Re: Wireless Channel error model (fwd)

[Karunaharan Ratnam <karu@ece.neu.edu>]

Hi Karunaharan, below is the definition of create-error in ns-lan.tcl. At
the end of the procedure the error is 'inserted' in both downlink, uplink:

		$self install-error $src $dst $e1
                $self install-error $dst $src $e2
 
Unless you change this, the error will be for up/down link. You can of
course use only uplink or downlink if you want, but as you said this is
not a good model for wireless. The other choice in ns-lan.tcl is when you
do not include the source and destination pair, in this case the error
model is inserted in the "channel" of the lan, which means it will create
errors for any transmission on the lan no matter from which mobile is
comming from.

You can post this if you want...

LanLink instproc create-error { src dstlist emname rate unit {trans ""}} {
        if { $trans == "" } {
                set trans [list 0.5 0.5]
        }
 
        # default is exponential errmodel
        if { $emname == "uniform" } {
                set e1 [new ErrorModel/Uniform $rate $unit] 
                set e2 [new ErrorModel/Uniform $rate $unit] 
        } elseif { $emname == "2state" } {
                set e1 [new ErrorModel/MultiState/TwoStateMarkov $rate
$trans \
                                $unit]
                set e2 [new ErrorModel/MultiState/TwoStateMarkov $rate
$trans \
                                $unit]
        } else {
                set e1 [new ErrorModel/Expo $rate $unit]
                set e2 [new ErrorModel/Expo $rate $unit]
        }       
 
        foreach dst $dstlist {
                $self install-error $src $dst $e1
                $self install-error $dst $src $e2
        }
}



--Javier
-----------------------------------------
COMET Group
Columbia University, New York. 	
 
On Sun, 9 Aug 1998, Karunaharan Ratnam wrote:

> > 
> > 
> > i do not think this is correct, i believe the error model 'injects' errors
> > in the LAN base on packets, bytes or bytes, independent if it is downlink
> > or uplink, you should check the code for that.
> > 
> > --Javier
> > -----------------------------------------
> > COMET Group
> > Columbia University, New York. 	
> 
> 
> Javier:
> 
> I agree. But, the LAN is made up of point-to-multipoint links, and the
> ErrorModel is installed seperately for downlink and uplink (see ns-lan.tcl).
> Hence, the error injection is independant.
> 
> Karu.
> 
> PS: Is it okay if I post this reponse to ns mailing list?
> 
> >>On Sat, 8 Aug 1998, Karunaharan Ratnam wrote:
> > 
> > > Hi,
> > > 
> > > Question on error model (particularly for wireless channels).
> > > 
> > > Looking at the ns-lan.tcl, the ErrorModel is installed independantly
> > > for forward link and reverse link.
> > > In other words, when the ErrorModel uses Expo or TwoStateMarkov,
> > > forward link can be in 
> > > burst error state (fading) but the reverse link may not be experiencing
> > > any fading, and transmitting error free.
> > > 
> > > Is it a correct model for wireless channel.
> > > 
> > > The links cannot be totally independant because,
> > > * Fadding affects on both links are almost same (even if different
> > > bands were used they are in similar spectrum).  
> > > 
> > > The links may not be totally dependant because,
> > > * Radio at the hub (base station) may control power differently
> > >   to handle the fading than the customer radio.
> > > 
> > > I'd like to see response on this (especially from radio engineers).
> > > 
> > > Karu.
> > > 
> > 
> > 
> 
>