Full Text:   <498>

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CLC number: TN928

On-line Access: 2021-04-15

Received: 2020-09-02

Revision Accepted: 2021-02-09

Crosschecked: 2021-03-03

Cited: 0

Clicked: 1432

Citations:  Bibtex RefMan EndNote GB/T7714

 ORCID:

Zhiqiang Wang

https://orcid.org/0000-0001-6398-5298

Guangrong Yue

https://orcid.org/0000-0001-7937-124X

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Frontiers of Information Technology & Electronic Engineering  2021 Vol.22 No.4 P.560-570

http://doi.org/10.1631/FITEE.2000451


Beam squint effect on high-throughput millimeter-wave communication with an ultra-massive phased array


Author(s):  Zhiqiang Wang, Jiawei Liu, Jun Wang, Guangrong Yue

Affiliation(s):  National Key Laboratory of Science and Technology on Communications, University of Electronic Science and Technology of China, Chengdu 611731, China

Corresponding email(s):   wangzq@std.uestc.edu.cn, 842927584@qq.com, junwang@uestc.edu.cn, yuegr@uestc.edu.cn

Key Words:  Ultra-massive phased array, Millimeter-wave (mmWave), Beam squint, Zadoff-Chu, Single-carrier frequency-domain equalization (SC-FDE)


Zhiqiang Wang, Jiawei Liu, Jun Wang, Guangrong Yue. Beam squint effect on high-throughput millimeter-wave communication with an ultra-massive phased array[J]. Frontiers of Information Technology & Electronic Engineering, 2021, 22(4): 560-570.

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Abstract: 
An ultra-massive phased array can be deployed in high-throughput millimeter-wave (mmWave) communication systems to increase the transmission distance. However, when the signal bandwidth is large, the antenna array response changes with the frequency, causing beam squint. In this paper, we investigate the beam squint effect on a high-throughput mmWave communication system with the single-carrier frequency-domain equalization transmission scheme. Specifically, we first view analog beamforming and the physical channel as a spatial equivalent channel. The characteristics of the spatial equivalent channel are analyzed which behaves like frequency-selective fading. To eliminate the deep fading points in the spatial equivalent channel, an advanced analog beamforming method is proposed based on the zadoff-Chu (ZC) sequence. Then, the low-complexity linear zero-forcing and minimum mean squared error equalizers are considered at the receiver. Simulation results indicate that the proposed ZC-based analog beamforming method can effectively mitigate the performance loss by the beam squint.

高通量毫米波超大规模相控阵通信系统波束倾斜效应

王志强,刘嘉伟,王军,岳光荣
电子科技大学通信抗干扰技术国家级重点实验室,中国成都市,611731
概要:毫米波频段巨大的通信带宽,为超高速率通信传输提供了有效途径。然而,毫米波频段路径损耗严重限制了系统传输距离。使用大规模阵列天线进行波束成形提高增益,可有效补偿高路径损耗的影响。但是,在大带宽条件下,大规模阵列天线波束特性的改变将影响远距离毫米波通信系统性能。本文讨论了大规模相控阵宽带波束倾斜效应对毫米波单载波频域均衡(SC-FDE)通信系统的影响。此外,基于恒包络零自相关序列设计了一种修正模拟波束成形方案,可有效弥补波束倾斜效应带来的性能损失。
考虑毫米波LoS-MISO系统,发射机部署大规模相控阵,接收机部署单个天线接收信号。空间无线信道假设为单径LoS信道。模拟相控阵列作用是形成空间波束指向固定方位接收机。当天线数目和信号带宽较小时,天线阵列响应符合窄带假设(天线单元间的基带信号时延可忽略不计),仅由空间角度决定。如果发射机已知接收机方位,则可以直接依据该方位信息计算出移相器网络各个移相器的移相值,这种方法称之为标准模拟波束成形方法。然而,当天线数目和信号带宽较大时,天线单元间的基带信号时延与通信码元周期相比拟,则该时延不再能够忽略。阵列矢量将由空间角度和频率共同决定。如果仍采用上述标准模拟波束成形方法,由于移相器的移相值与频率无关,则会导致不同频点的空间波束指向不同,该现象即为大规模相控阵中的宽带波束倾斜效应。
从通信角度而言,发射机移相器网络和空间无线信道被看作为空间多径等效信道。每个天线通道看作一条信号路径,则该等效信道是由多条等功率但具有一定时延差的信号路径组成。波束倾斜效应产生的影响主要可以分为两方面:(1)等效信道频率选择性:随着天线数目和空间角度增加,等效信道频率响应逐渐从不平坦性表现为频率选择性;(2)系统等效信噪比损失,且该信噪比损失不可弥补。
本质上,上述空间多径等效信道频域响应相当于模拟波束成形矢量关于天线空间采样的离散傅里叶变换。为使等效信道尽可能平坦,可以寻找一种在频域具有平坦特性的序列设计模拟波束成形加权矢量。恒包络零自相关序列即是满足该要求的序列。本文使用恒包络零自相关序列中的Zadoff-Chu(ZC)序列对标准模拟波束成形进行修正。
此外,信道频率选择性会导致传输系统出现码间干扰。这可以在单载波系统中通过时域或频域均衡消除。另外,可以使用多载波系统,将信道划分为多个正交子载波,每个子载波信道可以看作频率平坦信道。对于毫米波通信而言,选择单载波频域均衡(SC-FDE)方案更适合实际实现。单载波避免了多载波系统峰均功率比(PAPR)很大的问题,使得在系统设计中可以采用更经济高效的功率放大器,技术更成熟,系统稳定性更高。在接收机端,我们使用低复杂度迫零(ZF)均衡和最小均方误差(MMSE)均衡算法。本文提出的修正模拟波束成形方法能够有效抵抗由于波束倾斜效应产生的码间干扰。
综上,在毫米波通信系统中采用大规模相控阵可以提高通信传输距离。但在大规模阵列和高宽带情况下,大规模相控阵列中的宽带波束倾斜效应会导致波束增益降低和系统码间干扰。本文提出的基于恒包络零自相关序列修正模拟波束成形方法通过对模拟波束成形矢量进行修正设计,使得空间等效信道尽可能平坦,从而有效消除宽带波束倾斜效应带来的码间干扰。

关键词:超大规模相控阵;毫米波;波束倾斜;Zadoff-Chu;单载波频域均衡

Darkslateblue:Affiliate; Royal Blue:Author; Turquoise:Article

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