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Alexey S. Volkov, National Research University of Electronic Technology, Moscow, Russia, leshvol@mail.ru
Alexey V. Solodkov, National Research University of Electronic Technology, Moscow, Russia, solodkov_aw@mail.ru
Ilya V. Chugunov, National Research University of Electronic Technology, Moscow, Russia, ivchiginov2016@gmail.com

In urban conditions the path loss of radio signals is much higher than in the case of propagation in free space and as a result of GNSS signal could be not detected, even if the satellite is in radio visibility. This degrades positioning accuracy with GNSS or even makes positioning impossible at low signal levels at the receiving point. Using of algorithms for the initial search of signals based on the increased correlation calculation time received signal and local replica of the spreading code allows to increase the probability of acquisition and to improve the basic consumer characteristics of the GPS receiver: the positioning accuracy and time of the cold start.
A lot of devices, that are capable to receive such signals, have limited resources (computing power, memory), comparable to the minimum required resources for the operation of these algorithms. That should be taken into account when choosing signal acquisition algorithm. In this work compares the developed mathematical models of algorithms for initial search of C/A signals of GPS system by the criteria of probability of correct acquisition of the signal using only one cold start and the time of the required post-processing.
A mathematical model of the received signal with impact of the Doppler shift and modulation by data is obtained. Both effects reduce the magnitude of the main peak of autocorrelation function. All the considered algorithms are focused on the increased of correlation interval the received signal and the reference replica of the spreading code, taking into account this model.
The measurement of the characteristics was carried out on the recorded sample of real signal with additional noise, simulating the attenuation of the signal power with its proper structure. The gain from using the considered algorithms is about 7 to 11 dB with the probability of successful detect and determining signals’ characteristics from the first run Pd=0,99, and the number of detected satellites increases on average by two times. The drawbacks of use researched algorithms are determined: the post-processing time of improved search algorithms is increased by 5-7 times, in addition, either more memory or more FFT calculations are required.

Keywords: GNSS, signal detection, PN signals, DSSS, GPS, coarse acquisition.


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Information about authors:
Alexey S. Volkov, PhD, assistant professor of the Department of Telecommunications, National Research University of Electronic Technology, Moscow, Russia
Alexey V. Solodkov, lector of the Department of Telecommunications, National Research University of Electronic Technology, Moscow, Russia
Ilya V. Chugunov, bachelor of the Department of Telecommunications, National Research University of Electronic Technology, Moscow, Russia