QPSK: Advantages and Disadvantages

This page covers the pros and cons of the QPSK (Quadrature Phase Shift Keying) modulation technique. It highlights the benefits and drawbacks of QPSK.

What is QPSK?

Introduction:

QPSK stands for Quadrature Phase Shift Keying. It’s a digital modulation technique where two binary bits are represented by a change in the carrier phase of 90 degrees relative to adjacent constellation points. The maximum phase transition between two constellations is 180 degrees. This is visualized in the constellation diagram shown below.

In QPSK, each carrier carries two bits, making the symbol rate half of the bit rate. QPSK is known for being bandwidth-efficient but not power-efficient.

Advantages of QPSK

Here are the key benefits of using QPSK modulation:

• Increased Bandwidth Efficiency: QPSK carries two bits on a single analog carrier. This makes it twice as bandwidth-efficient compared to BPSK modulation. The symbol rate is half of the raw bit rate.
• Bandwidth Efficient: As mentioned above, QPSK is a bandwidth efficient modulation technique because a single carrier transmits two bits.

Disadvantages of QPSK

Here are the main drawbacks of QPSK:

• Receiver Complexity: In QPSK, each complex symbol represents two binary bits. This increases the complexity of the QPSK receiver compared to a BPSK receiver because it needs to distinguish between four states to recover the binary data.
• Lower Power Efficiency: Due to the increased complexity, QPSK is not as power-efficient as other modulation techniques. More power is required to transmit two bits simultaneously.