Abstract
We propose a novel cross-layer scheme to reduce energy consumption in wireless sensor networks composed of IEEE 802.15.4 IoT devices with adjustable transmit power. Our approach is based on the IETF’s Routing Protocol for Low power and lossy networks (RPL). Nodes discover neighbors and keep fresh link statistics for each available transmit power level. Using the product of ETX and local transmit power level as a single metric, each node selects both the parent that minimizes the energy for packet transmission along the path to the root and the optimal local transmit power to be used. We have implemented our cross-layer scheme in NG-Contiki using the Z1 mote and two transmit power levels (55mW and 31mW). Simulations of a network of 15 motes show that (on average) 66% of nodes selected the low-power setting in a 25m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times25\text{m}$ </tex-math></inline-formula> area. As a result, we obtained an average reduction of 25% of the energy spent on transmission and reception of packets compared to the standard RPL settings where all nodes use the same transmit power level. In large scenarios (e.g., 150m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times150\text{m}$ </tex-math></inline-formula> and 40–100 motes), our approach provides better results in dense networks where reducing the transmit power of nodes does not translate into longer paths to the root nor degraded quality of service.
Highlights
The IPv6 Routing Protocol for Low power and Lossy Networks (RPL) [1], [2] is the IETF standard for routing in the Internet of Things (IoT) widely used in wireless sensor networks
These statistics are related to RPL performance, RPL messages sent by the node at each power level, application-level counters, and general traffic counters such as the number of frames sent and received, number of retransmissions, etc
Using the settings described above, we have simulated the operation of our cross-layer scheme x-RPL(METOF) and standard RPL(MRHOF) with default (H) transmit power
Summary
The IPv6 Routing Protocol for Low power and Lossy Networks (RPL) [1], [2] is the IETF standard for routing in the Internet of Things (IoT) widely used in wireless sensor networks. Safaei et al have proposed ELITE [23] a cross-layer scheme that operates at the link layer and RPL by using a routing metric that accounts for information about the radio duty cycle This scheme achieves a significant energy reduction, but it is restricted to the radio duty cycling protocol ContikiMAC and, like the previous one, it fails to consider nodes with different levels of transmit power. This work is different from ours in the following aspects: (a) it creates a new routing protocol rather than using standard RPL, (b) the criterion used to set the node’s transmit power level is related to delay and not to energy, (c) it requires to have prior knowledge of the nodes layout and the application-layer traffic pattern.
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