guest Post subject: Fade margin estimation for spread spectrum
systems Unread postPosted: Tue Mar 15, 2005 10:46 pm
I am an RF Engineer, developing Spread Spectrum Radios to be used
in Point to multipoint fixed telecommunication systems .
Fading estimation of Signals (unspreaded) in LOS link : Propagation
channel characteristics of our system is very much similar to that
of Lineofsight (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 Barnettvignant 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 ( 1R
) – 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 BarnettVignant 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 equation1. For eg: for one of our links, fade margin
when estimated using equation1, 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.
Lookig forward for simple equation /empirical formula: Hence,
I am looking for any simple equation or empirical formula to estimate
fade margins for spread spectrum system , similar to the equation1
. 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
11/12/2012
