Doppler-Tags with Self-Interference Cancellation for High-Accuracy Chirp Sequence Radars (DoSIS)

• Applicants: Dr.-Ing. Benjamin Nuß; Professor Dr.-Ing. Ahmet Ulusoy
• Subject Area: Communication Technology and Networks, High-Frequency Technology and Photonic Systems, Signal Processing and Machine Learning for Information Technology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 533282729

An energy efficient Doppler tag is proposed as radar tag together with a chirp sequence radar system exploiting the signal phase to reach high accuracy above the bandwidth related value. The Doppler tag introduces an artificial Doppler shift characteristic for the tagged object of interest to the radar signal reflected off this object. The radar signal is received at the tag, mixed with a frequency acting as artificial Doppler, and sent back in direction towards the radar sensor. In the processing of the raw radar data, the velocity and range of the tagged object are estimated with high accuracy. Here, the velocity estimation is required to correct phase errors that would affect the range estimation. The artificial Doppler shift is corrected in the signal after identification. After the removal of the Doppler shift, a chirp Z-transform along the samples of the chirp can give a first, coarse range estimate. This is used as starting point for the phase-based range estimation within the range bin determined by the frequency analysis. The high-accuracy range within this bin is determined using the phase offset, where the main challenge is the sufficient suppression of quadratic phase terms. Another critical aspect to consider is self-interference. Even if the receive and transmit channels of the tag are separated, there will be a finite leakage of the transmit signal into the receiver, which will generate a tone at twice the intended Doppler shift. This will potentially have a significant impact on the overall radar performance, as the leakage signal may not only saturate the receiver, but could also create wrong target signatures after being remixed with the Doppler frequency again, that could potentially swamp out the actual signal of interest. To overcome this limitation, we will investigate enhancing the proposed tag architecture by a self-interference cancellation stage. The delay in this cancellation path has to be equal to the one from the coupling path from the Tx to the Rx antenna. This way, combined with additional measures, such as optimized placement and design of the receive and transmit antennas, the impact of interference on the tag performance can be minimized. By subtracting the internal leakage signal with the correct delay, phase and amplitude from the receive signal, the unwanted external leakage signal will be cancelled. The quality of this cancellation strongly depends on the ability to accurately adjust the internal cancellation path to the external coupling path. Here, variable delay lines are required. And finally, if not only a single tag but multiple tags per object are used in conjunction with a multi-sensor setup, the determination of the object orientation in 3D can be enabled with high accuracy. For the envisioned application, it is important that the tags have a low energy budget and they are highly miniaturized. Therefore, we will investigate an IC-based solution at 60 GHz.

• DFG Programme: Research Grants