Modulate using orthogonal frequency division modulation
OFDM, in Digital Baseband sublibrary of Modulation
The OFDM Modulator Baseband block applies OFDM modulation to an incoming data signal. The block accepts one or two inputs depending on the state of the Pilot input port.
Pilot Input Port  Signal Input  Pilot Input  Signal Output 

false  N_{data}byN_{sym}byN_{t}  N/A  N_{CPTotal}+N_{FFT}×N_{sym}byN_{t} 
true  N_{pilot}byN_{sym}byN_{t} 
where
N_{data} represents the number of data subcarriers.
For further information on how N_{data} is determined,
see the info
reference page.
N_{sym} represents the number of symbols determined by Number of OFDM symbols.
N_{t} represents the number of transmit antennas determined by Number of transmit antennas.
N_{pilot} represents the number of pilot symbols determined by the first dimension size in the Pilot subcarrier indices array.
N_{CP} represents the cyclic prefix length as determined by Cyclic prefix length.
N_{CPTotal} represents the cyclic prefix length over all the symbols. When N_{CP} is a scalar, N_{CPTotal} = N_{CP} × N_{sym}. When N_{CP} is a row vector, N_{CPTotal} = ∑ N_{CP}.
N_{FFT} represents the number of subcarriers as determined by FFT length.
Specify the FFT length, which is equivalent to the number of subcarriers. The length of the FFT, N_{FFT}, must be greater than or equal to 8.
Assign the number of subcarriers to the left and right guard bands. The input is a 2by1 vector. The number of subcarriers must fall within [0,N_{FFT}/2 − 1].
Select to insert a null on the DC subcarrier.
Select to allow the specifying of pilot subcarrier indices.
Specify the pilot subcarrier indices. This field is available only when the Pilot input port check box is selected. You can assign the indices to the same or different subcarriers for each symbol. Similarly, the pilot carrier indices can differ across multiple transmit antennas. Depending on the desired level of control for index assignments, the dimensions of the indices array vary. Valid pilot indices fall in the range
$$\left[{\text{N}}_{\text{leftG}}+1,\text{\hspace{0.17em}}{\text{N}}_{\text{FFT}}/2\right]\cup \left[{\text{N}}_{\text{FFT}}/2+2,\text{\hspace{0.17em}}{\text{N}}_{\text{FFT}}{\text{N}}_{\text{rightG}}\right],$$
where the index value cannot exceed the number of
subcarriers. When the pilot indices are the same for every symbol and
transmit antenna, the property has dimensions
N_{pilot}by1. When the pilot indices vary across
symbols, the property has dimensions of
N_{pilot}byN_{sym}. If there
is only one symbol but multiple transmit antennas, the property has
dimensions of
N_{pilot}by1byN_{t}. If the
indices vary across the number of symbols and transmit antennas, the
property will have dimensions of
N_{pilot}byN_{sym}byN_{t}.
If the number of transmit antennas is greater than one, ensure that the
indices per symbol are mutually distinct across antennas to minimize
interference. The default value is [12; 26; 40;
54]
.
Specify the length of the cyclic prefix. If you specify a scalar, the prefix length is the same for all symbols through all antennas. If you specify a row vector of length N_{sym}, the prefix length can vary across symbols but remains the same through all antennas.
Select to apply raised cosine windowing. Windowing is the process in which the OFDM symbol is multiplied by a raised cosine window before transmission to reduce the power of outofband subcarriers, which serves to reduce spectral regrowth.
Set the length of the raised cosine window. The field is available only
when Apply raised cosine windowing between OFDM symbols
is selected. Use positive integers having a maximum value no greater than
the minimum cyclic prefix length. For example, in a configuration in which
there are four symbols with cyclic prefix lengths of [12 16 14
18]
, the window length cannot exceed 12.
Specify the number of OFDM symbols in the timefrequency grid.
Specify the number of transmit antennas, N_{t}, as a positive integer such that N_{t} ≤ 64.
Select the simulation type from these choices:
Code generation
Interpreted execution
This block implements the algorithm, inputs, and outputs described in the OFDM Modulator
System object reference page. The object properties
correspond to the block parameters.
Port  Supported Data Types 

Input 

Pilot (optional) 

Output 

[1] Dahlman, E., S. Parkvall, and J. Skold. 4G LTE/LTEAdvanced for Mobile Broadband.London: Elsevier Ltd., 2011.
[2] Andrews, J. G., A. Ghosh, and R. Muhamed. Fundamentals of WiMAX.Upper Saddle River, NJ: Prentice Hall, 2007.