Reliable, Low-delay Communication in Wireless Sensor Networks

Abstract: Wireless sensor networks consist of tiny computers embedded into an environment which can monitor almost anything - such as light, motion, proximity, temperature, biometrics and chemical substances. Actuators conjoined to sensor networks can be used not only to sense the environment, but also to interact with it. Such a design is used to develop automatic control systems, ex. a production line in a factory. These systems are delay critical and demand high reliability. Hence wireless sensor networks incorporated into such systems must provide su-cient reliability as well as low delay communication. However, wireless sensors possess power-constrained radios. Furthermore, wireless communication is expensive in terms of power consumption. Wireless link conditions are often harsh, unpredictable and vary considerably in both space, and time. Wireless sensor networks are formed by multi-hop wireless meshes. Consequently, the communication in wireless sensor networks lacks the required reliability, and often exhibits long communication delays. This Master's thesis investigates about the development of a reliable, and low end-to-end delay data collection scheme for wireless sensor networks. The approach is to decrease the number of retransmissions for a packet at the data link layer in order to decrease the end-to-end delay. However, a decrease in the number of retransmissions for a packet leads to lower reliability. In order to compensate for the reliability suered, an erasure coding scheme, and a multipath routing paradigm are investigated. Accordingly, the thesis focuses on an implementation, and evaluation of an e-cient combination of fountain coding, braided multi-path routing, and proportionally fair packet scheduling. The thesis concludes that fountain coding in combination with braided multipath routing and proportionally fair packet scheduling is an e-cient solution for a wireless sensor network with high loss rates.