Why Multilevel Modulation used with PSK?

Multilevel modulation is used with Phase Shift Keying (PSK) to enhance data transmission rates without requiring additional bandwidth. By encoding multiple bits of information in each symbol through different phase shifts, it allows for increased data throughput while maintaining the robustness of the PSK scheme. This approach effectively balances the trade-off between spectral efficiency and error performance, making it suitable for high-capacity communication systems. Additionally, it can improve the signal-to-noise ratio in challenging environments.