sensors

Communication Dynamic Spectrum Sharing for Future LTE-NR Networks †

Gordana Barb, Florin Alexa * and Marius Otesteanu

Department of Communications, Politehnica University Timis, oara, 300006 Timis, oara, Romania; [email protected] (G.B.); [email protected] (M.O.) * Correspondence: fl[email protected] † This manuscript is extension version of the conference paper: Barb, Gordana, Marius Otesteanu, and Marius Roman. “Dynamic Spectrum Sharing for LTE-NR Downlink MIMO Systems.” In Proceedings of the 2020 International Symposium on Electronics and (ISETC), Timisoara, Romania, 5–6 November 2020; pp. 1–4.

Abstract: 5G is the next mobile generation, already being deployed in some countries. It is expected to revolutionize our society, having extremely high target requirements. The use of spectrum is, therefore, tremendously important, as it is a limited and expensive resource. A solution for the spectrum efficiency consists of the use of dynamic spectrum sharing, where an operator can share the spectrum between two different technologies. In this paper, we studied the concept of dynamic spectrum sharing between LTE and 5G New Radio. We presented a solution that allows operators to offer both LTE and New Radio services using the same frequency bands, although in an interleaved mode. We evaluated the performance, in terms of throughput, of a communication system using the dynamic spectrum sharing feature. The results obtained led to the conclusion that using the dynamic spectrum sharing comes with a compromise of a maximum 25% loss on throughput. Nevertheless, the decrease is not that substantial, as the mobile network operator does not need to buy an additional  15 MHz of , using the already existing bandwidth of LTE to offer 5G services, leading to  cost reduction and an increase in spectrum efficiency. Citation: Barb, G.; Alexa, F.; Otesteanu, M. Dynamic Spectrum Keywords: dynamic spectrum sharing; LTE; 5G NR; throughput; spectrum efficiency Sharing for Future LTE-NR Networks. Sensors 2021, 21, 4215. https:// doi.org/10.3390/s21124215 1. Introduction Academic Editor: Dimitrie The next mobile generation following Long Term Evolution (LTE) that has started its C. Popescu deployment in some countries is the 5th Generation (5G). The main focus of LTE was set to increase data transfer rates, while 5G is expected to revolutionize our society, focusing Received: 10 May 2021 not only on delivering extreme mobile broadband, but also in the fields of critical machine Accepted: 16 June 2021 Published: 19 June 2021 communication and massive machine communication. New applications will emerge, and the target values and requirements proposed are extremely demanding [1]. The main

Publisher’s Note: MDPI stays neutral challenges of 5G systems consist of increasing data transfer rates, reducing latency, and with regard to jurisdictional claims in increasing capacity, spectrum efficiency, and network energy efficiency, which will be published maps and institutional affil- necessary for different application scenarios [2]. iations. The current network architecture cannot sustain all the requirements and target val- ues of 5G New Radio (NR). Therefore, the 3rd Generation Partnership Project (3GPP) released two variations for the new network architecture of 5G NR communication sys- tems: Non-standalone (NSA) and Standalone (SA) [3]. The main difference between both types is that the NSA architecture is based and depends on the LTE core network, while Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. the SA architecture uses a novel next-generation core network, not depending of any This article is an open access article LTE infrastructure. distributed under the terms and The of Things (IoT), mobile internet, and Cognitive Radio (CR) stand as conditions of the Creative Commons relevant driving forces for 5G development [4–7]. The IoT technology has the potential Attribution (CC BY) license (https:// ability to connect almost everything to the internet, which will lead to the massive growth creativecommons.org/licenses/by/ of devices that require network acceptance. Particularly, in 2018, there were approximately 4.0/). 22 billion connected devices, which is the equivalent of around 2.9 devices/person. It

Sensors 2021, 21, 4215. https://doi.org/10.3390/s21124215 https://www.mdpi.com/journal/sensors Sensors 2021, 21, 4215 2 of 15

is expected that by 2025, the number of connected devices to be nearly 38.6 billion [8]. Simultaneously, the mobile internet has surpassed the traditional mobile communications, offering users innovative experiences. On the other hand, cognitive radio represents a technology that has evolved in order to improve the spectrum usage, exploiting both licensed and unlicensed bands. It became a promising communications technology that is able to solve spectrum problems by: observation, learning, and intelligent adaptation to obtain an optimal frequency band [9]. In addition to the network architecture, another major challenge of 5G systems consists of the available frequency spectrum. Presently, the spectrum used for mobile communi- cations is located between 300 MHz and up to 6 GHz. Due to the fact that most of it is completely saturated, new frequency bands above 6 GHz need to be taken into consider- ation. Hence, it is expected that 5G NR systems will use frequency bands above 6 GHz, reaching up to 300 GHz [10]. Therefore, the main frequency spectrum to be used for 5G systems can be in licensed, shared, and unlicensed bands, see Table1. The low-band spec- trum has the goal of supporting high coverage and penetration; the mid-band spectrum provides data transfer rates up to 1 Gbps; the high-band spectrum supports peak data transfer rates up to 20 Gbps. The last group, even though it supports such high data rates, comes with the inconvenience of low coverage and penetration, being indicated to be applied in closed/indoor environments.

Table 1. 5G spectrum options.

Frequency Band Characteristics Spectrum Use Wide area coverage 600–2600 MHz Spectrum sharing Reframing from old technologies Mid-band mainstream for 5G 3.3–5 GHz Massive MIMO-crowded and urban areas Independent deployment Unlicensed spectrum (without old technologies) 5–6 GHz No spectrum licensed necessary Allocated mmWaves for 5G 24–39 GHz Increased data rates

It is clear that the frequency spectrum is a scarce and limited resource that constitutes an important factor in mobile communication systems, as well as the related cost for the Mobile Network Operator (MNO). In this context, new spectrum explorations [11,12], higher energy efficiency [13], and dynamic spectrum usage [14–18] have become the new features of communication networks. The topic of spectrum sharing in the bands of old communication systems started drawing the attention of researchers, as it is the safest and most economical solution [19]. The standardization procedure for the spectrum sharing principles started in March 2017 by 3GPP. One of the solutions presented regarding the spectrum allocation for 5G NR systems comprises the use of the existing frequency spectrum used by the already deployed mobile generations. Spectrum sharing is based on the flexibility of the physical layer and the fact that in the LTE network, all channels are assigned in the time-frequency domain. This way, the flexibility of the 5G NR radio interface can be used for reference signals, allowing dynamic configuration and minimizing collisions between NR and LTE during simultaneous data transmission. Consequently, there is the possibility of sharing a frequency domain within the same communication channel. A comprehensive overview on the different ways of spectrum sharing that has been investigated in recent years is found in [14]. In addition, in [20,21], new schemes and algorithms for dynamic spectrum sharing between Global System for Mobile Communications (GSM) and LTE technologies were investigated. Regarding the IoT, spectrum sharing is a preferable approach to cope with the conflicts between massive Sensors 2021, 21, 4215 3 of 16

between massive IoT connections and limited spectrum resources as it was discussed in

Sensors 2021, 21, 4215 [22–25]. It can also be used to solve vertical requirements and the competition3 of in 15 the ac‐ quisition of frequency bands between MNOs [26,27], as well as to improve spectrum uti‐ lization in Cognitive Radio (CR) and TV white space [28–30]. The leading mobile produc‐ ers have shown massive interest in developing solutions for dynamic spectrum sharing. IoT connections and limited spectrum resources as it was discussed in [22–25]. It can also Thesebe used are to presented solve vertical in requirementsTable 2. and the competition in the acquisition of frequency bands between MNOs [26,27], as well as to improve spectrum utilization in Cognitive TableRadio 2. (CR) Leading and TV producers white space and [ 28adopted–30]. The DSS leading solution. mobile producers have shown massive interestLeading in developing Producers solutions for dynamic spectrumName sharing. of DSS These Solution are presented in Table2. ESS—Ericsson Spectrum Sharing Table 2. LeadingHuawei producers and adopted DSS solution. CloudAIR MediaTeck Dimensity 1000 Leading Producers Name of DSS Solution Dynamic Spectrum Sharing (DSS) Ericsson ESS—Ericsson Spectrum Sharing QualCommHuawei SnapdragonCloudAIR X60 SamsungMediaTeck DimensityDSS 1000 ZTENokia DynamicSuperDSS/Magic Spectrum Sharing Radio (DSS) Pro QualComm Snapdragon X60 Samsung DSS The Dynamic ZTESpectrum Sharing (DSS) solutionSuperDSS/Magic allows mobile Pro operators to offer LTE and NR services using the same frequency bands, although in an interleaved mode.The This Dynamic allows Spectrum NR services Sharing without (DSS) solution the need allows of acquiring mobile network new and operators dedicated to fre‐ quencyoffer LTE spectrum, and NR services antenna, using or theradio same frequency frequency units. bands, The although solution in anis interleavedintended to assist operatorsmode. This in allows the short NR services‐term rollout without deployment the need of acquiring of 5G services new and through dedicated LTE frequency already‐in‐use spectrum.spectrum, antenna, It is not orintended radio frequency to provide units. substantial The solution performance, is intended to as assist that operators would necessitate in newthe short-term dedicated rollout spectrum deployment for NR, of but 5G servicesto provide through coverage, LTE already-in-use reduce costs, spectrum. and improve It is spec‐ not intended to provide substantial performance, as that would necessitate new dedicated trum efficiency for the operator. Figure 1 presents the DSS technology with LTE and NR spectrum for NR, but to provide coverage, reduce costs, and improve spectrum efficiency sharingfor the operator. the same Figure frequency1 presents band the DSSin comparison technology with to using LTE and two NR separate sharing the bands same for each technology.frequency band in comparison to using two separate bands for each technology.

FigureFigure 1. DSS vs. vs. using using dedicated dedicated bands bands for for NR NR and and LTE LTE [31]. [31].

The deploying of DSS technology is divided into two phases: Phase 1, which is based The deploying of DSS technology is divided into two phases: Phase 1, which is based only on the NSA architecture and accepts a sharing ratio between 20 and 60% with a fixed onlyUL sharing on the ratio;NSA andarchitecture Phase 2, which and accepts introduces a sharing a dynamic ratio UL between sharing 20 ratio and and 60% accepts with a fixed ULboth sharing NSA and ratio; SA architectures. and Phase 2, The which main introduces differences between a dynamic both UL phases sharing are presented ratio and in accepts bothTable NSA3. The and sharing SA architectures. ratio refers to the The ratio main of shared differences resources between between both both phases technologies. are presented inFor Table example, 3. The considering sharing ratio a sharing refers ratio to the of ratio 20% refers of shared to 5G resources NR occupying between 20% both of the technol‐ ogies.available For resources, example, while considering LTE occupies a sharing 80%. Another ratio of example 20% refers is for to a sharing5G NR ratio occupying of 60%, 20% of themeaning available that 5Gresources, NR uses while 60% of LTE the available occupies resources 80%. Another while LTE example uses only is 40%.for a sharing ratio of 60%,For meaning downlink, that the 5G allocation NR uses of the60% subframes of the available is based resources on Time Division while MultiplexingLTE uses only 40%. (TDM). In one frame, regardless of the sharing ratio adopted, subframes 0, 5, and 9 are strictly dedicated to LTE transmission. Subframes 1, 2, 3, 4, 6, 7, and 8 can be used for both LTE and NR transmission, depending on the sharing ratio and the architecture mode adopted, see Figure2[32].

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Table 3. Comparisons between two phases of DSS implementation. Sensors 2021, 21, 4215 4 of 16

Phase 1 Phase 2 Sharing ratio 20–60% Sharing ratio 5–70% Table 3. Comparisons between two phases of DSS implementation. Fixed UL sharing ratio Dynamic UL sharing ratio Only NSAPhase architecture1 PhaseNSA 2and SA architectures Sensors 2021, 21, 4215 Sharing ratio 20–60% Sharing ratio 5–70% 4 of 15 FixedSupports UL sharing only ratio FDD Dynamic ULSupports sharing ratioFDD and TDD SharingOnly NSA ratio architecture update is slow NSASharing and SA ratio architectures update takes up to 100 ms Table 3. ComparisonsSupports between only FDD two phases of DSS implementation.Supports FDD and TDD ForSharing downlink, ratio theupdate allocation is slow of the subframesSharing ratio is update based takeson Time up to Division 100 ms Phase 1 Phase 2 (TDM). In one frame, regardless of the sharing ratio adopted, subframes 0, 5, and 9 are Sharing ratio 20–60% Sharing ratio 5–70% strictlyFor dedicated downlink, theto LTEallocation transmission. of the subframes Subframes is based on1, 2,Time 3, 4, Division 6, 7, and Multiplexing 8 can be used for both (TDM). In oneFixed frame, UL sharing regardless ratio of the sharing ratio adopted,Dynamic subframes UL sharing ratio0, 5, and 9 are LTE and NROnly transmission, NSA architecture depending on the NSAsharing and SA ratio architectures and the architecture mode strictly dedicatedSupports to LTE only transmission. FDD Subframes 1, 2, 3,Supports 4, 6, 7, and FDD 8 can and be TDD used for both adopted,LTE and Sharing NRsee transmission,Figure ratio update 2 [32]. depending is slow on the sharingSharing ratio ratio updateand the takes architecture up to 100 ms mode adopted, see Figure 2 [32].

Figure 2. Frame allocation for DL Phase 2 DSS [32]. FigureFigure 2. Frame allocation allocation for DLfor Phase DL Phase 2 DSS [232 DSS]. [32]. The downlink resource allocation, when considering the transmission of severalseveral frames,The varies downlink depending resource on the sharingallocation, ratioratio implementedimplementedwhen considering [[33].33]. Different the transmission patterns are of several frames,depicted varies in Figure depending 33,, forfor the the NSA NSAon architecturethe architecture sharing mode. mode. ratio It Itimplemented cancan bebe observedobserved [33]. thatthat forDifferentfor every every patterns are frame, subframes 0, 5, and 9 are always dedicated to LTE. In addition, for the first frame depictedframe, subframes in Figure 0, 5, 3, and for 9 arethe always NSA dedicatedarchitecture to LTE. mode. In addition, It can for be the observed first frame that for every only, slot 1 1 is is represented represented with with yellow yellow (slot (slot type type B) B)and and slot slot 2 with 2 with orange orange (slot (slot type type B*), frame,andB*), andboth subframes both are used are used for 0, transmitting for5, and transmitting 9 are synchronization always synchronization dedicated and CSI and to‐RS CSI-RS LTE. signals, signals,In respectively.addition, respectively. for Ad ‐the first frame only,Additionalditional slot synchronization 1 synchronization is represented signals signals with are are sentyellow sent with with (slota aperiod period type of of 20B) 20 msand ms in in slot slot 1 12 of of with the the remaining orange (slot type B*), andframes, both represented represented are used byfor by green green transmitting (slot (slot type type B**). synchronization B**). The The remaining remaining slots and slots are CSI are used‐ usedRS for signals, LTE for LTE and respectively. and NR Ad‐ ditionaltransmission.NR transmission. synchronization signals are sent with a period of 20 ms in slot 1 of the remaining frames, represented by green (slot type B**). The remaining slots are used for LTE and NR transmission.

Figure 3. Resource allocation patterns for DL Phase 2 DSS [[34].34].

Figure 3. Resource allocation patterns for DL Phase 2 DSS [34].

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For uplink,uplink, thethe allocationallocation ofof the the resources resources is is based based on on Frequency Frequency Division Division Multiplexing Multiplex‐ (FDM).ing (FDM). As depictedAs depicted in Figure in Figure4, the 4, the Physical Physical Resource Resource Blocks Blocks (PRB) (PRB) available available for for LTE LTE or NRor NR transmission transmission are are represented represented by by the the color color green green andand depend on the the sharing sharing ratio ratio adoptedadopted and carrier bandwidth. Furthermore, Furthermore, there there are are seven seven PRBs PRBs dedicated dedicated to to NR NR UL UL transmissiontransmission only, representedrepresented by the color yellow yellow in in the the right right outer outer edge edge of of the the frequency frequency band.band. These PRBs depend on on the the positioning positioning of of the the LTE LTE PRACH PRACH PRBs. PRBs. In In Figure Figure 4,4 ,these these areare locatedlocated in the left outer edge of the frequency band. band. If If the the LTE LTE PRACH PRACH PRBs PRBs were were locatedlocated inin thethe right right outer outer edge, edge, the the seven seven NR NR UL UL PRBs PRBs would would then then be be positioned positioned in in the the left outerleft outer edge edge (meaning (meaning the oppositethe opposite side). side).

Figure 4. Resource allocation for UL Phase 2 DSS [34]. Figure 4. Resource allocation for UL Phase 2 DSS [34]. The calculation of the maximum available NR/LTE sharing ratio is given by the followingThe calculation equation: of the maximum available NR/LTE sharing ratio is given by the fol‐ lowing equation:   N + PUCCHMax_LTE = − N + PUCCHMax_LTE SharingSharing ratio ratioMax_UL 1= 1‐ (1)(1) Max_UL LTELTE BW BW in in PRBs PRBs wherewhere N represents represents the the number number of of PRBs PRBs that that are are necessary necessary for forLTE LTE transmission, transmission, for in for‐ instance,stance, the the LTE LTE PRACH PRACH PRBs. PRBs. InIn this paper, we studied the the concept concept of of dynamic dynamic spectrum spectrum sharing sharing between between LTE LTE and and 5G5G NRNR technologies for the same same mobile mobile network network operator. operator. We We assessed assessed the the performance performance ofof an LTE-NRLTE‐NR communication system using the the DSS DSS feature, feature, in in terms terms of of throughput, throughput, using using differentdifferent sharing ratios ratios for for both both NSA NSA and and SA SA architectures architectures and and for both for both transmission transmission di‐ directionsrections (downlink (downlink and and uplink). uplink). We We performed performed a acomparison comparison of of the the performance performance while while usingusing differentdifferent modulation schemes and and numbers numbers of of layers. layers. The The remainder remainder of of the the paper paper isis organized as as follows. follows. Section Section 2 2presents presents the the sharing sharing ratio ratio calculation calculation for downlink for downlink and anduplink; uplink; Section Section 3 provides3 provides the equipment the equipment and methods and methods used usedfor the for measurements; the measurements; and andSection Section 4 presents4 presents the results the results obtained obtained and analysis. and analysis. Lastly, Lastly,Section Section5 delivers5 delivers the conclu the‐ conclusionssions of this ofpaper. this paper.

2.2. Sharing Ratio Calculation The sharing ratio between LTE LTE and NR NR is is defined defined and and managed managed by by a a new new system system unit unit denominateddenominated Common Common Resource Resource Manager Manager (CRM). (CRM). It has It has the theresponsibility responsibility to compute to compute the thesharing sharing ratio ratio and andupdate update it according it according to traffic to traffic demands. demands. In order In order to do toso, do the so, CRM the con CRM‐ continuouslytinuously gathers gathers information information from fromboth LTE both and LTE NR and sites. NR The sites. CRM The component CRM component is com‐ isposed composed by 3 objects: by 3 objects: CRM, situated CRM, situatedin the base in thestation; base LTE station; CRM, LTE situated CRM, in situated the LTE in sys the‐ LTEtem systemunit; NR unit; CRM, NR CRM,situated situated in the in NR the NRsystem system unit. unit. Figure Figure 5 5presents presents the the main main responsibilities of the CRM. Initially, it starts by gathering information from LTE and NR

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Sensors 2021, 21, 4215 6 of 15 responsibilities of the CRM. Initially, it starts by gathering information from LTE and NR sites and, based on the information receives, it defines the resources to be shared. It then allocatessites and, based the shared on the information resources receives, to both it technologies. defines the resources According to be shared. to traffic It then conditions and allocates the shared resources to both technologies. According to traffic conditions and demands for for a specific a specific moment, moment, it evaluates it evaluates the optimal the sharing optimal ratio sharing to be selected ratio andto be selected and finallyfinally updates updates it for it LTEfor LTE and NR. and NR.

Figure 5. 5.CRM CRM main main responsibilities responsibilities [31]. [31]. For downlink, depending on the traffic demands for a specific moment, the CRM receivesFor information downlink, concerning depending load on indication the traffic and takes demands a decision for on a thespecific DL sharing moment, the CRM receivesratio that needs information to be adopted. concerning To calculate load the indication DL load, the and weighted takes load a decision (based on on PRB the DL sharing ratiooccupancy), that needs average to LTE be DSSadopted. Guaranteed To calculate Bit Rate (GBR) the DL load, load, NR DSS the GBR weighted load, and load NR (based on PRB PDCCH load need to be determined [35]. The algorithm for the sharing ratio calculation occupancy),for DL is presented average in Figure LTE6. DSS The first Guaranteed step consists Bit of Rate the verification, (GBR) load, from NR the CRMDSS GBR load, and NRentity, PDCCH of the average load need LTE GBR to be load, determined as well as the[35]. NR The PDCCH algorithm load against for the a definedsharing ratio calcula‐ tionthreshold, for DL so that is presented a decision can in beFigure taken 6. regarding The first the step resources consists to be of assigned. the verification, If the from the CRMaverage entity, LTE GBR of loadthe average is higher thanLTE 70%GBR and load, the NRas well PDCCH as loadthe NR is lower PDCCH than 70%, load against a de‐ then the sharing ratio for NR will decrease. Else, if the average LTE GBR load is equal or fined threshold, so that a decision can be taken regarding the resources to be assigned. If lower than 70% and the NR PDCCH load is higher than 70%, then the sharing ratio for NR willthe average increase. Lastly,LTE GBR if both load the is average higher LTE than GBR 70% load and and the NR NR PDCCH PDCCH load are load higher is lower than 70%, thenthan 70%, the thensharing one of ratio the two for followingNR will conditionsdecrease. is Else, applied: if the average LTE GBR load is equal or lower• If the than LTE 70% GBR and resource the deltaNR (PDCCHn; n − 1) > load 0, the is sharing higher ratio than for NR70%, will then be reduced; the sharing ratio for NR• Ifwill the increase. LTE GBR resourceLastly, deltaif both (n; nthe− 1)average≤ 0 and LTE the NR GBR PDCCH load resourceand NR delta PDCCH load are − higher(n; n than1) >70%, 0, the then sharing one ratio of the for NRtwo will following increase. conditions is applied: The second step of the algorithm is based on the load information received from step 1. TheIf CRM the thenLTE calculates GBR resource the LTE-weighted delta (n; loadn − 1) and > the0, the NR weightedsharing load,ratio from for NR which will be reduced; the LTEIf andthe NRLTE total GBR loads resource are determined. delta (n Finally,; n − 1) in ≤ step0 and 3, the the number NR PDCCH of LTE and resource NR delta (n; n − subframes1) > 0, is calculated,the sharing taking ratio into for account NR will the increase. LTE and NR total loads from step 2. The resulting number of subframes matches to a specific sharing ratio value. The second step of the algorithm is based on the load information received from step 1. The CRM then calculates the LTE‐weighted load and the NR weighted load, from which the LTE and NR total loads are determined. Finally, in step 3, the number of LTE and NR subframes is calculated, taking into account the LTE and NR total loads from step 2. The resulting number of subframes matches to a specific sharing ratio value.

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Figure 6. Algorithm for DL Phase 2 DSS sharing ratio calculation [34].

For uplink, a similar procedure as for downlink is taken. Depending on the traffic demands for a specific moment, the CRM receives information concerning load indication and takes a decision on the UL sharing ratio that needs to be adopted. To calculate the UL load, the weighted load (based on PRB occupancy) and the average LTE DSS GBR load need to be determined. Figure7 presents the algorithm for the UL sharing ratio calculation. For step 1, the average LTE GBR load is verified by the CRM, so a decision can be taken regarding the assignment of resources. If the average LTE GBR load is higher than 70%, then the sharing ratio for NR will be decreased. The second step of the algorithm is based on the load information received from step 1. The CRM then calculates the LTE weighted load and the NR weighted load, from which the LTE and NR total loads are determined. Finally, in step 3, the number of LTE and NR subframes is calculated, taking into account the LTE and NR total loads from step 2. The resulting number of subframes matches to a specific sharing ratio value. 1

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FigureFigure 7. 7.Algorithm Algorithm for for UL UL Phase Phase 2 2 DSS DSS sharing sharing ratio ratio calculation calculation [ 34[34].]. 3. Equipment and Methods 3. Equipment and Methods This section presents the parameters adopted for our work, as well as the scenarios tested.This We section considered presents a MIMO the parameters system, composed adopted for of oneour basework, station as well for as LTE, the scenarios one for NR,tested. and We one considered mobile station a MIMO that system, is composed composed of a of Qualcomm one base station chipset for prototype LTE, one thatfor NR, is frequentlyand one mobile used on station commercial that is Samsungcomposed devices. of a Qualcomm We used chipset both 64QAM prototype and that 256QAM is fre‐ modulationquently used for on the commercial measurements. Samsung A bandwidth devices. We of used 15 MHz both was 64QAM selected. and 256QAM The Absolute mod‐ Radio-Frequencyulation for the measurements. Channel Numbers A bandwidth (ARFCN) of 15 for MHz NR was were selected. 175,800 The for Absolute downlink Radio and ‐ 166,800Frequency for uplink. Channel The Numbers NR-ARFCN (ARFCN) is a code for NR that were refers 175,800 to the carrierfor downlink frequency and to 166,800 be used for foruplink. both transmissionThe NR‐ARFCN directions is a code of the that radio refers channel to the andcarrier is defined frequency in the to 3GPPbe used TS for 38.104 both Releasetransmission 16 specification directions [ 36of ].the The radio NR-ARFCN channel and can is be defined converted in the to frequency,3GPP TS 38.104 resulting Release in 75,80016 specification = 879 MHz [36]. for The downlink NR‐ARFCN and 166,800 can be =converted 834 MHz to for frequency, uplink. Frequency resulting in Division 75,800 = Duplex879 MHz (FDD) for wasdownlink selected and for 166,800 all cases. = 834 We MHz performed for uplink. throughput Frequency measurements Division Duplex using physical(FDD) was and selected static equipment for all cases. from We Nokia performed Networks throughput R&D laboratory, measurements considering using a physical Signal- to-Interference-plus-Noiseand static equipment from Ratio Nokia (SINR) Networks higher R&D than laboratory, 25 dB and a considering Reference Signal a Signal Receive‐to‐In‐ Powerterference (RSRP)‐plus higher‐Noise than Ratio− 70(SINR) dBm higher with Line than of 25 Sight dB (LoS)and a and Reference without Signal the presence Receive ofPower fading. (RSRP) These higher are standard than −70 values dBm with used Line at the of laboratorySight (LoS) for and testing without the the performance presence of offading. new technologies. These are standard They are values considered used at very the good laboratory radio conditions,for testing andthe performance the reason for of choosingnew technologies. them is to They create are almost considered ideal radio very conditionsgood radio in conditions, order to verify and the and reason confirm for thechoosing aptness them of DSS is to technology create almost and ideal its peak radio performance conditions in using order physical to verify measurements,and confirm the asaptness it is a technologyof DSS technology under development and its peak performance and testing. Weusing considered physical measurements, both NSA and as SA it architectures.is a technology For under NSA, development we measured and using testing. sharing We considered ratio values both between NSA and 20 and SA archi 70%.‐ Fortectures. SA, we For measured NSA, we usingmeasured sharing using ratio sharing values ratio between values 30between and 70%. 20 and Table 70%.4 below For SA, summarizeswe measured the using scenario sharing parameters ratio values adopted between for the 30 work.and 70%. Table 4 below summarizes the scenario parameters adopted for the work.

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Table 4. Set of parameters adopted for our work. Table 4. Set of parameters adopted for our work. Case Direction Bandwidth Nr. of Layers Modulation MIMO Case1 DL Direction Bandwidth15 Nr. of2 Layers Modulation64QAM MIMO2 × 2 2 1DL DL 15 15 2 2256QAM 64QAM 22× ×2 2 3 2DL DL 15 15 4 2 256QAM64QAM 24× ×2 4 3 DL 15 4 64QAM 4 × 4 4 4DL DL 15 15 4 4256QAM 256QAM 44× ×4 4 5 5UL UL 15 15 1 164QAM 64QAM 11× ×1 1

EachEach network architecturearchitecture type type has has different different possible possible variations. variations. The The NSA NSA architecture architec‐ tureis based is based on the on LTE the core LTE network core network and uses and LTE-based uses LTE interfaces.‐based interfaces. For this For type this of architec-type of architecture,ture, the gNodeB the gNodeB needs to needs support to support these interfaces these interfaces and acts asand a secondaryacts as a secondary , while node, the whileeNodeB the acts eNodeB as a primaryacts as a orprimary master or node. master There node. are There different are different options tooptions deploy to an deploy NSA anarchitecture—option NSA architecture—option 3, 3a, 3x, 3, 4, 3a, 4a, 3x, 7, 4, and 4a, 7a. 7, and The 7a. option The usedoption for used our for measurements our measure is‐ mentsNSA option is NSA 3x, option where 3x, the where control the plane control is routed plane through is routed the through master eNodeB the master and eNodeB the user andplane the is user directly plane routed is directly through routed the secondary through the gNodeB. secondary The eNodeBgNodeB. also The communicates eNodeB also communicatesdirectly with the directly gNodeB with and the both gNodeB communicate and both communicate directly with directly the Evolved with Packetthe Evolved Core Packet(EPC). Core The SA (EPC). architecture The SA architecture has 2 options—option has 2 options—option 2 and 5. Option 2 and 2 is5. thatOption adopted 2 is that for adoptedour work for and, our as work it can and, be seenas it incan Figure be seen8b, in consists Figure of 8b, a Nextconsists Generation of a Next Core Generation (NGC) Coreand a(NGC) gNodeB and that a gNodeB communicates that communicates directly with directly it, without with needingit, without any needing support any of sup LTE‐ portstructures. of LTE For structures. both network For both architectures network architectures studied, we usedstudied, two we radio used modules two radio that mod have‐ ulesattached that have to them attached one attenuator, to them one as attenuator, the measurements as the measurements were performed were in performed a laboratory in awith laboratory close proximity with close to proximity the mobile to user. the Wemobile used user. either We 2 orused 4 antennas, either 2 or depending 4 antennas, on de the‐ pendingcase studied. on the case studied.

(a) (b)

FigureFigure 8. Architecture diagram diagram adopted adopted for for the the measurements: measurements: (a) NSA(a) NSA architecture; architecture; (b) SA (b architecture.) SA archi‐ tecture.

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4. Results and Discussion This section presents the results obtained from our measurements. We divide it into two subsections: downlink and uplink results. In each subsection, we present results for both NSA and SA architectures. We considered sharing ratios ranging from 20 to 70% for the NSA architecture and from 30 to 70% for the SA architecture, meaning that 5G NR occupies Sensors 2021, 21, 4215 10 of 16 between 20 and 70%, and 30 and 70% of the available resources, while LTE occupies between 80 and 30%, and 70 and 30% for the NSA and SA architectures, respectively.

4.1.4. Results Downlink and Discussion FigureThis 9section presents presents the throughput the results results obtained using from the DSSour featuremeasurements. from the We first divide four cases it into oftwo Table subsections:2, comprising downlink the NSA and architecture. uplink results. The differencesIn each subsection, between we the present cases consist results of for theboth modulation NSA and type, SA architectures. that is either We 64QAM considered or 256QAM sharing modulation, ratios ranging and MIMOfrom 20 type, to 70% that for isthe either NSA 2 × architecture2 or 4 × 4 MIMO. and from Each 30 case to 70% depicts for fivethe differentSA architecture, curves. Themeaning green that (NR 5G only) NR andoccupies purple between (LTE only) 20 curves and 70%, represent and 30 the and values 70% forof the throughputavailable resources, achieved while without LTE the oc‐ usecupies of DSS between technology. 80 and The 30%, yellow and curve70 and (DSS 30% LTE for +the NR) NSA is the and most SA architectures, important one respec as it ‐ presentstively. the total throughput obtained with DSS. The remaining blue (DSS LTE) and red (DSS NR) curves represent the individual throughputs for each technology while using DSS.4.1. NoticeDownlink that the DSS LTE + NR throughput equals the sum of the individual DSS LTE and DSS NR throughputs. It can be observed that, for all cases, when we increased Figure 9 presents the throughput results using the DSS feature from the first four the sharing ratio, the values for the DSS NR TP also increased while the DSS LTE TP cases of Table 2, comprising the NSA architecture. The differences between the cases con‐ values decreased. This was an expected behavior, as the higher the sharing ratio, the more sist of the modulation type, that is either 64QAM or 256QAM modulation, and MIMO resources will be available for NR transmission and the fewer for LTE transmission. It can alsotype, be observedthat is either that 2 from × 2 or a sharing4 × 4 MIMO. ratio of Each approximately case depicts 57%, five meaning different that curves. NR occupiesThe green 57%(NR of only) the resources and purple while (LTE LTE only) occupies curves 43%, represent the individual the values throughput for the throughput for NR surpassed achieved thewithout LTE throughput. the use of InDSS addition, technology. it is visibleThe yellow that the curve overall (DSS throughput LTE + NR) using is the DSS most was im‐ slightlyportant lower one thanas it thatpresents for the the LTE total or NR-onlythroughput throughputs. obtained Thiswith isDSS. understandable, The remaining as theblue available(DSS LTE) frame and resources red (DSS are NR) shared curves between represent both the technologies. individual throughputs for each tech‐ nologyComparing while using case 1 DSS. and caseNotice 2, where that the the DSS difference LTE + NR is the throughput modulation equals type that the increasessum of the fromindividual 64QAM DSS to 256QAM LTE and modulation,DSS NR throughputs. it can be concluded It can be observed that the majorthat, for difference all cases, is when on thewe maximum increased values the sharing for throughput. ratio, the values For case for 1,the depending DSS NR TP on also the increased sharing ratio while adopted, the DSS betweenLTE TP 90 values and 100 decreased. Mbps were This obtained, was an expected while for behavior, case 2, the as values the higher for throughput the sharing were ratio, approximatelythe more resources 120–135 will Mbps. be available An increase for NR of transmission 35% was observed. and the Afewer similar for LTE comparison transmis‐ cansion. be conductedIt can also be for observed cases 3 and that 4. from For case a sharing 3, the ratio maximum of approximately DSS throughput 57%, values meaning were that 175–200NR occupies Mbps, 57% while of for the case resources 4, the valueswhile LTE varied occupies between 43%, 240 the and individual 260 Mbps, throughput depending for onNR the surpassed sharing ratio. the LTE For these throughput. cases, an In increase addition, of 37%it is invisible throughput that the was overall observed throughput for a sharingusing DSS ratio was of 20%, slightly while lower for a than 70% sharingthat for ratio,the LTE the or throughput NR‐only throughputs. increase was This 30% (seeis un‐ Tablederstandable,5). as the available frame resources are shared between both technologies.

(a) (b)

Figure 9. Cont.

SensorsSensors2021 2021, 21, ,21 4215, 4215 1111 of of 15 16

(c) (d)

FigureFigure 9. 9.DL DL throughput throughput results results for for NSA NSA architecture, architecture, with with sharing sharing ratios ratios from from 20% 20% up toup 70%: to 70%: (a) Case(a) Case 1 results; 1 results; (b) Case(b) Case 2 results;2 results; (c) Case (c) Case 3 results; 3 results; (d) Case (d) Case 4 results. 4 results.

TableComparing 5. DL throughput case 1 resultsand case for DSS2, where LTE + NRthe indifference Mbps. is the modulation type that in‐ creases from 64QAM to 256QAM modulation, it can be concluded that the major differ‐ DL NSA DSSence LTEis on + the NR maximum (Mbps) values for throughput. DL For SA case DSS 1, LTE depending + NR (Mbps) on the sharing ratio 30% 40%adopted, 50% between 60% 90 and 70% 100 Mbps 30% were obtained, 40% while 50% for case 60% 2, the values 70% for Case 1 97.5 95.9throughput 94.4 were 92.9 approximately 91.4 120–135 90.9 Mbps. 88.3 An increase 85.8 of 35% was 83.2 observed. 80.7 A sim‐ Case 2 132.9 130.6ilar comparison 128.3 126 can be conducted 123.8 for 123.9 cases 3 and 120.1 4. For case 116.4 3, the maximum 112.7 DSS through 109 ‐ Case 3 192.6 188.8put values 185 were 181.2 175–200 177.4Mbps, while 179.8 for case 4, 174 the values 168.1 varied between 162.3 240 156.5 and 260 Case 4 257.1 251.4Mbps, 245.7 depending 240 on the sharing 234 ratio. 239.9 For these 231.3 cases, an 222.7 increase of 214.2 37% in throughput 205.6 was observed for a sharing ratio of 20%, while for a 70% sharing ratio, the throughput increaseRegarding was 30% case (see 1 and Table case 5). 3, where the difference consists of the number of transmit- ting and receiving antennas, 2 × 2 MIMO and 4 × 4 MIMO, respectively, an increase in allTable throughput 5. DL throughput values of results approximately for DSS LTE 50% + NR could in Mbps. be observed, along with an increase in complexity. Figure 10DL depicts NSA the DSS DL LTE throughput + NR (Mbps) results with theDL DSS SA feature DSS LTE for the + NR first (Mbps) four cases from Table 2,30% using the40% SA architecture,50% 60% contrary 70% to the30% results 40% from Figure50% 8 that60% made 70% use of the NSA architecture. The main difference of both types of architectures is that NSA is Case 1 97.5 95.9 94.4 92.9 91.4 90.9 88.3 85.8 83.2 80.7 an intermediary solution that is based on the LTE network, while the SA architecture does notCase depend 2 132.9 in any way130.6 on the128.3 LTE network,126 123.8 using a123.9 Next-Generation 120.1 116.4 Core 112.7 (NGC) along109 withCase NR 3 protocols. 192.6 Moreover,188.8 185 the SA181.2 architecture 177.4 leads179.8 to an174 improved 168.1 efficiency 162.3 with 156.5 less complexity. Comparing case 1 and case 2, we can observe that maximum DSS throughput valuesCase varied 4 257.1 between 251.4 80 and245.7 90 Mbps,240 and234 110 and239.9 120 Mbps,231.3 respectively. 222.7 214.2 The increase205.6 from one case to another was approximately 36%. For cases 3 and 4, the DSS values varied betweenRegarding 160 and 180case Mbps, 1 and andcase 2003, where and 240 the Mbps, difference respectively. consists of For the these, number an increase of transmit of ‐ approximatelyting and receiving 29% was antennas, observed. 2 × 2 MIMO and 4 × 4 MIMO, respectively, an increase in all throughputRegarding values case 2of and approximately case 4, the increase 50% could in the be DSS observed, throughput along was with approximately an increase in 87%complexity. for both sharing ratios of 30% and 70%. In addition, it can be remarked that for all cases, theFigure values 10 depicts for the the NR-only DL throughput throughput results for the with SA the architecture DSS feature were for smaller the first than four thosecases of from the NSA Table architecture, 2, using the with SA aarchitecture, difference of contrary around 15to Mbpsthe results for case from 1, 20 Figure Mbps 8 for that casesmade 2 and use 3,of and the 40NSA Mbps architecture. for case 4. The reasonmain difference for this is of that both in the types SA of architecture, architectures the is numberthat NSA of broadcast is an intermediary signals was solution higher that than is that based in theon NSAthe LTE architecture. network, while An example the SA is ar‐ thechitecture presence does of System not depend Information in any Blockway on (SIB) the signals,LTE network, as well using as paging a Next with‐Generation information Core regarding(NGC) along the cell. with NR protocols. Moreover, the SA architecture leads to an improved ef‐ ficiency with less complexity. Comparing case 1 and case 2, we can observe that maximum DSS throughput values varied between 80 and 90 Mbps, and 110 and 120 Mbps, respec‐ tively. The increase from one case to another was approximately 36%. For cases 3 and 4, the DSS values varied between 160 and 180 Mbps, and 200 and 240 Mbps, respectively. For these, an increase of approximately 29% was observed.

SensorsSensors 2021,2021 21, ,421521, 4215 12 of 1512 of 16

(a) (b)

(c) (d)

FigureFigure 10. DL 10. DLthroughput throughput results results for for SA SA architecture, architecture, with with sharing sharing ratios ratios from from 30% 30% up to up 70%: to (70%:a) Case (a) 1 Case results; 1 results; (b) Case ( 2b) Case 2 results;results; (c) ( cCase) Case 3 3results; results; ( (d) Case 4 4 results. results.

RegardingTable6 provides case 2 the and percentage case 4, the loss increase of the throughput in the DSS that throughput occurs when was using approximately DSS 87%instead for both of an sharing NR-only system.ratios of It can30% be and observed 70%. thatIn addition, there was it a losscan in be throughput remarked values that for all between a minimum of 10% and a maximum of 26%, depending on the sharing ratio and cases, the values for the NR‐only throughput for the SA architecture were smaller than case adopted. The existence of a decrease in throughput was expected, as with DSS, the thoseavailable of the resources NSA architecture, are shared with with LTE, a difference and hence, of there around are fewer 15 Mbps resources for case available 1, 20 Mbps for for casesNR, 2 compared and 3, and to a40 system Mbps that for iscase based 4. The only reason on NR. for However, this is that from in the the results SA architecture, obtained, the numberfor the NSAof broadcast architecture, signals having was a losshigher between than 14that and in 25% the isNSA not aarchitecture. considerable An decrease example is thetaking presence in account of System the fact Information that there is Block no need (SIB) for signals, new dedicated as well spectrum as paging to bewith allocated information regardingfor NR, as the it shares cell. the bandwidth with LTE technology. For case 1, the average loss was 19.8%Table for NSA6 provides and 17.2% the for percentage SA. For case loss 2, theof the loss throughput was 17.5% for that NSA occurs and 15.6% when for using SA. DSS insteadFor case of 3,an we NR had‐only a 21.2% system. loss It for can NSA be andobserved 19% for that SA. there Lastly, was for a case loss 4, in the throughput loss was val‐ 20.6% for NSA and 19.2% for SA. ues between a minimum of 10% and a maximum of 26%, depending on the sharing ratio We can observe that the decrease in the DSS throughput was higher with the increase andin thecase sharing adopted. ratio. The This existence is due to theof a fact decrease that, as thein throughput sharing ratio was increases expected, (meaning as with that DSS, thea higheravailable number resources of the are available shared resources with LTE, were and used hence, for NR there transmission are fewer and resources fewer for availa‐ bleLTE), for moreNR, compared synchronization to a signalssystem are that transmitted is based inonly the slotson NR. dedicated However, to NR, from as well the as results obtained,overhead for signals. the NSA architecture, having a loss between 14 and 25% is not a considerable decrease taking in account the fact that there is no need for new dedicated spectrum to be allocated for NR, as it shares the bandwidth with LTE technology. For case 1, the average loss was 19.8% for NSA and 17.2% for SA. For case 2, the loss was 17.5% for NSA and 15.6% for SA. For case 3, we had a 21.2% loss for NSA and 19% for SA. Lastly, for case 4, the loss was 20.6% for NSA and 19.2% for SA.

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Table 6. Loss of DL throughput, in %, of the DSS LTE + NR value in comparison to NR only.

Sharing 20% 30% 40% 50% 60% 70% 30% 40% 50% 60% 70% Ratio NSA ARCHITECTURE SA ARCHITECTURE Case 1 −17% −18% −19% −20% −22% −23% −12% −15% −17% −20% −22% Sensors 2021, 21, 4215 13 of 15 CASE 2 −14% −15% −17% −18% −20% −21% −10% −13% −16% −18% −21% CASE 3 −17% −19% −20% −22% −24% −25% −13% −16% −19% −22% −25%

Table 6. LossCASE of DL throughput,4 −16% −18% in %, − of20% the DSS −22% LTE − + NR23% value −25% in comparison −13% −16% to NR − only.19% −22% −26%

Sharing Ratio 20% 30% 40% 50% 60% 70% 30% 40% 50% 60% 70% We can observe that the decrease in the DSS throughput was higher with the increase in the NSAsharing ARCHITECTURE ratio. This is due to the fact that, as the sharing SA ratio ARCHITECTURE increases (meaning that Case 1 −17% −a18% higher number−19% of− 20%the available−22% resources−23% were−12% used −for15% NR transmission−17% −20% and fewer−22% for Case 2 −14% −15% −17% −18% −20% −21% −10% −13% −16% −18% −21% Case 3 −17% −LTE),19% more−20% synchronization−22% − 24%signals −are25% transmitted−13% in− the16% slots− dedicated19% − 22%to NR, as− 25%well Case 4 −16% −as18% overhead−20% signals.−22% −23% −25% −13% −16% −19% −22% −26%

4.2.4.2. Uplink Uplink FigureFigure 11 11 depicts depicts the the UL UL throughput throughput results results for for case case 5 5from from Table Table 6,6 ,using using both both NSA NSA andand SA SA architecture. architecture. Regarding Regarding the NSA architecture,architecture, it it can can be be observed observed that that the the maximum maxi‐ mumthroughput throughput values values for LTEfor LTE and and NR NR only only (not (not considering considering the the DSS DSS feature) feature) were were 40 and40 and22 22 Mbps, Mbps, respectively. respectively. Moreover, Moreover, if if we we compare compare the the resultsresults of the DSS DSS LTE LTE + + NR NR and and NRNR-only‐only throughputs throughputs from from both both architecture architecture types, types, we we can can conclude that they were similar.simi‐ lar.Therefore, Therefore, there there is is no no difference difference between between the the SASA and NSA architecture, architecture, as as there there are are no no additionaladditional channels channels that that need need to to be be transmitted transmitted and and hence hence occupy occupy extra extra resources. resources.

(a) (b)

FigureFigure 11. 11. ULUL throughput throughput results results for for case case 5. 5. (a ()a NSA) NSA architecture; architecture; (b ()b SA) SA architecture. architecture.

TableTable 77 presents presents the the percentage percentage loss loss of of throughput throughput when when using using the the DSS DSS technology. technology. WeWe can can observe observe that that for for both both architecture architecture types, types, a amaximum maximum loss loss of of 25% 25% occurred occurred for for a a sharingsharing ratio ratio of of 70%, 70%, meaning meaning that that NR NR occupied occupied 70% 70% of of the the available available resources resources while while LTE LTE occupiedoccupied only only 30%. 30%. Therefore, Therefore, we we can can conclude conclude that that using using the the DSS DSS technology technology comes comes with with a acompromise compromise of of a amaximum maximum 25% 25% loss loss on on throughput. throughput. However, However, the the decrease decrease observed observed is is notnot that that considerable considerable if if taking taking into into account account that, that, instead of needing anan additionaladditional 15 15 MHz MHz of ofbandwidth, bandwidth, the the system system shares shares the the actual actual 15 MHz15 MHz between between both both technologies. technologies. Subsequently, Subse‐ quently,from the from operator’s the operator’s point of view,point DSS of view, brings DSS the advantagebrings the ofadvantage cost reduction of cost and reduction spectrum andefficiency, spectrum while efficiency, being able while to being present able the to “5G present icon game”the “5G and icon provide game” coverage and provide strategies. cov‐ erage strategies. Table 7. Loss of UL throughput, in %, of the DSS LTE + NR value in comparison to NR only.

Sharing Ratio 20% 30% 40% 50% 60% 70% 30% 40% 50% 60% 70% NSA ARCHITECTURE SA ARCHITECTURE Case 5 −2% −5% −10% −17% −20% −25% −5% −10% −17% −20% −25%

5. Conclusions In this paper, we analyzed the impact and the advantages of using the DSS technology in an LTE-NR communication system. We proposed different schemes for the resource allocation, according to the selected sharing ratio. The results obtained provided insight into the behavior of the system with DSS and showed that it is a technology that brings advantages from the operator’s point of view, mainly regarding the spectrum efficiency Sensors 2021, 21, 4215 14 of 15

and cost reduction. In conclusion, from the results obtained, it is clear that using the DSS technology brings a major advantage of not needing extra dedicated bandwidth for NR systems, which, from the operator’s point of view, leads to an improvement of spectrum efficiency and cost reduction. We performed a comparison of the spectrum usage for LTE and NR when adopting the DSS feature and without. In addition, we measured the throughput obtained for both LTE and NR, using the proposed allocation schemes for each sharing ratio. The results obtained clearly demonstrated that even if a maximum loss of 25% on throughput is observed, there is a major advantage in using the DSS technology due to the fact that there is a cost reduction for the mobile operator alongside an optimization on the spectrum usage, due to the fact that the MNO can re-use the already existing 15 MHz bandwidth of LTE and does not need to buy any new dedicated supplementary 15 MHz for 5G services. In conclusion, the deployment of DSS technology is useful, especially for the initial deployment of 5G NR, as the operator is able to build strategies while presenting the initial 5G picture to the consumer, through LTE already-in-use spectrum.

Author Contributions: Conceptualization, G.B., F.A. and M.O.; software, G.B.; validation, G.B., F.A. and M.O.; formal analysis, G.B., F.A. and M.O.; investigation, G.B. and F.A.; resources, G.B. and F.A.; data curation, G.B. and F.A.; writing—original draft preparation, G.B.; writing—review and editing, G.B. and F.A.; project administration, F.A.; funding acquisition, F.A. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Acknowledgments: This work was developed using Nokia’s equipment and infrastructure. For this reason, the authors wish to acknowledge the support provided by Nokia. Conflicts of Interest: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

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