Outdoor propagation models (any two)

Outdoor propagation models predict path loss over irregular terrain and built-up areas. Two widely used empirical models are the Okumura model and the Hata model.

1. Okumura model

Based on extensive measurements in Tokyo. It gives median path loss as free-space loss plus correction curves.

L50(dB) = LF + Amu(f,d) − G(hte) − G(hre) − GAREA

• LF = free space loss; Amu = median attenuation relative to free space (from curves); GAREA = gain due to environment (from curves).
• G(hte) = 20 log(hte/200), for 1000 m > hte > 30 m
• G(hre) = 10 log(hre/3) for hre ≤ 3 m; 20 log(hre/3) for 3 m < hre < 10 m
• Valid for 150–1920 MHz (extendable to 3 GHz), d = 1–100 km, hte = 30–1000 m.
• Simple and accurate for urban/suburban areas (standard deviation about 10–14 dB), but slow to respond to rapid terrain changes and needs curves, so it is hard to use in software.

2. Hata model

An empirical formula fitted to Okumura's curves, so no graphs are needed.

L50(urban) = 69.55 + 26.16 log fc − 13.82 log hte
             − a(hre) + (44.9 − 6.55 log hte) log d

• fc in MHz, d in km, heights in m.
• Small/medium city: a(hre) = (1.1 log fc − 0.7)hre − (1.56 log fc − 0.8) dB
• Large city: a(hre) = 3.2(log 11.75hre)² − 4.97 dB (fc ≥ 300 MHz)
• Suburban: L50 = L50(urban) − 2[log(fc/28)]² − 5.4
• Open rural: L50 = L50(urban) − 4.78(log fc)² + 18.33 log fc − 40.94
• Valid for fc = 150–1500 MHz, hte = 30–200 m, hre = 1–10 m, d = 1–20 km. Good for large-cell systems, not for PCS micro-cells.

Other outdoor models: Longley–Rice, Durkin's model, the PCS extension of Hata (COST-231, up to 2 GHz) and the Walfisch–Bertoni model.