Multi-tier multi-hop routing in large-scale wireless sensor networks for real-time monitoring

Our research team at the University of Nebraska's Advanced Telecommunications Engineering Lab (TEL) is working closely with the North American freight railroad industry to leverage wireless sensor networks (WSN) onboard railcars for advanced monitoring and alerting. Because freight train WSNs exhibit a linear chain-like topology of significant length, the existing IEEE 802.15.4 communication protocol, based on a star topology, is unable to provide acceptable service. The routing performance and reliability degrades significantly with increasing number of hops. The proposed multi-tier multi hop network is a practical solution for large-scale multi-hop WSNs in railroad environments. The idea is to have longer distance communication overlaid on the top of the shorter distance communication of WSNs to reduce the number of hops needed for route discovery and data forwarding. This approach has significant advantages, such as more data bandwidth and higher reliability. Our simulation results show that our proposed multi-tier communication approach is a feasible and reliable solution for implementing chain-topology WSNs with a high number of hops onboard freight trains.