Impact of Carrier Leakage on NavIC Signal Performance

Homodyne-based digital modulators are widely used in navigation satellite systems, such as in the Navigation with Indian Constellation (NavIC). In these systems, the mixer plays a crucial role by up-converting zero-IF complex modulated signals to the desired carrier frequency. However, insufficient port-to-port isolation in the mixer can cause leakage of the local oscillator (LO) carrier into the output, resulting in unwanted in-band signals within the transmitted spectrum. When these leaked signals are amplified by transmit filters and onboard high-power amplifiers, they distort the transmitted navigation signals, impairing system performance. Traditional analytical methods for assessing interference in Global Navigation Satellite Systems (GNSS) often assume ideal signal conditions, mainly focusing on intersystem and intrasystem interference. This paper extends the current interference analysis framework by integrating the effects of carrier leakage and other imperfections specific to homodyne transmitter designs. We introduce a system model for a homodyne transmitter and provide a mathematical representation of the NavIC interplex signal, including in-band carrier leakage. The impact of these imperfections is analyzed by examining the degradation in the effective carrier-to-noise ratio (C/No) and the data demodulation thresholds at the receiver. The proposed methodology allows for a more accurate and practical evaluation of NavIC receiver performance, facilitating improved optimization of modulator designs and effective interference mitigation strategies. These findings are vital for enhancing the robustness and accuracy of NavIC services and advancing efficient GNSS operations in various environments.