VoIP Measurements for WiMAX Application Note

Transcription

1 VoIP Measurements for WiMAX Application Note Products: R&S CMW270 R&S UPV R&S UPV-K1 R&S UPV-K4 R&S UPV-K61 R&S UPV-K9 R&S UPV-K91 This application note describes the necessary steps and configuration to perform VoIP speech and audio quality measurements of a WiMAX data module. Application Note Ottmar Gerlach MA149_0e 49_0e Rohde & Schwarz VoIP Measurements for WiMAX 1

2 Table of Contents Table of Contents 1 Overview Hardware and Software Configuration Hard- and Software Requirements WiMAX Stand-alone, USB or PC-Card Module R&S UPV Audio Analyzer M-Audio Transit USB Soundcard R&S CMW270 WiMAX Communication Tester Network configuration Hardware Configuration Calibrating the Soundcard Manual DAC / Decoder Calibration (Uplink) Manual ADC / Encoder Calibration (Downlink) Automatic Decoder / Encoder Calibration with 1GA Speech Quality (PESQ) Measurements Downlink UPV Generator Settings UPV Analyzer Settings PESQ Measurement Uplink UPV Generator Settings UPV Analyzer Settings PESQ Measurement Audio Measurements with R&S UPV-K9/K Codec Calibration GPP Receiving Handset, max. Volume GPP Sending Handset Sidetone Distortion (generic) Test Results Overview Literature Additional Information MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 2

3 Table of Contents 5 Ordering Information MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 3

4 Overview 1 Overview The VoIP (Voice Over IP) protocol is finding its way into nearly all data oriented communication standards such as GSM/EDGE, 1xEVDO, HSPA+ and WiMAX and will replace the traditional speech oriented standards in the future. This application note shows how easy an audio test system for WiMAX mobile equipment is configured with a R&S CMW270 WiMAX Communication Tester and R&S UPV Audio Tester. The described tests comprise Perceptual Evaluation of Speech Quality (PESQ) measurement according to recommendation ITU-T P.862 and several typical mobile audio tests such as frequency response and distortion measurements provided by the R&S UPV-K9/K91 UMTS/GSM Mobile Phone Test option which also applies for WiMAX. The following abbreviations are used in the following text for R&S test equipment: The R&S CMW270 WiMAX Communication Tester is referred to as CMW270. The R&S UPV Audio Analyzer is referred to as UPV. R&S refers to Rohde & Schwarz GmbH und Co KG 1MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 4

5 2 Hardware and Software Configuration 2.1 Hard- and Software Requirements WiMAX Stand-alone, USB or PC-Card Module In case you have a stand-alone WiMAX mobile DUT you only need to turn it ON Set the desired IP address as shown in section 2.2 If you have a USB or PC-Card WiMAX module Install driver for the WiMAX USB or PCcard module Plug in the module Start the WiMAX controller software. Set the desired IP address as shown in section R&S UPV Audio Analyzer A VoIP server application, e.g. freeware PhonerLite ( has to be installed on the UPV audio analyzer first. The server running on the UPV windows environment needs a Windows compatible sound device in order to digitize analog audio signals. The UPV has no internal Windows sound device therefore an external USB soundcard is necessary. In this application note an M-Audio Transit USB soundcard is used due to its excellent specifications. When using a different soundcard keep in mind that its quality affects the measurement results. The VoIP server software provides the necessary codecs for coding / decoding the digital audio data into / from VoIP data packets for transmission via LAN. Please identify the UPV front end PC by pressing START SYSTEM PROPERTIES in the Windows environment. If the type is FMR7SPC proceed with the next step. If it is FMR6SPC execute the file UPV_AUDIO_UPDATE_4_FMR6.exe available from the R&S 1MA149 application note site. This adds the necessary files for detecting the external sound card M-Audio Transit USB and only needs to be performed once. 1MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 5

6 Figure 1: Identify UPV front end PC Install M-Audio Transit USB driver Transit_ v3.exe (updates available at and plug in the card. Wait approx. 30 seconds until the card appears in the Windows device manager and driver update is automatically started. There are six unknown devices that disappear after a while leaving only the M-Audio Transit left. Figure 2: M-Audio Transit Device Driver M-Audio Transit USB Soundcard The M-Audio Transit USB soundcard is the official R&S choice due to its excellent specifications and can be purchased from R&S directly or any authorized M-Audio sales representative R&S CMW270 WiMAX Communication Tester The CMW270 must be equipped with the options CMW-KA700 application enabler and CMWB660A and CMU661A which provides an IP port to connect to an external PC. 1MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 6

7 Figure 3: Ethernet switch board connectors on the rear side of the CMW Network configuration For the network configuration please use the IP addresses shown in Figure 4. UPV (Server) CMW270 RF WiMax module CMW IP Subnet Mask Figure 4: Network Configuration UPV (Server) PC: IP: Subnet Mask: CMW270: IP: Subnet Mask: WiMAX DUT IP: Subnet Mask: (Stand-alone or USB or PC-Card module) The CMW270 IP address for the Ethernet switch board is set within the WiMAX signalling menu (Figure 3) Figure 5: Configuration of Ethernet switch board IP address To configure the network IP address of the DUT and the Ethernet address of the server PC please use the Windows Network Connections setup menu (Figure 6 and 7). 1MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 7

8 Figure 6: UPV (Server PC) Figure 7: DUT (Client PC) On the UPV server PC it is necessary to configure an additional rule for routing the IP packages. Open the CMD shell on the UPV server PC Add a new routing rule using the command route add <DUT address> <CMW address> In our case type route add After that check with route print whether the rule was created and added to the routing table. These two commands are contained in the included batch file RA.BAT. 1MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 8

9 Figure 8: Routing table after route add After changing the routing table of the server PC please switch on CMW270 WiMAX signalling and establish a connection to the DUT. NOTE: When the R&S CMW270 is shut down the R&S UPV server PC loses the created rule. For reconnection repeat this step. After the network entry you can check the IP connection setup with a PING command. e.g. DUT Host PC UPV Server PC (PING ) Figure 9: Ping UPV Server from DUT host Same for: UPV Server PC DUT Host PC (PING ) UPV Server PC CMW (PING ) NOTE: It is not possible to PING the CMW from the DUT Host PC! DUT --> CMW (PING ) NOTE: Switch OFF Firewall on UPV Server PC and DUT Host PC! 1MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 9

10 2.3 Hardware Configuration CMW270 RF Fader (opt.) Direct. Coupler (opt.) RF WiMAX Module (in PC or standalone) to CMW -B660 A/B LAN switch to headset speaker from headset microphone UPV from artificial ear to artificial mouth Line In Line Out M-Audio Transit USB Figure 10: Hardware Configuration The configuration consists of a CMW270 WiMAX Communication Tester which is connected to the WiMAX DUT via RF and transmits VoIP data packets to and from the DUT. UPV Audio Analyzer which uses one generator output / analyzer input for calibrating and the other one for the actual measurement, e.g. PESQ measurement. The VoIP server software runs on the UPV Windows environment. The VoIP data is transmitted to and from the CMW270 via LAN connection. M-Audio Transit USB soundcard which can be accessed by a VoIP server running on the UPV. WiMAX DUT that can be stand-alone module with internal VoIP client or connected to a laptop via USB or PC-Card slot with VoIP client software. When inserting an RF fader into the RF downlink path, a directional coupler is needed for the uplink path. This issue is not considered in this application note. The solid audio related lines show the RF signals involved in the downlink path while the dashed ones show the uplink path. 1MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 10

11 For remote application control via LAN an additional LAN switch is required. CMW270 LAN switch CMW -B660 LAN Remote LAN LAN Switch LAN1 LAN2 LAN3 LANn Remote PC LAN UPV Figure 11: Remote Configuration 2.4 Calibrating the Soundcard The calibration of the M-Audio Transit USB soundcard determines the peak input voltage necessary for achieving digital full scale (ADC) and the peak voltage output voltage when applying digital full scale (DAC). The DAC calibration is also referred to as Decoder Cal since this is the uplink direction and the ADC calibration as Encoder Cal since this is the downlink direction. UPV USB Gen2 Ana2 M-Audio In Out Figure 12: Codec Calibration This can be done manually (see section and 2.4.2), automatically with the calibration tool of application note 1GA50 (see 2.4.3) or the installed UPV-K9/K91 option (see 2.6.1). The DAC calibration is not necessary when connecting the M-Audio Transit USB optical TOSLINK output to the UPV optical TOSLINK input (S/PDIF = Sony / Philips Digital InterFace). 1MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 11

12 2.4.1 Manual DAC / Decoder Calibration (Uplink) This calibration value is required for uplink measurements, for the encoder calibration and mobile input calibration routines and for measurements with loopback on the mobile side. 1. Use a Windows program on the UPV to generate a 1 khz sine wave with maximum level at the M-Audio line-output, e.g. freeware audio tool Audacity ( and measure the RMS voltage with UPV Analyzer 2 input. Set to digital full scale with e.g. Audacity DAC / Decoder D A M-Audio Measure RMS voltage ANALYZER 2 UPV Figure 13: Decoder Calibration 1MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 12

13 2. Start AUDACITY from the UPV Windows environment and select menu GENERATE TONE. Waveform = SINE Frequency = Hz Amplitude = 1.00 (maximum) Length = 60 seconds or more. Press on the green arrow to start the waveform. Figure 14: Generate Sine wave with Audacity 1MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 13

14 3. Open UPV ANALYZER FUNCTION and ANALYZER CONFIG windows. Figure 15: M-Audio DAC level at full scale 4. Set the RMS value just measured to the Analyzer Ch2 reference by clicking the right mouse button and selecting CONFIG. Figure 16: Setting UPV analyzer reference level 1MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 14

15 5. Select STORE from the REFERENCE control in the FUNCTION CONFIG window. Remote: SENSe1:REF:MODE2 STORE Figure 17: Store measured level to reference 6. Set analyzer Channel 2 UNIT to dbu. Remote: SENSe6:UNIT DBU Figure 18: Configure analyzer function 1MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 15

16 2.4.2 Manual ADC / Encoder Calibration (Downlink) This calibration value is required for downlink measurements and for measurements with loopback on the mobile side. 1. Use Audacity to digitally loop the M-Audio ADC output to the DAC input. In/Out loop with Audacity D A GENERATOR 2 D A ANALYZER 2 M-Audio UPV Figure 19: ADC Calibration Select AUDACITY menu EDIT PREFERENCES and check the SOFTWARE PLAYTHROUGH box. Figure 20: Audacity In/Out loop 2. Open the UPV GENERATOR FUNCTION and GENERATOR CONFIG windows. Tweak Voltage in the Generator Function window until the Ch2 RMS value is closest to 0.0 dbr, corresponding to full scale at the ADC input (e.g V). Remote: SOURce:VOLTage 2.032V 1MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 16

17 Figure 21: Result of ADC Calibration 3. Copy generator VOLTAGE (2.032 V) to REF VOLTAGE Remote: SOURce:VOLTage:REFerence 2.032V 4. Set VOLTAGE to dbr Remote: SOURce:VOLTage 0.0dBR Figure 22: Use relative generator level 1MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 17

18 2.4.3 Automatic Decoder / Encoder Calibration with 1GA50 The program "Input and Output Calibration for PESQ" (application note 1GA50) offers automatic calibration of the uplink (decoder) and downlink (encoder). Start the application on the UPV. Select the tab UPLINK and press DECODER CAL menu. Figure 23: 1GA50 Decoder Calibration A message box shows the result. Figure 24: 1GA50 Decoder Calibration result The encoder is calibrated by selecting the DOWNLINK tab and pressing ENCODER CAL. Figure 25: 1GA50 Encoder Calibration result Digitally loop M-Audio's ADC output with the DAC input with Audacity (see 4.3.2). The press ok to start calibration. When done, a calibration file may be stored. The results of decoder and encoder calibration are displayed. 1MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 18

19 Figure 26: 1GA50 Downlink Calibration Result At UPV restart the calibration settings will be available after running 1GA50 Input Output calibration for PESQ. 2.5 Speech Quality (PESQ) Measurements For the Perceptual Evaluation of Speech Quality (PESQ) function the UPV must be equipped with the option R&S UPV-K61. The PESQ measurements according to the recommendation ITU-T P.862 enable to measure the quality of speech signals transmitted at low bit rates using highly compressive psychoacoustic coding methods. The example below uses the MOS-LQON (Listening Quality Objective Narrowband) according to ITU-T P ranging from -0.5 (worst) to +4.5 (best). PESQ is a registered trademark of OPTICOM Dipl.-Ing. M. Keyhl GmbH, Erlangen, Germany and of Psytechnics Ltd., U.K Downlink The schematic below shows the simplified downlink signal path and the components, mainly speech codec, affecting the speech quality (without fading and artificial ear). VoIP Software Encoder UPV LAN Switch UPV-B71 LAN CMW270 RF WiMax DUT Decoder PESQ file USB Gen1 Gen2 Ana1 Ana2 M-Audio USB Line-In Figure 27: Signal Path for Downlink PESQ Measurements from speaker out 1MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 19

20 UPV Generator Settings In the UPV GENERATOR CONFIG window set Channel = 2 Remote: OUTput:CHANnel CH2 Bandwidth = PLAY AUTO Remote: OUTPut:BANDwidth:MODE AUTo Ref Voltage = V Remote: SOURce:VOLTage:REFerence In the UPV GENERATOR FUNCTION window set Function = PLAY Remote: SOURce:FUNCtion PLAY File = MOSREFERENCE.WAV Remote: MMEM:LOAD:ARBitrary 'MOSreference.wav' Scale Pk to FS = ON Remote: SOURce:PLAY:SCALepktofs Play Mode = TOTAL CONT Remote: SOURce:PLAY:MODE TOSingle Volt Peak = dbr Remote: SOURce:VOLTage:TOTal 6.0dBR Note: The peak voltage must be 6 db above the reference voltage. Under the assumption that the crest factor is quite high, this value may even be increased to a certain extent without affecting the MOS score. Figure 28: UPV Generator Settings for Downlink PESQ Measurement 1MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 20

21 UPV Analyzer Settings In the UPV ANALYZER CONFIG window set Channel = 1 Remote: INPut:CHANnel CH1 Ch1 Range = FIX, 1V RMS Remote: SENSe:VOLTage:RANGe:VALue 1V In the UPV ANALYZER FUNCTION window set Function = PESQ Remote: SENSe:FUNCtion PESQ According to = MOS P862.1 Remote: SENSe:FUNCtion:PESQ:ACCording MP8621 Meas Mode = DUT Remote: SENSe:FUNCtion:MMODe DUT Level Monitor = PEAK Remote: SENSe6:FUNCtion PEAK PESQ Measurement For a PESQ measurement a reference file MOSReference.wav is played on the UPV generator and compared with the signal received by the DUT at the Analyzer 1 input. The file is played continuously and the measurement is initiated by pressing the UPV Start button. In our example the resulting PESQ score is approx. 80% of the maximum possible quality (= 4.5) due to the software codecs used in the VoIP server and client. Figure 29: PESQ Measurement 1MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 21

22 In order to check the PESQ functionality you may assign generator 2 output to analyzer 2 source. The resulting PESQ score is maximum. Figure 30: Maximum PESQ score Uplink The schematic below shows the uplink signal path and the components, mainly speech codec, affecting the speech quality (without fading and artificial ear). VoIP Software Decoder UPV LAN Switch UPV-B71 LAN CMW270 RF WiMax DUT Encoder PESQ file USB Gen1 Gen2 Ana1 Ana2 M-Audio USB LineOut to microphone in Figure 31: Signal Path for Uplink PESQ Measurements 1MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 22

23 UPV Generator Settings In the UPV GENERATOR CONFIG window set Channel = 1 Remote: OUTput:CHANnel CH2 Bandwidth = PLAY AUTO Remote: OUTPut:BANDwidth:MODE AUTo Ref Voltage = V Remote: SOURce:VOLTage:REFerence In the UPV GENERATOR FUNCTION window set Function = PLAY Remote: SOURce:FUNCtion PLAY File = MOSREFERENCE.WAV Remote: MMEM:LOAD:ARBitrary 'MOSreference.wav' Scale Pk to FS = ON Remote: SOURce:PLAY:SCALepktofs Play Mode = TOTAL CONT Remote: SOURce:PLAY:MODE TOSingle Volt Peak = dbr Remote: SOURce:VOLTage:TOTal 6.0dBR Note: The peak voltage must be 6 db above the reference voltage. Under the assumption that the crest factor is quite high, this value may even be increased to a certain extent without affecting the MOS score UPV Analyzer Settings In the UPV ANALYZER CONFIG window set Channel = 2 Remote: INPut:CHANnel CH1 Ch2 Range = FIX, 1V RMS Remote: SENSe:VOLTage:RANGe:VALue 1V In the UPV ANALYZER FUNCTION window set Function = PESQ Remote: SENSe:FUNCtion PESQ According to = MOS P862.1 Remote: SENSe:FUNCtion:PESQ:ACCording MP8621 Meas Mode = DUT Remote: SENSe:FUNCtion:MMODe DUT Level Monitor = PEAK Remote: SENSe6:FUNCtion PEAK PESQ Measurement For a PESQ measurement a reference file MOSReference.wav is played on UPV generator 1 and compared with the signal received by the DUT at the Analyzer 2 input. The file is played continuously and the measurement is initiated by pressing the UPV Start button. 1MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 23

24 2.6 Audio Measurements with R&S UPV-K9/K Codec Calibration Start the UPV-K9/K91 application on the UPV. Select menu CALIBRATION CODEC. A message box tells you to establish a call and set 'Bit Stream' to 'DecoderCal'. The message is originally designated for using the CMU with internal GSM or WCDMA codecs. In this case the codecs are provided by the VoIP server software running on the UPV and complies to generating a 1 khz sine wave with the M-Audio Transit soundcard (see section 2.4.1). Figure 32: UPV-K9 Decoder Cal Press OK and after a few seconds the result appears. Figure 33: Result of Decoder Calibration After pressing Ok a message box tells you to set 'Bit Stream' to 'DecoderCal'. This complies to the ADC calibration where the UPV generates a sine wave which is looped through the M-Audio Transit soundcard (see section 2.4.2). Figure 34: UPV-K9 Encoder Cal 1MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 24

25 Press OK to start the calibration. The result appears after several seconds. Figure 35: Encoder Cal Result After pressing OK a message tells you to set the handset to 'Speechcodec/Handset Low'. Figure 36: Speechcodec / Handset Low Then start the VoIP server (e.g. freeware PhonerLite) on the UPV and the VoIP client on the WiMAX module and establish a call. PhonerLite uses an A-Law codec by default. Figure 37: VoIP Server PhonerLite 1MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 25

26 GPP Receiving Handset, max. Volume This and the following 3GPP audio tests run on the UPV also apply for VoIP with WiMAX. The measurement of frequency response is important to ensure that the telephone does not inappropriately emphasize or attenuate certain frequencies. A weighted average of the frequency response is calculated to provide a single number representing perceived loudness of the telephone. The Receive Loudness Rating (RLR) is calculated. The nominal loudness ratings are specified in the network loss plan to ensure that loudness is consistent between different telephones on different connections and that there is adequate head room to accommodate peak signal levels. Figure 38: 3GPP Receiving Handset, nom. Vol If no ear simulator or artificial mouth is available and you only have an electrical connection between the handset and the UPV, the UPV-K9/K91 software allows to select this scenario in the OPTIONS menu. 1MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 26

27 Figure 39: Select Ear Simulator Figure 40: Select Mouth Type 1MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 27

28 GPP Sending Handset A weighted average of the frequency response is calculated to provide a single number representing perceived loudness of the telephone. The Send Loudness Rating (SLR) is calculated. The nominal loudness ratings are specified in the network loss plan to ensure that loudness is consistent between different telephones on different connections and that there is adequate head room to accommodate peak signal levels. Figure 41: 3GPP Sending Handset 1MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 28

29 2.6.4 Sidetone Distortion (generic) The sidetone distortion test determines 3 rd order harmonic distortion at a given set of frequencies (in the case of 3GPP TS at 315, 500 and 1000 Hz) with a level of -4.7 dbpa at the MRP. The 3 rd order harmonic distortion is required to be less than 10% (-20dB) at all frequencies. Figure 42: Sidetone Distortion (generic) 1MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 29

30 2.6.5 Test Results Overview The test results overview shows the verdicts of all performed tests. Figure 43: Test Results Overview 1MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 30

31 Literature 3 Literature R&S UPV Operating Manual Application Note 1GA49, Psychoacoustic Audio Quality Measurements Using R&S UPV Audio Analyzer Application Note 1GA50, Calibration Tool for PESQ Speech Quality Measurements Application Note 1MA119 "PESQ Measurement for GSM with R&S CMUgo" Application Note 1MA136 "PESQ Measurement for CDMA2000 with R&S CMUgo" Application Note 1MA137 "PESQ Measurement for WCDMA with R&S CMUgo" 3GPP test specification TS MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 31

32 Additional Information 4 Additional Information Please send your comments and suggestions regarding this application note to TM-Applications@rohde-schwarz.com Visit the CMUgo website at dio/cmu200- -Software html or as a registered user in GLORIS the CMU Customer Web at 5 Ordering Information Ordering Information WiMax Communication Tester CMW Audio Analyzer UPV Audio Analyzer Or UPV66 Audio Analyzer without Display UPV-K1 Universal Sequence Controller UPV-K4 Remote Control UPV-K61 Software f. PESQ Measurements UPV-K9 UPV-K91 Base Software for Mobile Phone Tests UMTS/GSM Mobile Phone Tests (requires UPV-9) MA149_0e Rohde & Schwarz VoIP Measurements for WiMAX 32

33 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 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 * or customersupport@rohde-schwarz.com North America TEST-RSA ( ) customer.support@rsa.rohde-schwarz.com Latin America customersupport.la@rohde-schwarz.com Asia/Pacific customersupport.asia@rohde-schwarz.com 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. Rohde & Schwarz GmbH & Co. KG Mühldorfstraße 15 D München Phone Fax