Sensor Network Navigation without Locations

Mo Li, Yunhao Liu, Jiliang Wang, and Zheng YangDepartment of Computer Science and Engineering

Hong Kong University of Science and Technology, Hong Kong

Study group at 5/11 by Jason

Outline

• System introduction• Design principles• Implementation experience• Performance evaluation

System introduction

• Traditional sensor network – data centric ,efficiently collecting, routing, and processing in-network sensory data.

• Difference of human navigation network– no physically multicast or copied– Limited human speed– Frequent updating of emergency or dangerous

situation changing

System introduction

• Human navigation system based on sensor network with two characteristics: – Release the necessity of utilizing location

information– Address the dynamic leading to variations of

dangerous area

System introduction

• Small-scale with 36 TelosB Motes on 802.15.4• Objectives and requirements:Safe: Be apart from

dangerous areaEfficient: A shorter path is

needed for rapid departure. Scalable: Building and

updating should be local and lightweight

Design principles

• 4 components of designing principles:– Building the road map– Guiding navigation on the road map– Reacting to emergency dynamics– Improving routing efficiency

Building the road map

•In 2D, the medial axis of a plane curve S is the locus of the centers of circles that are tangent to curve S in two or more points, where all such circles are contained in S. (It follows that the medial axis itself is contained in S.)

Medial axis

Building the road map

(a) Un-sensed place are defined as dangerous area(b) Preliminary information on boundary, like

indoor environment, safely surrounded by walls or fences

Medial axis are expressive and can capture the topological features of safe region R

Guiding navigation on the road map

(1)Connecting the exit to the road map backbone - Defining potential field: p=1/d, extending each step on the most descending direction (2)Assigning directions on the road map - Flooding dc and dr from the gateway to all network(3)Exploring the routes for users - 3 stages, from cell to backbone, backbone routing and from gateway to exit(4)The safety of the navigation route -Guarantee maximizing the minimum distance from dangerous areas along the selected path

Reacting to emergency dynamicsExpanding or shrinking of dangerous areas means points that switches in to or out from areas. Lemma 3.5. When the dangerous area

in a cell c expands or shrinks continuously, only the points within c are affectedLemma 3.6. The emerging of a new dangerous point affects the points within the newly constructed cell and the diminishing of a dangerous point affects the points within the originalcell.

Theorem 3.7. The impact of the emergency dynamics in the field is local

Implementation experiences.danger is 0 when the node is out of dangerous area.s.border is a boolean variable that indicates whether the current node is on the boundary of the dangerous areas.mDist records the distance from the current node to the nearest dangerous areas.mSet records the set of nodes on the boundaries of dangerous areas that are of s.mDist to the current nodes.road is a boolean variable that indicates whether the current node is on the road map backbones.nextHop stores the ID of the next hop node along the path direction on the road.s.rDist records the minimum distance to the dangerous areas on the path from thecurrent node to the exit

Implementation experience

• Emergency happening deciding s.danger and generate danger ID.

• Confirming all boundary nodes(set s.border), and then flood to all network to decide s.mDist and s.mSet.

• Examine s.mSet of all nodes to decide if it contains boundary modes on two or more dangerous areas(setting s.road)

Implementation experience

• Calcculating s.potential=1/s.mDist• Gate way node flooding the exit information

through the road backbone:– dc, which records the minimum number of hops to

the dangerous areas along the road from the current node to the gateway,

– dr, which records the number of hops along theroad from the current node to the gateway.

Implementation experience

• Originally , every node sets its s.nextHop to be null, and s.rDist to be 0.

• IF(s.rDist < dc), switches its s.nextHop to be the ID of the node that forwards the message and sets its s.rDist to be dc.

• Assign dc as min(dc, s.mDist) and forward this message

Implementation experience

Performance evaluation

Performance evaluation

Performance evaluation

• Simulating randomly deploying sensor nodes with average node degree of 28

• Network size ranges from 1000 to 16000• 10 internal users• Number of randomly inserting dangerous

areas is uniformly chosen from 3 to 6.

Performance evaluation

• SG=Skeleton Graph , PF=Potential Graph , RM=Road Map

• A. Minimum Distance to the Danger: performance ratio=d/dOPT

• B. Shortest Path: performance ratio= l/lOPT• C. Minimum Exposure Path: S=sum(1/dist^2),

performance ratio =S/SOPT• D. Update Overhead

Performance evaluation