Turbo Coded Modulation for Partially Coherent Channels

摘要：研究了部分相干信道下带宽高效编码调制的设计问题。实际上，当相干接收器以低信噪比或中等信噪比(SNR)操作时，这样的信道就会出现，从而产生噪声的相位估计。这例如发生在无线信道上，其中多径衰落会导致接收信噪比的波动。这项研究利用了称为Turbo编码的最新突破，其中在发射机处的两个或更多个编码器的输出在接收器处被迭代解码，从而在信道容量的1db范围内以SNR进行可靠的通信。该研究将相位跟踪误差融入Turbo编码调制设计的方方面面，从而降低了实际相干通信系统所需的信噪比。因此，这项研究所产生的新的设计技术将不仅引起通信和编码理论界的兴趣，而且也将引起设计实际通信系统的工程师的兴趣。本研究的目标是在部分相干(PC)信道上，包括部分相干(PC)信道，包括部分相干(PC)加性高斯白噪声(AWGN)信道和有或无信道状态信息(CSI)的PC衰落信道，以及在有和没有相关衰落以及闭环和开环相位估计的情况下，发展基于理论的、实用的并行和串行级联Turbo编码调制设计方法。研究人员研究了PC信道的信息容量，确定了在平均功率和峰值功率约束下等概率和非等概率信号的容量实现输入概率密度函数(PDF)和容量最优星座。对于PC衰落信道，将推导出基于成对符号错误概率的距离度量，并将开发基于联合界和收敛域分析的迭代译码性能预测工具。然后，研究人员将研究用于在级联网格编码调制方案中用作组成码的线性和非线性递归卷积编码器的集合划分、比特到符号映射和代码搜索过程。最后，基于已知的非高斯信道的容量实现PDF，将开发用于功率受限PC信道上的Turbo编码调制的整形码设计技术。这些编码将对编码器输出符号序列的高维空间进行整形，使得诱导出的二维PDF将接近容量最优的输入PDF。

Abstract:This research considers the design of bandwidth efficient coded modulation for partially coherent channels. Such channels occur in practice when coherent receivers are operated at low or moderate signal-to-noise ratios (SNRs), resulting in noisy phase estimates. This happens for example on wireless channels, where multipath fading causes fluctuations in received SNR. This research leverages a recent breakthrough known as turbo coding, wherein the outputs of two or more encoders at the transmitter are iteratively decoded at the receiver, resulting in reliable communication at SNRs within 1 dB of channel capacity. This research integrates phase-tracking error into all aspects of turbo coded modulation design, thereby reducing the required SNR for practical coherent communication systems. The new design techniques stemming from this research will therefore interest not only communication and coding theorists, but also engineers designing practical communication systems.The goal of this research is to develop theoretically based, practical design methods for parallel and serially concatenated turbo coded modulation over partially coherent (PC) channels, including PC additive white Gaussian noise (AWGN) channels, and PC fading channels with and without channel state information (CSI), with and without correlated fading, and with closed-loop and open-loop phase estimation. The investigators study the information capacity of PC channels, and determine capacity-achieving input probability density functions (PDFs) and capacity-optimal constellations for equiprobable and non-equiprobable signaling under average and peak power constraints. Distance metrics based on pairwise symbol error probabilities will be derived for PC fading channels, and iterative decoder performance prediction tools based on union bounds and convergence-region analysis will be developed. The investigators will then study set-partitioning, bits-to-symbol mapping, and code-search procedures for both linear and non-linear recursive convolutional encoders used as constituent codes in concatenated trellis-coded modulation schemes. Finally, shaping code design techniques for turbo coded modulation on power-constrained PC channels will be developed, based on the capacity-achieving PDFs of these channels, which are known to be non-Gaussian. These codes will shape the high-dimensional space of encoder output symbol sequences so that the induced two-dimensional PDF will closely approximate the capacity-optimal input PDF.