Effect of multipath fading on millimetre wave propagation: a field study A.A. Ali M.A. Alhaider Indexing terms: Muftipathfading, Millimetre waue propagation Abstract: Analysis of clear air fading encountered on millimetric wave and infrared radio links are presented. The analysis is based on data obtained during a four-year field study in the city of Riyadh, Saudi Arabia. The region can be con- sidered as a typical arid climate where the rate of evaporation is higher than the rate of precipi- tation. Maximum rain rate is of the order of 30 mm/h for 0.001% of the year. A brief descrip- tion of the experimental setup is presented, together with the results of measuring clear air fading experienced by the radio links. Statistical characterisation of fading is given for both the millimetric wave links operating near 40 GHz and the infrared radio link at a wavelength of 0.88 pm. It is shown that fading is dominated by multipath, having a Rayleigh amplitude distribution and an occurrence factor similar to the microwave band. Fades were highly correlated for the two links sharing the same path and separated in frequency by 1%. Multipath fading was also measured on the infrared link. Even at the short hop length at 0.75 km, the occurrence factor was about 1%. Time duration of fades are also analysed, and fade durations were essentially exponentially distrib- uted. Small fades, however, have normal duration distribution. 1 Introduction The increasing demand for new services, coupled with the crowding of lower microwave bands, has promoted the research for new bands to meet such demand. The new frontier is the millimetric waveband which provides a potential for more services than all the lower radiobands put together. Unfortunately, shorter wavelengths are more attenuated by absorption and scattering from rain. Hence short hops of 3 to 5 km may be considered for climatic regions dominated by rain. Saudi Arabia can be considered as a typical arid climate where the rate of evaporation is higher than the rate of precipitation. For most of the year rainfall is very little [l] and hence rain attenuation may not be the dom- 0 IEE, 1993 Paper 9403H (Ell), first received 10th July and in revised form 20th November 1992 Adel A. Ali is with the Electrical and Electronic Engineering Depart- ment, College of Engineering, Sultan Qaboos University, Muscat, Oman Mohammed A. Alhaider is with the Electrical Engineering Department, College of Engineering, King Saud University, Riyadh, Saudi Arabia IEE PROCEEDINGS-H, Vol. 140, No. 5, OCTOBER 1993 inant propagation factor. Much longer hops may be feas- ible in and climate, resulting in a lower cost and higher reliability. For longer hops, however, multipath and other clear air fading phenomenon may play a dominant role in link reliability. Together with rain attenuation and clear air fading, sand and dust storms result in a signifi- cant attenuation, especially when coupled with high humidity [2-41. The results of measuring attenuation due to rain- and sandstorms are reported elsewhere [S-71. In this paper we present results of measuring the effect of multipath fading on wave propagation at 40 GHz and near infrared. 2 Experimental system description 2.1 Path parameters The geographical arrangement of the experimental links is shown in Fig. 1. The receivers are situated at the N I KSUl ,R K?U 0.75 km 657m y limit (TX) (RXS) 0.88pm Fig. 1 Geographical arrangement of experimental links College of Engineering, King Saud University (KSU). The transmitters are located at Khazan Residential Centre (KRC) 14 km distant at azimuth 135", and at the maintenance building (KSU1) 0.750 km distant at azimuth 270". Path profiles along the links are shown in Fig. 2. The elevation angles are 0.029", 0.3" for the KRC, and KSUl paths, respectively. The KRC path is partly over open arid area and partly over an urban area of Riyadh city. The KSUl path is over the KSU compound which is an This work is supported by grant No. AR-5/29 from King Abdulaziz Cirty for Science and Tech- nology (KACST). 343