What Will 5G Be?

Abstract: 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.

• The paper presents a comprehensive analysis of 5G, outlining ambitious targets like a 1000-fold data rate increase and 1 ms latency to meet future demands.
• It employs detailed evaluations of extreme densification, mmWave propagation, and massive MIMO to tackle connectivity and capacity challenges.
• The study highlights the integration of LTE and WiFi, novel waveform designs, and innovative spectrum policies as crucial for successful 5G deployment.

Overview of "What Will 5G Be?"

The paper "What Will 5G Be?" by Jeffrey G. Andrews et al. provides a comprehensive analysis of the anticipated evolution of cellular technology from 4G to 5G. The authors argue that unlike the incremental advancements seen between previous generations, 5G will represent a substantial paradigm shift in several dimensions: carrier frequencies, bandwidth, device density, and antenna configurations. Crucially, 5G is projected to integrate LTE and WiFi more seamlessly, striving for universal high-rate coverage and a better user experience.

Engineering Requirements for 5G

5G technology must meet several stringent requirements to address future demands:

1. Data Rate: A 1000-fold increase in aggregate data rate (bits/sec/area) is anticipated, with aims for edge and peak rates to reach as high as 100 Mbps and tens of Gbps, respectively.
2. Latency: The target roundtrip latency is 1 ms, markedly lower than the current 15 ms in 4G systems, to support emerging applications like two-way gaming and virtual reality.
3. Energy and Cost Efficiency: It is necessary to achieve a 100-fold improvement in energy efficiency and cost per bit to handle the enhanced data rates without a proportional increase in power consumption or costs.
4. Device Support: Support for a massively increased number of devices, particularly due to the rise of machine-to-machine communication, will be essential.

Key Technologies and Research Focus

The paper identifies three core technologies—ultra-densification, millimeter wave (mmWave), and massive MIMO—as pivotal to meeting the data rate requirements for 5G.

Extreme Densification and Offloading

To increase network capacity, cells will shrink in size, resulting in "extreme densification." This approach has proved effective across several technological generations by improving area spectral efficiency due to better spatial reuse of spectrum. Important challenges include:

• Load Balancing: Ensuring that gains from densification are preserved as each BS becomes more lightly loaded.
• Multi-RAT Integration: Managing associations between users and BSs, especially given the increasing integration across multiple radio access technologies.
• Mobility Management: Addressing challenges in maintaining seamless connectivity amidst diverse and dense network architectures.
• Cost Considerations: Tackling the logistical and financial barriers of deploying numerous small cells.

Millimeter Wave

Utilizing high-frequency mmWave bands is posited as a solution to spectrum scarcity in lower bands. Key considerations include:

• Pathloss and Blocking: Strategies to mitigate increased pathloss and susceptibility to blockages characteristic of mmWave propagation.
• Large Arrays and Narrow Beams: Exploiting large antenna arrays to form narrow beams, which can significantly influence the design and performance of cellular systems.
• Semiconductor Technology: Addressing the challenges associated with power consumption and beam alignment in mmWave bands.

Massive MIMO

Massive MIMO, involving a large number of antennas at the BS, offers the potential for substantial gains in spectral efficiency and power savings:

• Pilot Contamination: Overcoming interference among pilots reused across cells to ensure accurate channel estimation.
• Architectural Challenges: Designing scalable and cost-effective antenna configurations to realize the vision of massive MIMO.
• Channel Models: Developing accurate models to capture the intricate behavior of channels in massive MIMO systems.

Design Issues for 5G

In addition to enhancing data rates, 5G must lower latencies and energy consumption and improve cost efficiency.

Waveform Design

OFDM and OFDMA are the default waveform choices due to their robustness and computational efficiency. However, alternative waveforms such as time-frequency packing, nonorthogonal signals, and generalized frequency division multiplexing (GFDM) are being investigated to address PAPR and other limitations.

Spectrum Policy and Standardization

5G necessitates new approaches to spectrum regulation. The paper discusses the advantages and drawbacks of exclusive licenses, open access, spectrum sharing, and market-based dynamic allocation. The ITU and other organizations are gradually aligning on spectrum policy to accommodate future 5G networks.

Economic Considerations

The financial challenges of transitioning to 5G are significant. Solutions include infrastructure sharing, use of small cells by mobile virtual network operators, and innovative backhaul strategies. Efficient backhaul is crucial for realizing the gains promised by 5G technologies.

Conclusion

The paper accentuates the multi-faceted challenges and opportunities in the journey towards 5G. It posits that the combined advances in network densification, mmWave technology, and massive MIMO, along with innovations in waveform design, spectrum policy, and economic models, will be critical in shaping the future of wireless communication. The collaborative efforts in research and standardization will pave the way for the realization of the ambitious goals set forth for 5G.