How to demodulate signals composed of different modulation schemes with USRP?

[0711]

Hi everyone,

     These days I was trying to receive and decode signals composed of different modulation schemes. The frame of the frame is shown in the following image:

   

   The frame is composed of two parts. The first part uses the 2GFSK modulation, and the second part uses 2GFSK or 4GFSK according to the PSF field in the first part: when PSF=0, PSDU is modulated by 2GFSK, and when PSF=2, PSDU is modulated by 4GFSK.

    When PSF=0, I can receive and decode the frame correctly because I can demodulate and decode all the data in the frame with one demodulation scheme--2GFSK.

   The question is when PSF=2, the PSDU part is modulated with 4GFSK, and how can I get the precise starting offset of PSDU in the sample sequence?

   Firstly, I tried to  calculate the offset of PSDU by calculating samples/symbol * 128(here samples/symbol is 4), and demodulate the following samples according to value of the PLW field( when demodulating the PSDU part, the reset parameter of the FSK demodulator is set to false because I think it may need some phase information obtained in demodulating PLCP header). However, I found that  even when PSF=0, the demodulated PSDU bitstream is not correct.

   Then I doubt that the sample length of PLCP may be not 128*samples/symbol(here i.e. 512), and I do some experiments to see how many samples do I need to demodulate a correct PLCL header. I find that I need at least 574 samples. Here another question occurs: the bit length of PLCP header is 128, why do I need 574 samples to demodulate PLCP header?

   Can any one give me some good advices? Thanks in advanced!

[sshearman]

You could parse the incoming signal into the components that you expect to have differing modulation schemes and then feed the parsed components into the appropriate demodulation VIs from the Modulation Toolkit.

[sampath1234]

hi i have same doubt i have MIMO transmitter

but i am transmitting 4 contellation sizes from 4 antennas ,they are 16-QAM,8-QAM,16-QAM,32-QAM

my modulation scheme is QAM

my MIMO receiver has to demdulate these antennas data with different constellation sizes

i want demodulate data from these 4 antennas using QAM demodulator

how it will be possible 

please give the advice if any

thanku 

[YYYs]

Little push for this interessting topic/question.