Subject: [manet] Cost Function - PARO

From: "vikas p verma" <[email-masked]>
Date: 1 Mar 2002 13:10:20 -0000

Hi,

I just wanted to know if Power Aware Routing Optimization 
Algorithm 'balances the power at each node' or 'minimizes the 
overall power of the Ad hoc n/w'.
As per the internet draft the cost function is just the minimum 
transmission power Tmin. This indicates that it will 'minimize 
over all power of the n/w'. On the other hand one of the paper on 
PARO states that the cost function is Tmin*f(B) where B - power 
resourse of a node and f(B) is inversly proportional to B. This
would implicate that PARO is trying to 'balance the power at 
individual node'. Can somebody please explain what is the actual 
cost function.

Thanks
Vikas.

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From: Javier Gomez-Castellanos <[email-masked]>
Date: Fri, 1 Mar 2002 13:40:24 -0500 (EST)

hello Vikas,

hope i can answer your questions below.

The cost function in the PARO internet draft considers reducing transmission 
power only as the cost function. We did so because not only minimizing 
transmission power increases the lifetime of nodes, but also because 
the definition of such a cost function is unambiguous to understand.

We are aware that such a cost function is likely to consume the power 
reserves of nodes in different proportions. One way to avoid this problem, 
as you mentioned, is to take into account the power reserves in each node 
in order to "balance the power" in the network. This statement is, is 
general true. However the definition of such a cost function is more 
difficult to define formally, and therefore more difficult to understand. 
For this reason we did not include such a cost function in the internet 
draft.

Balancing power in the network is a tricky issue. Basically when you 
try to balance the power in the network, you consume the power resources 
of nodes in the present in some way that you "guess" it will increase the 
overall lifetime of the nodes in the future. Unfortunately unless you can 
predict the future you are not totally sure you are doing the "right" 
thing in the present. Nodes may change locations over time, traffic 
patters may change, etc. Similarly, do we want to maximize the time until 
the first node run out of power?, or the the first 5% of the nodes run 
out of power?. There are some papers that discuss this trade off between 
minimizing transmission power and balancing power that provide very useful 
and interesting insights about this.

cheers.  

--
--Javier
-----------------------------------------
COMET Group
Columbia University, New York.
http://www.comet.columbia.edu/~javierg

-- 
--Javier
-----------------------------------------
COMET Group
Columbia University, New York. 	
http://www.comet.columbia.edu/~javierg

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From: Javier Gomez-Castellanos <[email-masked]>
Date: Fri, 1 Mar 2002 13:40:24 -0500 (EST)

hello Vikas,

cheers.