QPSK Demodulation in Software?

I am using a PC to aquire data, this data will be QPSK modulated.  Can
anyone tell me if there is anywhere I can find information on how to
demodulate a QPSK modulated signal in software, any language will do.

I have searched the internet for this but all I can find is
implementations using electronics methods.

Thanks,

joseph

On Sep 17, 11:20 am, JB <josephby...@yahoo.com> wrote:
> I am using a PC to aquire data, this data will be QPSK modulated.  Can
> anyone tell me if there is anywhere I can find information on how to
> demodulate a QPSK modulated signal in software, any language will do.
>
> I have searched the internet for this but all I can find is
> implementations using electronics methods.
>
> Thanks,
>
> joseph

You can use the same "electronics methods" to demodulate QPSK in
software. Instead of having hardware do each step for you, you can
implement identical (or close to identical) operations in your
software receiver. With that said, you probably won't do everything in
software; if your signal is carrier-modulated, you'll want to
downconvert it before you sample, which requires some front-end
hardware. Once you have your QPSK signal at some reasonable IF
frequency, you can implement discrete versions of the same operations
that you're reading about in hardware receivers.

Jason

cincydsp@gmail.com writes:

> On Sep 17, 11:20 am, JB <josephby...@yahoo.com> wrote:
>> I am using a PC to aquire data, this data will be QPSK modulated.  Can
>> anyone tell me if there is anywhere I can find information on how to
>> demodulate a QPSK modulated signal in software, any language will do.
>>
>> I have searched the internet for this but all I can find is
>> implementations using electronics methods.
>>
>> Thanks,
>>
>> joseph
>
> You can use the same "electronics methods" to demodulate QPSK in
> software. Instead of having hardware do each step for you, you can
> implement identical (or close to identical) operations in your
> software receiver. With that said, you probably won't do everything in
> software; if your signal is carrier-modulated, you'll want to
> downconvert it before you sample, 

That's not at all necessarily so. The soundblaster audio interface
is commonly used as a "bandpass signal" for low-rate modulations.
That is, the carrier is somewhere in the audio band and downconversion
_is_ performed in software.
-- 
%  Randy Yates                  % "She tells me that she likes me very much,
%% Fuquay-Varina, NC            %     but when I try to touch, she makes it
%%% 919-577-9882                %                            all too clear."
%%%% <yates@ieee.org>           %        'Yours Truly, 2095', *Time*, ELO  
http://home.earthlink.net/~yatescr

On Sep 17, 11:52 am, Randy Yates <ya...@ieee.org> wrote:
> cincy...@gmail.com writes:
> > On Sep 17, 11:20 am, JB <josephby...@yahoo.com> wrote:
> >> I am using a PC to aquire data, this data will be QPSK modulated.  Can
> >> anyone tell me if there is anywhere I can find information on how to
> >> demodulate a QPSK modulated signal in software, any language will do.
>
> >> I have searched the internet for this but all I can find is
> >> implementations using electronics methods.
>
> >> Thanks,
>
> >> joseph
>
> > You can use the same "electronics methods" to demodulate QPSK in
> > software. Instead of having hardware do each step for you, you can
> > implement identical (or close to identical) operations in your
> > software receiver. With that said, you probably won't do everything in
> > software; if your signal is carrier-modulated, you'll want to
> > downconvert it before you sample,
>
> That's not at all necessarily so. The soundblaster audio interface
> is commonly used as a "bandpass signal" for low-rate modulations.
> That is, the carrier is somewhere in the audio band and downconversion
> _is_ performed in software.
> --
> %  Randy Yates                  % "She tells me that she likes me very much,
> %% Fuquay-Varina, NC            %     but when I try to touch, she makes it
> %%% 919-577-9882                %                            all too clear."
> %%%% <ya...@ieee.org>           %        'Yours Truly, 2095', *Time*, ELO  ttp://home.earthlink.net/~yatescr


The main reason to sample at an audio IF is to avoid the crappy or
nonexistent DC response of the soundcard.

John