The Perceptual Evaluation of Speech Quality measurement can not be concurrent with the Audio Analyzer instrument or the Real Time vocoder, nor can it be concurrent with the Swept Audio or the Multi-tone audio measurement. Hence starting the PESQ measurement will turn off any other measurement that is active, and vice versa.
How is a PESQ measurement made?
Perceptual Evaluation of Speech Quality (PESQ), as defined in the ITU-T P.862 standard, is a objective method to test the speech quality of the mobile station. The objectivity is based on the comparison to the traditional MOS (Mean Opinion Score) method in which a group of listeners are used to rate the voice quality to a value ranging from 1(bad) to 5 (excellent).
When any of the voice service options is active (see
Service Option
) and the
Voice SO Mode
is set to PESQ, the test set supports the PESQ measurement by comparing the original signal with the received signal passed through a communication system. After the PESQ analysis, a score is given ranging from -0.5 to 4.5. A higher score means a better speech quality.
There are three modes provided for this measurement: Uplink Audio, Downlink Audio and Both.
-
Uplink Audio: The test set acts as an audio generator, generates the original signal and sends it to the front-panel
AUDIO OUT
port which is connected to the mobile station's audio in port. The mobile station encodes the signals into speech frames of the uplink traffic channel. The test set then decodes the received speech frames, compares the original signal with the received signal and makes the PESQ measurement. See
Typical Signal Flow with Uplink Audio Mode
.
Typical Signal Flow with Uplink Audio Mode
-
Downlink Audio: The test set acts as an audio generator, generates the original signal and encodes it into speech frames of the downlink traffic channel. The mobile decodes the received speech frames and outputs it to its audio out port which is connected to test set' s
AUDIO IN
port. The test set then compares the original signal with the received signal and makes the PESQ measurement. See
Typical Signal Flow with Downlink Audio Mode
.
Typical Signal Flow with Downlink Audio Mode
-
Both: The test set performs the Uplink Audio measurement and Downlink Audio measurement simultaneously.
Known issue with PESQ algorithm for EVRC family of vocoders used in cdma2000: The PESQ algorithm does not properly score the more advanced vocoders used in cdma2000 (EVRC, EVRC-B and EVRC-WB), which causes the PESQ score to be lower than the MOS score given by human test subjects. The measurement scores obtained from the test set's PESQ measurement should not be used to compare vocoder voice quality with other vocoders (such as AMR). In addition, the test results should not be used to compare the voice quality of phones running at different operating points for vocoders that use variable operating points (such as EVRC-B). For details, see
http://www.qualcomm.com/common/documents/white_papers/PESQ_Limitations_Rev_C_Jan_08.pdf.
PESQ Measurement Parameters
The parameters shown in the PESQ Setup menu include:
-
Measurement Mode - specifies the measurement mode to perform the PESQ measurement. When
Uplink Audio
is selected, the test set generates the original signal and analyzes the received uplink signal from the mobile to perform the PESQ measurement. When
Downlink Audio
is selected, the test set generates the original signal and analyzes the signal at its
AUDIO IN
port. If the
Measurement Mode
is set to Both, the test set performs the uplink and the downlink PESQ measurement simultaneously.
It is suggested to do the uplink and downlink PESQ measurement respectively although the test set supports the "Both" measurement mode. This is because some mobile phones have bad isolation between their audio in and audio out path. If performing the downlink and uplink measurement simultaneously, the uplink measurement will be affected a lot by the Downlink measurement.
-
Speech Source - specifies the speech source for use to perform the PESQ measurement. The test set supports two speech sources in accordance with the ITU-T P.862 standard:
Male
and
Female
.
-
Expected Audio In Peak Voltage - Specifies the
absolute peak
voltage of the audio signal expected at the
AUDIO IN
port of the test set.
-
Maximum Audio Out Peak voltage - Specifies the
maximum peak
voltage of the audio signal that can be output at the
AUDIO OUT
port of the test set.
-
Trigger Arm - (see
Trigger Arm (Single or Continuous) Description
).
-
Measurement Timeout - (see
Timeouts
).
PESQ Measurement Results
-
Integrity Indicator - (see
Integrity Indicator
).
-
Uplink PESQ Score - indicates the uplink PESQ score, with the range from -0.5 to 4.5.
-
Downlink PESQ Score - indicates the downlink PESQ score,with the range from -0.5 to 4.5.
-
PESQ Uplink Headroom - indicates the signal headroom value before PESQ analysis when doing uplink PESQ measurement. This value can help you to adjust the signal level at the audio in port of the mobile so that the uplink signal level is not too large or too small to affect the PESQ score.
-
PESQ Downlink Headroom - indicates the signal headroom value before PESQ analysis when doing downlink PESQ measurement. This value can help you to adjust the downlink signal level so that the signal at the AUDIO IN port of the test set is not too large or too small to affect the PESQ score.
-
PESQ Measurement Status - indicates the whether the PESQ measurement is
In Progress
or
Completed
.