QPSK signal generation - labAlive experiment (2024)

Quadrature phase-shift keying (QPSK) modulator varies the signal's phase to transmit information.

At first let us appoint the in-phase component of the carrier as phase reference.

In-phase component of the carrier has phase 0°.

Each QPSK symbol assigns a specific phase shift to the carrier wave.

Phase shifts of the four constellation points: 45°, 135°, 225°, and 315°

Start

Now let's generate a QPSK signal from a bit sequence.

• Two bits are mapped to a symbol.
• The symbol specifies a phase shift that is imposed on the carrier. For the symbol duration the phase shifted carrier signal is transmitted.

QPSK signal generation

Exercise

Now it's your turn! Work out the transmit signal for this bit sequence.

Next steps

• Switch to random bit sequence and see the generated QPSK signal.
• Note that for the signals shown above the carrier frequency has been selected in a way that it fits nicely to the symbol duration. Now change the carrier frequency to any arbitrary value.

All symbol transitions are possible.

I/Q Signals of quadrature modulation. Adding in-phase (blue) and quadrature (red) components yields the transmit-signal (black).