spatial correlations of the errors. Since a room and its major fixtures such as furniture and windows, as well as the surrounding building(s), are largely static, the temporal correlation of pseudorange errors measured at a fixed point introduced by the propagation channel is high and slowly decreasing with time (note that the satellites motion is too slow to cause sudden channel changes due to changes in the incoming wave angles). A certain spatial correlation is present but less distinct and fast decreasing with distance. For the case of a moving object, such as a pedestrian, both temporal and spatial correlations will play a role for optimal model estimators.