--- title: "Outdoor propagation models (any two)" subject: "Wireless Communication" chapter: 3 key: "semester_7/wireless_communication:outdoor-propagation-models" source: https://www.bctengineer.com/q/semester_7/wireless_communication/outdoor-propagation-models site: BCT Engineering --- # Outdoor propagation models (any two) Wireless Communication · Chapter 3: Radio Wave Propagation in Mobile Networks - Asked in: 2075 Bhadra, 3+3 marks; 2073 Magh, 5 marks; 2071 Magh, 3+3 marks (asked 3 times) - Video: [Outdoor Propagation Model Okumura - Mobile Radio Propagation - Mobile Communication System](https://www.youtube.com/watch?v=GqploKEmD3w) — Ekeeda - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/wireless_communication/outdoor-propagation-models - Whole chapter: https://www.bctengineer.com/md/semester_7/wireless_communication/chapter-3 ## Question Explain any two outdoor propagation models used in mobile radio environment. ## Short answer Okumura model predicts median path loss as free-space loss plus empirical curves for attenuation and height gains, valid for 150–1920 MHz. Hata model fits Okumura’s curves into closed-form formulas for urban, suburban and open areas, valid for 150–1500 MHz, with corrections for antenna heights and distance. ## Answer 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. ```text 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. ```text 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. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Okumura median path loss is expressed as: A. Free space loss plus shadowing B. Only free space loss C. 10 n log(d) alone D. Free space loss plus Amu minus antenna height gains minus GAREA Answer: D. L50 = LF + Amu - G(hte) - G(hre) - GAREA. (Key point: Okumura formula) 2. What is a drawback of the Okumura model? A. It has no frequency range B. It is inaccurate in urban areas C. It relies on curves, so it is slow to use in software and to respond to terrain change D. It works only below 100 MHz Answer: C. It needs graph reading for Amu and GAREA. (Key point: Okumura drawback) 3. How does the Hata model relate to Okumura? A. It is a closed-form formula fitted to Okumura's curves B. It extends Okumura to 6 GHz C. It is an unrelated theoretical model D. It uses ray tracing Answer: A. Hata fits equations to Okumura's curves, removing the need for graphs. (Key point: Hata model) 4. Hata's model is suited for: A. Large-cell systems, 150-1500 MHz, d = 1-20 km B. Indoor use C. Micro-cells with 1 km radius PCS D. Distances up to 100 km Answer: A. It is valid for macrocells and not for PCS microcells. (Key point: Hata validity) ## Related in Wireless Communication - [Indoor propagation models (any two)](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Aindoor-propagation-models) — Wireless Communication, chapter 3 - [Large vs small scale models; propagation mechanisms](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Alarge-small-scale-propagation) — Wireless Communication, chapter 3 - [Basic propagation models and far-field distance](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Apropagation-models-far-field) — Wireless Communication, chapter 3 - [Numerical: λ/4 monopole and two-ray received power](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Amonopole-two-ray-received-power) — Wireless Communication, chapter 3 - [Source coders used in speech coding](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Aspeech-source-coders) — Wireless Communication, chapter 6 ## Related in other subjects - [Path loss in radio wave propagation](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Apath-loss-derivation) — Propagation and Antenna, chapter 5, asked 2× - [Marconi transmitter, mobile vs nomadic, Telecom Act](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Amarconi-mobile-nomadic-act) — Telecommunications, chapter 1 - [Short note: Radio frequency spectrum](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Arf-spectrum-short-note) — Propagation and Antenna, chapter 4, asked 3× - [Radio wave types and band characteristics](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Aradio-wave-designation-bands) — Propagation and Antenna, chapter 4, asked 2×