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LTE frequency shift in FFTC

rq 86
Prodigy 10 points

I'd like to know how to set SHIFT_FACTOR and SHIFT_PHASE parameters for LTE frequency shift in FFTC_QUEUE_X_LTE_FREQUENCY_SHIFT_REGISTER.

LTE frequency shift is expressed as: H(n)=exp (j*2*pi*(n+4*no)*a/M), what is the meaning of "no" and "a" terms? How can I determine "no" and "a" values?

Thanks.

 

 

 

  • 0
    TI__Mastermind 23525 points

    I don't know if you found your answer for this.  I am not a user of the FFTC, but I asked around and this is the answer I received.  Hope it helps.

    Regards,

    Travis

     

     

    For FFT size 2048, 1024 and 512, M should be set to 16384. For FFT size 1536, M should be set to 12288.

    “a” should be set based on FFT size. “a” should be 4 for FFT size 2048, 8 for 1024 and 16 for 512 etc. Basically a/M should be equal to 1/(2N) with N being FFT size for the 7.5KHz freq shift in LTE. Please also note that in FFTC, it is not “a” that is set in the register but SHIFT_FACTOR such that 2^SHIFT_FACTOR equals “a”.

    “n0” is just the initial phase to be added or corrected.

  • 0 in reply to tscheck
    Expert 1610 points
    Hi I'm trying use the FFTC for LTE Uplink. I have configured FFTSize = 1024, M = 16384, a = 8, n0 = 0; But my output values are not matching the reference output. Without the frequency shift I have verified that the FFTC output matches the reference. Please help me.