Re: [Discuss-gnuradio] Help using simple_framer and simple_correl ator

[Eric Blossom]

On Mon, Nov 28, 2005 at 11:20:59AM -0700, Robitaille, Michael wrote:
> Use of gmsk2 versus simple_framer & simple_correlator.
> 
> 
> The project I am working on has the following characteristics:
> 
> 1.       Remote telemetry using optical link.  For proof of concept need to
> measure temperature from multiple sensors (5 thermocouples).  The
> temperature is represented by 8 bit word and sampled every 0.2 seconds per
> thermocouple (limited by the MAX6675 chip).  This would results in data rate
> of 200 bits/sec.
> 
> 2.       Carrier frequency - 1 KHz to 2 KHz due to the modulator we are
> presently using for the proof of concept.  In phase II we will have the
> funds to improve the modulator and increase the frequencies.  For proof of
> concept we will have two transmitters at different carrier frequency, 1Khz
> and 2 Khz.
> 
> 3.       ASK modulation. - turning on/off a reflected optical beam that is
> illuminating the transmitter.
> 
> 4.       The data is continuously transmitted and the microprocessor
> controlling the modulation is very limited on what it can implement (cant do
> CRC32).
> 
>  
> 
> Please let me know what you suggest.

I guess the first question that comes to mind is "why modulate at
all"?  Why not just send your digital data as on-off-keying across
your optical interconnect?

You're still going to have to deal with framing, somehow.  You may
want to treat it as async data (using start and stop bits per byte),
or perhaps something like SDLC/HDLC framing (flags, bit-stuffing, CRC).

Eric