Elektronik Destek Sistemleri için Frekans Kestirim Yöntemlerinin Performans Analizi

Öz

Elektronik harp sistemlerinde, tehdit radarının frekansının doğru olarak kestirimi radarın kimliklendirilmesi ve elektronik atak uygulanabilmesi için oldukça önemlidir. Hızlı Fourier dönüşümü (FFT) ve Sayısal anlık frekans kestirimi (DIFM) en yaygın kullanılan frekans kestirim yöntemleridir. Tehdit radarının ara frekans (IF) değeri FFT bin’lerinin tam katı değilse FFT yöntemi ile frekans kestirimi istenilen doğrulukta elde edilemez. Doğruluğu artırmak için genellikle FFT’nin çıkışına interpolasyon teknikleri uygulanır. DIFM yönteminde ise, sayısallaştırılmış I/Q sinyali belirli bir süre geciktirilip eşleniği alınır ve eşlenik ile orijinal I/Q sinyali çarpılarak faz hesaplanır. Bu çalışmada, Jacobsen ve iyileştirilmiş Quinn interpolasyon teknikleri uygulanmış FFT yöntemi ile uygun gecikme süresi hesaplanmış DIFM yönteminin frekans kestirim performansları, işaret gürültü oranı (SNR) değiştirilerek Gauss gürültüsü altında kapsamlı bir şekilde analiz edilmiştir. Ayrıca, gerçek zamanlı sistemler için frekans kestiriminin hızlı olması oldukça önemli olduğu için FFT, FFT ve Jacobsen, FFT ve iyileştirilmiş Quinn ve DIFM frekans kestirim yöntemleri hesaplama zamanı açısından da karşılaştırılmıştır. Her bir yöntem için 100 adet Monte Carlo denemesi uygulanmış ve frekans kestirimindeki hata, ortalama hata kare kökü (RMSE) cinsinden sunulmuştur. Matlab ortamında gerçekleştirilen simülasyonların sonuçlarına göre FFT ve iyileştirilmiş Quinn yönteminin FFT ve Jacobsen yöntemine göre genellikle daha iyi frekans kestirimi yaptığı gözlemlenmiştir. Ayrıca, SNR seviyesi arttıkça, FFT, FFT ve iyileştirilmiş Quinn ve FFT ve Jacobsen yöntemlerine göre DIFM yönteminin daha iyi performansa (düşük RMSE değerine) sahip olduğu gözlemlenmiştir.

Anahtar Kelimeler

• Frekans kestirimi
• İnterpolasyon yöntemleri
• Jacobsen
• Quinn
• FFT
• DIFM

Performance Analysis of Frequency Estimation Methods for Electronic Support Systems

Öz

In electronic warfare systems, accurate estimation of the threat radar frequency is so important for radar identification and electronic attack. Digital instantaneous frequency estimation (DIFM) and fast Fourier transform (FFT) are the most widely used frequency estimation methods. If the intermediate frequency (IF) value of the threat radar is not an exact multiple of the FFT bins, frequency estimation with the FFT method cannot be obtained with the desired accuracy. Interpolation techniques are often applied to the output of the FFT to improve accuracy. In the DIFM method, the digitized IF signal is delayed for a certain time and its conjugate is taken and phase is calculated by multiplying the conjugate with the original I/Q signal. In this study, the frequency estimation performances of the FFT technique that Jacobsen and Improved Quinn interpolation techniques were applied and DIFM method with appropriate delay time extensively analyzed by changing the signal to noise ratio (SNR) under Gauss noise. Also, since fast frequency estimation is so important for real time systems, FFT, FFT and Jacobsen, FFT and improved Quinn and DIFM frequency estimation methods were also compared in terms of computation time. For each method, one hundred Monte Carlo trials were applied and the error in the frequency estimation is presented in terms of the root mean square error (RMSE). According to the simulation results performed in the MATLAB environment, it has been observed that the FFT and the improved Quinn method generally provide better frequency estimation than the FFT and Jacobsen method. In addition, as the SNR level increased, it was observed that the DIFM method had better performance (lower RMSE value) than the FFT, FFT and improved Quinn and FFT and Jacobsen methods.

Anahtar Kelimeler

• Frequency estimation
• interpolation methods
• Jacobsen
• Quinn
• FFT
• DIFM

Kaynakça

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