Alfred.Reynolds at dsto.defence.gov.au
Thu Dec 6 14:25:52 EST 2001
After talking to more knowledgeable people around me and reading this email
I think the answer is maybe ;)
The DSSS gives you a system gain for a transmitter on the same freq (of
about 10 dB I believe). So, if your AP's are distant from each other (put
the two overlapping AP's as far apart as possible) then hopefully the gain
will allow you to operate at higher speeds. Use of directional antenna is
also useful :) Or reducing the power output of a AP (if possible).
I believe there may also be an issue with the chipping codes not being
orthogonal to each other causing problems with the system gain, I don't know
details however :(
> -----Original Message-----
> From: Tony Langdon [mailto:tlangdon at atctraining.com.au]
> Sent: Thursday, December 06, 2001 2:22 PM
> To: 'Reynolds, Alfred'; wireless at samba.org
> Subject: RE: Channel usage
> > Okay, I am going to take a long walk down a short jetty here,
> > but doesn't
> > the use of DSSS within the wireless lan cards mean that this
> > isn't a major
> > issue. The other base stations will raise the noise floor of
> > the receiver
> > but given the low powers and high rate chipping rates I
> > suspect that the
> > effects would be minimal.
> To some extent, this is true. However, there is a point
> where the extra
> noise floor caused by the interfering station exceeds that of
> the desired
> signal (i.e. the capture ratio may be -x dB, but it's not -infinite).
> > I would guess that when the IEEE designed the channels for
> > 802.11 they did
> > the calculations to make sure that a 1 channel separation
> > provided enough
> > attenuation on the base receiving frequency to remove any
> > problems.
> I dunno if they expected multiple APs to be co located. IOW,
> the frequency
> separation may be OK for multiple networks sharing the same
> physical space,
> but not if two transmitters are co-located.
> On the positive side, it's likely you'll be OK, because you
> will be running
> gain antennas and you won't have APs in each others beam (the
> power off the
> side or back should be less than the normal omni case).
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