Re: [Discuss-gnuradio] complex multiplication question

[Bob McGwier]

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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