Geographic Centroid Routing for Vehicular Networks Effects of GPS Error on Geographic Routing Dr. Justin P. Rohrer jprohrer@nps.edu Naval Postgraduate School TaNCAD Lab ( https://tancad.net ) VEHICULAR – June 25, 2018
Abstract Geographic Centroid Routing for Vehicular Networks Paper Abstract [Rohrer, 2018] A number of geolocation-based Delay Tolerant Networking (DTN) routing protocols have been shown to perform well in selected simulation and mobility scenarios. However, the suitability of these mechanisms for vehicular networks utilizing widely-available inexpensive Global Positioning System (GPS) hardware has not been evaluated. We propose a novel geolocation-based routing primitive (Centroid Routing) that is resilient to the measurement errors commonly present in low-cost GPS devices. Using this notion of Centroids, we construct two novel routing protocols and evaluate their performance with respect to positional errors as well as traditional DTN routing metrics. We show that they outperform existing approaches by a significant margin. www.nps.edu 2 / 39
Outline Introduction Background Centroid-Based Routing Simulations Conclusion www.nps.edu 3 / 39
Introduction A Word About Us... Justin P. Rohrer: ◮ Assistant Professor, Network Group, Computer Science Department, Naval Postgraduate School ◮ Teaches: CS3502 (Networks I), CS4538 (Wireless Security), CS4558 (Network Traffic Analysis) ◮ Developed, teaches: CS4554 (Network Modeling and Analysis) ◮ Leads: Center for Tactical Networked Communications @NPS ◮ Pi/Co-PI on Disruption Tolerant Networking and Network Measurement Projects www.nps.edu 4 / 39
Introduction TaNCAD Lab @ NPS Naval Postgraduate School (NPS) ◮ Navy’s Research University ◮ Located in Monterey, CA ◮ ≃ 1500 graduate students: military officers & DoD civilians Center for Tactical Networked Communication Architecture ◮ 3 NPS professors, 2 NPS staff ◮ Sponsors: USN, USMC, NSF, NSA, ONR, DARPA, . . . Focus: ◮ Network Survivability and Resilience ◮ Disruption Tolerant Networks for Tactical Environments www.nps.edu 5 / 39
Introduction Goals for this work ◮ Quantify the potential effects of GPS positional error on geolocation-based routing protocols ◮ Evaluate the effectiveness of a simple routing primitive designed to mitigate those effects www.nps.edu 6 / 39
Introduction Goals for this work ◮ Quantify the potential effects of GPS positional error on geolocation-based routing protocols ◮ Evaluate the effectiveness of a simple routing primitive designed to mitigate those effects ◮ Not “create the worlds best DTN routing protocol” www.nps.edu 6 / 39
Introduction Goals for this work ◮ Quantify the potential effects of GPS positional error on geolocation-based routing protocols ◮ Evaluate the effectiveness of a simple routing primitive designed to mitigate those effects ◮ Not “create the worlds best DTN routing protocol” ◮ (That’s future work...) www.nps.edu 6 / 39
Outline Introduction Background Centroid-Based Routing Simulations Conclusion www.nps.edu 7 / 39
Background Disruption Tolerant Routing Disruption tolerance is the ability of a system to tolerate disruptions in connectivity among its components. Disruption tolerance includes tolerance of environmental challenges, weak and episodic channel connectivity, mobility, long & unpredictable delay, energy and power constraints. ◮ Make local forwarding decisions without globally consistent information ◮ More information = better decisions ◮ Geolocation is an increasingly common external data source ◮ Readily available www.nps.edu 8 / 39
Background GPS Positional Samples ◮ GPS hardware receiver constantly updates estimated position ◮ Software applications sample position periodically ◮ Per-sample precision and accuracy vary widely ◮ Receiver quality (cost), antenna gain, view of sky all factors ◮ Cheap receivers with tiny antennas and occluded view of sky are typical ◮ How bad? www.nps.edu 9 / 39
Background GPS Positional Samples ◮ GPS hardware receiver constantly updates estimated position ◮ Software applications sample position periodically ◮ Per-sample precision and accuracy vary widely ◮ Receiver quality (cost), antenna gain, view of sky all factors ◮ Cheap receivers with tiny antennas and occluded view of sky are typical ◮ Some days it’s really bad... www.nps.edu 9 / 39
Background GPS Positional Samples ◮ GPS hardware receiver constantly updates estimated position ◮ Software applications sample position periodically ◮ Per-sample precision and accuracy vary widely ◮ Receiver quality (cost), antenna gain, view of sky all factors ◮ Cheap receivers with tiny antennas and occluded view of sky are typical ◮ Advertised (intentional) error is ± 20 m ◮ Error can be order of 1000 m ◮ 100 m error commonplace [Ben-Moshe et al., 2011] www.nps.edu 9 / 39
Background Commercial GPS navigation ◮ Commercial GPS navigation devices do significant post-processing of samples, snap to nearest road, and present best-guess position to user ◮ Smartphones incorporate data from WiFi and cellular radios ◮ All these innovations driven by errors/limitations in using GPS position only www.nps.edu 10 / 39
Background Network Simulators ◮ Position typically provided as cartesian coordinates ◮ Location is accurate to arbitrary precision ◮ Geographic routing protocols are designed and tested under these conditions (mobile testbeds are hard) www.nps.edu 11 / 39
Background Network Simulators ◮ Position typically provided as cartesian coordinates ◮ Location is accurate to arbitrary precision ◮ Geographic routing protocols are designed and tested under these conditions (mobile testbeds are hard) ◮ No basemap (from the routing protocol’s perspective) ◮ No WiFi MAC location database lookups ◮ We are as guilty of this as anyone [Rohrer et al., 2008, Rohrer and Killeen, 2016] www.nps.edu 11 / 39
Background Network Simulators ◮ Position typically provided as cartesian coordinates ◮ Location is accurate to arbitrary precision ◮ Geographic routing protocols are designed and tested under these conditions (mobile testbeds are hard) ◮ No basemap (from the routing protocol’s perspective) ◮ No WiFi MAC location database lookups ◮ We are as guilty of this as anyone [Rohrer et al., 2008, Rohrer and Killeen, 2016] ◮ What if we introduce error into simulation-reported locations? www.nps.edu 11 / 39
Outline Introduction Background Centroid-Based Routing Centroid Router Center-Mass Router Simulations Conclusion www.nps.edu 12 / 39
Centroid-Based Routing Centroid Primitive ◮ Designed for simplicity ◮ Intended as building-block to be combined with other techniques Node Centroid ◮ Average position over time ◮ Updated at fixed time-interval www.nps.edu 13 / 39
Outline Introduction Background Centroid-Based Routing Centroid Router Center-Mass Router Simulations Conclusion www.nps.edu 14 / 39
Centroid Router Centroid Routing Protocol ◮ Epidemic-based, multi-copy [Rohrer and Mauldin, 2018] ◮ Nodes exchange Centroid and message list at encounter ◮ Copy more messages to nodes with distant Centroid www.nps.edu 15 / 39
Centroid Router Centroid Routing Protocol ◮ Epidemic-based, multi-copy [Rohrer and Mauldin, 2018] ◮ Nodes exchange Centroid and message list at encounter ◮ Copy more messages to nodes with distant Centroid ◮ Comparable complexity to Vector routing ◮ Improves efficiency by reducing message copying to nodes with similar Centroids ◮ Intuition: Nodes with distant Centroids more likely to encounter nodes not encountered by this node www.nps.edu 15 / 39
Outline Introduction Background Centroid-Based Routing Centroid Router Center-Mass Router Simulations Conclusion www.nps.edu 16 / 39
Center-Mass Router Center-Mass Routing Protocol ◮ Builds on Centroid protocol ◮ Nodes record Centroid & timestamp of all encountered nodes ◮ Nodes exchange Centroid list and message list at encounter ◮ Merge into own Centroid list ◮ Copy more messages to nodes with distant Centroid ◮ Only copy messages to neighbors with Centroid closer to destination Centroid www.nps.edu 17 / 39
Center-Mass Router Center-Mass Routing Protocol ◮ Builds on Centroid protocol ◮ Nodes record Centroid & timestamp of all encountered nodes ◮ Nodes exchange Centroid list and message list at encounter ◮ Merge into own Centroid list ◮ Copy more messages to nodes with distant Centroid ◮ Only copy messages to neighbors with Centroid closer to destination Centroid ◮ Intuition: Minimize message copies sent away from destination www.nps.edu 17 / 39
Outline Introduction Background Centroid-Based Routing Simulations Effects of Positional Sample Error Comparison of Probabilistic-Predictive Routing Protocols Protocol Efficacy Metric Conclusion www.nps.edu 18 / 39
Simulations Network Simulator The ONE [Keränen et al., 2009] is a discrete-time simulator designed specifically for DTN protocol simulations. It abstracts away details of propagation, medium access, and network layers and is written in Java. ◮ We use the default mobility and traffic scenario provided ◮ Commonly used Helsinki scenario in literature ◮ Nodes include pedestrians, cars, and trams ◮ Map-based mobility www.nps.edu 19 / 39
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