A Propagation Study of the 28 GHz LMDS System Performance under Rain Fading

In this paper, rain statistics of 10 years record in Taiwan area was used to investigate the transmission performance of the Ka-band LMDS system with QAM modulation. Emphasis was placed to investigate the effects of rain fading under MQAM modulation schemes. It is found that for LMDS cellular network, M-QAM modulation is difficult to provide an effective and reliable high speed transmission for the case of 6 km radius of cell coverage unless the frequency and polarization diversities are applied; otherwise, the cell coverage of service should be reduced. 1. RAIN DISTRIBUTION STATISTICS Taiwan is an island located around 24°N, 120°E covering the boundary of tropical and subtropical zones. Fig.1 shows yearly rain statistics for 4 large cities from north to south for 12 years from 1989-2000 records. For rain measurement, two kinds of rain gauge were used to record and compared to each other: the tipping bucket rain gauge with 0.1mm sensitivity and optical rain gauge with 0.001mm sensitivity sampling at every 5 seconds. It is well known that rain rate in hourly basis from annual observation is not suitable for fading margin estimation of telecommunication system [7-8]. It is necessary at this point to convert a long-term hourly data to short-term minutely measurements. To do so, we follow the procedure proposed in [9] by introducing a conversion factor (CF)