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

From: "Mullen, John P. (Contractor)" <[email-masked]>
Date: Wed, 10 Jul 2002 07:53:57 -0600

Hi Bert,

Good points.  However, just a couple of wrinkles.

There is certainly no reason you cannot have multiple MANETs in the same
geographical region, but some mechanism is needed to assure channels are
allocated in a way that will avoid interference.  Cellular systems use a
supercel of seven channels which is repeated as needed to cover the area.
The result is much like a honeycomb.  The reused channels are separated by
two cell diameters so interference is unlikely.  Cellular antennas do not
move, so, once established, this pattern reliably prevents interference.
However, the hosts in MANETs do move, so there is the additional problem of
making sure clusters using the same channel stay far enough apart from each
other.  The alternative is to give each of the MANETs its own channel, but
we need to remember there is only so much BW available.

If the different MANETs have occasional need to communicate with each other,
some hosts will have to be gateways.  These will either need two
transceivers each or have to drop out of one MANET to communicate with the
other.  The first solution would be the best to avoid the need to rejoin
after every gateway operation.  Then, there is the problem of which hosts
are to be gateways.  If you cannot be sure that the right host will be in
the right place, you may need to have two transceivers in every host.  There
is also the problem that if each MANET has its own channel, the gateways
will have to determine which other MANETs are in the area and which one(s)
to join.  (Of course, if a gateway joins k other MANETS, it will need k
additional transceivers).  A way around this is to have a single channel
solely for communication between MANETs.  Then, each gateway only needs to
monitor two channels.  Of course, there can be contention on the inter-MANET
channel and, using the additional channel reduces BW available for the
individual MANETs.

Looking more deeply into the matter of available bandwidth, if the band is
sliced up among different users, then each user will have less bandwidth
available.  The most efficient use of a shared resource is usually a pooled
approach so that whoever needs higher capacity can get it, without
limitations caused by subdividing the band.  Of course, there could be
security reasons or technical limitations for subdividing.  For example, one
MANET could be for police, one for fire fighters, one for EMT, etc.
However, a fixed allocation will limit the BW available for each.  A shared
channel allows each to use what they need (up to channel limits).  

Perhaps, a solution could be a dynamic allocation, in which each MANET has a
minimal assignment, but there is a pool of BW which any MANET can use,
providing there is a need.

Sincerely,

John Mullen

-----Original Message-----
From: Manfredi, Albert E [mailto:[email-masked]]
Sent: Tuesday, July 09, 2002 4:02 PM
To: [email-masked]'; [email-masked]
Subject: RE: [manet] Interference in ad hoc network

Within a single MANET, the nodes need to contend for channel access, and
perhaps even reduce their transmitter power level (this was discussed
recently) so as not to interfere with each other. The basic scheme used in
IEEE 802.11 is similar to Ethernet CSMA. Since MANET depends on each node
acting as a relay station potentially, all nodes must be capable of hearing
one another, if within range. This is essential. You do not rely on base
stations for coverage, with MANET.

But there's no reason why multiple MANETs can't be created in a given
geographical area, is there? If you use IEEE 802.11b for the RF solution,
for example, you could assign a different DSSS code to different MANETs, so
the nodes of different MANETs will not interfere with one another. This is
analogous to your Bluetooth example, where different frequency hop sequences
are used.

Or you could use a simple frequency divided radio scheme for this too. Just
assign a different RF frequency band to each MANET in the area, and let
these nodes broadcast to all nodes within reach, within their own MANET.

If the packets are explicitly routed, this should work fine.

If there are clusters of nodes in a given MANET that are very far apart, you
could have cases where intra-cluster traffic of these far-apart clusters
occurs simultaneously, without causing interference. That would happen
naturally, as the clusters move away from one another, and don't need to
worry about hearing other traffic from the remote cluster any longer.

Bert

-----Original Message-----
From: Jack Wang [mailto:[email-masked]]
Sent: Tuesday, July 09, 2002 5:28 PM
To: [email-masked]
Subject: [manet] Interference in ad hoc network
Importance: High

How to prevent interference in ad hoc network? If there are several node
within a node's transmission range, they may interfere with each other. In
traditional cellular network, this is done by channel allocation. And in
bluetooth, frequency hopping is used and master node of a piconet decides
the frequency.
How about ad hoc network? Are there any published papers about it? Thanks.
Regards,
Jack

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From: Nikhil Jain <[email-masked]>
Date: Thu, 11 Jul 2002 07:57:35 -0700

I would recommend that we think about using CDMA. In CDMA we use a reuse of 
1. Which means that the same channel is used in all the cells. Ofcourse the 
moving users present new issues that have to be solved.

--
Nikhil Jain
Office Location L-503E
Phone (858) 658-4501
Fax (858) 658-1033
email: [email-masked]
email: [email-masked]

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From: Nikhil Jain <[email-masked]>
Date: Thu, 11 Jul 2002 07:57:35 -0700

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From: "Phil Neumiller" <[email-masked]>
Date: Thu, 11 Jul 2002 12:09:04 -0400

MeshNetworks uses CDMA, but not the Qualcomm type.  Rather, a version that
is suitable for ad hoc networks.  The Qualcomm type (3G type) has asymetric
channel structure, i.e. the reverse and forward links are structured differently at
the phy and link layers.  This poses problems for a peer-to-peer network like a
MANET.  There is also a lot of intelligence in the IS-94A/B/C (3G) BTS that
you would not want to replicate in an inexpensive ad hoc radio.  Our MAC
is called QDMA.  It supports aspects of CDMA, TDMA, FDMA, and CSMA
all simultaneously.

----- Original Message -----
From: "Nikhil Jain" <[email-masked]>
To: "Mullen, John P. (Contractor)" <[email-masked]>; "Manfredi, Albert E" <[email-masked]>;
<[email-masked]>
Sent: Thursday, July 11, 2002 10:57 AM
Subject: RE: [manet] Interference in ad hoc network

---

From: "Phil Neumiller" <[email-masked]>
Date: Thu, 11 Jul 2002 12:09:04 -0400

----- Original Message -----
From: "Nikhil Jain" <[email-masked]>
To: "Mullen, John P. (Contractor)" <[email-masked]>; "Manfredi, Albert E" <[email-masked]>;
<[email-masked]>