Improved Active Interference Canceling Algorithms for Real-Time Protection of 2 nd/3 rd Level Facilities in Electronic Warfare Environment  
[PERSON]  
1 Electronic Warfare Research Center, Gwangju Institute of Science and Technology, Gwangju 61005, Korea; [EMAIL_ADDRESS] (J.L. ); [EMAIL_ADDRESS] (K.H.J. ); [EMAIL_ADDRESS] (Y.C.) Department and Computer Engineering, Seoul National University, Seoul 08826, Korea; [EMAIL_ADDRESS] (J.L.) Department of Electronic Engineering, Inha University, Incheon 22212, Korea (J.  
to reduce them. To date, these facilities have added thicker barriers or shielding filters to meet the internal shielding standards [7]. High costs and space are required to make a shielding facility with a high shielding effect using this method. Among the protection studies, there is a technique of canceling through directly analyzing the penetrated electromagnetic waves, rather than adding a shielding facility or using a shielding filter [8]. In this reference, the penetrated external electromagnetic wave is measured, and the signal is canceled by generating the same signal as the measured electromagnetic wave. The internally generated signal has an identical magnitude and frequency to the measured external electromagnetic waveform, but it is 180 degrees out of phase for eliminating internal interference. This principle is similar to the Active Noise Cancellation (ANC) method used in the acoustic field [9]. Since sound is also a wave, it can create a destructive interference phenomenon that can be used to make a noise-free zone at a particular location. To cancel in real-time, it requires a microphone and speaker, as well as an algorithm capable of processing a signal input through the microphone. The Finite Impulse Response (FIR) filter is mainly used, and various algorithms such as the Filtered-x Least Mean Square (FxLMS) and Filtered Error Least Mean Square (FELMS) exist in the algorithm applied to the filter [10; 11]. Wavefield synthesis and wavefield analysis are based on wave equations using the Helmholtz-Kirchhoff integration without filters [12]. Each of these techniques uses the Helmholtz-Kirchhoff integration and appropriate boundary conditions to calculate the inner field or control the inner field. Several speakers and microphones are placed based on the quiet zone to apply this method. This method is called the massive multichannel ANC [13]. However, it is hard to apply this technique to electromagnetic waves. The most important reason is that the speed of the wave is different. The speed of waves used in electromagnetic waves is 300 million meters per second, like the speed of light, but the speed of waves applied to sound is 343 m per second, which is about 900,000 times different. In addition, the audible frequency uses a frequency of 20 Hz to 20 kHz, while the frequency range used in electronic warfare varies from the UHF band to the W band. It is challenging to produce precisely the same frequency to cancel this frequency band. Additional analysis algorithms are needed to solve this problem, after the first cancellation, since only a slight frequency difference between the external and internally generated waveform can cause amplification rather than cancellation of the internal field. Previous studies have used the matrix pencil method to predict these frequency differences [14]. The MPM can predict the frequency difference very accurately but requires an adequate number of samples to find the frequency. The time required to collect this sample can be fatal to the protective equipment in some cases. The real-time noise reduction technique presented in this paper can estimate the frequency difference much faster than the conventional methods under the assumption that the externally incident electromagnetic waves are complex sinusoids. Theoretically, it can be obtained with only one sampling information, but the accuracy is much lower in noisy situations.