1. *** School of Information, Renmin University of China, China
Bandwidth-aware Breach-free Barrier Construction with VANET nodes for Realtime Fugitive Search
Donghyun Kim*, Junggab Son*, Wei Wang** , Deying Li***, Alade O. Tokuta*, Sunghyun Cho+ * Department of Mathematics and Physics, North Carolina Central University, Durham, NC, USA
** Schoo of Mathematics and Statistics, Xi'an Jiaotong University, Xi'an, China
*** School of Information, Renmin University of China, China
+ Department of Computer Science and Engineering, Hanyang University, South Korea

2. Agenda Introduction Problem Formulation
Abstraction of Metropolitan Area Topology
Breach of Sensor Barriers
Formal Definition of Problem
Main Contribution – Polynomial Time Exact Algorithm
Checking Integrity of a VANET Barrier
Barrier-breach between Two VANET Barriers
Scheduling Subsets for Breach-free Barrier
Concluding Remarks

3. Image source: http://adrianlatorre.com/projects/pfc/img/vanet_full.jpg
Introduction
Vehicular Ad hoc NETwork (VANET)
An adhoc network of highly mobile nodes, in particular vehicles travelling on the road
Image source:

4. Introduction VANET applications
Remote vehicle personalization and diagnostics
Internet access
Digital map downloading
On-demand-basis real-time visual data collection
Pics-on-wheel (POW): mobile cloud-based real-time street visual data collection system [2]
Vehicle Witnesses as a Service (VWaaS): privacy enhanced version of POW [3]
and many more.

5. Image source: http://humandrama.tistory.com/975
Introduction
Q: Collecting Real-time Visual Images of Suspects Who Are Trying to Leave Area of Interest using VANET nodes?
VANET nodes are expected to have visual sensors and wireless transceivers
Image source:

6. Image source: http://ipvm.com/
Introduction
People care their privacy
Normally, reluctant to reveal their current locations and/or their future travel schedule
Under urgent/emergent situation, e.g. Boston Bombing
Previous experiences show many people may voluntarily disclose their locations and give up their privacy
Image source:

7. Introduction
Still, the future trajectories of VANET nodes may not be controllable, but may provide their current locations and short-term future trajectories
Asking all nodes to transmit real-time video would generate too much network traffic ?

8. Agenda Introduction Problem Formulation
Abstraction of Metropolitan Area Topology
Breach of Sensor Barriers
Formal Definition of Problem
Main Contribution – Polynomial Time Exact Algorithm
Checking Integrity of a VANET Barrier
Barrier-breach between Two VANET Barriers
Scheduling Subsets for Breach-free Barrier
Concluding Remarks

9. Problem Formulation Problem Statement
How to operate a subset of VANET nodes
to provide (inside-out) barrier-coverage over an area of interest to detect fugitives leaving an area of interest during a given mission period
Assume
the area of interest is a huge metropolitan area,
the mission period consists of a series of time slots,
the travel schedule of each VANET node is known for next T time slots,
each participating VANET node is with visual sensors and wireless connectivity to the central authority, and
are either moving on the road and parked on a parking lot,

10. r (a) (b) Problem Formulation
Abstraction of Metropolitan Area Topology
Assume the shape of the map M of a metropolitan area is a rectangle
Partition M into regular squares whose length and width are r
Construct a topology graph G=(V, E)
(a)
(b) r

11. Problem Formulation
Barrier coverage of a sensor network and breach [27]

12. (a) (b) (c) Problem Formulation
Adoption of the Concept of Breach to Our Context
(a)
(b)
(c)

13. (a) (b) Problem Formulation
Seamless VANET barrier coverage problem (SVBCP)
Given
the location of each VANET node at each time slot in [0, T],
find a VANET node operation schedule (a collection of subsets of nodes) which does not have two subsets at t-time slot and (t+1)-time slot, between which there exists a breach, and (b) the size of each subset does not exceed a network limit, b.
(a)
(b)

14. Problem Formulation Seamless VANET barrier coverage problem (SVBCP)
Q: There might be more than one choice from one slot to the next slot – which one does not lead to the dead end?

15. Agenda Introduction Problem Formulation
Abstraction of Metropolitan Area Topology
Breach of Sensor Barriers
Formal Definition of Problem
Main Contribution – Polynomial Time Exact Algorithm
Checking Integrity of a VANET Barrier
Barrier-breach between Two VANET Barriers
Scheduling Subsets for Breach-free Barrier
Concluding Remarks

16. Main Contributions Three Key Questions
Given a city map abstraction 𝐺=(𝑉,𝐸), the initial location 𝑝, and a subset of nodes 𝐵 𝑖 , the locations of participating VANET nodes at the 𝑖-th time slot, how to determine if 𝐵 𝑖 provides a (inside-out) barrier coverage over 𝐺 against 𝑝?
Given 𝐺 and two barriers 𝐵 𝑖 and 𝐵 𝑖+1 , how to determine if there is no breach when 𝐵 𝑖 is replaced by 𝐵 𝑖+1 .
How to design a polynomial time exact algorithm for SVBCP?

17. Checking Integrity of a VANET Barrier
Given a city map abstraction 𝐺=(𝑉,𝐸), the initial location 𝑝, and a subset of nodes 𝐵 𝑖 , the locations of participating VANET nodes at the 𝑖-th time slot, how to determine if 𝐵 𝑖 provides a (inside-out) barrier coverage over 𝐺 against 𝑝?
Step 1: modify 𝐺 to a directional graph
Step 2: compute a path from 𝑝 to 𝑞
the existence of such path implies the existence of a covert path for the fugitive
such that any incoming directional edge to a VANET node in 𝐵 𝑖 is removed

18. Barrier-breach between Two VANET Barriers
In our context,
a breach between two barriers is a node in 𝐺 such that
used to reachable to 𝑝, but not reachable to 𝑞, but
now, not reachable to 𝑝, but reachable to 𝑞 (outside the current barrier, and thus get to 𝑞 almost immeidately)

19. Scheduling Subsets for Breach-free Barrier
For each i-th time slot
find all possible configurations (a subset with size b)
edge from one configuration at i-th time slot to another configuration at i+1 time slot
find s-t path … … … … … …

20. Analysis Theorem 1 The proposed strategy solves the SVBCP correctly.
The running time of the proposed algorithm is polynomial

21. Agenda Introduction Problem Formulation
Abstraction of Metropolitan Area Topology
Breach of Sensor Barriers
Formal Definition of Problem
Main Contribution – Polynomial Time Exact Algorithm
Checking Integrity of a VANET Barrier
Barrier-breach between Two VANET Barriers
Scheduling Subsets for Breach-free Barrier
Concluding Remarks

22. Concluding Remarks Proposed a polynomial exact algorithm for SVBCP
Will Consider
Smaller running time
Less assumptions
more sophisticated assumption for network bandwidth
more practical VANET node mobility
unpredictability