hey, i had the idea that somehow you'd appreciate this.
https://fahrplan.events.ccc.de/congress/2019/Fahrplan/events/10630.htmlThis talk is about modifying cheap wifi dongles to realize true
unidirectional broadcast transmissions that can transport digital data
like HD drone video with guaranteed latency over a range of tens of
kilometers. The talk will show the necessary changes to the firmware and
kernel of the wifi dongle, the forward error correction and software
diversity (fuse several receivers in software) that is added to improve
reliability and the most prominent use case: Flying a remote controlled
drone at a distance of tens of kilometers.
Wifi as it is implemented in the 802.11 standard tries (as best as it
can) to guarantee to a user the delivery of data and the correctness of
the data.
To increase the chance of delivery, the standard includes techniques
like automatic retransmission, automatic rate reduction, CSMA/CA. To
guarantee correctness, the packets are using CRC sums. These measures
are very useful in a typical 1-to-1 communication scenario. However,
they do not adapt very well to a 1-to-n scheme (broadcast). Even in case
of a 1-to-1 scenario the techniques mentioned above make it impossible
to guarantee a latency and throughput of a transmission.
Wifibroadcast uses the wifi hardware in a mode that is very similar to
the classic analog broadcast transmitters. Data will immediately be sent
over the air, without any association of devices, retransmissions and
rate reductions.
The data can be picked up by an arbitrary number of receivers that
decode the data stream, repair damaged packages via software diversity
and repair damaged bits via forward error correction.
The Wifibroadcast software is an easy to use Linux program into which
arbitrary data can be piped. The same data will then appear on the
receiving program on standard output and can thus be piped into further
programs.
All software developed has been made available under the GPL license.
A prominent use case for Wifibroadcast is the transmission of live video
from a drone. Compared to standard wifi this offers the following
advantages:
* Guaranteed latency
* No association (that might get lost)
* Multiple receivers work out of the box
* True unidirectional communication allows to use asymmetrical antenna
setups
* Slow breakup of connection instead of complete communication loss
The talk will show the details of the Wifibroadcast protocol, the
changes to the firmware & driver, the forward error correction, software
diversity and finally will show the HD video transmission over tens of
kilometers as an application example.
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Envoyé depuis mon périphérique avec Sailfish