Issues, Challenges, and Research Trends in Spectrum Management: A Comprehensive Overview and New Vision for Designing 6G Networks  
[PERSON]  
1 Faculty of Information Science and Technology, Universiti Kebangsaan Malaysia (UKM), Bangi, Selangor 43600, Malaysia; [PERSON]@ukm.edu.my1 Faculty of Information Science and Technology, Universiti Kebangsaan Malaysia (UKM), Bangi, Selangor 43600, Malaysia; [PERSON]@ukm.edu.my1 Faculty of Information Science and Technology, Universiti Kebangsaan Malaysia (UKM), Bangi, Selangor 43600, Malaysia; [PERSON]@ukm.edu.my1 Faculty of Information Science and Technology, Universiti Kebangsaan Malaysia (UKM), UKM, Bangi, Selangor 43600, Malaysia; [PERSON]@ukm.edu.my1 Faculty of Information Science and Technology, Universiti Kebangsaan Malaysia (UKM), Bangi, Selangor 43600, Malaysia; [PERSON]@ukm.edu.my1 Faculty of Information Science and Technology, Universiti Kebangsaan Malaysia (UKM), UKM, Bangi, Selangor 43600, Malaysia; [PERSON]@ukm. for data, the mobile data traffic must be boosted by 1000\(\times\)[1]. Records show that the amount of data managed by wireless systems has increased from under 3 exabytes in 2010 to over 190 exabytes in 2020; therefore, if a data request is carried with the same speed, the demand for data is expected to grow by more than 500 exabytes by 2025 and beyond [2]. This expected leap of high mobile data demand and other machine-type communication services makes it necessary to ponder on the requirements for future 6G networks [3]. Spectral efficiency, energy efficiency, high bandwidth, and low power consumption are regarded as a critical challenge and should be considered before designing 6G networks [4, 5]. To substantiate future data necessities and support a diverse set of devices, New Radio (NR) 6G networks are predicted to meet these demands with competently managed spectrum resources [6]. According to researchers, NR is a combination of various radio access technologies that help supply expected data with low latency, high-spectrum efficiency, and low power consumption [7]. It is broadly classified as low-power small cells utilizing the millimeter-wave (mmWave) spectrum, considering effective use of an unlicensed spectrum of Wi-Fi in a 5 GHz band and the implementation of Massive Multiple-Input-Multiple-Output (M-MIMO) technology instead of the conventional \(2\times 2\) MIMO system [8]. The utilization of high-spectrum access, i.e., mmWave frequency band [9], Cognitive Radio (CR) [10], M-MIMO [11], Cooperative Networks (CNs) using Relay Nodes (RNs) [12], Coordinated Multipoint Operation (CoMP) [13], Wireless Sensor Networks (WSN) [14], Mobile Ad Hoc Networks (MANETs) [15, 16], Device-to-Device (D2D) communication [17], Internet of Things (IoT) [18, 19], Ethernet Passive Optical Networks (EPON) [20], Heterogeneous Networks (HetNet) [21], and cellular cloud computing, including big data [22], are some of the current approaches that can be modified to deliver the 6G requisites. Moreover, the use of various power optimizations [23, 24], handover processes [25], interference cancellation [26], data security management [27], routing protocols [28], and scheduling algorithms [29] with optimal enhancement can also deliver ultimate results. New approaches, such as satellite communication at the mmWave spectrum [30], Artificial Intelligence (AI)-based micro Base Stations (BSs) [31], machine learning-based communication [32, 33], blockchain [34], and human-centric communication [35], are some promising ideas for designing 6G networks. Furthermore, in 6G radio access technologies, Spectrum Sharing (SS) and Radio Resource Management (RRM) are a critical part of the design of a future network [36]. Looking after and using the spectrum resources wisely are important when moving toward a new frequency spectrum, specifically in the mmWave frequency band [37]. The demand for a new spectrum has increased tremendously as the number of users and diverse electronic communication devices expands exponentially [38].