Minimizing energy consumption in 802.15.4 IoT devices with multilevel xRPL (MxRPL)

IoT devices using IEEE 802.15.4 radio links may offer adaptable transmit power. But, since transmit power determines coverage, the problem of choosing the optimal tx power for each node is intertwined with the routing problem. We present a new cross-layer routing approach for reducing energy consumption in IEEE 802.15.4 IoT devices with adjustable radio power level termed multilevel cross-layer RPL (MxRPL). In our scheme, each node sets its tx power level according to the RPL parent chosen in the path with the lowest additive product of ETX and nodes' tx power. We also propose a new probing mechanism that maintains fresh link statistics for each neighbor and power level restraining the associated control messages. We have implemented our approach in Cooja's Z1 mote and simulated a network with 15 nodes in areas of different size. The results show that MxRPL achieves energy savings in the radio of up to 34% in reception and 20% in transmission compared to a simpler cross-layer binary approach previously published by the authors (i.e., each node chooses either its maximum or minimum tx power level). Energy savings are even greater compared to default RPL (up to 40% in reception and 26% in transmission). This is mostly attributable to the generation of less control messages and a more efficient use of tx power. Our scheme exhibits better results in medium and large size scenarios (e.g., >= 25 m x 25 m, 42 m2/node), whereas a simpler binary approach is slightly more advantageous in small and dense scenarios.