On 24 September 2014 10:22, Kamran Nishat <kamran.nis...@gmail.com> wrote: > > > >> Hi, >> FIRST, Will there be any difference in duration of PHY header for 20MHz >> and >> 40Mhz. >> Do u think 40Mhz header will take lesser time? > > Which bits of the header are you talking about? Just the initial PLCP > bits? I'm not sure how HT40 PLCP works. > > I am not talking about the training (preamble) part. I was asking about MAC > header.
Ok, so the MAC header is already being transmitted at the HT40 rate. So, take a look at the different symbol rate/timing for HT20 versus HT40. Yes, they're slightly different. > So, you can do some tricks by watching the success rate of HT40 > transmissions and the primary/extension MIB channel busy counters and > determine what's going on. > > Instead of monitoring MIB counters. If some controllers tells me its better > to switch to 20MHz do u have any idea what will be the delay and what rate > would be picked. Well, it doesn't work that way with the atheros MAC. You have four rate table entries. You get to select how many retries for each of them and whether to use 20 or 40MHz. I don't know if there's a cute way to have it fast-fail short retries (eg if it fails to get the RTS/ACK pair in time) in HT40 mode and fall back to the HT20 rate. So you could tag the last rate entry as being 20MHz regardless of channel width. The chip isn't doing that dynamically. You can have it happen about as fast as you can fail to transmit frames and get that feedback from the MAC. -a _______________________________________________ ath9k-devel mailing list ath9k-devel@lists.ath9k.org https://lists.ath9k.org/mailman/listinfo/ath9k-devel
