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Potential first steps in 5G New Radio focusing on spectrum, sharing and deployment issues

May 2017

Opinion Paper

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Potential first steps in 5G new radio

Opinion Paper 2 Detecon International GmbH

Table of Contents

Motivation ................................................................................................................. 3

Introduction ............................................................................................................. 5

TDD as more favorable 5G-NR solution than FDD ................................................. 7

Deployment options for 5G-NR ............................................................................. 10

Massive MIMO vs higher order MIMO .................................................................. 12

Spectrum sharing .................................................................................................. 14

Future multi-hop mesh networks for IoT-based devices ....................................... 16

Summary ................................................................................................................. 18

Appendix ................................................................................................................. 21

5G requirements ................................................................................................... 21

5G RAN evolution ................................................................................................. 22

5G-NR modulations ............................................................................................... 24

Potential TDD bands ............................................................................................. 25

IMT450 (TDD-extension of band 31): 380-470MHz .............................................. 25

FDD-Band 22 refarming to TDD-band 42 together with 43 ................................... 26

Spectrum sharing already in 4G-LTE .................................................................... 27

L-Band as new low band spectrum candidate for spectrum sharing ..................... 28

Abbreviations ........................................................................................................ 29

The Author .............................................................................................................. 31

The Company .......................................................................................................... 32

This paper intends to show general trends related to spectrum allocations potentially used for 5G (especially <6GHz), even potentially/currently not available in all regions due to (inter)national alignments for alternative usage. Some mentioned bands e.g. for region 1 might be substituted by equivalent region 2 or 3 bands.



Motivation

This paper starts a series of detailed views on latest evolutions in 5G-RAN, 5G-Core, slicing, SDN/NFV, security, edge computing et al. in close cooperation with commercial use case considerations.

The paper emphasizes some practical challenges of network deployments at different spectrum bands, e.g. shorter coverage ranges at higher bands which need to be enhanced by massive MIMO schemes, which increase computational efforts and equipment size again limiting numbers of active elements, bandwidth and power (due to EMF). To keep deployment cost reasonable, potential opportunities with slicing and sharing of equipment arise in radio and core networks within 5G evolution.

One purpose is to indicate some of the latest trends in 5G development and direction around 5G-NR, new spectrum and sharing opportunities, and highlight implications for special deployments.

Within the last years, mobile broadband traffic forecasts increased exponentially leading to higher demands in spectrum, but also improved technological responses to cope with these demands in the requested quality. Therefore, one first step is to cater for higher bandwidths, (currently easier) available in higher bands1, but with poor2 short range coverage conditions. More important, spectrum in general remains limited, and new spectrum bandwidth could be added only linearly, potentially not covering the exponentially forecasted demands per area. Since the current 4G-LTE standard reached a very effective and spectral efficient level, higher orders of antenna elements might not bring enough additional capacity to the users. This in general requires also smaller form factors of antenna and equipment and higher computational efforts. One additional extension is to increase spectral efficiency by enhanced interference mitigation measures, either within one site (enhanced resource scheduling for all bands (favourable for D-RAN)) or between neighbour sites, requiring additional exchange and computational efforts on the control plane (C-RAN) in close alignment with the required backhaul network capacities.

All in all, it is expected to rollout much more new equipment in new spectrum ranges in macro as well as small cell deployments with significant technical, operational and commercial challenges to the mobile operators. To keep network complexity at least at a reasonable level, the next generation also targets more efficient operations and higher flexibility in more efficient usage of existing (or new) hardware with specialized software functions at distributed levels (slicing, virtualization). To keep investments reasonable, spectrum and equipment sharing is recommended in some levels to keep also competition.

In addition to mobile broadband traffic, new specialized kinds of traffic arise within the area of machine type communications, better known as Internet of Things (MTC, IoT) connecting everything in unforeseen use cases and traffic demands. These services of billions of devices and traffic volumes need special consideration (=slices) in the next generation of wireless network standardization. In the networks, these MTC services would be realized in special

1 Within this paper, the band notation mean low: <1GHz, medium: 1-3GHz, high: 3-6GHz, highest: >6GHz, especially 26/28/32GHz and >60GHz 2 “Poor” means, short range of coverage and therefore the need to deploy more sites per area. Of course this “poor” characteristic is the essential step to reuse the same frequency in the nearby area which increase capacity density. There is no good or bad spectrum, it depends on the requested use case.



(own) spectrum bands (=slices) with specialized access schemes, which are supported by the new 5G-NR on the same hardware types as eMBB services.

5G-NR means the new radio interface access technology which is expected to provide optimized support for a variety of different services, different traffic loads, and different end users by flexible, scalable assignment of network resources. 5G-RAN means the optimized radio access network resource management using 5G-NR and/or 4G-LTE resources, connected to the (joint 4G and) 5G-core network.

While most of the new 5G services and use cases are widely possible with existing 4G-LTE (Advanced Pro) standardized radio access, 5G-NR should support at least lowest latencies as well as increase flexibility. 5G-NR should be capable to simultaneously support multiple combinations of reliability, latency, throughput, positioning, and availability, but not necessarily at the same time everywhere. 5G-NR will not offer full ubiquitous coverage at highest capacities, rather enable smart-spot capacity at lowest ranges e.g. using millimetre waves in urban and indoor environments. 4G-LTE-Advanced Pro has been already enhanced in various areas (e.g. D2D, V2X) to have the potential to address most of the “5G use cases”. Special services might move to 5G-NR bands or might benefit from the additional capacity and/or reduced latency provided by a 5G-NR working alongside LTE as booster.

The main messages of this paper are condensed in the Summary section. For short:

1. In the long term, all IMT spectrum will be assigned technology agnostic and will be used for 5G, but in the short term new bands would be used first for 5G, while legacy bands would be refarmed to 5G within normal modernization cycles, but not necessarily to higher order or massive MIMO. TDD-spectrum would gain more importance in the future. 5G technology will also support service migration from currently used lower bands to enable more efficient spectrum usage also in valuable coverage spectrum which is currently out of focus due to limited bandwidth.

2. The high and highest spectrum use would not be favourable for the classical macro cell deployments due to limited coverage range and limited spatial diversity in macro cell deployments in these bands. In high and highest bands, small cell deployment will dominate, but with shortest ranges and therefore highest capacity densities, which naturally would require a lot of small cells to reach homogeneous performance perception. The physical realizations need to be kept very small as well and almost invisible to people, also compliant to EMF regulations. In this case, MIMO would increase signal quality but less signal coverage. Backhauling would be one critical issue.

3. In parallel to competition, sharing of equipment and spectrum will enable more cost efficient rollouts. New slicing concepts would gain importance in distributed core functionality using normal commercial of the shelf (COTS) hardware which could also be shared to different Core Networks (CN). The RAN hardware might remain highly specialized, usable only for dedicated bands and limited bandwidths, and with special signal processors, but with overall enhanced resource management software which is seen at (or near) the site in virtualized RAN-clouds on COTS hardware and openRAN software.

4. Some network functions will be also transferred into the user terminals (smartphone, laptop) respective smart aggregation routers (HUBs) controlling meshed networks on multi-hop basis. This would enable higher battery life times, enlarged coverage and capacity and lower the overall traffic on backhauling. These aggregations units might perforrm some edge computing as well as complexity reductions within local areas.



Introduction

While in the past, every ~10years a new technology was introduced to fulfil the new or increased demands, the next evolution of 5G technology intends to break with this tradition. In the long term 5G will be much more than the simple evolution of mobile broadband. 5G is designed as key enabler of the next generation of infrastructures that will support the digital transformation of processes in all economic sectors and the growing consumer market demand.

In the future with 5G-NR, we will see different spectrum owners, different spectrum users with dedicated access to some parts of the spectrum, all using the same (own or shared) hardware components and (potentially) same software, adapted to their individual purposes. 5G will enable new markets for suppliers aside telecommunication service providers. Enterprises or PPDR service providers etc. might deploy their own (standardized) equipment (HW&SW) using licensed or unlicensed spectrum at least in a locally limited range. New networks might be deployed and operated within unlicensed spectrum with LAA-capabilities, either 4G or 5G, depending on latency and other requirements.

This paper starts a series of detailed views on latest evolutions in 5G-RAN, 5G-Core, slicing, SDN/NFV, security, edge computing et al. in close cooperation with commercial use case considerations.

The paper emphasizes some practical challenges of network deployments at different spectrum bands. To keep deployment cost reasonable, potential opportunities with slicing and sharing of equipment arise in radio and core networks within 5G evolution.

One purpose is to indicate some of the latest trends in 5G development and direction around 5G-NR, new spectrum and sharing opportunities, and highlight implications for special deployments.



Figure 1: equivalent evolution of mobile technologies

Figure 1 tries to depict the evolution of mobile communications standards in a very simplified example of a (lemonade) vending machine, where initially only two types/services were possible (2G), increasing in flexibility to get different flavours/services in higher, but limited quality (3G). In the next 4G machine, more services could be offered with more efficient techniques and higher quality and capacities. The 5G machine then turns to a holistic machine, to enable the needed service flexible on demand.

So almost all service requests might be realized in 4G already, but would be enabled much more flexible and cost efficient in or together with 5G-NR. In general, every advantage comes in junction with some disadvantage, some 5G-NR high data rate service would be limited to a very short range as physics are applicable for 5G as 4G. One expected disadvantage of higher flexibility is higher ratio of control data between all nodes, higher efforts in pre and post processing of data and therefore more and higher capacity backhaul infrastructure.

For the agile3 introduction of new technology, independent evolutions of radio and the core network is mandatory as well as the convergence between the 3GPP access and other access technologies to enable high flexibility for deploying networks and network slices of different characteristics for addressing various users and services’ needs adequately and efficiently.

In the future with 5G-NR, we will see different spectrum owners, different spectrum users with dedicated access to some parts of the spectrum, all using the same (own or shared) hardware components and (potentially) same software, adapted to their individual purposes. There will be operation centres for mobile network services providers, parallel to CCTV and PPDR service providers. Enterprises might use the same HW&SW components within their isolated environments for massive Machine Type Communications (mMTC) and special low latency applications and security demands. 5G will enable new markets for suppliers aside telecommunication service providers. Enterprises or PPDR service providers etc. might deploy their own (standardized) equipment (HW&SW) using licensed or unlicensed spectrum at least in a locally limited range. New networks might be deployed and operated within unlicensed spectrum with LAA-capabilities, either 4G or 5G, depending on latency and other requirements.

These multiple heterogeneous networks will need unified control mechanisms through functional architectures across many operators’ frameworks (and ownership) of underlying wireless or optical networks and technologies. 5G subsystems and interfaces need to be

3 simple, flexible, scalable and extensible



integrated into modern operating system architectures: converged optical, wireless or satellite infrastructure for network access, back-hauling and front-hauling. The latter is in general a hot topic in discussion, since equipment vendors are not keen to open their proprietary interfaces between radio units and baseband units.

New technologies like Software Defined Networking (SDN) and Network Functions Virtualization (NFV) provide new design principles for more flexibility and tighter infrastructure integration. NFV allows the flexible placement and scaling of network functions eliminating proprietary special purpose hardware. SDN allows to program the network to provide the required connectivity. The overall architecture of 5G will change significantly compared to previous generations to meet a large variety of business and performance requirements, especially in terms of varying targets for cost, speed, latency and reliability.

Expecting very high throughput targets, small cell concepts for highest capacity density will lead to smarter Ultra Dense Networks (UDN) with numerous small cells requiring new interference mitigation and backhauling to be real smart cells. To increase flexibility and improve user data rates, access networks will require very wide contiguous carrier bandwidths which are potentially available at higher carrier frequencies with reduced coverage.

TDD as more favorable 5G-NR solution than FDD

The past decades have been dominated by frequency division duplex (FDD) technologies within low to medium range spectrum bands. Now the era of time division duplex (TDD) might arise with 5G-NR technologies, especially in the high and highest ranges of spectrum. Latest research is also focusing on full duplex methods with transmitting and receiving at the same time at the same frequency. This is achieved with high computational pre and post processing at base and terminal equipment which is not expected for 5G-NR in the near future due to high complexity at terminal side.

5G-NR will also improve performances of existing FDD-bands, while higher improvements are expected (due to reciprocity and higher order MIMO) in higher spectrum allocations with large bandwidths and more flexible TDD-spectrum assignments. The combination of TDD and highest spectrums favours the support of highest capacities with shortest coverage ranges. High capacity densities are desired in urban areas or indoors with high capacity and high connectivity demand, but also require proper highest capacity backhauling.

In mobile communications, two main spectrum usage options exist:

1. Frequency Division Duplex (FDD): uplink and downlink can send at the same time at different spectrum parts. The spectrum band is divided in three locations: 1. Uplink related part of the spectrum (in general lower part) 2. Downlink related part of the spectrum (in general upper part) 3. The guard band (duplex gap) between both parts

2. Time Division Duplex (TDD): uplink and downlink use the same spectrum, but at different times 1. Since for eMBB the traffic demand is asymmetrical in favour to downlink, more

time is reserved for downlink than uplink. For massive IoT the uplink generates higher demands, while more balance for ultra-reliable low latency services.

2. TDD also leads to the performance reduction in uplink: less time is available for uplink transmission, respectively reduced coverage for the same performance. E.g. for 10% of time for uplink, the coverage range is reduced by ~1/10.



Table 1: ITU-TDD-band definitions

It will be shown in the following, that TDD-based schemes will be more relevant for 5G-NR than FDD:

1. Uplink and downlink share the same channel at different times. Due to reciprocity of the channel, uplink and downlink channel impulse response functions are identical (depending on stationarity of the channel). This is the essential advantage of TDD schemes for beamforming and MIMO algorithms. In case a (known) trainings sequence is transmitted, the channel impulse response can be estimated and re-used for perfect transmission back to the transmitter. In FDD, the channel responses of uplink band and downlink band are “only” similar due to different band parts, but not identical and would not match perfectly. TDD-schemes will result in higher performances than FDD in MIMO algorithms and beamforming.

2. Dynamic, faster UL/DL-switching on a per-cell basis for more flexible capacity also based on traffic condition: In 3G and 4G the different configurations have to be selected statically and in alignment with neighbour spectrum allocations in order to minimize interference. In 5G-NR, the switching will be done more flexible and shorter depending on latency requirements (scalable transmission time interval (TTI)). The 5G-NR uplink might send short trainings sequences, acknowledgements et al. for each (or a subset of) narrowband resource (blocks), the downlink responds optimally for a longer period with user data. Same in the opposite direction: the short uplink user data is optimally received due to the knowledge of the channel, therefore the disadvantage of TDD due to limited uplink coverage is compensated (depending on the number of antenna). The estimation accuracy of the channel responses would improve at least for stationary end-user devices, like CCTV-cams, IoT devices, etc., even if there would remain a time-variant mobile channel. The above mentioned ratio of 10% uplink would require ~10 antenna array elements for beamforming. In case of >50% uplink traffic, the coverage loss would be overcompensated in case of more than 2 antennas.

E-UTRA TDDBand MHz

33 1900 – 192034 2010 – 202535 1850 – 191036 1930 – 199037 1910 – 193038 2570 – 262039 1880 – 192040 2300 – 240041 2496 – 269042 3400 – 360043 3600 – 380044 703 – 80345 1447 – 146746 5150 – 5925

Due to this uplink coverage issue (and the initial voice dominated service), for most bands currently the favoured usage is for FDD.



In the beginning, 5G-NR will be deployed in currently not used frequency bands, especially in the higher downlink capacity focused bands (e.g. bands 38, 40, 42, 43), followed by the currently assigned, but widely unused bands (33-37, 39). The latter bands become more attractive and enable larger coverage as the deployments are quite solid in urban areas and might be used as broadband TDD-successor 5G-NR-IoT for the FDD low band 4G-NB-IoT services, since for most IoT-services the uplink demands might be higher. In the above mentioned bands with 5-20MHz bandwidth, maximum 4*4MIMO/beamforming seems appropriate, while for the bands 40, 42 and 43 with bandwidths ~100MHz per operator a higher order of 8-16 antenna4 is expected, but at the expense of coverage reduction. Massive MIMO deployments with significant higher numbers of antenna would be only possible for highest bands (>>6MHz, 26, 28GHz).

The TDD-bands 38 and 40 are already deployed in some networks as macro deployment, otherwise these bands would be very beneficial for early 5G macro deployments. Any upgrade or refarming to 5G-NR would be dependent on the real improvements based on trials and the corresponding costs to switch from 2*2MIMO to 4*4 or 8*8MIMO and the reusability of existing baseband equipment. The refarming of FDD-spectrum currently used for 3G (e.g. band 1) to 5G seems viable, if the new 5G-FDD upgrades would improve significantly relative to 4G-LTE-Adv pro (or further 4.5G-evolutions). It is expected, that future 5G-NR windowing techniques (see appendix) will reduce out-of-band (OOB) emissions (for FDD as well TDD) and reduce guard band demands e.g. between band 33, 34 and band 1. It is expected, that current FDD-spectrums would remain FDD, but upgraded in the long term with improved 4.5G or 5G modes with improved OOB-filtering. Band 22 might be one exemption here, which might be better assigned as TDD. On the opposite, one long term alternative (up to ~2027) is to combine band 33, band1, MSS-spectrum and band 34 to one enhanced “band1-e” (1900-2025//2090-2215MHz with in total 2*125MHz FDD-spectrum, but this needs to be aligned on global international basis with freeing potentially used parts in the DL-equivalents of band 33, 34.

Currently NB-IoT is an early enabler of machine type communications which use (in the best case) unused small spectrum in LTE-guard band or other residual spectrum portions. In the least favourable case, the NB-inband solutions compete with LTE-capacity. It is expected to enhance early inband deployments in low spectrum bands to guard band deployments with higher numbers of NB-IoT carriers. This alternative option for NB-IoT is in guard bands of LTE-assignments with at least 10MHz, mainly in band 3. The IoT-capacity is naturally limited, as bandwidth would be n*180kHz, possible for maximum n=11. In the mid-term, the higher bandwidth option (1.4MHz) of Cat-M could enhance the options of flexibility regarding coverage vs capacity. As alternative, the NB-IoT-guard band deployments could be used for LTE service extension with same/optimized control channels etc. to extend the bandwidths to narrowband services with lower quality, but larger coverage requirements. In analogy to TTI-bundling, many repetitions could be sent on narrow band resources, which we call Voice over Narrowband (VoN). Summarizing, NB-IoT might compete with Cat-M at lower bands (700-900MHz), and survive in guard band option (of 10MHz LTE-carrier). Any NB-IoT deployment in medium bands (e.g. 1800MHz) is less probable, since VoN would gain additional low quality services in guard bands.

4 Keep in mind, one antenna might consist in multiple phased array elements with quasi-static elevation angle (including remote electrical tilt RET), with reduced vertical beam width according to antenna length relative to wavelength.



It is therefore expected, that mobile operators might join spectrum and equipment sharing agreements (in case of bandwidth <40MHz) for the potentially/currently unused TDD-bands, e.g. in band 33, 34 for 5G-NR-IoT-TDD services with uplink focus. Despite no beamforming in the uplink, the coverage might be initially poor, but could be improved by a twostep transmission of first narrowband training sequences followed by improved quality/coverage due to beamforming, keeping in mind that >50% uplink ratio only needs 2 base station antennas to compensate coverage issues.

5G-NR-TDD-bands 42, 43 are expected to be deployed in small cells for dedicated short range coverage with reduced power settings. It is not recommended to deploy these bands as macro cells, because additional transmit power requirements (for 400MHz bandwidth) would put the risk to reduce other band power settings accordingly. In case higher power settings would be needed in higher bands to achieve larger coverage, the power settings in low and medium bands need to be reduced accordingly to compensate EMF-effects, which reduces coverage in these bands of course. In the long term, operators would need to introduce inhomogeneous power settings per site which also increases complexity. The latter is already expected (at least at some locations) with the introduction of SDL within L-bands and potential 5G-NR-TDD-deployments in bands 33, 34.

Deployment options for 5G-NR

Due to easier miniaturization within highest frequency bands, the higher orders will increase significantly to the so called massive MIMO. In this context, all three parts of the communication chain need special consideration e.g. for downlink:

1. Transmission from base station with higher power settings, higher antenna orders, etc.

2. Reception at terminal station which limited space and power, and with uncontrollable human behaviour potentially degrading performance

3. Propagation channel in between: the channel diversity is essential for any MIMO. A lower rank would not enable mMIMO, but beamforming for multiple users would be more applicable.

Since propagation mechanisms trend from predominantly reflection in low bands to scattering in higher bands, the spatial channel diversity reduce in macro cells from many NLOS components in low bands to LOS dominance in high bands. Therefore any channel diversity is quite limited in macro cell designs, while small cell environments keep higher probability of larger spatial diversity. In other words, the higher bands should not be used for MIMO macro cell design since the required spatial channel is not sufficient to justify higher order MIMO. Small cell environment, either indoor or outdoor, benefit from higher NLOS diversity (=> MIMO) or LOS (=> beamforming). In macro cell designs, the MIMO order of 2-4 seems reasonable for medium bands (<3GHz). For high bands (3-6GHz) this might increase to 8-16, but in small cell environments with antenna below building height. Highest bands would use massive numbers of antenna elements to form finer beams instead of exploration of the full rank of the channel.

As depicted in Figure 2, the cell range is decreasing significantly with frequency (in urban macro cell deployments even stronger) and also due to indoor penetration losses. Compared to the 1800MHz cell range, the cell range at 2600MHz is less than 50% for indoor coverage



and less than 50% for outdoor at 3600MHz.5 Also seen in Figure 2 (green dots on the right axis), the average DL cell capacity for full bandwidth of all carriers per band is approximated, either for 4G-LTE or 5G-NR, with the assumptions for spectral efficiency and MIMO-gains listed below6. Therefore Figure 3 shows the average capacity density for f<4GHz, normalized to the value of 1800MHz, with the assumptions (!) of same macro design and same total transmit powers (EIRP: equivalent isotropic radiated power). Despite the capacity is almost the same, the 4G-LTE capacity density at 2600MHz increased up to 3 times relative to 1800MHz due to reduced macro cell ranges at 2600MHz. 5G-NR-TDD-8*8MIMO offer densities larger than 11-times, with small cell LOS indoor or outdoor channel responses with higher spatial diversity assumed in this case. At the moment, we assumed here a conservative ratio of 2 between 5G-NR and 4G-LTE due to higher LOS probability and improved channel estimations (reciprocity) of TDD-channels. If a higher improvement (due to improved intercell interference mitigations) of 4 and higher channel ranks would be assumed, 5G-NR capacity densities could be 30-40times higher than today with LTE at 1800MHz. Keep in mind, that transmit powers have to be reduced at small cell deployments due to EMF limits which would further increase capacity density, but also the need for more small cells!

Figure 2: approximation of average cell capacity (right, green) as well free space propagation (normalized to 1800MHz) for indoor and outdoor coverage

As an initial assumption, small cell deployment become short range smart spots with ~100times higher capacity density than macro cells. Assuming the bands 42, 43 are fully used with 5G-NR, each 8*8-MIMO cell would need in average more than 6Gbps backhauling or more than 30Gbps in peak conditions. Fixed-mobile convergence with fibre to the smart spot (FTTSS, leaky fibre7) is mandatory to enable the mobile network to reuse the existing fixed network infrastructure for the rollout.

5 This approximation assumes that total DL transmission powers per bandwidth remain the same, which is not realistic: it is expected, that small cell environments reduce transmit powers significantly in order to be compliant to regulatory safety/health limits at lower antenna heights. There is also a high probability for some sites to reduce all bands macro cell transmission powers as well due to regulatory safety/health limits. 6 Here we assumed 1.5 only to include the reduced average probability of full rank channels 7 In analogy to the classical leaky feeder cable systems in tunnels/trains where the signal is pouring out of the coax-cable at defined slots, 5G-NR would build a leaky fibre line system with dedicated optical to mm-wave transforming access points covering a short range only.

LTE-FDD, 2*2MIMO 1.8 bps/HzLTE-TDD, 2*2 MIMO 1.3 bps/Hz

5G-NR to 4G-LTE ratio 22*2MIMO to 4*4 MIMO ratio 1.54*4MIMO to 8*8MIMO ratio 1.5

Figure 3: average cell capacity density (normalized to 1800MHz)



The leaky fibre smart spot deployment is not expected to be homogeneous within the same area as current macro cells, since the investments would be extremely high compared to the expectations of reduced revenue.

Deployments in L-band 32 and TDD-bands 33, 34 as well as SDL in 738-758MHz would cover 4G or 5G demands for macro coverage until 2020 and beyond, especially depending on capable terminal penetrations per band. In the latter bands with limited bandwidths spectrum sharing is expected.

Massive MIMO vs higher order MIMO

One major difference of higher order MIMO and massive MIMO is the individual weighting of each single antenna element in row and column dimensions (aka active antenna) in case of mMIMO. The latter would enable full 3D beam steering (in the half sphere of antenna direction), while at higher order MIMO in general one dimension of antenna feeding remains mainly static and only azimuth beam steering would be enabled at fixed elevation beam. In macro deployments, active antenna played only a minor role so far compared to the RET-driven elevation beam steering. It is expected to continue with 4G-FDD 2 or 4 hoMIMO deployments in macro cells in medium bands, and to switch to 5G-NR-TDD higher order MIMO from high bands (>3GHz) in micro or small cell deployment. Highest bands (>>6GHz) will enable massive MIMO with full 3D steering.

In case of massive MIMO concepts with significantly higher numbers of antenna elements (e.g. 128*128) there has to be a technological switch of antenna design and materials. For example, if 128 antenna elements would be used at 28GHz, the single radiating element would be ~16times smaller, but 128 elements would be ~8 times larger than an antenna used for 1800MHz which needs to be compensated by other materials, e.g. dielectric antenna with significantly reduced power levels per radiating element. The requirement to reduce power levels in small cell deployments is also inline with potential regulator`s perspective limiting overall radiation according to EMF safety limits, but significantly limits coverage and performance.

In addition, 128*128 single antenna elements could form very sharp beams (<1°) towards the user (or the other receiving base station in case of backhauling usage). Since base stations are in most cases stationary, the directional patterns remain (mainly) constant for backhauling links which ease computational efforts. Within deployment both mMIMO-antennas need to be fixed against wind loads or vibrations, otherwise the beam width might need to be increased again (=less antenna needed per beam) or the beam steering effort increase again significantly. The very sharp beam angle requirements limit the maximum number of useful antenna and the EIRP calculations. A maximum of ~32 antenna elements is expected for highest bands, and ~8 for high bands (3…6GHz).

Since currently deployed radio units for small cells (f<6GHz) support ~40…60MHz (2-3 times 20MHz-carriers), next realizations are expected to support 100MHz bandwidth per equipment8, so for full usage of bands 42 and 43 with 400MHz would require 4 radio units in a cost-efficient and small size form factor including active antenna array and baseband processing for all the smart 5G-NR algorithms, pre- and post-processing, etc.. Since the computational effort increase with numbers of antenna elements, finally built beams and

8 In 5G up to 400MHz per carrier are foreseen in standard, but need HW&SW realizations as well.



especially with used bandwidth, the equipment might be too large to be deployed in small cell environments. Current Base Band Units (BBU) support 1 20MHz-carrier with 4 antenna layers, or equivalent 2 20MHz-carriers with 2 antenna layers, which means 80MHz bandwidth support. mMIMO with e.g. N*M*B ~ 32*32*100= 90000MHz would increase efforts ~1300 times which needs to be compensated by more efficient hardware and software.

The step from existing 2*2 or 4*4 MIMO antenna schemes towards higher order MIMO would depend on the size of the new antenna system. This step might effort a larger investment, since most 2*2 MIMO equipment would not support 4*4MIMO which might be therefore postponed to end of life of hardware. It is recommended to upgrade to one combined antenna for many bands in one radome, but this might not be possible for all deployments due to space and weight reasons. Also upgrades of 2 non co-located antenna systems with each 2*2 MIMO might include different, severe issues of performance degradation when using them as pseudo-4*4MIMO, announced as “distributed MIMO”. In general, MIMO might be more resistant to imbalances compared to beamforming. If operators put more antennas next to each other, n-MIMO is possible, but not necessarily n-beamforming, until the antenna separation would be between 0.5...0.9 of wavelength.

Some issues with the mixed 2*2MIMO at band_x and 2*2MIMO at band_y might be with the different elevation phased array physics (=beam directions) of band_x and band_y. Two dislocated antennas with higher distance than half of wavelength do not support beamforming. In case of colocation of both antennas in one radome (=shield), the rank of the channel might still be less than/equal 2 due to correlation within the bands.

Example: Within current macro cell deployments 2*3W/MHz were exemplarily used with high gain antennas (15…18dBi) to secure macro cell DL-coverage. For a total bandwidth of 400MHz in bands 42, 43, the variations from macro to small cell are summarized in the following Table in the steps 1 to 8.

1. LTE1800 (0.) and NR3500 (1.) as reference for comparison with 2 polarizations and 30W per Tx for 10MHz (=3W/MHz (w/o antenna gain)); one cross polarized antenna array with 18dBi is assumed.

2. Introduction of vertical antenna array f. fixed beam: exemplarily M=12 elements (11dBi) + 7dB single antenna element factor. Each antenna element would feed 2.5W per polarization. Each beam has a vertical beam width of 5° to 8°

3. Addition of more antenna columns (N=8) could lead to more vertical beams, but no horizontal beamforming yet. Additional power increases EIRP.

4. Combination/beamforming of all powers to one beam with maximum coverage with additional increase of EIRP. The horizontal beam width is also ~8° (in this example9)

5. Reduction of antenna element power by N² to renormalize to previous EIRP. This is needed in case EMF limits have to be considered.

6. Reduction of transmit power per single-user-beam for N separable users leads to reduction of coverage in multi-user case. EIRP would not change since N beams/users benefit from (in average) 1/N of total power, here 8 times ~5mW result in ~40mW per antenna element.

7. Reduction of transmit power per full band for highest performances. Instead of 10MHz now up to 400MHz might be used per small cell site. This might happen for different spectrum owners at the same location, independent from equipment sharing. In this case, the uplink limitation would trend to downlink power limitation.

9 In case of 64*64 antenna elements, the beam width would reduce to ~1°, which seems not appropriate anymore for backhauling usage with both BS have beam widths of ~1°. M=N<32 seems maximum.



8. Reduction of transmit powers to reach administrative EIRP threshold (in Germany of 10W) in total for small cells sites within permission process. In case of collocation of WiFi, LTE2600, LAA5000 and NR3500 all powers reduce further. In the medium term, it is expected to come back to more differentiated view of small cells like micro, pico and femto cells. Micro and pico cells might be allowed/certified for higher or medium power settings at the expense of more severe issues in EMF security distance consideration which cause delays and additional costs in the overall rollout process. The small pico cells might act as the multi-hop mesh network smart aggregation units with first content based processing capability (edge computing) in addition to the simple relay function.

Table 2: Higher Order MIMO: (example!) power settings in macro and small cells

Conclusion: Due to EMF power limits, the azimuth beamforming with N=8 combined antenna reduce the coverage by 9dB in multi user/beam case. The full band usage at one cell with 400MHz bandwidth reduce further by 16dB leading in total to 25dB in macro, 42dB in small cell reduction due to further reduced EIRP limits. It might not be possible to combine full spectrum (=capacity) usage with the EMF-limits. Instead of full 400MHz, the single small cell might only use smaller bandwidths of the frequency band at the beginning to keep more coverage, and increase bandwidth step by step with small cell site densification.

Spectrum sharing

Currently the highest performance improvements in 4G result due to the operational control of higher bandwidths and enlarged selection of better resources e.g. Carrier Aggregation. In typical 3 to 4 operator cases per country, the usual available bandwidth per band and per operator is in the range of 10-20MHz. Any improvement in 5G-NR to handle e.g. 100MHz bandwidth carriers would also require the willingness of operators to share their existing spectrum assets in spectrum sharing agreements, which remains of lower probability in general to keep proper competition, but could be agreed for some bands. Only new spectrum in bands 42, 43 would allow >100MHz bandwidth assignments for short cell ranges10. It is also possible to assign/auction the total bandwidth of 400MHz to 3-4 mobile operators and one industry consortium which could share their spectrum in their different (isolated) locations/facilities11. In this case, Industry 4.0 related use cases need a special consideration

10 In cases of non-fiber backhauling, inband backhauling concepts might be used which are generally less attractive due to access bandwidth reduction. This might change with mMIMO and dedicated backhauling beams towards fixed fibre-access antennas. 11 In band 43, some FSS usage might persist in co-existence, therefore some regional bandwidth reduction could also be handled proper by sharing concepts, at least in these areas.

# band #Pol num elements vertical M

num elements horizontal N

single ant gain

vertical beamforming gain ~ log(M)

horizontal beamforming gain ~log(N)

single ant transmit power

EIRP bandwidth W/MHz

0 LTE1800 2 1 1 18.0 dBi 0.0 dBi 0.0 dBi 30. W 3.79 kW 10 MHz 378.57

1 NR3500 2 1 1 18.0 dBi 0.0 dBi 0.0 dBi 30. W 3.79 kW 10 MHz 378.572 NR3500 2 12 1 7.2 dBi 10.8 dBi 0.0 dBi 2.5 W 3.79 kW 10 MHz 378.573 NR3500 2 12 8 7.2 dBi 10.8 dBi 0.0 dBi 2.5 W 30.29 kW 10 MHz 3028.604 NR3500 2 12 8 7.2 dBi 10.8 dBi 9.0 dBi 2.5 W 242.29 kW 10 MHz 24228.765 NR3500 2 12 8 7.2 dBi 10.8 dBi 9.0 dBi 39.1 mW 3.79 kW 10 MHz 378.576 NR3500 2 12 8 7.2 dBi 10.8 dBi 9.0 dBi 4.9 mW 3.79 kW 10 MHz 47.327 NR3500 2 12 8 7.2 dBi 10.8 dBi 9.0 dBi 4.9 mW 3.79 kW 400 MHz 1.188 NR3500 2 12 8 7.2 dBi 10.8 dBi 9.0 dBi 0.1 mW 10. W 400 MHz 0.03



in business cases. Equipment vendors might offer 5G managed services to industries complementary to Telco also including LAA-bands.

Since deployment of new spectrum related equipment is quite expensive and proper site acquisition is limited, it would be beneficial to share costs of equipment, align network planning in coverage and capacity and to share spectrum between all operators. This could be seen as wireless open access network extension of the fibre network (leaky fibre). Market realities and competitive marketing may hinder this. More realistic may be bilateral or multilateral network sharing agreements based on federated network slicing.

The backhaul capacity requirements have to be aligned between all partners as early as possible to be upgraded in time. The ownership of the new equipment could be split to different MNOs independent from the ownership of the used spectrum assets. The operation of the shared 5G spectrum could also be done in a Joint Venture, but this seems more a financial issue (to share OPEX costs) than a technical. In this sharing mode, the spectrum resource remains under full control and maintenance of the operators, enabling QoS services.

All corresponding operators have their own Core Network(s) (CN) and access the commonly used spectrum via their own PLMN-ID12 including their individual neighbour relations and handover threshold of each MNO (Figure 4). Potential MVNOs for special user groups (e.g. PPDR) or services (e.g. IoT) could be connected to the MNOs spectrum/networks or directly to the shared (e.g. 5G) open access spectrum. Using federated network slicing, the core network of one operator extends into the physical domain of another operator.

Early 4G based slicing concepts (considering consistency with existing user terminals) could start with this approach of multiple flexible CN with one or more MMEs (=core-slices) controlling the traffic and services with special QoS. The radio resource management will remain responsible for each radio spectrum (=radio-slice), enhanced by special overall uplink and downlink scheduling strategies combining multiple streams in different bands according to quality requirements for 5G-RAN capable devices. The current 4G EPS bearers to one UE with defined QoS requirements are mapped to resources in one band (or more with CA), which would be extended in 5G to multiple bearers to the same UE, but these might be handled within different spectrum bands for uplink and downlink as well. Which bands per site would be applicable is different, keeping in mind that inter-site carrier aggregation or dual connectivity etc. are challenges in today`s 4G-LTE Networks depending on X2-latencies.

12 Public Land Mobile Network Identifier, currently limited to 4-6, which might be increased in case of NW slicing for special services



Figure 4: Multi Operator Core network access to a wireless open access radio network

In addition to the above mentioned spectrum sharing options of licensed spectrum assignment (LSA) which guarantee coordinated spectrum access and QoS, new concepts are already standardized in LTE-advanced Pro (R13) which will be used as well in 5G:

General Authorized Access (GAA): Common use of unlicensed spectrum by different users in uncoordinated manner (e.g. LBT: listen before talk), mainly used by WiFi access

Licensed Assisted Access (LAA): GAA in combination with own licensed spectrum

Future multi-hop mesh networks for IoT-based devices

The pure existence of millions of cheap, “dumb” sensors in a “smart environment” measuring and transmitting data (position, temperature, pressure, etc.) with different measurement cycles will increase small data transmission hardly predicable. One option is to evaluate these data at central servers instantaneously to give proper feedback to the unit, and for long term evaluations (big data). Another option is to smart up at least some dumb sensor units by applications to perform simple algorithms to send only critical values violating defined thresholds (alarms), or to send only min/avg./max-value per day/month. These smarter IoT devices/smartphones might act as aggregator of meshed network of dumb MTC units. Despite these device to device communication is already standardized in 4G-LTE and evolving in 5G, the aggregator unit could already be a smartphone, a WiFi-router- or fixed access router with integrated IoT functionalities. This aggregator functionality opened non-3GPP-devices the door to IoT-market.

Each machine type communication (and also all other 5G use cases) needs to be analysed in coverage, mobility and capacity and costs of deployments and operations. Based on these results it needs to be analysed how to monetize mMTC (or 5G) by connectivity providers to cover new investments in the new technologies.

MOCN (Multi-Operator Core Network) – Wireless Open Access Network

Core Network – Operator A

DB DB

Core Network – Operator B

DB

Core Network – Operator C

DB

Core Network – Operator D

DB

Core Network – Operator E

Core Network – WOAN

DB

RAN - WOAN

DB

DB

DB

DB

DB

DB

DB

DB

DB

DB

DB

DB

DB

DB

DB

DB

DB

DB

DB

DB

DB

DB

DB

DB

MVNOs MVNOsMVNOsMVNOsMVNOs

All Core Networks are connected to common 5G RAN and individual RAN

PLMN ID APLMN ID 5G-WOAN

MVNOs

2G, 3G, 4G RAN5G RAN

5G RAN in highest spectrum



Some IoT applications benefit from eMBB improvements in downlink introduced in LTE Advanced (e.g. HD security cameras, smart glassed, virtual reality)

LTE Cat-M1 (eMTC) enables the broadest range of IoT capabilities, delivering data rates up to 1Mbps, while utilizing only 1.4 MHz device bandwidth (6 resource blocks, 1.08MHz) in existing LTE FDD/TDD spectrum (inband). It will be designed to fully coexist with regular LTE traffic, also support voice (VoLTE or VoN (Voice over Narrowband)).

LTE Cat-NB1 (NB-IoT) reduce in complexity, cost and power for low-end IoT use cases. (IoT at dumb devices: no MIMO, single transmit, half-duplex, grant free access with higher probability of interference)

LTE IoT also enhances the core network (SDN/NFV) to more efficiently handle IoT-centric traffic and to support large number of devices.

The more often data are sent, the shorter is the battery life time, especially in poor coverage conditions. Therefore multi-hop mesh networks enlarge coverage and enable reduced transmit powers and longer battery life times. Hopping scenarios via at least 2 relays might enable 10-15years of battery life times. In addition, if coverage is improved, less repetitions are needed, which saves capacity.

Figure 5: Multi-Hop mesh network to enhance coverage and battery life times

5G will support novel schemes/hierarchies of network controlled device-to-device (D2D) communication, including point-to-point, multicast and broadcast communication. Other novel mechanisms include device duality schemes, where a device can act both as a “normal” end user device (including sensor types) and as a network node extending the infrastructure part of the system, e.g. IoT-router. These schemes will have to be supported over a wide range of physical deployments, from distributed base stations to centralized cloud-RAN deployments or distributed edge clouds. Self-backhauling, where devices can act as base stations and self-establish wireless backhaul links to suitable donor base stations, is regarded as another important feature. A multi-hop mesh network with these smart devices have also to be compliant to EMF regulations.

Multi-Hop network scenario

D2D Advantage UL coverage extension Power consumption reduction Increase of throughput, security

Challenge Increased intelligence of IoT devices (cat-M) Unlicensed access or fixed access Non cellular IoT technology

Direct access with licensed spectrumOperator controlled D2D communication Mesh on unlicensed or with

uplink licensed spectrum to extend coverage in deep spots

No coverage



Summary

5G-NR would break traditional principles of mobile communications, such as the strict combination of paired spectrum allocations for uplink and downlink as well as the fundamental separation of user and control planes. The beauty of 5G-RAN will be in the most flexible usage of uplink and downlink resources, independent from the used spectrum or the underlying technology. The 5G-RAN capability to in/exclude specific parts of different spectrum bands will enable smoother refarming strategies also protecting some narrowband parts (including guard band) while using the currently unused spectrum parts to increase spectrum efficient usage. The new step in 5G RAN is less in the new air interface 5G-NR, which among others enables lower latencies, but would be more in the flexible coordination of all resources in different bands.

5G RAN related key messages:

1. The dual (or multiple) connectivity concept could support FDD-bands for uplink and downlink coverage and TDD-bands for massive downlink capacity. 5G-NR would break traditional principles of mobile communications, i.e. the strict combination of paired spectrum allocations for uplink and downlink. The beauty of 5G-NR will be in the most flexible usage of uplink and downlink resources, independent from the used spectrum or the underlying technology, 4G/5G.

2. Today NB-IoT and 4G-LTE devices are not integrated. In future realizations, NB-IoT would be just a flavour (=slice) of 4G-LTE running in parallel to classical 4G-LTE services, e.g. to extend poor coverage issues with reduced quality requirements, e.g Voice over Narrowband (VoN).

3. The 5G-NR network structure in high(est) bands might shift to multi-hop meshed networks, transmitting and receiving on same or different frequencies or bands. Especially for IoT-devices, multi-hop mesh would enable larger coverage at lower battery consumption and higher capacity and lower the overall traffic on backhauling. Some aggregation terminals (smartphone, laptop) might act as wireless backhaul integrator for any (also non-)3GPP mesh-technology. These aggregations HUBs might fulfil some edge computing functions as well as complexity reductions within local areas.

5G deployment related key messages:

1. The high and highest spectrum use would not be favourable for the classical macro cell deployments due to limited coverage range and limited spatial diversity in macro cell deployments in these bands. In high and highest bands, small cell deployment will dominate, but with shortest ranges and therefore highest capacity densities, which naturally would require a lot of small cells to reach homogeneous performance perception. The physical realizations need to be kept very small as well and almost invisible to people, also compliant to EMF regulations. In this case, MIMO would increase signal quality but less signal coverage. Backhauling would be one critical issue.

2. Massive MIMO (mMIMO) deployments with larger numbers of antenna elements in both dimensions need significant miniaturization and power limitation, and would be suitable only at highest bands for Line-of-Sight (LOS) environments. With mMIMO, the number of individually controlled radiating elements (“active” antenna) would increase in both dimensions, enabling more flexible beamforming or MIMO algorithms. It needs to be planned by radio planning, in which macro deployments the higher angular flexibility in elevation is really required and beneficial. In the predecessor,



higher order MIMO (hoMIMO), the number of controllable(!) antenna-sub-arrays increase in one dimension, while the sub-array might keep their classical phased array fixed beam settings. For all MIMO solutions, the EIRP would increase significantly and needs to be reduced according to EMF limits which limits MIMO coverage related benefits in general.

5G Spectrum related key messages:

1. In the long term, all spectrum will be assigned technology agnostic and will be used for 5G, but in the short term new bands would be used first for 5G, while legacy bands would be refarmed to 5G within normal modernization cycles, but not necessarily to higher order or massive MIMO. TDD-spectrum would gain more importance in the future. 5G technology will also support service migration from currently used lower bands to enable more efficient spectrum usage also in valuable coverage spectrum which is currently out of focus due to limited bandwidth.

2. Existing 4G-LTE networks will persist, complement and cooperate with 5G-NR. Some 5G-NR requirements need also macro cellular deployments/realizations in low and medium bands to be commercially successful. Current 5G-spectrum activities focus on bands >6GHz and especially mm-wave bands due to higher bandwidth`s availability and small antenna sizes favourable for massive MIMO. The major challenge would be in the low and medium bands to enable spectral efficient macro deployments. 5G-NR macro deployments would enable better latencies at larger cells and at lower capacities. Otherwise, 5G-NR in highest bands would focus on isolated, shortest range smart spot use cases due to extremely high costs of full coverage. New 5G technologies would enable spectrum refarming/migrations by integration of existing services, or protected co-existence with existing (analogue) services.

3. TDD has some essential advantages and might become the major 5G-NR mode. TDD-bands 33, 34 might become the first 5G-NR macro deployments13. Since there would be some challenges with the small available bandwidth (5-20MHz), these bands could be used by all operators in equipment (and spectrum) sharing independent from spectrum ownership. They might get first attention as optimized 5G-NR-IoT-successor of the FDD based 4G-NB-IoT networks (as the IoT traffic demand would more favour for uplink) with realistic MIMO order up to 4. eMBB for downlink demands will follow in higher TDD-bands 38, 40, 42, 43 with higher order MIMO and dominantly beamforming. A logical combination of uplink dominated TDD-bands 33 and 34 with downlink dominated TDD-Bands 42, 43 seems possible with 5G-NR independent from duplex mode. Current FDD-bands above 3GHz might be reassigned to TDD, e.g. band 22 to band 42.

4. For larger coverage demands in non/less urban areas, the FDD-band 31 (450-470MHz) might be refarmed to TDD and potentially enlarged as well (digital dividend) to enable at least higher bandwidths and larger coverage, at maximum 2*2MIMO (due to antenna size restrictions). Railways and highways need special deployments with dedicated coverage depending on the used frequency, which would be quite expensive. In a larger view 380-470MHz, which is widely used for TETRA and other specialized narrowband applications, could be used for 5G sharing and slicing usage

13 Comment within review phase: Currently CEPT foresees an alternative usage of band 33, 34, e.g. for PMSE (Programme Making, Special Events), which might exclude bands 33, 34 in Europe for mobile communications, as well as band 40 or further parts of L-band (1427-1518MHz), but not necessarily worldwide. Bands in 470-694MHz, and others will follow step by step after worldwide harmonization. In the long term, band 1 might also be extended by the bands 33, 34 and the MSS-part to one enhanced “band1-e” (1900-2025//2090-2215MHz).



for critical infrastructure, railways, energy, governmental and other use cases favourable with slicing in larger coverage demands. This larger bandwidth would be more applicable to fit expected demands in this band than currently only 2*5MHz bandwidth of band 31. SDL spectrum in 738-758MHz is favourable for sharing as RAN-slice for eMBB services.

Sharing related key messages:

1. In parallel to competition, sharing of equipment and spectrum will enable more cost efficient rollouts. New slicing concepts would gain importance in distributed core functionality using normal commercial of the shelf (COTS) hardware which could also be shared to different Core Networks (CN). The RAN hardware might remain highly specialized, usable only for dedicated bands and limited bandwidths, and with special signal processors, but with overall enhanced resource management software which is seen at (or near) the site in virtualized RAN-clouds on COTS hardware and openRAN software.

2. For spectrum bandwidths up to 40MHz, spectrum and equipment sharing is essential to reduce deployment and maintenance costs per operator. Also at higher bands with potentially higher bandwidths per operator (40…100MHz), spectrum and equipment sharing remains beneficial. Despite the hardware capabilities might be less than the spectrum assignments per operator in highest bands, almost continuous coverage per operator should be secured.

3. The “new” L-band with supplementary downlink may be deployed to increase the 4G-LTE DL-capacity. Depending on the spectrum assignments per country, the L-band would be a first candidate for equipment (and spectrum) sharing of operators to reduce costs and gain more experiences in spectrum sharing.

4. In order to enable highest small cell site densities within EMF regulatory boundaries, an independent infrastructure company/joint venture is reasonable to benefit from coordinated small cell deployment and (fibre) backhauling. This site sharing with open access should prevent that some areas would be blocked for the 2nd / non-incumbent operators. Alternatively, a local deployment per operator remains possible with roaming to other operators. Equipment and spectrum sharing is highly recommended to save investments for all operators, especially in early deployments.

5. It is not recommended to assign any (highest band) spectrum directly to such an infrastructure joint venture to prevent monopoly in 5G spectrum. Spectrum sharing could be done independently from spectrum ownership and is recommended for all operators within increasing equipment rollout with capacity (=spectrum) demand. Reduced spectrum usage enables higher power levels (EMF) and larger distances at the beginning.

6. Since sharing could be one supporting element of new slicing concepts, sharing of network resources will become one essential element of 5G in general. The main focus of slicing is seen in distributed core network functions but also in RAN:

o Benefits of slicing in CN result due to higher diversity/specialization at different network locations according to reduced latency and realization costs.

o Within RAN the resource management of available spectrum and improved operations (neighbour planning, handovers, etc.) is also subject to virtualization within openRAN initiatives, but is expected to remain with dominantly vendor proprietary software and specialized signal processors limiting the opportunity for a standard based dynamic RAN slicing.

Sharing and slicing might help in spectrum migration strategies to refarm analogue to digital applications as well to protect narrowband applications outside of 5G, e.g. LAA in 380-470MHz.



Appendix

5G requirements

New services such as IoT, Cloud-based services, industrial control, autonomous driving, and mission critical communications are emerging and may require massive connectivity, extreme broadband, ultra-low latency and ultra-high reliability. In many 5G publications, the enormous data volume increase in all domains induced by human and non-human machine type users give reason to also increase technical requirements in capacity, efficiency and reduced response times:14

Low latency: <1ms

Low energy: >10years of battery life time

Low complexity at low data rates, but full scalability to bandwidth

High site density: ~1million nodes per km²

High reliability for mission critical services/applications: only 1 of 100Million packets lost or 500ms per year out of service

High capacity (density): 10Tbps per km²

High data rates, >1Gbps as total cell capacity, >100Mbps per user

High spectral efficiency due to spatial multiplexing

Various mobility requirements: static to high-speed trains

Deep coverage, also within the use of multi-hop networks

Not all of the above mentioned 5G requirements will be reached in all bands and for all coverages, but 5G-NR will support techniques to enable most of these with the same air interface options.

Not all services will need e.g. these lowest latencies of 1ms. Many services in relation with human interaction/reaction would work as well with low latencies of 20 to 200ms. Other, mainly machine type communications MTC would need lower latencies which limit the relative distance of these MTC units. 5G-NR would be able to support these MTC-use cases in optimized air interfaces, which would be used less in other use cases, e.g. in 5G macro cells. Especially latency requirements need to be considered in an overall latency budget calculation with the major contributions beyond the air interface delays. Therefore, different service requirements require different solutions, e.g. mobile edge computing optimized for a broader set of services, but not one-fits-all. There will be islands of lowest latency capability within a set of larger coverage cells related low to medium latency capability.

14 Omitting superlatives like “mega-ultra-super-extreme” which also indicates 5G as the last step in the evolution.



5G RAN evolution

In the following overview, the 3GPP technologies were briefly summarized by their main differentiators.

3GPP Start Short description

1G 1980 Analogue voice service

2G, GSM, TDMA/ FDMA

1990 Digital voice service; basic data.

For a dedicated time a dedicated frequency is used per user. Everything is standardized quite strict to harmonize worldwide ecosystems.

Between uplink and downlink sub bands a fixed duplex gap is defined per band and a subset of frequencies is assigned statically to cells.

3G, UMTS, HSPA+,

WCDMA

2000 Digital voice (CS) , data (PS) and high speed HS

In addition to F/TDMA, predefined (wideband) code sequences were used to add 3rd dimension of multiple access. The carrier bandwidth was limited to 5MHz. Dual and Multi Carrier solution were predecessors of 4G-Carrier Aggregation (CA).

Within initial UMTS the power settings were controlled to reach minimum required service quality. The high speed HSPA+ extensions used the remaining power to increase quality and data rates. In the latter, the transmit time intervals reduced significantly the overall latency.

Spatial separation with multiple antennas is foreseen, but not widely used to improve quality/capacity.

With HSPA+ the operational modes increased in the standards to react more flexible on different scenarios and to add recent improvements to existing hardware by (static) software updates.

Within the higher bandwidth of 5MHz, the uplink and downlink resources could be used more flexible and fast frequency hopping increase performance.

4G, LTE, OFDMA

2010 Broadband data service only, voice services via packet.

Instead of code sequences, different orthogonal carriers are used with minimum interference to improve quality. The smallest controllable resource in time and frequency is significantly reduced relative to 3G. Same transmit power is used for all subcarrier. The total carrier bandwidth is static, but scalable up to 20MHz.

Spatial separation by different transmission modes (MIMO, transmit diversity, beamforming, etc.) is possible, dominantly used with 2*2MIMO, also up to 4*4MIMO in FDD, 8*8MIMO in TDD in trials only.



In most countries, FDD-systems are deployed in <1GHz-bands for better coverage and in >1GHz for capacity. In some higher bands TDD is already used for higher capacity in smaller coverage.

Carrier Aggregation allows the combination of up to 5 carrier with the possibility to combine a low band coverage improved uplink with a higher band downlink which would not have the same uplink coverage. Here some limitations of intermodulation products need to be considered.

CA is favourable in downlink (and esp. supplementary downlink), but increasingly used for uplink as well despite of reduced coverage in this case. The broadband reception at terminal is better realized, but transmission in different bands by dual radio terminals is not expected soon.

5G, NR, RSMA, NOMA+

>2020 In the new radio, the resources might be filtered (windowing) to reduce out-of-band transmissions. This would improve quality and control finer parts of the frequency individually. With a reduction of subcarrier bandwidth, the coverage increase for lower data rates (like in 4G-NB-IoT).

In addition, the same resources could be multiple re-used with different transmit powers in case of improved sequential separation in time (SIC) at base station.

In previous generations FDD was dominant due to coverage focus. In the future mainly higher bands would be available. Due to channel reciprocity, TDD would become the main favourable scheme which gives also opportunity to switch uplink and downlink directions as well as transmit durations more flexible than in 4G. The UL/DL-switching is more flexible according to service latency requirements.

It is expected to use short uplink transmissions in high band for channel estimations to form improved beamforming in downlink to compensate for higher band losses.

In consequent extension of 4G-CA, the uplink stream and the downlink could be taken from different bands, e.g. by combining an 4G-LTE FDD (or 5G-NR) uplink with a 5G-NR TDD-downlink resource. Dual radio transmission would be needed for broadband uplink.

Table 2: simplified comparison of 3GPP technologies15

15 GSM: Global Standard for Mobile Communications, UMTS: Universal Mobile Telecommunications Standard, LTE: Long Term Evolution, NR: New Radio; CS: circuit switched, PS: packet switched, HS: high speed packet switched; FDD: frequency division duplex, TDD: time division duplex; TDMA: time domain multiple access, FDMA: frequency domain multiple access, WCDMA: wideband code DMA, SDMA: space DMA, OFDMA: Orthogonal Frequency DMA, RSMA: Resource shared MA, NOMA: non-orthogonal multiple access; MIMO: multiple input multiple output; SIC sequential interference cancelation



5G-NR modulations

Since 5G-NR is still in process of standardization, only a few new or updated options for 5G waveforms or techniques are highlighted briefly in the following.

Orthogonal multiple access (OMA): here mainly improvements of 4G-LTE access schemes would be used, which would not be a major step for justification of 5G-NR equipment/investments.

Downlink: CP-OFDMA (already in 4G-LTE defined)

Cyclic Prefix (CP-OFDMA) with windowing/filtering delivers higher spectral efficiency with comparable out-of-band emission performance and lower complexity than alternative multi-carrier waveforms under realistic implementations

Additional weighting, e.g. WOLA (weighted overlap add) increases OOB16 suppression relative to CP-OFDM

There exist further windowing/filtering techniques to reduce OOB emissions to improve signal to interference per resource, each with different pros/cons, which will be finally selected by standardization. The overall improvement on quality or coverage needs to be analysed. All options are characterized more as 4G-upgrades than a big step in a new radio for 5G. No significant investments for operators are expected here.

Uplink: Single Carrier (SC)-OFDMA for scenarios with higher power efficiency requirements is still the 4G-LTE selected option

Non-orthogonal multiple access (NOMA): for mMTC (massive Machine Type Communication, IoT) non-orthogonal access and “autonomous, grant-free, contention based” UL transmission is under discussion.

Resource Spread Multiple Access (RSMA) in 5G-NR uplink only enables grant-free transmissions efficient for sporadic transfer of small data with asynchronous, non-orthogonal, contention-based access, especially useful for NR-IoT applications, but not suitable for higher spectral efficiency.

In this case of uncoordinated, asynchrony transmission, the interference probability increases reducing quality and reliability, and due to retransmission finally the capacity will reduce as well.

For NOMA, special SIC (sequential interference cancellation) techniques are under consideration to combat increased interferences, which increases the effort of post processing at the base station.

16 OOB: out of band emissions: interference into neighbor resource blocks which reduce signal quality.



Potential TDD bands

In the past, the majority of bands were assigned to FDD, based on voice-driven demand, with limited TDD spectrum in between the FDD assigned sub-bands or in higher ranges. Recently, the amount of spectrum assigned for TDD has increased. The asymmetric nature of TDD brings a number of advantages. One key advantage of this is the flexibility it allows in the adjustment of the downlink and uplink resource ratios to fit perfectly with current user behaviour, where streaming and downloads take up a high proportion of downlink resources. In addition to high volume downlink-centric eMBB applications, unpaired LTE is also optimally suited to cover future M2M and Internet of Things demands which will be predominantly uplink-oriented. Also, video uploads from closed-circuit television (CCTV) result in a higher uplink bandwidth capacity requirement which have to be taken into account in specialised schemes.

For a lower band such as the 380-470MHz band good propagation conditions together with uplink-oriented configuration schemes are quite beneficial, no (higher order) MIMO or beamforming is needed. In higher bands, such as band 42, 43 with poor propagation and downlink-oriented configuration, the cell sizes reduce significantly. Therefore, higher order beamforming/MIMO would be more applicable, especially due to reduced antenna dimension size. In higher bands, the reduced cell size is generally not an issue, because deployments will be more capacity-oriented and capacity density is higher in that case.

IMT450 (TDD-extension of band 31): 380-470MHz

Currently FDD-band 31 (452.5-457.5 // 462.5-467.5MHz) use 2*5MHz partly refarmed from previous CDMA-deployments (3 times 2*1.25MHz) for wide range rural coverage, especially in Finland, Russia and Brazil. ITU-option-D8 foresee full TDD-usage of 20MHz. Depending on the digital dividend evolution, further extensions seem possible here as well (DVBT ch21-25).

Since 2*5MHz would not be sufficient for the expected demands and also not commercially successful, alternatively 380-470MHz could be seen as long term sharing and slicing opportunity to integrate nationwide coverage of critical services in government, energy, infrastructure, PPRD and others. Some essential (inter)nationally defined (analogue) services might need special considerations and protection, which could be considered within 5G by LAA techniques (e.g. LBT), see Figure 6 with one or many 5G carriers. The critical spectrum parts (including guard bands) would not be used (masked) by 5G resource management or used only locally/temporarily if not used by licensees.

The same technologies could be used also for other bands, e.g. band 33, 34 with temporary and locally limited PMSE usage.



Figure 6: exemplary 5G (TD-based) overall resource management for refarming and co-existence with

legacy services.

User terminals constitute the most critical piece of equipment in a cellular network, as constraints on their cost, size and weight are more stringent than the constraints on base stations. The 380-470 MHz capable terminals could evolve steadily with the user demand, starting with larger fixed CPEs with external (or additional outdoor) antennas or embedded in cars and Wi-Fi capability to support the classical smart phones (Wi-Fi offload). In a second wave, multimode smart phones or tablets might arise which offers direct access to the IMT450-network also in real mobile situations. M2M devices should be small in general, but for 380-470 MHz, the required antenna should be larger which might be an issue for some applications. Due to larger antenna size requirements, this band pose challenges for integration into mobile handsets, but could be one aggregation band for incar applications, large device tracking or rural focus.

FDD-Band 22 refarming to TDD-band 42 together with 43

Currently FDD-band 22 (3410-3490//3510-3590MHz) could use 2*80MHz for fixed wireless broadband access. A potential refarming is only possible after reassignment or auctions. In the TDD-bands 42, 43 WiMAX networks have been widely used in the past, with a clear trend to migrate to LTE-TDD, but with still poor ecosystem support, at the moment less than 100 device types support the new bands 42 & 43. In the long run, these band would attract global ecosystems due to worldwide availability for 5G, and in the very long term C-band up to 4.2GHz is the next promising option after partial migration and coordination with current (satellite) usage.

Spectrum efficient usage of centralized frequency resource management

5G

380MHz 470MHz

5G 5G

5G carrier controls all 5G resources within the band

Narrowband analogue carrierse.g. amateur radio, TETRA



Figure 7: GSA 2017-device support of LTE FDD-bands

Spectrum sharing already in 4G-LTE

Currently spectrum is statically assigned to operators, which might not fully utilize their assets everywhere full time, especially less in rural areas. Sharing of equipment and spectrum is beneficial for rural and low traffic areas to minimize network infrastructure costs and operations & maintenance. In such a case, one operator (or a consortium, Joint Venture) builds the network as the HOST. The other operators or MVNOs use the coverage and capacity via (National) Roaming as GUESTS. The operators are not required to share any common network elements or spectrum. Traffic from one GUEST carrier is carried over the network of the HOST. The shared RAN shall be capable of differentiating traffic associated with individual participating MNOs or individual services, e.g. IoT, PPDR, and shall be able to conduct admission control based on allocated RAN resources for each MNO.

In addition to geographical equipment sharing, it is important to provide flexible mechanisms to control the usage of LSA (licensed shared access). In the case of 4G-LTE sharing, several core network operators can dynamically “compete” for radio resources. The eNodeB offers allocation of resources through different strategies, catering for all possible kinds of contractual agreements between these operators. The split can be different from one operator to another and evolve over time. The split is not necessarily related to spectrum ownership and could be adapted individually depending on operators` needs. Strategies range from “fully pooled” to “fully split” (Figure 9):

Fully pooled / dynamic overbooking: This model allows complete sharing of all radio resources between the different CN operators. There are no resources reserved per CN operator. In the extreme (worst) case, subscribers from one CN operator can use all the resources, a fair access to resources for each CN operator cannot be guaranteed. This strategy can be useful at the early staged of deployments when the number of subscribers are relatively low compared to the radio resources available.

Fully split / static case: This model allows strict reservation of resources per CN operator (which could be changed over time). If resources are reserved for a given CN operator and if they are fully used, then a network attachment request or a new connection request from a subscriber of this CN operator will be rejected even if resources reserved for other CN operators are not fully used. This strategy is most often adopted in areas where there is a risk of having subscribers of a given CN operator using all the radio resources. Thus a fair access to resources is enforced.

Figure 8: GSA 2017-device support of LTE TDD-bands



Partial reservation: This model allows to reserve resources per CN operator and to leave a part of the resources unreserved. Thus a fair access to resources can be enforced and non-reserved resources can be used when needed by the different subscribers. This is probably the best compromise in resources sharing.

All mentioned strategies could be different for different frequency bands and services, e.g. band 33, 34 for IoT services. Some higher PPDR-priorities might overrule any resource management strategy in case of emergency, e.g. in 380-470MHz band.

Figure 9: spectrum sharing options in case of equipment & spectrum sharing in frequency domain

An alternative spectrum sharing of all spectrum for one operator at a dedicated time seems less viable.

L-Band as new low band spectrum candidate for spectrum sharing

The ITU World Radio communication Conference in 2015 (WRC-15) has decided to identify the frequency band 1427-1518MHz (L-band) for International Mobile Telecommunications (IMT) which would be used for 4G assignments in the near future, but 5G-NR seems possible as well. In 3GPP, there are three arrangements in portions of this L-band (1427 – 1518 MHz) as follow:

1. FDD: band 11 (UE transmit: 1427.9-1447.9MHz, BS transmit: 1475.9-1495.9MHz) and band 21 (UE transmit: 1447.9-1462.9MHz, BS transmit: 1495.9-1510.9MHz).

2. TDD: Band 45 (UE / BS transmit: 1447-1467MHz). (used in China) 3. SDL: Band 32 (BS transmit: 1452-1496MHz).

In Europe, ECC/DEC/(13)03 currently harmonises a 40MHz portion of L-Band (1452-1492 MHz, Band 32) for Mobile/Fixed Communications Networks Supplemental Downlink (MFCN SDL), for example in Germany 20MHz are assigned to Deutsche Telekom and Vodafone each. The new band will provide significant DL coverage benefits in carrier aggregation within low bands, in particular Band 20. Band 32 could be used as shared spectrum for CA, with maximum 20MHz carrier in 4G usage and full 40 MHz in case of 5G-SDL-usage.

Analog, the 20MHz of 738-758MHz might be used as SDL or for 5G-NR.

Fully pooled/dynamic

MNO1 MNO2 MNO3 MNO4 MNO5 MNO6

MNO1 MNO2 MNO3 MNO4 MNO5 MNO6

Fully shared spectrum: Soft capacity for all MNOs

Fully split/static

Partial reservation

Fully shared spectrum: Soft capacity for all MNOs

Spectrum sharing options between operators



In most cases new antennas are needed for band 28 or band 32, so both rollouts might be realized in one step, e.g. in rural areas first.

It needs to be mentioned, that within L-band from 1427-1518MHz, only the SDL part is considered in region1 while in region 2 and 3 the full band is identified for IMT purpose.

Abbreviations 3GPP 3rd Generation Partnership Program 4G-LTE Long Term Evolution 5G-NR Next / New Radio CA Carrier Aggregation CAT-M Terminal category for machine type CCTV closed-circuit television COTS commercial of the shelf CoMP Coordinated MultiPoint CN core network CPE Customer premise equipment CP-OFDMA Cyclic Prefix OFDMA CS circuit switched C-RAN Centralized RAN: CoMP, (fe)ICIC, HetNet, … D-RAN Distributed or De-centralized RAN: slicing at site, EDGE D2D device-to-device dBi Decibel relative to isotropic radiated antenna dB Decibel (as ratio) DL Downlink DVBT Digital Video Broadcast Television eMBB Enhanced Mobile Broadband EIRP equivalent isotropic radiated power EMF electromagnetic force EPC, EPS Enhanced Packet Core, System FDD frequency division duplex FDMA Frequency Domain Multiple Access GAA General Authorized Access GSM Global Standard for Mobile Communications HS high speed packet switched (fe)ICIC Further enhanced Intercell Interference Coordination IMT International Mobile Telecommunications IoT Internet od Things ITU International Telecommunications Unit LAA Licensed Assisted Access LBT Listen before talk LOS Line of Sight LSA licensed spectrum assignment¸ licensed shared access M2M Machine to Machine MIMO multiple input multiple output



MNO Mobile Network Operator mMTC (massive) Machine Type Communication NFV Network Functions Virtualization NB-IoT Narrowband Internet of Things NLOS Non Line of Sight NOMA Non-Orthogonal Multiple Access NSA Non-Standalone 5G-NR NW Network OMA Orthogonal Multiple Access OFDMA Orthogonal Frequency Division Multiple Access OOB Out of Band Emission PMSE Program Making, Special Events PLMN-ID Public Land Mobile Network Identifier PPDR Public Protection Disaster Recovery PS Packet Switched QoS Quality of Service RAN Radio Access Network RET Remote Electrical Tilt RSMA Resource shared multiple access SC-OFDMA Single Carrier OFDMA SDL Supplemental Downlink SIC sequential interference cancelation TDD time division duplex TDMA Time Domain Multiple Access TTI transmission time interval SDN Software Defined Networking SDMA Space Division Multiple Access UDN Ultra-Dense Networks UL Uplink UMTS Universal Mobile Telecommunications Standard V2X Vehicular to everything VoLTE Voice over LTE VoN Voice over Narrowband WCDMA Wideband Code Division Multiple Access WRC World Radio Conference



The Author

Dr. Dietert joined Detecon International in 2012, focused on many international projects in areas of radio network strategy, planning, optimization, capacity dimensioning, and spectrum management.

Dr. Dietert is part of the Detecon knowledge team with focus on 5G led by F. Schröder, Dr. A. Gerwens and Dr. W. Knospe.

The author thanks all colleagues for intensive and fruitful discussions and feedbacks, esp. N. Zhelev, Dr. T. Eckstein, and L. Reith.

I greatly acknowledge my family for the endless support, patience and understanding during this paper.



The Company

Leading Digital

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Our company's history is proof of this: Detecon International is the product of the merger of the management and IT consulting company Diebold, founded in 1954, and the telecommunications consultancy Detecon, founded in 1977. Our services focus on consulting and implementation solutions which are derived from the use of information and communications technology (ICT). All around the globe, clients from virtually all industries profit from our holistic know-how in questions of strategy and organizational design and in the use of state-of-the-art technologies.

Detecon’s know-how bundles the knowledge from the successful conclusion of management and ICT projects in more than 160 countries. We are represented globally by subsidiaries, affiliates, and project offices. Detecon is a subsidiary of T-Systems International, the business customer brand of Deutsche Telekom. In our capacity as consultants, we are able to benefit from the infrastructure of a global player spanning our planet.

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