1

Inter-Contact Time Study for MANETs

with Random Walk Mobility

Juntao Gao1, Xiaohong Jiang2

1Nara Institute of Science and Technology

2Future University Hakodate

July 10, 2014

2

Tokyo Ring Roads

3

Tokyo Ring RoadsVehicles rely on mobility and physical contacts to communicate (e.g. spreading safety messages)

4

Inter-Contact Time (ICT)1. Inter-contact time (ICT): time interval between two consecutive contacts of a pair of vehicles.

2. ICT significantly affects throughput and packet delay, and thus serves as a fundamental metric to be studied.

ICT1

ICT2

5

2. No accurate analytical results on inter-contact times in MANETs.

Limitations of available works on ICT

1. Only empirical results (via simulation and real trace) and analytical estimation results (without error analysis).

This hinders the performance evaluation and protocol design in MANETs!

Inter-Contact Times (ICT)

6

Outline

•System assumptions (random walk mobility, preliminary definitions)

•Inter-contact time modeling

•Inter-contact time evaluation

Random Walk MobilityTime is slotted and road is discretized into n sites.p: counterclockwise move probability

q: clockwise move probability r: r=1-p-q

7

8

Definitions

Node contact: If d(t) = 0, we say X1 and X2 contact each other at time slot t.

Distance d(t): the number of sites vehicle X1 has to travel clock wise to reach another vehicle X2 at time slot t.

Inter-contact time:is the time slots between two consecutive

contacts of X1 and X2

9

Outline

•System assumptions (random walk mobility, preliminary definitions)

•Inter-contact time modeling

•Inter-contact time evaluation

10

ICT Modeling

Step 1: Analyze the distribution of the initial distance between the two vehicles just after they lose contact

Step 2: Model how the distance between them evolves with time slots until they contact again

11

Initial distance could only be 1, 2, n-2 and n-1.

Step 1: distribution of the initial distance

Probability of initial distance being 1.

ICT Modeling

12

Step 2: distance evolvement

ICT Modeling

13

Step 2: distance evolvement

ICT Modeling

14

Step 2: distance evolvement

ICT Modeling

15

Step 2: distance evolvement

ICT Modeling

16

Step 2: distance evolvement

ICT Modeling

17

ICT AnalysisTransition matrix

18

ICT AnalysisTransition matrix

19

ICT AnalysisAccurate analytical results on inter-contact times

20

Outline

•System assumptions (random walk mobility, preliminary definitions)

•Inter-contact time modeling

•Inter-contact time evaluation

21

ICT EvaluationMean value vs. mobility parameters

22

ICT EvaluationMean value vs. number of network sites n

23

We proposed theoretical models to derive accurate analytical results on inter-contact times.

Conclusion