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(2pift) and cos(2pift). Let’s call the
sin(2pift)stream as C and
cos(2pift) stream as D. The multiplier after the ADC stage does the
following.
- Multiplies the cos(2pifc*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(2pifc*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(2pift) and cos(2pift). 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