DEMO_OFDM Demo of Gabor systems used for OFDM
This demo shows how to use a Gabor Riesz basis for OFDM.
We want to transmit a signal consisting of 0's and 1's through a
noisy communication channel. This is accomplished in the following
steps in the demo:
1) Convert this digital signal into complex valued coefficients by
QAM modulation.
2) Construct the signal to be transmitted by an inverse Gabor
transform of the complex coefficients
3) "Transmit" the signal by applying a spreading operator to the
signal and adding white noise
4) Convert the received signal into noisy coefficients by a Gabor
transform
5) Convert the noisy coefficients into bits by inverse QAM.
Some simplifications used to make this demo simple:
We assume that the whole spectrum is available for transmission.
The window and its dual have full length support. This is not
practical, because all data would have to be processed at once.
Instead, an FIR should be used, with both the window and its dual
having a short length.
The window is periodic. The data at the very end interferes with
the data at the very beginning. A simple way to solve this is to
transmit zeros at the beginning and at the end, to flush the system
properly.
Figure 1: Received coefficients.
This figure shows the distribution in the complex plane of the
received coefficients. If the channel was perfect, all the points
should appear at the complex roots of unity (1,i,-1 and -i). This
demo is random, so everytime it is run it produces a new plot, and
the error rate may vary.
Package: ltfat