Re: [Discuss-gnuradio] in-band signaling & dependent packets (i.e., ACK generation)

[Brian Padalino]

On Dec 4, 2007 2:00 PM, George Nychis <address@hidden> wrote:
> I see, I want to go lower than the PHY layer really...

You can't go lower than the PHY layer.  There's a reason it's the
lowest on the stack.

> Here's the thing, I don't want the solution to be dependent on the
> physical layer.  The goal is a development platform, and by choosing a
> solution dependent on GMSK, I essentially lock all MAC development in to
> using GMSK.  Is there a solution independent of the PHY layer?  I
> suppose I'm still not sure :)

You can use a matched filter for this, but a generalized matched
filter uses multipliers.  If you limited yourself to GMSK, PSK, or QAM
you can get away with sign manipulations.  OFDM would require
different processing in general.

> If some mechanism could be built in the FPGA that was highly
> reconfigurable, that would be fine... but it seems to be boiling down to
> different techniques per-modulation.

Not really an option for the USRP as it currently is due to the lack
of hardware multipliers.  Maybe more of an option for the USRP2.

On a side note, you should not feel bad about making something that
considers a trade-off in the realm of software defined radio.  You are
giving up (slight) PHY layer flexibility for much improved latency.
We're still using an antenna.  We're still using a super heterodyne
receiver.  Some things just can't be software and are limitations -
working around them is fine.

Brian