The Research And Implementation Of Emergency Communication System Voice Dispatching Techniques Based On TD-LTE

Emergency Communication System is used to provide a variety of voice services including the single-call, group-call, broadcast, inserting and dismantling, playing an important role in the emergency rescue. Dispatching techniques is necessary for the voice services, ensuring transmission reliability in the limited-resource setting. In the traditional emergency communication system, voice services are implemented based on circuit switched domain, which are bandwidth-limited and difficult to be combined with other media services. In the broadband digital emergency communication system which is based on Time Division Long Term Evolution(TD-LTE), voice services are implemented based on packet switched domain. This scheme takes advantage of bandwidth and time-delayed in TD-LTE system, which is considered as the main direction of voice services.Based on the above background, the overall architecture scheme of emergency communication is described in this thesis firstly. Then requirements of the system are analyzed. After dividing the priorities of system calls, M/M/1 queuing model without priorities and M/M/1 queuing model which have preemptive priorities are used to model the system calls. The average response time for a call of the two models are compared, and the result indicates that M/M/1 queuing model which have preemptive priorities is more in line with the requirements of quick response for a call in emergency communication system.After that, the design scheme of voice services is proposed. This scheme is divided into two modules, including the signaling controlling module and the voice processing module. The signaling controlling module uses the open source stack oSIP and its expansion stack eXosip which are based on Session Initiation Protocol(SIP) to achieve the establishment of voice services. The voice processing module utilizes the functions which are provided by Low-level audio to achieve the acquisition, encoding, decoding and replay of voice data. Real-time Transport Protocol(RTP) is used to complete the transmission of voice data.Finally, the functions of voice services are tested in TD-LTE network. Corresponding to these voice services, the statistics including calling set-up time and packet lose rate are obtained respectively. The statistical data reveals that the calling set-up time is in line with the specification for broadband emergency communication system proposed by China's Ministry. The packet lose rate is between one percent and three percent, meeting the requirements of real-time voice transmission in emergency communication system.