Subject: RE: [manet] Interference range

From: "Mullen, John P. (Contractor)" <[email-masked]>
Date: Fri, 12 Jul 2002 13:15:14 -0600

Hi Jim,

You got me thinking on this a bit more.

One problem that MANETs face is that there is no assurance that there will
be sufficient nodes in an area to provide end-to-end connectivity.  At the
other extreme, if node density is too high, many nodes end up receiving
packets that do not concern them and they often need to wait for the channel
to become idle because someone else is using it.

A MANET radio that has the ability to adjust its output power essentially
has the ability to modify the local topology of the MANET.  If there are
many nodes, it can use a low power mode, which reduces the number of nodes
it will interfere with as well as the number it can directly link to.  In a
topological sense, it has changed the local metric to make these nodes
appear to be further away.

On the other hand, a radio normally using low power may find itself in a
situation in which no other nodes can receive it.  By increasing power, the
node is more likely to be able to connect to a "near by" node.  Again, it
has changed the local metric so that the distant nodes appear to be nearer.
There will be an increase in interference, but only so much as necessary to
assure connectivity.

Of course, this is not all free.  For example, if an isolated node uses
higher power to reach a member of a distant cluster, that member will also
have to use high power to reply, causing a higher level of interference
among the nodes nearby.  However, on the average ...

What this means is that transmitter power can "tweak" to local conditions
somewhat to reduce the variability in link capacity and connectivity.  This
could probably be handled at Layer 2 and below without the higher levels
being aware of what is going on.  However, in order to fully exploit the
advantages of such an approach, there needs to be some interaction with the
MANET protocol.

What it also means is that some current systems that are stub nets might
perform better if they used variable power output together with MANET
technology.

John Mullen

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]
Sent: Friday, July 12, 2002 12:35 PM
To: [email-masked]
Subject: [manet] Interference range

2 more comments:

1.  Kaixin Xu wrote that he has found "that interference range is usually
1.7 times the transmitter-receiver distance."  From working with a variety
of different signals-in-space (modulation waveform types), this is about
the average of what we have seen as well, although the actual ratios have
ranged from less than 1 to greater than 3 times the transmitter-receiver
distances in actual fielded networks depending upon the type of
signals-in-space used.

2.  Martin Haenggi wrote that "if all nodes use the same power level, then
the effect of the interference is completely independent of that power
level, since the signal-to-interference ratio remains constant.  So, a
(global) reduction of the power level does not help alleviate the
interference problem."  Yes, but why should all nodes use the same power
level instead of adaptively using different power levels depending upon
which neighbor node (or set of neighbor nodes) they are trying to talk to.
Also, by reducing transmit power across the network, frequency reuse goes
up, which increases total network throughput.

Jim Stevens
JTRS Network Engineering Gruop
Rockwell Collins
[email-masked]

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---

From: Chip Elliott <[email-masked]>
Date: Fri, 12 Jul 2002 15:30:20 -0400

Ram Ramanathan led some nice DARPA work in this area a few
years ago. For overview, architecture, & details, check out:

http://www.ir.bbn.com/projects/dawn/dawn-index.html

Cheers,

-- Chip

---

From: Chip Elliott <[email-masked]>
Date: Fri, 12 Jul 2002 15:30:20 -0400

Cheers,

-- Chip