Characterizing XBee S2Cs in a DigiMesh Topology for WSN Applications

Digi XBee S2Cs are wireless communications modules that can be programmed to operate various wireless topologies. Applications may require certain hierarchical topologies while others need more robust, redundant topologies. The work here explores the implementation of a mesh topology, using the DigiMesh network protocol, a Digi proprietary protocol in which there is no node hierarchy. This protocol is based on the IEEE 802.15.4 standard for wireless communications. The effects of various obstructions on data transmission must be quantified in order to build a reliable network and understand the challenges that mobile wireless nodes may face in given indoor or outdoor environments. To characterize performance, the Received Signal Strength Indication (RSSI) values were analyzed to show the range of RSSI values at which data can be reliably transmitted. The amount of data transmitted over time (in kilobits per second) shows the speed of the network in various environments. Range and throughput tests recorded RSSI and amount of data transmitted. Experiments were designed for both in line-of-sight (LOS) environments, involving no obstacles between nodes, and non-line-of-sight (NLOS) environments, which may have obstacles interfering with communication. Hop tests were conducted to measure transmission failure and throughput using single-hop and double-hop packet transmissions. Data were acquired in triplicate using different modules.