Subject: [manet] one question regarding RSSI and distance estimation

From: Chris Yao <[email-masked]>
Date: Sun, 30 Oct 2005 13:23:38 -0800 (PST)

hi,
 
in wireless networks, based on the received Received Signal Strength Indicator (RSSI), a node can estimate its distance to the beacon node.
 
could someone point out some related articles about how to estimate the distance? what popular theory/emperical RF models have been used?
 
Best Regards,
 
Chris

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From: Joe Carey <[email-masked]>
Date: Mon, 31 Oct 2005 08:43:31 -0700

Chris Yao wrote:

> hi,
>  
> in wireless networks, based on the received Received Signal Strength 
> Indicator (RSSI), a node can estimate its distance to the beacon node.
>  
> could someone point out some related articles about how to estimate 
> the distance? what popular theory/emperical RF models have been used?

Like so many things, this is an easy question to ask and a difficult one 
to answer.  In fact, you can't measure distance directly, but you can 
measure path loss and estimate distance based on that.  The problem is 
that in practice there is typically a wide statistical variance on path 
loss vs. distance.

I would recommend Ted Rappaport's book "Wireless Communications" for a 
review of the effects typically encountered in the wireless environment 
and some models that address them.

We begin by assuming you know the transmit power.  Perhaps this is 
obvious, but if you don't know this then it is impossible to estimate 
the distance based on receive power.  You must also know the gain of 
both the transmit and receive antennas.

The most obvious model is the free space transmission model.  It is only 
accurate in free space (i.e. outer space), you can find it by searching 
on "Friis Transmission formula".  Beyond that, modeling indoors and 
outdoors tends to be very different.

In typical terrestrial propagation environments the Friis formula 
doesn't apply because of absorbtion, reflections, etc..  Cellular 
networks typically use the "Hata-Okumura Model," in planning, which is 
an empirical model.  

NIST in Boulder has done extensive research on modeling the indoor 
propagation environment.  Here's a  link to a bibliography they've put 
online.
http://w3.antd.nist.gov/wctg/manet/wirelesspropagation_bibliog.html

good luck!
joe

>  
> Best Regards,
>  
> Chris
>
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