Digital Audio Interface (DAI) Description

Last updated: September 29, 2009

This section is only applicable to the lab applications and the test application with a required feature license.

Digital Audio Interface (DAI) is a special interface to offer a platform that complete the conformance of speech codec test and the SLR/RLR (Sending/Receiving Loudness Rating) performance test of the analogue and acoustic devices. Through DAI, you can insert and extract speech data in both the transmit and receive directions. Note that only the speech coder/decoder test is discussed in this section.

See 3GPP TS 44.014 for more information about Digital Audio Interface information.

Digital Audio Interface (DAI) Overview

The following figure shows the location of Digital Audio Interface in the Mobile Station. You can test the codec implementation of the Mobile Station based on a number of digital audio files sending or receiving through the Digital Audio Interface.

The interface provides the data exchange of 13 bit linear PCM at 8000 samples per second. In order to keep the pin count low, the data are transferred on a duplex set of serial lines at 104 kbits/s.

Digital Audio Interface (DAI) test process

DAI test process are displayed as the following steps:

SS (System Simulator) sends a TEST_INTERFACE message by means of the layer 3 message or applies the appropriate test control signal on the DAI to activate a test.
After more than one second, test system applies a reset pulse.
Mobile Station starts test by issuing clock pulse with the release of the reset pulse at the same time.
Uplink speech transcoding/DTX function test: Encode the first speech sample bit at first falling clock edge requests from the SS. The data transmission starts at the next earliest possible interleaved block TDMA frame after the release of the reset pulse.
Downlink speech transcoding/DTX function test: Decode the first speech sample bit at the first falling clock edge requests from the SS. The data transmission starts at the next earliest possible interleaved block TDMA frame after the release of the reset pulse.
By the end of the reset pulse, the Mobile Station transcoder is reset. The DAI is always in one of the active states (Test of speech decoder/DTX function (downlink), Test of speech encoder/DTX function (uplink), Test of acoustic devices and A/D and D/A).

The figure below shows the timing of the Digital Audio Interface:

Digital Audio Interface (DAI) Typical Test System Configuration

The following diagram shows a typical Digital Audio Interface test system configuration.

The Digital Audio Interface (DAI) typical test system is made up of Custom Test Station, GSM Mobile Station, 8960 Test set. The Customer Test Station connects with the Test Set via the GP-IB Interface and http Interface with Host Lan Cable. The Customer Test Station connects with the Mobile Station via Digital Audio Interface with suitable LAN Cable. The Test set connects with the Mobile Station via RF Interface.

The Customer Test Station acts as the control center of the DAI test system. The Customer Test Station can download/upload digital audio file into the test set using the 8960 DAI File Manager software, start the DAI Test, command the test set to start/stop playing or recording the digital audio files, and query the play or record status of the digital audio file by sending GPIB command to the test set.

The Customer Test Station or Controller releases reset pulse to command the Mobile Station to start test by issuing clock pulses when data transfer. The DAI doesn't have access to send the reset pulse.

The figure below shows the detailed view of the Digital Audio Interface test path. The test file is associate with codecs which can be Full Rate Speech (FS), Enhanced Full Rate Speech (EFS) and Half Rate Speech (HS), Adaptive Full Rate Speech (AFS), Adaptive Half Rate Speech (AHS) and Wideband Adaptive Full Rate Speech (WFS).

You can Test the Speech Decoder by performing the Digital Audio Interface (DAI) Downlink Test steps and the Speech Encoder by performing the Digital Audio Interface (DAI) Uplink Test steps .

Digital Audio Interface (DAI) Downlink Test steps

DAI Downlink Test is used to test the performance of the Speech Decoder in the Mobile Station. To perform a downlink test, You should follow the following steps:

Select which Logical Speech Channel is to be tested in the test set.
Customer test station upload the COD/DEC reference file into the test set using the DAI File Manager, indicating which codec it applies to. An error message is displayed if the parse checking failed on the COD reference file.
Note, the DAI File Manager is an unofficial tool provided by Agilent, which helps you to upload/download the DAI files to/from the test set. You can launch the DAI File Manager from the following webpage:

url: http://wireless.agilent.com/rfcomms/dloads/swdownloads.aspx?pageid=45

Access code: bdv2ghk
Starts a voice call between the test set and the DUT (either Mobile Originated or Mobile Terminated).
Set the DAI Test Interface to `Speech Decoder' in the test set, this action will result in the Layer 3 Test_Interface message being sent to DUT over the air interface. However, for the mobile stations which do not respond to the layer 3 Test_Interface message, Customer test station should send the test control signal through the DAI to notify the DUT to enter the Speech Decoder test mode.
Customer test station applies reset pulse to DUT.
Customer test station starts recording the OUT file from the Mobile Station.
The test set starts playing the COD/DEC reference file which has been uploaded to it.
Customer Test Station requests interrupt from the test set until the COD/DEC reference file playing complete.
Customer test station stops recording the OUT files from Mobile station and processes results.
Set the DAI Test Interface to `Off' in the test set and stop the voice call connection.

See How to play the Digital Audio Interface (DAI) File for instructions on how to play the COD/DEC file and upload the digital audio file via the test set.

See Programming a Downlink DAI Test for instructions on how to program a automatic DAI Downlink Test.

Digital Audio Interface (DAI) Uplink Test steps

DAI Uplink Test is used to test the performance of the Speech Encoder in the Mobile Station.To perform a uplink test, You should follow the following steps:

Select which Logical Speech Channel is to be tested in the test set.
Starts a voice call between the test set and the DUT (either Mobile Originated or Mobile Terminated).
Set the DAI Test Interface to `Speech Encoder' in the test set, this action will result in the Layer 3 Test_Interface message being sent to DUT over the air interface. However, for the mobile stations which do not respond to the layer 3 Test_Interface message, Customer test station should send the test control signal through the DAI to notify the DUT to enter the Speech Encoder test mode.
Customer test station applies reset pulse to DUT.
The test set to start recording the COD file it received from the DUT.
Customer test station start playing the INP file to the Mobile Station.
The test set stop COD file recording.
Customer test station download the COD file from the test set using the DAI File Manager.
Set the DAI Test Interface to OFF and stop the call connection.

See How to record the Digital Audio Interface (DAI) File for instructions on how to record the COD/DEC file and download the digital audio file via the test set.

See Programming a Uplink DAI Test for instructions on how to program a automatic DAI Uplink Test.

Impact on Other Measurements

The following measurements shall be shut down for the duration of the play/record operation.

GSM Bit Error
GSM Fast Bit Error
AMR In-band Frame Error

Digital Audio Interface (DAI) Parameters

DAI Test Interface
This parameter allows you to select which component in the mobile station is to be tested (Speech Encoder, Speech Decoder, or Acoustic), or just command the mobile station to work in normal state by setting the DAI to `Off'. The DAI Test Interface setting is stateless. Selecting the DAI Test Interface will result in the Layer 3 Test_Interface command being sent to the MS.

If an attempt is made to select Speech Decoder, Speech Encoder or Acoustic while the Operating Mode is not active cell an error message is generated: "Cell operation rejected; Protocol request ignored ."

The GPIB command to set this parameter is CALL:TCHannel:DAINterface:TINTerface .
Start COD Play
This parameter is used to start playing the COD/DEC reference file in the test set.

The following conditions are checked if you attempt to start playing a COD/DEC file. If one of these conditions is not met, an error message is generated:
- COD/DEC reference file has been downloaded successfully.
- COD/DEC reference file matches the currently set 'Logical Speech Channel'.
- If 'logical Speech Channel' is AMR' then the COD/DEC file refers to only those AMR codec rates specified in the codec set and all codec rate changes are on odd or even frames. See Adaptive Multi-Rate (AMR) Feature Descriptions for more information.
- Voice call is in progress.
The GPIB command to set this parameter is CALL:DAINterface:PLAY:STARt .
Stop COD Play
This parameter is used to stop playing the COD/DEC reference file in the test set.

The GPIB command to set this parameter is CALL:DAINterface:PLAY:STOP .
Playing StatusThis parameter queries the Playing Status of the COD/DEC reference file.
The GPIB command to set this parameter is CALL:DAINterface:PLAY:STATus .
Start COD Record
This parameter is used to start recording the COD file in the test set.

The following conditions are checked if you attempt to start recording a COD/DEC file. If one of these conditions is not met, an error message is generated:
- The test set is capable of recording for the specified Logical Speech Channel.
- Voice call is in progress.
In addition to the above conditions, an error message is generated on the following conditions:
- The record COD file reaches its 2 MByte limit.
- The voice call end for any reason during recording and the recording terminate immediately.
The GPIB command to set this parameter is CALL:DAINterface:RECord:STARt .
Stop COD Record
This parameter is used to stop recording the COD file in the test set.

The GPIB command to set this parameter is CALL:DAINterface:RECord:STOP .
Recording Status
This parameter queries the Recording Status of the COD file.

The GPIB command to set this parameter is CALL:DAINterface:RECord:STATus .
Playing / Recording Progress
The Playing Progress indicates how far through playing the uploaded COD/DEC reference file the test set is.

The Recording Progress indicates how far through the maximum possible capture COD file the test set is.

The Playing / Recording Progress indicators are displayed on the front panel and updated frequently.

Operating Considerations

The Digital Audio Interface test is only available in active cell operating mode. If the 'Operating Mode' is changed to anything other than 'Active Cell', any active playing or recording of COD/DEC files is stopped.

On either full or partial preset the following actions are taken

any uploaded COD/DEC file is removed.
any recorded (or partially recorded) COD file is removed.
playing or recording is stopped
play and record indicators go to `idle', and Progress and Record Buffer Usage indicators go to `0%'.

The DAI Test also applies to the Dual Transfer Mode, You can perform the test on the voice call portion of the DTM connection.