Abstract
Modern mobile devices are now equipped with GPS-receivers to provide
E911 and other location based services. Working indoors, the GPS receiver
is likely to experience a situation where some of the received signals are
stronger than others. These strong signals can prevent the acquisition of a
desired weak signal or lead to false acquisition, due to high cross correlation
between the strong and weak signals. The C/A Gold code used in GPS L1
signal has an inherent correlation protection of about 24 dB. This becomes
inadequate for weak signal acquisition in the presence of multiple strong
signals. Various cross correlation mitigation techniques are used to deal with
this problem. The impact of cross correlation on weak signal acquisition
largely depends on the relative power level and carrier offset of the desired
weak signal with reference to the strong interfering signals. This paper first
presents an analysis of the L1-C/A cross correlation in the presence of
multiple strong signals under different conditions of relative Doppler offset
and dwell time. Acquisition of weak signals with different SNR levels is
then performed under these conditions, using the ¿Tong¿ search algorithm
and the results of acquisition are presented. The results indicate that, for
certain relative Doppler offsets, extended dwell times assist in combating the
cross correlation noise hence improving the detection probability.