Why the sample rate in nrOFDMModulate seems not satisify Nyquist principle？

I use 'nrOFDMModulate' function to generate NR signal.

I use 264 RB, and it corresponds to 3168 (=264*12) subcarrier. 14 OFDM symbols corresponds to 0.125 ms.(0.125ms 120khz subcarrier).

According to one second, there are 354816000(3168*14*8*1000) data in resourcegrid while the default sample rate is 491520000(4096*120*1000).

And it seems that default sample rate (491520000) is not more than twice the the number of data (354816000)?

Anyone knows that when I do ADC with NR signal, should I do upsample with a upsameple = clock frequency/signal bandwidth?

Answer 1

[Abhijeet Singh]

Hi,

I understand that you are using 'nrOFDMModulate' to perform ADC with NR signals, but the default sample rate does not satisfy the Nyquist principle.

When performing ADC on an NR signal, the goal of upsampling is to meet or exceed the Nyquist rate, which is twice the bandwidth of the signal to prevent aliasing. The upsampling factor is not necessarily determined by the ratio of the clock frequency to the signal bandwidth. Instead, it should be chosen to bring the sampling rate up to at least the Nyquist rate for the signal's bandwidth.

Also, on closely inspecting the calculations shared by you the number 354816000(3168*14*8*1000) represents the count of data points in the resource grid per second, not the signal bandwidth. The signal bandwidth should be calculated as

.

The upsampling factor (U) can be calculated by dividing the desired sampling rate (which should be at least the Nyquist rate) by the current sampling rate. In this case, the Nyquist rate would be:

If the ADC's clock frequency is lower than the Nyquist rate, you need to determine the upsampling factor by comparing the ADC's sampling rate to the Nyquist rate. For example, if the ADC's sampling rate is the default rate of 491,520,000 samples/second, then the upsampling factor would be:

Since, you cannot upsample by a non-integer factor, you would typically round up to the nearest integer. In this case, you would upsample by a factor of 2 to ensure that the sampling rate after upsampling is at least the Nyquist rate.

Note: After upsampling, you may also need to apply a low-pass filter to remove any spectral images that result from the upsampling process and to ensure that the signal's bandwidth fits within the new sampling rate's Nyquist frequency.

I hope it helps !!

Thanks !!