C.11 Ambient noise rejection

03.503GPPTransmission planning aspects of the speech service in the GSM Public Land Mobile Network (PLMN) systemTS

– A 1/2 inch pressure microphone is calibrated using a known sound source and mounted at the MRP, without the LRGP head present. A frequency analyser is calibrated to enable the sound pressure levels at the microphone to be determined in 1/3rd Octave bands.

– Flood the room in which the measurement is to be made with the selected noise file, and adjust the level such that the noise level at the MRP is 70 dBA. A single noise file of real noise, covering the various noise environments that the MS could be subjected to is used ([Filename TBD]). This file is three minutes long and also commences with a three minute calibration signal. Once this tone has been adjusted to a level of 70 dBA, the average level of the noise will be 70 dBA. The resulting sound spectrum is Prn dBPa, measured in 1/3rd Octave bands.

– To ensure that the sound field is diffuse enough, the following apply:

– The diffuse sound field is calibrated in the absence of any local obstacles. The averaged field shall be uniform to within 3 dB within a radius of 0,15 m of the MRP, when measured in one‑third octave bands from 100 Hz to 3,15 kHz.

NOTE 1: The pressure intensity index, as defined in ISO 9614, may prove to be a suitable method for assessing the diffuse field.

NOTE 2: Where more than one loudspeaker is used to produce the desired sound field, the loudspeakers my require to be fed with non‑coherent electrical signals to eliminate standing waves and other interference effects.

– Position an LRGP in the correct relative position to the MRP and mount the MS under test. Recalibrate the 1/3rd Octave frequency analyser using a known voltage source to facilitate the analysis of the voltage Vrn, where Vrn is the voltage at the audio output of the SS due to the noise spectrum input.

– Set up a speech path between the MS and the System Simulator (SS).

– Determine, as a function of frequency, using the frequency analyser, in 1/3rd Octave bands, the electrical output Vrn, (expressed as dB rel . 1V) at the audio output of the SS for the applied acoustic pressure Prn (expressed as dB rel 1Pa) at the MRP. Since, the MS sending sensitivity is not defined above 3,4 kHz and below 300 Hz the measurement shall be cut off at 3,4 kHz and for the bands below 300 Hz, the noise level shall be referenced to the speech level at 300 Hz to yield the DELSM.

The room noise sensitivity is expressed as:‑ Smj rn= Vrn (dBV) – Prn (dBPa).

The MS ambient noise send sensitivity has now been determined.

– The MS speech send sensitivity is now required. The required sensitivity is defined as the electrical output from the MS, measured at the audio output of the SS, as a function of the free field sound pressure at the MRP of the artificial mouth.

The measurement is made using an artificial speech source at the MRP of the artificial mouth. The 1/2 inch pressure microphone is calibrated using a known sound source. The frequency analyser is calibrated to measure in 1/3rd Octave bands. The artificial mouth output shall be in accordance with the CCITT P.50 male artificial voice. Whilst maintaining the CCITT P.50 "male" spectrum, adjust the total signal level to –4,7 dBPa. The resulting sound spectrum is Po dBPa, measured in 1/3rd Octave bands. The 1/3rd Octave frequency analyser should be re‑calibrated, using a known voltage source, to facilitate the analysis of the voltage Vj.Where Vj is the voltage at the audio output of the SS due to the speech spectrum input. Set up a speech path between the MS and the SS. Determine the function of frequency, using the frequency analyser, and in 1/3rd Octave bands, the electrical output, Vj, (expressed as dB rel. 1V), at the audio output of the SS for the applied acoustic pressure, Po, (expressed as dB rel. 1Pa/V), at the MRP.

The sending sensitivity is expressed as:

– Smjs (dB) = Vj (dBV) – Po (dBPa) dBrel. 1V/Pa.

The DSM for the MS is determined as:

– DSM = Smj rn – Smjs (dB).

C.11.1 Full‑Rate, (TCH‑FS) MS Ambient Noise Rejection (handset MS)

Compliance shall be checked by calculating the Single Figure DELSM (SFDELSM) according to the following formula, the SFDELSM shall be > 0 dB.

Where:‑ n = The of third octave band centre frequencies from 160 Hz to 3 150 Hz inclusive.

Deln = is the 1/3rd Octave band pressure level centred on the nth frequency.

Wm = is the SLR weighting for the nth 1/3rd Octave band centre frequency.

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SFDELSM = ‑4/5 x n = 1 Deln x 10 (‑0.0175 x Wm)

C.11.2 Full‑Rate, (TCH‑FS) MS Ambient Noise Rejection (handsfree MS)

[TBD]

C.11.3 Half‑Rate, (TCH‑HS) MS and Dual‑Rate (TCH‑FS and TCH‑HS) MS Ambient Noise Rejection

[TBD]

Annex D (normative):
MS delay requirement definition