Optimal and Suboptimal Architectures of Millimeter-wave Large-scale Arrays for 6G

HONG Wei; XU Jun; CHEN Jixin; HAO Zhangcheng; ZHOU Jianyi; YU zhiqiang; YANG Guangqi; JIANG Zhihao; YU Chao; HU Yun; HOU Debin; ZHU Xiaowei; CHEN Zhe; ZHOU Peigen

doi:10.11999/JEIT250109

Volume 47 Issue 8

Aug. 2025

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Article Navigation > Journal of Electronics & Information Technology > 2025 > 47(8): 2405-2415

HONG Wei, XU Jun, CHEN Jixin, HAO Zhangcheng, ZHOU Jianyi, YU zhiqiang, YANG Guangqi, JIANG Zhihao, YU Chao, HU Yun, HOU Debin, ZHU Xiaowei, CHEN Zhe, ZHOU Peigen. Optimal and Suboptimal Architectures of Millimeter-wave Large-scale Arrays for 6G[J]. Journal of Electronics & Information Technology, 2025, 47(8): 2405-2415. doi: 10.11999/JEIT250109

Citation:

HONG Wei, XU Jun, CHEN Jixin, HAO Zhangcheng, ZHOU Jianyi, YU zhiqiang, YANG Guangqi, JIANG Zhihao, YU Chao, HU Yun, HOU Debin, ZHU Xiaowei, CHEN Zhe, ZHOU Peigen. Optimal and Suboptimal Architectures of Millimeter-wave Large-scale Arrays for 6G[J]. Journal of Electronics & Information Technology, 2025, 47(8): 2405-2415. doi: 10.11999/JEIT250109

Citation:

HONG Wei, XU Jun, CHEN Jixin, HAO Zhangcheng, ZHOU Jianyi, YU zhiqiang, YANG Guangqi, JIANG Zhihao, YU Chao, HU Yun, HOU Debin, ZHU Xiaowei, CHEN Zhe, ZHOU Peigen. Optimal and Suboptimal Architectures of Millimeter-wave Large-scale Arrays for 6G[J]. Journal of Electronics & Information Technology, 2025, 47(8): 2405-2415. doi: 10.11999/JEIT250109

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Optimal and Suboptimal Architectures of Millimeter-wave Large-scale Arrays for 6G

doi: 10.11999/JEIT250109 cstr: 32379.14.JEIT250109

HONG Wei^{1, 2},
XU Jun^{1
,
,},
CHEN Jixin^{1, 2},
HAO Zhangcheng^{1, 2},
ZHOU Jianyi^{1, 2},
YU zhiqiang^{1, 2},
YANG Guangqi^{1, 2},
JIANG Zhihao^{1, 2},
YU Chao^{1, 2},
HU Yun²,
HOU Debin³,
ZHU Xiaowei¹,
CHEN Zhe¹,
ZHOU Peigen¹

1.
State Key Laboratory of Millimeter Waves, Southeast University, Nanjing 210096, China
2.
Purple Moutin Laboratory, Nanjing 211111, China
3.
MiSic Microelectronics Ltd., Nanjing 211111, China

Funds: The National Natural Science Foundation of China (62301152, 62188102), The Major Project of Jiangsu Province (BG2024034), The Natural Science Foundation of Jiangsu Province (BK20230819)

Received Date: 2025-02-24
Rev Recd Date: 2025-03-27

Available Online: 2025-04-03

Publish Date: 2025-08-27

Abstract

Abstract

Objective Beamforming array technology is a key enabler for modern radio systems, evolving across three primary dimensions: advancements in electromagnetic theory, innovations in semiconductor manufacturing, and iterations in system architectures. The development of mobile communication has driven the progress of beamforming array technologies. Hybrid beamforming array technology, in particular, was established as a critical solution for 5G millimeter-wave communications under the 3GPP Release 15 standard. To address the needs of future 6G communication and sensing, millimeter-wave beamforming arrays will evolve towards ultra-large-scale (>1000 elements), intelligent (AI-driven), and heterogeneous (integration of photonics and electronics) architectures, serving as the foundation for ubiquitous intelligent connectivity. This article investigates optimal and suboptimal large-scale beamforming array architectures for 6G millimeter-wave communications. Methods Large-scale beamforming arrays can be classified into three primary types: analog-domain beamforming arrays, digital-domain beamforming arrays, and hybrid-domain beamforming arrays. These arrays can be further categorized into single-beam and multi-beam configurations based on the number of supported beams. Each category includes various architectural variants (Figure 1). Analog-domain beamforming arrays (Figure 2) consist of passive and active beamforming arrays. Active beamforming arrays are further divided into Radio Frequency (RF) phase-shifting, Intermediate Frequency (IF) phase-shifting, and Local Oscillator (LO) phase-shifting architectures. Digital-domain implementations (Figure 3) include symmetric and asymmetric full-digital beamforming architectures. Hybrid-domain configurations (Figure 4) offer various combinations, such as architectures integrating RF phase-shifting phased subarrays with digital beamforming, or hybrid multi-beam arrays that combine passive beamforming networks with digital processing. In terms of performance, the symmetric full-digital beamforming architecture (Figure 5) is considered the optimal solution among all beamforming arrays. However, it faces challenges such as high system costs, excessive power consumption, and increased complexity due to the need for numerous high-speed ADCs and real-time processing of large data streams. To address these limitations in symmetric full-digital multi-beam large-scale arrays, an asymmetric large-scale full-digital multi-beam array architecture was proposed (Figure 6). Additionally, a spatial-domain orthogonal hybrid beamforming array (Figure 8) is proposed, which uses differentiated beamforming techniques across spatial dimensions to implement large-scale hybrid beamforming arrays. Results and Discussions Current 5G millimeter-wave base stations primarily utilize hybrid beamforming massive MIMO array architectures (Figure 7), which integrate RF phase-shifting phased subarrays with digital-domain beamforming. In this configuration, each two-dimensional RF phase-shifting phased subarray is connected to a dedicated Up-Down Converter (UDC), followed by secondary digital beamforming processing. However, this architecture limits independent beam control flexibility, often leading to the abandonment of digital beamforming in practical implementations. Therefore, each beam achieves only subarray-level gain. For mobile communication base stations, the adoption of asymmetric full-digital phased arrays (Figure 6), which include large-scale transmit arrays and smaller receive arrays, offers an optimal balance between cost, power consumption, complexity, and performance. This configuration meets uplink/downlink traffic demands while enabling wider receive beams (corresponding to compact receive arrays) that support accurate angle-of-arrival estimation. Theoretically, hybrid multi-beam architectures that combine digital beamforming in the horizontal dimension with analog beamforming in the vertical dimension (or vice versa) can reduce system complexity, cost, and power consumption without degrading performance, potentially outperforming current 5G mmWave hybrid beamforming solutions. However, these architectures face limitations due to beam bundling. Building upon the 4-subarray hybrid beamforming architecture (256 elements) used in existing 5G mmWave base stations (Figure 7), a spatial-domain orthogonal hybrid beamforming array is proposed (Figure 8). In this configuration, vertical-dimension elements are grouped into sixteen 1D RF phase-shifting phased subarrays (16 elements each), with each subarray connected to individual UDCs and ADC/DAC chains. The 16 data streams are processed through horizontal-dimension digital beamforming, achieving spatial orthogonality between the analog and digital beamforming domains. This architecture preserves full-aperture gain for each beam, supporting enhanced transmission rates and system capacity. This hybrid multi-beam solution maintains the same beamforming chip count as conventional hybrid architectures (Figure 7) for identical array scales, requiring only an increase in UDC channels from 4 to 16, with minimal cost impact. The proposed solution supports 16 simultaneous beams/data streams, resulting in a significant capacity improvement. For dual-polarization configurations, this extends to 32 beams/data streams, further enhancing system capacity. In horizontal-digital/vertical-analog implementations, all beams align along the horizontal plane, with vertical scanning limited to simultaneous elevation adjustment (Figure 9). Although vertical beam grouping enables independent elevation control, it results in beam gain degradation. Conclusions From a performance perspective, the symmetric full-digital beamforming array architecture can be considered the optimal solution. However, it is hindered by high system complexity and cost. The asymmetric full-digital beamforming array architecture significantly reduces system complexity and cost while closely approaching the performance of its symmetric counterpart, making it a suboptimal yet practical choice for large-scale beamforming arrays. Additionally, the spatially orthogonal hybrid beamforming array architecture—such as the design combining vertical analog phased subarrays with horizontal digital beamforming—represents another suboptimal solution. Notably, this hybrid architecture outperforms current 5G mmWave hybrid beamforming systems in terms of performance.
- Beamforming,
- Antenna array,
- Millimeter waves,
- 6G

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References(15)

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