Intermittent sampling and forwarding interference

DRFM Jamming strategy

Intermittent sampling and forwarding interference （Interrupted sampling repeater jammer,ISRJ） It is a radar active deception jamming , The implementation of this interference depends on digital RF storage （digital radio fequency memory,DRFM） technology ,DRFM The principle is very simple , It can receive the RF signal from the radar , After sampling, it is stored and sent .DRFM There are two ways to intercept radar signals , One is full pulse storage , One is intermittent sampling storage . So it's called Siyi , One is to collect all the signals transmitted by the radar and then send them , One is to collect only a small segment and then send it .

Interference one ： Full pulse storage

When full pulse storage mode is adopted , Jammer can achieve maximum signal processing gain , however , Since the forwarding delay is greater than the duration of the pulse , Therefore, the jammer can only repeat at the next pulse interval （Pulse repeat interrupt,PRI） Send inside . In view of this feature , The waveform diversity proposed by people is an effective method to combat this kind of interference . for example , Each pulse retransmission interval sends different phase coded LFM signals , Different matched filters are used to focus the target echo and jamming signal , The position of the interference signal is estimated and suppressed . Compared with intermittent storage , The interference in the full pulse storage mode is relatively easy to suppress .

Interference II ： Intermittent sampling storage

It is due to the interference under full pulse storage , The delay between sampling and sending is large , Easily suppressed , Intermittent sampling storage mode has been proposed , stay 2006 In, scholars from National University of defense technology proposed intermittent sampling and forwarding jamming （Interrupted sampling repeater jammer,ISRJ）,[ reference ： Wang Xuesong , Liu Jiancheng , Zhangwenming , Fuqixiang , Liu Zhong , Xiexiaoxia . The mathematical principle of intermittent sampling and forwarding interference [J]. Science in China E Compilation : information science ,2006(08):891-901.]. In this mode, the jammer first intercepts a segment of the radar signal , Then delay and forward the fragment several times . The principle of intermittent sampling and forwarding interference is shown in the figure below . By changing the interception width and the number of forwarding , It can achieve the double effects of deception and suppression . Research in this area is quite popular , There is a lot of literature .

chart 1. Schematic diagram of intermittent sampling and forwarding interference Above picture , A radar pulse is sliced into 9 paragraph （slice）,Intercepting This is the sampling phase ,Forwarding It is the forwarding phase .

Mathematical model of intermittent sampling and forwarding interference

For the most commonly used LFM signal , The sample fragment can be expressed as ：
$$S_{\mathrm{I}}(t)=\sum _{n=0}^{N-1}\mathrm{rect}\left(\frac{t-\tau -n{T}_{\mathrm{u}}}{T_{\mathrm{I}}}\right){\mathrm{e}}^{\mathrm{j}\pi K_{\mathrm{r}}(t-\tau {)}^2}\text{\hspace{1em}(1)}$$
among $\mathrm{r}\mathrm{e}\mathrm{c}\mathrm{t}(\cdot )$ Is a rectangular window function ,$T_{\mathrm{I}}$ Is the slice width ,$N$ Is the number of slices ,$\tau$ Is the slice delay . Then a complete interference signal can be expressed as ：
$$\begin{array}{rl}{S}_{\mathrm{J}}(t)& =\sum _{m=1}^M{S}_{\mathrm{I}}\left(t-m{T}_{\mathrm{I}}\right)\\ & =\sum _{m=1}^M\sum _{n=0}^{N-1}\mathrm{rect}\left(\frac{t-\tau -n{T}_{\mathrm{u}}-m{T}_{\mathrm{I}}}{T_{\mathrm{I}}}\right){\mathrm{e}}^{\mathrm{j}\pi K_{\mathrm{r}}{\left(t-\tau -m{T}_{\mathrm{I}}\right)}^2}\end{array}\text{\hspace{1em}(2)}$$

When does the intermittent sampling and forwarding interference end ？

In the paper [Zhou, C., Q. Liu and X. Chen (2018). “Parameter estimation and suppression for DRFM-based interrupted sampling repeater jammer.” IET RADAR SONAR AND NAVIGATION 12(1): 56-63.] There is a saying :
the intercept-delay-forward process is repeated for several cycles until the falling edge of the transmission signal is detected.
He means , This interception - Delay - The forwarding process will terminate when the falling edge of the radar signal is detected .