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What Will 5G Be?

Jeffrey G. Andrews, Stefano Buzzi, Wan Choi, Stephen Hanly, Angel Lozano, Anthony C. K. Soong, Jianzhong Charlie Zhang

arXiv:1405.2957v1cs.ITcs.NI

TL;DR

The paper examines the technical, economic, regulatory, and architectural challenges of making 5G a highly integrative paradigm shift rather than an incremental 4G advance. Through a comprehensive literature overview, it concludes that disruptive 5G networks remain technically feasible but face substantial cross-layer challenges.

  • Problem

    Future 5G must support extreme bandwidth, density, and antenna requirements while integrating new air interfaces with LTE and WiFi, creating unresolved cross-layer challenges.

  • Method

    The paper synthesizes current literature and discusses key technologies, research challenges, and preliminary standardization activities across the 5G ecosystem.

  • Results

    The paper concludes that mmWave propagation losses are surmountable with large antenna arrays, while many technical and implementation challenges remain across the protocol stack.

  • Takeaways & Limitations

    Disruptive 5G networks require coordinated advances in radio technologies, network architecture, regulation, and cost and energy efficiency.

  • Takeaways & Limitations

    The paper identifies substantial unresolved challenges spanning all protocol-stack layers and intersecting with regulatory, policy, and business considerations.

Abstract

from arXiv · show

What will 5G be? What it will not be is an incremental advance on 4G. The previous four generations of cellular technology have each been a major paradigm shift that has broken backwards compatibility. And indeed, 5G will need to be a paradigm shift that includes very high carrier frequencies with massive bandwidths, extreme base station and device densities and unprecedented numbers of antennas. But unlike the previous four generations, it will also be highly integrative: tying any new 5G air interface and spectrum together with LTE and WiFi to provide universal high-rate coverage and a seamless user experience. To support this, the core network will also have to reach unprecedented levels of flexibility and intelligence, spectrum regulation will need to be rethought and improved, and energy and cost efficiencies will become even more critical considerations. This paper discusses all of these topics, identifying key challenges for future research and preliminary 5G standardization activities, while providing a comprehensive overview of the current literature, and in particular of the papers appearing in this special issue.

I. INTRODUCTION … 1) Data Rate:

5G is motivated by rapidly growing wireless data, device counts, and performance demands, requiring a paradigm shift rather than incremental 4G evolution. The paper surveys major technologies and engineering requirements, emphasizing aggregate and edge rates as its main quantitative targets.

  • A. The Road to 5G: Wireless networks face rapidly increasing data volumes, device counts, and data rates, with devices potentially reaching tens or hundreds of billions by 5G.IP traffic was projected to exceed 500 exabytes by 2020, while new applications beyond personal communications were expected to drive device growth.
  • A. The Road to 5G: 5G is presented as a paradigm shift involving mmWave spectrum, ultra-densification, massive MIMO, network virtualization, and improved energy efficiency.The paper also discusses transmission waveforms, regulatory issues, and standardization.
  • B. Engineering Requirements for 5G: The paper organizes 5G requirements across key dimensions, while noting that different applications need not satisfy all requirements simultaneously.Some peak requirements apply only in particular configurations.
  • 1) Data Rate:: Mobile data traffic growth is identified as the main driver of 5G and motivates separate targets for aggregate, edge, and peak data rates.The paper distinguishes several ways to measure data rate.
  • 1) Data Rate:: 1000x is the consensus target for increasing aggregate data rate from 4G to 5G, measured in bits/s/area.Aggregate data rate denotes the total data the network can serve per unit area.
  • 1) Data Rate:: 100 Mbps to 1 Gbps are proposed goals for the 5G edge rate, with 100 Mbps for 95% of users requiring about a 100x advance over typical current 4G systems.The edge rate represents the worst rate a user can reasonably expect while within network range.
  • 1) Data Rate:: Tens of Gbps is the likely 5G peak-rate range, although the paper treats peak rate as a marketing figure with limited engineering meaning.Peak rate is the best-case rate under any conceivable network configuration.
  • 1) Data Rate:: The paper focuses primarily on meeting the approximately 1000x aggregate-rate and 100x edge-rate improvements over current 4G technology.These requirements correspond to the aggregate and edge metrics described above.

2) Latency: … A. Extreme Densification and Offloading

The paper frames 5G around demanding latency, energy, cost, device-scale, and 1000x data-rate requirements. It emphasizes extreme densification and offloading while identifying associated mobility, interoperability, infrastructure, and resource-management challenges.

  • 2) Latency:: Current 4G roundtrip latency is about 15 ms, but 5G applications such as two-way gaming, tactile Internet services, and virtual or enhanced reality motivate more stringent latency requirements.Current latency relies on a 1 ms subframe plus overhead for resource allocation and access.
  • 3) Energy and Cost:: Per-link data rates are expected to increase about 100x, requiring Joules per bit and cost per bit to fall by at least 100x.The article does not quantify energy and cost, but advocates solutions with reasonable cost and power scaling.
  • C. Device Types and Quantities.: A single macrocell may need to support 10,000 or more low-rate devices alongside traditional high-rate mobile users.This diversity and scale require major changes to 4G control-plane and network-management mechanisms.
  • II. KEY TECHNOLOGIES TO GET TO 1000X DATA RATE: The required 1000x data-rate increase is expected to come mainly from extreme densification and offloading, increased bandwidth, and increased spectral efficiency.These categories respectively provide more active nodes, more Hz, and more bits/s/Hz per node.
  • A. Extreme Densification and Offloading: Making cells smaller increases network capacity through spectrum reuse and fewer users competing for resources at each base station.Cell sizes have progressively shrunk from hundreds of square kilometers to often fractions of a square kilometer in urban areas.
  • A. Extreme Densification and Offloading: Under power-law pathloss models, signal-to-interference ratio is preserved as networks densify, allowing cells to shrink without sacrificing SIR in principle.The model ceases to apply in the near field, very close to the transmitter.
  • A. Extreme Densification and Offloading: Extreme densification creates challenges in preserving cell-splitting gains, associating users across radio access technologies, supporting mobility, and funding installation, maintenance, and backhaul.These issues become especially important as base stations become more lightly loaded, particularly low-power nodes.

1) Base Station Densification Gains: · 2) Multi-RAT Association:

Base-station densification gains depend on loading, interference, muting, and propagation conditions, with mmWave potentially enabling gains far above proportional scaling. Multi-RAT association becomes a complex optimization problem across heterogeneous radios, loads, frequencies, standards, and mmWave blockage conditions.

  • 1) Base Station Densification Gains:: Densification gain ρ measures the effective data-rate increase relative to the increase in network density, treated here as a proxy for cost.It compares rates R1 and R2 at base-station densities λ1 and λ2.
  • 1) Base Station Densification Gains:: In interference-limited full-buffer networks, ρ ≈1 is the best-case scenario because densification leaves the SIR distribution approximately constant.With non-full buffers, lighter small-cell loading can instead increase SINR as density rises.
  • 1) Base Station Densification Gains:: Macro-BS muting, including eICIC, improves ρ and can approach 1 relative to continuous macrocell transmission that interferes with small cells.This is notable because macrocells are the network bottleneck.
  • 1) Base Station Densification Gains:: At mmWave frequencies, densification gains ρ ≫1 may be possible because added density both lightens load and dramatically increases SINR in largely noise-limited communication.The cited example increases the base-station count in a given area from 36 to 96 under a plausible urban grid-based deployment.
  • 2) Multi-RAT Association:: User association in multi-RAT networks trades off the gain from each BS against its experienced traffic load or congestion.The figure depicts a mobile user associating with different BSs across many frequency bands according to this tradeoff.
  • 2) Multi-RAT Association:: A multi-RAT 5G device may integrate 5G, 3G, multiple LTE releases, WiFi, and possibly D2D radios across many spectral bands.This increased RAT integration makes heterogeneous networks a central 5G feature.
  • 2) Multi-RAT Association:: Optimal user association is a massive combinatorial optimization problem involving every user-to-BS SINR, instantaneous BS loads, other users’ choices, and uplink-downlink consistency constraints.Because of this complexity, simplified association procedures must be adopted.
  • 2) Multi-RAT Association:: MmWave further complicates association because blockages blur cell boundaries and can cause users to bypass nearby blocked BSs for farther unblocked ones, although reduced interference lessens blanking needs.The broader multi-RAT association problem remains an area for modeling, analysis, and optimization.

3) Mobility Support: · 4) Cost: · B. Millimeter Wave

Extreme densification makes mobility support and deployment cost major challenges, while mmWave offers abundant spectrum but introduces difficult propagation and equipment constraints. Addressing these challenges requires automation, new deployment paradigms, and revised models of coverage and association.

  • 3) Mobility Support:: Extreme densification and heterogeneity make mobility support difficult, despite mobility and always-on connectivity remaining cellular networks’ key advantage over WiFi.The paper anticipates somewhat ad hoc mobility solutions, such as those in LTE Rel-11, because mobility effects are difficult to model and analyze.
  • 4) Cost:: Smaller cells require smaller, lower-power, cheaper base stations, but permits, reliable backhaul, and site rental fees hinder operator-controlled small-cell deployment.The paper notes no fundamental reason that a base station should cost more than a user device or WiFi node.
  • 4) Cost:: End-user femtocells and WiFi access points reduce capital and operating expenses, but enterprise-grade coordination requires automated self-organization at deployment scale.These deployments also depend on the end user’s backhaul connection and access network, creating additional concerns.
  • B. Millimeter Wave: At mmWave frequencies, blocking, line-of-sight versus non-line-of-sight propagation, and beam directionality make conventional cell boundaries obsolete.Calculated base-station associations with real building locations illustrate this altered notion of coverage.
  • 4) Cost:: Open access to small cells could greatly reduce 5G costs by avoiding inefficient end-user backhaul arrangements.Fon is cited as a preliminary successful example, with over 13 million shared WiFi access points as of press time.
  • 4) Cost:: 5G networks will be extremely dense and heterogeneous, creating challenges for network modeling, analysis, design, and optimization.The paper identifies direct device-to-device communication as a second densification approach besides cell shrinking.
  • B. Millimeter Wave: At 30–300 GHz, mmWave provides vast relatively idle spectrum with 1–10 mm wavelengths, alongside several GHz of plausible spectrum at 20–30 GHz.Conventional microwave beachfront spectrum, spanning several hundred MHz to a few GHz, is nearly fully occupied in peak times and markets.
  • B. Millimeter Wave: mmWave was historically unsuitable for mobile communications because of strong pathloss, atmospheric and rain absorption, weak diffraction and penetration, phase noise, and high equipment costs.These propagation and hardware problems explain why substantial mmWave spectrum has remained idle until recently.

1) Propagation Issues: · 2) Large arrays, narrow beams:

MmWave propagation losses are surmountable with large coherent antenna arrays, but narrow beams introduce new challenges in blockage, alignment, interference, control, and transceiver design. Integrating microwave control links with mmWave data links can improve reliability.

  • 1) Propagation Issues:: A tenfold carrier-frequency increase from 3 to 30 GHz adds 20 dB of free-space power loss when antenna electrical size is fixed.Holding one antenna aperture constant leaves free-space pathloss unchanged; holding both constant makes it diminish with f^2.
  • 1) Propagation Issues:: Arrays preserve antenna aperture as frequency rises, but increasingly many elements must be cophasing to steer and collect energy coherently.Cophasing becomes harder when channels change rapidly because of mmWave Doppler shifts or device-orientation changes.
  • 1) Propagation Issues:: MmWave signals diffract less and propagate more specularly, making blockage severe and producing nearly bimodal channels based on Line-of-Sight presence.Measured pathloss approaches 20 dB/decade under LoS and 40 dB/decade plus additional blockage-related loss otherwise.
  • 1) Propagation Issues:: Propagation losses are ultimately surmountable, but require large arrays to steer beam energy and collect it coherently.Narrow-beam communication is physically feasible yet introduces difficulties unfamiliar to traditional cellular design.
  • 2) Large arrays, narrow beams:: Highly directional mmWave beams create intermittent, on/off interference and increase sensitivity to beam misalignment.Most beams do not interfere, but strong interference occurs intermittently.
  • 2) Large arrays, narrow beams:: Narrow beams complicate initial access and handoff because users and base stations must search many angular positions or use multistage beam acquisition.An alternative is a wider beam with large coding or spreading gains that is successively narrowed.
  • 2) Large arrays, narrow beams:: Using microwave macro-cell control links alongside short-range mmWave small-cell payload links can preserve reliable connectivity during mmWave interruptions.The control plane supports rapid data transmission, while retransmissions recover data lost during sporadic link disruptions.
  • 2) Large arrays, narrow beams:: Large-bandwidth systems require new transceiver architectures because A/D and D/A converters have exorbitant power consumption.This hardware constraint can directly shape communication-system design.

C. Massive MIMO · 1) Pilot Contamination and Overhead Reduction:

Massive MIMO expands spatial signaling through many base-station antennas, promising higher spectral efficiency and simpler transmission while introducing pilot contamination and pilot-overhead challenges. The section considers MU-MIMO, coordinated transmission, and pilot-design strategies for addressing these limitations.

  • C. Massive MIMO: MIMO supplies a spatial communication dimension when base stations and mobile units have multiple antennas, provided channel-matrix entries exhibit sufficient statistical independence.Spacing, cross-polarization, and angular disposition can provide the relevant independence.
  • C. Massive MIMO: MU-MIMO overcomes portable-device antenna limits by allowing each base station to serve several users concurrently and aggregate their antennas into signaling dimensions.The available dimensions are limited by the smaller of the users’ aggregate antennas and the base station’s antennas.
  • C. Massive MIMO: CoMP allows multiple base stations to cooperate as one effective MIMO transceiver, converting some system interference into useful signals.This approach supports interference and mobility management.
  • C. Massive MIMO: Massive MIMO extends LTE-era configurations of two-to-four mobile-unit antennas and up to eight base-station-sector antennas by envisioning more than an order-of-magnitude increase.This vision was articulated by Marzetta and later formalized in subsequent work.
  • C. Massive MIMO: Massive MIMO can deliver enormous spectral-efficiency gains without increased base-station densification, while trading some gains for power-efficiency improvements.Its large antenna arrays also smooth channel responses through spatial diversity and the law of large numbers.
  • 1) Pilot Contamination and Overhead Reduction:: Pilot contamination persists because pilots orthogonal among same-cell users must be reused across cells, creating intercell pilot interference and a channel-estimate quality floor.This impairment does not vanish as the number of base-station antennas grows large.
  • 1) Pilot Contamination and Overhead Reduction:: FD-MIMO downlink simulations at 2.5 GHz used half-wavelength horizontal and vertical BS spacings, 2 antennas per user, and 30% overhead.The baseline was SU-MIMO with 4 antennas per BS; FD-MIMO used MU-MIMO with 16 or 64 antennas per BS sector, corresponding to 4 × 4 or 8 × 8 planar arrays.
  • 1) Pilot Contamination and Overhead Reduction:: Pilot-overhead reduction requires careful pilot-structure design to prevent overhead from exploding while retaining necessary channel-estimation functionality.Proposed approaches include exploiting spatial correlations to share pilot symbols among antennas and segregating pilots into classes transmitted at their necessary rates.

2) Architectural Challenges: … III. DESIGN ISSUES FOR 5G

5G design requires new massive-MIMO architectures, elevation-aware channel models, and coordination across massive-MIMO, small-cell, and mmWave deployments. These changes must support higher throughput while also reducing latency, energy consumption, and cost and accommodating many low-rate connections.

  • 2) Architectural Challenges:: Massive-MIMO architectures must replace a few high-power amplifiers and sector antennas with many tiny antennas, likely integrating each antenna with its own low-power amplifier.Key architectural concerns include scalability, antenna correlations and mutual coupling, and cost.
  • 2) Architectural Challenges:: Electromagnetic lens-focusing antennas are explored as an alternative, innovative massive-MIMO design.
  • 3) Full-Dimension MIMO and Elevation Beamforming:: Planar 2D arrays enable full-dimension MIMO to house more antennas within the same form factor while exploiting elevation as well as azimuth.Tailored vertical beams can increase signal power and reduce interference.
  • 4) Channel Models:: Sound massive-array channel models require extensive field measurements of antenna correlations, mutual coupling, channel orthogonalization, and elevation effects.FD-MIMO modeling must incorporate elevation in addition to azimuth.
  • 5) Coexistence with Small Cells:: Massive-MIMO base stations may coexist with small cells by using excess antennas for spatial nulling and interference avoidance instead of segregating transmissions by frequency.The feasibility of this approach requires confirmation.
  • 5) Coexistence with Small Cells:: As networks densify and small-cell offloading reduces active users per cell, the need for massive MIMO may decline, with cost and backhaul determining the balance.
  • 6) Coexistence with mmWave:: At mmWave frequencies, very large antenna arrays can fit in portable devices and provide beamforming gain and MIMO opportunities, requiring a balance with interference reduction.
  • III. DESIGN ISSUES FOR 5G: 5G design must support 1000x higher throughput while decreasing latency, energy consumption, and costs and supporting many low-rate connections.The design issues include waveforms, cloud-based and virtualized architectures, latency and control signaling, and energy efficiency.

A. The Waveform: Signaling and Multiple Access … 3) Potential Alternatives to OFDM:

5G waveform design may mark another major change in signaling and multiple access, although OFDM remains the leading candidate. Investigated alternatives target OFDM’s power, spectral-efficiency, synchronization, guard-band, and mmWave limitations, while tunable OFDM could adapt parameters to channel conditions.

  • A. The Waveform: Signaling and Multiple Access: Each cellular generation has significantly changed its defining waveform, making another major signaling and multiple-access transition plausible for 5G.The progression moved from analog frequency modulation with FDMA in 1G toward digital approaches in later generations.
  • 1) OFDM and OFDMA: The Default Approach:: OFDM dominates high-speed wireless communication, including WiFi and LTE, because it handles frequency selectivity, enables efficient FFT/IFFT implementation, and pairs well with MIMO.It also supports dynamic, fine-grained digital-domain resource allocation.
  • 2) Drawbacks of OFDM:: OFDM’s high peak-to-average-power ratio creates a tradeoff between transmitted-signal linearity and power-amplifier cost.The high PAPR arises because IFFT outputs sum uncorrelated inputs, producing nearly Gaussian envelope samples.
  • 2) Drawbacks of OFDM:: OFDM’s spectral efficiency is satisfactory but may improve if strict orthogonality is relaxed and cyclic prefixes are shortened or removed.FQAM is reported to improve downlink throughput for cell-edge users.
  • 2) Drawbacks of OFDM:: OFDM’s applicability to mmWave is an open concern because of enormous bandwidths and the difficulty of developing efficient power amplifiers at those frequencies.A proposed alternative uses single-carrier signaling with a null cyclic prefix.
  • 3) Potential Alternatives to OFDM:: Most investigated alternatives are incremental departures from OFDM, while time-frequency packing and faster-than-Nyquist signaling target strict orthogonality and cyclic-prefix limitations.Faster-than-Nyquist signaling accommodates symbol-interval/subcarrier-spacing products below 1, with claimed spectral-efficiency improvements on the order of 25%.
  • 3) Potential Alternatives to OFDM:: Nonorthogonal multicarrier approaches include filterbank multicarrier, UFMC, and GFDM, addressing synchronization, sidelobes, interference, guard bands, propagation delays, and noncontiguous spectrum.GFDM uses tail biting for a shortened cyclic prefix and can adaptively fill frequency-domain holes for spectrum sharing.
  • 3) Potential Alternatives to OFDM:: Single-carrier transmission is regaining interest through low-complexity frequency-domain nonlinear equalizers, particularly for mmWave, while tunable OFDM could vary FFT size, subcarrier spacing, and cyclic-prefix length.The proposed parameter adaptation is motivated by software-defined radios and channel-dependent delay spreads.

B. Cloud-based Networking · 1) Network Function Virtualization:

Cloud-based networking will make future mobile networks more nimble, flexible, and scalable by separating network functions from hardware and combining NFV with SDN. NFV will enable elastic support for changing demands and new virtual services, while virtualization may eventually extend from the core toward the network edge.

  • B. Cloud-based Networking: Moving data to the cloud will redefine network endpoints and the time frames over which network services are provisioned.Cloud access will support availability from anywhere and through varied platforms.
  • B. Cloud-based Networking: NFV and SDN will be paramount trends, fundamentally changing how mobile network services are provided.Together, they are characterized as the biggest advance in mobile communication networking in the last 20 years.
  • B. Cloud-based Networking: Virtualization currently focuses on the core network but may eventually extend toward the edges, including virtualized base stations down to the MAC and PHY.The term cloud-RAN currently largely describes cooperation among multiple base stations rather than full base-station virtualization.
  • 1) Network Function Virtualization:: NFV runs network functions traditionally tied to hardware appliances on cloud-computing infrastructure in data centers.NFV infrastructure is not expected to equal commercial or enterprise cloud, although it will reuse many commercial-cloud capabilities.
  • 1) Network Function Virtualization:: Separating network functions from hardware infrastructure will be the cornerstone of future architectures despite some mobile-network requirements being infeasible in commercial cloud.The text specifically identifies separation of the data, control, and management planes as potentially infeasible within commercial cloud.
  • 1) Network Function Virtualization:: NFV will elastically support network functional demands while enabling virtual networks and new types of network services.These capabilities are presented as sources of significant architectural nimbleness.
  • 1) Network Function Virtualization:: SDN will revive user-controlled management of network elements as advances in computing make that architecture feasible.The concept dates to the 1990s and has recently been termed software defined networking.

2) Software Defined Networking: … 4) Hardware solutions:

The paper presents SDN as a programmable, centrally intelligent architecture for 5G networks, while identifying energy efficiency as a major cross-cutting research theme spanning allocation, planning, renewable power, and hardware.

  • 2) Software Defined Networking:: SDN decouples control and data planes, logically centralizes network intelligence and state, and abstracts infrastructure from applications.This architecture is an intelligent, programmable network framework.
  • 2) Software Defined Networking:: Open interfaces and programmability let software controllers expose network capabilities through APIs and let applications request or manipulate network services.NFV and SDN still face open challenges in scalability, migration, management, automation, and security.
  • C. Energy efficiency: 5G energy efficiency, measured in Joules/bit or bits/Joule, must improve by about the data-rate increase to maintain power consumption, requiring several orders of magnitude improvement.Greater improvement is needed if power consumption is to decrease.
  • 2) Network Planning:: Network planning reduces energy use by minimizing base stations for coverage and adapting BS sleep/wake states when traffic or active-user demand is low.These strategies exploit networks designed for peak-hour traffic.
  • 1) Resource allocation:: Resource-allocation studies show that accepting moderate data-rate reductions can yield large energy savings, including through coordinated beamforming in HetNets.The literature includes contributions optimizing system energy efficiency.
  • 3) Renewable energy:: Renewable-powered BSs can support drop-and-play small-cell deployment, and plausible per-BS traffic loads in dense HetNets may be served solely by energy harvesting.Solar power is especially relevant where reliable, ubiquitous power grids are unavailable.
  • 4) Hardware solutions:: Hardware approaches target power consumption through low-loss antennas, antenna muting, adaptive sectorization, cloud-RAN centralization, and greener data centers.True cloud-RAN may save energy by centralizing baseband processing.
  • 4) Hardware solutions:: Hardware research also examines the power tradeoff between many small cells and fewer macrocells, while the energy consumed by massive-MIMO circuitry remains incompletely characterized.Energy efficiency spans multiple 5G research topics.

IV. SPECTRUM, REGULATION AND STANDARDIZATION FOR 5G … 2) Unlicensed Spectrum:

5G spectrum policy must integrate diverse frequency bands and reconsider allocation methods as saturated microwave spectrum contrasts with idle mmWave capacity. The paper examines licensed and unlicensed approaches, balancing investment and interference control against entry barriers and infrastructure needs.

  • IV. SPECTRUM, REGULATION AND STANDARDIZATION FOR 5G: 5G policy must address intersections among technology, public policy, industry standardization, and economic considerations.These intersections frame the paper’s transition from technical issues to policy and standardization concerns.
  • A. Spectrum Policy and Allocation: Saturated peak-market microwave spectrum and idle mmWave capacity motivate integrating low frequencies for coverage, mobility, and control with high frequencies for small cells.Different propagation characteristics and the concept of phantom cells support this broad frequency integration.
  • A. Spectrum Policy and Allocation: Spectrum policy and allocation are essential 5G issues, including efficient-spectrum-use technologies such as massive MIMO and small cells.The section considers the advantages and disadvantages of different spectrum-regulation approaches.
  • 1) Exclusive Licenses:: Exclusive licensing gives licensees interference-management control, investment incentives, and quality-of-service guarantees, but creates high entry barriers and elevated sunk costs.Regulators assign a band to a particular purpose subject to limitations such as power levels or geographic coverage.
  • 1) Exclusive Licenses:: Market-based approaches, including spectrum auctions and digital-dividend refarming, seek to address inefficiencies in traditional exclusive licensing.Refarming moves long-held commercial radio and television allocations into different, smaller bands to release spectrum for wireless communications.
  • 2) Unlicensed Spectrum:: Open access allows certified devices to share unlicensed bands, lowering entry barriers and enhancing competition; ISM bands are prominent examples used by WiFi and many other devices.Examples include microwave ovens, medical devices, sensor networks, and cordless phones.
  • 2) Unlicensed Spectrum:: Open access risks unmanageable interference, absent quality-of-service guarantees, and a tragedy of the commons, yet may support small-cell infrastructure with multiple players.Cellular operators already offload about half of cellular data traffic through unlicensed spectrum, while mmWave systems may be limited more by signal strength than interference.

3) Spectrum Sharing: … 2) 5G Spectrum Standardization:

5G spectrum policy combines controlled sharing and more fluid market mechanisms with evolving standardization efforts. Reliable sharing requires specified protections, while mmWave deployment depends on lengthy regulatory and international harmonization processes.

  • 3) Spectrum Sharing:: Spectrum sharing can use intermediate frameworks between exclusive licensing and open access, including TV white-space reuse and licensed sharing by limited parties.Authorized Shared Access and Licensed Shared Access let licensees coordinate use under specified conditions and seek interference protection, improving predictability and reliability.
  • 4) Market-Based Approaches to Spectrum Allocation:: Exclusive licenses are likely to remain common for beachfront spectrum, but fluid markets could enable faster trading and reallocation under liberal licenses.Dynamic allocations require careful definition of spectrum assets.
  • 4) Market-Based Approaches to Spectrum Allocation:: Dynamic spectrum markets may let operators buy, sell, or lease spectrum and share infrastructure as small-cell traffic fluctuates.Brokers could manage transactions on timescales ranging from hours and minutes to milliseconds, potentially decoupling infrastructure, spectrum, and services.
  • 4) Market-Based Approaches to Spectrum Allocation:: Adding unlicensed bands to environments with exclusive operator spectrum can reduce total welfare when operators offload traffic against overall social welfare.The paper identifies this outcome as Braess’ paradox, arising from operators’ incentives to offload traffic.
  • 1) 5G Standardization Status:: Regional projects and forums are shaping the 5G vision, while industry and ITU groups increasingly use the IMT-2020 designation for prospective deployments around 2020.EU METIS has released documents addressing 5G scenarios and requirements.
  • 1) 5G Standardization Status:: An ETSI summit concluded that LTE evolution may not satisfy anticipated 5G requirements, although formal 3GPP standardization had not yet begun while LTE Rel-12 was being finalized.The summit was held in November 2013, and LTE Rel-12 was described as the third LTE-Advanced release.
  • 2) 5G Spectrum Standardization:: ITU spectrum studies for 5G cover bands above 6 GHz and assess channel models, semiconductor readiness, coverage, mobility, deployment scenarios, and coexistence.These studies address the technical feasibility of higher-frequency spectrum.
  • 2) 5G Spectrum Standardization:: mmWave spectrum requires national regulatory repurposing and international WRC agreement, with lengthy processes and substantial hurdles before 5G availability.WRC-18 was identified as the prospective venue for agreeing mmWave allocations for 5G.

C. Economic Considerations … V. CONCLUSIONS

Moving to 5G will impose substantial economic and backhaul challenges, motivating infrastructure-sharing models and renewed investment in fiber and wireless solutions. The paper concludes that disruptive 5G is becoming increasingly plausible, but significant technical challenges remain.

  • C. Economic Considerations: 5G deployment will require costly network densification, especially because BS sites and backhaul connections are expensive.Reducing spectrum costs alone will not remove these economic barriers.
  • 1) Infrastructure Sharing:: Infrastructure sharing could separate infrastructure ownership from network operation and support new 5G business models.The passage identifies infrastructure sharing as a possible new business model.
  • 1) Infrastructure Sharing:: Passive sharing of sites, backhaul, power, and cooling could expand coverage at lower cost and power consumption, particularly in dense 5G networks.Regulation may be needed to require site sharing and improve competition.
  • 1) Infrastructure Sharing:: Active sharing of antennas, BSs, radio access networks, or core networks may benefit small-cell rollouts but requires safeguards against collusion.The passage also identifies economies of scale as a positive effect.
  • 1) Infrastructure Sharing:: Mobile virtual network operators could provide enterprise small-cell coverage by accessing another operator’s spectrum and enabling roaming beyond the enterprise.The model does not require the virtual operator to own spectrum.
  • 2) Backhaul:: Backhaul is a major challenge for hyper-dense, ultra-fast networks, but fiber expansion and improving wireless solutions provide grounds for optimism.Wireless-backhaul innovation is supported by startup activity, competition, and potential mmWave small-cell backhauling.
  • V. CONCLUSIONS: The paper concludes that 5G’s demanding requirements are accelerating creative research and technology development, while disruptive networks remain a long-term undertaking.mmWave cellular systems have shifted from seeming almost fantastical to being viewed as nearly inevitable.
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