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Sampling and FFT Size derivation in LTE


Sampling and FFT Size derivation in LTE
















Ts = 1 / (15000 x 2048) seconds, which
corresponds to the 30.72 MHz sample clock for the 2048 point FFT used with the 20 MHz system bandwidth.

In the frequency domain, the number of sub-carriers N ranges from 128 to 2048, depending on channel bandwidth with 512 and 1024 for 5 and 10 MHz, respectively, being most commonly used in practice.

The sub-carrier spacing is ∆f = 1/T u = 15 kHz.
The sampling rate is fs = ∆f · N = 15000 N.
This results in a sampling rate that’s multiple or sub-multiple of the WCDMA chip rate of 3.84 Mcps: LTE parameters have been chosen such that FFT lengths and sampling rates are easily obtained for all operation modes while at the same time ensuring the easy implementation of dual-mode devices with a common clock reference.

Sampling frequency is Multiple's of 2,

For 15 Mhz Bandwidth -
Sampling Frequency = 23.04 (6 * 3.84).
FFT SIZE = Sampling Freq / 15k.
23.04MHz/15k = 1,536
so FFT size is 1,536 = 901 (Used subcarriers including DC subcarriers) + 635 (Guard subcarriers)

References -



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