Parameter estimation of frequency shift keying radar signal intercepted by Nyquist folding receiver using periodic linear frequency modulation local oscillator

Abstract

Frequency shift keying (FSK) signal has been widely used in modern radar systems. To intercept the FSK radar signal with a high interception probability, radar reconnaissance receiver should have an ultra-wideband receiving ability. The Nyquist folding receiver (NYFR) is a novel non-cooperative ultra-wideband receiver and it requires a small amount of equipment. When the FSK radar signal is intercepted by the NYFR, the corresponding output is a hybrid modulation signal. Therefore, it is necessary to investigate the parameter estimation of FSK radar signal intercepted by the NYFR. Herein, based on the NYFR using sinusoidal frequency modulation local oscillator (LO), the drawbacks of several existing parameter estimation methods are first analysed. To overcome these drawbacks, the NYFR architecture is improved by changing the LO modulation type to periodic linear frequency modulation. Then, based on the improved NYFR, a novel parameter estimation approach is proposed according to the LO modulation characteristics and the template matching rule. The proposed method is suitable for different kinds of common FSK radar signal code schemes and its computational load is low. At last, several simulation results show the merits of the proposed method.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Analysis of Sampling Aperture Impact on Nyquist Folding Receiver Output

“…1 [3]. The nonuniform pulse train p(t) is generated from the LO by using the sample pulse template p(t) and the RF sample clock at zero-crossing rising (ZCR) time t k [6], [9]. In the LO, the RF sample clock is controlled by a modulation, and the typical modulation is the sinusoidal frequency modulation (SFM) [3], [4].…”

“…In Fig. 1, the LO modulation using the SFM can be expressed as θ(t) = z θ sin (2π f θ t), where z θ = T θ ∆F is the modulation coefficient, T θ = 1/ f θ is the LO modulation period, f θ is the modulation frequency and ∆F is the bandwidth of the LO modulation [6], [9]. The average frequency of the RF sample clock is f s1 that equals the bandwidth of NZ when the input is complex, and the cut-off frequency of F( f ) is f s = f s1 [5].…”

“…where the NZ index is k H = f ix ( f c / f s1 ) and it can indicate the carrier frequency of the input signal [3], [12]. On the other hand, considering the simplified situation and according to (5), the NYFR output in time domain is [9]…”

“…Finally, the impact of sampling aperture on parameter estimation is analyzed. The algorithm of NZ index k H estimation is the multiple channel method [9]. The parameters of the NYFR and the input signal are the same as those in Fig.…”

An improved local oscillator modulation of modulated sampling scheme for multiple mono-pulse radar signals reconstruction

“…The result in ( 12) can be interpreted as the demodulation of the signal in each NZ by using the recover signal r(m) = e jk sin (2πfLOmTADC) , k = 0, 1, • • • , K − 1 and calculating the corresponding DFT results. The process in ( 12) is similar to the method that using the maximum peak value in frequency domain to estimate the NZ index k i based on the SFM demodulation [13,24].…”