Voice over LTE (VoLTE) Speech Quality Measurements

Transcription

1 Application Note O. Gerlach MA204_ 6e Voice over LTE (VoLTE) Speech Quality Measurements Application Note Products: R&S CMW500 R&S UPV R&S UPV66 R&S AMU200 This application note and associated application software may be used to conduct psychoacoustic speech quality evaluation for Voice over LTE (VoLTE) connections. The measurements are based on recommendations ITU-T P.862 and ITU-T P.863. The included software sequence performs decoder/encoder calibration, connection setup for the UE under test and subsequent speech quality analysis under fading conditions.

2 Table of Contents Table of Contents 1 Overview Hardware Setup VoLTE Test Setup with MEDIA Server on CMW VoLTE Test Setup with Media Server on Media PC Software Requirements CMW UPV VoLTE Media Server POLQA_CAL R&S Run VoLTE POLQA / PESQ Measurements with RSrun RSrun Configuration Test Plan Description Basic Initialization Fading Scenario LTECallSetup Speech_Quality_Measurement LTECallDisconnect Program Flow Expected MOS/LQO Results Running the Test Literature Additional Information Ordering Information MA204_ 6e Rohde & Schwarz Voice over LTE (VoLTE) Speech Quality Measurements 2

3 Overview VoLTE Test Setup with MEDIA Server on CMW500 1 Overview Cellular Radio Operators face an increasing pressure to free existing spectrum as currently used for voice-centric services in order to allow its re-use for a broad range of integrated media applications. This means existing circuit-switched voice services have to be offered as just one of many applications on a packet-switched network without sacrificing the quality users have come to expect. Stand-alone or integrated media voice is and will remain a key application for mobile radio service subscribers. Operators of such services strive to ensure or even improve voice quality despite the additional challenges that a packet-based transmission of speech entails. The VoLTE (Voice over LTE) packet service uses the IMS (IP Multimedia Subsystem) as architecture. One of the key enablers for the architecture is the Session Initiation Protocol (SIP) e.g. used for negotiating the codec type, AMR-NB (Adaptive Multiratenarrow band) or AMR WB (wideband) and coderate (e.g kbps). VoLTE uses the AMR-WB codec and can transfer signals with twice the sample rate (16000 Hz) as classic circuit switched systems, e.g. AMR-NB, GSM-HR (half-rate) or GSM-FR (full rate). VoLTE on one hand has advantage of an enhanced frequency spectrum and on the other hand variable latency and possible IP impairments. The described solution in this application note explains the measuring of speech quality with the PESQ (Perceptual Evaluation of Speech Quality) and POLQA (Perceptual Objective Speech Quality Assessment) algorithm. As successor of PESQ, the new POLQA method is designed for additional test applications such as SWB (Super Wideband Mode), bandwidth extensions etc.. A further benefit of this algorithm is that the resulting MOS-LQO (Mean Objective Score Listening Quality Objective) results measured with other radio access technologies (e.g. GSM, CDMA2000) are comparable to each other. This application note describes how to perform VoLTE PESQ and POLQA measurements with an R&S CMW500 Wideband Communication Tester, an R&S UPV Audio Tester using the included test sequence for the R&S Run Sequencer Software Tool. It contains an automated POLQA / PESQ measurement similar as described in reference [7]. The test establishes a call to a LTE mobile or PC card, configures fading & AWGN on the R&S AMU, calibrates the audio interface for R&S UPV (decoder/encoder ) and performs either a POLQA measurement according to recommendation ITU-T P.863 or PESQ measurement according to recommendation ITU-T P.862 of the speech signal received (downlink) or transmitted (uplink) by the user equipment (UE). The following abbreviations are used in the following text for R&S test equipment: The R&S CMW500 Wideband Communication Tester is referred to as CMW500. The R&S UPV Audio Analyzer is referred to as UPV. The R&S AMU200A Fading Simulator is referred to as AMU. R&S Run is referred to as RSrun. R&S refers to Rohde & Schwarz GmbH und Co KG POLQA and PESQ are a registered trademarks of OPTICOM Dipl.-Ing. M. Keyhl GmbH, Germany and of Psytechnics Ltd., UK 1MA204_ 6e Rohde & Schwarz Voice over LTE (VoLTE) Speech Quality Measurements 3

4 Hardware Setup VoLTE Test Setup with MEDIA Server on CMW500 2 Hardware Setup The CMW will provide an internal audio board with various speech codecs in the near future but in the meantime, the audio connection can be established by an external audio interface connected to the CMW or an additional PC. It is not recommended to use the on-board audio interface of the external PC. The described setup is used for measurements based on an electrical audio connection as shown in the following figures. External USB audio interfaces usually have balanced XLR inputs and balanced or unbalanced ¼ output jacks. This requires following cables: XLR female (UPV generator output) XLR female (audio interface input) standard microphone cable. XLR male (UPV analyzer input 2) stereo jack ¼ (audio interface output) cable. 4-pin jack 1/8 (3.5 mm, mobile output) XLR male cable (UPV analyzer input 2 for downlink) and XLR female cable (UPV generator out 1 for uplink). The 4-pin jack can have two different pin outs depending on the mobile phone manufacturer. The UP-Z9 cable set contains these two different types. The described setup is used for measurements based on an electrical audio connection as shown in the following figures. It would also be possible to use an acoustical audio interface (artificial head with artificial mouth and ear) instead of the pure electrical connection. An additional calibration step is required in that case and not described here. The following sections describe several different setup variations. 2.1 VoLTE Test Setup with MEDIA Server on CMW500 This setup consists of 1. CMW500 Communication Tester is connected to the LTE UE via RF. It provides IMS infrastructure, establishes a VoLTE call and transmits RTP packets to and from the UE. The remote client application VoLTE Media Server starts and stops the FFMPEG, FFPLAY processes depending on TCP commands received from the CMW500 DAU (port 1000) or the Remote PC (port 9900). Be sure to use the LAN Switch 2 (rear) connector for remote control. 2. USB Audio Interface connected to the CMW500. Install the appropriate driver on the CMW500 before connecting the audio interface. The Windows XP OS on the CMW500 requires the UPV generator 2 output to be fed equally to the left and right line or mic inputs of audio interface via XLR Y-cable (see Figure 2-1). If only one input is used, the maximum detected level limited to 6 dbfs. 3. AMU200A Baseband Fading Simulator for simulating fading effects of the downlink RF path. 4. UPV Audio Analyzer for performing POLQA and PESQ measurements of downlink and uplink audio signals. 5. Remote PC equipped with a LAN interface with a fixed IP address (default ) and the RSRUN test case SPEECH QUALITY MEASUREMENT.RSTP for performing POLQA / PESQ measurements remotely. 6. LTE UE with IMS / VoLTE capability. 1MA204_ 6e Rohde & Schwarz Voice over LTE (VoLTE) Speech Quality Measurements 4

5 to microphone in (UL) from speaker out (DL) Hardware Setup VoLTE Test Setup with MEDIA Server on CMW500 CMW500 (VoLTE Media Server) LAN Switch 2 (Rear) RF LTE UE from CMW DHCP I/Q Dig. Baseband In I/Q Dig. Baseband Out Ref 1 Out Ref In LAN AMU200A LAN UPV Line/Mic In L/R Line Out USB USB Audio Interface LAN Switch LAN1 LAN2 LAN3 LAN4 Remote PC (CMWrun + VoLTE POLQA / PESQ add-on DLL) LAN Figure 2-1: VoLTE test setup with Media Server running on CMW500 1MA204_ 6e Rohde & Schwarz Voice over LTE (VoLTE) Speech Quality Measurements 5

6 Hardware Setup VoLTE Test Setup with Media Server on Media PC CMW500 LAN Switch 2 (Rear) UPV LAN connector Figure 2-2: CMW500 LAN remote config Figure 2-3: UPV LAN remote configuration AMU LAN Connector Remote PC LAN connector Figure 2-4: AMU LAN Configuration Figure 2-5: Remote PC LAN configuration Note: For demo purposes it may be convenient to use an LTE USB data device connected to the Remote PC in conjunction with an IMS client also running there. In this case you must use different subnets for remote control (e.g. CMW , UPV , AMU and Remote PC ) and audio data stream traffic (e.g. CMW500 P-CSCF Address UE (received from CMW500 DAU DHCP). Figure 2-6: UE IP configuration Figure 2-7: CMW500 P-CSCF config If the subnets are not separated it can happen that the audio data stream takes the direct IP path without being degraded by the encoder (FFMPEG) and decoder (FFPLAY) resulting in perfect (POLQA , PESQ ), but false MOS-LQO values. 2.2 VoLTE Test Setup with Media Server on Media PC This setup is similar to 2.1 with the difference that the VoLTE Media Server runs on a separate Media PC. It uses no CMW or UPV CPU resources and is ideal for performing demos at various locations without the need of installing additional software on the CMW500 or UPV. It consists of 1. CMW500 Communication Tester which is connected to the LTE UE via RF, provides IMS infrastructure, establish a VoLTE call and transmits VoLTE data packets to and from the UE. Be sure to use the LAN Switch 2 (rear) connector for remote control. 2. UPV Audio Analyzer which uses one analyzer input / generator output pair for measuring the downlink and the other one for the uplink data stream. 1MA204_ 6e Rohde & Schwarz Voice over LTE (VoLTE) Speech Quality Measurements 6

7 to microphone in (UL) from speaker out (DL) Hardware Setup VoLTE Test Setup with Media Server on Media PC 3. AMU200A Baseband Fading Simulator for simulating fading effects of the downlink RF path. 4. Media PC with Windows 7 OS, LAN interface and an internal or external USB audio interface. Both interface types require the appropriate driver to be installed first. 5. LTE UE with IMS / VoLTE capability. 6. Remote PC controlling the test setup via RSrun for performing POLQA / PESQ measurements CMW500 RF LTE UE LAN Switch 2 (Rear) AMU200A I/Q Dig. Baseband In I/Q Dig. BB Out Ref 1 Out Ref In LAN LAN UPV LAN Switch Media PC with Windows 7 OS Line-In Line-Out (VoLTE Media Server + internal or external USB audio interface) LAN LAN1 LAN2 LAN3 LAN4 LAN5 Remote PC (RSrun + VoLTE POLQA / PESQ add-on DLL) LAN Figure 2-8: VoLTE test Setup with Audio Interface in external PC 1MA204_ 6e Rohde & Schwarz Voice over LTE (VoLTE) Speech Quality Measurements 7

8 Software Requirements CMW500 3 Software Requirements For running the VoLTE POLQA / PESQ test plan with RSrun you need following software environment to be installed on the CMW500, UPV and PC units: 3.1 CMW500 On the CMW500 following software options are mandatory (the version numbers should be equal are higher): CMW BASE v CMW Data Application Support v CMW LTE Sig v UPV Please use UPV firmware version or higher. 3.3 VoLTE Media Server The VOLTE MEDIA SERVER program installer (CMW-MEDIA-SERVERv exe or higher) can be downloaded from the GLORIS CMW Customer Web. It contains MEDIASERVERGUI.EXE Receives command strings via TCP from CMW500 DAU (default , port 1000) and Remote PC (default , port 9900). FFMPEG.EXE VoIMS (Voice over IMS) customized downlink encoder. FFPLAY.EXE VoIMS customized uplink decoder. and must be installed where the audio interface is located, either on the CMW500 (see 2.1) or an external Media PC (see 2.2) to the selected directory (default C:\Program Files\Rohde-Schwarz\MediaServer\). Note: The MEDIASERVER icon should be placed into the START PROGRAMS STARTUP menu so it will automatically start when the CMW500 or Media PC is booted. 1MA204_ 6e Rohde & Schwarz Voice over LTE (VoLTE) Speech Quality Measurements 8

9 Software Requirements POLQA_CAL 3.4 POLQA_CAL Install POLQA_CAL_102.msi on the UPV to the default directory as shown below. Figure 3-1: POLQA_CAL installation on UPV The UPV settings files and reference wave files are located in the C:\Program Files\Rohde&Schwarz\POLQA_CAL\Files\ subdirectory. The files in that directory can be copied to e.g. D:\UPV\POLQA_CAL\. This directory name must be used in the Speech_Quality_Measurement GUI (see Figure 4-10). 3.5 R&S Run Install R&S RUN or higher on the REMOTE PC. Download it from It contains the SPEECH_QUALITY_MEASURMENT (requires existing LTE connection) and VOLTE_SPEECH_QUALITY_MEASUREMENT (automatic LTE connection) test case and test plan. The VoLTE_Speech_Quality_Measurement test plan is dimmed in case the option CMW-KT055 CMWrun/RSrun Sequencer LTE is not installed on the CMW500. 1MA204_ 6e Rohde & Schwarz Voice over LTE (VoLTE) Speech Quality Measurements 9

10 RSrun Configuration 4 VoLTE POLQA / PESQ Measurements with RSrun 4.1 RSrun Configuration Start RSrun first. In this example the hardware setup described in section 2.1 is used. Before loading the test plan it is necessary to define the devices resource strings in the Resources SCPI Connections menu. In this example a CMU500 Communication Tester, a UPV Audio Analyzer and an AMU200 Fading Simulator are used. Figure 4-1: RSrun SCPI Connections menu Make sure to set the UPV Timeout to 60 seconds by pressing CONFIGURE to avoid timeout errors. Do the same for the CMW500 and AMU. Figure 4-2: Set UPV Resource Name and Timeout 1MA204_ 6e Rohde & Schwarz Voice over LTE (VoLTE) Speech Quality Measurements 10

11 Test Plan Description 4.2 Test Plan Description The test plan VOLTE SPEECH QUALITY MEASUREMENT.RSTP needs the CMW-KT055 Sequencer LTE option to be installed. The example test plan in chapter 4.4 (SPEECH QUALITY MEASUREMENT.RSTP) is platform independent and does not need this option. Figure 4-3: RSrun test plan VoLTE Speech Quality Measurement The test plan consists of several test items and custom SCPI sequences Basic Initialization This component handles the basic configuration and e.g. resets the CMW500 to default settings. By double clicking BASICINITIALIZING a configuration window opens. Check RESET INSTRUMENT(S). This should always be performed to ensure identical starting conditions on different systems. Figure 4-4: Basic Initialization 1MA204_ 6e Rohde & Schwarz Voice over LTE (VoLTE) Speech Quality Measurements 11

12 Test Plan Description Recall CMW Configuration (SCPIPollState) This function recalls the test setup for a certain UE. Figure 4-5: LTE Call Setup Parameters Fading Scenario Figure 4-6: Fading & AWGN Settings FADER Selects external AMU fader (connected via digital I/O) or CMW internal fader (default External). FADING SCENARIO Choose type of signal path in the CMW and AMU. Either SISO (Single In Single Out) Path A or B or MIMO (Multiple In Multiple Out). The Scenario must be set in the CMW before the mobile is attached. SYSTEM BANDWIDTH Defines the expected bandwidth (10 or 20 MHz) of the LTE signal (default 10 MHz). 1MA204_ 6e Rohde & Schwarz Voice over LTE (VoLTE) Speech Quality Measurements 12

13 Test Plan Description MIN.NOISE TO SBW RATIO Defines the ratio of the noise bandwidth to the system bandwidth. High precision power measurements (tolerance 0.01 db) require the noise signal have at least the same bandwidth as the signal. This can be ensured by increasing the noise bandwidth (e.g. Ratio = 1.2). BIT RATE Only important in case En/N0 of the corresponding SNR (Signal to Noise Ratio) should be display correctly. IMS Configuration (SCPICommandList) This command sequence allows to change the IMS settings independently from the recalled CMW configuration, e.g. CONF:DATA:CONT:IMS:UAUT OFF; // User Authentification OFF CONF:DATA:CONT:IMS:VOIC:PREC WNPR; // No Preconditions CONF:DATA:CONT:IMS:VOIC:LOOP OFF; // Loopback OFF CONF:DATA:CONT:IMS:VOIC:MEND:IPAD ' '; // Media Endpoint SOUR:DATA:CONT:IMS:STAT ON; // Turn IMS ON IMS ON? (SCPIPollState) Waits until IMS is turned ON or timeout occurred. Figure 4-7: LTE Call Setup Parameters 1MA204_ 6e Rohde & Schwarz Voice over LTE (VoLTE) Speech Quality Measurements 13

14 Test Plan Description LTECallSetup As soon as IMS is turned ON, an LTE cell is established were the UE can attached to. The following screen shot shows the configuration window which opens when double clicking LTECALLSETUP in the list: Figure 4-8: LTE Call Setup Parameters Please make sure that the UE parameters are entered correctly or else the UE will not be attached and the test terminated. LTE Call Setup parameters in our example that differ from default: SCENARIO = OL Spatial MUX BAND = Band7 RF DOWNLINK CONNECTOR 1 = RF 1 COM RF DOWNLINK CONNECTOR 2 = RF 3 OUT RF UPLINK CONNECTOR = RF 1 COM SCHEDULING TYPE = User def. Channels #RB = 45 (DL), 50 (UL) MODULATION = 64-QAM (DL 1&2), QPSK (UL) TBS IDX. = 15 (DL 1&2), 10 (UL) 1MA204_ 6e Rohde & Schwarz Voice over LTE (VoLTE) Speech Quality Measurements 14

15 Test Plan Description Connection Type Advanced parameters: Figure 4-9: Connection Parameters CONNECTION TYPE = Data Application This is required to establish a VoLTE call over the IP Layer. The IP handling in the direction to the UE is handled by the DAU (IPv4 or IPv6). UE registered? (SCPIPollState) Checks if the UE has been registered on IMS level. VoIMS Configuration (SCPICommandList) If the UE has been correctly registered the following VoIMS parameters are set in this test item. CONF:DATA:CONT:IMS:VOIC:TYPE AUD; CONF:DATA:CONT:IMS:VOIC:AMRT WID; CONF:DATA:CONT:IMS:VOIC:COD 9:ENAB ON; // Call Type: Audio // AMR Wideband Codec // kb/s 1MA204_ 6e Rohde & Schwarz Voice over LTE (VoLTE) Speech Quality Measurements 15

16 Test Plan Description This corresponds to following manual settings: Figure 4-10: Voice over IMS Configuration Speech_Quality_Measurement If UE has been successfully registered in the preceding step this test makes a VoIMS call if not already established manually, calibrates the sound interface and performs a POLQA or PESQ measurement. By double clicking the SPEECH_QUALITY_MEASUREMENT test item the following configuration window opens. 1MA204_ 6e Rohde & Schwarz Voice over LTE (VoLTE) Speech Quality Measurements 16

17 Test Plan Description Figure 4-11: Speech Quality Measurement Parameters Codec Calibration LINE IN The UPV generator output fed to the audio interface input (always Generator 2). LINE OUT The UPV analyzer input where the audio interface output is fed to (always Analyzer 2). UE IN The UPV generator output fed to the UE input (always Generator 1). UE OUT The UPV analyzer input where the UE output is fed to (always Analyzer 1). CAL TONE FREQ Frequency used for UPV decoder/encoder calibration (always 1000 Hz). UPV DIRECTORY The directory on the UPV where the files from section 4.2 are installed (default D:\UPV\POLQA_CAL\). UPV CAL SETTINGS UPV settings for decoder/encoder calibration (always UpvCal.set ). 1MA204_ 6e Rohde & Schwarz Voice over LTE (VoLTE) Speech Quality Measurements 17

18 Test Plan Description DECODER CAL File for decoder calibration result (always DecoderCalibration.txt ). ENCODER CAL File for encoder calibration result (always EncoderCalibration.txt ). MOBILE CAL File for UE output calibration (always MobileDLCalibration.txt ). Remote PC --> VoLTE Media Server TARGET IP IP address or computer name of the instrument or PC where the Media Server is running (default , Media Server installed on CMW500). DIRECTORY Installation directory of Media Server (default C:\Program Files\Rohde-Schwarz\Media Server\1.2\) depends on VoLTE Media Server version number (e.g. v ) TARGET PORT Port number for command transmission between Remote PC and instrument or PC where VOLTE MEDIA SERVER is running on (default 9900). CMW DAU --> VoLTE Media Server DIRECTION Choose between DOWNLINK (default) and UPLINK. MEDIA ENDPOINT Indicates IP address of instrument or PC where VOLTE MEDIA SERVER is running on (same as TARGET IP, default ). Fading Simulator STANDARD Select from all available LTE fading standards for SISO and MIMO (default LTE EPA 5Hz (SISO Path A)). Figure 4-12: LTE Fading Standards 1MA204_ 6e Rohde & Schwarz Voice over LTE (VoLTE) Speech Quality Measurements 18

19 Test Plan Description AWGN Turns AWGN ON/OFF (default ON). SNR Signal to Noise Ratio of AWGN signal (default 10.0 db). CALIBRATE EXT. FADER INSERTION LOSS Determines insertion loss of the current fading standard which is added to the cable loss and fed to CMW EXTERNAL ATTENUATION of the RF OUTPUT (TX). Figure 4-13: RF External Attenuation Ext.Attenuation (TX) = Insertion Loss + Cable Loss = 10.5 db db = 12.5 db Ext.Attenuation (RX) = Cable Loss = 2.0 db CAB. LOSS The cable loss is fed to the CMW EXTERNAL ATTENUATION of the RF INPUT (RX). POLQA / PESQ Measurement UPV MEAS SETTINGS UPV settings file for performing POLQA or PESQ measurements (default POLQA_Wide_Downlink_Autogain.set ). The measurement type is defined by the name POLQA Measurement of superwideband downlink audio signal with UPV autogain turned ON. The Autogain feature adjusts the analyzer input level (degraded signal) to the generator level (reference signal). The POLQA algorithm requires the reference and degraded signal to have the same level (difference < 0.5 db). MOS SAMPLE SIZE Number of measurements used for obtaining an average MOS value (default 3). SHOW DETAILS Shows all POLQA results if checked, and only the average, minimum, maximum and standard deviation if unchecked (default ON). MOS LIMIT The lower MOS limit for passing a test (default 3.00). 1MA204_ 6e Rohde & Schwarz Voice over LTE (VoLTE) Speech Quality Measurements 19

20 Test Plan Description Speech Quality Measurement Subroutines The DLL contains the following subroutines which can be switched ON or OFF. Figure 4-14: Speech Quality Measurement Subroutines UPVINIT Resets the UPV audio analyzer. AMUINIT Resets the AMU fader. LTEFADINGAWGN Set fading standard and SNR. Turns fading and AWGN ON. DECODERCAL A full scale sine wave is generated on the USB audio interface of the UPV / Media PC and the actual voltage level measured by the defined UPV analyzer input. This voltage level serves as reference value for the UPV generator output. It is measurement system dependent and only needs to be performed from time to time. ENCODERCAL Measures the Media PC audio interface input voltage after A/D conversion by looping its input and output on the digital side and measuring its output with the corresponding UPV analyzer. The calibration value is system dependent and only needs to be performed from time to time. VOIMSCALLESTABLISH Checks if the VoIMS call state is ON and establishes a call if necessary. As soon as the call has been automatically or manually answered the VoLTE Media Server starts the FFMPEG encoder for DL and FFPLAY for UL instances on the CMW or Media PC. Now the system is ready to transfer an audio data stream in either direction. 1MA204_ 6e Rohde & Schwarz Voice over LTE (VoLTE) Speech Quality Measurements 20

21 Test Plan Description FFMPEG and FFPLAY are customized versions of the FFMPEG open source software package. Figure 4-15: FFMPEG encoder and FFPLAY decoder MOBILEOUTCAL Measures the line output voltage of the UE. The Mobile output calibration must be performed after changing the UE. POLQAPESQMEASUREMENT Measures the POLQA or PESQ MOS-LFO value by starting the MOS Reference file on the UPV and comparing the original with the received signal. VOIMSCALLRELEASE Drops the VoIMS call LTECallDisconnect Drops the LTE connection. 1MA204_ 6e Rohde & Schwarz Voice over LTE (VoLTE) Speech Quality Measurements 21

22 Program Flow 4.3 Program Flow The VoLTE Media Server must be running either on the CMW or Remote PC before performing the RSrun sequence. It is convenient to put the Media Server program icon into the Start Programs Startup menu so it will automatically start when the CMW or Remote PC is booted. The following sequence shows the simplified program flow for a downlink POLQA measurement. The Remote PC sends and reads SCPI messages via VISA protocol to and from the UPV, AMU and CMW500, and TCP messages to and from the VoLTE Media Server program running on the CMW or Remote PC. Start RSrun on Remote PC CMW (VISA):Init CMW AMU (VISA): Fading Scenario CMW (VISA):Attach LTE UE CMW (VISA):Register VoIMS // Reset CMW // SISO A/B or MIMO // CMW turns LTE signalling ON and attaches to the UE // CMW turns IMS ON and registers UE on IMS level The SPEECH QUALITY MEASUREMENT test case (marked red) begins here: UPV (VISA): Init UPV // Reset UPV AMU (VISA): Fading + AWGN // Set LTE fading standard and AWGN UPV (VISA): Load UpvCal.set MPC: RUN CsSinWav.exe UPV (VISA): Calibrate Decoder MPC: STOP CsSinWav.exe MPC: RUN CsWavRec.exe UPV (VISA): Calibrate Encoder MPC: STOP CsWavRec.exe CMW (VISA):Perform VoIMS call // Load UPV setting for decoder / encoder cal // Play sine wave on USB audio interface // Measure signal level of USB audio interface and set UPV generator reference accordingly // UPV generator 2 sends sine wave to USB audio interface. The digital signal at the ADC is looped to the DAC and the level measured with UPV analyzer 2 // After answering the phone, FFMPEG coder and FFPLAY decoder are started by the Media Server. UPV (VISA): Calibrate Mobile Out // Measure UE output voltage UPV (VISA): Load POLQA_Wide_Downlink_Autogain.set // Load UPV setting for POLQA measurement UPV (VISA): Measure MOS-LQO // Starts a reference wave file on the UPV and measures the MOS-LQO for a defined number of times CMW (VISA): Release VoIMS call CMW (VISA): Disconnect UE // CMW turns LTE signalling OFF 1MA204_ 6e Rohde & Schwarz Voice over LTE (VoLTE) Speech Quality Measurements 22

23 Expected MOS/LQO Results 4.4 Expected MOS/LQO Results The following table shows ideal PESQ / POLQA MOS/LQO results for different narrowband codec types. PESQ (P.862.1) POLQA (P.863) AMR 12.2 kbps AMR 7.95 kbps AMR 6.70 kbps AMR 4.75 kbps Table 4-1: Expected MOS/LQO Results with various code rates The following table shows POLQA (P.863) MOS/LQO results for AMR narrowband (NB) 12.2 kbps code rate under fading condition and various AWGN levels. The MOS SAMPLE SIZE was set to 20 resulting in a measurement duration of 5 minutes (= 15 seconds per sample). For a MOS precision < 0.1 the MOS Sample Size needs to be increased to > 50. Fading Standard AWGN MOS/LQO Std.Dev None (baseband routed through CMW) OFF None (baseband routed in AMU) OFF db db db LTE EPA 5Hz (SISO Path A) OFF db db LTE ETU 300Hz (SISO Path A) OFF db db db db Table 4-2: MOS/LQO results for AMR Narrow Band 12.2 kbps code rate 1MA204_ 6e Rohde & Schwarz Voice over LTE (VoLTE) Speech Quality Measurements 23

24 Running the Test The following table shows POLQA MOS/LQO results for AMR Super-Wideband (WB) kbps code rate under fading condition and various AWGN levels. Fading Standard AWGN MOS/LQO Std.Dev None (baseband routed through CMW) OFF None (baseband routed through AMU) OFF db db db db LTE EPA 5Hz (SISO Path A) OFF db db LTE ETU 300Hz (SISO Path A) OFF db db db db Table 4-3: MOS/LQO results for AMR Super-Wideband kbps The conclusion of both NB and WB tables is that the speech quality is hardly affected by fading or AWGN on their own, but decreases significantly when fading and AWGN are engaged. The LTE EPA 5Hz fading standard in conjunction with AWGN degrades the speech quality more than the LTE ETU 300 Hz one. The standard deviation is also higher since a single measurement only covers a certain portion of all possible states due to the slow speed (5 Hz). 4.5 Running the Test The example below shows how to run the SPEECH QUALITY MEASUREMENT.RSTP test plan. The VoLTE device (mobile or USB stick with additional IMS server software) must be attached and registered before the test is run. To start the test press the RUN arrow in RSrun. Figure 4-16: Start a Test Plan RSrun switches to the Measurement Report view and shows the status and results of the VoLTE POLQA / PESQ Measurement. The results for the decoder / encoder calibration are shown as well as the POLQAPESQMEASUREMENT results. The 1 st line shows the average value, the following numbered lines with the POLQA / PESQ MOS values of the single measurements are shown in case the DETAILS checkbox is ON. The ANALYZER ATTENUATION shows the level difference between reference and degraded signal and should range inside the limits -1.0 db to +1.0 db. AVG.DELAY displays the delay of the degraded signal to the reference signal. The last line shows statistic information such as the minimum, maximum and standard deviation of the MOS-LQO values. 1MA204_ 6e Rohde & Schwarz Voice over LTE (VoLTE) Speech Quality Measurements 24

25 Running the Test 1MA204_ 6e Rohde & Schwarz Voice over LTE (VoLTE) Speech Quality Measurements 25

26 Running the Test Figure 4-17: Measurement Report 1MA204_ 6e Rohde & Schwarz Voice over LTE (VoLTE) Speech Quality Measurements 26

27 Literature Running the Test 5 Literature [1] R&S UPV Operating Manual [2] Application Note 1GA49, Psychoacoustic Audio Quality Measurements Using R&S UPV Audio Analyzer [3] Application Note 1GA50, Calibration Tool for PESQ Speech Quality Tests [4] Application Note 1MA119 "PESQ Measurement for GSM with R&S CMUgo" [5] Application Note 1MA136 "PESQ Measurement for CDMA2000 with R&S CMUgo" [6] Application Note 1MA137 "PESQ Measurement for WCDMA with R&S CMUgo" [7] Application Note 1MA149 VoIP Measurements for WiMAX" [8] Application Note 1MA202 Next-Generation (3G/4G) Voice Quality Testing with POLQA " 1MA204_ 6e Rohde & Schwarz Voice over LTE (VoLTE) Speech Quality Measurements 27

28 Additional Information Running the Test 6 Additional Information Please send your comments and suggestions regarding this application note to [email protected] 1MA204_ 6e Rohde & Schwarz Voice over LTE (VoLTE) Speech Quality Measurements 28

29 Ordering Information Running the Test 7 Ordering Information Ordering Information Wideband Radio Communication Tester CMW500 Wideband Radio Comm. Tester K50 CMW-PS502 Basic Assembly CMW-S550B Basic Interconnection, flex. Link, for non-signaling, signaling and IQ access CMW-S590D RF front end, advanced funct CMW-S600B CMW500 front panel CMW-B300A Signaling Unit Wideband (SUW), for WCDMA / LTE CMW-B570B Extra RF Converter (TRX) CMW-B660A Option Carrier CMW-B661A Ethernet Switch CMW-B690B OCXO, high stability CMW-KAA20 IMS basic service CMW-B450A Data Application Unit (hw opt.) CMW-KA100 Enabling of IP-Data interface for IPV CMW-KS500 LTE FDD Release 8, SISO, signaling/network emulation CMW-KS510 LTE Release 8, SISO, signaling / network emulation, advanced functionality CMW-KS520 LTE MIMO2x2, signaling / network emulation, generic feature CMW-KT055 CMWrun/RSrun Sequencer LTE xx CMWPC Smartcard for CMWPC K90 CMW-S089A USB Smartcard for CMWPC CMW-KM050 IP Based Measurements Audio Analyzer UPV Audio Analyzer Or UPV66 Audio Analyzer without Display UPV-K61 PESQ Software Option UPV-K63 POLQA Software Option UPV-K1 Universal Sequence Controller UPV-K4 RC for IEC625 / IEEE488, RS232, USB and LAN UP-Z9 Headset Cable Set for UPV Fading Simulator AMU 200 Baseband Signal Generator AMU-B13 Baseband Main Module AMU-B14 Fading Simulator AMU-B15 Fading Simulator Extension AMU-B17 Analog/Digital Baseband Inputs AMU-B18 Digital I/Q Output MA204_ 6e Rohde & Schwarz Voice over LTE (VoLTE) Speech Quality Measurements 29

30 Ordering Information Running the Test 1MA204_ 6e Rohde & Schwarz Voice over LTE (VoLTE) Speech Quality Measurements 30

31 PAD-T-M: /02.00/CI/1/EN/ About Rohde & Schwarz Rohde & Schwarz is an independent group of companies specializing in electronics. It is a leading supplier of solutions in the fields of test and measurement, broadcasting, radiomonitoring and radiolocation, as well as secure communications. Established more than 75 years ago, Rohde & Schwarz has a global presence and a dedicated service network in over 70 countries. Company headquarters are in Munich, Germany. Regional contact Europe, Africa, Middle East [email protected] North America TEST-RSA ( ) [email protected] Latin America [email protected] Asia/Pacific [email protected] China / [email protected] Environmental commitment Energy-efficient products Continuous improvement in environmental sustainability ISO certified environmental management system This application note and the supplied programs may only be used subject to the conditions of use set forth in the download area of the Rohde & Schwarz website. R&S is a registered trademark of Rohde & Schwarz GmbH & Co. KG; Trade names are trademarks of the owners. Rohde & Schwarz GmbH & Co. KG Mühldorfstraße 15 D München Phone Fax