5 Test descriptions for speech related transcoding function

11.243GPPGSM Transcoding and Rate Adaptation: Base Station System Equipment SpecificationTS

5.1 Test descriptions for full rate speech related transcoding functions

The Full Rate (FR) speech transcoding process consists of two fundamental steps. In the uplink, the first step transforms the 13 kbit/s bitstream into 104 kbit/s (13 bit linear PCM at 8 kHz). The second step transforms this 13 bit linear PCM into 8 bit A law PCM. In the downlink, the order is reversed. This is exactly followed in BSS types 1 and 3. For other BSS types, there is an intermediate step in which the 13 kbits/s data is mapped into a 16 kbit/s bitstream containing TRAU frames. TRAU frames are used to transport coded speech and data between the TRAU and CCU. In addition, specific speech functions are needed to support Discontinuous Transmission (DTX).

The test sequences for full rate speech transcoding are defined in GSM 06.10 [8] clause 5 and GSM 06.32 [12] clause 4 and can be obtained from ETSI Secretariat.

For further information see GSM 06.01 [7], GSM 06.10 [8], GSM 06.11 [9], GSM 06.12 [10], GSM 06.31 [11], GSM 06.32 [12] and GSM 08.60 [17].

5.1.1 Uplink tests

5.1.1.1 Uplink speech transcoding ‑ 13 kbit/s to 104 kbit/s conversion

Test purpose

To verify the bit exact conversion of the net 13 kbit/s radio path bit stream to 104 kbit/s (13 bit linear PCM at 8 kHz) by the transcoding function operating on speech.

This test is applicable to BSS types 1 and 3.

Test case

Method of test

At 13 kbit/s level in the BSS, after channel decoding, a test sequence shall be input synchronized to the channel/speech decoders interface frame structure. Alternatively, the test sequence may be input via the air interface before channel encoding at 13 kbit/s level in the BSSTE. In the latter case the Layer 1 functions of the BSS must already be verified and the test must be performed under perfect radio conditions.

The sequences to be input in this test are contained in the files SEQ01.COD, SEQ03.COD, SEQ04.COD and SEQ05.COD. The files contain 16 bit words for all speech encoded parameters and are justified as described in GSM 06.10 [8] table 5.1. 76 words must be input in a period of 20 ms and the speech decoder must be reset before the start of the test (i.e. exactly before the start of the test sequences).

At 104 kbit/s level in the BSS, the output bit stream shall be recorded.

The transcoder may be put into test mode in order to accept the new input interface conditions (speech decoder reset), to generate output data at the test rate (104 kbit/s) and in order to disable the uplink DTX functions, which are not part of this test.

NOTE: The test sequences are stored on the diskettes as 16 bit words (2 bytes) where the least significant byte occurs first and the most significant byte occurs last (e.g. stored 10 0A hex is to be understood as 0A 10 hex).

Test Requirements

The output test point for all BSS types is test point x’ shown in figure 11.24‑2.

The output bit stream from the speech transcoder shall be continuous and bit by bit exactly the same as the predefined output sequences (SEQ01.OUT, SEQ03.OUT, SEQ04.OUT, SEQ05.OUT).

Conformance requirement

The transcoding algorithm requires that the 13 kbit/s compressed speech be first converted into a 104 kbit/s linear PCM bit stream. For correct interworking between the MS and BSS the conversion process is precisely defined.

Requirement reference

GSM 06.01 [7] clause 2

GSM 06.10 [8] clause 5.2.2

5.1.1.2 Uplink speech transcoding ‑ 13 kbit/s to 16 kbit/s conversion

Test purpose

To verify the bit exact conversion of the net 13 kbit/s radio path bit stream to TRAU frames at 16kbit/s by the transcoding function operating on speech.

This test is applicable to BSS types 2, 4‑7.

Test case

Method of test

At 13 kbit/s level in the BSS after channel decoding a test sequence shall be input synchronized to the channel/speech decoders interface frame structure. Alternatively, the test sequence may be input via the air interface before channel encoding at 13 kbit/s level in the BSSTE. In the latter case the Layer 1 functions of the BSS must already be verified and the test must be performed under perfect radio conditions.

The test sequences for speech transcoding are defined in GSM 06.10 [8] clause 5 and can be obtained from ETSI Secretariat (see GSM 06.10 [8]).

The input shall be maintained for a duration of at least a duration of 40 ms or 2 speech frames.

At the Abis‑interface (position T) the output bit stream shall be recorded.

The uplink DTX functions may be disabled as it is not part of this test.

Test requirements

The data in the TRAU frames shall be bit exact with the input data.

Conformance requirement

The 13 kbit/s raw data taken from the radio interface is mapped onto TRAU frames which are used to send the data to the transcoder located at the remote end.

Requirement reference

GSM 08.60 [17] clause 3.1

5.1.1.3 Uplink speech transcoding ‑ 16 kbit/s to 104 kbit/s conversion

Test purpose

To verify the bit exact conversion of the encoded data in the TRAU frames to 13 bit/8 kHz linear PCM by the transcoding function operating on speech.

This test is applicable to BSS types 2, 4‑7.

Test case

Method of test

Conditions are as in clause 5.1.1.1 except that the test sequence shall be inserted at the 16 kbps TRAU interface with the traffic bits being the same as the bits used in the 13 kbps interface point as used for BSS types 1 and 3 in clause 5.1.1.1.

Test requirements

As in clause 5.1.1.1.

Conformance requirements

The 13 kbit/s data is extracted from the TRAU frames by the transcoder and converted to 104 kbit/s linear PCM.

Requirement reference

GSM 06.10 [8] Speech decoder parts

5.1.1.4 Uplink speech transcoding ‑ 104 kbit/s to 64 kbit/s conversion

Test purpose

To verify that the transcoding function correctly transforms 13 bit linear PCM to 8 bit A‑law PCM in a bit exact manner.

This test is applicable to BSS types 1‑7.

Test case

Method of test

A test sequence containing all possible 13 bit codewords shall be input at 104 kbit/s level in the BSS. Test point x’ shall be used for inserting the test signal. At 64 kbit/s level in the BSS (position Z) the output shall be recorded.

The transcoder may be put into test mode in order to enable the input test interface (104 kbit/s).

Test Requirements

The correspondence between codewords at input and output shall be according to recommendation CCITT G.721 clause 4.2.1 subblock COMPRESS. The parameter LAW=1 shall be used.

Conformance requirement

The transcoding algorithm requires that the 104 kbit/s linearly encoded speech be converted to a 64 kbit/s A law PCM data stream. For correct interworking between the MS and BSS, the conversion process must be totally compatible.

Requirement reference

GSM 06.10 [8]

5.1.1.5 Uplink Speech Decoder ‑ 13 kbit/s to 104 kbit/s conversion with DTX

Test purpose

To verify the correct operation of the SID‑frame detector, comfort noise generator, speech extrapolation and muting functions when the TRAU is at the radio interface.

This test is applicable to BSS types 1 and 3.

Test case

Method of test

At 13 kbit/s level in the BSSTE (before channel encoding) coded "speech" traffic frames containing a special test signal defined below shall be input and transmitted over error‑free radio conditions. All traffic frames shall be identical with the exception of some frames which are SID‑frames as defined in GSM 06.31 [11].

At 104 kbit/s level in the BSS (13 bit linear PCM at 8 kHz), the signal shall be output and the signal energy of the PCM signal shall be evaluated (as a mean square average) and recorded for each block of 20 ms synchronized to the 20 ms speech frame structure.

The TDMA frames of the TCH/FS transmitted on the radio path shall be ramped "on" or "off" on a traffic frame by traffic frame basis, taking into account the block‑diagonal interleaving scheme defined in GSM 05.03 [5]. The first traffic frame in step 1 shall occur one frame after the window of the SACCH multiframe (TDMA frame 60 modulo 104) allocated for the SID‑frame (see GSM 05.02 [4] and 05.08 [6]). The SACCH shall be transmitted.

NOTE: 8 timeslots in 8 consecutive TCH/FS TDMA‑frames shall be seen as one traffic frame and the next traffic frame starts in the middle of the previous one (i.e. after 4 TDMA‑frames of the previous one) due to the block diagonal interleaving scheme defined in GSM 05.03 [5].

The special test frame is an encoded "speech" traffic frame of 260 bits obtained from white Gaussian noise band limited to 300 ‑ 3 400 Hz. When repeated, the special test frame results in a humming sound with a fairly constant level when decoded, and is defined in table 11.24‑1:

Table 11.24‑1: Special test traffic frame for receiver DTX tests

Encoded parameter:

Value:

LARc(1)

38

LARc(2)

42

LARc(3)

24

LARc(4)

20

LARc(5)

10

LARc(6)

9

LARc(7)

5

LARc(8)

3

Subblock no:

0

1

2

3

Grid position (Mc)

1

3

2

0

Block amplitude (xmaxc)

40

40

40

40

LTP gain (Bc)

0

0

0

0

LTP lag (Nc)

40

120

40

120

RPE pulses (xmc)

‑ pulse no 1

4

6

6

6

‑ pulse no 2

4

5

4

3

‑ pulse no 3

2

1

3

4

‑ pulse no 4

6

2

1

3

‑ pulse no 5

3

6

4

1

‑ pulse no 6

5

1

6

3

‑ pulse no 7

5

2

5

5

‑ pulse no 8

5

6

2

1

‑ pulse no 9

1

3

4

4

‑ pulse no 10

3

2

4

3

‑ pulse no 11

5

5

4

5

‑ pulse no 12

6

1

2

2

‑ pulse no 13

1

3

4

3

The signal energy of the special test frame is controlled with the block amplitude parameter (xmaxc). Reducing xmaxc from 40 to 32 reduces the signal energy by 6 dB, and reducing xmaxc from 40 to 24 reduces the signal energy by 12 dB.

The sequence of frames shall be as follows:

1. 23 test frames "on".

2. 20 frames "off".

3. 20 test frames "on".

4. 1 SID‑frame followed by 6 frames "off", another identical SID‑frame and 23 frames "off". Except for the SID codeword, the SID‑frames shall be identical to the special test frame.

5. 1 different SID‑frame, however with 2 to 15 errors inserted in the SID codeword, followed by 23 frames "off".

6. 20 test frames "on", but with the block amplitude parameter xmaxc=24.

7. 1 SID‑frame followed by 50 frames "off". Except for the SID codeword, the SID‑frames shall be identical to the special test frame.

8. The whole test shall be repeated, but the frames "off" shall be replaced by frames "on" with the FACCH flag set.

Test Requirements

1) In the case of step 1, the signal energy shall be fairly constant within +/‑ 3 dB.

2) In the case of step 2, the signal energy shall decrease by greater than 40 dB within 17 frames.

3) In the case of step 3, the same requirements as in step 1 apply.

4) In the case of step 4, comfort noise shall be generated. The same requirements as in step 1 apply (in terms of level).

5) In the case of step 5, the same requirements as in step 4 apply.

6) In the case of step 6, the same requirements as in step 1 apply. However, the signal energy shall be 12 dB lower.

7) In the case of step 7, the signal energy shall be fairly constant within +/‑ 3 dB for 28 frames. Then the signal energy shall decrease by greater than 40 dB within 16 frames.

8) In the case of step 8, the same requirements as in all previous steps apply.

Conformance requirement

1) The output level of the decoder be constant for an input signal consisting of identical speech frames.

2) When, after the first lost speech frame has been substituted, subsequent speech frames are lost, a muting technique shall be used that will gradually decrease the output level, resulting in silencing of the output after a maximum of 320 ms.

3) As in 1).

4) A valid SID‑frame followed by a sequence of lost speech frames shall result in comfort noise generation with constant block amplitude parameters.

5) An invalid SID‑frame followed by a sequence of lost speech frames shall result in comfort noise generation, using the set of parameters from the last valid SID‑frame.

6) The energy of the output signal is controlled by the block amplitude parameter xmaxc.

7) The first SID‑frame that is expected and not received shall be substituted by the last valid SID‑frame and the procedure for valid SID‑frames shall be applied. For the second lost SID‑frame, a muting technique shall be used that will gradually decrease the output level, resulting in silencing the output after a maximum of 320 ms.

8) Speech frames with the FACCH flag set provoke a Bad Frame Indication (BFI=1) and are hence regarded as lost speech frames.

Requirement reference

1) GSM 06.10 [8]

2) GSM 06.01 [7] clause 6

GSM 06.11 [9] clauses 2.1, 2.2, 3

3) As in 1)

4) GSM 06.01 [7] clauses 3, 5

GSM 06.12 [10] clauses 3, 3.1

GSM 06.31 [11] clauses 1.2.2, 3.1, 3.1.1, 3.1.2

5) GSM 06.01 [7] clauses 3, 5

GSM 06.12 [10] clauses 3, 3.1

GSM 06.31 [11] clauses 1.2.2, 3.1, 3.1.1, 3.1.2

6) GSM 06.10 [8] clauses 3.1.20, 3.1.21, 3.2.1

7) GSM 05.08 [6] clause 8.3

GSM 06.01 [7] clause 6

GSM 06.11 [9] clauses 2.3, 2.4

GSM 06.31 [11] clauses 1.2.2, 3.1.1, 3.1.2

8) GSM 06.31 [11] clauses 1.2.2, 3.1.1

5.1.1.6 Uplink Speech Decoder ‑ 13 kbit/s to 16 kbit/s conversion with DTX

Test purpose

To verify that the TRAU frames generated by the Channel Coder Unit respond correctly to the reception of SID frames on the radio interface.

This test is applicable to BSS types 2, 4‑7.

Test case

Method of test

At 13 kbit/s level in the BSSTE (before channel encoding), the same sequence as defined in clause 5.1.1.5 shall be input in the uplink direction and transmitted over error-free radio conditions. The first traffic frame in step 1 shall occur one frame after the window of the SACCH multiframe (TDMA frame 60 modulo 104) allocated for the SID‑frame (see GSM 05.02 [4] and 05.08 [6]). The SACCH shall be transmitted.

At Abis‑interface (position T) the output bit stream shall be recorded.

Test Requirements

1) For frames no. 1 to 23, the recorded values for BFI and SID in the TRAU frames shall be: BFI = 0, SID = 0.

2) For frames no. 24 to 43, the recorded values for BFI and SID in the TRAU frames shall be: BFI = 1, SID = 0.

3) For frames no. 44 to 63, the recorded values for BFI and SID in the TRAU frames shall be: BFI = 0, SID = 0.

4) For frame no. 64, the recorded values for BFI and SID in the TRAU frames shall be: BFI = 0, SID = 2. For frames no. 65 to 70, the recorded values for BFI and SID in the TRAU frames shall be: BFI = 1, SID = 0. For frame no. 71, the recorded values for BFI and SID in the TRAU frames shall be: BFI = 0, SID = 2. For frames no. 72 to 94, the recorded values for BFI and SID in the TRAU frames shall be: BFI = 1, SID = 0.

5) For frame no. 95, the recorded values for BFI and SID in the TRAU frames shall be: BFI = 0, SID = 1. For frames no. 96 to 118, the recorded values for BFI and SID in the TRAU frames shall be: BFI = 1, SID = 0.

6) For frames no. 119 to 138, the recorded values for BFI and SID in the TRAU frames shall be: BFI = 0, SID = 0.

7) For frame no. 139, the recorded values for BFI and SID in the TRAU frames shall be: BFI = 0, SID = 2. For frames no. 140 to 189, the recorded values for BFI and SID in the TRAU frames shall be: BFI = 1, SID = 0.

8) The recorded value for TAF in the TRAU frames shall be TAF = 1 for frame no. 24, 48, 72, 96, 120, 144 and 168. For all the other frames TAF = 0.

9) When the test is repeated with frames "off" replaced by frames "on" with the FACCH flag set, the same requirements as in all previous steps apply.

Conformance requirement

The overall operation of the full rate DTX receiver functions consists of, apart from the channel decoder, a SID frame detection function which is part of the Speech Handler in the BTS. The side information to be transmitted uplink from the BTS with the speech frame over the TRAU frames is a binary Bad Frame Indication (BFI) flag, a binary Time Alignment Flag (TAF) and a ternary Silence Descriptor (SID) flag.

The channel decoder including the BFI is tested in GSM 11.21 [19].

NOTE: When special test frames are input on the radio interface, TRAU frames containing (BFI,SID) = (0,0) occur on the TRAU interface. When SID frames are input on the radio interface, TRAU frames containing (BFI,SID) = (0,2) occur on the TRAU interface under nonlimiting radio transmission conditions. When SID frames are input on the radio interface under limiting radio transmission conditions, TRAU frames containing BFIs of 0 and 1 and SIDs of 0,1 or 2 shall occur on the TRAU interface. Under all conditions, when the input test frame or SID frame on the radio interface comes in the middle of a SACCH multiframe according to GSM 05.08 [6], the TAF flag shall be set to 1. Other wise TAF = 0.

Requirement reference

GSM 06.31 [11]

5.1.1.7 Uplink Speech Decoder ‑ 16 kbit/s to 104 kbit/s conversion with DTX

Test purpose

When the TRAU is remote from the radio interface it should correctly respond to the DTX modulated 16 kbit/s signal. The output is tested at the 104 kbit/s level.

This test is applicable to BSS types 2, 4‑7.

Test case

Method of test

A call shall be set up on a full rate speech TCH, and then TRAU frames containing traffic bits being the special test frame defined in clause 5.1.1.5 shall be input on the Abis‑interface (position T). All TRAU frames shall contain identical traffic bits. The continuous sequence of TRAU frames shall contain the following combinations of flags:

1. 50 frames with (BFI,SID)=(0,0) and TAF=0 (good speech frames).

2. 20 frames with (BFI,SID)=(1,0) and TAF=0 (unusable frames).

3. 50 frames with (BFI,SID)=(0,0) and TAF=0 (good speech frames).

4. 1 frame with (BFI,SID)=(0,2) and TAF=0 (valid SID frame) followed by 30 frames with (BFI,SID)=(1,0) and TAF=0 (unusable frames).

5. 1 frame with (BFI,SID)=(0,1) and TAF=0 (invalid SID frame) followed by 50 frames with (BFI,SID)=(1,0) and TAF=0 (unusable frames).

6. 1 frame with (BFI,SID)=(1,2) and TAF=0 (invalid SID frame) followed by 50 frames with (BFI,SID)=(1,0) and TAF=0 (unusable frames).

7. 1 frame with (BFI,SID)=(1,1) and TAF=0 (invalid SID frame) followed by 50 frames with (BFI,SID)=(1,0) and TAF=0 (unusable frames).

8. 50 frames with (BFI,SID)=(0,0) and TAF=0 (good speech frames), but with the level parameter xmaxc=24.

9. 1 frame with (BFI,SID)=(0,2) and TAF=0 (valid SID frame) followed by 30 frames with (BFI,SID)=(1,0) and TAF=0 (unusable frames).

10. 1 frame with (BFI,SID)=(1,0) and TAF=1 (unusable frame , but SID expected) followed by 20 frames with (BFI,SID)=(1,0) and TAF=0 (unusable frames).

11. 1 frame with (BFI,SID)=(1,0) and TAF=1 (unusable frame , but SID expected) followed by 20 frames with (BFI,SID)=(1,0) and TAF=0 (unusable frames).

12. Step 1 shall be repeated, and then 20 frames with (BFI,SID)= (0,0) and TAF=0 (good speech frames), but with errors in the control bits.

13. Step 1 shall be repeated, and then 20 frames with (BFI,SID)= (0,0) and TAF=0 (good speech frames), but each with at least one framing bit error.

At 104 kbit/s level in the BSC (13 bit linear PCM at 8 kHz), the signal shall be output and the signal energy of the PCM signal shall be evaluated (as a mean square average, see clause 5.1.1.5) and recorded for each block of 20 ms synchronized to the 20 ms speech frame structure.

The transcoder may be put into test mode in order to enable the test output interface (104 kbit/s).

Test Requirements

1) In the case of step 1, the signal energy shall be fairly constant within +/‑ 3 dB.

2) In the case of step 2, the signal energy shall decrease by greater than 40 dB within 17 frames.

3) In the case of step 4, comfort noise shall be generated. The same requirements as in step 1 apply.

4) In the case of steps 5, 6 and 7 the same requirements as in step 4 apply.

5) In the case of step 8, the same requirements as in step 1 apply. However, the signal energy shall be 12 dB lower.

6) In the case of step 9, the same requirements as in step 4 apply. However, the signal energy shall be 12 dB lower.

7) In the case of step 10, the same requirements as in step 9 apply.

8) In the case of step 11, the same requirements as in step 2 apply.

9) In the case of step 12, the same requirements as in step 1 apply.

10) In the case of step 13, the signal energy shall decrease by greater than 40 dB within 320 ms + 60 ms = 380 ms. See also clause 7.3.3.6.3 (frame synchronization monitoring and recovery).

Conformance requirement

The overall operation of the full rate DTX receiver functions are described in GSM 06.31 [11], consisting of, apart from the speech decoder, a Comfort Noise (CN) generation function and an extrapolation and muting function for lost speech frames. These functions are parts of the remote Speech Handler in the BSC.

The side information to be received in the BSC with the speech frame over the TRAU interface is a binary Bad Frame Indication (BFI) flag, a binary Time Alignment Flag (TAF) and a ternary Silence Descriptor (SID) flag.

The speech decoder is tested in clauses 5.1.1.1 ‑ 5.1.1.2.

Requirement reference

Details of the overall DTX operation for full rate speech are given in GSM 06.31 [11] , the speech extrapolation and muting functions are described in in GSM 06.11 [9] and the comfort noise aspects in GSM 06.12 [10].

5.1.2 Downlink tests

Both standard and DTX tests are provided. It is a national or operator specific matter whether or not to implement downlink DTX in a BSS.

5.1.2.1 Downlink speech transcoding ‑ 64 kbit/s to 104 kbit/s conversion

Test purpose

To verify that the transcoding function correctly transforms 8 bit A‑law PCM to 13 bit linear PCM. For further information see GSM 06.10 [8].

This test is applicable to BSS types 1‑7.

Test case

Method of test

A test sequence containing all possible 8 bit codewords shall be input at 64 kbit/s level in the BSS. At 104 kbit/s level in the BSS the output shall be recorded.

The transcoder may be put into test mode in order to enable the output test interface (104 kbit/s).

Test Requirements

The correspondence between codewords at input and output shall be according to recommendation CCITT G.721 clause 4.2.1 subblock EXPAND. The parameter LAW=1 shall be used.

Conformance requirement

The relationship between A law and linear PCM given by the transcoder shall be compliant with CCITT G.721.

Requirement reference

GSM 06.10 [8] clause 5.1.2.1.

5.1.2.2 Downlink speech transcoding ‑ 104 kbit/s to 13 kbit/s conversion

Test purpose

This transcoding transforms 13 bit linear PCM at 8 kHz to the 13 kbit/s net radio path bit stream.

This test is applicable to BSS types 1 and 3.

Test case

Method of test

At 104 kbit/s level in the BSS a test sequence shall be input synchronized to the speech encoder input interface frame structure. The test sequences for speech transcoding are defined in GSM 06.10 [8] clause 5 and can be obtained from ETSI Secretariat (see GSM 06.10 [8]).

The sequences to be input in this test are contained in the files SEQ01.INP, SEQ02.INP, SEQ03.INP and SEQ04.INP. The files contain 16 bit words for 13 bit linear PCM left justified. See also GSM 06.10 [8] table 5.1. The speech encoder must be reset before the start of the test (i.e. exactly before the start of the test sequences).

At 13 kbit/s level in the BSS the output bit stream shall be recorded. The output may be read directly via physical access in the BSS or via the air interface at 13 kbit/s level in the BSSTE. In the latter case the Layer 1 functions of the BSS must already be verified and the test must be performed under perfect radio conditions.

The transcoder may be put into test mode in order to enable the new input interface conditions (speech encoder reset and 104 kbit/s rate) and in order to disable the downlink DTX functions, which are not part of this test.

NOTE: The test sequences are stored on the diskettes as 16 bit words (2 bytes) where the least significant byte occurs first and the most significant byte occurs last (e.g. stored 10 0A hex is to be understood as 0A 10 hex).

Test Requirements

The bit stream output shall be bit by bit exactly the same as the sequence given in the files SEQxx.COD on the floppy disks. These files contain 16 bit words of all the 76 parameters in a speech frame justified as in GSM 06.10 [8] table 5.1. 76 codewords shall occur in a frame of 20 ms.

Conformance requirement

The output bit stream from the transcoder shall be bit by bit exactly the same as the predefined output sequences SEQ01.COD, SEQ02.COD, SEQ03.COD and SEQ04.COD.

Requirement reference

GSM 06.01 [7] clause 2

GSM 06.10 [8] clauses 5.2, 5.2.1

5.1.2.3 Downlink speech transcoding ‑ 104 kbit/s to 16 kbit/s conversion

Test purpose

This transcoding transforms 13 bit linear PCM at 8 kHz to the 16 kbit/s level.

This test is applicable to BSS types 2, 4‑7.

Test case

Method of test

This test shall be performed in the same way as in clause 5.1.2.2 except that the output test point is the 16 kbit/s level where the traffic bits in the TRAU frames shall be treated in the same way as the traffic bits at the 13 kbit/s level for the test results.

Test Requirements

As is clause 5.1.2.2 with the output data taken from the TRAU frame.

Conformance requirement

The output bit stream from the transcoder that is embedded in the TRAU frames shall be bit by bit exactly the same as the predefined output sequences SEQ01.COD, SEQ02.COD, SEQ03.COD and SEQ04.COD.

Requirement reference

GSM 06.01 [7] clause 2

GSM 06.10 [8] clause 5.2, 5.2.1

5.1.2.4 Downlink speech transcoding ‑ 16 kbit/s to 13 kbit/s conversion

Test purpose

To verify the bit exact conversion of the data in the TRAU frames at 16kbit/s to the net 13 kbit/s bit stream prior to the channel coding by the speech handler.

This test is applicable to BSS types 2,4‑7.

Test case

Method of test

At the Abis‑interface (position T) a test sequence of data shall be fed to the BTS by means of TRAU frames at the 16 kbit/s level. The TRAU frames may have timing advance bits that command "no change".

The test sequence recommended to be used is SEQ01.COD as referred to in GSM 06.10 [8] clause 5 and can be obtained from the ETSI secretariat.

At the 13 kbit/s level the output data shall be monitored. Alternatively the output can be monitored via the air interface at the 13 kbit/s level in the BSSTE after channel decoding. In the latter case the layer 1 functions of the BTS must already have been verified and the test must be performed under perfect radio conditions.

The input and output shall be monitored for the duration of the sequence.

The downlink DTX functions may be disabled as it is not part of this test.

Test requirements

The output data shall be bit exact with the input data held within the TRAU frames.

Conformance requirement

In the downlink (at the BTS) the data bits in the TRAU frames should be extracted and used to produce a 13 kbit/s data stream for the channel encoder.

Requirement reference

GSM 08.60 [17] clause 3.1

5.1.2.5 Downlink transmitter DTX/VAD functions ‑ 104 kbit/s to 13 kbit/s level conversion with DTX

Test purpose

To verify that

1) To verify that the combination of VAD and DTX operates correctly.

2) To verify that SID‑frames are generated and positioned correctly after the start of a speech pause.

This test references the conversion from the 104 kbit/s level to the 13 kbit/s level on the radio interface.

This test is applicable to BSS types 1, 3.

Test case

Method of test

a) The test sequence SPECT_A1.INP of PCM samples, which are grouped into frames of 20 ms synchronized to the TDMA and traffic frame structure on the air interface, is sent downlink on the 104 kbit/s level (13 bit linear PCM at 8 kHz).

The start of the test sequences is synchronized with the radio transmission on the air interface so that the first traffic frame on the air occurs just after the traffic frame allocated for the SID frame (TDMA frame 56 modulo 104, see GSM 05.02 [4] and GSM 05.08 [6]).

NOTE: 8 timeslots in 8 consecutive TCH/FS TDMA frames are seen as one traffic frame and the next traffic frame starts in the middle of the previous one (i.e. after 4 TDMA frames of the previous one) due to the block diagonal interleaving scheme defined in GSM 05.03 [5].

b) The BSSTE detects whether or not there is any power transmitted over the radio path on a timeslot basis excluding SACCH frames. The speech frame by speech frame on/off transmission (on = 1) is recorded.

c) The test is repeated for all test sequences *.INP described in GSM 06.32 [12] clause 4.

Test Requirements

The traffic frame on/off sequence recorded shall be bit‑exact like the sequence of SP‑flags stored as bit 15 of LAR(2) on the reference files *.COD defined in GSM 06.32 clause 4, with the following exceptions:

1. The occurrence of a SID‑frame in its allowed window within the SACCH multiframe as defined in GSM 05.08 [6].

2. The occurrence of a SID‑frame after 1 or more real speech frames consecutively transmitted on the air.

Conformance requirement

The DTX/VAD transmitter functions allow only those frames to be transmitted that are either marked with SP = 1 or that are properly positioned SID frames.

Requirement reference

GSM 05.08 [6] clause 8.3

GSM 06.01 [7] clauses 3, 4

GSM 06.31 [11] clauses 2.1, 2.1.1, 2.1.2

GSM 06.32 [12] clauses 1, 2, 2.1, 2.2.8

5.1.2.6 Downlink transmitter DTX/VAD functions ‑ 104 kbit/s to 16 kbit/s conversion process

Test purpose

To verify that the TRAU frame’s speech flag SP = 1 when it is a speech frame and SP=0 when it is not.

This test is applicable to BSS types 2, 4, 5, 6 and 7.

Test case

Method of test

a) The test sequence SPECT_A1.INP of PCM samples, which are grouped into frames of 20 ms synchronized to the TDMA and traffic frame structure on the air interface, is sent downlink on the 104 kbit/s level (13 bit linear PCM at 8 kHz).

The start of the test sequences is synchronized with the radio transmission on the air interface so that the first traffic frame on the air occurs just after the traffic frame allocated for the SID frame (TDMA frame 56 modulo 104, see GSM 05.02 [4] and GSM 05.08 [6]).

NOTE: 8 timeslots in 8 consecutive TCH/FS TDMA frames are seen as one traffic frame and the next traffic frame starts in the middle of the previous one (i.e. after 4 TDMA frames of the previous one) due to the block diagonal interleaving scheme defined in GSM 05.03 [5].

b) On the TRAU interface, the sequence of SP‑flags is recorded.

c) The test is repeated for all test sequences *.INP described in GSM 06.32 [12] clause 4.The transcoder may be put into test mode in order to activate the 104 kbit/s level input test interface.

Test Requirements

In step b), the recorded SP‑flag sequence shall be bit‑exact compared to the sequence of SP‑flags stored as bit 15 of LAR(2) on the reference files *.COD.

Conformance requirement

If implemented, the overall operation of the full rate DTX transmitter functions are described in GSM 06.31 [11], consisting of, apart from the speech encoder, a Voice Activity Detector (VAD) and a TX DTX handler, in this case both being a part of the remote Speech Handler in the BSC.

The side information to be transmitted with the speech frame over the TRAU interface is a binary flag Speech (SP). SP=1 indicates that the TRAU frame is a speech frame and SP=0 indicate that the TRAU frame is a special SID‑frame. This flag is used in the BTS for control of the radio transmission.

The speech encoder is tested in clauses 5.1.2.1 and 5.1.2.2.

Requirement reference

GSM 06.01 [7] clauses 3, 4

GSM 06.31 [11] clauses 2.1, 2.1.1, 2.1.2

GSM 06.32 [12] clauses 1, 2, 2.1, 2.2.8

5.1.2.7 Downlink transmitter DTX/VAD functions ‑ 16 kbit/s to 13 kbit/s conversion

Test purpose

To verify that:

1. The frames on the radio interface are transmitted continuously when the speech flag SP=1.

2. The frames on the radio interface occur in the middle of the SACCH multiframe when SP=0 except for the first one after the SP=1 to 0 transition which is transmitted.

This test references the conversion from the 16 kbit/s level to the 13 kbit/s level on the radio interface.

This test is applicable to BSS types 2, 4, 5, 6 and 7.

Test case

Method of test

A call shall be set up on a full rate speech TCH, and then TRAU frames with random traffic bits accompanied with SP=0 or 1 in a random order shall be input on the TRAU interface.

Test requirements

On the radio interface the following full rate "speech" traffic frames shall be transmitted on the air on the TCH/FS:

1. All frames with SP=1.

2. The first frame with SP=0 after one or more with SP=1.

3. Those marked with SP=0 and occurring in the middle of the SACCH multiframe as defined in GSM 05.08 [6].

No other frames with SP=0 shall be transmitted on the air.

NOTE: Due to the block diagonal interleaving scheme defined for the TCH/FS, every traffic frame is transmitted in 8 TDMA frames. Since every TDMA frame contains 2 different traffic frames, there is not a one to one mapping between traffic frames "on" and TDMA frames transmitted on the air.

Conformance requirement

If implemented, the overall operation of the full rate DTX transmitter functions are described in GSM 06.31 [11], consisting of, apart from the channel encoder, an SP flag handling and monitoring function which in this case is in the Speech Handler in the BTS.

The side information to be transmitted with the speech frame over the TRAU interface is a binary flag Speech (SP). SP=1 indicates that the TRAU frame is a speech frame and SP=0 indicate that the TRAU frame is a special SID‑frame. This flag is used in the BTS for control of the radio transmission.

The channel encoder is tested in subclause 7.2 of GSM 11.21 [19].

Requirement reference

GSM 06.31 [11]

5.2 Test descriptions for half rate speech related transcoding functions

The two steps for the Half Rate (HR) speech transcoding process consists in the following. In the uplink the first step transforms the 5.6 kbit/s bitstream into 104 kbit/s (13 bit linear PCM at 8 kHz). The second step transforms this 13 bit linear PCM into 8 bit A law PCM. In the downlink the order is reversed. This is exactly followed in BSS types 1 and 3. For other BSS types there is an intermediate step in which the 5.6 kbits/s data is mapped into a 16 kbit/s or an 8 kbit/s bitstream containing TRAU frames.

The test sequences for half rate speech transcoding are defined in GSM 06.07 [24] and can be obtained from ETSI Secretariat. The tests for half rate are the same as the ones described for full rate.

For further information see GSM 06.02 [22], GSM 06.06 [23], GSM 06.07 [24], GSM 06.20 [25], GSM 06.21 [26], GSM 06.22 [27], GSM 06.41 [28], GSM 06.42 [29] and GSM 08.61 [30].

5.3 Test descriptions for enhanced full rate speech related transcoding functions

The two steps for the Enhanced Full Rate (EFR) speech transcoding process consists in the following. In the uplink the first step transforms the 12.2 kbit/s bitstream into 104 kbit/s (13 bit linear PCM at 8 kHz). The second step transforms this 13 bit linear PCM into 8 bit A law PCM. In the downlink the order is reversed. This is exactly followed in BSS types 1 and 3. For other BSS types there is an intermediate step in which the 12.2 kbits/s data is mapped into a 16 kbit/s bitstream containing TRAU frames.

The test sequences for enhanced full rate speech transcoding are defined in GSM 06.54 [31] and can be obtained from ETSI Secretariat. The tests for half rate are the same as the ones described for full rate.

For further information see GSM 06.51 [32], GSM 06.53 [33], GSM 06.60 [34], GSM 06.61 [35], GSM 06.62 [36], GSM 06.81 [37], GSM 06.82 [38] and GSM 08.60 [17].

5.4 Alternative use of the 64 kbit/s A-Interface for full, half and enhanced full rate speech transcoding tests

As an alternative to the use of the 104 kbit/s interface marked as x and x’ in the figures 11.24-2 and 3, the A-Interface marked as z and z’ at a level of 64 kbit/s can be used for transcoder testing. In this case no special test interface or test mode is required at the transcoder and the test can be performed in operational mode.

Except for the use of interface z/z’ and the appropriate test sequences, the tests are identical to the ones described in subclause 5.1. Interfaces x and x’ and the conversion tests between 104 kbit/s and 64 kbit/s are not necessary in this case.

All tests for conversion from and to 104 kbit/s can alternatively be substituted by tests from and to A- or µ-law compressed speech at 64 kbit/s. The specifications are same as described above.