OFDM Transmitter: Difference between revisions

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; FFT Length
; FFT Length
: The length of FFT (integer).
: The number of sub-carriers.


; Cyclic Prefix Length
; Cyclic Prefix Length
: The length of cyclic prefix in total samples (integer).
: The maximum possible length of multi-paths in their time dispersion


; Packet Length Tag Key
; Packet Length Tag Key
Line 16: Line 16:


; Occupied Carriers
; Occupied Carriers
: A vector of vectors describing which OFDM carriers are occupied.
: A vector of vectors describing which OFDM carriers are occupied with data symbols. occupied_carriers[0] identifies the carriers that are used for the first OFDM symbol, and so on.


; Pilot Carriers
; Pilot Carriers
Line 22: Line 22:


; Pilot Symbols
; Pilot Symbols
: The pilot symbols.
: A vector of vectors indicating the pilot symbols.


; Sync Word 1
; Sync Word 1
: The first sync preamble symbol. This has to be with zeros on alternating carriers. Used for fine and coarse frequency offset and timing estimation.
: The first sync preamble symbol. This has to be with zeros on alternating carriers (0., 1.536, 0., -1.536, 0., ...). Used for fine and coarse frequency offset and timing estimation. Length of sync sequence must be the same as the value of  FFT length. To not use a sync word, '''None''' can be entered as this parameter's value.


; Sync Word 2
; Sync Word 2
: The second sync preamble symbol. This has to be filled entirely. Also used for coarse frequency offset and channel estimation.
: The second sync preamble symbol. This has to be filled entirely. Also used for coarse frequency offset and channel estimation. Length of sync sequence must be the same as the value of  FFT length. To not use a sync word, '''None''' can be entered as this parameter's value.


; Header Modulation
; Header Modulation
:  
: It has two options:
:* BPSK (Binary Phase Shift Keying)
:* QPSK (Quadrature Phase Shift Keying)


; Payload Modulation
; Payload Modulation
:  
: It has three options:
:* BPSK (Binary Phase Shift Keying)
:* QPSK (Quadrature Phase Shift Keying)
:* 8-PSK (Eight Phase Shift Keying)


; Rolloff length (samples)
; Rolloff length (samples)
Line 47: Line 52:
== Example Flowgraph ==
== Example Flowgraph ==


Insert description of flowgraph here, then show a screenshot of the flowgraph and the output if there is an interesting GUI. Currently we have no standard method of uploading the actual flowgraph to the wiki or git repo, unfortunately. The plan is to have an example flowgraph showing how the block might be used, for every block, and the flowgraphs will live in the git repo.
This flowgraph can be found at https://github.com/gnuradio/gnuradio/blob/master/gr-digital/examples/ofdm/ofdm_loopback.grc
 
[[File:Ofdm_loopback_example_fg.png|807px]]


== Source Files ==
== Source Files ==


; Python files
; Python files
: [https://github.com/gnuradio/gnuradio/blob/master/gr-digital/python/digital/ofdm_txrx.py]
: [https://github.com/gnuradio/gnuradio/blob/main/gr-digital/python/digital/ofdm_txrx.py ofdm_txrx.py]


; Block definition
; Block definition
: [https://github.com/gnuradio/gnuradio/blob/master/gr-digital/grc/digital_ofdm_tx.block.yml]
: [https://github.com/gnuradio/gnuradio/blob/main/gr-digital/grc/digital_ofdm_tx.block.yml digital_ofdm_tx.block.yml]

Latest revision as of 13:22, 1 June 2022

Hierarchical block for OFDM modulation.

The input is a byte stream (unsigned char) and the output is the complex modulated signal at baseband.

Parameters

FFT Length
The number of sub-carriers.
Cyclic Prefix Length
The maximum possible length of multi-paths in their time dispersion
Packet Length Tag Key
The name of the tag giving packet length at the input.
Occupied Carriers
A vector of vectors describing which OFDM carriers are occupied with data symbols. occupied_carriers[0] identifies the carriers that are used for the first OFDM symbol, and so on.
Pilot Carriers
A vector of vectors describing which OFDM carriers are occupied with pilot symbols.
Pilot Symbols
A vector of vectors indicating the pilot symbols.
Sync Word 1
The first sync preamble symbol. This has to be with zeros on alternating carriers (0., 1.536, 0., -1.536, 0., ...). Used for fine and coarse frequency offset and timing estimation. Length of sync sequence must be the same as the value of FFT length. To not use a sync word, None can be entered as this parameter's value.
Sync Word 2
The second sync preamble symbol. This has to be filled entirely. Also used for coarse frequency offset and channel estimation. Length of sync sequence must be the same as the value of FFT length. To not use a sync word, None can be entered as this parameter's value.
Header Modulation
It has two options:
  • BPSK (Binary Phase Shift Keying)
  • QPSK (Quadrature Phase Shift Keying)
Payload Modulation
It has three options:
  • BPSK (Binary Phase Shift Keying)
  • QPSK (Quadrature Phase Shift Keying)
  • 8-PSK (Eight Phase Shift Keying)
Rolloff length (samples)
The rolloff length in samples. Must be smaller than the CP.
Scramble Bits
Activates the scramblers (set this to True unless debugging)
Log Debug Info
Write output into log files (Warning: creates lots of data!)

Example Flowgraph

This flowgraph can be found at https://github.com/gnuradio/gnuradio/blob/master/gr-digital/examples/ofdm/ofdm_loopback.grc

Ofdm loopback example fg.png

Source Files

Python files
ofdm_txrx.py
Block definition
digital_ofdm_tx.block.yml
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