TETRA Technology Advantages & Benefits

TETRA Technology Advantages & Benefits page 3 of 12RF CoverageThe extent of RF coverage is mainly determined by transmitted RF power andreceiver sensitivity, combined with the propagation characteristics of the radiofrequency being used. Assuming these determining factors are the same betweenanalogue and digital the difference in RF coverage performance should beminimal.However, the way in which receiver sensitivity is specified in analogue is differentthan that with digital. For example, the accepted method of specifying analoguereceiver sensitivity is the RF signal level required to produce a 20 dB signal to noiseratio, whereas with digital it is the RF signal level at which a particular Bit Error Rate(BER) is exhibited.The relationship between BER and minimum acceptable voice quality (the receiversensitivity) is a function of the forward error correction and detection algorithm usedto protect the integrity of the voice codec. A pictorial representation of analogue anddigital RF coverage performance as well as voice quality performance can be seenin Chart 1.Chart 1: Analogue and Digital RF coverage and Voice Quality PerformanceNote: The differences shown in chart 1 are not representative of any particulardigital technology and have been provided for general illustration purposes only.Another factor that affects voice quality is bearer circuits. In a large nation-widesystem several hundred km of bearer circuits could be used to connect basestations to switches as well as switches to switches. In some countries analoguebearer circuits are still used which means that communications between userslocated a large distance apart could experience poor voice quality caused by addednoise, variations in signal amplitude and frequency response distortion.TETRA Association January 2006