REPUBLIC OF SERBIA

MINISTRY OF DEFENCE

www.mod.gov.rs

MINISTRY OF DEFENCE

Material Resources Sector

Defensive Technologies Department

Military Technical Institute

www.vti.mod.gov.rs

INTERFERENCE CALCULATION IN A RADIO-RELAY NETWORK AT FREQUENCIES ABOVE 70GHz

Miroslav Perić

Vlatacom d.o.o. , Beograd, tel. 063 24 77 20, e-mail: Miroslav.Peric@vlatacom.com

Dragana PERIĆ

IMTEL Komunikacije A.D., Beograd, tel. 064 823 6524, e-mail: dragana@insimtel.com

Vladimir ORLIĆ

Vlatacom d.o.o. , Beograd, tel. 063 89 38 606, e-mail: Vladimir.Orlic@vlatacom.com

Abstract: Radio-relay links at frequencies above 70GHz are suitable solution for realization of dense high capacity (above 1Gbit/s per link) radio network, since small size antennas could achieve good gain, small main lobe width and good suppression of side lobes. The main drawback of such systems susceptibility to rain attenuation, which causes capacity reduction or outage of some links in then networks. Due to this effect maximal hop ranges are limited to several kilometers. Interference in network additionally degrades fading margins, and therefore hop ranges also. In this paper we describe method for interference calculation, which differs from similar methods at lower frequencies by: (a) it considers both azimuth and elevation unwanted signal discrimination and (b) it considers also the effect that rain cell besides wanted signal, also attenuated interfering signal. Both effects contribute that more dense networks could be achieved. Proposed method is demonstrated at network which covers geographical area of 7 x 7 km. A method for results visualization in Google Earth geographical information system, based on satellite images is proposed. It is shown that this method greatly helps in determining potential interference problems in network, which might be solved by proper frequency and/or polarization planning.

Key words: Radio-relay link, millimeter wave communication, interference, propagation, geographical information system.