#10397 NORM Not Tri: XOs may fail to communicate in noisy 802.11 environment

Zarro Boogs per Child bugtracker at laptop.org
Fri Oct 15 00:38:39 EDT 2010

#10397: XOs may fail to communicate in noisy 802.11 environment
           Reporter:  greenfeld  |       Owner:  wad          
               Type:  defect     |      Status:  new          
           Priority:  normal     |   Milestone:  Not Triaged  
          Component:  hardware   |     Version:  not specified
         Resolution:             |    Keywords:               
        Next_action:  never set  |    Verified:  0            
Deployment_affected:             |   Blockedby:               
           Blocking:             |  
Changes (by greenfeld):

 * cc: martin.langhoff (added)


 I actually have a bit of an EMI/EMC/ESD testing background as well as
 Amateur Radio, so I am reasonably aware of RF effects.  I already was a
 bit suspicious given the noise floor reported by one of the XO Wifi card
 types was always ~-96 dBm or higher, as I have worked with receivers
 designed to receive signals at -100 dBm or even -120 to -140 dBm
 {typically test equipment}.

 But it has been about 10 years since I last studied digital RF theory or
 did any significant EMI/EMC work.  The rough analog equivalent would be
 trying to listen to a strong signal on an SSB HF receiver in the middle of
 a contest/pileup with no squelch, wouldn't it?

 Unfortunately there is not much one can do about moving the Miami OLPC
 office from the 11th story of a building or out of near-downtown, even if
 other buildings tower around it.  The office used already is in the
 interior even if the entire office suite is not.

 I doubt we can afford to purchase significant amounts of RF absorbing foam
 nor the extra space such cones tend to require.  Access to a fully RF
 shielded room requires locating one in the area and for the signal level
 802.11 equipment puts out likely is overkill.  I would have to see if RF
 shielding paint is available/permissible, if that helps at all.
 Deployments tend not to be shielded rooms (but are any as urban/modern as
 we are)?

 Another idea I had is hiding the access point off in a corner somewhere
 since the worse case for MIMO antenna systems tends to be a straight line
 RF path.  This may or may not do anything though.  Unfortunately I do not
 have a set of bi-directional attenuators to play with either.

Ticket URL: <http://dev.laptop.org/ticket/10397#comment:3>
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