Hi Florian, that's an interesting approach!
On 06/07/2017 02:58 PM, Florian Adamsky wrote: > Hi all, > > in one of our projects we need to measure the distance between two > 802.11 devices as accurately as possible. Our idea is to use the > round-trip time (RTT). To avoid any delay from the operation system and > from the network stack, our idea is to measure the arrival time of the > acknowledgment control frame. Means, we take a timestamp when device A > sent a small data frame to device B; when B has received the frame, it > replies with an acknowledgment control frame and when A has received it > we will take another timestamp. Of course we would repeat that n-times > to avoid outliers. Your observation, that Wifi chipsets typically delegate most of what is necessary to be a working Wifi device to the operating system. Highly timing-sensitive things, however, are typically handled by the chip firmware itself. If I remember correctly, there's some degree of adjustability in that firmware, at least in Atheros chipsets; [1] might be an interesting talk for you. > > We bought a HackRF and tried to get the examples from gr-ieee802-11 > running. After some minor problems (dc offset) we were able to receive > 802.11 frames. However, we are not able to send any 802.11 packets, > because the hackrf driver does not support burst transmission with > tagged streams. One reader of this mailing list suggested to give > soapysdr a try. We did that as well, but again without success. Here we > didn't see any "UUUUU" in the debug console but we were still not able > to see any packets with another wireless card in monitor mode. Another takeaway from [1] that in usual operation, the hardware doesn't even hand over packets that don't make the checksum test – maybe it'd be interesting to disable that filtering. Best regards, Marcus [1] https://www.irongeek.com/i.php?page=videos/defcon-wireless-village-2014/20-inside-the-atheros-wifi-chipset-adrian-chadd _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
