PUNTA GORDA, FLThe Satellite Users Interference Reduction Group (SUIRG), a non-profit association, announced the findings of a field test on the compatibility of Fixed Satellite Services (FSS) and WiMAX services sharing the C-band spectrum. The test, conducted in late 2007, demonstrated that WiMax communications pose a significant interference threat to satellite signals transmitted in the C-band frequency.

The purpose of the test was to validate previous tests and provide conclusive results on the incompatibility of C-band spectrum sharing between FSS satellite transmissions and WiMAX services.

The primary objective was to measure interference levels generated by fixed WiMAX transmissions into an FSS satellite receiving station. The method employed taking measurements of carrier/noise (C/N), interference/noise (I/N), bit error rate (BER), and spectrum plots of a satellite downlink video channel. Testing was performed in two phases:

  1. The FSS antenna remained in a fixed location while a WiMAX base unit was moved to several locations operating at various angles and distances from the FSS antenna to simulate subscriber waveforms. This test modeled WiMAX subscribers in a nomadic deployment affecting FSS. Tests conducted up to 1 km away showed that the digital signal was rendered unacceptable for use.
  2. The WiMAX base antenna was fixed at a height of approximately 50 meters on top of a water tower. The FSS antenna was positioned at several different locations and at various angles and significantly greater distances from the WiMAX antenna (up to 12 km) than during phase 1. This was to model WiMAX base units being deployed on cellular towers.

The test results showed that the WiMAX transmit signal could cause significant problems to a satellite digital signal in excess of 12-km distance. At the extreme measurement distance, the video program was fully operational with the WiMAX carrier centered on the video carrier. However, BER was degraded from a nominal 10-8 to 10-4. This is an unacceptable quality of digital service.

Subsequent calculations based on the initial measured data, and scaling with ITU criteria for WiMAX output power along with additional path loss, resulted in a required separation distance of 278 km to reduce the level of interference to meet the -10-dB specification. Combining the two analyses, from a flat non-blocking terrain to a wooded hilly terrain, results show that the criteria whereby FSS antennas cannot co-exist with WiMAX systems ranges from 50 to more than 200 km dependent upon the local terrain and the WiMAX output levels.

The full text of the WiMax frequency sharing with FSS earth stations field test report and detailed test plan & procedures are available on the SUIRG web site at www.suirg.org.