User`s guide

IFFT
5-232
5IFFT
Purpose Compute the IFFT of the input.
Library Transforms
Description The IFFT block computes the inverse fast Fourier transform (IFFT) of each
channel in the M-by-N or length-M input, u, where M must be a power of two.
To work with other input sizes, use the Zero Pad block to pad or truncate the
length-M dimension to a power-of-two length. The output is always
frame-based, and each output column contains the M-point inverse discrete
Fourier transform (IDFT) of the corresponding input channel.
y = ifft(u,M) % Equivalent MATLAB code
The kth entry of the lth output channel, y(k, l), is the kth point of the M-point
IDFT of the lth input channel.
(5-3)
You can choose to output a scaled version of the input’s IDFT, , by
setting the parameter
Skip normalization by transform length, N.
(5-4)
For information on block output characteristics and how to configure the block
computation methods, see the following sections:
•“Input and Output Characteristics” on page 5-233
•“Conjugate Symmetric Input” on page 5-235
•“Inputs in Bit-Reversed Order” on page 5-236
•“Selecting the Twiddle Factor Computation Method” on page 5-236
•“Optimizing the Table of Trigonometric Values” on page 5-236
•“Algorithms Used for IFFT Computation” on page 5-236
•“Example” on page 5-237
ykl,()
1
M
-----
uml,()e
j2π m 1–()k 1–()M⁄
m 1=
M
∑
= k 1 … M,,=
Mykl,()⋅
Mykl,()⋅ uml,()e
j2π m 1–()k 1–()M⁄
m 1=
M
∑
= k 1 … M,,=