QPSK signal generation

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QPSK modulator varies phase
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
In-phase component of the carrier has phase 0°.

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

Four phases of QPSK symbols
Phase shifts of the four constellation points: 45°, 135°, 225°, and 315°

Start

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

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QPSK signal generation

Exercise

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


Bit sequence 1101001110
Bit sequence 1101001110
Transmit signal for this bit sequence.

Next steps

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

QPSK symbol transitions
All symbol transitions are possible.
QPSK inphase and quadrature signals
I/Q Signals of quadrature modulation. Adding in-phase (blue) and quadrature (red) components yields the transmit-signal (black).


1. The bit sequence on the left shall be QPSK modulated. Assign the corresponding transmission signal on the right per drag & drop!
The figure below is the in-phase component of the carrier.