ZigBee based wireless sensor networks and performance analysis in various environments

To achieve a reliable and robust system for environmental monitoring, there is an available technology that can be used to resolve this problem and moreover provide for better living. Wireless sensor networks (WSN) have been successfully applied in many environmental monitoring. An ad-hoc wireless sensor network consists of a number of small and self-power sensing devices (nodes) connected using effective wireless networks. Compared to wired networks, there are several challenges that must be addressed in wireless networks. These challenges are limitation in communication bandwidth and energy constraint in sensor node, therefore it is important to know their reliability and performance. This paper reports the development and performance analysis of an embedded wireless sensor network for temperature and humidity monitoring in the environment. The network itself consists of a coordinator or data gateway which wirelessly collect temperature and humidity data from several sensor nodes that are responsible to provide those data. Each sensor node is developed from an Arduino based microcontroller, Xbee wireless module based on ZigBee/IEEE 802.15.4 standards, and temperature and humidity sensor devices. The network quality of service (QoS) is investigated in terms of delay, throughput and packet loss as a function of sensor node distance and transmitted packet size over line of sight (LOS) and non-line of sight (NLOS) conditions. The throughput and packet delay are also measured as a function of the baud rate in point to point link. This experiment is performed to have an insight how the baud rate affects the latency of the communication over the ZigBee protocol. Next, we also considered the multi-hop scenario with the presence of router for relaying packets from the sensor node to the coordinator. The performance of multi-hop configuration is compared to that of direct transmission. Based on our analysis, it is concluded that the ZigBee based WSN is more suitable for low data rate applications.