Abstract: This paper is based on the MIMO-OFDM system module.First the singular value decomposition for ideal channel transformation matrix is done，and the eigenvalues of channel matrix is used to transform the spatial multiplexing channel into parallel subchannels in subchannel adaptive modulation design.Then the multi-carriers adaptive bit allocation algorithm is applied to MIMO-OFDM system.With the principle of minimizing the sending power and reducing the system complexity，a optimized various-step subchannel bit allocation algorithm is proposed.The simulation shows that not only can this algorithm have a performance close to the Campello method，but also reduce the calculation complexity.

Key words: MIMO-OFDM, adaptive modulation, bit allocation

摘要： 从MIMO-OFDM系统模型出发，首先对理想信道传输矩阵进行奇异值分解，在子信道自适应调制设计中应用信道矩阵特征值把空分复用信道转化为并行子信道，将用于多载波自适应比特分配算法应用于MIMO-OFDM系统。然后以实现系统发射功率最小为原则，以降低系统比特分配算法复杂度为目标，提出了一种可变步长的子信道比特分配优化算法。仿真结果表明，这种算法不但可以实现和Campello方法相当的比特分配性能，还可以较大地降低系统的计算复杂度。

关键词: MIMO-OFDM, 自适应调制, 比特分配