The Study And Development Of Key-technologies Of VoIP Based On ARM

With the great development of Internet nowadays, communication technology basedon IP is widely used, that is VoIP(Voice over Internet Protocol). VoIP encodes thecompressed speech first, and then packages the data according to IP. These packages will betransmitted via IP net. At the receiving end, the process will be done in reverse order toreconstruct the original speech. This is the process of how to transmit speech over theInternet. However, the quality of speech is not high enough to popularize the technology, sostudying and developing key-technologies of VoIP becomes important.Firstly, the paper introduces the theory of producing and detecting DTMF (Dual-ToneMulti-Frequency) signals which is usually used to transmit dial number intelecommunication system. A usually DTMF signals detection method is Goertzelalgorithm, which is analyzed and studied in the paper. Pre-process and validity test of resultmodules are added in detection process.Codec is one of the most important part in VoIP, various codec scheme are widelyapplied to VoIP system at present. In this paper, ITU-G.729A codec is chosen. Firstly, theprinciple of G.729A codec is introduced, and the coding and decoding process are alsoexplained in detail. Then a brief analysis about delay and complexity and memoryrequirements of the algorithm are given. In the end, how to optimize the source code toimprove the speed based on the real system is presented.The research and algorithm development about the key-technology echo cancellationin VoIP are proposed in the paper. Firstly, it illustrates the reasons that causes echo, thenanalyzes some usual methods to solve it, and explains the MDF(Multidelay BlockFrequency Domain) filter theory detailed. In the algorithm, some parameters are analyzedand chosen to the best, including echo cancellation quality evaluation. Finally, assemblyoptimization on ARM is used to reduce complexity to apply to the real system.