Fade margin estimation for spread spectrum systems - RF Cafe Forums
Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would
be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate
that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views.
It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if
you would like to post something on RF Cafe's
page, please do.
Below are all of the forum threads, including all
the responses to the original posts.
Post subject: Fade margin estimation for spread spectrum systems
Posted: Tue Mar 15, 2005 11:28 pm
Joined: Sun Aug 03, 2003
Location: Erie, PA
Note: I moved this from
the Employment forum to here - Kirt B.
I am an RF Engineer, developing Spread Spectrum
Radios to be used in Point to multipoint fixed telecommunication
Fading estimation of Signals (unspreaded)
in LOS link :
Propagation channel characteristics
of our system is very much similar to that of Line-of-sight
(LOS) Digital microwave link used in telecommunication
systems, where the fading is mainly due to multipath
caused by the gradients of atmospheric index of
refraction and ground reflections. The Barnett-vignant
reliability equation (equation –1) below holds good
for estimating fade margins of LOS link where the
signal is not spread.
FM = 30 log d +10
log ( 6ABf ) - 10 log ( 1-R ) – 70 -----------------------
( 1 )
FM= Fade margin in dB
d = Path
length in Km
f = Carrier frequency in GHz
A = Rough ness factor
B = Climate factor
R = Reliability
Cannot use Barnett-Vignant
reliability equation for spread spectrum system
Since the signals in our system is spreaded
the above equation cannot be used to estimate the
fade margins. It is well known that Spread spectrum
systems are resistant to multipath fading , but
I do not have definite figure by which I can relax
from the figures I get using the equation-1. For
eg: for one of our links, fade margin when estimated
using equation-1, gives a figure of 13 dB , as our
system is spread spectrum system 13 dB fade margin
is not required but I am not sure by how much I
can come down on this figure.
for simple equation /empirical formula:
I am looking for any simple equation or empirical
formula to estimate fade margins for spread spectrum
system , similar to the equation-1 . Coming down
on the fade margin figures will bring down the cost
of our systems but I want to be sure by how much
I can relax on the fade margins, so that the performance
of the link is not affected .
Posted: Tue Mar 22, 2005 3:01 pm
More than 10,000 searchable pages indexed.
Your RF Cafe
single-handedly redefining what an engineering website should be.
Progenitor & Webmaster
(Seize the Day!)
My USAF radar shop