## 1 Introduction
It was shown that the former was capable of achieving better BER results. Layered OFDM-IM (L-OFDM-IM) is another example of an IM scheme that divides the OFDM subcarriers into multiple layers [16]. Dual-mode OFDM-IM (DM-OFDM-IM) and multimode OFDM-IM (MM-OFDM-IM) and their generalized versions are other good examples of IM-based OFDM schemes. Both of these schemes use groups of designed constellations, which can be selected according to their indices and desired communication [17; 18; 19; 20]. All of these mentioned schemes tried to improve SE over OFDM-IM. It is important to note that IM can also be applied to time and channel domains. In [21], the authors presented a scheme where IM is applied in the time domain. It uses the concept of time slots, similar to time-division multiple access (TDMA), which is named IM multiple access (IMMA). On the other hand, the IM approach in [22] uses the channel approach to convey additional information through channel realizations. This is also known as media-based modulation (MBM). Many recent works on IM are focused on multiuser (MU) communications, especially in downlink situations. The receivers usually have a limited number of antennas, which are prone to multiuser interference (MUI). On the other hand, the uplink has less complexity and can be addressed like an extension of GSM [23]. Some authors have proposed versions of IM based on multidimensional schemes, which are built with a combination of spatial and frequency domains [7]. In [24], the authors have merged both SM and OFDM-IM schemes simultaneously to produce a scheme named generalized space-frequency IM (GSFIM). In this new technique, the index bits can select which antenna and subcarrier should be activated at each transmission. Although only single user (SU) cases were explored, the authors showed good results in BER performance and transmission rates, when compared with other schemes. More recently, in [25] the authors extended the same concept, proposing multidimensional IM schemes that work in MU scenarios. Both frequency and spatial domains are exploited for downlink MU communications with the assistance of signal space diversity (SSD), showing promising results. In [26], a scheme that combines space-frequency code and MIMO OFDM-IM was proposed. It was shown that the presented scheme was capable of increasing the transmit diversity order. 5G and beyond networks using radio access virtualization strategies and advanced computational platforms will exploit network densification. The virtual cell concept removes the traditional cell boundary for the device and provides a consequent reduction in the detrimental \"cell-edge experience\" by the terminal. Traditionally, devices are associated with a cell and, as a consequence, the link performance may degrade as a terminal moves away from the cell center. In a virtualized cloud radio access network (C-RAN), the network determines which BSs or access points (APs) are to be associated with each terminal. The cell moves with the terminal in order to provide a cell-center experience throughout the entire network. Each terminal is served by its preferred set of APs. The actual serving set for a terminal may contain one or multiple BSs and the terminal's data are partially or fully available at some or a small set of potential serving BSs. The BS controller (central processor) will accommodate each terminal with its preferred set and transmission mode at every communication instance while considering load and channel state information (CSI) knowledge associated with the BS [27]. The 5G NR system [28; 29; 30] uses scalable OFDM numerology introducing specific subcarrier spacings (\(\Delta f\)), transmission time interval (TTI), cyclic prefix (CP) and the number of slots. Higher numerology indices correspond to larger subcarrier spacings (SCSs), ranging from 15 to 480 kHz according to the equation: \(\Delta f=15\) kHz \(\times\) 2\({}^{n}\). The numerology index \(n\) depends on various factors (i.e., service requirements, deployment type, carrier frequency, etc.).