GNSS system vulnerability to interference is a major concern for civil applications particularly for either weak signal environment or consumer-grade receivers. This thesis provides a comprehensive analysis of the quantization and acquisition loss incurred in a conventional GNSS receiver in the presence of CW interference. It also proposes some low complexity solutions to improve the receiver performance in terms of quantization and acquisition metrics.
This work contributes to the field of interference resilience consumer-grade GNSS receiver in three different ways. First, a general framework for quantization loss in a low resolution GNSS receiver is developed. Simulation results show that traditional techniques used to estimate C/N0 are unreliable when interference is present. To avoid this problem, the BER metric is employed in this work. Afterwards, it is shown that in this case, there is an optimum configuration in terms of BER and detection probability performance for a quantization process in which the AGC is allowed to dynamically adjust the gain applied to the input signal.
Second, an LMS-based adaptive FIR notch filter is proposed and developed to adaptively detect, locate and reject the narrowband interference signal with negligible side effects on desired GNSS signal. Next, this NF is modified to have linear phase response in order to eliminate the bias and distortion on pseudorange measurements. Compared to IIR notch filters, an FIR notch filter is always stable and induces less numerical errors into the filtered signal.
Third, the problem of GNSS signal acquisition using a consumer-grade receiver is investigated. After proposing a general framework for cell level and system level signal acquisition of a GNSS receiver, a detailed model of the impact of interference signals on the CAF of a GNSS signal is presented, and is employed in the development of novel acquisition strategies. These new strategies are examined under a selection of operating scenarios including: acquisition in the presence of interference when the receiver has some, or no a priori information regarding the interference. It is shown that, by employing these new schemes, a receiver can operate under a JNR 20 dB higher than when using traditional schemes.