The Design And Realization Of The Emergency Communication Based On Android Mobile Phone

With the rapid development of smart phone techniques,smart phones become more powerful and perfect and its penetration rate is getting higher and higher.In addition to supporting wireless mobile communication(voice,data),smart phones also has rich hardware supports for Wi-Fi,Bluetooth,NFC and other communication functions.Since smart phones are not only portable and convenient for software development,but also have rich hardware resources,the development of communication application based on mobile platform is attracting more and more attentions.The normal communication of smart phone is heavily dependent on the normal operation of base stations and quality of covering signals.In recent years,sudden and large earthquake has occurred from time to time,such as Wenchuan earthquake,Yushu earthquake.The communication base stations in the earthquake would have been severely damaged.Then this directly caused the paralysis of communication system,which brings great difficulty to know the earthquake situation and carry out relief work in the first time.Making use of other communication resources on smart phones,such as Wi-Fi,Bluetooth,etc,through ad hoc network,developing intra-regional emergency voice communications and inter-regional information transfer technology in the absence of base conditions has great significance and value.This paper presents the issue about the design and implementation of emergency communications based on Android mobile phone platform,which mainly considers the communication and information sharing in region and the transmission of information between regions based on Wi-Fi resources in the absence of infrastructure(communication base station).This paper mainly accomplishes the design and realization of two communication programs:the information sharing system in a region based on Wi-Fi hotspot and the multi-hop communication system based on Wi-Fi.In this paper,the main research works are as follows:(1)This paper built a regional network based on Wi-Fi and AllJoyn framework,to manage devices using networking mechanisms of AllJoyn framework,and achieved the non-real-time data communication within the region,including the design and implementation of the signaling system,instant messaging,file transfer and voice transmission module.(2)Through studying the principle of voice codecs and echo cancellation,this paper transplanted Speex voice codecs and echo cancellation library on Android platform using JNI technology,to accomplish voice codecs and echo cancellation to improve voice quality.(3)This paper introduced the multi-threading technology to complete the acquisition of voice,echo cancellation,voice coding,UDP transmission,voice decoding,voice playback threads running in parallel,in order to achieve real-time voice calls within the network area.(4)Based on the switch between Wi-Fi infrastructure mode and the Wi-Fi hotspot mode,this paper set up a multi-hop network to realize the interconnection between regions.Study the characteristics of multi-hop network,design communication protocols and routing protocols of the network to realize information transmission in multi-hop network.