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DESCRIPTION On the basis of extensive measurements carried out in Tokyo at frequencies in the range of 100 MHz to 1920 MHz, Okumura et al. [1] published one of the most widely used models for path loss prediction in urban areas. The main result of Okumura's work was a set of curves, giving the median attenuation, relative to free space, as a function of frequency, distance, heights and several path-specific correction factors. This model is considered to be among the simplest and best in terms of accuracy in path loss prediction. It has become a standard for system planning in modern mobile radio systems. With the aim to make this method easy to apply, Hata [2] defined a series of empirical relationships describing the graphical method proposed by Okumura. Such expressions, which are of empirical nature, are known as the Okumura-Hata model, also called as Hata model. The main result provided by the model is the median value of the basic propagation loss, as a function of frequency, distance, base station height and mobile antenna height. Although it does not include any of the path-specific correction factors which are available in Okumura's model, the expressions proposed by Hata have significant practical value. The Okumura-Hata model is restricted to the following limits: •f: 150 to 1500 MHz •hb: 30 to 200 m •hm: 1 to 10 m •d: 1 ato 20 km DEVELOPMENT The Okumura-Hata model expresses the basic propagation loss, Lb, as follows [3]:
where a(hm) is the correction factor for mobile antenna height and is computed as follows: 1) for urban areas: a) for small or medium-sized city:
where 1 ≤ hm ≤ 10 m b) for large city:
2) for suburban areas:
3) for rural areas:
Generally this model is quite good in urban and suburban environments, but not as good in rural areas, due to the fact that it does not take into account neither terrain undulation nor the effects derived from the urbanization degree along the propagation path. REFERENCES [1] Y. Okumura, E. Ohmori, T. Kawano and K. Fukuda, "Field strength and its variability in the VHF and UHF land mobile radio service", Review of the Electrical Communications Laboratories, vol. 16, no. 9/10, pp. 825-73, Sep 1968. [2] M. Hata, "Empirical formula for propagation loss in land mobile radio services," in IEEE Transactions on Vehicular Technology, vol. 29, no. 3, pp. 317-325, Aug 1980. doi: 10.1109/T-VT.1980.23859 [3] J. D. Parsons, "The Mobile Radio Propagation Channel", New York: John Wiley & Sons, 1992. |