Subject: RE: [manet] tx power adjustment

From: "Mullen, John P. (Contractor)" <[email-masked]>
Date: Tue, 2 Jul 2002 07:10:01 -0600

Hi Miguel,

I follow your argument, but come to a different conclusion.

If we assume that only nodes on the path from sender to receiver "whisper,"
then a repeated whisper will affect only nodes in the vicinity of the
end-to-end path, whereas a loud shout will affect every node within the
radius of the distance from the originator to the destination.  

For example, if the MANET consists of 100 nodes arranged in a 10 by 10 array
with each at the limit of "whisper" range, a whisper path from the middle to
the right edge will affect, maybe 10 or so nodes, but a shout from the
center to one edge would involve about 80 nodes (pi r^2).

Also, reception power, though significant, is usually a couple of orders of
magnitude or more, less than transmission power and may actually be less
than idle power.  (A receiver searching for a signal may have its gain
cranked much higher than one actually locked on a signal).

I agree that circumstances could affect the analysis, which is why some sort
of adaptive control will probably be the answer. 

John Mullen

-----Original Message-----
From: Miguel Sanchez [mailto:[email-masked]]
Sent: Monday, July 01, 2002 4:21 PM
To: [email-masked]
Cc: [email-masked]
Subject: Re: [manet] tx power adjustment

Hi Dave,

You wrote:

>...  a choice between shouting at a
>far away neighbor, or whispering to a nearer neighbor who will whisper
>to the far away neighbor. A strategy for choosing between one "loud"
>hop and several quiet ones could be quite complex, it seems. Suppose
>you tried to estimate and minimize the product of a packet's on-air time
>and the area silenced by its (re)transmission?
>
>Dave
>  
>
As a rule of thumb if you look at the tx power only, it is more energy 
efficient to whisper the packet twice than to transmit it loud once (due 
to the power law on the atenuation). However if you  take into account 
that receiving is not coming for free either, and if you assume that all 
neighbor nodes will receive a packet before they can check if it is 
addressed  to them or not (and therefore they will draw reception 
energy) then whispering twice could be a worse choice than one loud 
transmission. Of course this analysis may be interesting when you are 
worried about network survivability (i.e. low power sensor networks).

What it is more, the numbers of this observation will change a lot 
depending on the nodal density about these three involved nodes (i.e. 
sender, reciver and forwarder).

I just wanted to add this thought to the discussion.

Miguel Sanchez
Universidad Politecnica de Valencia, Spain

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---

From: Miguel Sanchez <[email-masked]>
Date: Tue, 02 Jul 2002 16:18:40 +0200

Hi John,

See my comments below ...

>I follow your argument, but come to a different conclusion.
That's the point of discussing things :-)

>radius of the distance from the originator to the destination.  
Hmm, I agree. But if you whisper twice some nodes will receive this 
packet twice too.  Depending on where  nodes are located this can be a 
large or small number of nodes ...

>center to one edge would involve about 80 nodes (pi r^2).
I agree.

>cranked much higher than one actually locked on a signal).
As other folks on the list, my thinking is tightly coupled to 802.11 
standards. Most of the available products require while receiving around 
70% of the energy used when transmitting (so transmit and receive energy 
consumption is, for this particular technology  now, withing the same 
magnitude order). Other technologies (or even the new generations of 
CMOS 802.11 chipsets could change this dramatically ...)

>of adaptive control will probably be the answer. 
Several authors (and I think Broadcom too) have proposed different 
adaptive schemes to do so. Cell phones , although not an ad-hoc network, 
have been routinely using transmission power control to achieve higher 
cell usage and/or to improve link quality.

Please note that I am not claiming that "whispering" twice is 
necessaryly better than one loud transmission, but I wanted to show that 
packet reception energy cost can be significant  and can favor one or 
the other choice, again strongly tied to the network topology and traffic.

Best regards,

Miguel Sanchez

---

From: Miguel Sanchez <[email-masked]>
Date: Tue, 02 Jul 2002 16:18:40 +0200

Hi John,

I agree.

Best regards,

Miguel Sanchez