Study On The Weak Signal Process Method Of Incoherent Scatter Radar

There are two methods to detect the Ionosphere, point detection and remote sensing. Incoherent Scattering Radar(ISR) is a remote sensing method which can detect the whole Ionosphere. ISR is an important method to know the parameter of Ionosphere, such as the density, drift velocity and temperature of plasma. Because of the long detect distance of ISR, the echo of it can be very weak. To solve the problem, the transmission power of ISR must be megawatt. Besides, the array of ISR need to be very huge.The echo of Software-defined Incoherent Scattering Radar(SDISR) will be weaker because it works with low transmission power and small send-receive array. The Signal to Noise Ratio(SNR) of echo is “-10dB” in average, these echo signal data is useless for us to make a parameter inversion. In order to make these data become useful, this paper mean to study the method of SDISR weak signal denoising. The traditional denoising method of ISR echo is incoherent accumulation, this method works but costs lots of time. But the echo of SDISR need to be real-time processed. The traditional method based on fourier transform can work real-time but have two shorts: first, denoising result isn’t that ideal when met the suddenly change part and the non-stationary part of signal; second, traditional method work in frequency domain, if signal and noise overlap in frequency domain, then this part of noise can not be wipe out. Which wavelet is different, wavelet have a characteristics of multiresolution, at the low frequency part of signal, wavelet have high resolution of time while it have high resolution of frequency at the high frequency part. So we can disintegrate the signal with multiresolution and reconsitution it. Even in the overlap part between signal and noise, wavelet can wipe out the noise. Study the advantage and disadvantage of both mentioned upside, a denoising method which include traditional method and wavelet method has been put forward in this paper, after make sure the steps of this method, simulations has been done to prove the method will work and useful. Besides, it can work real-time. This paper will explain the denoising method in three steps.First, Introduce the base structure of SDISR, learned the waveform design of SDISR and the characteristic of transmitted waveforms.Second, After study the traditional method and wavelet threshold method, and analyzed the possibility that if these methods can work together to denoise. Then put forward a denoising method based on wavelet threshold aim at weak signal. First, learn about the traditional denoising method, and use FFT to preprocess the signal to wipe out part of noise. Then study the wavelet and wavelet threshold denoising, and make some simulation to make sure four steps of wavelet threshold denoising include wavelet function, disintegrate level, threshold function and threshold.Third, use three kind of ISR transmitted waveform, imnoise it with the ISR channel noise. Then denoise these noisy transmitted signals with traditiong method and the method put forward by this paper. And analyze the advantage of wavelet denoising method.The result of simulation prove that the method this paper put forward is useful and better in SDISR system.