LMCS field tests in Canada

The Communications Research Centre (CRC) conducted field tests on a pilot local multipoint communications system (LMCS) at 28 GHz, in a major urban centre in September of 1997. About 400 test sites were visited. The coverage of two multisystem cells was studied. This system was configured to broadcast digital video and audio programs originating from a satellite signal. Other services such as interactive multimedia (IMM) data services and dedicated access services (DAS) were to be evaluated later. Measurements were taken for 395 sites within a 5-km radius to evaluate the system´s availability. The availability is highly dependent on terrain, path clearance, and transmitter/receiver antenna height. Another noteworthy point is that, for both cells, there were sites available outside the 5-km radius. The signal power after downconversion (SPAD) measured at the test sites and the calculated free space propagation SPAD fit well. The SPAD measured at the sites that can receive reliable video signals are very close to the calculated free space propagation SPAD. The difference between the received SPAD and values predicted by free space propagation increases with the receiving distance. This could be caused by atmospheric absorption, partial path blockage, depolarization, etc. For example, vegetation attenuation and building diffraction can easily result in more than 10 dB SPAD attenuation. Measurements were done within clusters consisting of three-by-three test sites, spaced at a distance equal to one residential house, to simulate a real LMCS implementation case. This test´s purpose was to confirm that no large SPAD variations within a small area existed where there were no major blockage. From the results it can be noted that the SPAD variations are only a few dB within a cluster and that all measured SPAD match closely with the free-space SPAD curves