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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 of a 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 multi-media (IMM) data services and Dedicated Access Services (DAS) were to be evaluated later.Most of the field tests were completed when the tree leaves were still green: a seasonal period that is considered to represent the worst operating conditions. 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 transmitterkeceiver 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 threeby-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's within a cluster and that all measured SPADs match closely with the free space SPAD curves.During the tests, some weak multipath reflections were observed. However, the level of multipath was quite low, less than 15 dB. The delay spread was also quite small, less than 10 nanoseconds. This will not cause receiving errors.More studies are required regarding: long-term time availability under different weather and seasonal conditions; advanced modulation and channel coding for better spectrum efficiency and reliability; interference between services and problems with the installation of high rooftop directional receiving antenna.CRC is now evaluating different modulation techniques for better reliability and/or higher data throughput and is planning to study the problems related with the return channel required for two-way communications services.

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