1、 Rec. ITU-R RS.1749 1 RECOMMENDATION ITU-R RS.1749 Mitigation technique to facilitate the use of the 1 215-1 300 MHz band by the Earth exploration-satellite service (active) and the space research service (active) (Question ITU-R 234/7) (2006) Scope This Recommendation describes the mitigation techn
2、ique of using filtering with Fourier transformation of the received signal. This technique applies to interference to synthetic aperture radars (SARs) in the 1 215-1 300 MHz band from other services with relatively small bandwidth. This Recommendation also provides typical parameters for spaceborne
3、active sensors to be used in the development of additional mitigation techniques. The ITU Radiocommunication Assembly, considering a) that the 1 215-1 300 MHz band is allocated on a primary basis to the Earth exploration-satellite service (active); b) that this band is used by spaceborne synthetic a
4、perture radars (SARs) which applications are to monitor, under all-weather and day and night conditions, deformation of the Earths surface in most land areas, natural disasters, the environment, forests, land use, and others; c) that the 1 215-1 300 MHz band is also allocated to the radiolocation se
5、rvice on a primary basis, and to the radionavigation service on a primary basis in a certain number of countries; d) that Recommendations ITU-R SA.516 and ITU-R SA.1282 show that the operation of SARs is possible without harmful interference in the same frequency band as systems operating in the rad
6、iolocation service, including wind profiler radars, with the possible exception of radio-location service systems using frequency-modulated pulsed radars; e) that performance and interference criteria of spaceborne active sensors are given in Recommendation ITU-R SA.1166; f) that air route surveilla
7、nce radars (ARSRs) with higher isotropically radiated powers than the main beam powers of wind profiler radars have been in operation in this band for many years and harmful interference to spaceborne active sensor operations is normally not observed, although degraded performance is sometimes obser
8、ved which may be attributed to ARSR transmissions, recommends 1 that a mitigation technique applicable to the spaceborne active sensors as shown in Annex 1 could be used to reduce interference from radiolocation and radionavigation radar systems operating in the 1 215-1 300 MHz band to these sensors
9、; 2 that typical parameters of spaceborne active sensors operating in the 1 215-1 300 MHz band given in Annex 2 should be used in the development of additional mitigation techniques. 2 Rec. ITU-R RS.1749 Annex 1 Mitigation technique for interference to spaceborne SARs 1 Introduction At some location
10、s on Earth, bright lines appear in the images of the L-band Synthetic Aperture Radar/Japanese Earth Resources Satellite-1 (L-SAR/JERS-1). These bright lines are due to harmful radio frequency interference (RFI) from terrestrial radars. It has been shown that it is possible to eliminate the interfere
11、nce that causes these bright lines by conducting frequency analysis of the input data. The use of this technique will make it possible to resolve the current problem of RFI to SARs operating in the 1 215-1 300 MHz band. 2 Method and results 2.1 Method The power level of the interfering signal is lar
12、ger than that of the desired signal of the SAR as the interfering signal is a direct emission from the transmitter of terrestrial radars. So, when a Fourier transformation on the received signal is performed, the interfering wave components appear as spikes on the frequency axis. Focusing on these c
13、haracteristics, as a pre-processing operation of range compression, we compare the power of each frequency “bin” with both the power spectra taken by Fourier transformation from the received signal and the original SAR signal (assuming that each components total power is equal to the desired compone
14、nt of the received signal) and 0 is adopted for the power of the specified frequency “bins” that have more power than expected (hereinafter referred to as “filtering”). Furthermore, considering that the interference components that are not correlated with the SAR signal are suppressed by about 30 dB
15、 through range compression, and to prevent original signal loss, a 3 dB or more difference is adopted as the criterion between the desired signal and the interference in this case. When processed using longer time units, there is a tendency for spiked frequencies to scatter widely among the frequenc
16、y spectrum and occasionally to result in the loss of the desired signal. For this reason, the received signal is divided into appropriate segments and then processed by methods such as Fourier transformation. (In this process, 1 024 azimuth lines are regarded as 1 segment.) 2.2 Interference suppress
17、ion process Specific procedures for the interference suppression process are as follows: Step 1 : Divide received signal, including interference, into small segments Signal of segment: Sr= received signal including interference, fr= SAR reference signal (power adjusted with Sr)Step 2 : Apply Fourier
18、 transformation to each segment Transformed spectrum: F(Sr), F(fr) Step 3 : Compare power in each frequency bin Compare |F(Sr)| to |F(fr)| Rec. ITU-R RS.1749 3 Step 4 : Identify frequency bins containing interference I = |F(Sr)| |F(fr)| 3 dB Step 5 : Generate filter Filter: A(): I 3 dB A() = 0, I 200 15/60
