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Abstract
The Nyquist folding receiver (NYFR) can achieve a high-probability interception of an ultra-wideband (UWB) signal with fewer devices, while the output of the NYFR is converted into a hybrid modulated signal of the local oscillator (LO) and the received signal, which requires the matching parameter estimation methods. The linear frequency modulation (LFM) signal is a typical low probability of intercept (LPI) radar signal. In this paper, an estimation method of both the Nyquist Zone (NZ) index and the chirp rate for the LFM signal intercepted by NYFR was proposed. First, according to the time-frequency characteristics of the LFM signal, the accurate NZ and the rough chirp rate was estimated based on least squares (LS) and random sample consensus (RANSAC). Then, the information of the LO was removed from the hybrid modulated signal by the known NZ, and the precise chirp rate was obtained by using the fractional Fourier transform (FrFT). Moreover, a fast search method of FrFT optimal order was presented, which could obviously reduce the computational complexity. The simulation demonstrated that the proposed method could precisely estimate the parameters of the hybrid modulated output signal of the NYFR.
Highlights
Radar designers try their best to spread the energy of radar signals to multidimensional domains, including time, frequency, and space, making radar signals have a low probability of intercept (LPI) [1,2]
In Reference [22], a new synchronous Nyquist folding receiver (SNYFR) structure based on composite sinusoidal frequency modulation (SFM) local oscillator (LO) is proposed, and a parameter estimation algorithm based on instantaneous autocorrelation is presented
NYFR can achieve high-probability interception of a signal in the entire radar frequency band with a single low-speed analog-to-digital converter (ADC), and broadband signal acquisition can be realized without frequency sweeping in theory
Summary
Radar designers try their best to spread the energy of radar signals to multidimensional domains, including time, frequency, and space, making radar signals have a low probability of intercept (LPI) [1,2]. The RF under-sampling frequency modulation induces a Nyquist zone (NZ) dependent modulation on the received signals that allows separation and recovery of the signal information from a sparse broadband. Since the NYFR output contains the added local oscillator (LO) modulation, its signal processing is more complex compared to conventional receivers. In Reference [21], a parameter estimation algorithm based on peak search in frequency spectrum of the output signal is proposed. In Reference [22], a new synchronous Nyquist folding receiver (SNYFR) structure based on composite sinusoidal frequency modulation (SFM) LO is proposed, and a parameter estimation algorithm based on instantaneous autocorrelation is presented. Effective detection of multi-component LFM signals and accurate parameters estimation are achieved when the SNR is larger than −8 dB.
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