[ath9k-devel] 802.11p - Switching Channel

[ath9k-devel] 802.11p - Switching Channel

[Javier Fernández Pastrana]

Greetings everyone!



I have been working in 802.11p for several months. I used the 802.11p
CTU-IIG
<https://github.com/CTU-IIG/802.11p-linux/commit/bf45e0160af428dac8893e48d506ac428fed16b2>
as
a basis of all my work. I achieved to work in OCB mode as well as establish
communication between different devices. But Now I would like to check it
in a real environment, therefore it is compulsory changing between channels
(from Control channel to Service channel and vice versa) , as it is said in
ETSI ITS G5 standard. It means change one frequency to other, for example
from 5900MHz(CCH) to 5880MHz (SCH1).



I am able to change the channel through iw program *(ocb leave* and *ocb
join*). The problem that I saw, is that when you change to one channel o
other, you always lose the first packet (in the receiver station) since you
changed the channel, the second packet is received correctly. Someone have
an idea that shy is happening this?



I want to explain the problem with an example 1:



It is always a station sending packets in 5900 MHz, the packets are sent
per 2 seconds.

Then it is a receiver station that waits *1.5 second* to receive a packet,
if not receive packets, then it leaves and joins the channel (the same
frequency 5900MHz). Besides, if it receives a packet, the station reads it
and then leaves and joins the channel too.

I am always sending and receiving in the same channel, therefore I should
receive all the packets because I give enough time to the receiver station
to compute them.



On the other hand, I made a second test, example 2:



It is always sending packets in 5900 MHz and the packets are sent per 2
seconds.

Now the receiver station waits *2.5 seconds*, and it changes the channel if
it receives a packet or if it waits 2.5 seconds without receiving anything.

In this case I give enough time to the receiver station to receive 2
packets without leaving and joining the channel, and curiously it is able
to read the half of the packets.



To sum up, it looks that the receiver station needs one packet to read the
next one, maybe it is something relating with the station have to stablish
the bitrate or the modulation before.



Have someone work before with WLANp? Any idea? Suggestions are always
welcome!



Thank you very much!



Javier.
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