The Third Generation Of Mobile Communication In Amr Vocoder Research

One of main services in mobile communication is speech and the key technology is the coding and decoding of speech signal. Now, the low-rate speech coding has been the main research aspect so as to save frequency bands as many as possible. In recent years, coding algorithm (rate from 4. Skbps to 16kbps) usually use Code Excitation Linear Predictive(CELP) .With the development of the third generation mobile communication technology, next generation speech coding technology has been set up. Algebra Code Excitation Linear Predictive (ACELP) algorithm which is mature upon rate 4kbps has been chosen as the standard algorithm in 3G Adaptive Multi Rate(AMR) speech coder. To fit the third generation mobile communication, AMR coder can work in several mode with rate range from 4. 75kbps to 12. 2kbps. ACELP is widely used in AMR speech coder. ACELP algorithm has been proved high coding efficiency, low complexity and working stability. Many new generation speech coding standard has chose it as algorithm, such as ITUT G.723, G.729 etc. This speech coder is important in mobile speech communication in future. It is the kernel of the third generation speech communication.In AMR speech coder, many other techniques have been used beside ACELP algorithm. These techniques include voice activity detection, source controlled rate operation, comfort noise, rate switch, multi-band filtering etc. Voice activity detection can reduce actual transmission rate of speech data, comfort noise can improve natureness of speech. These engineering method and algorithm make up of the coder's core.The second chapter introduces the basic theory of ACELP speech coder. The third chapter mainly introduce controlling mechanisms.The forth chapter focus on rate switch in AMR coder. Finally, we give the computer emulation result and performance analyzation for this AMR coder.