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In this paper, we present a framework to give a comprehensive review of how to improve the spectrum utilization of millimeter-wave (mmWave) systems using indoor small cells in multi-operator network scenarios. More specifically, the framework concerns with the improvement of the utilization of the 28 GHz mmWave spectrum allocated to an arbitrary number of mobile network operators (MNOs) in a country using numerous spectrum allocation techniques, namely Static and Equal Spectrum Allocation (SESA), Flexible and Unequal Spectrum Allocation (FUSA), and Countrywide Full Spectrum Allocation (CFSA). A number of spectrum utilization improvement mechanisms such as spectrum trading, spectrum sharing, and spectrum reusing are then exploited into SESA, FUSA, and CFSA techniques in four major-interconnected domains, including time, frequency, power, and space. Using the Equal Likelihood Criterion and the properties of left-justified Pascal’s triangle, the average capacity, spectral efficiency (SE), and energy efficiency (EE) performance metrics for each spectrum allocation technique in each domain are derived. Extensive system-level numerical and simulation results and analyses are carried out to evaluate the performance of each technique in each domain for example scenario of a country with four MNOs. Overall, it is shown that, in the power-domain, CFSA outperforms SESA and FUSA (when operating either at the interweave or at the underlay spectrum access technique), whereas, in the time-domain and frequency-domain, SESA and FUSA outperform CFSA, in terms of the average capacity, SE, and EE. Finally, we show that CFSA in the power-domain outperforms SESA and FUSA operating in any domain to achieve the prospective SE and EE requirements for the sixth-generation (6G) mobile networks.

This paper presents a tactic to realize numerous in-building small cell base station (SBS) architectures for dynamic spectrum sharing by varying the number of physical transceivers as well as the number, amount, and characteristics of operating spectrums per SBS. Each SBS architecture is defined as a Type and the spectrum sharing mechanism of each Type of architecture is detailed and mathematically analyzed to define existing dynamic spectrum sharing techniques suggested in the literature. The high external wall penetration loss of a building and the eICIC technique are exploited to manage co-channel interference generated due to sharing the spectrum of one system to another. System-level capacity, spectral efficiency, and energy efficiency performance metrics are derived for each SBS architecture to show the relative outperformance of one to another. It is found that, unlike energy efficiency (EE), the spectral efficiency (SE) response of an SBS architecture is directly affected by the channel characteristics as well as the number and amount of operating spectrum bands. However, the number of transceivers of an SBS does not have a noticeable impact on both SE and EE so long as the feature of an operating spectrum is not altered. Finally, we show that each Type of the proposed SBS architectures can achieve the prospective SE and EE requirements for fifth-generation (5G) mobile networks.

In this paper, we propose two spectrum utilization improvement approaches (SUIAs), namely SUIA 1 and SUIA 2, based on whether or not the licensed 28 GHz millimeter-wave (mmWave) spectrum is allocated equally to each mobile network operator (MNO) in a country. Principally, SUIA 1 concerns with improving spectrum utilization if the 28 GHz spectrum is allocated equally to each MNO statically, also termed as static licensed spectrum allocation (SLSA). Whereas, SUIA 2 concerns with improving spectrum utilization if the spectrum is allocated unequally to each MNO in a flexible manner, also termed as flexible licensed spectrum allocation (FLSA). Since sharing and reusing of the licensed spectrum allocated to each MNO using either SLSA or FLSA can be exploited, and the secondary spectrum trading is required only in case of SLSA to redistribute the assigned spectra among MNOs, SUIA 1 employs SLSA, spectrum trading, spectrum sharing, and spectrum reusing techniques, whereas SUIA 2 employs FLSA, spectrum sharing, and spectrum reusing techniques. We present mathematical models for each technique and derive average capacity, spectral efficiency (SE), and energy efficiency (EE) metrics for SUIA 1 and SUIA 2. Extensive numerical and simulation results and analyses for SUIA 1 and SUIA 2 are carried out. It is shown that the spectrum reusing technique influences mostly SE and EE performances. Moreover, SE and EE performances of an MNO in SUIA 1 do not differ considerably from that in SUIA 2 such that depending on the spectrum allocation policies and practices in a country, either SUIA 1 or SUIA 2 can be employed. Finally, it is shown that by applying both SUIA 1 and SUIA 2, the prospective average SE and average EE requirements for sixth-generation (6G) mobile networks can be satisfied.

The traditional static allocation of a portion of the licensed spectrum specified for a country to a mobile network operator (MNO) is no longer sufficient to address the required spectrum demand, as well as efficient to utilize the allocated spectrum. To overcome these constraints, i.e. to increase the spectrum availability and utilization, in this paper, we present a new paradigm for the spectrum allocation called licensed countrywide full-spectrum allocation (LCFSA) to allocate the licensed countrywide full 28 GHz millimeter-wave (mmWave) spectrum to each MNO of a country to operate its small cells per building subject to avoiding co-channel interference (CCI). Since most data is generated indoors, the countrywide full mmWave spectrum allocated to an MNO is considered reusing further to its in-building small cells. CCI avoidance in both the time-domain and frequency-domain is presented along with deducing the conditions for optimality. We derive average capacity, spectral efficiency (SE), energy efficiency (EE), and cost efficiency (CE) for LCFSA, and perform extensive numerical and simulation results and analyses for a country consisting of four MNOs. It is shown that LCFSA with both the time-domain and frequency-domain CCI avoidance schemes provide similar performance improvement in average capacity, SE, EE, and CE by about 296%, 164%, 75%, and 60% respectively for no interfering user equipments (UEs), whereas by about 59.2%, 6.1%, 37.2%, and 0.45% respectively for all interfering UEs with the frequency-domain CCI scheme. Moreover, it is found that the improvement in the above metrics does not change with the spectrum reuse factor (RF) and the number of buildings of small cells per macrocell L, and the impact of interfering UEs can be compensated by adjusting RF. Finally, we show that LCFSA can satisfy the SE and EE requirements for sixth-generation (6G) systems by adjusting either RF or L, or both.

Power-domain based dynamic spectrum access (PDSA) techniques are proposed for sharing 28 GHz spectrum of any Mobile Network Operator (MNO) with in-building small cells (SCs) of the other countrywide. By controlling the transmission power of SCs, PDSA techniques explore the traditional interweave access by operating an SC at the maximum transmission power and the underlay access by allowing to operate an SC at a lowered transmission power separately, as well as jointly. Average capacity, spectral efficiency, energy efficiency, cost efficiency, and throughput per SC user equipment (UE) are derived for an arbitrary number of MNOs in a country. By varying the spectrum reuse factor for the millimeter-wave spectrum in each building of SCs, extensive numerical and simulation results and analyses for an illustrative scenario of a country consisting of four MNOs are carried out for the interweave and underlay techniques when applying separately, as well as the hybrid interweave-underlay technique and the static licensed spectrum allocation (SLSA) technique. It is shown that, due to gaining more shared spectra, the hybrid interweave-underlay technique provides the best, whereas the SLSA provides the worst, performances of all techniques in terms of the average capacity, spectral efficiency, energy efficiency, cost efficiency, and throughput per UE of an SC. Moreover, we show that the hybrid interweave-underlay technique, the interweave technique, and the underlay technique, respectively, can satisfy the expected requirements of spectral and energy efficiencies for Sixth-Generation (6G) networks by reusing each MNO’s 28 GHz spectrum to SCs of about 33.33%, 50%, and 50% less number of buildings than that required by the SLSA for a spectrum reuse factor of six per building of small cells.

In this paper, we first give an overview of the coexistence of cellular with IEEE 802.11 technologies in the unlicensed bands. We then present a coexistence mechanism for Fifth-Generation (5G) New Radio on Unlicensed (NR-U) small cells located within buildings to coexist with the IEEE 802.11ad/ay, also termed as Wireless Gigabit (WiGig). Small cells are dual-band enabled operating in the 60 GHz unlicensed and 28 GHz licensed millimeter-wave (mmW) bands. We develop an interference avoidance scheme in the time domain to avoid cochannel interference (CCI) between in-building NR-U small cells and WiGig access points (APs). We then derive average capacity, spectral efficiency (SE), and energy efficiency (EE) performance metrics of in-building small cells. Extensive system-level numerical and simulation results and analyses are carried out for a number of variants of NR-U, including NR standalone, NR-U standalone, and NR-U anchored. We also analyze the impact of the spatial reuse of both mmW spectra of multiple NR-U anchored operators with a WiGig operator. It is shown that NR-U anchored provides the best average capacity and EE performances, whereas NR-U standalone provides the best SE performance. Moreover, both vertical spatial reuse intrabuilding level and horizontal spatial reuse interbuilding level of mmW spectra in small cells of an NR-U anchored can improve its SE and EE performances. Finally, we show that by choosing appropriate values of vertical and horizontal spatial reuse factors, the proposed coexistence mechanism can achieve the expected SE and EE requirements for the future Sixth-Generation (6G) mobile networks.

In this paper, by exploiting the frequency-domain, we propose a countrywide millimeter-wave (mmWave) spectrum allocation and reuse technique to allocate and reuse spatially the countrywide 28 GHz licensed spectrum and 60 GHz unlicensed spectrum to small cells (SCs) on each floor of a building of each Fifth-Generation (5G) New Radio (NR) Mobile Network Operator (MNO) of an arbitrary country. We develop an interference management scheme, model user statistics per SC, and interferer statistics per apartment and formulate the amount of the 28 GHz and 60 GHz spectra per MNO. We derive average capacity, spectral efficiency (SE), energy efficiency (EE), and cost efficiency (CE) when employing the proposed technique, as well as the traditional static licensed spectrum allocation technique. We discuss the implementation of the proposed technique and evaluate the performance under two scenarios, namely, SCs operate only in the 28 GHz in scenario 1, and both 28 GHz and 60 GHz in scenario 2. Extensive results and analyses are carried out for four MNOs, i.e., MNOs 1, 2, 3, and 4, in scenario 1. However, in scenario 2, in addition to MNOs 1, 2, 3, and 4, an incumbent Wireless Gigabit (WiGig) operator is considered. It is shown that the proposed technique with no co-channel interference can improve average capacity, SE, EE, and CE of MNO 1 by 3 times, 1.65 times, 75%, and 60%, respectively, in scenario 1, whereas 6.12 times, 5.104 times, 85.8%, and 83.15%, respectively, in scenario 2. Moreover, with an increase in reuse factors, SE increases linearly and EE increases negative exponentially. Further, we show that the proposed technique can satisfy SE and EE requirements for sixth-generation (6G) mobile systems. Finally, we discuss offered benefits and point out key issues of the proposed technique for further studies.

In this paper, we present an analytical model to characterize co-channel interference between small cell base stations (SBSs), each enabled with dual-transceiver operating at 28 GHz and 60 GHz millimeter-wave bands, in a multistory building. Subject to satisfying a predefined co-channel interference limit, we then deduce a minimum distance in both intra-floor and inter-floor levels between co-channel SBSs. The optimal size of a 3-dimensional (3D) cluster of SBSs and the corresponding 3D spatial reuse factor are defined such that both millimeter-wave spectrums can be reused fully to each 3D cluster of SBSs within the building. We derive system-level average capacity, spectral efficiency, and energy efficiency metrics for an arbitrary number of L buildings of SBSs within a macrocell coverage. With extensive system-level numerical and simulation results, we show that the 3D spatial reuse of multi-millimeter-wave spectrums to each 3D cluster of SBSs per building can achieve the expected average spectral efficiency and average energy efficiency requirements for the sixth-generation (6G) mobile networks.

This paper presents a theoretical framework by exploiting the four most interconnected-domain, including, power, time, frequency, and space, with in-building small cells to address expected spectral efficiency and energy efficiency requirements for the future sixth-generation (6G) mobile networks. More specifically, the framework takes advantage of higher degrees of freedom by employing multiband enabled small cells in frequency-domain, non-orthogonal spectrum reuses to small cells per building in spatial-domain, on/off switching of small cells in power-domain, and eICIC techniques due to sharing spectrums with small cells in time-domain. System-level average capacity, spectral efficiency, and energy efficiency metrics are derived, and extensive numerical and simulation results are carried out to demonstrate the impact of each domain on spectral efficiency and energy efficiency performances. Finally, it is shown that the proposed framework can satisfy the expected spectral efficiency and energy efficiency requirements for 6G mobile networks.

In this paper, we propose an interweave strategy based shared-use (ISSU) model to share the licensed 28 GHz millimeter-wave (mmWave) spectrum of one mobile network operator (MNO) with another in a country. The proposed ISSU model considers sharing the whole mmWave spectrum of one MNO, termed as primary MNO (p-MNO), with small cells deployed in any building of another MNO, termed as secondary MNO (s-MNO), only if no user equipment (UE) of p-MNO is present inside the corresponding building of s-MNO to avoid co-channel interference between UEs of p-MNO and s-MNO. We derive average capacity, spectral efficiency (SE), and energy efficiency (EE) of an s-MNO in a country. Extensive numerical and simulation results and analyses for an s-MNO of a country consisting of four MNOs show that the maximum amount of shared mmWave spectrum obtained using ISSU is 1.5 times the licensed spectrum of s-MNO. This results in improving both average capacity and SE by about 150%, whereas EE by about 60%, of s-MNO. Finally, we show that the proposed ISSU model can satisfy the expected SE and EE requirements for sixth-generation (6G) mobile systems by reusing the mmWave spectrum of s-MNO to its small cells of roughly 56.67% less number of buildings.

In this paper, we propose a countrywide licensed full spectrum allocation (LFSA) technique to allocate each mobile network operator (MNO) countrywide full 28 GHz millimeter-wave (mmWave) spectrum to operate its small cells per building subject to avoiding co-channel interference (CCI). We present a time-domain CCI avoidance scheme and deduce the optimal amount of time for each MNO. We derive average capacity, spectral efficiency (SE), energy efficiency (EE), and cost efficiency (CE) for LFSA. Extensive numerical and simulation results and analyses for an example scenario of a country consisting of four MNOs is carried out for the best case, as well as the worst case, CCI scenarios for MNO 1. It is shown that LFSA can improve average capacity, SE, EE, and CE by 300%, 165%, 75%, and 60% respectively for the best case, whereas 100%, 32%, 50%, and 20% respectively for the worst case, CCI scenarios. Moreover, the proposed LFSA can satisfy the SE and EE requirements for sixth-generation (6G) mobile systems by reusing the countrywide full 28 GHz mmWave spectrum to small cells of MNO 1 of about 60% less number of buildings for the best case, whereas 23% less number of buildings for the worst case, CCI scenarios.

In this paper, we propose a flexible licensed spectrum allocation (FLSA) technique to liberalize allocating the licensed 28 GHz millimeter-wave (mmWave) spectrum to mobile network operators (MNOs) of a country to achieve countrywide high spectrum utilization. The proposed FLSA technique liberalizes allocating the licensed mmWave spectrum exclusively to an MNO for a certain renewal term in accordance with its number of subscribers with respect to that of other MNOs. The spectrum allocated to an MNO is updated at each renewal term compliant with the change in its number of subscribers over the previous term. We formulate FLSA and find the optimal amount of spectrum for each MNO at each renewal term. We derive average capacity, spectral efficiency (SE), energy efficiency (EE), and cost efficiency (CE) for all MNOs. Extensive numerical and simulation results for an example scenario of a country consisting of four MNOs show that FLSA can improve both average capacity and SE by 25%, whereas EE and CE by 20% countrywide. Moreover, we show that FLSA can achieve both SE and EE requirements for sixth-generation (6G) mobile systems by reusing the spectrum per MNO to small cells of about 18% less number of buildings.

In this paper, we present techniques for sharing, trading, and reusing the licensed 28 GHz millimeter-wave (mmWave) spectrum using in-building small cells to achieve high capacity, spectral efficiency (SE), and energy efficiency (EE) for next-generation mobile networks. In this regard, we assume that each mobile network operator (MNO) of a country is statically allocated to an equal amount of 28 GHz licensed spectrum to operate its in-building small cells. We describe each technique and present its mathematical model for an MNO. We then derive system-level average capacity, SE, and EE metrics and carry out extensive simulation and numerical results and analyses when employing each of these techniques individually, as well as jointly, to small cells per building of the MNO. It is shown that spectrum reusing has a substantial impact on the average capacity, SE, and EE performances as compared to spectrum sharing and spectrum trading techniques due to reusing flexibly the mmWave spectrum of the MNO itself to it small cells per building. Moreover, employing all three techniques jointly to small cells provides the best performance of all techniques each employing individually. Finally, it is shown that each of the three techniques employing either individually or jointly can achieve the expected SE and EE requirements for sixth-generation (6G) mobile networks.

In this paper, we propose an underlay cognitive radio spectrum access (UCRSA) technique to share the licensed 28 GHz millimeter-wave (mmWave) spectrum of one mobile network operator (MNO), termed as primary MNO (p-MNO), with small cells in a building of another MNO, termed as secondary MNO (s-MNO), in a country. The proposed UCRSA considers operating each in-building small cell of an s-MNO at the maximum transmission power on its licensed spectrum, whereas at a reduced transmission power on a shared spectrum of any p-MNO at any time. The reduction in the transmission power varies in accordance with the predefined interference threshold set by the corresponding p-MNO. We derive average capacity, spectral efficiency (SE), and energy efficiency (EE) and carry out extensive numerical and simulation results and analyses for an s-MNO of a country consisting of four MNOs. It is shown that UCRSA can improve SE by 2.67 times, whereas EE by 72.74%, of the s-MNO as compared to that of the traditional static licensed spectrum allocation (SLSA) technique that allocates each MNO an equal amount of 28 GHz mmWave spectrum. Finally, we show that the proposed UCRSA technique can satisfy the expected SE and EE requirements for sixth-generation (6G) mobile systems by reusing the licensed, as well as shared, 28 GHz mmWave spectra of the s-MNO to its small cells of 71.8% less number of buildings than that required by the traditional SLSA technique.

In this paper, we propose a dynamic exclusive-use spectrum access (DESA) method to improve the overall licensed millimeter-wave (mmWave) spectrum utilization of all mobile network operators (MNOs) in a country. By exploiting secondary spectrum trading, the proposed DESA method shares partly and exclusively the licensed mmWave spectrum of one MNO to another in a dynamic and on-demand basis for a certain agreement term. We formulate the proposed DESA method for an arbitrary number of MNOs in a country. We then present an iterative algorithm to find the optimal amount of shared spectrum for each MNO, which is updated at each agreement term. We derive average capacity, spectral efficiency, energy efficiency, and cost efficiency performance metrics for all MNOs countrywide and present extensive numerical and simulation results and analyses for an example scenario of a country with four MNOs each assigned statically with an equal amount of 28-GHz mmWave spectrum. By applying DESA, we show that MNOs with a lack of minimum licensed spectra to serve their data traffic can lease at the cost of payment of the required additional spectra from other MNOs having unused or under-utilized licensed spectra. Moreover, it is shown that the overall countrywide average capacity, spectral efficiency, energy efficiency, and cost efficiency can be improved, respectively, by 25%, 25%, 17.5%, and 20%. Furthermore, we show that, by applying DESA to all MNOs countrywide, the expected spectral efficiency and energy efficiency requirements for sixth-generation (6G) mobile systems can be achieved by reusing the same mmWave spectrum to 20% fewer buildings of small cells. Finally, using the statistics of subscribers of all MNOs, we present a case study for fifth-generation (5G) networks to demonstrate the application of the proposed DESA method to an arbitrary country of four MNOs.

In this paper, we propose multiple communication systems incorporating an integrated satellite-mobile system (iSMS) and an autonomous terrestrial-mobile system (aTMS), and a technique to share multiple reused spectrum bands of iSMS and aTMS with in-building small cell base stations (SBSs) of aTMS by exploiting high external wall penetration loss of a building. The aTMS consists of a set of small cells enabled with either a single-band or multiband and deployed in a number of buildings. The iSMS consists of a satellite station integrated with the complementary ground components (CGC) stations which are deployed alongside small cells one-to-one basis. An interference management scheme to coordinate interference, a global resource scheduler to allocate resources, and an algorithm for the technique is proposed. We derive expressions for capacity, spectral efficiency, and energy efficiency under various SBS configurations for L buildings where L ≥ 1. An optimal value of L satisfying both energy and spectral efficiencies and an optimal number of almost blank subframes (ABSs) are derived. With extensive analysis, we show that the spectral efficiency improves linearly with the number of spectrum bands per SBS as well as L. However, the energy efficiency improves largely for low values o L and is hardly affected by the number of spectrum bands per SBS. An optimal value of L is obtained by choosing a slope on the energy efficiency curve for 0 ≤ L ≤ 100. The multiband enabled SBSs to provide with the best capacity, spectral efficiency, and energy efficiency performances of all SBS configurations. Furthermore, we show that the proposed technique outperforms several existing techniques in terms of energy efficiency, spectral efficiency, and average capacity per user equipment (UE) and can surpass the requirements of spectral and energy efficiencies for the fifth generation (5G) systems. Finally, we point out the significance, challenges, and future research perspectives of the proposed technique.

Addressing high capacity at low power as a key design goal envisages achieving high spectral efficiency (SE) and energy efficiency (EE) for the next-generation mobile networks. Because most data are generated in indoor environments, an ultra-dense deployment of small cells (SCs), particularly within multistory buildings in urban areas, is revealed as an effective technique to improve SE and EE by numerous studies. In this paper, we present a framework exploiting the four most interconnected-domain, including, power, time, frequency, and space, in the perspectives of SE and EE. Unlike existing literature, the framework takes advantage of higher degrees of freedom to maximize SE and EE using in-building SCs for 5G and beyond mobile networks. We derive average capacity, SE, and EE metrics, along with defining the condition for optimality of SE and EE and developing an algorithm for the framework. An extensive system-level evaluation is performed to show the impact of each domain on SE and EE. It is shown that employing multiband enabled SC base stations (SBSs) to increase operating spectrum in frequency-domain, reusing spectrum to SBSs more than once per building in spatial-domain, switching on and off each in-building SBS based on traffic availability to reduce SBS power consumption in power-domain, and using eICIC to avoid co-channel interference due to sharing spectrum with SBSs in time-domain can achieve massive SE and EE. Finally, we show that the proposed framework can satisfy SE, EE, as well as user experience data rate requirements for 5G and beyond mobile networks.

In this paper, we propose a technique for cloud coordinated clustering and scheduling of small cells, i.e., femtocells, in CRAN to improve capacity and spectral efficiency in 3D in-building environments. Control-and user-plane of each cell is decoupled. The clustering technique consists of two levels of clustering such that level 1 clustering defines an initial 3D femtocell cluster size. Level 2 clustering defines a cooperating set of femtocells per floor within each level 1 cluster to explore joint transmission coordinated multipoint (CoMP) during off-states of their transmit power. Femtocells are split at the MAC layer, and a mechanism is presented to model the bandwidth and latency fronthaul constraints. We derive the system level aggregate capacity, spectral efficiency, and energy efficiency. We then develop a heuristic algorithm and discuss its scheduler implementation. With numerical and simulation results, we show with an example scenario that the proposed technique can achieve the maximum CoMP capacity gain of 44% per building and 32.15% in overall system level. Finally, we demonstrate that the proposed technique can achieve the performance requirements of 5G cellular systems and point out the significance and further research issues.

In this paper, we propose two co-primary spectrum sharing (CoPSS) techniques, namely dynamic spectrum pooling (DySP) and static spectrum renting (StSR), for small cells deployed in 3-dimensional (3D) buildings for the fifth-generation (5G) mobile networks. We consider a scenario of two mobile network operators (MNOs) where the whole spectrum of one MNO is considered sharing only with small cells per building of the other MNO by exploiting the external wall penetration loss of each building. More specifically, in DySP, unlike spectrum pooling, only the licensed spectrum of one MNO can be shared deterministically with small cells within each building of the other MNO and vice versa such that the network capacity demand of an MNO can be scaled easily. Likewise, in StSR, unlike mutual renting, a certain portion of the spectrum of one MNO is rented exclusively for a certain time period so that the rented spectrum can solely be used to small cells within each building of the buyer MNO without any preemptive priority of the owner MNO. Hence, the proposed CoPSS techniques can overcome the limitations of the generic CoPSS techniques, i.e. the spectrum pooling and mutual renting techniques. We derive average capacity, spectral efficiency, and energy efficiency metrics for both techniques and extensive performance evaluation is carried out to show the relative outperformance of the DySP in terms of spectral and energy efficiencies over the StSR. Finally, we show that the proposed CoPSS techniques can meet the requirements of spectral and energy efficiencies for 5G mobile networks.

In this paper, we propose a technique to share the licensed spectrums of all mobile network operators (MNOs) of a country with in-building small cells per MNO by exploiting the external wall penetration loss of a building and introducing the time-domain eICIC technique. The proposed technique considers allocating the dedicated spectrum Bop per MNO only its to outdoor macro UEs, whereas the total spectrum of all MNOs of the country Bco to its small cells indoor per building such that technically any small indoor cell of an MNO can have access to Bco instead of merely Bop assigned only to the MNO itself. We develop an interference management strategy as well as an algorithm for the proposed technique. System-level capacity, spectral efficiency, and energy efficiency performance metrics are derived, and a generic model for energy efficiency is presented. An optimal amount of small indoor cell density in terms of the number of buildings L carrying these small cells per MNO to trade-off the spectral efficiency and the energy efficiency is derived. With the system-level numerical and simulation results, we define an optimal value of L for a dense deployment of small indoor cells of an MNO and show that the proposed spectrum sharing technique can achieve massive indoor capacity, spectral efficiency, and energy efficiency for the MNO. Finally, we demonstrate that the proposed spectrum sharing technique could meet both the spectral efficiency and the energy efficiency requirements for 5G mobile networks for numerous traffic arrival rates to small indoor cells per building of an MNO.

This paper presents a technique to share extensively both licensed and unlicensed spectrums with densely deployed small cells (SCs) in 3- dimensional (3D) multistory buildings to achieve high spectral and energy efficiencies for fifth generation (5G) mobile networks. We consider non- orthogonal spectrum sharing with SCs in each building by forming 3D clusters of SCs subject to a minimum distance between co-channel SCs. Therefore, the same spectrum can be reused multiple times per building by sharing with SCs in each 3D cluster. We assume that SCs are enabled with multiband, i.e. dual-band, to exploit licensed shared access (LSA) to share the licensed space-satellite spectrum and licensed assisted access (LAA) to share the 60 GHz unlicensed spectrum with SCs. We derive system- level capacity, spectral efficiency, and energy efficiency metrics for non-orthogonal spectrum sharing with SCs in L>1 buildings over a macrocell coverage of a mobile network. Extensive system level simulation is carried out. It is shown that the proposed non-orthogonal spectrum sharing technique outperforms significantly the technique for orthogonal spectrum sharing for both LSA and LAA and can meet easily the expected spectral efficiency and energy efficiency requirements for 5G mobile networks.

In this paper, we present a technique for sharing spectrums of multiple systems with small cells deployed in 3D buildings to enhance spectral and energy efficiencies of heterogeneous mobile networks for 5G and beyond systems. The multiple systems consist of a space-satellite system and a terrestrial-mobile system incorporating in- building small cells. By taking advantage of high external wall penetration loss of a building and employing the ABS based eICIC technique to small cell base stations (SBSs), both the satellite spectrum and the mobile spectrum are proposed to share with SBSs by managing co-channel interference of SBSs with satellite and mobile systems. We derive system-level capacity, spectral efficiency, and energy efficiency metrics for multiband enabled SBSs and find the conditions for optimality in terms of the small cell density over a macrocell coverage to trade-off spectral and energy efficiencies of the mobile system. With extensive system-level simulation and numerical analysis, we evaluate the performance of the proposed technique for the multiband enabled SBSs and show its outperformance over a single band enabled SBSs as well as the requirements of the 5G mobile system, in terms of spectral and energy efficiencies.

In this paper, we show how to realize numerous spectrum licensing policies by means of time-domain enhanced inter-cell interference coordination (eICIC) technique to share both the licensed and unlicensed spectrums with small cells in order to address the increasing demand of capacity, spectral efficiency, and energy efficiency of future mobile networks. Small cells are deployed only in 3-dimensional (3D) buildings within a macrocell coverage of a mobile network operator (MNO). We exploit the external wall penetration loss of each building to realize traditional dedicated access, co-primary shared access (CoPSA), and licensed shared access (LSA) techniques for the licensed spectrum access, whereas, for the unlicensed spectrum access, the licensed assisted access (LAA) technique operating in the 60 GHz unlicensed band is realized. We consider that small cells are facilitated with dual-band, and derive the average capacity, spectral efficiency, and energy efficiency metrics for each technique. We perform extensive evaluation of various performance metrics and show that LAA outperforms considerably all other techniques concerning particularly spectral and energy efficiencies. Finally, we define an optimal density of small cells satisfying both the spectral efficiency and energy efficiency requirements for the fifth-generation (5G) mobile networks.

The sixth-generation (6G) mobile networks are expected to operate at a higher frequency to achieve a wider bandwidth and to enhance the frequency reuse efficiency for improved spectrum utilization. In this regard, three-dimensional (3D) spatial reuse of millimeter-wave (mmWave) spectra by in-building small cells is considered an effective technique. In contrast to previous works exploiting microwave spectra, in this paper, we present a technique for the 3D spatial reuse of 28 and 60 GHz mmWave spectra by in-building small cells, each enabled with dual transceivers operating at 28 and 60 GHz bands, to enhance frequency reuse efficiency and achieve the expected spectral efficiency (SE) and energy efficiency (EE) requirements for 6G mobile networks. In doing so, we first present an analytical model for the 28 GHz mmWave spectrum to characterize co-channel interference (CCI) and deduce a minimum distance between co-channel small cells at both intra- and inter-floor levels in a multistory building. Using minimum distances at both intra- and inter-floor levels, we find the optimal 3D cluster size for small cells and define the corresponding 3D spatial reuse factor, such that the entire 28 and 60 GHz spectra can be reused by each 3D cluster in each building. Considering a system architecture where outdoor macrocells and picocells operate in the 2 GHz microwave spectrum, we derive system-level average capacity, SE, and EE values, as well as develop an algorithm for the proposed technique. With extensive numerical and simulation results, we show the impacts of 3D spatial reuse of multi-mmWave spectra by small cells in each building and the number of buildings per macrocell on the average SE and EE performances. Finally, it is shown that the proposed technique can satisfy the expected average SE and EE requirements for 6G mobile networks.

In this paper, we present two spectrum sharing techniques for a multisystem, incorporating an integrated satellite-mobile system and an autonomous terrestrial-mobile system (iSMS/aTMS), namely orthogonal spectrum sharing (OSS) and non-orthogonal spectrum sharing (nOSS) techniques. aTMS consists of numerous small cells deployed in several buildings, and iSMS consists of a satellite station integrated with complementary ground component (CGC) stations deployed within buildings. By exploiting the high external wall penetration loss of a building, the iSMS spectrum is shared with small cells per building in OSS, and small cells per 3-dimensional (3D) cluster per building in nOSS. An interference management scheme, to avoid interference in apartments with collocated CGC stations and small cells, was developed and an optimal number of almost blank subframes (ABSs) per ABS pattern period (APP) was defined. System-level capacity, spectral efficiency, and energy efficiency performance metrics were derived. Furthermore, we present an algorithm for both OSS and nOSS techniques. With extensive simulation and numerical analysis, it is shown that the proposed nOSS significantly outperforms OSS in terms of spectral efficiency and energy efficiency, and both techniques can meet the expected spectral efficiency and energy efficiency requirements for the fifth-generation (5G) mobile networks.