Do Not Lose Bandwidth: Adaptive Transmission Power and Multihop Topology Control

We show that a multihop wireless network can achieve better bandwidth and routing stability when transmission power and routing topology are jointly and adaptively controlled. Our experiments show that the predominant 'fixed and uniform' transmission power strategy with 'link quality and hop distance'-based routing topology construction loses significant bandwidth due to hidden terminal and load imbalance problems. We design an adaptive and distributed control mechanism for transmission power and routing topology, PCRPL, within the standard RPL routing protocol. We implement PC-RPL on real embedded devices and evaluate its performance on a 49-node multihop testbed. PC-RPL reduces total end-to-end packet losses ~7-fold without increasing hop distance compared to RPL with the highest transmission power, resulting in 17% improvement in aggregate bandwidth and 64% for the worst-case node.

I. Introduction

The subtlest aspect of routing in low-power and lossy wireless networks (LLNs) is topology formation. In modern routing protocols, such as RPL (IPv6 routing protocol for LLNs) [1] and CTP (collection tree protocol) [2], the goal of this process is to form a DAG (directed acyclic graph) rooted at one or more border routers, typically connected to LAN or WAN networks and thereby part of a private or public Internet. Each node discovers neighbors through communication events and computes certain statistics, such as hop count or expected transmission (ETX) [3], to select a small subset of neighbors that are closer to the roots to serve as parents [1] [2]. The dominant traffic pattern is then generating and forwarding packets through parents toward border routers and beyond. All aspects of this process, link capacity, neighbor table size, routing table size, and queue size, are severely constrained.