Voice Transmission over Wireless Sensor Networks Lin-Huang Chang, Chao-Chieh Chen, Tsung-Han Lee Department of Computer and Information Science, National Taichung University, Taichung, Taiwan lchang@mail.ntcu.edu.tw Abstract. There is a growing need to support voice communication in wireless sensor networks for use in emergency scenarios. In this paper we develop an end-to-end rescue communication voice gateway to provide a stable voice transmission over Bluetooth and Zigbee networks for mountain climber. The performance analyses, in terms of end-to-end throughput, packet loss rate, jitter and delay, show that our implementation can efficiently support voice transmission over wireless sensor networks. Keywords: Zigbee, Bluetooth, Xbee, Arduino, Speex, Voice over Zigbee. 1 Introduction Traditional wireless sensor network (WSN) has focused on sensing and reporting physical phenomenon or environmental parameters, such as temperature, sound and pressure etc. Currently, using WSN for emergency response has gained significant attention due to the development of WSN technology. The data types transmitted over WSN becomes diversity. There are many hazard scenarios, such as emergency response, rescue, and disaster during mountain climbing, which need to support voice transmission over WSN (VoWSN). Several standards are currently under developed for WSN. The Institute of Electrical and Electronics Engineers (IEEE) approved the 802.15.4 Standard [1] to define the physical and media access control (MAC) for Low-Rate wireless Personal Area Network (LR-WPAN). Upper layer are defined by Zigbee Alliance [2]. The features of Zigbee include the standard specified operation in the unlicensed 2.4 GHz worldwide, low power consumption, low transfer rate (default rate: 250kbps), short- range communication capability, (maximum: 300m), limited computational capacity and memories. The research from Brunelli et al. [3] has investigated and analyzed the performance of Zigbee network for voice transmission. They adjusted the sensor network deployment to maximize transmission performance. Their simulation and experimental results have demonstrated that by adjusting the input and output queue size properly, WSN is capable of providing most common voice streaming applications. Several voice transmission mechanisms and architectures for communication over WSN have been studied in [4-7]. 158