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DSP based High Speed Data



Being curious about this High Speed Data stuff, I thought Iíd try to put
some numbers to the idea
presneted by John Stephensen, KD6OZH.

Iím new to DSP, but here goes anyway;

Given the following:

No info in the amplitude.
20KHz audio upper limit.
20Msps 10 bit A/D converter.
DSP chip that can do the calculations fast enough.
   a) ignore the DSP processing overhead
A minimum of 2 data points on the highest Tone (20 kHz).
   a) and the system can resolve the difference between tones reliably.

Question:

   How do I get some serious bit rates (200Kbps or better) out of this
stuff?


An 8bit (128 tone) system has a speed limit of <160Kbps.  If the signal
BW is <=1KHz (from 20KHz down) you will have to resolve tones that
differ by 7.8Hz.  You will have to wait at least 52.6us (19KHz, lowest
frequency) for the entire waveform to arrive before you can decompose
the signal.  This gives you a bit rate of about 152Kbps.  Decreasing the
signal BW doesnít help all that much since you canít break 160Kbps with
an 8bit tone structure anyway.

So what about a 16bit word?

Now there are 32768 tones.  For the same signal BW (1KHz) you will have
to resolve tones to 31mHz.  Given the above constraints your A/D
converter can give you 2mHz, double it (Nyquist times 2) and you are
still only at 4mHz.  The same latency period of 52.6us holds since 19KHz
is still the lowest frequency.  Now the data rate is 304Kbs.

If we relax the signal BW to 5KHz the difference between tones jumps to
153mHz, the latency period goes up to 66.67us (15KHz) and the bit rate
drops to 240Kbps.

Have I overlooked anything?

Absolutely... Noise (in the RF channel and Audio channel),  Throughput
of the DSP system,  Additional tuning tones, Separation of each
composite (all 32768 tones) audio signal in the data stream, My
ignorance and lack of experience in the DSP field.

How bout someone else taking a crack at it?

Don't hurt me... DSP is not my field.

--
/***************************************
Bronson Crothers
17 Charles St.
Orono  ME  04473

Phone: 207 866 0405
Fax:.....207 866 0405

Radio Call: N1ZAQ

--... ...--

Email: bronson@eece.maine.edu
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