|
C-band Interference Field Test Report
C-band frequency sharing between satellite and terrestrial wireless has been a hotly contested topic of late. SUIRG members and the satellite industry as a whole have been very vocal on the need to reserve the precious C-band spectrum for satellite communications. The controversy prompted SUIRG, in conjunction with the Global VSAT Forum (GVF), the U.S. Navy and several other satellite organizations, to perform a live field test in the United States in late October.
The Field Test
 A coordinated effort was undertaken to confirm whether WiMax systems would cause severe interference to satellite systems operating in the 3.4-4.2 GHz-frequency band. The test was conducted in two phases in RF quiet areas to ensure no external signals contaminated the test results:
Phase 1: A Prodelin-provided Fixed Satellite Service (FSS) antenna, Vertex/RSI-provided LNA and a WiMax unit were moved to several locations with various angles and distances up to 1 km from the FSS antenna. The testing simulated a subscriber unit operating within the vicinity of an FSS antenna system.
Phase 2: In this case, the WiMax base antenna was fixed at a height of 50 m on a water tower, while the FSS antenna was positioned at several locations at various angles and significantly greater distances from the WiMax antenna than in Phase 1. The purpose of Phase 2 was to provide field data as to the distance required to meet the maximum long-term WiMax-generated I/N (interference/noise) of -10 dB specified for an exclusion zone where WiMax systems could not be installed.
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 (Telemetry, Tracking & Control) earth station in Manassas, Virginia. The FSS antenna was aligned to receive a video program channel at 3,515 MHz.
Phase 1 was conducted in Punta Gorda, Florida where the FSS antenna stayed at a fixed location while the WiMax transmitter, at a slightly elevated level of about 3 m, was moved to a variety of locations. The FSS receive video signal 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, BER, and video-quality results were then measured at the FSS antenna along with spectrum plots for each phase of the test.
Article continues »
| 
