Sub-Nyquist Sampling OFDM Radar

TL;DR

This paper introduces a sub-Nyquist sampling method for OFDM radar that reduces ADC sampling rates without hardware changes, using signal unfolding and noise cancellation techniques to maintain range resolution and improve SNR.

Contribution

It proposes a novel sub-Nyquist sampling scheme for OFDM radar and a noise cancellation method to mitigate symbol-mismatch noise, enabling lower sampling rates with minimal performance loss.

Findings

Achieves target range estimation with full bandwidth resolution at reduced sampling rates.

Introduces a symbol-mismatch noise cancellation technique to improve SNR.

Validates the approach through simulations and measurements across various sub-sampling ratios.

Abstract

In this paper, we propose a sub-Nyquist sampling (SNS) orthogonal frequency-division multiplexing (OFDM) radar system capable of reducing the analog-to-digital converter (ADC) sampling rate in OFDM radar without any additional manipulations of its hardware and waveform. To this end, the proposed system utilizes the ADC sampling rate of B/L to sample the received baseband signal with a bandwidth of B, where L is a positive proper divisor of the number of subcarriers. This divides the baseband signal into L sub-bands, folding into a sub-Nyquist frequency band due to aliasing. By leveraging known modulation symbols of the transmitted signal, the folded signal can be unfolded to the full-band signal. This allows an estimation of target ranges with the range resolution of the full signal bandwidth B without the degradation of the maximum unambiguous range. During the signal-unfolding process, the signals from other sub-bands remain as symbol-mismatch noise (SMN), which significantly degrades the signal-to-noise ratio (SNR) of the detected targets. It also causes weaker targets to be submerged under the noise in range profiles. To resolve this, a symbol-mismatch noise cancellation (SMNC) technique is also proposed, which reconstructs the interfering signals from the other sub-bands using the detected targets and subtracts them from the unfolded signal. As a result, the proposed sub-Nyquist sampling OFDM radar and corresponding signal processing technique enable a reduction in the ADC sampling rate by the ratio of L while incurring only a 10 log10 L increase in the noise due to noise folding. This is validated through simulations and measurements with various sub-sampling ratios.