Study On Voice Quality In GSM Cellular Radio Communication

With the rapid development of GSM networks and the voice traffic in it, the demand of network capacity expansion increased greatly. Particularly in the ultra-high-traffic urban density region, small interval between consecutive base stations which contain large number of carrier frequency leads to that the frequency of existing resources may not be able to meet the rapid growth of traffic in networks. To ease the pressure on network expansion and to protect investments effectively, telecommunication operators should focus on the enhancing of traffic on each carrier frequency.Half-rate speech coding technology (HR) is a fast way to improve network capacity. The rate of semi-rate of source coding which uses VSELP (vector Excited Linear Predictive Coding) compression, is only 50% of full-rate coding rate. That means possible voice quality difference between them. How to assess the difference and how to find ways to improve the voice quality becomes urgent to solve the problem.(1) Firstly, the voice quality assessment algorithm and testing methods were studied. Through research of ITU-T voice quality assessment algorithm, the scope and accuracy level of algorithm is understood and the appropriate assessment method is selected. The voice quality assessment system works with different measuring techniques to simulate the human ear. And algorithms are used to replace the listening process and the final value is equivalent of MOS. This paper introduced the voice quality assessment tests, and conducted testing and comparison in a targeted manner.(2) The voice quality is related to GSM relevant technical characteristics. In the second part, the optimization problems of voice quality were summarized. The impact factors of GSM voice quality were analyzed and corresponding optimization methods were presented. And then common voice engineering optimization methods were summarized.(3) In the third part, voice quality of half-rate coding was compared with that of full-rate coding through engineering test.(4) Finally, the optional new technologies were studied, and optional solutions were analyzed and summarized.