Re: [Discuss-gnuradio] Physical layer for packet-based communication

[Rahul Dhar]

On Mon, Feb 07, 2005 at 08:53:39PM -0600, David Young wrote:
> 
> Rahul,
> 
> I have been thinking a little about how to produce a novel MAC, without
> spending gobs of time & money.  Here are some ideas:
> 
>         1 Use an off-the-shelf 802.11 card.  Change its mode from
>           PCF/DCF using software that runs on the host.
> 
>         2 Use an off-the-shelf 802.11 card.  Tweak its MAC/PHY parameters
>           until the default carrier-sensing and such are effectively
>           disabled---this could get hairy!  Use the host CPU or a
>           coprocessor to schedule packet transmissions.

Do you know how to access those parameters?  As far as I know, most of
the useful ones are stuck in firmware, and vendors don't want to tell us
how to play with the firmware.  Otherwise, this sounds like the best
solution, especially if I can write my own firmware (or edit the
existing one).  Given 802.11's tight timing requirements (discussed
briefly earlier in this thread), can the CPU schedule and send packets
fast enough?

>         3 Use an existing 802.11 PHY, but replace the MAC
>           with a microcontroller [*].  Design a PHY abstraction.
>           Implement, in C (say), the PHY abstraction for the PHY of your
>           choice [**].  Program your MAC in C.

This is actually what I'd like to do for GNU Radio, but I'm not sure
where to start, nor am I sure if it's even feasible.  It has been noted
that PHY's tend to be too diverse to make a meaningful abstraction very
difficult.

>         4 Use an existing 802.11 PHY.  Replace the MAC with
>           an FPGA.  Program your MAC in VHDL.  (I don't see much advantage
>           to this over #2.)

Um, yeah.  This sounds like the last resort option. :)

> All those ideas need a lot of development, but I hope the general ideas
> are clear.

They're interesting ideas.  I've already considered #2, but given the
delays in getting the USRP equipment, I'm not sure I have time to wait
for a vendor to get me specs.  I need to be done by end of April.  I
hate time constaints.

-- 
Rahul Dhar
address@hidden
Actually, my goal is to have a sandwich named after me.

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