The SECOND ORDER Costas loop produces foptr(n) and poptr(n) which is the
frequency and phase estimate for the carrier.
sin(poptr(n)) is the estimated carrier.
If S(n)*sin(poptr(n) is the spreading code modulating the estimated
carrier, then
S(n)*P(n) * complex_conjugate(S(n)*sin(poptr(n)) should be approximately
P(n) up to error in
a) your estimate of the carrier
BUT ALSO
b) the clock of the transmit system and its initial phase offset for the
complex spreading code MUST ALSO be estimated to close this system and
track. My little equation above ASSUMES perfect knowledge of S(n) which
is NEVER the case in a real system.
Bob
On 8/3/2010 9:45 PM, John Andrews wrote:
Hi,
can someone guide me a little here please. I have a complex signal S(n)
that I multiply with a sequence P(n) of length N (the sequence consists
of {-1,1} ). I pass the product into a Costas Loop to track the carrier.
Btw, the complex_input signal a spread signal spread using the sequence
P(n) and BPSK modulated.
S(n)*P(n) ---> Costas Loop
Then I want to remove the carrier from the original signal which can be
done by multiplying the frequency output of the costas loop which is
foptr[i] with S(n). Is that right? I want to do this in GRC. Can someone
guide me a little here and tell me if I am understanding it right.
Will be eagerly waiting for a reply. I am not good at Communications
stuff as this is not my major but I am trying hard. :) A little help
will greatly appreciated.
Thanks
John
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