The C-band frequency is used worldwide by fixed satellite services (FSS) operators to eliver TV transmissions, distancelearning, telemedicine, disaster recovery, meteorological and earth observation services, and also by certain military services. Today, there are approximately 160 geostationary satellites operating in the C-band frequency worldwide. In addition, two out of every three commercial satellites under construction will utilize C-band. The deployment of broadband wireless access (BWA) services, including WiMax, has been gaining momentum in several countries. BWA equipment, slated to operate within the 3.4-3.7 GHz ranges of the FSS extended C-band frequency, has been demonstrated to severely interfere with satellite communications operating within the C-band. Early Indications With several national administrations having designated portions of the C-band for terrestrial wireless applications, including BWA and future mobile services, massive interruptions of satellite services, radar and microwave links has occurred in those regions. Interference has also been reported in other parts of the world, including Australia, Bolivia, Fiji, Hong Kong, Indonesia, Pakistan, Kazakhstan, and Sub-Saharan Africa. Compatibility testing in areas where WiMax services are being implemented has clearly indicated the potential for significant threat to satellite services operating in Cband. A BWA field trial in Hong Kong, for example, inadvertently knocked off the TV-signal feeds to an estimated 300,000 households throughout Asia.Taking on Spectrum Sharing The satellite industry mobilized effectively to lobby the ITU and governing organizations against sharing the 3.4-3.7 GHz ranges of the FSS extended C-band frequency spectrum. Several prominent organizations, including APSCC, the Asia- Pacific Broadcasting Union, Asia- Pacific Telecommunity, and the Global VSAT Forum (GVF),
When Broadband Wireless and Satellite Services Collide SATELLITE TRENDS The well organized “no change” lobbying campaign orchestrated by the satellite industry resulted in a landlark decision during WRC'07 to preserve the C-band srpectrum for interference- free delivery of satellite communications. Robert Ames President and CEO SUIRG, Inc. 34 APSCC Quarterly Newsletter ted position papers to the ITU while major satellite operators vigorously engaged the ITU and other regulatory administrations on this issue. In preparation for the November ITU World Radiocommunication Conference (WRC) 2007, the Satellite Users Interference Reduction Group (SUIRG), in collaboration with GVF, the U.S. Navy and several other industry organizations conducted a field test to assess whether WiMax systems would cause severe interference to satellite systems and to measure the xtent of such interference. The test was conducted in two phases in RF-quiet areas to ensure no external signals contaminated the test results.
Testing was performed using a Prodelin-provided fixed satellite service antenna, Vertex/RSI-provided LNA and a WiMax unit. The NSS 806 satellite, located at 319.5°E, was used for both phases of the test with the baseline video signal sent from a TT&C earth station in Manassas, Virginia. The FSS antenna was aligned to receive a video program channel at 3,515 MHz. Phase 1: The testing was conducted in Punta Gorda, Florida where the FSS antenna stayed at a fixed location and the WiMax transmitter, positioned at a slightly elevated level of about 3 meters, was moved to a variety of locations. The FSS receive C/N (carrier/noise) was set to a nominal 10 dB. At the receiver down-converter (D/C) output, the Bit Error Rate (BER) and digital power of the carrier were measured to establish a baseline. The WiMax transmitter and omni-directional antenna were fixed to a vehicle and set to transmit at various frequencies and power outputs. Field testers adjusted the WiMax transmitter to various frequencies and various output power levels. C/N, I/N (interference /noise), BER, and video quality results were then measured at the FSS antenna along with spectrum plots for each phase of the test. Phase 1 testing was designed to simulate a subscriber unit operating within the vicinity of an FSS antenna system. Phase 2: The second test phase was held in the Southern Maryland and Northern Virginia areas. The WiMax antenna and base station were mounted on a water tower at an elevation of 50 meters, with a down tilt angle of 8 vertical (typical of cellular tower antennas). The FSS antenna was moved to several locations transmitting at differing angles from the WiMax antenna. Before the start of Phase 2 testing the C/N, I/N, BER, and video quality results were measured at the FSS antenna along with spectrum plots for each phase of the test. These results acted as a baseline for the Phase 2 testing.
The FSS antenna was moved varying distances and placed at differing angles relative to the fixed WiMax transmitter, with the same measurements made at each location. Field testers adjusted the WiMax transmitter to various frequencies and various output power levels, and measured the same parameters as in Phase 1. The purpose of Phase 2 testing was to provide field data relative to the distance required to meet the maximum long-term WiMax generated IN of -10 dB specified for an exclusion zone where WiMax systems could not be installed. Results the WiMax Forum provides for an interference to- noise ratio of -10 dB, whereby the WiMax signal should be at least 10 dB below the carrier noise floor. However, the findings of the field test indicate significant interference where the lowest I/N level measured at the test FSS antenna was found to be 7 dB above the noise floor. In addition, the WiMax base station and antenna used during Phase 2 have a maximum Eq uivalent Isotropic Radiated Power (EIRP) of 34 dBm. ITU studies and regulating bodies have used 44 dBm for the protection of FSS earth stations. Extrapolating the test data for defining the distance required between FSS and WiMax systems indicate an exclusion zone of 280 km, which would restrict WiMax systems to extremely remote locations. “The results identified significant levels of interference generated by the WiMax system,” said Robert Ames, President of SUIRG. “The importance of C-band services dictates urgency when dealing with this potential threat. We hope that the results of our field test will make a difference in the decision-making process for re-allocating this critical frequency for terrestrial wireless services.” The well organized “no change” lobbying campaign orchestrated by the satellite industry resulted in a landmark decision during the ITU World Radiocommunication Conference (WRC) 2007, held 22 October- 1 November in Geneva, to preserve the C-band spectrum for interference- free delivery of satellite communications. The resulting decision restricts International Mobile Telecommunications (IMT), including WiMax, from any part of the satellite C-band (3.4-4.2 GHz). The ITU table of allocations remains unchanged, with the limited number of countries in favor of change identified in an opt-in footnote. By taking this approach, the world’s regulators participating in the WRC have made it clear that the C-band is off limits for IMT and have preserved the precious spectrum for satellite communications. The WRC further restricted IMT, specifying adherence to stringent requirements for the protection of existing and future satellite services in the C-band, including transborder protection. For example, in Region 2 (the Americas and the Caribbean), there is no identification for IMT, just an upgrade through a footnote, in 14 countries of the mobile service allocation in 3.4-3.5 GHz. In Region 3, only eight countries inserted their name to the footnote identifying IMT. Only in Region 1 was there broader support from countries to be included in the footnote identifying IMT for national use.
