Line-of-sight Propagation - Mobile Telephones

Mobile Telephones

Although the frequencies used by mobile phones (cell phones) are in the line-of-sight range, they still function in cities. This is made possible by a combination of the following effects:

• r−4 propagation over the rooftop landscape
• diffraction into the "street canyon" below
• multipath reflection along the street
• diffraction through windows, and attenuated passage through walls, into the building
• reflection, diffraction, and attenuated passage through internal walls, floors and ceilings within the building

The combination of all these effects makes the mobile phone propagation environment highly complex, with multipath effects and extensive Rayleigh fading. For mobile phone services these problems are tackled using:

• rooftop or hilltop positioning of base stations
• many base stations (a phone can typically see six at any given time)
• rapid handoff between base stations (roaming)
• extensive error correction and detection in the radio link
• sufficient operation of mobile phone in tunnels when supported by split cable antennas
• local repeaters inside complex vehicles or buildings

Other conditions may physically disrupt the connection surprisingly without prior notice:

• local failure when using the mobile phone in buildings of concrete with steel reinforcement
• temporal failure inside metal constructions as elevator cabins, trains, cars, ships