Radio Wave Propagation Studies in Singapore

The radio wave propagation studies in Singapore carried out in recent 10 years are reviewed in this paper. Three research areas will be covered, namely, rainfall attenuation of microwaves propagating along both sight-of-line and satellite link paths, radio wave propagation in tropical forest environment, and radio wave propagation in urban environment. Brief description of the state-of-art R &D work in these areas will be given. I Introduction It is well-known that knowledge of radio wave characteristics in different electromagnetic environments is very essential for the design of telecommunication systems, for instance, planning of mobile phone station distribution. With the increasing demand of telecommunications especially mobile communications, radio wave propagation becomes important in the radio systems in global communication network system. In Singapore, the radio wave propagation studies started in 1960s when HF radio wave propagation through, and scattered by, ionosphere were investigated. After that, the research work on radio wave propagation stopped for more than 20 years until the telecommunication system requires the information of characteristics of radio waves in various environments. After a long break, studies on radio wave propagation were put on schedule in 1988 when the Singapore Telecommunication Pte Ltd (SingTel) sponsored a research into the specific microwave rainfall attenuation at 21.225 GHz. Also, a company in UK provided transmitter and receiver systems for the real-time data collection. Attached to the receiving system, a computer equipped with software is set up to extract automatically the rainfall parameters over a sight-of-line link of 1.1 km [1–16]. In about 1992, two satellite-to-ground links were set up to investigate experimentally the rainfall attenuation as well as the effects of troposphere. At the same time, various theoretical and modeling works were carried out to compute total (or extinction) cross section of raindrops of spherical, oblate-spheroidal and Pruppacherand-Pitter shapes. Effects of the rain drop shapes were thus investigated, sponsored by Ministry of Education, Singapore. Since 1994, investigations on radio wave characteristics in tropical rain forest environments started, sponsored by Defence Science Organization (DSO) National Laboratories. Both theory (of ray tracing, UTD approach, and full-wave method) and experiments were looked into. Theoretically, a forest model of four regions consisting of a semi-infinite free-space, a single-layered canopy, a single-layered trunk, and a semi-infinite ground plane was proposed and two cases are considered, namely, isotropic canopy and trunk media and anisotropic canopy and trunk media. Various wave propagation mechanisms were realized, including the direct wave, a dominant and two fast-decayed lateral waves. Since about 1995, radio wave propagation in urban environment for indoor communications was studied, sponsored by Ministry of Education, SingTel, and another mobile communication company, Mobile One (M1). Both theoretical (using UTD and Monte Carlo) and experimental studies were conducted. A fairly good prediction model for a few selected areas including the downtown city was obtained. Subsequently, we will briefly review the studies of radio wave propagation in the aforementioned three subareas.