Wake-up radio in short-range wireless sensor network: Master's thesis

Energy efficiency is one of the major issues of sensor network nodes. From a power consumption point of view, measurement nodes should stay in a low-power sleep mode for long periods and only wake up when the measurement is made or the node is requested to do something else. Wake-up radio architecture is one possibility for providing long sleep periods and still enabling real-time controllability of the nodes. In this architecture a node has an additional very low power radio that listens to a wake up signal. The main radio is switched on only when a wake up request is received. As the main and the wake-up radios can have different operating ranges, many current multi-hop routing protocols are not optimal, as such, in these kinds of networks. This work investigates the effects a wake-up radio has on single and multi-hop sensor networks, focusing on energy saving possibilities. The requirements and limitations of sensor networks are discussed. After that, the characteristics of ad hoc routing protocols and wake-up radio solutions are examined. Most importantly, the effect of different ranges of the main and wake-up radios on routing is analysed. A solution is proposed for applying a RPL routing protocol to the wake-up radio equipped sensor network. In the chosen approach, both radios built up independent routing graphs used in their communication. In the evaluation part of this thesis, a complete testing network was built to measure key figures of the communication. That network was made by connecting AS3931 wake-up radio chips with the compatible transmitters to the sensor network motes (Redbee Econotag). The results show that notable energy savings can be achieved on both single-hop and multi-hop scenarios. On a packet rate of one packet per minute, the energy saving was 86 % on a single-hop scenario and 66 to 82 % on a two-hop scenario, when comparing to a system without a wake-up radio. The communication delay was on the same level on both systems, but the variation was significantly lower, when the wake-up radio was used.