[OLPC Networking] RSSI value questions

[david at lang.hm]

On Wed, 2 Apr 2008, Oliver Mattos wrote:

> To be honest I very much doubt the hardware in the wireless adaptors could
> measure time in single digit nanoseconds, and even if they could it would
> probably require a change in the over the air signal to use more bandwidth
> (spectrum) for a "pulse" to get better time resolution, which in turn would
> require hardware modification.

the commercial products are able to do it with unmodified laptops, so it 
should not require a change to the over-the-air signal (unless this 
generation of active antenna hardware isn't up to the task)

> I would think the sound and signal strength meter are better metrics.
> Remember although signal strength is a bad indicator by itself, it can be
> much improved with 2 aerials and the large number of possible pairs to
> measure signal strength between in a well linked mesh.

the problem with trying to use sound is that it requres a clear path from 
the servers to the laptops, something I would not expect to see very much. 
it's also very sensitive to the direction the laptops are pointing.

David Lang

> On Wed, Apr 2, 2008 at 3:14 PM, Martin Langhoff <martin.langhoff at gmail.com>
> wrote:
>
>> On Wed, Apr 2, 2008 at 4:27 AM,  <david at lang.hm> wrote:
>>>  trying to work from signal strength won't work well, but you may be
>> able
>>>  to triangulate based on the arrival time of the signal at various
>>>  locations.
>>>
>>>  there are companies that do this commercialy with 3+ access points
>>
>> The recommended configuration for mid-to-high-end school servers has 3
>> active antennaes attached, and our recommendation is that they are
>> placed well apart. They can be up to 10m apart due to USB cable lenght
>> limits, and Wad mentioned 2m minimum recommended distance. If the
>> distance is enough (in relation to the granularity of timers in the
>> antennaes) then telling the XS about relative location of the
>> antennaes could provide enough info.
>>
>> Having said that, I suspect that being able to do any of the above is
>> somewhat far ahead in time ;-)
>>
>> cheers,
>>
>>
>>
>> m
>> --
>>  martin.langhoff at gmail.com
>>  martin at laptop.org -- School Server Architect
>>  - ask interesting questions
>>  - don't get distracted with shiny stuff - working code first
>>  - http://wiki.laptop.org/go/User:Martinlanghoff
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>