Abstract

Accurate link quality estimation is an important building block in quality aware routing. In an inherently lossy, unreliable and dynamic medium such as wireless, the task of accurate estimation becomes very challenging. Over the years ETX has been widely used as a reliable link quality estimation metric. However, more recently it has been established that under heavy traffic loads ETX performance gets significantly worse [4, 18, 19]. Contributions made in this paper are twofold. Firstly, we examine the ETX metric's behavior in detail with respect to the MAC layer and UDP data; and identify the causes of its unreliability. Secondly, we present the design and implementation of the xDDR link quality measurement metric -- a variation of ETX - motivated by the observations made in our analysis. Our experiments show that xDDR substantially outperforms minimum hop count, ETX and HETX in packet delivery ratio.

Highlights

  • A wireless transmission medium is inherently lossy, dynamic as well as unpredictable

  • We examined the role of MAC layer in influencing and effecting ETX estimates at network layer

  • While xDDR on average improves absolute packet delivery ratio percentage of 14%, 10% and 8% as compared to Minimum Hop Count, ETX and HETX respectively. This implies a 3 times gain over Minimum Hop Count, a 1.94 times gain over ETX and a 1.7 times gain over HETX in actual packet delivery

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Summary

Introduction

A wireless transmission medium is inherently lossy, dynamic as well as unpredictable. The goal of quality driven routing is to achieve a more deterministic behavior such that the network resources can be efficiently utilized resulting in improved performance in terms of delivery ratio, bandwidth, latency, throughput etc. A number of quality driven metrics have been proposed over the years where throughput and packet delivery ratio have gained special interest. Among them the Expected Transmission Count (ETX) [7] metric has been one of the most widely used metrics aimed at improving end-to-end throughput in wireless networks. We propose xDDR (estimated Directional Delivery Ratio) an improved link quality estimation mechanism that is motivated by the observations made from the behavior of ETX. Comparisons in end-to-end packet delivery ratio confirm the overall gain yielded as a result of more accurate link level estimates

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