MATLAB Code for BPSK, QPSK, 8-PSK, 16-PSK, 32-PSK
Output
16-PSK
MATLAB Code for BER vs SNR for BPSK, QPSK, 8-PSK, 16-PSK, 32-PSK
Real-World Applications of PSK Modulation
M-ary PSK modulation is widely used in modern telecommunications:
- BPSK: Used in deep-space telemetry and low-cost passive RFID tags.
- QPSK: The backbone of Satellite Television (DVB-S), cable modems, and 4G LTE control channels.
- 8-PSK: Commonly used in the EDGE cellular network and aircraft communication systems.
- Higher Order PSK: Used in high-speed optical fiber communications where SNR is strictly controlled.
Why are Constellation Diagrams Important?
To understand any digital modulation scheme, constellation diagrams are extremely important because they visually represent how signals vary in amplitude and phase. In the case of Phase Shift Keying (PSK), the signal amplitude remains constant while only the phase changes.
Communication engineers often analyze the distances between constellation points to evaluate the performance and efficiency of a modulation scheme. The minimum distance between constellation points directly affects the error performance of the system. For example, it is well known that PSK can provide approximately a 3 dB SNR advantage over FSK under certain conditions. This performance difference originates from the separation between constellation points and the corresponding Euclidean distance in the signal space.
Similarly, constellation point spacing plays a critical role in the performance of M-ary PSK modulation schemes. When the signal-to-noise ratio (SNR) is high, higher-order M-PSK schemes can be used to achieve greater spectral efficiency and higher data rates. However, as the modulation order increases, the angular separation between adjacent constellation points decreases, making the system more susceptible to noise and phase errors.
Therefore, in low-SNR environments, lower-order modulation schemes such as BPSK are generally preferred because their constellation points are more widely separated, resulting in better bit error rate (BER) performance and improved reliability. You can try the interactive online (web based) simulations below to understand how constellation diagram works.
Try Interactive Online Simulators
Comparison of M-PSK Modulation Schemes
| Modulation | M (Symbols) | Bits per Symbol | Noise Immunity |
|---|---|---|---|
| BPSK | 2 | 1 | Highest |
| QPSK | 4 | 2 | High |
| 8-PSK | 8 | 3 | Medium |
| 16-PSK | 16 | 4 | Low |
Theoretical Bit Error Rate (BER) for m-ary PSK
For M-PSK in an AWGN channel, the symbol error probability P_s can be approximated for high SNR as:
Ps ≈ 2Q( √(2Es/N0) sin(ฯ/M) )
Where Es/N0 is the energy-to-noise density ratio and M is the modulation order.
Read More about BER vs SNR for m-ary PSK and QAM
Why Is QPSK an Important Modulation Scheme?
Quadrature Phase Shift Keying (QPSK) is an important digital modulation technique because it can transmit twice the data rate of Binary Phase Shift Keying (BPSK) while maintaining nearly the same bit error rate (BER) performance at low signal-to-noise ratio (SNR) levels when Gray coding is employed.
Compared with higher-order modulation schemes, QPSK offers a good balance between data rate, spectral efficiency, and reliability. Its spectral efficiency is comparable to that of 4-QAM and, under low-SNR conditions, it can outperform higher-order schemes such as 16-QAM in terms of robustness. In highly noisy communication channels, QPSK may even provide better overall spectral efficiency than 4-QAM or 16-QAM due to its lower error susceptibility.
As a result, QPSK is widely used in practical wireless communication systems and is often combined with QAM-based modulation techniques in adaptive modulation schemes, where the modulation order is dynamically adjusted according to channel conditions.
Frequently Asked Questions
Q1: Why does the constellation plot look blurry at low SNR?
A: At low SNR, the noise power is high, causing the received symbols to deviate significantly from their ideal positions.Q2: Can I use this code for M=64?
A: Yes, thepskmod function supports any power of 2 for M, but note that 64-PSK is rarely used in practice because QAM is more efficient for such high orders.