Fundamentals of Voice-Quality Engineering in Wireless Networks

Contents......Page 7
Preface......Page 13
Abbreviations......Page 18
Introduction......Page 25
Plan of the book......Page 27
1.1 Introduction......Page 35
1.2 Pulse-code modulation......Page 36
1.3 Wireless codecs......Page 37
1.4 Summary......Page 46
1.5 Transmission media......Page 49
1.6 Audio illustrations......Page 50
2.1 Introduction......Page 52
2.2 Measuring and quantifying voice quality......Page 53
2.4 Mean opinion scores of wireless codecs......Page 56
2.5 Standard computerized tools for speech-quality assessment......Page 61
Perceptual speech-quality measure (PSQM)......Page 62
Perceptual analysis measurement system (PAMS)......Page 63
PESQ: perceptual evaluation of speech quality – ITU P.862 recommendation......Page 64
ITU P.563 draft recommendation: a non-intrusive procedure for evaluating vocoder performance......Page 66
ITU G.107 recommendation: E model......Page 69
ITU G.168 recommendation: appraisal of echo-cancelation performance......Page 70
ITU G.160 recommendation – appendix II......Page 71
3.1 Electrical echo......Page 75
Echo as a function of delay and return loss......Page 76
3.2 Echo in wireless and long-distance networks......Page 80
Echo suppression......Page 82
Echo cancelation......Page 85
3.4 Placement in the network......Page 90
3.5 Convergence and adaptation processes......Page 93
3.6 Tail delay and its impact on performance......Page 96
3.7 Far-end echo cancelation......Page 97
ITU-T no. 7 solution......Page 99
ITU-T no. 5 solution......Page 100
3.8 Background music – music on hold......Page 102
3.10 Hot signals......Page 103
3.11 Voice-band data and fax......Page 104
3.13 Conclusions......Page 105
4.1 Introduction......Page 107
Acoustic echo in digital-wireless applications is non-stationary......Page 108
4.2 Round-trip delay and echo dispersion......Page 109
4.4 Controlling acoustic echo in digital-wireless networks – main considerations......Page 111
Error type I (with and without noise reduction)......Page 116
4.6 Residual acoustic-echo control in the frequency domain......Page 117
Time-domain versus frequency-domain representation......Page 118
4.7 The impact of comfort-noise matching on the performance of acoustic-echo control......Page 120
5. A case of acoustic-echo control with colored comfort-noise matching......Page 129
Intelligent noise estimate......Page 130
4.9 Network topology of acoustic-echo control......Page 132
4.10 Conclusions......Page 135
5.1 Noise in wireless networks......Page 136
5.2 Introduction to noise reduction......Page 138
5.3 The noise-reduction process......Page 139
Signal classification......Page 145
Noise reduction......Page 146
5.4 Noise reduction and GSM DTX......Page 148
5.6 Noise-reduction level compensation......Page 150
Ring-back tone......Page 152
Background music......Page 153
5.8 Network topology of noise reduction......Page 154
6.2 Basic signal-level measurements and definitions......Page 157
6.3 Automatic level control (ALC)......Page 159
Placement of the ALC within the voice-quality system......Page 161
ALC applied prior to Sin......Page 163
6.4 Noise compensation (NC)......Page 165
6.5 Combined NC and ALC......Page 167
6.6 High-level compensation......Page 168
7.1 Introduction......Page 171
Signal processing in mobile-to-mobile call applications......Page 172
Back-to-back echo-canceler arrangement......Page 174
Combined PSTN and A-interface echo-canceler architecture arrangements......Page 175
Interworking function (IWF)......Page 177
Circuit-switched data communications with VQ systems on the MSC to PSTN interface......Page 178
Data communications with VQ systems on the GSM A-interface......Page 179
High-speed circuit-switched data (HSCSD)......Page 180
VQ system transparency......Page 181
7.4 TFO (a.k.a. vocoder bypass)......Page 183
3G promotions and promises......Page 187
3G applications......Page 188
3G deployment......Page 189
GSM data – GPRS......Page 190
Evolution to 3G......Page 191
Voice services and VQS as 3G killer applications......Page 193
2G/3G network topology......Page 194
8.4 Conclusions......Page 196
9.1 Introduction......Page 199
9.2 Judging audio quality and performance of hybrid-echo cancelation......Page 200
Do the test results only indicate "pass or fail" ratings?......Page 201
Test 2 – convergence and steady-state residual and returned echo level......Page 202
Test 3 – performance under conditions of double talk......Page 203
Test 3B – true double talk......Page 204
Test 4 – leak-rate test......Page 205
Test 7 – stability under narrowband signals......Page 206
9.3 Subjective testing......Page 207
Subjective test configurations......Page 208
Double talk without clipping – test 2a......Page 209
Double talk with background noise – test 2c......Page 210
9.4 Judging audio quality and performance of acoustic-echo control......Page 211
Test 2 – single talk with surrounding noise......Page 212
Test 4 – single talk with music playing through the mobile phone with no acoustic echo......Page 213
Test 7 – double talk with surrounding noise......Page 214
ITU-T G.160 recommended procedure......Page 215
Test signals......Page 216
The case of double enhancement......Page 220
Caution in relying solely on automated MOS algorithms......Page 221
9.7 Automating MOS improvement estimate due to NR......Page 225
Test 1 – testing for ALC (send side) stability when operating post an echo canceler......Page 227
Test 2 – noise tolerance......Page 228
Test 4 – maximum gain......Page 229
9.9 Testing for data compatibility on a fully featured system......Page 230
Dual-tone multi-frequency (DTMF)......Page 231
Test sequence......Page 232
Ring-back tone......Page 233
Test sequence......Page 234
Wireless modems......Page 235
Test sequence......Page 236
Tandem-free operations......Page 237
Test procedure (lab)......Page 239
9.10 Subjective evaluation through a simulated network......Page 241
9.12 Subjective listening with voice recordings......Page 242
Survey instructions......Page 243
General requirements......Page 245
Administration of local user profiles......Page 246
Procedure documentation......Page 247
Running/fallback version......Page 248
Applicability......Page 249
Software listing......Page 250
Self healing......Page 251
Data export......Page 252
Loss of heart beat......Page 253
Bulk-data downloads and activates......Page 254
Operation and maintenance control trace tools......Page 255
Graphical user interface (GUI) for all applications......Page 256
Operation and maintenance control jobs......Page 257
Installation......Page 258
Online backup......Page 259
Documentation......Page 260
Generating command files......Page 261
Inventory information......Page 262
Storage at the OMC......Page 263
Data recovery......Page 264
Event logging......Page 265
User comments on alarms......Page 266
Unambiguous fault localization......Page 267
Remote access......Page 268
Network-analysis system......Page 269
Physical-damage test results......Page 270
Electromagnetic compatibility......Page 271
10.4 Training......Page 272
11.2 State-of-the-art performance and feature richness......Page 273
Stand-alone EC configurations......Page 274
Switch-integrated EC or VQS configurations......Page 275
11.6 Conclusions......Page 278
11.7 Fully featured VQS versus echo-cancelation only......Page 279
Just moved the stand-alone EC from the PSTN interface to the A-interface and there is echo......Page 285
Is it acoustic or electrical echo?......Page 287
Noise gets louder when the far end stops speaking......Page 289
Loud echo from a wireless phone when enabling the EC......Page 290
Clipped music......Page 291
It takes longer to converge due to long, persistent echo at the beginning of the call......Page 292
Distorted speech especially with noise......Page 294
Ring tone fades while noise between rings ramps up......Page 295
DTMF not going through......Page 296
Persistent echo throughout calls......Page 297
A sudden burst of echo complaints......Page 299
Partial acoustic echo......Page 300
Echo bursts in the middle of a conversation......Page 301
Noise bursts......Page 302
Noise reduction does not reduce noise......Page 303
Noise compensation does not work......Page 306
Music from mobile handset gets clipped......Page 307
Although the EC specs clearly state that its tail-delay capacity is 128ms, it does not cancel any echo with delay greater than 124ms. Are the specs wrong?......Page 308
Speech sounds unnatural and overly robotic......Page 309
13.2 Case study......Page 313
13.3 Description of tracer probe......Page 315
13.5 Conclusion......Page 317
14.1 Introduction......Page 318
My jingle and my singing telegram......Page 319
14.3 Architecture......Page 320
Phase 1 (see Figure 15.1)......Page 323
Phase 2 – lab analysis......Page 324
16 The theory of sleep......Page 325
17.1 Codec illustrations......Page 329
17.2 Echo as a function of delay and ERL......Page 331
17.4 Acoustic-echo control and comfort-noise matching......Page 332
17.5 Before and after VQS......Page 333
17.6 Trouble shooting......Page 334
Test and verification of DTMF......Page 335
Glossary of common voice-quality systems terminology......Page 337
Brief summary of echo cancelation and VQS major standards......Page 354
Brief summary of key voice-quality assessment standards......Page 356
Bibliography......Page 357
Index......Page 375