| WiMAX Wars - What kind of interference can satellite operators expect from WiMAX operation? |
| Posted: January 2009 | ||||||
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Page 7 of 8 6. What kind of interference can satellite operators expect from WiMAX operation?At the FSS earth station antenna the BWA terrestrial signal is much more powerful than the signal from the satellite. Typically, the power-flux density (pfd) of a C-band satellite signal at the FSS earth station antenna is about -122 dBW/m2 while the pfd of a 25 watt BWA transmitter at a distance of 500 meters is around -50 dBW/m2. There is difference in power between the two signals of 72 dB. It is difficult to overcome this power difference either by shielding or filtering. At best, the FSS earth station antenna has a sidelobe/backlobe discrimination of about 30 dB. The interference caused into the FSS earth station can be divided into three types1: a) Co-frequency Interference If no shielding is available at the satellite antenna site, then interference can be caused as distances up to about 150 km. (b) Out-of-band Interference With the existing out-of-band emission limits for BWA transmitters, interference can be caused at distances up to 2 km. If additional filtering is implemented at the BWA base station and the use of outdoor BWA terminal stations is not allowed, the distance may be shortened to about 0.5 km. (c) FSS Receiver Saturation Problem Signals from nearby BWA equipment transmitting in the 3.4 – 3.6 GHz band will cause saturation of FSS receivers with their LNB operating in the 3.7 – 4.2 GHz range. In this case saturation can be caused in satellite receivers located at a distance up to about 1.2 km. Off-the-shelf filters can reduce the interference level by about 10 dB in which case the interference can be caused at distances up to about 0.5 – 0.6 km.
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