16 QAM and 8DPSK (8PSK) are two different modulation schemes used in digital communication systems. Here are some key differences between the two:

1. Constellation Diagrams: 16 QAM uses a constellation diagram with 16 points, while 8DPSK uses a constellation diagram with 8 points. This means that 16 QAM is capable of transmitting 4 bits of information per symbol, while 8DPSK is capable of transmitting 3 bits of information per symbol.
2. Spectral Efficiency: Due to its higher number of points on the constellation diagram, 16 QAM is more spectral efficient than 8DPSK. This means that 16 QAM can transmit more information per unit of bandwidth compared to 8DPSK.
3. Robustness: 8DPSK is generally more robust than 16 QAM in noisy environments because it uses fewer points on the constellation diagram. This means that it is less susceptible to errors caused by noise and interference.
4. Implementation Complexity: 16 QAM is more complex to implement than 8DPSK due to its higher number of points on the constellation diagram. This means that 16 QAM requires more processing power and more complex hardware than 8DPSK.
5. Applications: 16 QAM is commonly used in high-speed data transmission applications such as cable modems, digital subscriber line (DSL) modems, and wireless local area networks (WLANs). 8DPSK, on the other hand, is commonly used in satellite communications, mobile phones, and digital audio broadcasting.

In summary, while both 16 QAM and 8DPSK are commonly used in digital communication systems, they differ in terms of their constellation diagrams, spectral efficiency, robustness, implementation complexity, and applications. The choice of which modulation scheme to use depends on the specific requirements of the application.