自适应调制根据瞬时信道信噪比选择适当的调制方式，能够改善系统的BER性能以及平均吞吐量性能。在常用于高速移动环境的六径瑞利衰落信道模型下，研究自适应调制系统的最佳信噪比门限值，使系统的平均吞吐量最大，同时保证了目标BER性能，得到的最佳门限值可以用于ITU-R M1225 Vehicular Test A模型的自适应调制系统。

Adaptive modulation techniques can improve the BER (bit error rate) performance or the average throughput by employing a suitable modulation mode depending on the instantaneous channel SNR (signal-to-noise ridio). In this paper the optimum SNR thresholds over a 6-path Rayleigh channel are derived, which shows a superior BPS (bit per symbol) throughput performance while maintaining the target average BER. The 6-path Rayleigh channel is often applied to mobile environment with high-speed. The results achieved in this paper can be applied to the adaptive modulation system with the channel of ITU-R M. 1225 Vehicular Test A mode.