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IEEE TRANSACTIONS ON BROADCASTING VOL. 43, NO. 2, JUNE 97 Study of the Local Multipoint Distribution Service Radio Channel Peter B. Papazian, George A. Hufford, Robert J. Achatz, Randy Hoffman National Telecommunications and Information Administration Institute for Telecommunication Sciences 325 Broadway, Boulder, CO 80303 Abstract. This paper summarizes radiowave propagation impairments for local multipoint distribution services (LMDS) and reports measurement data for small cells. Results include area coverage estimates over a range of basic transmission losses for 0.5- 1.0- and 2.0- km suburban cells with foliated trees. Multipath, signal attenuation, depolarization, and cell to cell coverage also are discussed. Data indicates a high probability of non-line-of- sight paths due to trees which can cause signal attenuation and signal variability when wind is present. Signal variability was studied using k factors and compared to the Rician cumulative distribution function. Depolarization caused by vegetation and other signal scatterers was found to be an order of magnitude greater than rain-induced depolarization. A simple tapped delay line model is presented to describe multipath for three channel states. Introduction Millimeter wave communication systems in the 27.5 to 29.5 GHz band are being developed in the United States and Canada for use in a local multipoint distribution service (LMDS). It is envisioned that these systems could broadcast voice, video, and data, and would allow for interactive communications in small cells. To compete successfully with standard broadcasting, cable, and satellites, the signal would need to be reliable and of high quality. Critical propagation issues are clear-air absorption, signal attenuation by rain, vegetation and buildings, signal depolarization, multipath, and cell-to-cell interference. An initial study of the radio channel for a suburban neighborhood with defoliated trees was made by Papazian, Roadifer, and Hufford [1]. Clear-air absorption at millimeter-wave frequencies has been modeled by Liebe [2,3]. Summary results, applicable to LMDS propagation, for clear air absorption, attenuation, and depolarization by rain have been reported by Dalke and Hufford [4]. This study quantifies area coverage, attenuation by vegetation, depolarization, and multipath for two suburban neighborhoods with foliated trees. A method for determining area coverage is presented and coverage estimates are made for several cell sizes and two transmitter heights. Equipment Measurements were made using a radio channel probe configured to transmit a 28.8-GHz narrowband continuous wave (CW) signal and a 30.3-GHz wideband signal through a common traveling wave tube amplifier. These signals were received using a parabolic dish antenna, and then split, down converted and processed in separate receivers. The narrowband signal is band pass filtered with a 2-kHz filter and then detected using a log amplifier. The narrowband receiver has a sensitivity of -130 dBm and a dynamic range of 70 dB. The wideband transmitter uses a 500-Mb/s pseudo-random noise code to modulate the carrier. Its receiver is a sliding correlator that uses a duplicate pseudo noise generator. The correlator produces co-phase and quadrature-phase impulse response data with 2 ns resolution. The wideband receiver has a sensitivity of -102 dBm and a dynamic range of 50 dB. We used a vertically polarized horn transmit antenna with 14 dB gain. The horn antenna has a 90° azimuthal 3 dB beamwidth, and a 20° vertical beamwidth. Equivalent isotropically radiated power for the transmitter was 51 dBm. The receiver antenna system consisted of two 2.5° dishes with linearly polarized feeds. One dish was aligned for vertical polarization and the second was aligned for horizontal polarization. The signal was routed to the receiver using waveguides with a switch to select the vertically or horizontally polarized antenna. These antennas and the receiver were mounted on a 28-ft pneumatic mast fitted with a pan-tilt head to control the azimuth and elevation angle. Survey Sites Suburban areas in Northglenn, Colorado and in San Jose, California were surveyed. Both sites consist predominantly of one- and two-story single family residences which are about 30 years old. Both areas have small yearly rainfall totals and slow tree growth. Some relevant geographic statistics for each site are listed in Table 1. 
