中文摘要：

为了提高OFDM系统在平均信噪比较低条件下的系统性能，提出一种新的资源分配算法.首先将子载波数作为参变量优化系统容量，分析子载波选择对系统容量的影响，计算使系统容量最优的子载波数，并且考虑系统对误比特率的限制，确定子载波的选择准则.然后，在选定的子载波上进行自适应调制，通过信道容量的近似计算为各子载波初始分配比特数，能加快收敛速度，有效降低等功率OFDM系统资源分配算法的复杂度.仿真结果表明，在接收端获得完美和非完美信道增益信息条件下，所提出的资源分配算法都可提高自适应调制OFDM系统在低信噪比条件下的系统性能.

英文摘要：

A resource allocation algorithm is proposed to improve the frequency efficiency and computational efficiency of orthogonal frequency division multiplexing （OFDM） systems with low signal-to-noise ratios （SNR）. First, an analytical expression is derived for the capacity of adaptive modulation, and the capacity is maximized with respect to the number of subcarriers. For the case of the targeted bit err rate （BER）, the criterion of subcarrier selection scheme is deduced. Moreover, an adaptive modulation scheme with low computational complexity is proposed. Owing to initializing the modulation schemes of all the subcarriers by approximate capacity calculation, the scheme effectively improves convergence velocity. Simulation results show that the proposed resource allocation algorithm can provide improvement for the adaptive OFDM systems with perfect or imperfect channel state information.