frame header based speech quality analysis method in a circuit switched media gateway
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Frame Header Based Speech Quality Analysis Method in a Circuit-Switched Media Gateway. Master’s Thesis Presentation 18.10.2005. Author: Mika Väisänen Supervisor: Prof. Raimo Kantola Instructor: Ph.D. Peter Jungner. Contents. Introduction Circuit-Switched Media Gateway Speech Coding

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frame header based speech quality analysis method in a circuit switched media gateway

Frame Header Based Speech Quality Analysis Methodin a Circuit-Switched Media Gateway

Master’s Thesis Presentation 18.10.2005

Author: Mika VäisänenSupervisor: Prof. Raimo KantolaInstructor: Ph.D. Peter Jungner

contents
Contents
  • Introduction
  • Circuit-Switched Media Gateway
  • Speech Coding
  • Iu and Nb User Plane Protocols
  • Speech Quality Measurement
  • Estimation Method development
  • Analysis of the Method
  • Conclusions
introduction
Introduction
  • Background
    • On UMTS networks coded speech is transported in frames
    • On ideal situation only the used speech coding method degrades the speech quality of a call
    • In practise, frames are damaged on air-interface and lost on core network congestion
  • Problem
    • Operator may not know, how customers are perceiving the quality of the network
    • Operator will lose customers, if speech quality in the network drops
    • Operator must be able to monitor the speech quality in the network in real time
  • Objectives
    • To develop a method that can estimate speech quality of calls in UMTS Core Network by analysing only the speech frame headers
circuit switched media gateway cs mgw
Circuit-Switched Media Gateway (CS-MGW)
  • Adapts different Access Networks to the Core Network
  • Main functions:
    • Media conversion (ATM, IP, TDM)
    • Bearer control (Resource reservation)
    • Payload processing (Transcoding, echo cancelling, …)
speech coding
Speech Coding
  • Adaptive Multi-Rate (AMR) coding used in UTRAN
    • Variable bit-rate modes from 4.75 to 12.2 kbps
    • Source Controlled Rate of operation
      • During silence only Silence Descriptor (SID) frames are sent with low bit-rate
    • Uses efficient error concealment
      • Lost or damaged frames are “faded away”
      • Frame substitution and muting
    • AMR end-to-end = Transcoder Free Operation (TrFO)
  • Pulse Code Modulation (PCM) possibly used in CN
    • Compressed, 64 kbps
    • No error concealment
    • AMR-PCM-AMR = Coder tandeming, transcoding
iu and nb user plane protocols
Iu and Nb User Plane Protocols
  • Speech is carried in User Plane frames
    • 1 AMR frame in each Iu/Nb frame
    • 40 PCM samples in each Nb frame
  • Besides speech the Iu/Nb frames contain information
    • Frame numbering to detect lost frames
    • Frame Quality Classification (FQC)
    • Information of the frame type (AMR bit-rate, SPEECH/SID)
  • Transcoding in Tandem call cases re-creates the frame stream
    • All information regarding quality in the frame headers is lost
speech quality measurement
Speech Quality Measurement
  • Listening tests
    • Absolute Category Rating (ACR), scale 1-5
    • Mean Opinion Score (MOS)
  • Objective methods
    • Emulate listening tests
    • Speech signal based
      • Resource consuming
      • Perceptual Evaluation of Speech Quality (PESQ)
        • PESQ score, ranging from -0.5 to 4.5.
        • Correlation against listening tests 0.935.
    • Parameter based
      • Light, but not as accurate
      • ITU E-Model
      • PsyVoIP, VQMon
estimation method development
Estimation Method Development
  • Establish a model between frame loss/damage and speech quality
    • Frame losses and damages in simulated environment
    • Lost SID frames ignored, because they are 100 times less important than speech frames
    • Speech quality analysis with PESQ
  • Find out a way to determine types of lost frames
    • In PCM case simple, as all frames can be considered equal.
    • In AMR case SID frames complicate the determination
  • Create a method implementation to be run in CS-MGW
analysis of the method
Analysis of the Method
  • AMR TrFO case (AMR 12.2 kbps all the way)
    • Correlation of 0.90 was established between the method and real PESQ scores
      • Mean estimation error 0.14 PESQ-MOS units
analysis of the method1
Analysis of the Method
  • Tandem case (AMR 12.2 - PCM – AMR 12.2)
    • Correlation of 0.83 was established between the method and real PESQ scores
      • Mean estimation error 0.19 PESQ-MOS units
conclusions
Conclusions
  • The method proven to be surprisingly accurate, despite its simple implementation
    • PESQ-MOS differences < 0.5 are barely audible
  • Being able to determine the frame content (silence/speech) helps to improve the estimation
  • Ideal solution for operators using a leased RAN
    • In addition to price, also speech quality can be used to compare alternative networks
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