This discussion explores the functional differences between Xilinx's DFT, FFT, and LTE_FFT IP cores, specifically questioning why LTE_FFT exists as a separate entity. The thread concludes that the LTE_FFT core is specialized to handle non-power-of-two transform lengths required by the LTE standard, such as 1536 points, which the standard FFT core typically does not support.
- The standard FFT IP core is generally restricted to power-of-two (2^n) transform lengths.
- The LTE_FFT core includes a radix-3 stage specifically to support the 1536-point transform required for LTE.
- Including non-power-of-two support in a dynamic FFT core adds hardware overhead that may be undesirable for applications only requiring 2^n lengths.
- Some developers prefer using a larger 2048-point FFT with interpolation as an alternative to using the specific 1536-point LTE core.
Just started looking into Xilinx Fourier transform ip and found out that there are three versions:
DFT: apparently useful for any resolution
FFT: power of 2 resolution, i.e. subset of DFT
LTE_FFT: looks like subset of FFT as I see equal resource for same configuration
If I am right then may I ask why LTE_FFT is made a subset. Can't we just configure FFT for that.
Thanks
Kaz
According to https://www.xilinx.com/products/intellectual-prope... LTE fourier transforms include one length which is non-power-of-2 (specifically a 1536 point DFT). That specific transform will have been carefully factorised to optimise performance and/or size compared to a naive DFT of 1536 points.
Thanks for that Martin but I noticed the same option for 1536 is available with fft ip setup.
Moreover I assume they could have done one ip for DFT and fft and lte configured as required.
I just was worried I may have missed something especially regarding matlab model for testing for example.
Ahh, I see what you mean.. In that case, it's probably just a hangover from when the FFT only did powers of 2?
As says The LTE FFT contains this 1536, which adds a radix-3 stage in the FFT. If you want to be able to change dynamically the FFT size you will have to include this radix-3 stage whenever you will use it or not.
The standard FFT IP is JUST for 2^N FFT length, the 1536 (3x512) is not possible in this IP. Some of my customers prefer to use a 2048 FFT size and then an interpolation to recompute the 1536 bins.
