[Discuss-gnuradio] Acoustics instead of radio & what's possible in real-time?

[Jim Morash]

Hi,

I'm working on a software-defined acoustic communications transceiver, 
currently based on DSP-targeted code generated by MATLAB and Simulink. 
I'm looking into options for converting the project to free software and 
so far I have been reading about Scicos and GNURadio. As part of moving 
to a free software platform, I would also transition the system from a 
DSP target to a general purpose (PC) processor.

I'd like to make the whole system real time capable (rather than 
data-acq followed by post-processing) and I hope to get an idea from the 
gnuradio list membership of what is possible on a general purpose 
processor, and whether GNURadio is a good platform choice for my 
application. For example, one difference from more typical SDR projects 
is that we are doing direct quadrature sampling without a HW basebanding 
front end. In the current design, the receiver does:

- sampling at 4x the carrier (Fc @ 12kHz now, may go up -> 48ksps min, 
maybe 96ksps in the future?)
- digital I-Q demodulation, decimation
- correlation to detect start-of-packet
- demodulate & decode packet of QPSK symbols (training & data bits) 
using a digital PLL, decision feedback equalizer and viterbi decoder, 
currently 200 training symbols & 600 data symbols
- a bit of MAC and application layer stuff (but this is lower processor 
demand)

Is this possible? Or perhaps trivial, compared to RF data rates? Does it 
look like I'd need to write a bunch of new blocks if I moved to GNU 
Radio? :)

For comparison, the existing (floating-point) DSP implementation runs a 
bit behind real time. It takes about 3 seconds to process a packet of 
length ~0.7 second. I would like to do better. The PC-compatible 
hardware platform I had in mind is the Via PX10000 (for size/power 
reasons); it seems fairly fast and has a nice built in audio codec with 
a high sampling rate.

http://www.engadget.com/2007/06/03/via-epia-px10000-pico-itx-motherboard-gets-reviewed/

I am fairly new to software-defined radio in general. Thanks in advance 
for any suggestions.

--Jim Morash
address@hidden