Dear All,

I have a question regarding the first complex multiplication process

with

the IF sinusoid in the USRP. Which of the scheme mentioned below is

actually

happening in the USRP?

Let’s say that two ADCs provide the sampled received signal to the next

stage of processing. Let’s call the sampled stream of ADC_0 as A and

sampled

stream of ADC_1 as B.

SCHEME-1

The NCO produces two sinusoids that are in quadrature phase with each

other.

These are sin(2*pi*f*t) and cos(2*pi*f*t). Let’s call the

sin(2*pi*f*t)stream as C and
cos(2*pi

*f*t) stream as D. The multiplier after the ADC stage does the

following.

- Multiplies the cos(2
*pi*fc*t) stream, C, with the sampled data

stream of

ADC_0, which is the stream named A and the product is AC. - Multiplies the sin(2
*pi*fc*t) stream with the sampled data stream of

ADC_1, which is the stream named B and the product is BD.

Then sends the resultant product from these two steps as a complex

sample,

( AC + jBD )

SCHEME-2

The NCO produces two sinusoids that are in quadrature phase with each

other.

These are sin(2*pi*f*t) and cos(2*pi*f*t). The multiplier after the ADC

stage does the following.

The multiplier after ADC stage then multiplies the ADC outputs with the

NCO

outputs as

( A + jB ) * ( C + jD) = (AC - BD) + j(AD + BC)

and sends the above output as a complex sample.

Which one is true?

Thanks