# Qpsk pdf

**Keywords:** qpsk pdf

**Description:** The transmitted data points are taken from the signal space constellation below. The four points are equally spaced on a circle with radius A and are simply the four possible ordered pairs [

The transmitted data points are taken from the signal space constellation below. The four points are equally spaced on a circle with radius A and are simply the four possible ordered pairs [ ±A/sqrt(2), ± A/sqrt(2) ]. Each transmitted signal carries two information bits, as shown below.

After being corrupted by noise, the received signal is demodulated by the system below, which detects the transmitted signal space points and outputs the estimated values of the transmitted bits.

Using blocks from the SIMULINK Block Library, the Signal Processing Blockset, and the Communications Blockset, design a QPSK modulator, patterned after the one shown above, to meet the following specifications:

For the purposes of your design, you can omit the bit sequence and the look-up tables (LUTs), and just use two "Signal From Workspace" blocks as inputs to the system.

Using blocks from the SIMULINK Block Library, the Signal Processing Blockset, and the Communications Blockset, design a QPSK detector, patterned after the one shown above, that is compatible with the modulator from Part I. In your implementation, you might find it eaiser to output the signal space projections to the Matlab workspace and implement the decision logic in a post-processing fashion using a Matlab script.

You can test your designs from Parts I and II by connecting the output of your modulator to the input of your detector. Use the same data source as in the Binary PAM exercise (the Signal from Workspace block), except that you need separate sources for each arm in the modulator. Set the input to these sources such that you modulate the symbol pattern [00 01 10 11]'). In your project window, go to the menu Simulation --> Configuration Parameters and set the parameters to:

Note: The 4 corresponds to the number of transmitted symbols, the 12 corresponds to the combined delay of the modulator pulse and the detector matched filter, the 1 corresponds to the delay of the downsample operation in the detector, and the 8 is the number of samples per symbol.

Remember, it is very important that your Downsample block is sampling at the correct "phase". This may require some adjustment/experimentation on your part. You want to sample the matched filter outputs when the magnitude of the value is at a maximum. When you have successfully debugged your system, you are ready for the final part of the exercise.