3.14 MS Ambient Noise Rejection

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

The nature of mobile telephony is such that the MS will typically be operated in high ambient acoustic noise. Due to the adverse interaction of noise signals with the TCH‑FS and TCH‑HS speech codecs, a minimum noise rejection specification is required.

3.14.1 Full‑Rate, (TCH‑FS) MS Ambient Noise Rejection (handset MS)

The MS ambient noise rejection, calculated as a Single Figure DELSM (SFDELSM) shall be greater than or equal to 0 dB. For good performance, it is recommended that a figure of +3 dB should be achieved.

Compliance shall be checked by the test described in annex C, clause C.11.

3.14.2 Full‑Rate, (TCH‑FS) MS Ambient Noise Rejection (handsfree MS)

[TBD]

3.14.3 Half‑Rate, (TCH‑HS) MS and Dual‑Rate (TCH‑FS and TCH‑HS) MS Ambient Noise Rejection

[TBD]

NOTE 1: For transmission planning purposes. Interfaces A and A bis are not required.

NOTE 2: The speech transcoder may be at either the BTS or the BSC.

Figure 1: Basic Configuration for Interworking with the PSTN

NOTE 1: Speech detection is incorporated in the speech transcoder. Speech detection is needed to provide the function of DTX and, if required, acoustic echo control (see note 2).

NOTE 2: Acoustic echo control may not be provided in the case of the headset.

NOTE 3: Includes filtering.

NOTE 4: In the case of direct MSC to MSC connections, the EEC function should not be active. The EEC device should be either disabled or not inserted in the circuit.

NOTE 5: In single talk and in double talk, when no centre clipper is used, and in double talk only if a centre clipper is used, the level of quantizing noise introduced by the speech transcoding will effect the level of residual acoustic echo when echo cancellation techniques are used for AEC.

NOTE 6: The transmission system need not be present.

Figure 2: PLMN System Model Used for Consideration of Transmission Planning Issues

NOTE 1: A direct link between MSC and ISC may be used in cases where Signalling System No. 7 is not provided in the PSTN or where a link via the PSTN would have excessive delay.

NOTE 2: An echo canceller should be provided at every POI to cancel any echo returning to the PLMN from the PSTN. This is necessary because the one‑way echo path back to the MS greatly exceeds 25 ms (see ITU‑T Recommendation G.131).

NOTE 3: A direct link between MSCs reduces the number of echo control devices that need to be provided and avoids the tandem connection of such devices. These direct links may be expected to have less delay than PSTN connections.

NOTE 4: This arrangement may be provided.

Figure 3: PLMN to PSTN Interconnection Configurations

Direct routeing and re‑routeing where the overall delay of the transmission path has not been extended and no echo control in the PSTN.

Normal configurations.

Figure 4: (continued) Reference Configurations A

Where direct MSC‑MSC connections exist, these configurations may apply.

Figure 4: (concluded)

Direct routeing and re‑routeings where the overall delay of the transmission path has not been extended and with echo control in the PSTN.

Normal configurations.

Figure 5: (continued) Reference Configurations B

Where direct MSC – MSC connections exist, these configurations may apply.

Figure 5: (concluded)

Re‑routeings where the overall delay of the transmission path has been extended beyond transmission planning limits.

Figure 6: Reference Configuration C

No echo control in PSTN.

Echo control in PSTN.

Figure 7: End Delay Requirements for PLMN EEC

Annex A (informative):
Considerations on the Acoustic Interface of the Mobile Station