LTE: What is sampling frequency and use of it ?

Question

What is the Ultra extended CP and use of it ?
How it is better than normal cyclic and extended cyclic prefix ?

Answer 1

I think it is very generic question. Sampling frequency is "No of samples taken for a certain period of time(usually in seconds) to generate discrete signal from continuous signal.

To cover 20Mhz in LTE, Sampling frequency is (15Khz * 2048 time samples from IFFT).

Answer 2

The actual FFT size and sampling frequency for the LTE downlink are not specified.
According to Nyquist criteria ,wecan take basband sampling frequency greater then or equal to twice of maximum frequency component( >= 2fm).
for 20MHz
baseband sampling frequency ( fs ) = sub carrier Spacing * 2048= 15 * 2048 = 30.72Mhz
This is itself chosen for backward compatibility with UMTS, for which the chip rate is 3.84 MHz – exactly one eighth of the assumed LTE sampling frequency.

for 5 Mhz
baseband sampling frequency ( fs ) = sub carrier Spacing * 2048= 15 * 512 = 7.68Mhz

Comments

For 5 MHz, Baseband sampling frequency ( fs ) = sub carrier Spacing * 512= 15 * 512 = 7.68Mhz. Note that the sampling size differs with total BW and it is chosen so that sampling size is adequately greater than number of subacarriers and resulting sampling freq. is a factor of 3.84 MHz (UMTS clock).