The Research Of Enhancement Methods For Speech Quality Based On The VoIP-VHF Communication System

As a primary method of Air-Ground communication, VHF communication plays a key role in the field of civil ATM (Air Traffic Management). In recent years, with the rapid development of Chinese civil aviation and the extremely growth of air traffic flow, the air traffic is overcrowded and air traffic security issues are becoming more and more outstanding, this leads to ATM Departments need more reliable and stable equipments. VoIP-VHF communication technology is based on IP packets switching, voice data is transmitted on the IP network and VoIP technology reduce the possibility of malfunction, but the VoIP-VHF communication system has the problem of discontinuous voice distortion in the application, which is a deadly hazard for aircrafts in flight. The purpose of this paper is to research methods and technology to enhance the speech quality, which is based on the VoIP-VHF communication system introduced by Inner Mongolia ATM-Sub Bureau.Firstly, this paper analyzes the principle of VHF communication and the protocols of VoIP technology, and than we deeply analyze the signal flow and usage situation of both the analogue VHF communication system and the VoIP-VHF communication system. By analysis of methods for the measurement of speech quality and factors which weaken the speech quality of VoIP-VHF communication system, we research the causes of packets loss and methods to reduce them. In conclusion we proposed two methods to reduce the influence of packets loss on speech quality. One is to optimize the hardware route, the other one is the comprehensive coding which is used of parity chec^interleaving technique and packets copy technique. Finally, we make a hardware testing platform to test the optimized hardware route and design a program to simulate the comprehensive coding method in use of Matlab.The results of testing and simulating proved that the optimized hardware route and comprehensive coding not only reduce the packets loss but also improve the speech quality of VoIP-VHF communication system efficiently.