Subject: Node Movement Models in Ad hoc

From: He Dajiang <[email-masked]>
Date: Thu, 15 Jul 1999 10:04:05 +0800

Those who are doing routing,

Would you please tell me what node movement models you use when you
implement your routing schemes in network simulator? It would be even
better if you refer me to some references.

Thanks

Dajiang

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From: George Aggelou <[email-masked]>
Date: Thu, 15 Jul 1999 11:11:29 +0100

Hi He,

Have a look at Miguel's home page, at
http://www.disca.upv.es/misan/mobmodel.htm, for a discriptive reference
on various mobility models...

On my simulatations I am using a moving pattern similar to a "realistic"
model where mobiles roam freely throughout the coverage area according
to the following moving algorithm:
At any point in time, mobile movement is characterized by two
parameters, its velocity (with value v and direction f ) and its current
position(x, y).  In this model, then new moving direction at time (t +
1) is computed based in the previous direction at time t plus a steering
angle, which is generated randomly by a normal distribution process with
some mean, a, and deviation L degrees.  That is, at each update interval
of the position of the node, a node changes its direction by -L to +L
degrees.

I have selected the realistic model, instead of the Brownian model  for
example, in order to ensure a degree of correlation between a series of
moving iterations.
In the Brownian model, the moving direction of a node at time (t + 1) is
generated randomly from a uniform distribution process ranging from 0 to
360 degrees, so it is independent of its previous direction at time t. 
Thus, in the Brownian model, there may be a possibility where the motion
style of a node follows an oscillatory-type trajectory, moving forward
and backward, leading to an impractical mobility model.

Hope that helps!

Regards,
George A.

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George Aggelou			     	
Centre for Communications Systems Research   
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University of Surrey  		     

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From: Miguel Sanchez <[email-masked]>
Date: Thu, 15 Jul 1999 13:41:42 +0200

Hi He,

Liang and Haas, developed a new mobility model intended to be both,
realistic and adjustable. They have developed the Random Gauss-Markov
mobility model based on the idea of having a "tuning" value so you can have
a variable time correlation (that Brownian model does not provide).

I've implemented it in an applet you can find in
http://www.ee.cornell.edu/~misan/RGM/  so you can view node motion in this
algorithm.

Source code is not in this site, but I can provide it if needed.

Best,

Miguel Sanchez
Universidad Politecnica de Valencia (Spain)

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From: Ken Carlberg <[email-masked]>
Date: Thu, 15 Jul 1999 10:45:51 -0400

hello,

> ....

i take it you mean impractical in terms of non-realistic.  just out of 
curiosity, i was wondering if you had considered hybrid approach that 
places a percentage of objects within the 'realistic' model, and another
percent within the brownian model?

the reason i say ask is that i believe there are moving objects 
that actually behave in an oscilatory manner.  one that comes to mind 
are municipal snowplows that have assigned geographic locations and 
which spend their time going back and forth clearing the same set of 
streets.  

also, my intuition is taxi's in most cities tend to display a 
go-back-home type of oscilatory behavior, given that they try 
and focus on returning to a prime area that produces good business.

thus, in comparison to all moving vehicles, the percentage of those
resembling a brownian model small, but it does exist.

-ken

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From: Miguel Sanchez <[email-masked]>
Date: Thu, 15 Jul 1999 18:19:03 +0200

Hmmm,

Every time we are closer to the idea of modelling mobility in the same way as
traffic models. (I've thought before in this way and I think it makes sense).

The full picture can be something like viewing non-mobile networks dependent
in the traffic dimension and ad-hoc networks as dependent of the two
dimensions of traffic and mobility (at least, this is the way I see it).

In the same way as with traffic models, we can introduce the concept of
mobility classes and consider that the full system is built by adding several
kind of nodes (likely with different mobility patterns and, depending on the
application level also with different traffic patterns).

This is what I understand that Ken is propossing, to build mobilty models
with a mixture of different patterns for different nodes that, on the other
hand and given the example he posted, makes a lot of sense.

Of course I agree that traffic and mobility models are not the only variables
in the game.

Regards,

Miguel Sanchez

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From: George Aggelou <[email-masked]>
Date: Fri, 16 Jul 1999 12:28:59 +0100

> percent within the brownian model?

I believe that an ad hoc network is considered to be a *homogeneous*
wireless network. That means group of mobile wireless terminals with
similar charactristics, regarding technical.  Therefore, I believe any
simulation scenarios should assume that all terminals present the same
behavioral characteristics.

I wouldn't give many credits on the hybrid approach! The reason for this
is because an ad hoc network is considered (at least in most simulation
studies performed from various  ) to be a *homogeneous* wireless network
that comprise mobile hosts that have the same computation, power,
memory, capacity and communication characteristics as well as mobiles
are moving about under similar mobility platforms.

Overall I believe the relative performance of every routing protocol
depends on the moving behavior of mobiles.  By having a hybrid approach
will be an additional burden to study the behavior of your ad hoc
routing protocol.

> resembling a brownian model small, but it does exist.

Of course! I agree with you that in reality there are situations where
mobile may move under various mobility patterns.. but hey! in reality
you may find ad hoc groups with mobiles that run different routing
protocols too!  This is a hybrid approach as well...  

Again, these are my thoughts and by no means what you should do and what
not...

Regards,
George A.

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From: George Aggelou <[email-masked]>
Date: Fri, 16 Jul 1999 13:17:40 +0100

Ooops! I am afraid my previous mail was uncomplete...

studies in the literature) to be a *homogeneous* wireless network

Again, these are my thoughts and I am not trying to push specific
scenarios for simulating mobility in mobile networks...

Regards,
George A.

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From: George Aggelou <[email-masked]>
Date: Fri, 16 Jul 1999 13:10:00 +0100

Regards,
George A.

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From: Ken Carlberg <[email-masked]>
Date: Fri, 16 Jul 1999 09:18:13 -0400

just a final comment...

> are moving about under similar mobility platforms.

I'm not sure I would use previous _simulation_ literature as a basis
for constraining examination parameters.  As for *homogeneous* wireless
networks, there does exist stove-piped military systems that exhibit
a variety of power/memory and mobility patterns:  picture off-shore
ships, pilotless drone planes, tanks, and soldiers, all connected to the
same adhoc network.  Question becomes, will one see a similar disparity
of systems in the commercial world.  I'm not smart enough to give a
definitive answer on this last one.....maybe planes, trains, and
automobiles.

> will be an additional burden to study the behavior of your ad hoc

But isn't this the fun, and to a degree the expectation, of research?
I mean if one can't point to a definitive model that exists in the real
world, then I'd like to find out all the potential weaknesses of a design. 
And note, a weakness isn't always bad, it just lets me know the extent 
to which I can deploy a design.

As for measuring the relative weakness of an ad-hoc routing protocol, 
I would add that the characteristics of the application (e.g., short
vs. long transaction) is just as important as the potential mobility 
characteristics.

cheers,

-ken

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From: Nikos Triantafillis <[email-masked]>
Date: Fri, 16 Jul 1999 19:17:26 +0100

>behavioral characteristics.

I would have to disagree with this "homogenuity" label that you put on ad-hoc
networks. I'm sure existing or future commercial & military ad-hoc networks
won't be restricted to nodes having similar characteristics. Although this
"homogenuity" assumption might be useful and will make life easier in the
early stages of measuring the performance of an ad-hoc routing protocol, I
believe that at later stages the protocol itself should be tested and
challenged in more complex scenarios which of course should include a
diversity of power sources, link capacity, transmission ranges etc.

>depends on the moving behavior of mobiles.  By having a hybrid approach

Personally I'm not very convinced about that. There are other variables apart
from node movement (such as battery power for instance) that can be measured,
in order to judge the performance of an ad-hoc routing protocol.

>protocols too!  This is a hybrid approach as well...  

The unique characteristics of ad-hoc networks and diversity of its nodes make
it difficult (but not impossible) that a single protocol will emerge on top of
all the others and that it will be used in every case/instance/possible
scenario of an ad-hoc network. This is exactly why protocols should be tested
on hybrid approaches and these scenarios shouldn't be dismissed. In that way
protocols will be streched to the limit and usefull results can be obtained as
to their suitability for a specific ad-hoc network.

- Nick

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