A novel parameter estimation method of interrupted
sampling repeater jamming
Yunyun Meng
1
, Lei Yu
1
*, Yinsheng Wei
1
, Peng Tong
1
1
School of Electronic and Information Engineering,Harbin Institute of Technology,Harbin, China
*Email address: (yu.lei@hit.edu.cn)
Abstract—Interrupted sampling repeater jamming(ISRJ) is
an effective coherent jamming type for wideband chirp radar.
Different parameter settings correspond to different jamming
strategies, and the generated false target jamming can achieve
effects of both deception and suppression. In this paper, a
parameter estimation method for ISRJ with intra-pulse
modulation is proposed by analyzing the jamming
characteristics. The time-frequency(TF) distribution result can
be used to determine the jamming strategy. The sampling
duration and repeat sampling interval are estimated by Hilbert
transform and peak detection, and then sampling number and
forwarding times can be calculated. The results of simulation
and experimental data prove the validity of this method.
Keywords—LFM, ISRJ, TF, parameter estimation
I. INTRODUCTION
Linear frequency modulation(LFM) signal is widely used
in wideband radar system, which greatly improves the
resistance to noise jamming and non-coherent jamming.
Therefore, active deception coherent jamming based on
digital radio frequency memory(DRFM) has received
extensive attention. Among them, ISRJ is rapidly developed
in recent years, which can form multiple false target
deception and suppression jamming by intermittent sampling
and forwarding radar signal.
A jamming strategy named Chopping & Interleaving
(C&I) was proposed in 2006. The jammer partially intercepts
the radar signal, and then delays and forwards the sampled
slice multiple times. C&I jamming appears as a series of
coherent false target groups in the range direction after pulse
compression(PC) [1]. The mathematical mechanism of ISRJ
was developed in [2], where the effectiveness of jamming
under wideband and narrowband conditions was discussed,
as well as the influence of repeat sampling interval and
jamming power on the jamming effect was analyzed. In [3],
the overall framework of ISRJ technology was summarized,
including principle of jamming, matched filtering, de-chirp
processing. At the same time, the amplitude, spatial
distribution and phase characteristics of false targets were
discussed and the key factors that determine the
characteristics of false targets were pointed. At the same time,
jamming types that add additional modulation based on ISRJ
are also developing. A coherent noise jamming method
based on intercepted sampling and pseudo-random sequence
phase modulation was proposed. The jamming signal
bandwidth is extended after phase modulation. This
characteristic causes jamming to form multiple false targets
in the frequency domain after de-chirp processing[4].
The jamming strategy is flexible and directly related to
the setting of key parameters. Jamming strategy can be
identified by effectively estimating jamming parameters.
Meanwhile, the estimation results can provide premise and
basis for jamming countermeasure. Hence, some papers are
involved in this topic. Intra-pulse characteristics was
analyzed in the time domain and the periodic component was
extracted by threshold setting for PC results, the parameter
estimation of sampling duration and period was obtained
according to the time-frequency dual relationship of LFM
radar[5]. However, the method is not applicable to multiple
forwarding situations. In [6], the results of jamming
parameter estimation were acquired by wavelet de-noising,
amplitude difference and peak detection. The STFT results
of radar echo signals were used for ISRJ parameter
estimation by calculating the correlation values of the
sequences and using the peak detection algorithm based on
the discontinuity and periodicity of ISRJ in the TF domain[7].
In [8], the key parameters were estimated based on TF
analysis and time-domain deconvolution processing.
However, this method is not suitable for the case where
jammer-to-noise ratio(JNR) is relatively low and intra-pulse
modulation exists. Therefore, the algorithm performance
should be further evaluated. Moreover, the countermeasures
against ISRJ are not fully studied. The jamming was
suppressed by reconstruction and cancellation based on
parameter estimation results[8]. According to the
discontinuity of ISRJ in time domain and time-frequency
domain, jamming suppression methods based on band-pass
filter design were proposed[9-11].
In this paper, a parameter estimation algorithm based on
Hilbert transform and peak detection is proposed, which is
suitable for ISRJ with intra-pulse modulation and low JNR.
The remaining article is organized as follows: In Section II,
the model and effect of ISRJ are given. In Section III, The
jamming strategy discrimination and parameter estimation
method are researched. In Section IV, the algorithm
processing and analysis results based on simulation data and
experimental data are given. Finally, the main conclusions
are drawn in Section IV.
II. PRINCIPLES OF ISRJ
A. Jamming signal model
DRFM intercepts and stores a slice of radar signal, and
then delays and forwards the sampled slice multiple times.
The intercept-store-forward process is repeated until the
falling edge of the radar signal is detected. The jamming
principle of ISRJ is shown in Fig. 1.
Assumed that the intercepted conventional radar signal
form adopts a LFM signal, and the interrupted sampling
pulse signal p(t) is a rectangular envelope pulse train having
a pulse width of T
w
and a repetition period of T
s
, it can be
expressed as