Ruminations on the electronics industry from David Manners, Senior Components Editor on Electronics Weekly.
Putting Wimax Out Of Business
Wimax could be killed off by a report from the Satellite Users Interference Reduction Group (SUIRG) whjich states that Wimax interferes with satellite signals transmitted in the C-band frequency.
“We’re not trying to put WiMax out of business,” Robert Ames, president and CEO of SUIRG, told Satellite Today, “but C-band is in many ways the lifeline of the satellite industry. Protecting that spectrum from the threat of interference posed by sharing it with broadband wireless access services is of paramount importance.” SUIRG, based in Florida, conducted tests on the compatibility of fixed satellite services (FSS) and WiMax services sharing the C-band spectrum. The SUIRG report begins: ‘Several national administrations around the world have designated portions of the frequency band 3.4– 4.2 GHz for use by terrestrial wireless applications such as WiMAX and future mobile services (“IMT advanced,” beyond 3G, 4G). However, this band, commonly referred to as the C-band, is already in use by satellite services, radar systems and domestic microwave links. C-band services cover large areas, facilitate intercontinental and global communications and provide a wide range of services in developing countries. The C-band provides a robust, reliable platform for such critical applications as distance learning, telemedicine, universal access, disaster recovery, and television transmission in many remote and tropical regions. The sensitivity of C-band satellite receiving systems makes them particularly sensitive to disruptions by mobile terrestrial frequencies in immediately adjacent bands.’ The report goes on to say: ‘Field tests by the Office of the Telecommunications Authority in Hong Kong concluded that use of frequencies for terrestrial wireless services in the Extended C- and Standard C-bands was not practical.’ Lat year, the Global VSAT Forum (GVF) held an Emergency C-band Summit in Washington, to confirm whether WiMAX systems would cause severe interference to satellite systems operating in an adjacent frequency band. Subsequent discussions among the WiMAX Forum, GVF and the Satellite Users Interference Reduction Group (SUIRG) agreed to conduct a side-by-side test in advance of the World Radio Communication Conference 2007 (WRC 07), which occurred in November. The primary objective of the test plan was to measure the interference levels generated by fixed WiMAX transmissions into a Fixed Satellite Service (FSS) satellite receiving station. The method employed was 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: Phase 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 modelled WiMAX subscribers in a nomadic deployment affecting FSS. Tests conducted within the immediate area (up to 1 km away) showed that the digital signal was rendered unacceptable for use. Phase 2: The WiMAX base antenna was fixed at a height of approximately 50 metres 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 testing. This was to model WiMAX base units being deployed on cellular towers. The results of the testing showed that the WiMAX transmit signal could cause significant problems to a digital signal well in excess of 12 km away. At the extreme measurement distance, the video program was fully operational with the WiMAX carrier centred on the video carrier. However, the data BER was degraded from a nominal 10-8 to a BER of 10-4 which is an unacceptable quality of service in the digital telecommunications industry. ‘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’, concludes the report.Tags: band spectrum, frequency band, global vsat forum, national administrations, television transmission