4 General

06.513GPPGSM Enhanced full rate speech processing functions: General descriptionTS

Figure 1 presents a reference configuration where the various speech processing functions are identified. In this figure, the relevant Standards for each function are also indicated.

In figure 1, the audio parts including analogue to digital and digital to analogue conversion are included, to show the complete speech path between the audio input/output in the Mobile Station (MS) and the digital interface of the PSTN. The detailed specification of the audio parts are contained in GSM 03.50 [2]. These aspects are only considered to the extent that the performance of the audio parts affect the performance of the speech transcoder.

1) 8‑bit /A‑law or -law (PCS 1900) PCM (CCITT recommendation G.711), 8 000 samples/s.

2) 13‑bit uniform PCM, 8 000 samples/s.

3) Voice Activity Detector (VAD) flag.

4) Encoded speech frame, 50 frames/s, 244 bits/frame.

5) SIlence Descriptor (SID) frame, 244 bits/frame.

6) SPeech (SP) flag, indicates whether information bits are speech or SID information.

7) Information bits delivered to the radio subsystem.

8) Information bits received from the radio subsystem.

9) Bad Frame Indication.

10) SIlence Descriptor (SID) flag.

11) Time Alignment Flag (TAF), marks the position of the SID frame within the Slow Associated Control CHannel (SACCH) multiframe.

Figure 1: Overview of audio processing functions