Abstract
Due to its noise-like signal property, digital orthogonal frequency-division multiplexing (OFDM) radars are often assumed to be robust against interference. While a lot of research has been carried out for interference between different modulation schemes, the mechanisms of interference from OFDM to OFDM radars have been barely addressed. This paper provides a thorough analysis of mutual OFDM to OFDM interference based on radar measurements using a 4x4 77 GHz multiple-input multiple-output (MIMO) OFDM radar prototype. The effects of interference are described both qualitatively and quantitatively for cyclic-prefix and stepped-carrier OFDM. Second, it is shown that conventional mitigation methods in the spectrogram are not suitable due to the random coding of cyclic-prefix OFDM. As an alternative, the application of adaptive beamforming is proposed and two realization possibilities are provided. Finally, new mitigation strategies in the modulation domain are proposed. They allow to shape interference to specific range-Doppler cells, yielding an interference-free range-velocity map for the area of interest. Additionally, the method may be used as the basis to enable simple conventional interference mitigation strategies.
Highlights
Radar has an outstanding role in automotive safety and driving assistance systems due to its robustness to harsh weather conditions and the ability to measure distances and relative velocities
orthogonal frequency-division multiplexing (OFDM) signals are widely assumed to be robust against interference
The low power spectral density leads to a fast coverage of the interference by thermal noise with increasing distance compared to singlecarrier transmission schemes, and the random coding effectively prohibits the emergence of ghost targets
Summary
Radar has an outstanding role in automotive safety and driving assistance systems due to its robustness to harsh weather conditions and the ability to measure distances and relative velocities. Recent complementary metal-oxide-semiconductor (CMOS) technologies on the other hand allow for the first time to realize digital-centric radar designs on chip, shifting the effort to the digital domain This is partly driven by 5G developments in similar frequency bands requiring similar hardware. Simulation-based comparative studies about which modulation scheme is more robust against interference have been performed in [8] and on a multi-frame base in [9] revealing that the fluctuations in the noise floor are smaller for OFDM radars. They do not include any clear analysis, nor provide countermeasures.
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