Modeling and design of multi-hop energy efficient wireless networks for control applications

University dissertation from Stockholm : US-AB

Abstract:  Energy efficiency is essential for many industrial and commercial wireless network applications. In this thesis, we propose an analytical framework to model and design protocols for multi-hop wireless networks for industrial control and automation. We study the mutual interaction among medium access control (MAC), routing, and application layers. Accordingly, we provide three main contributions. First, MAC and routing layers are considered. The carrier sense multiple access (CSMA) of the unslotted IEEE 802.15.4 standard is modeled for multi-hop communications using the specifications of the IETF routing over low power and lossy networks (ROLL). The analysis considers the effects induced by heterogeneous traffic due to the routing mechanism and the node traffic generation patterns, and the hidden terminals due to the reduced carrier sensing capabilities. The interde-pendence between end-to-end performance indicators (reliability, delay, and energy consumption) and routing decisions is described. It is shown that routing decisions based on reliability or delay tend to direct traffic toward nodes with high packet generation rates, with significant negative effects on the energy consumption. Second, we propose TREnD, a cross-layer protocol solution that takes into account tunable performance requirements from the control application. An optimization problem is posed and solved to select the protocol parameters adaptively. The objective is to minimize the energy consumption while fulfilling reliability and delay constraints. TREnD is implemented on a test-bed and it is compared to existing protocols. The protocol model and analysis are validated through experiments. It is shown that TREnD ensures load balancing and dynamic adaptation for static and time-varying scenarios. Eventually, a building automation application is presented by considering the design of a robust controller for under floor air distribution system regulation. The communication performance of an IEEE 802.15.4 network is included in the controller synthesis. We show the impact of reliability and delay on the temperature regulation for synchronous and asynchronous networks.