Extra-high frequency line-of-sight propagation for future urban communications

Spectrum congestion at conventional microwave frequencies has forced communication system designers to explore and investigate higher and higher frequencies, well into the millimetric band. This part of the radio spectrum is currently underutilized and offers a very wide bandwidth and permits higher data rates as well as more channels. This paper presents measurements, analysis and modeling of propagation losses for a 97-GHz line-of-sight terrestrial link. The link was established in an urban environment over a path length of 6.5 km and operated over a period of more than a year. An overview of path geometry, experimental equipment and data acquisition, and data processing is first given. The annual distribution of the measured rain attenuation at 97 GHz is discussed in connection with that of the rainfall rate at the receiving point, and compared with the current ITU-R rain attenuation prediction model. Extensive experimental results on rain fade durations, long-term fade statistics and amplitude scintillations carried out using data recorded from this link are also presented. The experimental results concerning rain attenuation modeling indicate that the agreement between the measured rain attenuation values and those computed on the basis of the ITU-R rain attenuation prediction model is not entirely satisfactory. However, the results presented in this paper are only based on data collected over a period of one year, thus the difference between reported and modeled rain attenuation distributions may be attributed to expected year-to-year variations in rain fall rate and its associated attenuation distributions. Therefore, the experimental results appear to indicate that further research is necessary to fully validate the ITU-R rain attenuation model at higher millimeter wave frequency band over longer period of time. Nevertheless, the experimental results have established a considerable degree of confidence in the feasibility of millimeter wave link systems with short distance and low power requirements.