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  Okumura analyzed path-loss characteristics based on a large amount of experimental data collected around Tokyo, Japan. He selected propagation path conditions and obtained the average path-loss curves under flat urban areas. Then he applied several correction factors for other propagation conditions, such as: Antenna height and carrier frequency Suburban, quasi-open space, open space, or hilly terrain areas Diffraction loss due to mountains Sea or lake areas Road slope Hata derived empirical formulas for the median path loss (L50) to fit Okumura curves.