Codec Negotiated Technology Of 3rd Generation Mobile Communication

WCDMA mobile communication system is a 3G system based on GSM structure. It come though three network consultative moments for R99, R4, R5. In the Stage of R99, the circuit switch of core network is based on TDM, coding voice flow by 64Kbit/s PCM codec. However, wireless access network codecs voice flow by compress AMR codec in order to save resource of rarity wireless bandwidth. AMR codec must change to G.711 codec which is standard PCM codec, so transcoder is needed. Using transcoder not only adds burden of system resource, but also affects the quality and the real time of voice transmitting. In the Stage of R4, ATM and IP become main medium of circuit switch instead of TDM, which make codec modes of core network more agility. The work introduced in this thesis has researched codec negotiation in 3G core network and researched agility and uniform codec in order to solve the problem which mentioned above.Firstly, a brief introduction of 3rd generation telecommunication is given. And the main research of this thesis is explained. Then, a brief introduction of structure of WCDMA core network and material definition and use of network entity is given. After that, Transcoder Free Operation (TrFO) technology which is aboard use in R4 network is analyzed. This technology can avoid transcoder inserted by consolidating codec in all path. A particular discussion of main mechanism and founded flow is given. And the demand of network entity to achieve TrFO is given. Finally, a experiment is given to prove the effect of TrFO in advancing voice quality and reduce the voice time delay.Tandem Free Operation (TFO), another codec technology in 3G core network is analyzed in this chapter. Besides investigating the principle, the cause of transplanting TFO which used to be used in R99 network to R4 network which has already had TrFO technology and the principle and arithmetic about how to transplant is analysis. Then put forward a method to solve the conflict between TrFO and TFO. An experiment is given to prove the advantage of the method. Finally, the difference between TrFO and TFO is analysis.After introduce the two codec technology above, dynamic codec, a new codec technology is brought forward in this chapter. The application of dynamic codec is analysis, which is different from the application of the codec technology mentioned above. Then a particular discussion of actualized principle and method is given. Finally, a experiment is given to prove the outstanding advantage about the dynamic codec in solving the antinomy between advancing the voice quality to increasing the access users count.Lastly, a conclusion of this thesis and the discussion of future research directions are given.