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10 pages, 973 KiB

Open AccessCommunication

Variational Optimization for Sustainable Massive MIMO Base Station Switching

by Aida Al-Samawi and Liyth Nissirat

Sensors 2024, 24(2), 520; https://doi.org/10.3390/s24020520 - 14 Jan 2024

Viewed by 1023

Massive MIMO networks are a promising technology for achieving ultra-high capacity and meeting future wireless service demand. Massive MIMO networks, on the other hand, consume intensive energy. As a result, energy-efficient operation of massive MMO networks became a requirement rather than a luxury. [...] Read more.

Massive MIMO networks are a promising technology for achieving ultra-high capacity and meeting future wireless service demand. Massive MIMO networks, on the other hand, consume intensive energy. As a result, energy-efficient operation of massive MMO networks became a requirement rather than a luxury. Many NP-hard concavity search algorithms for optimal base station switching on-off scheme have been developed. This paper demonstrates the formulation of massive MIMO networks energy efficiency as a constrained variational problem. Our proposed method solution’s uniqueness and boundedness are demonstrated and proven. The developed system is a total energy optimization problem formulation. Furthermore, the order in which the base stations are switched on and off is specified for minimal handover overhead signaling and fair user capacity sharing. Results showed that variational optimization yielded optimal base station switching on and off with considerable energy saving achieved and maintaining the user capacity demand. Moreover, the proposed base station selection criteria provided suboptimal handover overhead signaling. Full article

(This article belongs to the Special Issue MIMO Technologies in Sensors and Wireless Communication Applications)

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17 pages, 404 KiB

Open AccessArticle

Efficient and Low-Complex Signal Detection with Iterative Feedback in Wireless MIMO-OFDM Systems

by Ying Chen, Yue Tang, Bin Jiang, Yinan Zhao, Jianrong Bao and Xianghong Tang

Sensors 2023, 23(24), 9798; https://doi.org/10.3390/s23249798 - 13 Dec 2023

Cited by 2 | Viewed by 1005

Abstract

To solve error propagation and exorbitant computational complexity of signal detection in wireless multiple-input multiple-output-orthogonal frequency division multiplexing (MIMO-OFDM) systems, a low-complex and efficient signal detection with iterative feedback is proposed via a constellation point feedback optimization of minimum mean square error-ordered successive [...] Read more.

To solve error propagation and exorbitant computational complexity of signal detection in wireless multiple-input multiple-output-orthogonal frequency division multiplexing (MIMO-OFDM) systems, a low-complex and efficient signal detection with iterative feedback is proposed via a constellation point feedback optimization of minimum mean square error-ordered successive interference cancellation (MMSE-OSIC) to approach the optimal detection. The candidate vectors are formed by selecting the candidate constellation points. Additionally, the vector most approaching received signals is chosen by the maximum likelihood (ML) criterion in formed candidate vectors to reduce the error propagation by previous erroneous decision, thus improving the detection performance. Under a large number of matrix inversion operations in the above iterative MMSE process, effective and fast signal detection is hard to be achieved. Then, a symmetric successive relaxation iterative algorithm is proposed to avoid the complex matrix inversion calculation process. The relaxation factor and initial iteration value are reasonably configured with low computational complexity to achieve good detection close to that of the MMSE with fewer iterations. Simultaneously, the error diffusion and complexity accumulation caused by the successive detection of the subsequent OSIC scheme are also improved. In addition, a method via a parallel coarse and fine detection deals with several layers to both reduce iterations and improve performance. Therefore, the proposed scheme significantly promotes the MIMO-OFDM performance and thus plays an irreplaceable role in the future sixth generation (6G) mobile communications and wireless sensor networks, and so on. Full article

(This article belongs to the Special Issue MIMO Technologies in Sensors and Wireless Communication Applications)

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19 pages, 778 KiB

Open AccessArticle

Enhanced MIMO CSI Estimation Using ACCPM with Limited Feedback

by Ahmed Al-Asadi, Ibtesam R. K. Al-Saedi, Saddam K. Alwane, Hongxiang Li and Laith Alzubaidi

Sensors 2023, 23(18), 7965; https://doi.org/10.3390/s23187965 - 19 Sep 2023

Viewed by 1295

Abstract

Multiple Input and Multiple Output (MIMO) is a promising technology to enable spatial multiplexing and improve throughput in wireless communication networks. To obtain the full benefits of MIMO systems, the Channel State Information (CSI) should be acquired correctly at the transmitter side for [...] Read more.

Multiple Input and Multiple Output (MIMO) is a promising technology to enable spatial multiplexing and improve throughput in wireless communication networks. To obtain the full benefits of MIMO systems, the Channel State Information (CSI) should be acquired correctly at the transmitter side for optimal beamforming design. The analytical centre-cutting plane method (ACCPM) has shown to be an appealing way to obtain the CSI at the transmitter side. This paper adopts ACCPM to learn down-link CSI in both single-user and multi-user scenarios. In particular, during the learning phase, it uses the null space beamforming vector of the estimated CSI to reduce the power usage, which approaches zero when the learned CSI approaches the optimal solution. Simulation results show our proposed method converges and outperforms previous studies. The effectiveness of the proposed method was corroborated by applying it to the scattering channel and winner II channel models. Full article

(This article belongs to the Special Issue MIMO Technologies in Sensors and Wireless Communication Applications)

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14 pages, 1403 KiB

Open AccessArticle

A Dual Load-Modulated Doherty Power Amplifier Design Method for Improving Power Back-Off Efficiency

by Yi Jin, Zhijiang Dai, Xiongbo Ran, Changzhi Xu and Mingyu Li

Sensors 2023, 23(14), 6598; https://doi.org/10.3390/s23146598 - 22 Jul 2023

Cited by 1 | Viewed by 1537

Abstract

In this paper, the load modulation process of a Doherty power amplifier (DPA) is analyzed to address the issue of why designed DPAs have a very low efficiency in the back-off state in some cases. A general formula of the real load modulation [...] Read more.

In this paper, the load modulation process of a Doherty power amplifier (DPA) is analyzed to address the issue of why designed DPAs have a very low efficiency in the back-off state in some cases. A general formula of the real load modulation process is also given for analyzing the load modulation of a peak PA matching network. This provides a new perspective for improving the back-off efficiency of a DPA. To improve the power back-off efficiency of a DPA, a dual load-modulated DPA (D-DPA) design method is proposed. The core principle of the proposed design method is to control the load modulation process from the carrier PA to the peaking PA based on the design method of the traditional two-way DPA. The efficiency of the peaking PA in the back-off region is enhanced, thereby improving the efficiency in the entire back-off region of the DPA. Based on the proposed design method, a D-DPA operating at 2 GHz is designed and fabricated. The test results show that the saturated output power and gain are 43.7 dBm and 9.7 dB, respectively, while the efficiency at 6 dB output power back-off is 59.2%. The designed D-DPA eliminates the efficiency pit of the traditional two-way DPA in the output power back-off region. Full article

(This article belongs to the Special Issue MIMO Technologies in Sensors and Wireless Communication Applications)

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16 pages, 1289 KiB

Open AccessArticle

Reinforcement Learning-Aided Channel Estimator in Time-Varying MIMO Systems

by Tae-Kyoung Kim and Moonsik Min

Sensors 2023, 23(12), 5689; https://doi.org/10.3390/s23125689 - 18 Jun 2023

Cited by 1 | Viewed by 1550

Abstract

This paper proposes a reinforcement learning-aided channel estimator for time-varying multi-input multi-output systems. The basic concept of the proposed channel estimator is the selection of the detected data symbol in the data-aided channel estimation. To achieve the selection successfully, we first formulate an [...] Read more.

This paper proposes a reinforcement learning-aided channel estimator for time-varying multi-input multi-output systems. The basic concept of the proposed channel estimator is the selection of the detected data symbol in the data-aided channel estimation. To achieve the selection successfully, we first formulate an optimization problem to minimize the data-aided channel estimation error. However, in time-varying channels, the optimal solution is difficult to derive because of its computational complexity and the time-varying nature of the channel. To address these difficulties, we consider a sequential selection for the detected symbols and a refinement for the selected symbols. A Markov decision process is formulated for sequential selection, and a reinforcement learning algorithm that efficiently computes the optimal policy is proposed with state element refinement. Simulation results demonstrate that the proposed channel estimator outperforms conventional channel estimators by efficiently capturing the variation of the channels. Full article

(This article belongs to the Special Issue MIMO Technologies in Sensors and Wireless Communication Applications)

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13 pages, 6603 KiB

Open AccessArticle

Surface-Mount Zero-Ohm Jumper Resistor Characterization in High-Speed Controlled Impedance Transmission Lines

by Aleksandr Vasjanov and Vaidotas Barzdenas

Sensors 2023, 23(9), 4472; https://doi.org/10.3390/s23094472 - 4 May 2023

Viewed by 2759

Abstract

Zero-ohm resistors, also known as jumpers, are commonly used in early radio frequency (RF) prototypes as they can help engineers identify the most optimal engineering solution for their system or create application-specific hardware configurations in products. One of the key considerations when using [...] Read more.

Zero-ohm resistors, also known as jumpers, are commonly used in early radio frequency (RF) prototypes as they can help engineers identify the most optimal engineering solution for their system or create application-specific hardware configurations in products. One of the key considerations when using zero-ohm jumpers in RF circuits is the potential for signal loss and interference. Every circuit connection creates a small amount of resistance and impedance, eventually adding up over long distances or in complex circuits. This paper proposes a quantitative characterization summary of standard 0201-, 0402-, 0603-, and 0805-size surface-mount package jumpers, as well as lead-free and lead solder wires, in high-frequency applications by means of time domain reflectometry (TDR) and S-parameter measurements. The typical offset from the target 50 Ω impedance was measured to be around 3 Ω, or 5.8% relative to the measured reference value. According to S-parameter measurement results, no visible impact on attenuation was spotted up to 5 GHz compared to the reference S₂₁ curve. Full article

(This article belongs to the Special Issue MIMO Technologies in Sensors and Wireless Communication Applications)

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12 pages, 19873 KiB

Open AccessCommunication

A Compact Aperture-Sharing Sub-6 GHz/Millimeter-Wave Dual-Band Antenna

by Qinghu Zhang, Bitian Chai, Jianxin Chen and Wenwen Yang

Sensors 2023, 23(9), 4400; https://doi.org/10.3390/s23094400 - 30 Apr 2023

Cited by 4 | Viewed by 2038

Abstract

In this article, a microwave (MW)/millimeter wave (MMW) aperture-sharing antenna is proposed. The antenna is constructed using two orthogonal columns of grounded vias from a 3.5 GHz slot-loaded half-mode substrate-integrated waveguide (HMSIW) antenna. These vias are reused to create two sets of 1 [...] Read more.

In this article, a microwave (MW)/millimeter wave (MMW) aperture-sharing antenna is proposed. The antenna is constructed using two orthogonal columns of grounded vias from a 3.5 GHz slot-loaded half-mode substrate-integrated waveguide (HMSIW) antenna. These vias are reused to create two sets of 1 × 4 MMW substrate-integrated dielectric resonator antenna (SIDRA) arrays. With this proposed partial structure reuse strategy, the MW antenna and MMW arrays can be integrated in a shared-aperture manner, improving space utilization and enabling dual-polarized beam steering capability in the MMW band, which is highly desirable for multiple-input multipleoutput (MIMO) applications. The integrated antenna prototype was manufactured and measured for verification. The 3.5 GHz antenna has a relative bandwidth of 3.4% (3.44–3.56 GHz) with a peak antenna gain of 5.34 dBi, and the 28 GHz antenna arrays cover the frequency range of 26.5–29.8 GHz (11.8%) and attain a measured peak antenna gain of 11.0 dBi. Specifically, the 28 GHz antenna arrays can realize dual-polarization and ±45° beam steering capability. The dual-band antenna has a very compact structure, and it is applicable for 5G mobile communication terminals. Full article

(This article belongs to the Special Issue MIMO Technologies in Sensors and Wireless Communication Applications)

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14 pages, 6748 KiB

Open AccessArticle

Design of Ultra-Wideband Doherty Power Amplifier Using a Modified Combiner Integrated with Complex Combining Impedance

by Jian Chen, Zhihui Liu, Tao Dong and Weimin Shi

Sensors 2023, 23(8), 3882; https://doi.org/10.3390/s23083882 - 11 Apr 2023

Cited by 2 | Viewed by 2139

Abstract

To be compatible with future wireless communication systems, it is very necessary to extend the bandwidth of the Doherty power amplifier (DPA). In this paper, a modified combiner integrated with a complex combining impedance is adopted to enable an ultra-wideband DPA. Meanwhile, a [...] Read more.

To be compatible with future wireless communication systems, it is very necessary to extend the bandwidth of the Doherty power amplifier (DPA). In this paper, a modified combiner integrated with a complex combining impedance is adopted to enable an ultra-wideband DPA. Meanwhile, a comprehensive analysis is performed on the proposed method. It is illustrated that the proposed design methodology can provide power amplifier (PA) designers with more freedom in implementing ultra-wideband DPAs. As a concept of proof, a DPA working over 1.2–2.8 GHz (a relative bandwidth of 80%) is designed, fabricated and measured in this work. Experimental results showed that the fabricated DPA delivers a saturation output power of 43.2–44.7 dBm with a gain of 5.2–8.6 dB. Meantime, the fabricated DPA achieves a saturation drain efficiency (DE) of 44.3–70.4% and a 6 dB back-off DE of 38.7–57.6%. Full article

(This article belongs to the Special Issue MIMO Technologies in Sensors and Wireless Communication Applications)

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