Re: [Discuss-gnuradio] QPSK modulation resampling

[irene159]

George Nychis wrote:
> 
> 
> irene159 wrote:
>> 
>>> 
>>> Hello, 
>>> 
>>> Just another question concerning the file "gr_mpsk_receiver_cc.cc". 
>>> 
>>> In the extract of code below, why are phase_error_detector_generic and 
>>> decision_generic  used for all BPSK, QPSK and other modulations? 
>>> Have optimized algorithms for BPSK and QPSK already been implemented? 
>>> 
>>> // Select a phase detector and a decision maker for the modulation   
>>> order 
>>>  switch(d_M) { 
>>>  case 2:  // optimized algorithms for BPSK 
>>>    d_phase_error_detector = 
>>> &gr_mpsk_receiver_cc::phase_error_detector_generic; //bpsk; 
>>>    d_decision = &gr_mpsk_receiver_cc::decision_generic; //bpsk; 
>>>    break; 
>>> 
>>>  case 4: // optimized algorithms for QPSK 
>>>    d_phase_error_detector = 
>>> &gr_mpsk_receiver_cc::phase_error_detector_generic; //qpsk; 
>>>    d_decision = &gr_mpsk_receiver_cc::decision_generic; //qpsk; 
>>>    break; 
>>> 
>>>  default: // generic algorithms for any M (power of 2?) but not pretty 
>>>    d_phase_error_detector = 
>>> &gr_mpsk_receiver_cc::phase_error_detector_generic; 
>>>    d_decision = &gr_mpsk_receiver_cc::decision_generic; 
>>>    break; 
>> 
> 
> This is just a guess based on the block names... But given that the   
> block names have "generic" in them, I'd guess they are generic enough   
> to work with psk modulations given some configuration. 
> 
> - George 
> 



Well actually I do think phase_error_detector_generic and decision_generic
work for PSK modulations (such as BPSK and QPSK). 

What I don’t understand is the use of the switch case block in the code (to
treat BPSK and QPSK separately from other modulations) as the code in all of
the cases considered is exactly the same. My first thought was that there
would be specific and more efficient functions for BPSK and QPSK but I only
see generic ones.



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