Subject: RE: [manet] Hiden- & exposed terminal problem in MANET

From: "Mullen, John P. (Contractor)" <[email-masked]>
Date: Mon, 23 Sep 2002 08:21:20 -0600

Hi Vikram,

The problem with GPS is that you also need to know the intervening terrain
and any local anomalies that would interfere with or modify a LOS path.
This can me a very tricky problem in an urban setting.  The smart receiving
antenna looks promising, though, since it sidesteps these problems.  The
trouble is, how does the one initiating the transmission decide which way to
point the antenna?  

If the platform is in motion, you would need some sort of correction element
to maintain the orientation.  If a car makes a left turn, something has to
know that and shift the antenna orientation 90 degrees to compensate.  Back
in the city, however, this may not be enough.  One may be communicating over
a reflected path, due to no LOS path being available, and as you move, the
manner in which the communication can be effected could be a very complex
problem.  Life becomes even more complicated if motion can be in 3D space,
such as in an airplane or with a PDA.  

John Mullen

-----Original Message-----
From: Vikram Dham [mailto:[email-masked]]
Sent: Monday, September 23, 2002 8:03 AM
To: Mullen, John P. (Contractor); Phillip Neumiller
Cc: manet
Subject: RE: [manet] Hiden- & exposed terminal problem in MANET

Hello John & Phil,

  We have been looking into use of Smart Antennas in MANET and have had to 
modify mac as well as routing protocols to accomodate smart antennas into 
network effectively.

  Using Smart Antennas doesn't necessarily mitigate interference unless use
is 
made of power control mechanisms besides the assumption of knowdelge of 
location of destination nodes in network.

 As pointed by John there is possibility of establishing "extended links " 
"multihop term -- used by John" by orienting receive and transmit antennas
of 
communicating nodes towards each other. This would involve use of signaling 
mechanism based on top of routing layer to send orienation commands. The 
question left answered is information about location of nodes ? One safe way

out might be to just assume the use of GPS by all nodes, ( I wonder how cost

effective it would be ? ) Another option which might be worth exploring is 
extending approaches such as CRICKET ( developed at LCS MIT ) to scenarios 
which invovle use of smart antennas. Smart Antennas provide edge over omni 
directional antennas as they can provide information regarding angle of 
arrival of arriving signal. Using received signal power and angle of arrival

it might be possible to establish relative location of nodes in network 
atleast in line of sight environments.

 Besides the possibility of establishing extended links the problem of
routing 
becomes even more murkier because of the availablity of multiple interfaces
on 
node using smart antennas.

 We have been running simulation for MANETS with Smart Antennas and the 
performance gain acheived with respect to omni directional nodes is
drastic.It 
might be sometime before smart antennas reach commerical setups but their 
incorporation would definately be a challenge for present mac and routing 
protocols. I even wonder if the time being spent in developing routing 
protocols assuming omni directional antennas is worth the effort :)

Best Regards

Vikram Dham
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---

From: Rex Buddenberg <[email-masked]>
Date: Mon, 23 Sep 2002 10:10:58 -0700

Looks like you're getting to the same reasoning that almost everybody else 
gets to when thinking through a revised MAC.  You need two queue's in the 
MAC, one for contention and one for traffic.  In this case, looking at the 
MAC from the physical layer, contention =~ omni -- see who's out there to 
link with (and where they are).  Once you have that data, you can inform the 
second queue and set up some kind of planned access (which way to point the 
directional antenna beam when).  

On Monday 23 September 2002 07:21 am, Mullen, John P. (Contractor) wrote:
> trouble is, how does the one initiating the transmission decide which way
> to point the antenna?
>
> If the platform is in motion, you would need some sort of correction
> element to maintain the orientation.  If a car makes a left turn, something
> has to know that and shift the antenna orientation 90 degrees to
> compensate.  Back in the city, however, this may not be enough.  One may be
> communicating over a reflected path, due to no LOS path being available,
> and as you move, the manner in which the communication can be effected
> could be a very complex problem.  Life becomes even more complicated if
> motion can be in 3D space, such as in an airplane or with a PDA.
>
> John Mullen
>

-- 
b

---

From: Rex Buddenberg <[email-masked]>
Date: Mon, 23 Sep 2002 10:10:58 -0700