Abstract: A new iterative method is proposed to overcome vibration in adaptive power and bit loading algorithms for wireless OFDM systems. The method is introduced into rate adaptive (RA) algorithms aiming at maximization of data rate under the constraint of total transmit power and bit error rate. Then two improved RA algorithms, named water-filling RA (WF-RA) and equalpower RA (EP-RA) algorithm respectively, are proposed. Simulation results show the improved WF-RA algorithm has approximately the same throughput as the optimal solution and the improved EP-RA algorithm has a lower computational complexity compared to the previous ones. Finally, the performance degradation due to imperfect channel state information is discussed.

Key words: OFDM, adaptive modulation, water-filling

摘要： 自适应正交频分复用（OFDM）技术是根据各子载波在频率选择性衰落信道中不同的瞬时增益，动态地分配数据比特和发射功率，从而达到优化系统性能，提高频谱效率的目的。研究了发射总功率和系统误码率上限不变时传输比特数最大化（RA）的自适应算法。提出了一种有记忆迭代方法，能有效克服由于比特数的离散性导致的迭代发散现象，并据此提出两种改进的RA算法。仿真结果表明，和过去的RA算法相比，改进的功率注水RA算法以增加少量的迭代次数为代价，能获得接近于最佳RA算法的传输速率；而改进的等功率RA算法在相同传输速率情况下具有更低的运算复杂度。

关键词: 正交频分复用（OFDM）, 自适应调制, 注水原理