Avaliação da qualidade de voz do serviço VoIP em sistemas HSDPA

Abstract

In recent years, we can observe the development and fast dissemination of VoIP services, being integrated by the present market, beside conventional telephony and cellular networks. For being a technological alternative that contributes to minimize costs, we see an increasing preference for voice transmission through IP networks. HSDPA, as a cellular system, allows high speed data transmission,increases the network width of band and creates new possibilities for multimedia services, as VoIP that transmits in wideband to mobile telephones. The delay inherent to this system, however, is a challenge for the need to assure good quality of voice transmissions, demanding a considerable effort of analysis of this service.These facts justify a study that focus on the quality of voice in VoIP over HSDPA.To evaluate the voice quality, in this study, we applied MOS method that makes numerical values correspond to categories like quality and intelligibility of transmitted voice, getting these data through objective and subjective methodologies. The evaluation process was divided in fases according to the characteristics of each methodology and to technical recommendations, and was done through dynamic computational simulations. For objective evaluation process,algorithm PESQ was employed to obtain MOS concepts, whereas, for subjective evaluation, voice files with a percentage of error have been placed in Internet for listening and for the attribution of MOS concepts based in the perception of the listener. The results of this research show that both evaluation methods got satisfactory concepts of quality, that QoS is steady and positive in the simulations, that a good quality for the voice files and the probable satisfaction of the users of the VoIP service on cellular system HSDPA is guaranteed for 2% FER rate. Finally, it shows that MOS concepts produced by objective methodology were close enough to those given by subjective evaluation to dispense with the arduous work of making diverse voice files to be heard and subjectively evaluated by a statisticaly valid amount of users.