MATLAB: Implementing QPSK modulation and Demodulation

Question

I have implemented QPSK modulation and demodulation system but does not give the 4 constellation points from the qpsk modulator block. The output is displayed on to discrete-time scatter plot scope and shows only 2 constellation points when I run the simulation. I have used Bernoulli binary generator for ease of analyzing and to generate a 2stage square wave.

Answer 1

The Bernoulli generator block is only going to generate a square wave with a value of 0 or 1. This explains why you are only seeing two constellation points at the output of the QPSK modulator. For QPSK, you want to have a message signal with possible values of 0, 1, 2 or 3 as an input to the QPSK modulator block. The Random Integer Generator block should do what you're looking for.

Or, you could still use the Bernoulli generator block with the output set to 2 samples per frame, and configure the QPSK modulator block to accept Bit input instead of Integer input.