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Internet Telephony Over Wireless Links

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Internet Telephony Over Wireless Links Internet Telephony over Wireless Links vorgelegt von Diplom-Ingenieur Christian Hoene von der Fakult¨at IV - Elektrotechnik und Informatik der Technischen Universit¨at Berlin zur Erlangung des akademischen Grades Doktor der Ingenieurwissenschaften – Dr.-Ing. – genehmigte Dissertation Promotionsausschuss: Vorsitzender: Prof. Dr. Heiß Berichter: Prof. Dr.-Ing. Wolisz Berichter: Prof. Dr.-Ing. Steinmetz Berichter: Prof. Dr.-Ing. Sikora Tag der wissenschaftlichen Aussprache: 16. Dezember 2005 Berlin 2006 D83 c 2005-2006 by Christian Hoene Jahnstr. 22 72144 Dußlingen Germany [email protected] As a small child, you never spoke that clearly, no wonder that you want to improve the speech perceptibility. My mother, after hearing my thesis topic. Abstract This thesis presents algorithms to enhance the efficiency of packetized, interactive speech communication over wireless networks. The results achieved are the following: We present an improved approach to assess the quality of voice transmissions in IP-based communication networks. We combined the ITU E-Model, the ITU PESQ algorithm, and various codec and playout schedulers to analyse VoIP traces. Parts of this algorithm have been included in ITU standards. By using this assessment approach we derived design guidelines for application and data-link protocols. Also, we developed a quality model to parametrise adaptive VoIP applications. Later results received a best-paper award. If highly compressed packetized speech is transported over packet networks, losses of in- dividual packets impair the perceptual quality of the received stream differently, depending on the content and context of the lost packets. We introduce the idea of the Importance of Individual Packets, which is defined by the impact of VoIP packet loss on speech quality. We present real-time and off-line algorithms to measure this importance. Using the concept of importance of packets we show that only a fraction of all speech packets needs to be trans- mitted if speech intelligibility is to be maintained. By applying this concept for Internet telephony over wireless links, significant transmission energy savings on wireless phones can be achieved, because fewer packets need to be transmitted. At the MAC layer we provided an open-source simulation model of IEEE 802.11e EDCA, which is used in many research projects and is often cited. Also, the ability of WLAN support voice traffic was studied qualitatively and quantitatively. Last, we proved that the distance between two WLAN nodes can be determined by packet round trip time measurements. This approach outperforms the previously used signal strength indications. Overall one can summarize, that this thesis contains relevant innovations and novel algo- rithms, which have a high potential to influence future research and product development. 5 6 Zusammenfassung Diese Dissertation pr¨asentiert innovative Algorithmen, um die Ubertragungseffizienz¨ von Te- lefonaten uber¨ drahtlose IP-Verbindungen zu steigern. Die folgenden Ergebnisse wurden er- reicht: Ein Algorithmus wurde entwickelt, der die wahrgenommene Qualit¨at von Internet Tele- fongespr¨achen instrumentell bewerten kann. Hierfur¨ kombinieren wir das ITU E-Modell, den ITU PESQ Algorithmus und unterschiedliche Sprachkodierungen und Ausspielpuffer. Teile dieses Algorithmus wurden in die Standards der ITU aufgenommen. Mit Hilfe dieses Bewer- tungsalgorithmus leiten wir daruber¨ hinaus wichtige Designentscheidungen fur¨ Transport- und Vermittlungsschichtprotokolle analytisch her. Auch entwickelten wir ein Qualit¨atsmodell, das fur¨ adaptive VoIP-Applikationen eingesetzt werden kann. Diese Arbeiten wurden mit einem Best-Paper-Award ausgezeichnet. Wenn hochgradig komprimierte Sprachdaten uber¨ das Internet ubertragen¨ werden, kann der Verlust eines Paketes sehr unterschiedliche Auswirkungen haben. Dies h¨angt unter ande- rem vom Inhalt und Kontext des Sprachpakets ab. Wir definieren die Paketwichtigkeit als die Verschlechterung der Sprachqualit¨at nach Verlust eines Sprachpakets. Wir entwickelten Ver- fahren, welche die Paketwichtigkeiten offline und in Echtzeit quantitativ bestimmen. Wendet man das Konzept der Paketwichtigkeiten an, zeigt sich, dass nur ein Bruchteil aller Sprachpa- kete ubertragen¨ werden muss, wenn zumindest Sprachverst¨andlichkeit gew¨ahrleistet werden soll. Wird das Konzept der Paketwichtigkeiten bei drahtlosen Internet-Telefonsystemen an- gewendet, l¨asst sich der Energieverbrauch der Funktelefone signifikant reduzieren, da weniger Pakete ubertragen¨ werden mussen.¨ Unsere Arbeiten auf der Vermittlungsschicht beinhalten ein open-source Simulationsmo- dell des IEEE 802.11e EDCA MAC-Standard sowie qualitative und quantitative Kapazit¨ats- untersuchungen von VoIP uber¨ WLAN. Unser Simulationsmodel wurde in vielen anderen Forschungsprojekten eingesetzt und ist h¨aufig zitiert. Schlussendlich zeigen wir, dass die Entfernung zwischen zwei Wi-Fi Ger¨aten einfach und ge- nau gemessen werden kann, indem man die Laufzeiten der Pakete bestimmt. Unser Verfahren stellte sich den bisher verwendeten Feldst¨arkemessungen als uberlegen¨ heraus. Zusammenfassend kann man sagen, dass diese Arbeit neue Algorithmen und relevante In- novationen enth¨alt, die ein hohes Potential haben, zukunftige¨ Forschung und Produktentwick- lungen zu beeinflussen. 7 8 Acknowledgements I would like to thank Professor Adam Wolisz for his advice during my doctoral program and for supporting my research throughout the lasts years. He always provided inspiring ideas and challenging feedback. Often, he was a key source of motivation and caused me to work hard. Also, I would like to thank my colleagues. Dr. Henning Sanneck wrote his PhD thesis on packet loss recovery and control for VoIP transmissions. His work inspired me a lot. Together with Professor Holger Karl I wrote a paper that won a best-paper award. I have to admit, you made the publication perfect! Professor Gunther¨ Sch¨afer was a great help in times of hard deadlines. He is somebody you always can rely on. Thanks a lot! My student Sven Wieth¨olter while doing this Studienarbeit has implemented the ns/2 EDCA model, which is cited so often, and helped me to write many publications. Andre Gunther¨ , it was a pleasure to work with you, listening to your stories and jokes was always fun. It is great to see somebody evolving like you. Together, we wrote two publications. Iacopo Carreras from Italy was my first diploma student. He wrote an email saying: “I want to do my master thesis, which should cover something with signal processing, something with programming and something with networking.” One morning I woke up and I had in mind his topic: “Prioritise speech packets over WLAN.” Iacopo wrote an excellent thesis and recommended to me the topic I shall study in my dissertation. Tuya Dulamsuren-Lalla has conducted the formal listening- only tests. It is a pleasure to work with you! Also Berthold Rathke, Cornelius Mahlo, and many more were a great help. Ein großes Dankesch¨on geht an Ian Marsh, KTH Stockholm, der die muhsame¨ Arbeit hatte, das Englisch meiner Dissertation zu verbessern. Ich h¨atte keinen Besseren finden k¨onnen, denn er beherrscht ein vorzugliches¨ Englisch und hat daruber¨ hinaus herausragende Fachkenntnisse. Last but not least, I would like to thank my family members and friends, who have been giving me constant support, encouragement and happiness that was indispensable for me to make this thesis become true. Especially my father, Dr. Ernst-Ludwig Hoene, has provided excellent feedback to my research and publications. 9 10 Contents 1. Introduction 35 1.1.Ideas.......................................... 36 1.2.Designscope..................................... 36 1.3.Marketdevelopment................................. 37 1.4.ArchitectureofaWireless-VoIPsystem...................... 38 1.5.Structureofthisthesis................................ 39 2. Background 41 2.1.Internettelephony.................................. 41 2.1.1.Acousticprocessing............................. 41 2.1.2.Speechcodecs................................. 41 2.1.3.Transportandnetworklayerprotocols................... 44 2.1.4.IPnetwork/backbone............................ 44 2.1.5.Playoutscheduler............................... 44 2.2.AdaptiveVoIP.................................... 45 I. TheImportanceofSpeechFrames 47 3. State of the Art 49 3.1.Qualityassessmentoftelephony........................... 49 3.1.1. Perceptual evaluation of speech quality (PESQ) . 49 3.1.2.TheE-Model................................. 52 3.1.3.Otherqualitymodels............................. 53 3.2.Apacketlossconcealmentalgorithm........................ 54 3.3.Classificationofspeechframes............................ 55 3.3.1.VoiceActivityDetection........................... 55 3.3.2.Voicing.................................... 55 3.3.3.Source-DrivenPacketMarking....................... 55 3.3.4.SPB-DiffMark................................ 56 11 Contents 4. Instrumental Assessment of a Telephone Call’s Perceptual Quality 59 4.1.Thenewqualitymodel................................ 60 4.1.1.CombiningPESQandtheE-Model..................... 62 4.1.2.Softwarepackage............................... 63 4.2.VerifyingPESQregardingsingleframelosses................... 64 4.2.1.Experimentaldesign............................. 65 4.2.2.Mongolia................................... 65 4.2.3.Testsampledesign.............................. 66 4.2.4.Formallistening-onlytests.......................... 66 4.2.5.Results.................................... 68 4.2.6.Analysis...................................
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