Yes. There's nothing really stopping you from doing this. You can just
associate in both directions and then only send data out one link.
Now, having the nic be _transmit only_ and the other nic be _receive
only_ is a little tricky, as there's a bunch of 802.11 negotiation
stuff that's going on that really assumes it's happening on a single
VAP. The net80211 code could be hacked to transmit things out a
different device - ie, one VAP has a transmit device and a receive
device. You'd have to turn off things like hardware ACK, hardware
RTS/CTS, etc. But it's doable.
On 21 May 2014 11:39, Richard Yao <r...@gentoo.org> wrote:
> Dear Everyone,
> I recently read about Ubiquiti’s AirFiber hardware and noticed that its link
> efficiency is remarkable. Air Fiber’s link speed is about 770Mbps up and
> 770Mbps down (a 1:1 split). People are reporting benchmarks that show 700Mbps
> throughput over miles. The link efficiency is therefore in the range of wired
> ethernet, which typically obtains iperf results in the range of 85% to 95%.
> So far, all benchmarks of WiFi that I have seen never touch 1/e or roughly
> 37% efficiency. A few have come rather close to 1/e though.
> The 1/e number is significant because I am told that it is the theoretical
> limit on the efficiency of wired ethernet when a there is a shared collision
> domain on a coaxial cable. After reading about how the Air Fiber hardware
> works, I hav suspicion that its link efficiency can be replicated between two
> computers with off the shelf Wi-Fi hardware by abusing the radios via the
> kernel driver. In specific, you would have two systems, each with two radios
> on different frequencies. I will call each system A and B and refer to their
> radios as indices into an array. e.g. A and B.
> Much like the AirFiber, I envision node A as having A be transmit-only on
> the frequency that B uses (frequency 0) with B being receive only.
> Similarly, I envision node B as having B be transmit-only on the frequency
> that A uses (frequency 1) with A be receive only. The kernel driver is
> to instruct the WiFi hardware to ignore everything about the 802.11 protocol
> possible (e.g. RTS is to be ignored), send frames when given a packet (in
> send mode) and receive forward frames when hearing a packet (in receive
> mode). No radio in send mode is to listen to packets and no radio in listen
> mode is to send packets. The radios would be attached to directional antennas
> and frequency 0 != frequency 1.
> I asked Adrian Chadd about this in IRC. He replied that it is possible to
> hack the driver to obtain tight control over when 802.11 frames are
> received/sent, but doing something like this would require oscillator
> isolation and baseband RF isolation. He also asked that I send my question to
> the list, so here it is.
> How doable is this with off the shelf hardware? Could simultaneous dual-band
> equipment be abused to obtain the proper isolation (where 2.4GHz is 1
> direction and 5GHz is another)? Would it be reasonable to expect wireless
> throughput to achieve 90% of the link speed in this configuration?
> Yours truly,
> Richard Yao
> P.S. I am not on the mailing list, so please include me on CC.
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