Why variable sub carrier spacing is introduced in 5G NR?

Question

As far as i see, 15Khz is the minimum we come across in LTE, is it same in 5G?

If it is less than 15Khz then how do they maintain orthogonal property as indicated in LTE?

Answer 1

15khz , 30Khz, 60khz are 3 carriers spacing only I know for 5Mhz , 10 MHz and 20 MHz using in FDD or TDD, but for TDD we can go up until 80MHZ ,160Mhz and 500 MHZ of bandwith ex 28Ghz using 120khz , 480khz and 9600 Khz of carrier spacing.

Answer 2

For low latency I can say for this yes.
IF you have many bandwith you will have for each one a number of RB(-10% from CP) //// . Group < 60 RB will correspond at 7 or 14 OFDM Symboles in 1 slot. Group >60RB will correspond at 14 OFDM symbols in 1 slot .

Answer 3

In high frequency like 28GHz, you must apply large sub carrier spacing.
Frequency error would be larger at high frequency, since crystal oscillator's clock error rate would not changed (ex. 0.5ppm).
So in high frequency, frequency error would larger than low frequency.
Then you need more large sub carrier spacing to tolerate large frequency error, otherwise it would cause deadly effect to sub carrier interference.

Answer 4

To facilitate mixed numerologies and low latency operations, 5G have variable carrier spacing in 5G NR.