Unambiguous Acquisition & Tracking Of IRNSS RS Signal

Abstract

Indian Regional Navigation Satellite System (IRNSS) is a space based Radio Navigation System managed by Indian Space Research Organization (ISRO) for the Government of India. The Binary O set Carrier (BOC) modulated signals are being used in the present as well as the upcoming Global Navigation Satellite Systems (GNSS) such as American Global Positioning System (GPS), European GALILEO System, Indian IRNSS System and Chinese COMPASS. BOC Signals have several advantages over the traditional BPSK modulation such as an in- creased resilience against multipath and improved tracking performance. However, BOC signals have an auto correlation function with multiple posi- tive and negative peaks that may lead to false locking. With such a modu- lation, the acquisition process becomes complex. Objective is to design, implement and analyze some of the receiver mod- ules like Acquisition, Tracking for IRNSS Restricted Service (RS) Signal. In order to track and decode the information in the navigation signal, an acquisition method must be used to detect the presence of the signal. Once the signal is detected, the input signal carrier frequency and the code phase are measured and fed to the tracking loop. The information regarding the Doppler frequency shift caused by satellite motion both on the carrier frequency and on the code phase are important for performing acquisition and tracking of the navigation signal. Because of the multiple correlation peaks of the BOC signal, tracked code phase will be ambiguous and lead to poor range accuracy, if not resolved. In order to mitigate the ambiguity one has to use special algorithms designed for BOC signals. The accuracy and unambiguousness of the tracking algorithm characterizes the entire receiver accuracy. So the tracking algorithm should be robust enough to accommo- date all kinds of signal variation and should provide unambiguous code phase and carrier frequency.