Relaying for Industrial Wireless Networks

Abstract: The interest in wireless technology for industrial applications has increased dramatically over the last few years. Wireless communication can reduce cost and complexity, enable mobility and provide much higher flexibility than its wired counterparts. However, to be considered for use in practice, wireless systems must provide sufficient levels of timeliness and reliability as required by industrial applications, while keeping reasonable levels of complexity as well as interoperability with existing wired networks. Wireless channels, characterized by pathloss, noise, multipath fading and shadowing, imply a particular challenge to fulfill the requirements on timely and reliable communication. To this end, this thesis work proposes and evaluates a number of techniques able to increase the reliability of wireless communication systems without causing excessive or unpredictable delays. In addition, all proposed solutions are implementable on top of commercially available devices, i.e., they require no large alteration of the standard IEEE 802.15.4 and minimal changes to the current infrastructure to be compatible with existing industrial communication systems. First, the characteristics of industrial communication environments are determined. Then, suitable models to approximate them are selected, since the effectiveness of different error control schemes able to increase reliability depends on the type of wireless channel encountered. Next, different possibilities for reliability improvements in wireless industrial networks, while subject to strict timing constraints, are evaluated. Based on this, relaying that has been proven to be beneficial for traditional wireless networks is evaluated for applicability in industrial systems. Finally, several different relaying strategies that are implementable at the link layer on top of existing chipsets are developed and evaluated. Depending on the specific type of industrial application and its corresponding performance metrics, relaying is combined with network coding, forward error control codes, packet aggregation and packet combining techniques – all of which support increased reliability with maintained delay, at reasonable complexity investments. To complete the framework, scheduling schemes tailored to various relaying protocols are also developed.