dead spot

In mobile communications, a dead zone is a geographical area in which no transmitter can be received. In a dead zone, the field strength drops to such an extent that cell phones or other radio or mobile communications devices cannot receive a transmitted signal. Such a radio hole can be caused by geological conditions, such as mountains and valleys, or by structures, such as high-rise buildings, or it can be caused by a low transmitter density.

Radio holes do not only exist in mobile communications, but in all radio technologies in general. They are dependent on wave propagation and occur mainly at higher frequencies that are transmitted with direct waves, because these waves are absorbed and reflected by earth elevations and buildings. As a result, radio shadows without receivable transmission signals are created behind such geological features.

In the case of WLANs, this is referred to as dead zones. These are locations in which no radio frequencies can be received. Dead zones can occur due to interference or frequency range problems. Such interference can be caused by thick walls or metallic partitions that attenuate the microwaves and thus reduce the received field strength. Interference can be caused by other WLANs or other radio equipment transmitting in the same frequency range. These include baby monitors, microwave ovens, alarm systems and cordless phones, to name just a few sources of interference. Dead zones can be reduced or avoided through accurate WLAN planning.