ADC and DAC for modulation and demodulation

Hi
I have written Matlab script for BPSK modulation. The way my code works
is
as follow:

series of 0 and 1----> NRZ data (continuous rectangular pulses with
amplitude -1 and 1)--->multiply by carrier----> add noise--> multiply by
carrier---> integration--->detection---> Bit Error collection?

I would like to know can anyone tell me where I should apply DAC and ADC
?
I am wondering should it be after NRZ data or before that for DAC ?
---------------------------------------
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On Fri, 10 Jul 2015 22:19:20 -0500, chess wrote:

> Hi I have written Matlab script for BPSK modulation. The way my code
> works is as follow:
> 
> series of 0 and 1----> NRZ data (continuous rectangular pulses with
> amplitude -1 and 1)--->multiply by carrier----> add noise--> multiply by
> carrier---> integration--->detection---> Bit Error collection?
> 
> I would like to know can anyone tell me where I should apply DAC and ADC
> ?
> I am wondering should it be after NRZ data or before that for DAC ?

Perhaps the best place would be in the same spot as in the system that 
you're trying to simulate.

-- 
www.wescottdesign.com

>On Fri, 10 Jul 2015 22:19:20 -0500, chess wrote:
>
>> Hi I have written Matlab script for BPSK modulation. The way my code
>> works is as follow:
>> 
>> series of 0 and 1----> NRZ data (continuous rectangular pulses with
>> amplitude -1 and 1)--->multiply by carrier----> add noise--> multiply
by
>> carrier---> integration--->detection---> Bit Error collection?
>> 
>> I would like to know can anyone tell me where I should apply DAC and
ADC
>> ?
>> I am wondering should it be after NRZ data or before that for DAC ?
>
>Perhaps the best place would be in the same spot as in the system that 
>you're trying to simulate.
>
>-- 
>www.wescottdesign.com
I have already written the code for modulation and demodulation but this
time I would like to use ADC and DAC to produce the digital and analog
signal but I wonder where to place them exactly ? do they come after the
multiplication by carrier?

---------------------------------------
Posted through http://www.DSPRelated.com

On Sat, 11 Jul 2015 01:53:25 -0500, chess wrote:

>>On Fri, 10 Jul 2015 22:19:20 -0500, chess wrote:
>>
>>> Hi I have written Matlab script for BPSK modulation. The way my code
>>> works is as follow:
>>> 
>>> series of 0 and 1----> NRZ data (continuous rectangular pulses with
>>> amplitude -1 and 1)--->multiply by carrier----> add noise--> multiply
> by
>>> carrier---> integration--->detection---> Bit Error collection?
>>> 
>>> I would like to know can anyone tell me where I should apply DAC and
> ADC
>>> ?
>>> I am wondering should it be after NRZ data or before that for DAC ?
>>
>>Perhaps the best place would be in the same spot as in the system that
>>you're trying to simulate.
>>
>>--
>>www.wescottdesign.com
> I have already written the code for modulation and demodulation but this
> time I would like to use ADC and DAC to produce the digital and analog
> signal but I wonder where to place them exactly ? do they come after the
> multiplication by carrier?

The reason I am being tart with you is because you seem to be living the 
fallacy that "to know Matlab is to know DSP".  Instead of asking where 
you should put a PRETEND device into a PRETEND simulation inside of a 
simulation environment, why don't you ask where you might put REAL 
devices in a REAL system that has to work in the REAL world and may even 
have to compete with other REAL devices in the REAL marketplace?

The place you put ADCs and DACs, exactly, in a REAL system, is nearly 
anywhere in the signal processing chain -- including off the table, 
because lots of radios can be built without DSP.  You can build a system 
that goes

antenna -> ADC -> signal processing -> DAC -> speaker

You can build a system that goes

antenna -> signal processing -> ADC -> signal processing -> DAC -> signal 
processing -> speaker

You can build a system that goes

antenna -> signal processing -> speaker

or any variation in between (you could even dive into and out of discrete 
time more than once, although when that's done it's usually an artifact 
of purchased modules or an old product and a convoluted upgrade program).

Where it is advantageous to transition from continuous-time to sampled-
time depends on a huge number of factors pertaining to the real world.  
Absolutely none of them have anything to do with Matlab.

I suggest you try again, with either your question or your project.  Tell 
us what you're trying to build (NOT some Matlab program: what real thing 
are you building, or what real thing are you designing, even if it won't 
ever get built).  Be specific to the point where we know what sort of 
data rates and carrier frequencies are involved, and what forms of 
modulation.  State what sort of a quality/cost compromise you have in 
mind.  Maybe even say what sort of production volume you're anticipating 
(it matters).  Then don't ask for the one spot where the ADC should go, 
and the one spot where the DAC should go.  Rather, because the answer 
isn't absolute, ask people where they would put the sampling and the 
reconstruction, and why.

-- 
www.wescottdesign.com

On 2015-07-11 5:19, chess wrote:
> Hi
> I have written Matlab script for BPSK modulation. The way my code works
> is
> as follow:
> 
> series of 0 and 1----> NRZ data (continuous rectangular pulses with
> amplitude -1 and 1)--->multiply by carrier----> add noise--> multiply by
> carrier---> integration--->detection---> Bit Error collection?
> 
> I would like to know can anyone tell me where I should apply DAC and ADC
> ?
> I am wondering should it be after NRZ data or before that for DAC ?

As Tim said it really depends on the actual system.

In a typical "state of the art" comm-radio it is usually before the
carrier multiplication, i.e. you prepare the baseband signal in digital
domain, DAC and mix it with the RF in analog domain. However, newer
systems can also use RFDACs and do even carrier modulation in digital.
Also you may want to apply pulse shaping as well.

-Peter