GSM [GSM 03.50] specifies an ambient noise rejection figure of at least 0dB (recommended +3dB). This figure is intended to prevent adverse interaction of the noise signals and the CODEC. The TETRA CODEC is different in design to the GSM CODEC so it may be more or less sensitive to noise. This sensitivity is measured according [GSM 03.50, Annex C.11].
This test involves creating a uniform noise field and measuring the sensitivity of the microphone in one-third octave bands. A weighted sum is then computed called the Single Frequency DELSM, the value of which should be greater than 0dB.
The TETRA CODEC noise sensitivity should be assessed and compared with that of the GSM. The Single Frequency DELSM requirement should then be adjusted accordingly.
Copyright ©2002 Andy Fletcher andy@x31.com