SUIRG Reports Unacceptable WiMAX Interference

The Satellite Users Interference Reduction Group (SUIRG) has released their formal findings of a field test on the compatibility of Fixed Satellite Services (FSS) and WiMAX services sharing the C-band spectrum. SUIRG, a non-profit association comprised of both private and public sector satellite organizations, is dedicated to combating the increasing and costly problem of satellite radiofrequency interference (RFI). The test, conducted in the latter quarter of 2007, conclusively demonstrated that WiMax communications pose a significant interference threat to satellite signals transmitted in the C-band frequency. The field test was performed with support from several key industry organizations. The primary objective of the plan was to measure interference levels generated by fixed WiMAX transmissions into an FSS satellite receiving station. The method employed taking measurements of C/N (carrier/noise), I/N (interference/noise), BER (bit error rate), and spectrum plots of a satellite down link video channel. Testing was performed in 2 phases and the results showed that the WiMAX transmit signal could cause significant problems to a satellite digital signal well 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, the data BER was degraded from a nominal 10-8 to a BER of 10-4. This is an unacceptable quality of service in the digital telecommunications industry.

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 over 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 website at http://www.suirg.org.