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

[Brian Padalino]

On Dec 4, 2007 1:07 PM, George Nychis <address@hidden> wrote:
>  From some discussion on comp.dsp, it seems as though I'm looking for a
> matched filter:
> http://groups.google.com/group/comp.dsp/browse_thread/thread/f93d7867f74dbe95#0dc48f2a8ed09e07

Yes, you are describing a matched filter.

> If you see what I'm getting at, if I implement a matched filter in the
> FPGA (given that it does what I think it does ;)), I can detect incoming
>   frames without using the PHY layer.

You're not getting rid of the PHY layer.  You're incorporating this
mechanism into the PHY layer as opposed to having it within the MAC
layer.

> Let's say that a simple requirement is this: the frame format must have
> the destination address directly after the framing sequence.  Therefore
> I could use the matched filter to detect incoming frames to my address
> in the FPGA using a single sequence, without the turnaround time to the
> host.
>
> By doing this, I could generate ACKs much faster by storing
> pre-modulated data in the FPGA which is triggered.

You can accomplish this by using some simple sign manipulation/zero
insertion and treating the GMSK as a simple PSK that only shifts 90
degrees for each transition.  No new multipliers should be required,
but memory will be needed for coefficients and samples.

How many bits is your address and how many bits is your frame sync?

Brian