Subject: RE: [manet] Interference in ad hoc network

From: Martin Haenggi <[email-masked]>
Date: Thu, 8 Aug 2002 16:37:08 -0500 (EST)

Bert:

>Martin, I agree that there's a difference between noise and interference. And 
that in a Rayleigh propagation channel, interference is usually the biggest 
problem. But this Rayleigh channel you mention is typically a problem in short 
range situations, where the echo paths equal the strength of the direct signal 
path.

>At longer range between hosts, two things happen. First, echo energy is reduced 
compared with the main signal path, because those longer-traveled echoes paths 
will dissipate more quickly than the direct signal path. And second, the main 
signal at the frequencies we're talking about here (at or above UHF frequencies) 
will soon start going off into space. So signal or carrier energy of the 
interfering and the wanted transmitters are reduced dramatically, and noise 
becomes the only concern when dealing with C/(N+I) reception thesholds. The 
propagation path goes to Ricean (echo energy less than direct path) and then 
Gaussian (direct signal and white noise only) as range between hosts increases.

You assume that there is a direct path, which may not be the case.

> At these longer ranges, C/(N+I) --> C/N rather than C/I.

I don't quite see why the interference should become smaller over
longer distances. Interferers may be close to the intended receiver,
irrespective of the transmission range.

>About saving battery life, I have not seen a good answer to this. Reducing 
transmitter output theoretically increases battery life, right? Not necessarily. 
If everyone reduces transmitter power to the lowest possible, the MANET routing 
protocol will involve many more hops. So more MANET hosts are going to be 
providing relay services for other communications than their own, and their 
battery will deplete unexpectedly. Just another one of those "it depends" MANET 
things.

Sure. Also, amplifier nonlinearities have to be considered. A reduction
of the transmit power does not lead to a proportional reduction of the
energy consumption.

>As to increasing the MANET aggregate throughput, seems to me that reducing the 
transmitter power should certainly increase aggregate throughout on average, as 
we already discussed.

If you consider the total amount of packets transmitted over the lifetime
of the battery, I agree. If energy consumption (or lifetime) is not an issue,
I don't. Then boosting power will increase the throughput.
To be more precise, maybe we should rather speak of transport capacity
of the network (bit-meters per second). This quantity certainly increases
with increased transmit power.

Martin

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From: Miguel Sanchez <[email-masked]>
Date: Fri, 09 Aug 2002 00:09:58 +0200

Hi Martin
I think I agree most of the time with your comments but, could you 
please elaborate a bit more on your last point (transport capacity bps/m 
increases with transmit power)? I do not understand why is this.

Thanks,

Miguel Sanchez
Universidad Politécnica de Valencia, Spain
 .
Martin Haenggi wrote:

>......

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From: Miguel Sanchez <[email-masked]>
Date: Fri, 09 Aug 2002 00:09:58 +0200

Hi Martin

Thanks,

Miguel Sanchez