Introduction to Wireless Communication System

1. Introduction to Wireless Communication System • Evolution of Mobile Radio Communication • Guillermo Marconi (1897) • Push to Talk telephone system (1940) • FCC doubled number of mobile telephone channels and Cut in half to 60 KHz channel bandwidth (1950) • FM bandwidth was cut to 30 KHz (1960) • AT&T proposed concept of cellular mobile system to the FCC (1968) • FCC allocated 666 duplex channels, 40 MHz in 800 MHz band, 30 KHz one way channel (1983). • SMR Down Banded Cellular (1990) • The first U.S. Digital Cellular System, EIA-IS-54, channel efficiency 3:1 (1991) • Code Digital Multiple Access, IS-95 (1993) • Personal Communication System (1995)

2. Introduction to Wireless Communication System • Growing • Techno-politics are fundamental driver in the evolution of new technology and services • Competitiveness in the rapid changing field of Wireless Personal Communication • Fastest Growth due wide spread deployment • Growth rates well in excess of 50% per year • First couple of decades of the 21th century, there will be an equal number of wireless and conventional wireline customer in the world

3. Introduction to Mobile Communication System • Use of higher frequencies • Urban area coverage • Mobile system signals suffer big variations • Reuse of frequencies without interfering with each other • Random phase Each component plane wave has associated with it, depending on the: • Mobile speed • Carrier frequency • Incidence angle

4. Frequency Bands

5. Factors affecting transmission • Free Space path losses The receive radiated power decrease 6 dB for each doubling of the frequency • Propagation over a plane earth Bullington simplified Norton’s solution into a set of waves: • Direct wave • Reflected wave • Surface wave • Rough Surface criterion Due surface irregularities • Refraction and Equivalent earth’s radius The refraction index of the atmosphere is not constant • Effects of rain and atmosphere Losses depend upon the frequency and upon the amounts of moisture in the path

6. Radio Propagation effects • Path Loss • Free Space Path Loss • Mobile Radio Environment Path Loss (OKUMURA) • Fading • Long term Fading Terrain configuration and human-made environment, log-normal variation for signal strength measured over 40 • Short term Fading (Rayleigh fading) Multiple signals interferences • Time delay Spread Two ray multipath delay • In-building, t < 0.1s • Open area , t < 0.2s • Suburban area , t < 0.5s • Urban area , t < 3s

7. d3 d1 d2 h2 h1 H Ant1 Ant2 d1 d2 d1<<d2 Factors affecting transmission • Transmission over smooth spherical earth Predict the signal attenuation over transhorizon path • Knife edge diffraction

8. Signal Prediction Models • OKUMURA • Signal Prediction Models for Urban areas (1968) • Relative to free space in an urban quasi-smooth environment • Reference curves were developed from extensive measurements using vertical omni antennas • Frequencies range 150 MHz to 1920 MHz • Distances range 1 Kmts to 100 Kmts • Base Station antenna heights 30 mts to 1000 mts • Simplest and best in terms of accuracy in path loss prediction for Cellular and LMR • Slow response to rapid change in the terrain (for urban areas) L50(dB) = LF + Amu(f,d) - G(hte) - G(hre) - GAREA

9. Signal Prediction Models • BULLINGTON • Published by Keneth Bullington 1947 • Modified basic free space and plane earth model by including diffraction losses. • Diffraction losses • Over smooth spherical earth • Curvature of the earth • Distance to horizon • Knife-edge • Signal Prediction Models for any areas • Response to rapid change in the terrain