Research On Real-time Speech Transmission System With Embedded Architecture

The VoIP technology that transmits digital speech by means of internet is the core platform in which many kinds of multimedia services are developed and applied now. At present, the research on VoIP are focusing on how to improve the quality of IP phone services, including applying advanced hardware, completing command interface and high reliability transport protocol for real-time applications, increasing compression rate. This paper tries to design a new digital real-time speech transmission system based on embedded architecture, which will make full use of embedded system, network communication, multimedia and speech technologies, together with high performance, lower power consumption and lower cost features.In the study of the overall framework of real-time speech transmission system, we accomplished a hardware implementation of embedded phone terminal based on PXA255 processor and established an optimized embedded Linux development system for this phone terminal. Then we also study the realization of speech coder and decoder about GSM06.10 based on this terminal, analyze some useful features of Real-time Transport Protocol's packet, and introduce the key technicality about media synchronization. Finally one trade-off synchronous strategy to reduce jitter performance and improve the speech playing quality is proposed and is applied to the real-time speech transmission system. In the end we realize one practical real-time speech transmission system, which is composed of embedded IP phone terminal software and information server software. The whole system has a friendly graphical user interface and can transmit the real-time speech through network.For the powerful capability of PXA255 and Linux, the embedded speech terminal owns the merit of low cost, high reliability, expansibility and transportability, which can be widely used in the intelligent large building. So there is a bright future.