基于摩尔状态机的LTE-R系统自适应调制编码方法

Adaptive modulation and coding method based on Moore state machine in LTE-R system

针对铁路长期演进(LTE-R)通信系统,开展自适应调制编码(AMC)研究。通过引入摩尔状态机(MSM)模型,提出一种AMC策略。根据LTE-R系统采用的调制和编码方式(MCS),设计MSM的有限状态集。针对不同调制方式,得到误码率(BER)与信噪比(SNR)的关系曲线。通过给定目标BER,获得不同调制方式对应的SNR阈值。在这些阈值基础上,通过加减一定的SNR常数,得到不同MCS对应的SNR阈值。同时,为了减少MCS在SNR阈值附近发生频繁切换,对SNR阈值设置上下界,得到MSM的状态转换SNR阈值区间。基于得到的SNR阈值上下界,设计MSM,实现MCS的动态调整。仿真结果显示,所提出的AMC方法比传统的基于分段函数的AMC方法具有更加稳定的频谱效率和吞吐量。此外,相比固定调制方式策略,提出的AMC方法具有更好的BER性能。

In this paper, the problem of Adaptive Modulation and Coding（ AMC） is investigated in the Long-Term Evolution for Railway（LTE-R） communication system. An AMC strategy is proposed by introducing the Moore State Machine（MSM） model. According to the Modulation and Coding Schemes（ MCS） adopted in the LTE-R system, the finite state set of the MSM is designed. Aiming at different modulation modes, the relationship between Bit Error Rate（ BER） and Signal-to-Noise Ratio（ SNR） is obtained. The SNR threshold of different modulation modes are derived by a given target BER. On the basis of these thresholds, the SNR thresholds corresponding to different MCS are achieved by plus and minus certain SNR constants. In order to overcome the frequent switching of the MCS in the vicinity of SNR threshold, the SNR threshold range of state transition is obtained by setting upper and lower bounds of SNR threshold. Based on SNR threshold bounds, the MSM is designed to dynamically adjust the MCS. The simulation results show that the AMC method presented in this paper has more stable spectrum efficiency and throughput than the traditional AMC method based on piecewise function. In addition, compared with the fixed modulation method, the proposed AMC method has better BER performance.