Research And Implementation On Speech Codec In TETRA Standard

As one of the most popular digital trunked standards in the world nowadays, TETRA digital trunked communication system has become one of the general standards in our country. TETRA system is an open system which is designed and set unified standard by ETSI to meet the requirement of mobile system in European specialized departments. Because TETRA system can provide services such as commanding and dispatching, data transmission and speech service in one technical platform, it is widely used in many private departments, such as police, port, railway and etc. China is among the later comers for trunked communication. It has a huge gap comparing with foreign countries no matter in the aspect of the research and development on trunked communication, or in the products of the terminals and equipment. Thus, researching and developing trunked communication system of our own is of great economic and social benefits.TETRA standard stipulates the advanced technologies that applied in TETRA system, such as speech coding, modulation, multiple accesses, group network and so on. Speech coding adopts ACELP speech compression schemes. ACELP is based on code linear predictive algorithm, which is low rate and high quality in reconstruction speech. The paper first studies the basic principle of ACELP algorithm, and analyses key steps of analysis and quantization of linear predictive parameters and code searching. Then, ACELP algorithm is realized and the performance is tested by software. Based on GNU Radio SDR(Software Defined Radio) platform, the paper designs the speech codec module, data process module and speech resample module. Combined with USRP radio peripherals, the paper builds real-time speech communication system which measures up to TETRA standard.