Design And Implementation Of A Portable Wireless Voice Conference System

Walkie-talkie, a portable half-duplex voice communication device is widely applied in production and daily life. But walkie-talkie is a half-duplex communication system that the send button need to be pushed down when someone use it to speak. But in field work, two hands of the worker are occupied by work. So he has no hand to push the button to speak. Voice conference system based on wired network is a system which is capable of multipart full-duplex voice communication. But it has the disadvantage of poor portability and the requirement of wired network. To meet the requirement of voice communication of field work, a portable full-duplex wireless voice communication system is required.This thesis proposes a portable wireless voice conference system based on wireless adhoc network. The system is consisted of multiple peer nodes which are connected by adhoc network.The node is implemented on embedded system whose hardware platform is ARM processor S5PV210 and software platform is embedded Linux to reduce the volume.The software of the node in the network is split to 3 modules by feature: network protocol module, voice transmission module, and button input module. The network protocol module implementing the network protocol designed by self which resolvs the problem of IP address allocation in ad-hoc network, is responsible for log the node into the network and maintain the online nodes list. The voice transmission module implements the capture, sending, receiving, and playback of voice. The voice signal captured by microphone is quantized to voice data. Voice data is encoded by encoder to encoded data. Encoded data is transferred in the IP network via UDP multicast. The receiver decodes the data from one node and mix it with other from other nodes. The earphone playbacks the mixed signal. The button input module read the input of button and dispatch it to other modules. The modules are implemented by multi-process model which UNIX domain socket is choosed as inter-process communication facilities with libraries. The network protocol moduls is implemented on the high performance network programming library libuv. Nodes communicats in the network protocol via UDP broadcast. The voice transmission module is implemented on the powful stream media library mediastreamer, and the codec uses high quality codec speex. To reach the better effect, acoustic echo canceller, voice activity detection and packet loss concealment are used.The system is tested on develop board. Test results show that system is capable of full-duplex voice communication. The maximum communication distance is 120 m. The system is capable of 3 nodes. The voice in the communication is clear and fluency.