Interference Elimination via Minimum Mean Square Error on Phased-Array Weather Radar Using Angular Imaging Technique

Currently, there are many radars installed in Japan, especially in urban areas. These radars are used for various applications such as weather observation, coastal surveillance, and air traffic control. Various information obtained from the radars have made a great contribution to social infrastructure. However the problem of interference waves is frequently caused when these radars are operated at the same time for different purposes. Radars are affected each other as interference waves due to the limited frequency band and small Japanese land.

Focusing on the X-band Phased Array Weather Radar (PAWR), a transmitted wave of the radar is a fan-shaped transmission beam, with a narrow beamwidth (1.2 [deg]) in azimuth and a wider beamwidth (5.0 [deg]) in elevation, the radar receives and gives more influence of interference waves.

In this research, a signal processing method for interference elimination via minimum mean square error (MMSE) is proposed. Signal processing methods via MMSE were proposed for various weather radar signal processing such as phased array beam digital beam forming [Yoshikawa et al. (2013)], pulse compression [Kikuchi et al. (2017)], and Doppler spectral processing, and showed remarkable performances. The proposed method is based on a governing equation which contains radar received signals and interference signals from the other radar. Here, waveform of the other radar is assumed to be known. MMSE solutions for both the radar received and interference signals can be analytically derived. Since the MMSE method need to be performed iteratively, the proposed method calculates iterations of MMSE method alternatively to the radar received and interference signals_.

In order to discuss the validity of the proposed method, the numerical simulation has conducted. In the simulation, the modulated long pulse, which has the pules width of 74 micro-seconds, and the short pulse, which has the pules width of 2 micro-seconds, are used as the radar transmitted signal, and as interference signals, respectively. The specification of the transmitted and interference signals are formed based on the specification of the operating PAWR.

As a result of the simulation, when a matched filter (MF), which is one of the most conventional pulse compression method, was applied to the radar received signal including the interference signals, the interference signals had an intensity of 5 dB, whereas when the proposed MMSE method was applied, the intensity decreased to -15 dB which was almost equal to the noise level. Also, when the proposed MMSE method was applied to the radar received signal including the interference signals which have various waveforms, the intensity of the interference signals decreased to the noise level in all cases. From these results, it was shown that interference signals can be eliminated by using the proposed MMSE method. It can be expected that interference signals can be eliminated when the proposed MMSE method is applied to a radar received signal including interference signals from any other radars.

References

Kikuchi, H., E. Yoshikawa, T. Ushio, F. Mizutani, and M. Wada, 2017 :Adaptive Pulse Compression Technique for X-Band Phased Array Weather Radar, IEEE Geoscience and Remote Sensing Letters, 14, 10, 1810-1814.

Yoshikawa, E., T. Ushio, Z. Kawasaki, S. Yoshida, T. Morimoto, F. Mizutani, and M. Wada, 2013: MMSE Beam Forming on Fast-Scanning Phased Array Weather Radar, IEEE Transactions on Geoscience and Remote Sensing, 51, 5, 3077-3088.