Re: How to efficiently implement dechannelization (combine multiple narrowband signals into a single broadband spectrum)

[Sylvain Munaut]

Hi,

> I'm working on an SDR project where I need to transmit a narrow
> baseband signal on multiple different carriers simultaneously, over a
> relatively wide bandwidth (1Mhz).

Is this the same baseband signals copied at several place ?

What you can do is :

 * First modulate the signal to a narrow sample-rate (just enough for
the modulation)

 * Upsample that signal to 1 Msps.
   - Depending on the ration between the narrow rate and wide rate, it might be
     beneficial to do that in several steps.
   - So for instance you would go from 10 kHz to 100 kHz first with a
filter that's relatively sharp
   - Then you would go from 100 kHz to 1 MHz with a second filter than
can be much more relaxed (i.e. larger transition bandwidth and so much
less CPU usage)

 * Then use several rotators to position it at the various places you
need it in the 1MHz bandwidth

 * And finally add the output of all the rotators.


There is also the so called Polyphase Filter Banks, but that only
works if you need carriers that are all equally spaced. And is also
only a benefic if you really fill a significant number of them.

Cheers,

     Sylvain