Z-Phone: Design and implementation of embedded Voice over Zigbee applications

Short range wireless technologies such as Bluetooth, WiFi and DECT are known to transmit voice, audio and/or video messages in real time. Energy consumption and transmission reach are critical in such networks, especially for portable and/or power autonomous devices. The purpose of the Voice over Zigbee technology is to provide a competitive offering that excels in these performance aspects. Due to the CSMA-CA mechanism implemented in the 802.15.4 layer a well-designed strategy must be taken into account in Zigbee to create a robust, reliable and full-duplex conversation. This article proves that the radio channel of Zigbee has enough bandwidth to support a full-duplex conversation with narrow band voice codecs. Furthermore, it presents the implementation and evaluation of a voice codec performed in the framework of the Z-Phone project, which targeted the development of a low cost, ultra low power, long range wireless headset using Zigbee technology to transmit voice in full-duplex mode for use with leading PC VoIP programs. Last but not least, it presents the results of the transmission range and power consumption tests involving the developed headset prototype. Talk time is comparable to Bluetooth, but its deep-sleep lifetime doubles the Bluetooth performance. Another significant contribution of this work is towards understanding and resolving the challenges faced when trying to achieve good quality transmission of media over constrained devices and networks. The way to new voice-related Zigbee applications is open.