Robust Adaptive Coded Modulation for Time-Varying Channels

最近的研究表明，自适应信令在理论上有望大大提高在无线信道上运行的数字通信系统的带宽效率。然而，由于无线信道随时间的变化，导致数据传输时的信道与信道估计时的信道不同，自适应信令的效用受到质疑。PI最近的结果表明，这些问题不容忽视；信道变化极大地改变了问题的性质，因此无线信道的鲁棒自适应信令方案的设计与有线信道的类似设计问题提出了明显不同的挑战。由于发射机对信道衰落过程统计数据的不确定性，这些算法必须具有鲁棒性，这是许多挑战的驱动因素。在这个项目中，对时变信道的鲁棒自适应信令方案的设计进行了全面的研究。本研究的主要部分包括：(1)采用给定自适应信号范式的鲁棒算法的设计和表征；(2)开发适合时变信道的自适应编码范式；(3)开发自适应混合arq方案，该方案增加了通过重传部分保证鲁棒性的灵活性。这项工作与必要的统计模型的发展相结合，特别是为信道衰落过程开发适当类别的自相关函数，将导致可用于在具有各种信道变化率的时变信道上运行的系统的自适应编码策略家族。这些结果将说明自适应编码有用的应用程序以及应该采用的方式。将用于获得这些结果的方法是从概率和随机过程，通信系统理论和统计信号处理领域绘制的。特别是，结果很大程度上依赖于随机过程理论的结果，编码调制方案的设计，以及极小鲁棒时间序列预测结果的扩展。

Recent work has suggested that adaptive signaling has the theoretical promise of greatly increasing the bandwidth efficiency of digital communication systems operating over wireless channels. However, the utility of adaptive signaling has been questioned due to the variation of the wireless channel over time, which results in a different channel at the time of data transmission than at the time of channel estimation. Recent results by the PI have shown that these issues cannot be disregarded; the channel variation greatly alters the nature of the problem and thus the design of robust adaptive signaling schemes for wireless channels presents significantly different challenges than the analogous design problem for wireline channels. Many of these challenges are driven by the robustness necessary in these algorithms due to uncertainties at the transmitter about the statistics of the channel fading process. In this project, a comprehensive study of the design of robust adaptive signaling schemes for time-varying channels is undertaken. The main portions of this study include: (1) The design and characterization of robust algorithms that employ a given adaptive signaling paradigm; (2) The development of adaptive coding paradigms that are well suited to time-varying channels; and (3) The development of adaptive hybrid-ARQ schemes, which have the added flexibility of partially guaranteeing robustness through retransmission. The coupling of this work with the development of the necessary statistical models, in particular the development of appropriate classes of autocorrelation functions for the channel fading processes, will lead to families of adaptive coding strategies that can be employed in systems operating over time-varying channels with various rates of channel variation. These results will illustrate both the applications where adaptive coding is useful and the manner in which it should be employed. The methods that will be used to obtain these results are drawn from the areas of pr obability and random processes, communication system theory, and statistical signal processing. In particular, the results rely heavily on results from random process theory, the design of coded modulation schemes, and extensions of results from minimax-robust time series prediction.