有限反馈下可重构智能表面辅助 FDD 系统的自适应比特分配
Adaptive Bit Partitioning for Reconfigurable Intelligent Surface Assisted FDD Systems with Limited Feedback
AI总结：
针对 RIS 辅助 FDD 系统的有限反馈问题，提出由 LoS/NLoS 子码本构成的级联码本及自适应比特分配策略，以降低遍历速率损失。
摘要：
在频分双工系统中，基站（BS）通过信道反馈获取下行链路信道状态信息（CSI），而在存在可重构智能表面（RIS）的情况下，这一问题尚未得到充分研究。本研究考察了有限信道反馈方案，提出了一种新型级联码本和自适应比特分配策略。RIS 将基站与移动台之间的信道分割为两个子信道，每个子信道均包含视距（LoS）和非视距（NLoS）路径。为量化路径增益，所提出的级联码本由两个子码本合成，其码字由 LoS 和 NLoS 分量级联而成。这使得所提出的级联码本能够通过灵活使用不同的反馈比特来设计码字结构，从而适应 LoS 和 NLoS 路径增益的不同分布。在所提出的级联码本基础上，我们推导了最大比传输下遍历速率损失的上界，并表明可以通过在码本生成过程中优化反馈比特分配来降低速率损失。为最小化该上界，我们提出了一种能够适应不同环境和系统参数的比特分配策略。大量仿真结果表明了级联码本的优越性与鲁棒性，以及自适应比特分配方案的有效性。
英文摘要：
In frequency division duplexing systems, the base station (BS) acquires downlink channel state information (CSI) via channel feedback, which has not been adequately investigated in the presence of RIS. In this study, we examine the limited channel feedback scheme by proposing a novel cascaded codebook and an adaptive bit partitioning strategy. The RIS segments the channel between the BS and mobile station into two sub-channels, each with line-of-sight (LoS) and non-LoS (NLoS) paths. To quantize the path gains, the cascaded codebook is proposed to be synthesized by two sub-codebooks whose codeword is cascaded by LoS and NLoS components. This enables the proposed cascaded codebook to cater the different distributions of LoS and NLoS path gains by flexibly using different feedback bits to design the codeword structure. On the basis of the proposed cascaded codebook, we derive an upper bound on ergodic rate loss with maximum ratio transmission and show that the rate loss can be cut down by optimizing the feedback bit allocation during codebook generation. To minimize the upper bound, we propose a bit partitioning strategy that is adaptive to diverse environment and system parameters. Extensive simulations are presented to show the superiority and robustness of the cascaded codebook and the efficiency of the adaptive bit partitioning scheme.
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