QPSK vs. 8-PSK: A Comparative Analysis of Modulation Techniques

modulation
qpsk
8-psk
digital communication
phase shift keying

QPSK and 8-PSK are both phase shift keying (PSK) modulation techniques. They encode data by varying the phase of a carrier signal. Both transmit multiple bits per symbol (2 bits for QPSK, 3 bits for 8-PSK), improving data rates over basic binary modulation schemes.

QPSK Modulation

QPSK (Quadrature Phase Shift Keying) is a digital modulation technique that encodes data by shifting the phase of a carrier signal among four distinct values: 0°, 90°, 180°, and 270°. Each phase shift represents a unique pair of bits (00, 01, 10, 11), allowing QPSK to transmit two bits per symbol. This modulation type balances bandwidth efficiency and signal robustness, making it more resistant to noise and signal degradation than higher-order PSK modulations.

QPSK

QPSK is commonly used in applications like satellite communications, Wi-Fi, and cellular networks, where moderate data rates and reliable performance are required.

8-PSK Modulation

8-PSK is an advanced form of PSK that increases the number of phase shifts to eight, spaced 45° apart (e.g., 0°, 45°, 90°, 135°, 180°, 225°, 270°, 315°). Each phase shift corresponds to a unique 3-bit combination (000 to 111), enabling 8-PSK to transmit three bits per symbol. This increase in bits per symbol provides higher data rates compared to QPSK. However, the closer spacing of phase states makes 8-PSK more susceptible to noise and phase errors, requiring a cleaner signal and higher signal-to-noise ratio for reliable performance.

8 psk

8-PSK is used in scenarios that prioritize data rate over robustness, such as digital broadcasting and some wireless communication systems.

Difference between QPSK and 8-PSK modulation

ParameterQPSK8-PSK
Full formQuadrature Phase Shift Keying8 Level Phase Shift Keying
Modulation techniqueUses 4 distinct phase states to represent dataUses 8 distinct phase states to represent data
Bits per symbol2 bits per symbol (00,01,10,11)3 bits per symbol (000, 001, 010, 011, 100, 101, 110, 111)
Constellation points4 constellation points , each 90 degrees apart8 constellation points , each 45 degrees apart
Data rateModerate data rate, lower compared to 8-PSK for the same symbol rateHigher data rate due to encoding more bits per symbol
Bandwidth efficiencyModerateHigher than QPSK due to more bits per symbol.
Signal robustnessMore robust against noise and phase errors due to wider phase separationLess robust againt noise; smaller phase separation makes it more error prone.
Error probabilityLower error probability due to fewer phase statesHigher error probability; more closely spaced phase states are more susceptible to errors.
Power efficiencyMore power-efficient; requires less signal power for the same error rate.Less power-efficient; requires higher signal power to maintain the same error rate.
ComplexitySimpler modulation and demodulation.More complex due to more phase states and tighter phase separation.
Spectral efficiencyModerate spectral efficiency; suitable for balanced data rate and robustness.Higher spectral efficiency, useful for maximizing data throughput in limited bandwidth.
ImplementationEasier to implement and less demanding on receiver design.More complex receiver design needed to distinguish closely spaced phases.
Common applicationsUsed in systems requiring moderate data rates and robustness (e.g., satellite, Wi-Fi).Used in systems needing higher data rates where bandwidth is limited (e.g., digital TV, GSM).

Conclusion

  • QPSK is generally preferred when robustness, simplicity, and power efficiency are crucial. It provides a good balance of data rate and error performance, making it suitable for a wide range of communication systems where moderate data rates and reliable transmission are needed.
  • 8-PSK offers higher data rates and better bandwidth efficiency by using more phase states. However, it is less robust to noise and requires more signal power to maintain performance, making it more suitable for applications where bandwidth efficiency is critical, and conditions are favorable for higher error performance.
PSK Advantages and Disadvantages: Phase Shift Keying

PSK Advantages and Disadvantages: Phase Shift Keying

Explore the pros and cons of Phase Shift Keying (PSK), a digital modulation technique, including bandwidth efficiency, error susceptibility, and implementation complexity.

modulation
psk
digital communication
QPSK: Advantages and Disadvantages

QPSK: Advantages and Disadvantages

Explore the pros and cons of QPSK modulation, including bandwidth efficiency and receiver complexity. Learn about the benefits and drawbacks of QPSK.

modulation
digital communication
qpsk