Fig. 1. QAM constellation diagram without carrier frequency offset and phase offset (SNR is 20 dB)

Fig. 2. Time-domain scatter plots of and for 16 QAM and 32 QAM (SNR is 20 dB)16 QAM和32 QAM的 与时域散点图（SNR 为 20 dB）

Fig. 3. Constellation diagrams of 16 QAM and 32 QAM with carrier frequency offset of 500 Hz or carrier phase offset of π/6 (SNR is 20 dB)

Fig. 4. Time-domain scatter plots of and for 16 QAM and 32 QAM with a carrier frequency offset of 500 Hz (SNR is 20 dB)载波频偏为500 Hz时16 QAM和32 QAM的与时域散点图（SNR 为 20 dB）

Fig. 5. Time-domain scatter plots of and for 16 QAM and 32 QAM with a carrier phase offset of π/6 (SNR is 20 dB)载波相偏为π/6时16 QAM和32 QAM的与时域散点图（SNR 为 20 dB）

Fig. 6. Network framework

Fig. 7. Computational process of multi-head attention mechanism

Fig. 8. Recognition rate without frequency offset and phase offset

Fig. 9. Recognition rate with frequency offset 500 Hz

Fig. 10. Recognition rate with phase shift π/6

Fig. 11. Confusion matrix on three datasets (SNR is 20 dB)

Fig. 12. Training and testing modulation classification accuracy and loss curves of three datasets (SNR is 20 dB)