# QPSK signal generation

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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.

 Bit sequence 1101001110 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.
 Bit sequence 0010001010 The QPSK signal is generated by phase-shifting the carrier. This applies for any carrier frequency.

All symbol transitions are possible.