Abstract: Aiming at the parallel transmission in frequency domain of OFDM and high complexity of modeling the cross-layer design as well as the low frequency spectrum efficiency for AMC/ARQ cross-layer design，a model with bidirectional feedback based on finite-state-Markov-model（FSMM） is set up，where the AMC parameters is mapped to the ARQ by evaluation of the FSMM and the parameters of the ARQ is mapped to the AMC by computation of the delay and the packet loss ratio.This model can not only dealt with the interaction between the AMC and ARQ but also overcome the high complexity resulted by the embed Markov link.An optimal algorithm of this model for the biggest spectrum efficiency under the specified QOS is proposed，which gets the optimal threshold by exhaustive search.The simulation show that the spectrum efficiency of the optimized cross-layer design outperforms the old one.

Key words: cross-layer combining AMC with H-ARQ, FSMM of the frequency subchannel of OFDM, throughput, frame error ratio, spectrum efficiency, optimization method

摘要： 针对OFDM频域并行传输及时、频二维资源分配特点和AMC/ARQ跨层设计存在的建模复杂、频谱效率低等问题，基于OFDM频域子信道FSMM模型，建立了AMC/ARQ双向反馈模型，通过时延、丢包率等参数将ARQ参数传递到AMC，通过对FSMM性能评估，将AMC参数反馈到ARQ，，既充分考虑了AMC/ARQ间的相互作用，又避免了内嵌MARKOV链导致的计算复杂性。给出了该跨层设计的优化算法，通过穷尽搜索获得最优的FSMM门限，在保证QOS参数的条件下，使频谱效率达到最优。仿真计算证明优化后的AMC/ARQ跨层设计系统频谱效率有较大提高。

关键词: AMC/ARQ跨层设计, OFDM频域子信道FSMM, 通过率, 误帧率, 频谱效率, 优化方法