Optical True Time Delay-Based Hybrid Beamforming for Limited-Feedback Millimeter-Wave Massive MIMO Systems

In this paper, a joint spatio–radio frequency resource allocation and hybrid beamforming scheme for the massive multiple-input multiple-output (MIMO) systems is proposed. We consider limited feedback two-stage hybrid beamformimg for decomposing the precoding matrix at the base-station. To reduce the channel state information (CSI) feedback of massive MIMO, we utilize the channel covariance-based RF precoding and beam selection. This beam selection process minimizes the inter-group interference. The regularized block diagonalization can mitigate the inter-group interference, but requires substantial overhead feedback. We use channel covariance-based eigenmodes and discrete Fourier transforms (DFT) to reduce the feedback overhead and design a simplified analog precoder. The columns of the analog beamforming matrix are selected based on the users’ grouping performed by the K-mean unsupervised machine learning algorithm. The digital precoder is designed with joint optimization of intra-group user utility function. It has been shown that more than 50 % feedback overhead is reduced by the eigenmodes-based analog precoder design. The joint beams, users scheduling and limited feedbacK-based hybrid precoding increases the sum-rate by 27 . 6 % compared to the sum-rate of one-group case, and reduce the feedback overhead by 62 . 5 % compared to the full CSI feedback.

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Design of True Time Delay Millimeter Wave Beamformers for 5G Multibeam Phased Arrays

Electronics ◽

10.3390/electronics9081331 ◽

2020 ◽

Vol 9 (8) ◽

pp. 1331 ◽

Cited By ~ 1

Author(s):

Dimitrios I. Lialios ◽

Nikolaos Ntetsikas ◽

Konstantinos D. Paschaloudis ◽

Constantinos L. Zekios ◽

Stavros V. Georgakopoulos ◽

...

Keyword(s):

Time Delay ◽

Millimeter Wave ◽

Communication Systems ◽

Phased Arrays ◽

High Capacity ◽

Wireless Systems ◽

Base Stations ◽

Small Cells ◽

True Time Delay ◽

True Time

Millimeter wave (mm-Wave) technology is likely the key enabler of 5G and early 6G wireless systems. The high throughput, high capacity, and low latency that can be achieved, when mm-Waves are utilized, makes them the most promising backhaul as well as fronthaul solutions for the communication between small cells and base stations or between base stations and the gateway. Depending on the channel properties different communication systems (e.g., beamforming and MIMO) can accordingly offer the best solution. In this work, our goal is to design millimeter wave beamformers for switched beam phased arrays as hybrid beamforming stages. Specifically, three different analog beamforming techniques for the frequency range of 27–33 GHz are presented. First, a novel compact multilayer Blass matrix is proposed. Second, a modified dummy-ports free, highly efficient Rotman lens is introduced. Finally, a three-layer true-time-delay tree topology inspired by microwave photonics is presented.

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