Implementation Of ILBC Codec Based On MIPS Embedded System

With the increasing development of voice technology during recent years, the applications of the communications in internet voice become more and more popular, the communicative quality of network telephones becomes an important factor that restricts its development. In order to reduce the impact of packet loss on voice quality in packet-switched network, a Long Term Prediction and the Packet Loss Concealment algorithm was brought up by the company named Global IP Sound, that is the iLBC algorithm.The full name of iLBC is Internet Low Bit-rate Codec, a new codec of IP voice technology. The iLBC algorithm is essentially a frame-based linear predictive coding algorithm, is an extention of CELP (Code Excited Linear Predictive Coding). It has a technology of dynamic code book updates, an algorithm of speech enhancement after spectrum, and packet loss concealment technique. Relative to the previous speech codec algorithms such as G.729A and G.723.1, iLBC has a better performance in packet switching network.This subject is a cooperative project with an integrated chip company, the main work is to investigate iLBC speech codec algorithm and realize it on the chip of MIPS32 24KE after optimization, and eventually apply to the network television as the audio codec in video phone. The project's implementation process can be divided into three steps. First, make the float-point to fixed-point conversion of the iLBC algorithm in C language. Secondly, transplant the iLBC codec into MIPS embedded platforms after the fixed-point conversion. Finally, in order to reduce the computational complexity of the voice algorithms and improve the speed of encoding and decoding, enhance the performance of DSP code from the compiler optimization and code optimization at two levels. The results have passed through the uniform debugging. The PLM3K chip with MIPS32 24KE core successfully eventually achieved the requirements of real-time voice codec, reached the level of commercialization, and mass produced by an integrated chip company.