The Hata-Okumura computation model was first described by Yoshihisa Okumura in 1968 in his publication "Field Strength and Its Variability in VHF and UHF Land-Mobile Radio Service". In 1980, Masaharu Hata simplified the considerations from Okumura ("Empirical formula for propagation loss in Land Mobile Radio Services"). These simplifications led to the restriction that only regions with less than 20 km distance to the transmitter can be predicted.