WARPLab 7 Example: SISO OFDM

File: wl_example_siso_ofdm_txrx.m​

This WARPLab example implements a SISO OFDM transmitter and receiver.

Transmitter

The OFDM transmitter code implements the following functions:

• Random data generation
• Modulation of random data to complex constellation symbols
• Mapping of symbols to data-bearing subcarriers
• Insertion of pilot tones in pilot subcarriers
• Inverse fast Fourier transform (IFFT)
• Cyclic prefix insertion
• Preamble construction and insertion
• Interpolation by 2x

Receiver

The OFDM receiver code implements the following functions:

• LTS correlation for synchronization
• CFO estimation and correcting use time-domain estimation from LTS
• Cyclic prefix removal
• Fast Fourier transform (FFT)
• Channel estimation from frequency-domain LTS
• Residual phase error estimation from frequency-domain pilot tones
• Equalization of data-bearing subcarriers using channel estimates and phase error estimates
• Demodulation of complex symbols to data values

Running the Example

The WARPLab OFDM example can be used in simulation only mode and in hardware-in-the-loop mode.

Simulation

To use the example in simulation mode set the top-level param USE_WARPLAB_TXRX = 0;, then run the m-script. When the script finishes 6 plots will show:

Transmitted waveform	Received waveform	Preamble correlation results (peaks indicate locations of preamble LTS)
Channel estimate per subcarrier (I/Q components and complex magnitude)	Phase error per OFDM symbol based on pilot tones	Tx and Rx constellations

Limitations

This example is intended as a staring point for researchers wishing to use WARPLab to prototype a wireless communications link. This examples does not implement some some blocks common in deployed OFDM systems, such as scrambling, interleaving and error correcting coding. For an example of a real-time OFDM implementation that implements all of these subsystems, please see the PHY in the 802.11 Reference Design.