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The underlying problem is NP-hard and non-convex due to the joint optimization of hybrid processing components and the constant amplitude constraint imposed by the analog beamformer in the radio frequency (RF) domain. Furthermore, the analog beamforming solution common to all sub-carriers adds another layer of design complexity. Two hybrid beamforming architectures, i.e., mixed and fully connected ones, are taken into account to tackle this problem, considering the decode-and-forward (DF) relay node. To reduce the complexity of the original optimization problem, an attempt is made to decompose it into sub-problems. Leveraging this, each sub-problem is addressed by following a decoupled design methodology. The phase-only beamforming solution is derived to maximize the sum of spectral efficiency, while digital baseband processing components are designed to keep interference within a predefined limit. Computer simulations are conducted by changing system parameters under different accuracy levels of channel-state information (CSI), and the obtained results demonstrate the effectiveness of the proposed technique. Additionally, the mixed structure shows better energy efficiency performance compared to its counterparts and outperforms benchmarks.<\/jats:p>","DOI":"10.3390\/s24123713","type":"journal-article","created":{"date-parts":[[2024,6,7]],"date-time":"2024-06-07T08:05:17Z","timestamp":1717747517000},"page":"3713","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":5,"title":["Spectral Efficiency Maximization for Mixed-Structure Cognitive Radio Hybrid Wideband Millimeter-Wave Transceivers in Relay-Assisted Multi-User Multiple-Input Multiple-Output Systems"],"prefix":"10.3390","volume":"24","author":[{"given":"Hafiz Muhammad Tahir","family":"Mustafa","sequence":"first","affiliation":[{"name":"Department of Information and Communication Engineering, Sejong University, Seoul 05006, Republic of Korea"},{"name":"Department of Convergence Engineering for Intelligent Drone, Sejong University, Seoul 05006, Republic of Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jung-In","family":"Baik","sequence":"additional","affiliation":[{"name":"Department of Information and Communication Engineering, Sejong University, Seoul 05006, Republic of Korea"},{"name":"Department of Convergence Engineering for Intelligent Drone, Sejong University, Seoul 05006, Republic of Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3274-4982","authenticated-orcid":false,"given":"Hyoung-Kyu","family":"Song","sequence":"additional","affiliation":[{"name":"Department of Information and Communication Engineering, Sejong University, Seoul 05006, Republic of Korea"},{"name":"Department of Convergence Engineering for Intelligent Drone, Sejong University, Seoul 05006, Republic of Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6374-9682","authenticated-orcid":false,"given":"Muhammad","family":"Adnan","sequence":"additional","affiliation":[{"name":"Department of Computer Science (SST), University of Management and Technology, Lahore 54770, Pakistan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Waqar Majeed","family":"Awan","sequence":"additional","affiliation":[{"name":"Department of Electrical Engineering, University of Management and Technology, Lahore 54770, Pakistan"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2024,6,7]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"7271","DOI":"10.1109\/TWC.2022.3157315","article-title":"Delay-Phase Precoding for Wideband THz Massive MIMO","volume":"21","author":"Dai","year":"2022","journal-title":"IEEE Trans. Wirel. Commun."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"1565","DOI":"10.1109\/TWC.2023.3290326","article-title":"Joint MIMO Communications and Sensing With Hybrid Beamforming Architecture and OFDM Waveform Optimization","volume":"23","author":"Liyanaarachchi","year":"2024","journal-title":"IEEE Trans. Wirel. Commun."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"28","DOI":"10.1109\/MVT.2019.2921208","article-title":"6G Wireless Networks: Vision, Requirements, Architecture, and Key Technologies","volume":"14","author":"Zhang","year":"2019","journal-title":"IEEE Veh. Technol. Mag."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"133995","DOI":"10.1109\/ACCESS.2020.3010896","article-title":"6G and Beyond: The Future of Wireless Communications Systems","volume":"8","author":"Akyildiz","year":"2020","journal-title":"IEEE Access"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"8941","DOI":"10.1109\/TVT.2023.3246632","article-title":"Low-Resolution Hybrid Beamforming in Millimeter-Wave Multi-User Systems","volume":"72","author":"Yu","year":"2023","journal-title":"IEEE Trans. Veh. Technol."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"2912","DOI":"10.1109\/JSAC.2021.3088681","article-title":"A Comprehensive Overview on 5G-and-Beyond Networks With UAVs: From Communications to Sensing and Intelligence","volume":"39","author":"Wu","year":"2021","journal-title":"IEEE J. Sel. Areas Commun."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"510","DOI":"10.1109\/JSAC.2016.2525418","article-title":"Internet of Things in the 5G Era: Enablers, Architecture, and Business Models","volume":"34","author":"Palattella","year":"2016","journal-title":"IEEE J. Sel. Areas Commun."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"114","DOI":"10.1109\/MCOM.2018.1701310","article-title":"From IoT to 5G I-IoT: The Next Generation IoT-Based Intelligent Algorithms and 5G Technologies","volume":"56","author":"Wang","year":"2018","journal-title":"IEEE Commun. Mag."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"40","DOI":"10.1109\/MCOM.2008.4481339","article-title":"A survey on spectrum management in cognitive radio networks","volume":"46","author":"Akyildiz","year":"2008","journal-title":"IEEE Commun. Mag."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"96052","DOI":"10.1109\/ACCESS.2023.3309877","article-title":"Frequency Selective Hybrid Beamforming and Optimal Power Loading for Multiuser Millimeter Wave Cognitive Radio Networks","volume":"11","author":"Chatterjee","year":"2023","journal-title":"IEEE Access"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"241","DOI":"10.1109\/OJVT.2023.3236525","article-title":"Hybrid Transceiver Design and Optimal Power Allocation for the Cognitive mmWave Multiuser MIMO Downlink Relying on Limited Feedback","volume":"4","author":"Singh","year":"2023","journal-title":"IEEE Open J. Veh. Technol."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"143458","DOI":"10.1109\/ACCESS.2021.3122331","article-title":"Dynamic Spectrum Allocation Following Machine Learning-Based Traffic Predictions in 5G","volume":"9","author":"Rony","year":"2021","journal-title":"IEEE Access"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"2231","DOI":"10.1109\/TVT.2022.3213752","article-title":"Precoder Design for Multi-Hop Cognitive MIMO Relay Systems With Finite-Alphabet Inputs","volume":"72","author":"Chen","year":"2023","journal-title":"IEEE Trans. Veh. Technol."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"4075","DOI":"10.1109\/TWC.2019.2920871","article-title":"Cognitive Multi-Hop Multi-Branch Relaying: Spectrum Leasing and Optimal Power Allocation","volume":"18","author":"Bastami","year":"2019","journal-title":"IEEE Trans. Wirel. Commun."},{"key":"ref_15","doi-asserted-by":"crossref","unstructured":"Sboui, L., Ghazzai, H., and Massoud, Y. (2022, January 16\u201318). Integrating Cognitive Radio MIMO UAVs in Cellular Networks for 5G and Beyond. Proceedings of the 2022 International Conference on Electrical, Computer, Communications and Mechatronics Engineering (ICECCME), Male, Maldives.","DOI":"10.1109\/ICECCME55909.2022.9988381"},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"3561","DOI":"10.1109\/TWC.2017.2684125","article-title":"End-to-End Throughput Maximization for Underlay Multi-Hop Cognitive Radio Networks With RF Energy Harvesting","volume":"16","author":"Xu","year":"2017","journal-title":"IEEE Trans. Wirel. Commun."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"5143","DOI":"10.1109\/TWC.2016.2553659","article-title":"Transmit Precoding in Underlay MIMO Cognitive Radio With Unavailable or Imperfect Knowledge of Primary Interference Channel","volume":"15","author":"Ho","year":"2016","journal-title":"IEEE Trans. Wirel. Commun."},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Al-Sudani, H., Thabit, A.A., and Dalveren, Y. (June, January 31). Cognitive Radio and Its Applications in the New Trend of Communication System: A Review. Proceedings of the 2022 5th International Conference on Engineering Technology and Its Applications (IICETA), Al-Najaf, Iraq.","DOI":"10.1109\/IICETA54559.2022.9888674"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"9201","DOI":"10.1109\/TWC.2023.3269056","article-title":"Alternating Optimization Based Hybrid Transceiver Designs for Wideband Millimeter-Wave Massive Multiuser MIMO-OFDM Systems","volume":"22","author":"Yuan","year":"2023","journal-title":"IEEE Trans. Wirel. Commun."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"7208","DOI":"10.1109\/TWC.2018.2865786","article-title":"On the Energy Efficiency of MIMO Hybrid Beamforming for Millimeter-Wave Systems With Nonlinear Power Amplifiers","volume":"17","author":"Moghadam","year":"2018","journal-title":"IEEE Trans. Wirel. Commun."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"5770","DOI":"10.1109\/TWC.2022.3142959","article-title":"Hybrid Beamforming Designs for Frequency-Selective mmWave MIMO Systems With Per-RF Chain or Per-Antenna Power Constraints","volume":"21","year":"2022","journal-title":"IEEE Trans. Wirel. Commun."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"99878","DOI":"10.1109\/ACCESS.2019.2930208","article-title":"Cell-Free Massive MIMO: A New Next-Generation Paradigm","volume":"7","author":"Zhang","year":"2019","journal-title":"IEEE Access"},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"1663","DOI":"10.1109\/JSAC.2021.3071836","article-title":"Multi-Hop RIS-Empowered Terahertz Communications: A DRL-Based Hybrid Beamforming Design","volume":"39","author":"Huang","year":"2021","journal-title":"IEEE J. Sel. Areas Commun."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"5075","DOI":"10.1109\/TWC.2021.3136788","article-title":"Multi-Hop Relaying Distribution Strategies for Terahertz-Band Communication Networks: A Cross-Layer Analysis","volume":"21","author":"Xia","year":"2022","journal-title":"IEEE Trans. Wirel. Commun."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"2943","DOI":"10.1109\/TVT.2020.2966122","article-title":"Hybrid Beamforming for Multi-User Millimeter-Wave Networks","volume":"69","author":"Nasir","year":"2020","journal-title":"IEEE Trans. Veh. Technol."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"4829","DOI":"10.1007\/s11276-018-1748-6","article-title":"Iterative hybrid precoder and combiner design for mmWave MIMO-OFDM systems","volume":"25","author":"Li","year":"2019","journal-title":"Wirel. Netw."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"8739","DOI":"10.1109\/TVT.2020.3000443","article-title":"Performance Analysis of Hybrid Beamforming Precoders for Multiuser Millimeter Wave NOMA Systems","volume":"69","author":"Badrudeen","year":"2020","journal-title":"IEEE Trans. Veh. Technol."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"95021","DOI":"10.1109\/ACCESS.2019.2928559","article-title":"Energy-Efficient Hybrid Precoding With Low Complexity for mmWave Massive MIMO Systems","volume":"7","author":"Liu","year":"2019","journal-title":"IEEE Access"},{"key":"ref_29","first-page":"998","article-title":"Energy Efficiency Maximization for Partially-Connected Hybrid Beamforming Architecture with Low-Resolution DACs","volume":"34","author":"Gao","year":"2024","journal-title":"IEEE Trans. Commun."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"1999","DOI":"10.1109\/TWC.2023.3294402","article-title":"Hybrid MMSE Precoding for Millimeter Wave MU-MISO via Trace Maximization","volume":"23","author":"Gautam","year":"2024","journal-title":"IEEE Trans. Wirel. Commun."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"1199","DOI":"10.1109\/TWC.2023.3287229","article-title":"Joint Precoding Design for Sub-Connected Hybrid Beamforming System","volume":"23","author":"Hu","year":"2024","journal-title":"IEEE Trans. Wirel. Commun."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"35457","DOI":"10.1109\/ACCESS.2023.3264838","article-title":"Direct Conversion of Hybrid Precoding and Combining From Full Array Architecture to Subarray Architecture for mmWave MIMO Systems","volume":"11","author":"Alouzi","year":"2023","journal-title":"IEEE Access"},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"3981","DOI":"10.1109\/TCOMM.2016.2590467","article-title":"On the Feasibility of Sharing Spectrum Licenses in mmWave Cellular Systems","volume":"64","author":"Gupta","year":"2016","journal-title":"IEEE Trans. Commun."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"155","DOI":"10.1109\/TCCN.2017.2707551","article-title":"Hybrid Spectrum Sharing in mmWave Cellular Networks","volume":"3","author":"Rebato","year":"2017","journal-title":"IEEE Trans. Cogn. Commun. Netw."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"1269","DOI":"10.1109\/TCCN.2020.2981031","article-title":"A Hybrid Model-Based and Data-Driven Approach to Spectrum Sharing in mmWave Cellular Networks","volume":"6","author":"Ghadikolaei","year":"2020","journal-title":"IEEE Trans. Cogn. Commun. Netw."},{"key":"ref_36","doi-asserted-by":"crossref","unstructured":"Li, G., Irnich, T., and Shi, C. (2014, January 2\u20134). Coordination context-based spectrum sharing for 5G millimeter-wave networks. Proceedings of the 2014 9th International Conference on Cognitive Radio Oriented Wireless Networks and Communications (CROWNCOM), Oulu, Finland.","DOI":"10.4108\/icst.crowncom.2014.255741"},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"2902","DOI":"10.1109\/JSAC.2016.2615259","article-title":"Spectrum Sharing in mmWave Cellular Networks via Cell Association, Coordination, and Beamforming","volume":"34","author":"Boccardi","year":"2016","journal-title":"IEEE J. Sel. Areas Commun."},{"key":"ref_38","doi-asserted-by":"crossref","unstructured":"Vrontos, C., Boccardi, F., Armour, S., Mellios, E., and Butler, J. (2020, January 25\u201328). Performance Evaluation of Spectrum Sharing in mmWave Cellular Networks using Ray-Tracing. Proceedings of the 2020 IEEE Wireless Communications and Networking Conference (WCNC), Seoul, Republic of Korea.","DOI":"10.1109\/WCNC45663.2020.9120742"},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"1818","DOI":"10.1109\/TNET.2020.2994134","article-title":"A Practical Spectrum Sharing Scheme for Cognitive Radio Networks: Design and Experiments","volume":"28","author":"Sangdeh","year":"2020","journal-title":"IEEE\/ACM Trans. Netw."},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"3264","DOI":"10.1109\/TWC.2013.052813121110","article-title":"Interference Management in Underlay Spectrum Sharing Using Indirect Power Control Signalling","volume":"12","author":"Khoshkholgh","year":"2013","journal-title":"IEEE Trans. Wirel. Commun."},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"6331","DOI":"10.1109\/TWC.2020.3002719","article-title":"Principal Component Analysis-Based Broadband Hybrid Precoding for Millimeter-Wave Massive MIMO Systems","volume":"19","author":"Sun","year":"2020","journal-title":"IEEE Trans. Wirel. Commun."},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"501","DOI":"10.1109\/JSTSP.2016.2520912","article-title":"Hybrid Digital and Analog Beamforming Design for Large-Scale Antenna Arrays","volume":"10","author":"Sohrabi","year":"2016","journal-title":"IEEE J. Sel. Top. Signal Process."},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"1432","DOI":"10.1109\/JSAC.2017.2698958","article-title":"Hybrid Analog and Digital Beamforming for mmWave OFDM Large-Scale Antenna Arrays","volume":"35","author":"Sohrabi","year":"2017","journal-title":"IEEE J. Sel. Areas Commun."},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"2907","DOI":"10.1109\/TWC.2017.2671869","article-title":"Dynamic Subarrays for Hybrid Precoding in Wideband mmWave MIMO Systems","volume":"16","author":"Park","year":"2017","journal-title":"IEEE Trans. Wirel. Commun."},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"8108","DOI":"10.1109\/TWC.2018.2874227","article-title":"Hybrid Precoding With Partially Connected Structure for Millimeter Wave Massive MIMO OFDM: A Parallel Framework and Feasibility Analysis","volume":"17","author":"Dsouza","year":"2018","journal-title":"IEEE Trans. Wirel. Commun."},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"8218","DOI":"10.1109\/TWC.2021.3091524","article-title":"Partially-Connected Hybrid Beamforming for Spectral Efficiency Maximization via a Weighted MMSE Equivalence","volume":"20","author":"Zhao","year":"2021","journal-title":"IEEE Trans. Wirel. Commun."},{"key":"ref_47","doi-asserted-by":"crossref","first-page":"518","DOI":"10.1109\/TWC.2018.2882490","article-title":"Sub-System SVD Hybrid Beamforming Design for Millimeter Wave Multi-Carrier Systems","volume":"18","author":"Tsai","year":"2019","journal-title":"IEEE Trans. Wirel. Commun."},{"key":"ref_48","doi-asserted-by":"crossref","first-page":"9698","DOI":"10.1109\/TVT.2019.2932128","article-title":"Weighted Spectral Efficiency Optimization for Hybrid Beamforming in Multiuser Massive MIMO-OFDM Systems","volume":"68","author":"Du","year":"2019","journal-title":"IEEE Trans. Veh. Technol."},{"key":"ref_49","doi-asserted-by":"crossref","first-page":"5775","DOI":"10.1109\/TVT.2021.3076691","article-title":"Constrained Tensor Decomposition-Based Hybrid Beamforming for Mmwave Massive MIMO-OFDM Communication Systems","volume":"70","author":"Zilli","year":"2021","journal-title":"IEEE Trans. Veh. Technol."},{"key":"ref_50","doi-asserted-by":"crossref","first-page":"983","DOI":"10.1109\/TVT.2018.2880787","article-title":"Low Complexity Hybrid Precoding for Multiuser Millimeter Wave Systems Over Frequency Selective Channels","volume":"68","author":"Yuan","year":"2019","journal-title":"IEEE Trans. Veh. Technol."},{"key":"ref_51","doi-asserted-by":"crossref","first-page":"485","DOI":"10.1109\/JSTSP.2016.2523903","article-title":"Alternating Minimization Algorithms for Hybrid Precoding in Millimeter Wave MIMO Systems","volume":"10","author":"Yu","year":"2016","journal-title":"IEEE J. Sel. Top. Signal Process."},{"key":"ref_52","doi-asserted-by":"crossref","first-page":"1499","DOI":"10.1109\/TWC.2014.011714.130846","article-title":"Spatially Sparse Precoding in Millimeter Wave MIMO Systems","volume":"13","author":"Ayach","year":"2014","journal-title":"IEEE Trans. Wirel. Commun."},{"key":"ref_53","doi-asserted-by":"crossref","unstructured":"Lee, J., and Lee, Y.H. (2014, January 10\u201314). AF relaying for millimeter wave communication systems with hybrid RF\/baseband MIMO processing. Proceedings of the 2014 IEEE International Conference on Communications (ICC), Sydney, Australia.","DOI":"10.1109\/ICC.2014.6884253"},{"key":"ref_54","doi-asserted-by":"crossref","unstructured":"Xue, X., Bogale, T.E., Wang, X., Wang, Y., and Long, B.L. (2015, January 2\u20134). Hybrid analog-digital beamforming for multiuser MIMO millimeter wave relay systems. Proceedings of the 2015 IEEE\/CIC International Conference on Communications in China (ICCC), Shenzhen, China.","DOI":"10.1109\/ICCChina.2015.7448664"},{"key":"ref_55","doi-asserted-by":"crossref","first-page":"2011","DOI":"10.1109\/TSP.2018.2799201","article-title":"Relay Hybrid Precoding Design in Millimeter-Wave Massive MIMO Systems","volume":"66","author":"Xue","year":"2018","journal-title":"IEEE Trans. Signal Process."},{"key":"ref_56","doi-asserted-by":"crossref","unstructured":"Xu, W., Wang, Y., and Xue, X. (2018, January 27\u201330). ADMM for Hybrid Precoding of Relay in Millimeter-Wave Massive MIMO System. Proceedings of the 2018 IEEE 88th Vehicular Technology Conference (VTC-Fall), Chicago, IL, USA.","DOI":"10.1109\/VTCFall.2018.8690879"},{"key":"ref_57","doi-asserted-by":"crossref","first-page":"1880","DOI":"10.1109\/JSAC.2020.3000808","article-title":"Hybrid Transceiver Optimization for Multi-Hop Communications","volume":"38","author":"Xing","year":"2020","journal-title":"IEEE J. Sel. Areas Commun."},{"key":"ref_58","doi-asserted-by":"crossref","first-page":"662","DOI":"10.1109\/TCOMM.2017.2756882","article-title":"Hybridly Connected Structure for Hybrid Beamforming in mmWave Massive MIMO Systems","volume":"66","author":"Zhang","year":"2018","journal-title":"IEEE Trans. Commun."},{"key":"ref_59","doi-asserted-by":"crossref","first-page":"8940","DOI":"10.1109\/TVT.2019.2930639","article-title":"Millimeter-Wave Massive MIMO Systems Relying on Generalized Sub-Array-Connected Hybrid Precoding","volume":"68","author":"Chen","year":"2019","journal-title":"IEEE Trans. Veh. Technol."},{"key":"ref_60","doi-asserted-by":"crossref","first-page":"107","DOI":"10.1109\/TCOMM.2018.2867490","article-title":"Hybrid Processing Design for Multipair Massive MIMO Relaying With Channel Spatial Correlation","volume":"67","author":"Fozooni","year":"2019","journal-title":"IEEE Trans. Commun."},{"key":"ref_61","doi-asserted-by":"crossref","first-page":"73093","DOI":"10.1109\/ACCESS.2018.2881714","article-title":"Robust Hybrid Beamforming in Millimeter Wave Relay Networks With Imperfect CSI","volume":"6","author":"Luo","year":"2018","journal-title":"IEEE Access"},{"key":"ref_62","doi-asserted-by":"crossref","first-page":"2273","DOI":"10.1109\/TSP.2018.2806358","article-title":"Hybrid Analog\u2013Digital Transmit Beamforming for Spectrum Sharing Backhaul Networks","volume":"66","author":"Blanco","year":"2018","journal-title":"IEEE Trans. Signal Process."},{"key":"ref_63","doi-asserted-by":"crossref","first-page":"109763","DOI":"10.1109\/ACCESS.2019.2933559","article-title":"Secure Hybrid Digital and Analog Precoder for mmWave Systems With Low-Resolution DACs and Finite-Quantized Phase Shifters","volume":"7","author":"Xu","year":"2019","journal-title":"IEEE Access"},{"key":"ref_64","doi-asserted-by":"crossref","first-page":"4019","DOI":"10.1109\/TIFS.2020.3039697","article-title":"Hybrid Analog-Digital Precoder Design for Securing Cognitive Millimeter Wave Networks","volume":"16","author":"Kong","year":"2021","journal-title":"IEEE Trans. Inf. Forensics Secur."},{"key":"ref_65","doi-asserted-by":"crossref","first-page":"310","DOI":"10.1109\/TCCN.2019.2933423","article-title":"Hybrid Analog-Digital Transceiver Designs for Multi-User MIMO mmWave Cognitive Radio Systems","volume":"6","author":"Tsinos","year":"2020","journal-title":"IEEE Trans. Cogn. Commun. Netw."},{"key":"ref_66","doi-asserted-by":"crossref","first-page":"157212","DOI":"10.1109\/ACCESS.2019.2949786","article-title":"Optimal Hybrid Beamforming Design for Millimeter-Wave Massive Multi-User MIMO Relay Systems","volume":"7","author":"Zhang","year":"2019","journal-title":"IEEE Access"},{"key":"ref_67","doi-asserted-by":"crossref","unstructured":"Song, N., Yang, T., and Sun, H. (2019, January 15\u201318). Efficient Hybrid Beamforming for Relay Assisted Millimeter-Wave Multi-User Massive MIMO. Proceedings of the 2019 IEEE Wireless Communications and Networking Conference (WCNC), Marrakesh, Morocco.","DOI":"10.1109\/WCNC.2019.8886016"},{"key":"ref_68","doi-asserted-by":"crossref","first-page":"66141","DOI":"10.1109\/ACCESS.2021.3073847","article-title":"Efficient Hybrid Beamforming Design in mmWave Massive MU-MIMO DF Relay Systems With the Mixed-Structure","volume":"9","author":"Han","year":"2021","journal-title":"IEEE Access"},{"key":"ref_69","doi-asserted-by":"crossref","first-page":"772","DOI":"10.1109\/TGCN.2022.3226801","article-title":"Hybrid Beamforming With Sub-Connected Structure for MmWave Massive Multi-User MIMO Relay Systems","volume":"7","author":"Han","year":"2023","journal-title":"IEEE Trans. Green Commun. Netw."},{"key":"ref_70","doi-asserted-by":"crossref","unstructured":"Abbasi, Z., Mustafa, H.M.T., Baik, J.-I., Adnan, M., Awan, W.M., and Song, H.-K. (2023). Hybrid Wideband Beamforming for Sum Spectral Efficiency Maximization in Millimeter-Wave Relay-Assisted Multiuser MIMO Cognitive Radio Networks. Mathematics, 11.","DOI":"10.3390\/math11244939"},{"key":"ref_71","doi-asserted-by":"crossref","first-page":"1445","DOI":"10.1109\/TWC.2017.2778258","article-title":"Low-Complexity and Robust Hybrid Beamforming Design for Multi-Antenna Communication Systems","volume":"17","author":"Molu","year":"2018","journal-title":"IEEE Trans. Wirel. Commun."},{"key":"ref_72","doi-asserted-by":"crossref","first-page":"2207","DOI":"10.1109\/TMTT.2016.2574851","article-title":"3-D Millimeter-Wave Statistical Channel Model for 5G Wireless System Design","volume":"64","author":"Samimi","year":"2016","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_73","doi-asserted-by":"crossref","first-page":"181","DOI":"10.1186\/s13638-017-0966-4","article-title":"Spectral efficiency of multi-user millimeter wave systems under single path with uniform rectangular arrays","volume":"2017","author":"Tan","year":"2017","journal-title":"EURASIP J. Wirel. Commun. Netw."},{"key":"ref_74","doi-asserted-by":"crossref","first-page":"1333","DOI":"10.1109\/TWC.2019.2953032","article-title":"mmWave Amplify-and-Forward MIMO Relay Networks With Hybrid Precoding\/Combining Design","volume":"19","author":"Jiang","year":"2020","journal-title":"IEEE Trans. Wirel. Commun."},{"key":"ref_75","doi-asserted-by":"crossref","first-page":"3879","DOI":"10.1109\/TCOMM.2018.2829511","article-title":"Hybrid Beamforming for Multi-User Massive MIMO Systems","volume":"66","author":"Wu","year":"2018","journal-title":"IEEE Trans. Commun."},{"key":"ref_76","doi-asserted-by":"crossref","first-page":"201","DOI":"10.1109\/TCOMM.2015.2502954","article-title":"Hybrid Block Diagonalization for Massive Multiuser MIMO Systems","volume":"64","author":"Ni","year":"2016","journal-title":"IEEE Trans. Commun."},{"key":"ref_77","doi-asserted-by":"crossref","first-page":"998","DOI":"10.1109\/JSAC.2016.2549418","article-title":"Energy-Efficient Hybrid Analog and Digital Precoding for MmWave MIMO Systems With Large Antenna Arrays","volume":"34","author":"Gao","year":"2016","journal-title":"IEEE J. Sel. Areas Commun."},{"key":"ref_78","doi-asserted-by":"crossref","first-page":"3064","DOI":"10.1109\/TCOMM.2024.3354199","article-title":"The Manifestation of Spatial Wideband Effect in Circular Array: From Beam Split to Beam Defocus","volume":"72","author":"Wu","year":"2024","journal-title":"IEEE Trans. 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