Communications, Radar & Electronic Warfare (201.. - Index of

94 Communications, Radar and Electronic Warfare• sectored antennas or null steering for both interferer and victim;• frequency re-assignment for either interferer or victim.The selection of which mitigation method is applied is usually based on the amountof interference and the implications of the potential changes. Some typical considerationsinclude:• Power management: one approach is to reduce the power of the interferer, to benefitfrom the change in relative signal strength. However, reducing the power of theinterferer will also reduce its service area and this will have an effect on networkcoverage and capacity in the region around the interfering base station.• Antenna height: the antenna heights of either the interferer or victim can be reduced(or both). This will have the effect of reducing the range of the interferer if its antennaheight is reduced (again this may have a knock-on effect to the overall networkcoverage and local capacity). The victim antenna height can also be reduced. Thiscan help in the situation where the reduction in height will result in benefits fromterrain or clutter shielding. Again, of course, the coverage area of the victim will bereduced in this case.• Antenna tilting: for antennas that have vertical directivity, it is possible to orientantennas used for paths within the horizon such that the energy radiated towards thehorizon is reduced. This will have the effect of maintaining the coverage in thewanted area but reducing interference outside of it.• Sectored antennas and null steering: antennas with directional patterns in thehorizontal plane can be used to minimise interference in the direction of the victimor interferer (as required). Antennas that have a null (very low response in aparticular direction) can be used to spatially filter out particular interferers. Thisapproach can only be used when the direction of the interfering energy is known, andthus it is applicable to the condition of base station to base station interference.• Frequency Assignment: either the victim or interfering system can have theirfrequencies changed to prevent interference between them. This of course maycause interference with other spectrum users and thus should only be done with care,and with checks to identify any potential problems that may be caused by the change.References and Further ReadingAI/ mternet references correct at tlllle oj writing.CEPT (2002), ADJACENT BAND COMPATIBILITY BETWEEN TETRA TAPS MOBILE SERVICES AT 870 MHz,http·l!wwwcrodocdb.dklDocsfdoc98fofficiallpdfIECCREPOI4 PDFCClR Report 945. MetllOd for the Assessment of Multiple Inleljerence.CCLRC RAL, dB Spectrum, Transfinile Systems, UniverSIty of York (2007), Model/mg Interference from MultipleSources. http Ilwww ofcomorg uklresearch/lechnology/research/prop/multmler/reporl.pdf.Saunders, S., Aragon-Savala, A (2007), Antennas and PropagatIOn jar Wlreles\ Coml1llllliwtions Systems, Wiley­Blackwell, ISBN 978-0470848791.