Radio Channel Characteristics of Zigbee Wireless Sensors in Machine Shop for Plant Floor Process Monitoring

Abstract

Wireless sensors are envisioned to be useful for plant floor process monitoring with unprecedented flexibility and low costs, where data can be relayed via a wireless network formed among the sensors. Factory environments, however, are known harsh for radio communications. For sensor radios engineered with extremely low power and simple circuitry, the sensor radio channel characteristics must be identified for optimal network design and reliability assessment. In this paper, a preliminary radio channel measurement study was performed based on the wireless sensor pairs in normal communication at the 2.4 GHz Industrial, Scientific and Medical (ISM) band to assess the sensor radio channel properties in a university machine workshop. The effect of both stationary and moving (forklift) obstacles on the radio propagation in terms of the received signal power, bit error and packet error rates was studied. The effect of stationary obstacles was further analyzed against a simple path loss model to find the path loss exponent. A spectrum analyzer was also used to capture the noise backgrounds in free space and the machine shop, which shows significantly different radio activities among the investigated scenarios. The proposed channel measurement methodology through directly utilizing the sensor platforms will help future radio channel characterization studies in manufacturing plant floor environments.