Speech Compression And Application In Railway Communication

With the rapid development of science and technology, the proportion of non-speech messages, such as data, image and video, in the field of communication is increasing. However, in the modern communication system, speech communication is still vital and indispensable. In railway communication, speech message is play an important role, affect the safety of railway transport. Speech message is useful to analyze and identify the traffic accident after accident and improve the standardization of cabin crew.The train dispatch portable radio is an important equipment in railway communication. The GP3688 portable only can communicate with speech, which is used in railway communication, but can not record speech data. It can not satisfied with the requirement of railway communication. In order to improve the safety of the railway transport, we have to upgrade the GP3688 portable. It needs to add the speech recorder module for it. We apply the speech compression algorithm in it to reduce the storage space and the transmission bandwidth of speech data. In addition, in order to manage the speech data in speech recorder module, It adds the wireless module on it.Finally, the upgraded portable is called TWX-I.Speech compression is a main task in this paper. By comparison, we select the current mainstream of middle and low bit-rate speech compression standard G.729 A.G.729 A has a good rebuild speech quality with 8 kbit/s. It is a kind of compression algorithm which has a higher compression ratio and speech quality. We can apply it on train dispatch portable radio for the requirement of speech compression and storage in railway communication.Due to the complexity of the G.729 A algorithm, we test the amount of computation and analyze the computation of it, and find out the mainly time-consuming function in G.729 A. we develop an optimization strategy, which is combine with C language and assembly language. In C language level, we use the structure optimization and remove the saturate operation method to reduce the complexity of algorithm. Inassembly language level, we use the ARM assembly language and the characteristics of ARM architecture Cortex-M3 to rewrite the basic function which are frequently called and spend much time in G.729 A algorithm.We apply the optimized speech compression to speech recorder module in new-style TWX-I train dispatch portable radio, and realize the 16 times real-time speech compression. We use the speech sequences to test the optimized algorithm.Under the condition of guarantee the speech quality, it is reduce the compression time by 81.8% in totally, which can meet the requirement of real-time speech compression.Practice tests show that the effect is satisfaction, and will be going to massive production.