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Abstract

Сontent

Introduction

The interest of various subjects in telecommunications (telecom operators, internet providers, equipment manufacturers and users) to VoIP has an unusually increased in recent years, because many new standards and protocols has been developed. The quality of conversation over IP–protocols comes close to the "classical" telephone networks. This interest is explained by the fact that IP–telephony lets you save desired channel bandwidth, which inevitably leads to a reduction of tariffs, especially on long distance and international telephone calls. Also, fleeting deploying of next–generation networks (NGN) caused the problem of high–quality voice transmission.

1. Theme urgency

For a competent network design, where VoIP service will be deployed, it is necessary to ensure all standards of quality of service (QoS). It is also necessary to ensure error–free transmission of speech in communication VoIP channel with diverse surrounding noise.

Master’s thesis is dedicated to the actual problem of the choice of network parameters that affect the quality of service, as well as improving specific components of VoIP service, such as echo canceller and voice activity detector (VAD).

2. Goal and tasks of the research

The objectives of the research is to improve the parameters of quality of VoIP service by making recommendations for configuring a telecommunication network elements.

Main tasks of the research:

  1. Analysis of existing solutions on the organization VoIP service.
  2. Selection of the mathematical apparatus and means of simulation of VoIP communication channel.
  3. Development and research of VoIP communication channel model.
  4. Association of functionally different optimization directions of Moore FSM hardware amount into the unified approach to synthesis and formation recommendations for it's use.
  5. Research of quality criterion for VoIP communication channel.

Research object: Model of the VoIP speech communication channel.

Research methods. In this paper simulation of VoIP voice channel is used. Also it used the mathematical apparatus of wavelet transform to improve the echo canceller and voice activity detector. The technique of spectral analysis is used. The methods of planning and analysis of experimental results are used.

Planned scientific and technical innovation:

  1. A simulation model of VoIP speech communication channel, which is taking into account the impact of quality of service.
  2. Criteria for assessing speech quality of VoIP service, taking into account the quality of service (MOS, E–model, combined method).
  3. Providing advice on configuring VoIP voice channel.

3. А general structure of the VoIP communication channel

To assess the quality of VoIP service a mathematical model of speech communication channel need to be developed. Typical structure of the VoIP channel is shown in Figure 1.

Figure 1 – The structure of the VoIP voice channel
(animation: 12 frames, 7 cycles of repeating, 30 kilobytes)

The analog voice signal from microphone with the help of analog–digital converter (ADC) is converted into a digital stream (typically 54 kbit/s) At a subsequent stage, the process of noise removing and echo cancellation are taking place. Then digital data is compressed by encroder at 16, 8, or 6.3 kbit/s. Packets are shaped with protocols headers and passed through the IP–based network to the subscriber B. First, packets are accumulated in jitter buffer to eliminate jitter effect, which appears by packet passage through the network. If a part of packets was lost, then the series of packets need to be interpolated. Further, voice data is decoded, converted to analog form using a digital–analog converter (DAC) and fed to the speaker B [1].

Each of the components of the VoIP speech communication cannel will make some adjustments to the quality of service (QoS). Such parameters, as delay, jitter and loss probability will affect the transmitted voice signal. Is should be noted that the capacity of channel does not take into account in this paper – it can be neglected, since the capacity of modern communication channel is much bigger than the required for VoIP service. Noise reduction and echo cancellation are specific problems of providing VoIP service[6–7].

Conclusion

For a qualitative representation of VoIP service in modern networks all requirements of quality of service (QoS) need to be provided. This requires a number of recommendations on network configuration and upgrading specific components of the VoIP service (voice activity detection, echo canceller). During the research:

  1. A model of VoIP speech communication channel was designed.
  2. A model of voice activity detector (VAD) was designed and anylzed.
  3. The existing methonds for evaluating the quality of transmitted speech were reviewed.

Further studies focused on the following aspects:

  1. Research and development of an echo canceller.
  2. Comprehensive assessment of speech quality in VoIP network, providing advices on network settings.

This master's work is not completed yet. Final completion: December 2012. The full text of the work and materials on the topic can be obtained from the author or his head after this date.

References

  1. Росляков А.В., Самсонов М.Ю., Шибаева И.В. IP–телефония // Эко–Трендз, 2–е издание. – 2003. – 468 с.
  2. Полканов Е.И., Шнепс–Шнеппе М.А., Крестянинов С.В. Интеллектуальные сети и компьютерная телефония // Радио и связь – 2001. – 240 с.
  3. Галичский К. Компьютерные системы в телефонии // BHV Санкт–Петербург. – 2002. – 400 с.
  4. Кофанов Н.С. Расчет пропускной способности канала связи VoIP трафика с использованием различных кодеков. [Электронный ресурс]. – Режим доступа: http://www.sworld.com.ua/index.php/ru/technical–sciences....
  5. Бобрицкмй С.М.«Алгоритм оценки качества передачи речи с анализом характеристик эффективных потерь пакетов на основе вейвлет–преобразования. [Электронный ресурс]. – Режим доступа: http://scipeople.ru/publication/107179.
  6. Salah K. Deploying VoIP in Existing IP Networks. [Электронный ресурс]. – Режим доступа: http://www.techrepublic.com/whitepapers....
  7. Unuth N. What Affects Voice Quality in VoIP Calls. [Электронный ресурс]. – Режим доступа: http://voip.about.com/od/voipbasics....
  8. Ding. L. Speech Quality Prediction in VoIP Using the Extended E–Model. [Электронный ресурс]. – Режим доступа: http://ieeexplore.ieee.org/xpl....
  9. Kung–Ching Wang. Robust Voice Activity Detection Based on Discrete Wavelet // Department of Information Technology & Communication. – Shin Chien University. – 2007. – 13 с.
  10. R. Venkatesha Prasad, Abhjeet Sangwan, Vishal Guarav. Comparsion of Voice Activity Detection Algorithms for VoIP // CEDT. – Indian Institute of Science. – 2002. – 6 с.
  11. Добеши И. Десять лекций по вейвлетам // Регулярная и хаотическая динамика. – Ижевск. – 2001. – 464 с.
  12. Смоленцев Н.К. Основы теории вейвлетов. Вейвлеты в Matlab // – ДМК. – Москва. – 2005. – 304 с.