Hi,
Recently I have a thinking to implement a baud 9600 modem using ADC and DAC and MCU. I know the implementation involves to encode and decode by QAM. Is it possible to do it? How fast the MCU needs to do that?
Thanks!
Only if the original signal is QAM. I did a quick web search and found V32 in the same sentence with "trellis coding" -- which ain't QAM. You need to find the specs for the modem you want to talk to and make sure you understand them.
Yes, but you have to know what you're doing.
I have decoded 400 baud MSK (a close relative to QAM) with a 68HC11 running at 8MHz (about 2MIPs), using 98% of the available processor power. If you scale from there you'd need about 24MIPs for your decoding -- but the 68HC11 is a very inefficient machine. If you use a DSP chip you can probably do it with half that many MIPs, but you want to have your SW app using no more than 50% of the available processor time.
So say a 25MHz DSP chip, or a 50MHz 16-bitter if _all_ you're doing is the modem.
You're welcome.
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com
Hi Terry,
It depends on the kinds of math the uC can do. As Tim said, the classic uCs have a hard time with signal processing but some newer versions run
16 bits internally and the 'leather seat' versions contain stuff like HW multipliers. An example is the MSP430. Check TI's code examples. I believe they had modem apps for situations much faster than 9600 baud. This could also save you much of the grunt work in writing the code and you can buy proto boards from Olimex at pretty low cost.Regards, Joerg
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