How to set FFT module so as to run OTFS.grc successfully.

[JackChen2023]

Hi, I emulated your OTFS file and I have some problems. First, I found that qam_mod could not run under GNUradio v3.10.7, so I replaced qam_mod with the constellation module, as shown in Figure 1. However, I found a problem with the first FFT block on the transmit side. I take the output of matrix_interleaver as the input of FFT, as shown in Figure 2. It can be seen that the output of the FFT is 0, as shown in Figure 3. Do you know the reason for this?

Fig 1

Fig 2

Fig 3

By the way, why don't you set the FFT size of the FFT block to 4 instead of 1?