Transmission Power Control for Large Scale Industrial Applications in Low Power and Lossy Networks

Abstract

Transmission power is an important factor which impacts on routing topology in low power and lossy networks (LLNs). LLNs have been designed for low rate traffic where use of maximum transmission power is the best choice for performance maximization since it results in reduced hop distance and transmission overhead. However, large scale applications also require LLNs to deliver very high rate traffic. In such large scale applications, the nodes which are near the root node will incur heavy traffic even though each node generates low rate traffic. As a result, it will cause severe link congestion. In this paper, we first investigate the effect of transmission power control on the performance of the routing protocol for LLNs (RPL) at heavy traffic load through testbed experiments. Our experiments show that, unlike LLNs in low rate applications, packet delivery performance at heavy load first increases and then decreases with transmission power. And we further investigate the reasons of what makes packet loss rate have a convex curve according to transmission power by per node analysis. We classify packet losses into link loss and queue loss. From the experiment results, we observe that link and queue losses are significantly unbalanced among nodes, which causes the load balancing problem of RPL. Furthermore, queue losses occur at the nodes which experience severe link loss. To solve this problem, we propose a simple power control mechanism, which allows each node to adaptively control its transmission power according to its own link and queue losses. Our proposal significantly improves the packet delivery performance by balancing the traffic load within a routing tree. We show performance improvement through experimental measurements on a real mutihop LLN testbed running RPL over IEEE 802.15.4.