Ambiguity Function Analysis for OFDM-Based LDACS Passive Multistatic Radar

The ambiguity function analysis is central to investigating the resolution capabilities of a radar system. It is particularly important for passive radar scenarios, where the signals of opportunity have not been originally designed for radar purposes. This paper focuses on studying the achievable resolution capabilities for a noncoherent orthogonal frequency division-multiplexing (OFDM)-based passive multistatic radar for L-band digital aeronautical communication system (LDACS) signals. For this purpose, the ambiguity function obtained when employing the OFDM-based LDACS communications signals as signals of opportunity is studied. A generic bistatic link is considered and closed-form expressions for the expectation of the corresponding ambiguity function when accounting for the different signal contributions are derived. The resulting expressions are then used to evaluate and analyze the overall multistatic radar ambiguity function for two sample radar scenarios. The results highlight the impact of the geometry on the shape of the ambiguity function, allowing therefore for a better understanding of the effect that the geometry has on the range and velocity resolution capabilities of the studied system.