Title: Stable mobility models for MANETS
1Stable mobility models for MANETS
- Kim Blackmore
- Roy Timo (DE/NICTA)
- Leif Hanlen (NICTA)
2What is a MANET?
3Whats in a data network?
- What if its Mobile Ad Hoc?
"Application" protocols
Routing
"Transport" protocols
4MANET Routing
- For example, DSR dynamic source routing
- Each source maintains a cache of known paths (to
previous destinations) - Route discovery
- if you want a path to somewhere not in the cache
- Route maintenance
- if you try to use a cached path but it fails
- Reactive routing (or could try proactive)
5Simulations to test routing protocols
- Because there are so many layers of complexity
below the routing - Control the lower layers to isolate effect of
routing protocol - Synthetic mobility model to describe node
movement - Random Waypoint is most popular
6Random Waypoint Mobility Model
- Start point
- Uniform at random
- Waypoint 1
- Uniform at random
- Travel to waypoint 1
- At random speed
- Choose waypoint 2
- Repeat
7The problem with simulations
- Are the results meaningful?
- J. Yoon, M. Liu, and B. Nobel, Random Waypoint
Considered Harmful," in Proc. IEEE INFOCOM,
2003. - J. Yoon, M. Liu, and B. Nobel, Sound Mobility
Models," in Proc. IEEE MobiHoc, 2003. - William Navidi and Tracy Camp. Stationary
distributions for the random waypoint model. IEEE
Transactions on Mobile Computing, 3(1), 2004. - J. Boudec, M. Vojnovic, The Random Trip Model
Stability, Stationary Regime, and Perfect
Simulation," IEEE/ACM Trans. Networking, vol. 14
no. 6, Dec. 2006.
8If node speed is randomly selected from 0,M,
then time averaged node speed goes to zero.
9Will simulation time-averages converge?
-
- Yes
- We prove a strong law of large numbers for the
RWPMM - Previous attempts used the wrong definition of
stability
10Notation
V4 nodes 6 possible positions
11Estimating probability from simulations
- Generate a long sample path
- Count the number of times event A appears over N
time steps
12Estimating probability from simulations
- Estimate the probability is
- But how do we know
- Converges to ProbA?
- Converges at all?
13A mobility model is Stable if
- For each bounded function
the limit - exists (with probability one).
14A mobility model is Ergodic iff
- For each event A, the limit
- converges to the stationary mean probability of
A.
15Result - The RWMM is stable and ergodic
16Contributions
- Definitions of stable and ergodic MANET mobility
models - RWPMM is stable and ergodic
17Where to next?
- Stable routing protocols
- DSR is stable..
- THE END