The real-time vocoder allows you to perform the audio test in two aspects:
The real-time vocoder functionality allows you to perform the functional test for the analog voice capability of the mobile station when the
Operating Mode
of the real-time vocoder is set to
Normal
:
The real-time vocoder functionality allows you to calibrate the audio output gain, audio input gain and internal codec loopback gain of the test set when the
Operating Mode
of the real-time vocoder is set to
Calibration
.
The audio output gain calibration is performed when the
Calibration Type
is set to
Audio out Path
. The test set sends a full scale sinewave to the AUDIO OUT port. The audio output gain can be determined by measuring the output analog signal.
The audio output gain calibration result helps to perform the acoustic measurements of the mobile station, for example, the sending sensitivity frequency response.
You can get the audio input gain of the test set in two ways:
Audio In Path
. The test set samples the input signal from the
AUDIO IN
port and loops them back to the
AUDIO OUT
port via the DAC. If an audio output path calibration has already been done, the audio input gain can be derived from the loopback gain and the audio output gain.
Audio Out Path
, looping the full scale sinewave from the
AUDIO OUT
port to the
AUDIO IN
port. As the audio output gain can be obtained by audio output path calibration, the audio input gain can be determined by reading the
Encoder Headroom
The audio input gain calibration result helps to perform the acoustic measurements of the mobile station, for example, the receiving sensitivity frequency response.
The internal codec loopback gain calibration is performed when the Calibration Type is set to Internal Codec. The test set samples the input signal from the AUDIO IN port, encodes the samples with the voice encoder and loops them back to the voice decoder, then sends the signals to the AUDIO OUT port via the DAC.
The internal codec loopback gain calibration result helps to perform the acoustic measurements of the mobile station, for example, the echo loss.
The following parameters can be set from the Real-Time Vocoder Parameters menu. To access the Real-Time Vocoder Parameters menu, see How Do I Use Real-Time Vocoder? .
When the test set is in the real-timer vocoder mode (see
Voice SO Mode
),
Expected Audio In Peak Voltage
sets the peak voltage of the analog audio input signal that can produce a full scale ADC output. It is used to adjust the audio input path gain before the ADC to produce a full scale ADC output. For example, if the input signal is 1V peak, then setting the
Expected Audio In Peak Voltage
to 1V will get the ADC output to be full scale. Then,
Expected Audio In Peak Voltage
to a value more than 1V (e.g. 2V) to avoid the clip.Whenever you change this setting, it is not applied until the test set is set to the real-timer vocoder mode.
GPIB command: CALL:RTVocoder:INPut:VOLTage[:EXPected][:SELected]
When the test set is in the real-timer vocoder mode (see
Voice SO Mode
),
Maximum Audio Out Peak Voltage
sets voltage of the peak analog audio output relative to the DAC full scale output. It is used to adjust the analog audio input path gain after the DAC to get a desired peak voltage output at the test set's AUDIO OUT port. For example, if the
Maximum Audio Out Peak Voltage
is set to 1V, then the peak output of a full scale sine wave will be 1 V.
Setting this value makes the test set adjust the audio output path gain to achieve the desired audio output level at the test set's AUDIO OUT port. However, the actual output signal also depends on the voice signal decoded from the received R-FCH/R-Traffic voice data. The decoded signal may not be normalized to DAC (Digital to Analog Converter) full scale range (The Decoder Headroom gives information on how close to full scale the current audio signal coming out of the vocoder is). So it is possible that the final signal level is lower than the configured level.
Whenever you change this setting, it is not applied until the test set is set to the real-time vocoder mode.
GPIB command: CALL:RTVocoder:OUTPut:VOLTage[:MAXimum][:SELected]
Sets how to select the encoding data rate to produce the encoded data frames.
Auto
is selected, the test set determines the encoding data rate based on the received signal level.
Fixed
is selected, the test set uses the encoding data rate set by
Encoder Data Rate
.
Limited
is selected, the test set uses the encoding data rate no greater than the setting of
Encoder Data Rate
.GPIB Command: CALL:RTVocoder:ENCoder:DRATe:MODE[:SELected]
Sets the encoding data rate used when the
Encoder Data Rate Mode
is set to
Fixed
or the maximum encoding data rate used when the
Encoder Data Rate Mode
is set to
Limited
.
GPIB Command: CALL:RTVocoder:ENCoder:DRATe[:SELected]
Sets whether the real-time vocoder works at the normal or calibration mode when a voice call (such as
SO1,
SO3, SO17, SO68, SO70
or
SO32768
, see
Service Option
) is established and the
Voice SO Mode
is set to
Real-Time Vocoder
.
Normal
is selected, you can perform the normal functional test for the analog voice capability of the mobile station.
Calibration
is selected, you can calibrate the audio input gain, audio output gain and the internal codec loopback gain of the test set. GPIB Command: CALL:RTVocoder:OPERating:MODE
When the
Operating Mode
is set to
Calibration
, Calibration Type determines whether the audio output path, the audio input path or the internal codec loopback gain of the test set is calibrated.
GPIB Command: CALL:RTVocoder:CALibration:TYPE
When the
Operating Mode
is set to
Calibration
and the
Calibration Type
is set to Audio Out Path, Audio Out Frequency sets the frequency of the sinewave sent out by the test set.
GPIB Command: CALL:RTVocoder:OUTPut:FREQuency
The following results are displayed on the Real-Time Vocoder Information window when a voice call (SO1, SO9, or SO32768) is established and the test set is in the real-timer vocoder mode (see Voice SO Mode ).
Indicates how close it is for the AUDIO IN input analog signal to produce a full scale ADC (Analog to Digital Converter) output. This result is updated at about one second period and calculated as follows:
Encoder Headroom (dB) = 20 *Log (( ADC positive full scale - ADC negative full scale ) / ( maximum encoder input sample - minimum encoder input sample )
The full scale ADC output occurs when the encoder headroom reports a value of 0dB. In order to know what input voltage produces a full scale ADC output, you can either adjust the input gain by setting the Expected Audio In Peak Voltage or adjust the input analog signal level.
When the input signal is over-range, the headroom is clipped to zero.
GPIB command: CALL:RTVocoder:ENCoder:HEADroom[:SELecte]?
Indicates how close it is for the audio signal coming out of the vocoder to hit the DAC (Digital to Analog Converter) full scale. You can adjust the encoder headroom by setting Maximum Audio Out Peak Voltage
This result is updated at about one second period.
GPIB command: CALL:RTVocoder:DECoder:HEADroom[:SELected]?
Active Cell
.
IS-95
or
IS-2000.
SO1,
SO3, SO17, SO68
, SO70, or
SO32768
(see
Service Option
).
Real-Time Vocoder
, all of the measurements and instruments except for the Frame Error Rate measurement, Audio Generator and Data throughput Monitor, are unavailable. This is because many of the DSP resources are consumed to meet the real-time requirements for vocoder frame delivery or analog audio generation.
Real-Time Vocoder
, you can not change the audio source parameters such as output level and the source to be routed to the AUDIO OUT connector (see
AFGenerator Subsystem
).