Error bound analysis for velocity estimation in near-field bistatic radar systems

Future wireless networks are envisioned to integrate joint communication and sensing (JCS) functionalities, enabled by technologies such as extremely large aperture arrays (ELAAs) and high-frequency operation. These advancements introduce near-field propagation effects that can be effectively exploited to enhance sensing capabilities. This paper focuses on Doppler-based velocity estimation in bistatic radar configurations, where spatial separation between transmitter and receiver offers greater geometric diversity compared to the monostatic case. Leveraging ELAA capabilities and near-field propagation effects, we show that distinct velocity components can be accurately estimated, thanks to the derivation of performance bounds that quantify the sensitivity of estimation accuracy to system design choices. Approximations are introduced to provide key insights into the impact of geometric parameters, such as the positions of the transmitter, target, and array, as well as the array orientation, and signal parameters, including carrier frequency and signal duration. Furthermore, the interplay among these factors is analyzed in relation to the number of antennas and array aperture, which are fundamental quantities determining the near-field effects. A comparative analysis with the monostatic case further elucidates the peculiarities of ELAA-based bistatic architectures.