1、Released: July 1, 1993 GSM 06.12 Version 4.0.1 Date: January 1993 Work Item No: Key words: European digital cellular telecommunication system (phase 2); Comfort Noise Aspects for Full Rate Speech Traffic Channels ETSI European Telecommunications Standards Institute ETSI Secretariat: F - 06921 Sophia
2、 Antipolis Cedex . France TP. + 33 92 94 42 00 TF. + 33 93 5 47 16 Tx. 47 00 40 F This is an unpublished work the copyright in which vests in the European Telecommunications Standards Institute. Ali rights reserved. The information contained herein is the propetry of ETSI and no part may be reproduc
3、ed or used except as authorised by contract or other written permission. The copyright and the foregoing restriction on reproduction and use extend to ail media in which the information may be embodied. Pig. 3 GSM 06.12 (4.0.1): January 1993 Contents O.SCOP . 5 1.GENERAL 5 2 . FUNCTIONS ON ME TRANSM
4、IT SIDE . 5 2.1, BACKGROUND ACOUSTIC NOISE EVALUATION . 6 2.2. SID-FRAME ENCOOlNa . 6 3 . FUNCTIONS ON ME RECEIVE SIDE 7 3.1. COMFORT NOiCE GENERATION AND UPDATING 7 Previous page is blank 3404583 0080481 703 Paga 5 GSM 06.12 (4.0.1): Janwty 1993 O. SCOPE This technical specification gives the detai
5、led requirements for the cotrect operation of th background acoustic noise evaluation, noise parameter eclcodinq/decoding and comfort noise generation in GSM Mobile Stat and Base Statim Systems during Discontinuous Transmissim (DTX) on full rate speech traffic chanmis. The requirements described in
6、this technicd specification are mandatory for implementation in ail GSM Mobile Statioris. The receiver requirements are mandatory for implementation in ail GSM Base Station Systems, the transmitter requirements oniy foc those where dcrwnlink DIX will be used. 1. GENERAL The definitions of terms usd
7、in this technical specification can be found in GSM 06.31. The overall operation of Discontinuous Transmission is described in GSM 06.31. A basic problem when using DIX is that the Wkgrwnd accustic noise, which is transmitted tcgethec with the speech, would disappear when the radio transmission is c
8、ut, resulting in a modulation of the backgrowid noise. Since the DTX switching can take piace rap*, it has been found that this effect can be very wing foc the listener - especially in a ca mirmerit with high background noise levels. In bad cases the speech may be har#y intelligible. This technical
9、specca!im specifies the way to overcome this problem by genetating on the receive side synthetic noise similar to the transmit side background noise. The parameters of this so called comfort noise BTB estimated on the transmit side and transmitted to the receive side Mote the radio transmission is C
10、IA and d a regular low rate afterwards. This allows 2. FUNCTIONS ON THE TRANSMIT SIDE th8 CwnfUt ndSe to adap tothe ChangeS af the On the banSm& Side. The comfort noise evakiabion aigorithm uses the unqumtized biock amplitude and Log Area Ratio (LAR) prvameiers give information m the leve( and the s
11、pectrum d the backgwnd noise, respecttvefy. wemeters d the hJI ra enCoder, wried in S&Ul 4.2.15 and 4.2.6 d GCM 06.10. Thece The evaluated comfort noise parameters are encoded into a special frame, called a Si0 (Silence Descripor) frame, fcr transmission to the receive side. The SiDfrms aQ0 saves to
12、 initiate the comfoct noise genetation m the receive side, as a S13 frame is always SBIi attie d of a speech burst, ie before the radio transmission is cut. The-d SiD u speech frames on the radio path is described in GSM 06.31. Previous page is blank 3404583 0080482 64r Page 6 GSM 08.12 (4.0.1): Jan
13、uary 1S3 21. BACKGROUND ACOUSTIC NOISE EVALUATION The comfort noise parameters to be encoded into a SID frame are calculated over N=4 consecutive frames marked with VAD=, as follows: The Log Area Ratio parameters shall be averaged accotding to th equation: mean (LAR() = l/N SUM n=l to N LARn(i) i =
14、1,28 where iARW(i) is the ith Lq Area Ratio coefficient of the curent frame j and j-n indicates th previous frames. The block amplitude parameter shall be averaged according to the equation: mean (xmax) = 1/(4N) SUM n=1 to NI SUM is1 to 41 xrnaxpn(i) i = i ,2,a where xmaxg(i) is the Mock amplitude i
15、n subsegment i of the current frame. The SI0 frame containing these averaged parameters is passed to the Radio Subsystem instead of frame number i. 2.2. SID-FRAME ENCODINQ The SID-frame encoding algorithm exploits the fact ttiat oniy some of the 260 bits in a frame are needed to code the comfort noi
16、se parameters. The other bits can theri be used to mark the SID-frame by meam of a fixed bit patrern, called the SID code word. 7he log area ratio coefficients are replaced by the mean (LAR() values defined above and encoded as described in GSM 06.1 O. The ock amplitude values are replaced by the me
17、an (xmax) value defined above, repeated four times inside the frame and encoded as described in GSM 06.10. The SID code word consists of 95 bits which are ali zero. The bits of the CID code word are insertd in the SID field defined as the positions of those 95 bits af the encoded RPE-pulses Xmc, whi
18、ch are in the error protection dass I (see GSM 05.03, table 2). 7he remaining bits in the SI0 frame are set to zero. The use of these bits is for further stuc3y. = 3404583 0080483 58b Paga 7 GSM 08.12 (4.0.1): January 1393 3. FUNCTIONS ON THE RECEIVE SIDE The situatiocr, in which comfort noise shall
19、 be gerierated on the receive side are defined in GSM 06.31, Generally speaking, the comfort noise generation is started o( upate whenevec a valid SID frame is received. 3.1. COMFORT NOISE GENERATION AND UPDATING The comfort noise generation procedure uses the RPE-LTP speech decoder algorithm define
20、d in GSM 06.1 o. When comfort noise is to be generated, then the various encoded parameters are set as fdiows: The RPE pulses (xmcr) are replaced by a locally generated random integer sequence, unrforrnty distributed been 1 and 6. Also the grid position parameters (Ma) are set to random integer valu
21、es, uniformly distributed between O and 3. The LTP gain values (bcr) are set to O. The LTP lag volues (Ncr) of the 4 subsegments are set to 4,120,4 and 120 respectively. The 4 Mock ampiitude values (Xmaxcr) used are those received in the SJD frame. The log area ratio parameters (LARcr) used are thos
22、e received in the SJO frame. Weh these parameters, the speech decoder w performs the standard operations described in GSM 06.1 o and synthesizes comfort noise. Updating cd the comfort noise parameters occurs each time a valid CID frame is received, as described in GSM 06.31. When updating the comfort roise, the parameters above should preferabiy be interpolated over a few frames to obtain smodh transitions.
