Characterization of Range and Time Performance of Indoor GNSS Signals

Small cells are now widely used to provide indoor wireless services and are gaining further importance as technology enablers for emerging applications. These techniques rely on accurate synchronization of signals broadcast from neighboring base stations. Therefore, the latters must have access to reliable and accurate time reference. GNSS signals can be used to provide a reliable global time reference in open sky conditions. However, owing to low levels of signals indoors, the detection and processing of these signals and obtaining an accurate time indoors are still a challenge. It is assumed that accurate position estimates are known for indoor static applications which are obtained either using GNSS or other indoor positioning technologies. Under this assumption, fine timing solution can be provided with reliable single satellite information. As such this paper characterizes GPS based measurement and timing accuracies for indoor signals. This study specifically focuses on assessing range and timing accuracies for static indoor locations. Actual GPS data was collected at two indoor sites having different indoor characteristics for duration of more than ten minutes at each site. Assuming a known user position, measurement accuracies are analyzed over time while simultaneously observing received signal power. Ranging (timing) accuracy in the order of 10 m (30 ns) was achievable for the indoor scenarios considered. Finally, to assess the capability of indoor measurements to sustain good time synchronization accuracy over a longer duration, two-minute data segments were collected at intervals of 30 minutes for three hours. The time variations of the pseudorange (time) and position errors are studied.