Subject: Multihop packet radio

From: Leonard Miller <[email-masked]>
Date: Wed, 14 Nov 2001 15:17:47 -0500

In connection with the current discussion of the suitability of IEEE
802.11 for multihop ad hoc networks, we have mentioned the issue of the
carrier detection range being larger than the communications range (also
called transmission range).  I just relocated a paper on the subject
that is worth reading:

Jens Zander and Peter de Laval, "Carrier Detection Range Control in
Multihop Packet Radio Networks," Proc. EUROCON '88, pp. 346-349.

The authors show that packet radio performance, in term of expected
forward progress, is enhanced by having carrier detection at a greater
distance than the transmission range, by about a factor 1 + a, where a
is a capture ratio: a transmission is successful if no other
transmission is received at the destination from a transmitter within
the factor a times the communication range of the receiver.

Related to this subject, I don't recall finding a value for a capture
ratio, if any, for IEEE 802.11 products or in the specifications.  Does
anyone know a good value for capture ratio?

-- Len Miller

._.. . _.   __ .. ._.. ._.. . ._.   ._ _   _. .. ... _

Leonard E. Miller, Wireless Commun. Technologies Group
    National Institute of Standards & Technology (NIST)
    100 Bureau Drive Stop 8920, Bldg. 820, Room 445
    Gaithersburg, Maryland 20899-8920
Phone: 301-975-8018        Fax: 301-590-0932
email: [email-masked], [email-masked]
http://w3.antd.nist.gov/wctg/
._ _. ._ ._.. _.__ ... .. ...   ._ _. _..  ... .. __ .._
.._. ._ _ .. ___ _. ___...   .__ .. ._. . ._.. . ... ...

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From: Phillip Neumiller <[email-masked]>
Date: Wed, 14 Nov 2001 17:57:56 -0500

The capture ratio is going to be a random variable, i.e. for 
mobile platform traveling at 100 Kph, its going to be different
than for a stationary terminal just due to channel coherence
time issues related to fading.  You have to specify your platform
velocity and fading environment.

--
Mesh Networks, Inc. (www.meshnetworks.com)
Phillip D. Neumiller, Staff Scientist
[email-masked] PH: 1-407-659-5387

> -----Original Message-----
> From: Leonard Miller [mailto:[email-masked]]
> Sent: Wednesday, November 14, 2001 3:18 PM
> To: MANET Discussion
> Subject: Multihop packet radio
> 
> 
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