The development of speech coding and the first standard coder for public mobile telephony

This thesis describes in its core chapter (Chapter 4) the original algorithmic and design features of the ??rst coder for public mobile telephony, the GSM full-rate speech coder, as standardized in 1988. It has never been described in so much detail as presented here. The coder is put in a historical perspective by two preceding chapters on the history of speech production models and the development of speech coding techniques until the mid 1980s, respectively. In the epilogue a brief review is given of later developments in speech coding. The introductory Chapter 1 starts with some preliminaries. It is de- ??ned what speech coding is and the reader is introduced to speech coding standards and the standardization institutes which set them. Then, the attributes of a speech coder playing a role in standardization are explained. Subsequently, several applications of speech coders - including mobile telephony - will be discussed and the state of the art in speech coding will be illustrated on the basis of some worldwide recognized standards. Chapter 2 starts with a summary of the features of speech signals and their source, the human speech organ. Then, historical models of speech production which form the basis of di??erent kinds of modern speech coders are discussed. Starting with a review of ancient mechanical models, we will arrive at the electrical source-??lter model of the 1930s. Subsequently, the acoustic-tube models as they arose in the 1950s and 1960s are discussed. Finally the 1970s are reviewed which brought the discrete-time ??lter model on the basis of linear prediction. In a unique way the logical sequencing of these models is exposed, and the links are discussed. Whereas the historical models are discussed in a narrative style, the acoustic tube models and the linear prediction tech nique as applied to speech, are subject to more mathematical analysis in order to create a sound basis for the treatise of Chapter 4. This trend continues in Chapter 3, whenever instrumental in completing that basis. In Chapter 3 the reader is taken by the hand on a guided tour through time during which successive speech coding methods pass in review. In an original way special attention is paid to the evolutionary aspect. Speci??cally, for each newly proposed method it is discussed what it added to the known techniques of the time. After presenting the relevant predecessors starting with Pulse Code Modulation (PCM) and the early vocoders of the 1930s, we will arrive at Residual-Excited Linear Predictive (RELP) coders, Analysis-by-Synthesis systems and Regular- Pulse Excitation in 1984. The latter forms the basis of the GSM full-rate coder. In Chapter 4, which constitutes the core of this thesis, explicit forms of Multi-Pulse Excited (MPE) and Regular-Pulse Excited (RPE) analysis-by-synthesis coding systems are developed. Starting from current pulse-amplitude computation methods in 1984, which included solving sets of equations (typically of order 10-16) two hundred times a second, several explicit-form designs are considered by which solving sets of equations in real time is avoided. Then, the design of a speci??c explicitform RPE coder and an associated eÆcient architecture are described. The explicit forms and the resulting architectural features have never been published in so much detail as presented here. Implementation of such a codec enabled real-time operation on a state-of-the-art singlechip digital signal processor of the time. This coder, at a bit rate of 13 kbit/s, has been selected as the Full-Rate GSM standard in 1988. Its performance is recapitulated. Chapter 5 is an epilogue brie y reviewing the major developments in speech coding technology after 1988. Many speech coding standards have been set, for mobile telephony as well as for other applications, since then. The chapter is concluded by an outlook

Testing of voice quality of VoLTE/VoWiFi technology

Tato diplomová práce se zabývá možnostmi použití ITU-T G.107 E-modelu pro objektivní neintrusivní měření kvality přenosu hlasu v sítích LTE a Wi-Fi. V první části práce jsou prezentovány používané metody měření hlasové kvality, zejména algoritmus POLQA, rozbor E-modelu a přehled technologií VoLTE a VoWiFi. Hlavní částí práce je návrh algoritmu výpočtu R-faktoru, lineárního ukazatele kvality přenosu hlasu, vycházejícího z parametrů měřených uživatelskými zařízení s OS Android. Návrh vychází z rozsáhlých měření technologie VoLTE a jeho úspěšnost predikce hlasové kvality je vyhodnocována na základě srovnání s měřeními algoritmem POLQA. V práci jsou dále uvedeny možnosti implementace algoritmu pro měření hlasové kvality na zařízeních s OS Android.This master’s thesis deals with application of the ITU-T G.107 E-model for objective non-intrusive voice transmission quality measurements in LTE and Wi-Fi networks. The first part presents techniques used for voice quality measurements, particularly algorithm POLQA, analysis of the E-model and overview of the VoLTE and VoWiFi technologies. The main part of this paper consists of design of the R-factor calculation formula using parameters measured by Android OS powered devices. The algorithm design is based on extensive VoLTE measurements and its voice quality prediction successfulness is evaluated by comparison with POLQA measurements. The paper also presents implementation possibilities of the proposed algorithm on devices with Android OS.

Design einer mobilen Anwendung zur verschlüsselten Sprachkommunikation auf Basis des Android Betriebssystems

Die unterschiedlichen Möglichkeiten und die Realisierung der abhörsicheren und verschlüsselten, mobilen Sprachkommunikation auf Basis des Android Betriebssystems, sind zentraler Bestandteil dieser Master-Thesis. Private und abhörsichere Kommunikation lässt sich in einem direkten Gespräch ohne größeren Aufwand realisieren. Bei indirekter Sprachkommunikation, wie einem Telefongespräch, muss erheblich mehr Aufwand betrieben werden, um abhörsicher und vertraulich kommunizieren zu können. Die Verwendung von Verschlüsselungsmechanismen ist hierfür eine Option zur Realisierung von abhörsicherer und privater Sprachkommunikation. In dieser Arbeit werden die verbreitetsten Protokolle und Technologien beschrieben und evaluiert, mit deren Hilfe man verschlüsselte prachkommunikation technisch realisieren kann. Die Technologie-Evaluation wird kategorisiert nach Netzzugangstechnologie, Audiocodec, Signalisierung, Medientransport und Schlüsselverwaltung durchgeführt. Dies geschieht unter Berücksichtigung von Angriffen und Sicherheits- lücken, den Besonderheiten der Medientransportebene bei drahtloser mobiler Datenübertragung und den Beschränkungen, denen mobile Endgeräte und der mobile Internetzugang unterworfen sind. Neben der Evaluation der Technologien wird auch der Einsatz und die Integration von Smartcards in Sprachkommunikationssoftware zur Verschlüsselung und Zertifikatsspeicherung diskutiert. Aufbauend auf der Analyse der existenten Protokolle und Technologien wird das Konzept einer Anwendung entwickelt, mit der die verschlüsselte Sprachkommunikation auf dem Android Betriebssystem realisiert werden kann. Dabei wird durch die Implementierung einzelner Teile des Konzepts, eine Machbarkeitsstudie durchgeführt.</p