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arXiv 1808.06402cs.ITmath.IT
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新无线电系统中基于CSI反馈的类型2码本的幅度Quantization

Amplitude Quantization for Type-2 Codebook Based CSI Feedback in New Radio System

Honglei Miao, Markus D. Mueck, Michael Faerber

摘要:

在3GPP新无线电系统中,已经标准化了两种类型的码本,即类型1和类型2码本,用于支持高级MIMO操作的信道状态信息(CSI)反馈。这两种类型的码本都是从基于2-D DFT的波束网格构建的,并且使得能够实现波束选择的CSI反馈以及两个极化之间的基于PSK的同相组合。此外,基于类型2码本的CSI反馈报告所选波束的宽带和子带幅度信息。因此,可以设想,将从基于类型2码本的CSI反馈中获得更准确的CSI,使得网络可以采用更好的预编码MIMO传输。为了减少CSI反馈信令,与基于3比特的宽带幅度反馈相结合,支持仅具有两个量化级别的基于1比特的子带幅度。通常,宽带幅度应计算为波束在所有子带上的线性平均幅度。然而,由于粗的子带幅度量化,已经观察到在联合宽带和子带幅度反馈的情况下,基于平均的宽带幅度可能导致大的幅度量化误差。本文研究了宽带和子带联合幅度计算的两种方法。具体而言,提出了最优和次优方法。该方法以较大的计算复杂度为代价,实现了幅度量化误差最小。并且借助于导出的缩放因子,次优方法比传统的基于线性平均的方法表现出明显更小的量化误差,特别是对于具有大频率选择性的信道。

英文摘要:

In 3GPP new radio system, two types of codebook, namely Type-1 and Type-2 codebook, have been standardized for the channel state information (CSI) feedback in the support of advanced MIMO operation. Both types of codebook are constructed from 2-D DFT based grid of beams, and enable the CSI feedback of beam selection as well as PSK based co-phase combining between two polarizations. Moreover, Type-2 codebook based CSI feedback reports the wideband and subband amplitude information of the selected beams. As a result, it is envisioned that more accurate CSI shall be obtained from the Type-2 codebook based CSI feedback so that better precoded MIMO transmission can be employed by the network. To reduce the CSI feedback signaling, 1 bit based subband amplitude with only two quantization levels is supported in combination to 3 bits based wideband amplitude feedback. Typically, wideband amplitude shall be calculated as the linear average amplitude of the beam over all subbands. However, due to the coarse subband amplitude quantization, it has been observed in case of joint wideband and subband amplitude feedback, the average based wideband amplitude can lead to a large amplitude quantization errors. In this paper, we study two methods for joint wideband and subband amplitude calculations. Specifically, both optimal and sub-optimal methods are proposed. The optimal method can achieve the minimum amplitude quantization errors at the cost of a relatively large computation complexity. And by virtue of a derived scaling factor, the sub-optimal method exhibits clearly smaller quantization error than the conventional linear average based method especially for the channel with large frequency selectivity.

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