Synchronization of Weak Indoor GPS Signals with Doppler Using a Segmented Matched Filter and Accumulation

This paper investigates GPS codephase acquisition with very low SNR signals found within large buildings. Conventional GPS receivers can acquire the GPS codephase relatively easily when in direct line of sight with the satellites. However, acquisition becomes difficult with highly attenuated signals found inside buildings. Recent government regulations aim to improve 911 service for wireless telephones by supplying dispatchers with caller location, however, this requires the development of new technologies. With extensive signal averaging, GPS signals can provide positioning within large buildings. We assume 5dB/floor of signal attenuation so the GPS signal would be -183 dBWor less at the bottom of a 5-story building. We assume 2 MHz system bandwidth and surrounding walls at room temperature of 290 K (17degC) so the Boltzmann noise is -141 dBW. More than 50 dB SNR improvement is provided by an accumulating segmented matched filter that is robust to polarity reversals caused by Doppler frequency offset and by GPS data transitions. Through simulation, performance comparisons are made to a conventional matched filter (CMF) operating without polarity reversals.