OFDM Demodulator Baseband
Demodulate orthogonal frequency division modulated data
Library
OFDM, in Digital Baseband sublibrary of Modulation
Description
The Orthogonal Frequency Division Modulation (OFDM) Demodulator Baseband block demodulates an OFDM input signal. The block accepts a single input and has one or two output ports, depending on the status of Pilot output port.
Signal Dimensions
| Pilot Output Port | Pilot Carrier Indices | Signal Input | Signal Output | Pilot Output |
|---|---|---|---|---|
| false | N/A | NCPTotal+NFFT×Nsym-by-Nr | Ndata-by-Nsym-by-Nr | N/A |
| true | 2-D | Npilot-by-Nsym-by-Nr | ||
| 3-D | Npilot-by-Nsym-by-Nt-by-Nr |
where
NCP represents the cyclic prefix length as determined by Cyclic prefix length.
NCPTotal represents the cyclic prefix length over all the symbols. When NCP is a scalar, NCPTotal = NCP × Nsym. When NCP is a row vector, NCPTotal = ∑ NCP.
NFFT represents the number of subcarriers as determined by FFT length.
Nsym represents the number of symbols as determined by Number of OFDM symbols.
Nr represents the number of receive antennas as determined by Number of receive antennas.
Ndata represents the number of data subcarriers. For further information on how Ndata is determined, see the
inforeference page.Npilot represents the number of pilot symbols determined by the second dimension in the Pilot subcarrier indices array.
Nt represents the number of transmit antennas. This parameter is derived from the third dimension of the Pilot subcarrier indices array.
Parameters
- FFT Length
Specify the FFT length, which is equivalent to the number of subcarriers. The length of the FFT, NFFT, must be greater than or equal to 8.
- Number of guard bands
Assign the number of subcarriers to the left, NleftG, and right, NrightG, guard bands. The input is a 2-by-1 vector. The number of subcarriers must fall within [0,NFFT/2 − 1].
- Remove DC carrier
Select to remove the DC subcarrier.
- Pilot output port
Select to separate the data from the pilot signal and output the demodulated pilot signal.
- Pilot subcarrier indices
Specify the pilot subcarrier indices. This field is available only when the Pilot output port check box is selected. You can assign the indices can be assigned 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 from 1 to 3. Valid pilot indices fall in the range
where the index value cannot exceed the number of subcarriers. If the number of transmit antennas is greater than one, ensure that the indices per symbol are mutually distinct across antennas to minimize interference.
- Cyclic prefix length
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 Nsym, the prefix length can vary across symbols but remains the same length through all antennas.
- Number of OFDM symbols
Specify the number of OFDM symbols, Nsym, in the time-frequency grid.
- Number of receive antennas
Specify the number of receive antennas, Nr, as a positive integer such that Nr ≤ 64.
- Simulate using
Select the simulation type from these choices:
Code generationInterpreted execution
Algorithms
This block implements the algorithm, inputs, and outputs described in the OFDM Demodulator System object reference page. The object properties
correspond to the block parameters.
Supported Data Types
| Port | Supported Data Types |
|---|---|
Input |
|
Pilot (optional) |
|
Output |
|
Pair Block
References
[1] Dahlman, E., S. Parkvall, and J. Skold. 4G LTE/LTE-Advanced 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.