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Tan F, Peng Y, Liu Q. Cluster Content Caching: A Deep Reinforcement Learning Approach to Improve Energy Efficiency in Cell-Free Massive Multiple-Input Multiple-Output Networks. Sensors (Basel) 2023; 23:8295. [PMID: 37837129 PMCID: PMC10574842 DOI: 10.3390/s23198295] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2023] [Revised: 10/01/2023] [Accepted: 10/03/2023] [Indexed: 10/15/2023]
Abstract
With the explosive growth of micro-video applications, the transmission burden of fronthaul and backhaul links is increasing, and meanwhile, a lot of energy consumption is also generated. For reducing energy consumption and transmission delay burden, we propose a cell-free massive multiple-input multiple-output (CF-mMIMO) system in which the cache on the access point (AP) is used to reduce the load on the link. In this paper, a total energy efficiency (EE) model of a cache-assisted CF-mMIMO system is established. When optimizing EE, forming the co-operation cluster is critical. Therefore, we propose an energy-efficient joint design of content caching, AP clustering, and low-resolution digital-to-analog converter (DAC) in a cache-assisted CF-mMIMO network based on deep reinforcement learning. This scheme can effectively cache content in APs and select the appropriate DAC resolution. Then, taking into account the channel state information and user equipment (UE)'s content request preference, a deep deterministic policy gradient algorithm is used to jointly optimize the cache strategy, AP clustering, and DAC resolution decisions. Simulation results show that the energy efficiency of the proposed scheme is 4% higher than that of other schemes without the resolution optimization and is much higher than that of the only AP clustering without the joint design of content caching and channel quality.
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Affiliation(s)
- Fangqing Tan
- Guangxi Key Laboratory of Wireless Wideband Communication and Signal Processing, Guilin University of Electronic Technology, Guilin 541004, China;
| | - Yuan Peng
- Guangxi Key Laboratory of Wireless Wideband Communication and Signal Processing, Guilin University of Electronic Technology, Guilin 541004, China;
| | - Qiang Liu
- College of Electronic and Information Engineering, Shandong University of Science and Technology, Qingdao 266590, China
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Huang X, Wang Y, Chen S, Li Y, Wu Y. Joint User Clustering and Graph Coloring Based Pilot Assignment for Cell-Free Massive MIMO Systems. Sensors (Basel) 2023; 23:s23115014. [PMID: 37299740 DOI: 10.3390/s23115014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/18/2023] [Revised: 05/22/2023] [Accepted: 05/22/2023] [Indexed: 06/12/2023]
Abstract
Pilot contamination due to pilot reuse seriously mitigates the performance of the cell-free massive multiple-input multiple-output (MIMO) systems. In this paper, we propose a joint pilot assignment scheme that employs user clustering and graph coloring (UC-GC) to reduce pilot contamination. The proposed method consists of two steps: firstly, we utilize AP selection to classify all users; secondly, we assign pilots to users with more severe pilot contamination using the graph coloring algorithm and then assign pilots to the remaining users. The numerical simulation results show that the proposed scheme outperforms existing pilot assignment schemes and significantly improves throughout with low complexity.
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Affiliation(s)
- Xinyu Huang
- School of Microelectronics and Communication Engineering, Chongqing University, Chongqing 400044, China
| | - Yubo Wang
- Beijing Smart-Chip Microelectronics Technology Co., Ltd., Beijing 100192, China
| | - Shiyong Chen
- School of Microelectronics and Communication Engineering, Chongqing University, Chongqing 400044, China
| | - Yan Li
- School of Microelectronics and Communication Engineering, Chongqing University, Chongqing 400044, China
| | - Yucheng Wu
- School of Microelectronics and Communication Engineering, Chongqing University, Chongqing 400044, China
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Oh JH, Shin BS, Kim MA, You YH, Hwang DD, Song HK. Efficient User-Serving Scheme in the User-Centric Cell-Free Massive MIMO System. Sensors (Basel) 2022; 22:s22103794. [PMID: 35632203 PMCID: PMC9143762 DOI: 10.3390/s22103794] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/21/2022] [Revised: 05/13/2022] [Accepted: 05/16/2022] [Indexed: 02/04/2023]
Abstract
A cell-free massive multiple input multiple output (MIMO) system is an attractive network model that is in the spotlight in 5G and future communication systems. Despite numerous advantages, the cell-free massive MIMO system has a problem in that it is difficult to operate in reality due to its vast amount of calculation. The user-centric cell-free massive MIMO model has a more feasible and scalable benefit than the cell-free massive MIMO model. However, this model has the disadvantage that as the number of users in the area increases, there are users who do not receive the service. In this paper, the proposed scheme creates connections for unserved users under a user-centric scheme without additional access point (AP) installation and disconnection for existing users. A downlink user-centric cell-free massive MIMO system model in which the APs are connected to the central processing unit (CPU) and the APs and users are geographically distributed is considered. First, the downlink spectral efficiency formula is derived and applied to the user-centric cell-free massive MIMO system. Then, the proposed scheme and power control algorithm are applied to the derived formula. The simulation results show that the unserved users within the area disappear by using the proposed scheme, while the bit error rate (BER) performance and sum rate improve compared to the existing scheme. In addition, it is shown that the proposed scheme works well even with a very large number of users in the area, and a significant service performance improvement for the worst 10% of users and the overall improvement of per-user throughput for the bottom 70% of users are ensured.
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Affiliation(s)
- Ji-Hye Oh
- Department of Information and Communication Engineering, Sejong University, Seoul 05006, Korea; (J.-H.O.); (B.-S.S.); (M.-A.K.)
- Department of Convergence Engineering for Intelligent Drone, Sejong University, Seoul 05006, Korea;
| | - Beom-Sik Shin
- Department of Information and Communication Engineering, Sejong University, Seoul 05006, Korea; (J.-H.O.); (B.-S.S.); (M.-A.K.)
- Department of Convergence Engineering for Intelligent Drone, Sejong University, Seoul 05006, Korea;
| | - Min-A Kim
- Department of Information and Communication Engineering, Sejong University, Seoul 05006, Korea; (J.-H.O.); (B.-S.S.); (M.-A.K.)
- Department of Convergence Engineering for Intelligent Drone, Sejong University, Seoul 05006, Korea;
| | - Young-Hwan You
- Department of Convergence Engineering for Intelligent Drone, Sejong University, Seoul 05006, Korea;
- Department of Computer Engineering, Sejong University, Seoul 05006, Korea
| | - Duck-Dong Hwang
- Department of Electronics and Communication Engineering, Sejong University, Seoul 05006, Korea;
| | - Hyoung-Kyu Song
- Department of Information and Communication Engineering, Sejong University, Seoul 05006, Korea; (J.-H.O.); (B.-S.S.); (M.-A.K.)
- Department of Convergence Engineering for Intelligent Drone, Sejong University, Seoul 05006, Korea;
- Correspondence:
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Han T, Zhao D. The Downlink Performance for Cell-Free Massive MIMO with Instantaneous CSI in Slowly Time-Varying Channels. Entropy (Basel) 2021; 23:e23111552. [PMID: 34828250 PMCID: PMC8619223 DOI: 10.3390/e23111552] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/25/2021] [Revised: 11/16/2021] [Accepted: 11/19/2021] [Indexed: 11/16/2022]
Abstract
In centralized massive multiple-input multiple-output (MIMO) systems, the channel hardening phenomenon can occur, in which the channel behaves as almost fully deterministic as the number of antennas increases. Nevertheless, in a cell-free massive MIMO system, the channel is less deterministic. In this paper, we propose using instantaneous channel state information (CSI) instead of statistical CSI to obtain the power control coefficient in cell-free massive MIMO. Access points (APs) and user equipment (UE) have sufficient time to obtain instantaneous CSI in a slowly time-varying channel environment. We derive the achievable downlink rate under instantaneous CSI for frequency division duplex (FDD) cell-free massive MIMO systems and apply the results to the power control coefficients. For FDD systems, quantized channel coefficients are proposed to reduce feedback overhead. The simulation results show that the spectral efficiency performance when using instantaneous CSI is approximately three times higher than that achieved using statistical CSI.
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Li J, Chen L, Zhu P, Wang D, You X. Satellite-Assisted Cell-Free Massive MIMO Systems with Multi-Group Multicast. Sensors (Basel) 2021; 21:s21186222. [PMID: 34577428 PMCID: PMC8472470 DOI: 10.3390/s21186222] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/02/2021] [Revised: 09/13/2021] [Accepted: 09/15/2021] [Indexed: 11/16/2022]
Abstract
In this paper, we use satellite-assisted and multi-group multicast mechanisms to relieve ground traffic pressure and improve data transmission efficiency of cell-free massive MIMO systems. We propose to estimate channel state information (CSI) by common pilot scheme. Given the estimated CSI, we derive the closed-form expressions of achievable rate with maximum ratio transmission (MRT) and zero-forcing (ZF) precoding. The correctness of the closed-form expressions is verified through simulations. The results show that with the help of satellite and multicast, the average system spectrum efficiency (SE) can be significantly improved.
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Affiliation(s)
- Jiamin Li
- National Mobile Communications Research Laboratory, Southeast University, Nanjing 210096, China; (J.L.); (D.W.); (X.Y.)
| | - Lingling Chen
- School of Information Science and Engineering, Southeast University, Nanjing 210096, China;
| | - Pengcheng Zhu
- National Mobile Communications Research Laboratory, Southeast University, Nanjing 210096, China; (J.L.); (D.W.); (X.Y.)
- Correspondence:
| | - Dongming Wang
- National Mobile Communications Research Laboratory, Southeast University, Nanjing 210096, China; (J.L.); (D.W.); (X.Y.)
| | - Xiaohu You
- National Mobile Communications Research Laboratory, Southeast University, Nanjing 210096, China; (J.L.); (D.W.); (X.Y.)
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Zhou M, Zhang Y, Qiao X, Tan W, Yang L. Analysis and Optimization for Downlink Cell-Free Massive MIMO System with Mixed DACs. Sensors (Basel) 2021; 21:s21082624. [PMID: 33918009 PMCID: PMC8068372 DOI: 10.3390/s21082624] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/24/2021] [Revised: 04/05/2021] [Accepted: 04/06/2021] [Indexed: 11/21/2022]
Abstract
This paper concentrates on the rate analysis and optimization for a downlink cell-free massive multi-input multi-output (MIMO) system with mixed digital-to-analog converters (DACs), where some of the access points (APs) use perfect-resolution DACs, while the others exploit low-resolution DACs to reduce hardware cost and power consumption. By using the additive quantization noise model (AQNM) and conjugate beamforming receiver, a tight closed-form rate expression is derived based on the standard minimum mean square error (MMSE) channel estimate technique. With the derived result, the effects of the number of APs, the downlink transmitted power, the number of DAC bits, and the proportion of the perfect DACs in the mixed-DAC architecture are conducted. We find that the achievable sum rate can be improved by increasing the proportion of the perfect DACs and deploying more APs. Besides, when the DAC resolution arrives at 5-bit, the system performance will invariably approach the case of perfect DACs, which indicates that we can use 5-bit DACs to substitute the perfect DACs. Thus, it can greatly reduce system hardware cost and power consumption. Finally, the weighted max–min power allocation scheme is proposed to guarantee that the users with high priority have a higher rate, while the others are served with the same rate. The simulation results prove the proposed scheme can be effectively solved by the bisection algorithm.
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Affiliation(s)
- Meng Zhou
- The Department of Wireless Communication Key Lab of Jiangsu Province, Nanjing University of Posts and Telecommunications, Nanjing 210003, China; (M.Z.); (Y.Z.); (X.Q.)
| | - Yao Zhang
- The Department of Wireless Communication Key Lab of Jiangsu Province, Nanjing University of Posts and Telecommunications, Nanjing 210003, China; (M.Z.); (Y.Z.); (X.Q.)
| | - Xu Qiao
- The Department of Wireless Communication Key Lab of Jiangsu Province, Nanjing University of Posts and Telecommunications, Nanjing 210003, China; (M.Z.); (Y.Z.); (X.Q.)
| | - Weiqiang Tan
- School of Computer Science and Cyber Engineering, Guangzhou University, Guangzhou 510006, China;
| | - Longxiang Yang
- The Department of Wireless Communication Key Lab of Jiangsu Province, Nanjing University of Posts and Telecommunications, Nanjing 210003, China; (M.Z.); (Y.Z.); (X.Q.)
- Correspondence: ; Tel.: +86-025-8349-2097
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