5.3 SID-frame encoding
3GPP46.062Comfort noise aspects for Enhanced Full Rate (EFR) speech traffic channelsRelease 17TS
The SID-frame encoding algorithm exploits the fact that only some of the 244 bits in a frame are needed to code the comfort noise parameters. The other bits can then be used to mark the SID-frame by means of a fixed bit pattern, called the SID code word.
The quantization indices of the LP parameters are replaced by the quantization indices derived from the averaged LSF parameter vector 
. The encoding of the quantization indices is defined in clause 5.1.
The fixed codebook gain quantization indices are replaced by the quantization index derived from the averaged fixed codebook gain value 
, encoded as defined in clause 5.1, repeated four times inside the frame.
The SID code word consists of 95 bits which are all set to one. The bits of the SID code word are inserted in the SID field as defined in table 1. All of the bits in the SID field are in the error protection Class I.
The remaining bits in the SID frame are set to zero. The use of these bits is for further study.
Table 1: SID codeword
|
Parameter |
Number of bits |
Bit positions (b0 = LSB) |
|
LTP LAG 1 |
2 |
b0, b1 |
|
LTP LAG 2 |
3 |
b0, b1, b2 |
|
LTP LAG 3 |
2 |
b0, b1 |
|
LTP LAG 4 |
4 |
b0, b1, b2, b3 |
|
LTP GAIN 1 |
3 |
b0, b1, b2 |
|
LTP GAIN 2 |
3 |
b0, b1, b2 |
|
LTP GAIN 3 |
4 |
b0, b1, b2, b3 |
|
LTP GAIN 4 |
4 |
b0, b1, b2, b3 |
|
PULSE 1 of 1st subfr. |
4 |
b0, b1, b2, b3 |
|
PULSE 2 of 1st subfr. |
4 |
b0, b1, b2, b3 |
|
PULSE 3 of 1st subfr. |
4 |
b0, b1, b2, b3 |
|
PULSE 4 of 1st subfr. |
4 |
b0, b1, b2, b3 |
|
PULSE 5 of 1st subfr. |
2 |
b2,b3 |
|
PULSE 1 of 2nd subfr. |
4 |
b0, b1, b2, b3 |
|
PULSE 2 of 2nd subfr. |
4 |
b0, b1, b2, b3 |
|
PULSE 3 of 2nd subfr. |
4 |
b0, b1, b2, b3 |
|
PULSE 4 of 2nd subfr. |
4 |
b0, b1, b2, b3 |
|
PULSE 5 of 2nd subfr. |
2 |
b2,b3 |
|
PULSE 1 of 3rd subfr. |
4 |
b0, b1, b2, b3 |
|
PULSE 2 of 3rd subfr. |
4 |
b0, b1, b2, b3 |
|
PULSE 3 of 3rd subfr. |
4 |
b0, b1, b2, b3 |
|
PULSE 4 of 3rd subfr. |
4 |
b0, b1, b2, b3 |
|
PULSE 5 of 3rd subfr. |
2 |
b2,b3 |
|
PULSE 1 of 4th subfr. |
4 |
b0, b1, b2, b3 |
|
PULSE 2 of 4th subfr. |
2 |
b2, b3 |
|
PULSE 3 of 4th subfr. |
4 |
b0, b1, b2, b3 |
|
PULSE 4 of 4th subfr. |
4 |
b0, b1, b2, b3 |
|
PULSE 5 of 4th subfr. |
2 |
b2,b3 |
The parameters in table 1 are defined in GSM 06.60 [3].