>Some time ago there has been a long discussion about RF Tx/Rx modules
>I have managed to get hold onto the small hybrid modules. The Tx operates
>in ON/OFF mode while the Rx has a bandwidth of about 2KHz.
>Now I would like to set up a digital data link using RS232C.
>To speed up the link I think about some sort of data packaging, compression
>and correction. All this would be burried into PIC (16C84) acting as
>a link controller.
>Do you have any suggestions and/or ready made examples?
>
>Regards,
>Janusz

Hi Januz,

I agree with most of the other comments regarding general
compression techniques. However, if you can factor the data
in some predetermined way, then quite often single bytes
can act as tokens for larger chunks of data. Both ends of
the RF link need to have prior agreement on what the
meaning of these compressed commands/data represent.

The second part of you question, is more difficult. Firstly
you need to detect errors and then decide what to do about
them. Error detection can be complex or simple. I would
probably go with 16bit CRC, again this is really application
dependant.

What do you expect the system to do if you detect an error.
IE you could opt to ignore errors, maybe retry a transmission a
limited number of times etc. etc.

Alternatively, you would be well advised to look at simple
methods of forward error correction, like Hamming codes.
This has been covered many times before on this list. And
some time spent with a search engine will probably get you
started.

The final part, packaging.... if you plan in future to
have multiple devices talking at once, some sort of contention
resolution is required. Also some means of addressing packets
is required.

Sorry this is long on generalities and short on specifics
but there are many issues that would just take too long to
detail.

Hope this helps get you started in the right direction.



Ray Gardiner  Technical Director DSP systems Pty. Ltd. ray@dsp-systems.com
private email to:- ray@netspace.net.au          http://www.dsp-systems.com