1、3404583 0080378 238 Released: July 1,1993 GSM 06.01 Version 4.0.2 Date: April 1993 Work Item No: Key words: European digital cellular telecommunication system (phase 2); Speech Processing Functions: General Description ETSI European Telecommunications Standards Institute ETSI Secretariat: F - 06921
2、Sophia Antipolis Cedex . France TP. + 33 92 94 42 00 TF. + 33 93 65 47 16 Tx. 47 00 40 F This is an unpublished work the copyright in which vests in the European Telecommunications Standards Institute. All rights resewed. me information contained herein is the propetry of ETSI and no part may be rep
3、roduced or used except as authorised by contract or other written permission. The copyright and the foregoing restriction on reproduction and use extend to all media in which the information may be embodied. 3404583 0080379 174 Paga 3 GSM 08.01 (4.0.2): Aprii 1- Contents 1.INTRODUCTlON 5 2. FULL RAT
4、E SPEECH TRANSCODING (GSM .10). . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. FUU RATE DISCONTINUOUS TRANSMISSION (DTX) (GSM 06.31) , . . . . . . . . . . . . . . . . 5 4. FULL RATE VOICE ACTIVITY DETECTION (VAD) (GSM 06.32) . . . . . . , . . . . . . . . . . . . . 6 5. FULL RATE COMFOFIT N
5、OISE INSERTION (GSM 06.12). . . . , , . . . . . . . . . . . . . . . . . . 6 6. FUU RATE LOST SPEECH FRAME SUBSTINTION AND MUTING (GSM 06.1 1) . . . . . . . . . . 7 7. SPEECH TRANSMISSION FUNCTIONS OF THE HALF RATE TRAFFIC CHANNEL . . . . . . , . . 7 Previous page is blank = 3404583 0080380 996 D Pag
6、a 5 GSM 06.01 (4.0.2): April 1993 1. INTRODUCTION This technical specification is an introduction to the 06 series of the GSM technical specifications dealing with the speech processing functions in the GSM system. A generd overview of the speech processing parts is given with reference to the techn
7、ical specicaons where each part is specified in detail. Fig 1-1 presents a reference configuration where the variau speech processing functions are idenufiecl. In this figure, the relevant technical specifications for each function are also indicated. In fig 1-1, the audio parts including analogue t
8、o digital and digital to analog cmersion are included to chow the complete speech paih between the audio inputloutput in the Mobile Station and the digital interface to the PSTN. The speciiicaon of the audio parts are contained in GSM 03.50 (Transmission plan aspects of the speech service in the Pan
9、-European PLMN system). These aspects am only considered in the GSM Wseries to the extent that the performance of the audio parts affect the performance of the speech transcoder. 2. FULL RATE SPEECH TRANSCODING (GSM 06.10) As shown in fig 1-1, the speech encoder takes its input as a 13 bit uniform P
10、CM signal either from the audio part of the mobile station or on the network side, from the PSTN via an 8 bit/A-law to 13 bit uniform PCM conversion. The encoded speech at the output of the speech encoder is delivered to the channel coding function defined in rec GSM 05.03 to produce an encoded Mock
11、 consisting of 456 bits leading to a gross bit rate of 22.8 kWs. In the receive direction, the inverse operations take piace. GSM 06.10 describes the detailed mapping between input Mocks of 160 speech sampies in 13 bit uniform PCM format to encoded Mocks of 260 bits and from encoded Mocks of 260 bit
12、s to output Mocks af 160 recorrstructe speech samples. The sampling rate is 8ooo samplels leading to an average bit rate for the encoded bit stream of 13 kbits. The coding scheme is the so-called Regular Pulse Excitation - Long Term prediction - Linear Predictive Coder, hereafter referred to as RPE-
13、LTP. The technical specification describes the codec down to the bit lwei, thus enabiing the verification of compliance to the technical specification to a high degree d confidence by use of a set of digital test sequences. These test cequences are also described and are available on floppy disks. 3
14、. FULL RATE DISCONTINUOUS TRANSMISSION (DTX) (GSM 06.31) During a normal conversation, the participants atternate so that, on the average, each direction of transmission is occupied about 50 % of the time. Discontinuous transmissiori (DTX) is a mode of operation where the transmitters are switched o
15、n only for those frames which contain useful information. mis may be dorie for ttie toilowing two purposes: 1) In the Mobile Station, battery life will be prolonged or a smaller battery could be used foc a given operatforial duration. The overall DTX mechanism is implemented in the DTX handlers (TX
16、and Rx) described in GSM 6.31 and requires the following functions which are described in separate technical specifications: - A Voice Activity Detector on the transmit side - Evaluation of the background acoustic noise on the transmit side, in or& to transmit characteristic parameters to the receiv
17、e side. Previous page is blank Page 6 GSM 06.01 (4.0.2): April 1993 - Generation on the receive side of a similar noise, called Cornfort noise, during periods where the radio transmission is cut. The transmission of comfort noise information to the receive side is achieved by means of a special fram
18、e (Silence descriptor=SiD). This frame is transmitted at the end of speech bursts and serves as an end of speech marker for the receive side. In order to update the comfort noise characteristics at the receive side, SID frames are transmitted at regular intervals also during speech pauses. This also
19、 serves the purpose of improving the measurement of the radio link quality by the radio subsystem. For the overall DTX functionality, the DTX handlers interwork via various flags with the Radio Subsystem, which is in control of the actual transmitter keying on the Tx side and which performs various
20、pre- processing functions on the RX side. This is also described in rec GSM 06.31. A common terminology used throughout the GSM Wseries of technical specifications is also defined in this technical specification. 4. FULL RATE VOICE ACTMTY DETECTION WAD) (GSM 06.32) The input to the VA0 is a sei of p
21、arameters computed by the full-rate speech encoder defined in GSM 06.10. The VAD uses this information to decide whether each 20 ms speech ccder frame contains speech or not. Note that the VAD flag is an input to TX DTX handler and does not control the transmittec keying directly. The technical spec
22、ification describes the VAD algorithm down to the bit level. The conventions used in the bit-exact specification are the same as those used in GSM 06.10. The verification of compliance to the technical specificatim is achieved by use of digrtal test sequences applied to the same interface as the tes
23、t sequences for the speech codec. These test sequences are also described and are available on floppy disks. 5. FULL RATE COMFORT NOISE INSERTION (GSM 06.12) When switching the transmission on and ofi during DTX operation, the effect would be a modulation of the background noise at the receiving end
24、 if no precautions were taken. When transmission is on. the background noise is transmitted together with the speech to the receiving end. As the speech burst ends, the connection is off and aie perceived noise would drop to a very low levei. This step modulation of noise is perceived as very annoyi
25、ng and may reduce the intelligibility of speech if presented to a listener wrthout modification. This socalled noise contrast effect is reduced in the GSM system by inserting an artificial noise, termed comfort noise, at the receiving end when speech is absent. Rec GSM 08.12 deais with the Wied aspe
26、cts of the comfort noise process: - the evaluation of the BcocLslic background noise in the transmitter, - the noise parameter encoding (SID frames) and decoding - and the generation of comfort noise in the receiver. The algorithm for updating the noise parameters during speech pauses is also define
27、d. The comfort noise mechanism is based on the full rate speech codec defined in rec GSM 06.1 O. W 3404583 0080382 769 W Page 7 GSW 08.01 (4.0.2): April 1993 i 6. FULL RATE LOST SPEECH FRAME SUBSTITUTION AND MUTING (GSM 06.1 1) In the receiver, frames may be lost due to ransrnissiori errors or frame
28、 stealing. GSM 06.1 1 describes the actions to be taken in these cases, both for lost speech frames and for lost SID-frames in DTX opetation. In order to mask the efect of an isolated lost frame, a scheme is used, where the lost speech frame is substituted by a predicted frame based on prwviw frames
29、. insertion of Si1enC8 irames is rtc4 allowed. For several lost frames in a row, some muting technique must be used to indicate to the customer that transmission is interrupted. 7. SPEECH TRANSMISSION FUNCTIONS OF THE HALF RATE TRAFFIC CHANNEL The gross bit rate of the hatf rate speech trac channel is 11.4 kbit/s. The algorithm for the haif ratbe speech transcoder as well as the associated DIX fundions are defined in technical specifications GSM 06.02, GSM 06.20, GSM 06.21 , GSM 06.22, GSM 06.41 and GSM 06.42. m 3404583 0080383 bT5 m d 1 Page 8 GSM 08.01 (4.0.2): April 1993 li SP flag j brts
