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Juan Ramon Gutierrez Agullo wrote: > Hello everyone > > This is my first message here and, of course, I'm a newbie click user. > > I have an 802.11a transmitter > (https://www.cgran.org/wiki/ftw80211ofdmtx) running in the USRP2, but it > only generates a standard-compliant IEEE802.11a/g/p OFDM frame - PHY > layer. > Looking at other projects I found the hydra project, and they used click > to implement the MAC layer (CSMA/CA and DCF). I have some questions and > I hope you could help me. USRP uses either usb (USRP1) or ethernet(USRP2) to communicate with the host, which probably means delays in the magnitude of 10s of us for a frame-transmission over the interface (Take Linux' interrupt latency for ethernet-frame-reception into account!) 802.11 slot time is 4 us, which is the time you have available to a) receive the last sample at the frontend b) decode it at the CPU c) deceide whether to ack it d) encode the ack at the CPU e) have the first samples available for transmission at frontend Click runs on the host as a scheduled kernel process, which brings you to probably 100s of us worst case reaction on incoming samples, especially on a Linux machine busy decoding samples. So I don't see any way to implement 802.11 MAC on USRP on the host side, no matter whether you use click or any other host side tool, IMHO: the FPGA is your only choice (maybe some fancy real-time kernels might just make it...) Please, please, prove me wrong on that, 802.11 on USRPs would be soooooo cool. > - How can click communicate with GNU Radio? My approach would be: a) implement the MAC on the FPGA, b) implement TX-queues on the FPGA that use this MAC, c) write a driver that accepts frames and meta-data for this MAC, d) write a click element, that takes Ethernet packets and transforms it into one of these meta-annotated-frames. e) implement things like rate control or scheduling algorithms as click elements and have them set proper packet meta-data. > - Is there any MAC implementation -by default- with click installation? Nope, as all Wifi cards implement the MAC in hardware, for above mentioned reasons. Now, can sombody please tell this poor guy that I'm a moron and there is a smooth and simple way to do all this .... Harald -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iEYEARECAAYFAktgJQYACgkQy8wrZ9OvkU0/HQCdF0piwwsk2vzDN1meoh9ysvTs 2bAAoJsTBPENPHHaQ/zhulqAH5rQutuz =Z2H4 -----END PGP SIGNATURE----- _______________________________________________ click mailing list [email protected] https://amsterdam.lcs.mit.edu/mailman/listinfo/click
