The Okumura model computes basic median field strength and then adjusts for factors such as terrain, type of area (urban, suburban, open, etc.), terrain slope, etc. from the families of curves, as described in “Field Strength and its Variability in VHF and UHF Land-Mobile Radio Service”, Review of the Electrical Communications Laboratory, Vol. 16, Numbers 9-10, Sep.-Oct, 1968, by Yoshihisa Okumura, et. al. The Okumura adjustments for area type, terrain slope, street orientation, etc., can be included or excluded individually from calculations. Facility and path parameters (transmitter power, directional antenna, beam tilt, earth curvature correction, antenna heights, etc.) are all user-specified to provide maximum flexibility in system design. Field intensity values are calculated at specified radial, tile or individual locations, based on terrain data for the site and path, transmitter power, directional antenna, etc., using basic median field and adjustments based on the Okumura method.
Okumura is most prominently used for predicting field strength in urban areas since the underlying measurements were taken in Tokyo, Japan. However, corrections for Suburban and Open terrain are included, if needed. The explicit frequency range is 150 MHz to 1920 MHz although extrapolations up to a few GHz are not uncommon. The Okumura curves directly apply to propagation distances of 1 km – 100 km although, again, the curves can be extrapolated for longer ranges.
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