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TECHNOLOGY

High expectations for 5G confront practical realities

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The next wave of mobile network innovation is provoking great excitement in the industry. And indeed, there is substantial potential for improvement.

However, the exact form of the technology and the appropriate policy support are still far from clear. And we should beware of over-ambitious promises about the impact and uptake of new network technologies.

The next generation of mobile technology, 5G, is being developed along markedly different lines from previous generations. In the past, mobile generations were generally characterised by a core technology (or sometimes by two or more core technologies), and were designed to fulfil the requirements of a fairly small number of mobile voice and data applications. By contrast, 5G is being developed to fulfil the needs of multiple use cases.

Most definitions of 5G assume that it will provide some combination of (1) high speed, (2) low latency, (3) the ability to use high frequencies well above 6 GHz, and (4) the ability to support huge numbers of users (some of which will be machines rather than human users) and applications. Some applications require high bandwidth and low latency; many machine-to-machine applications, by contrast, require only modest bandwidth, but imply the need to support huge numbers of devices.

The technical means of implementing this wide range of capabilities is still very much a work in progress.

Functional requirements for 5G are interlinked, but there is a degree of tension between them. To provide higher speeds, bandwidth is needed that is simply not available in the heavily used sub-6 GHz bands; however, the use of higher frequencies implies faster attenuation of the signal, and thus limitations in the distance that can be covered by a base station. (The use of directional antennas might possibly help to overcome this.)

This in turn implies a need for more cells, and thus greater cost. One study found that the cost (CAPEX) of coverage at 3500 MHz using presently available technologies (not 5G) was roughly 6.7 times as great as the cost of coverage at 700 MHz (see Figure 1).

Whether this is a problem depends on the use cases that the network operator is seeking to fulfil. Not every use case or business model requires nationwide coverage.

Indeed, if we are seeking capacity rather than coverage, the rapid attenuation at high frequencies can be a positive rather than a negative factor. It enables greater re-use of the same radio spectrum in the same frequency bands within a given geographic area. For areas where bandwidth demands are high (for instance, dense urban areas), a dense deployment of 5G small cells might be entirely appropriate.

Figure 1. Frequency, cell radius in Km, and the impact on cost (CAPEX).

Source: Simon Forge, Robert Horvitz and Colin Blackman (2014): Is Commercial Cellular Suitable for Mission Critical Broadband?

Figure 1

Not so long ago, many experts assumed that all 5G deployments would entail ultra-fast services at high frequencies – a view that ignores fundamental underlying economic realities. It would however be equally wrong-headed to assume that all deployments will take place in the desirable frequencies below 1 GHz.

The real opportunity that 5G offers is the ability to customise deployments to meet requirements. A deployment that needs extensive coverage might use a mix of widely dispersed sub-1 GHz deployments for rural areas, together with high density deployments of small cells at higher frequencies for dense urban areas. This kind of mixed or hybrid approach might be much more common under 5G than under current technologies.

Source: RSPG (2016), Strategic Roadmap towards 5G for Europe.

The roadmap of the Radio Spectrum Policy Group (RSPG) needs to be understood in this light. Their key recommendations are:

(1) that the 3400-3800 MHz band should be the primary band for the introduction of 5G use in Europe before 2020;

(2) that 5G will also need existing mobile bands, including the 700 MHz band, in order to enable nationwide and indoor 5G coverage;

(3) that additional bands are required above 6 GHz.

Some argue that Network Virtual Functionalisation (NFV), implemented using Software Defined Networking (SDN) and OpenFlow protocols, might be the key to providing the required dynamic configurability.

It is also possible that 5G will co-exist for an extended period of time with earlier technologies (LTE, 2G, and perhaps to a lesser extent 3G), not only to support legacy equipment, but also due to gaps in 5G capabilities. This would be analogous to the situation with LTE, where voice services are most often provided today using Circuit Switched Fall-Back (CSFB) (i.e. to 2G/3G) rather than using Voice over LTE (VoLTE).

Every previous mobile generation has offered the promise of being better, faster, and cheaper. In the early design phase, all things are possible. Sooner or later, however, hard rules of physics, of engineering, and of economics must be confronted. Even so, every generation has indeed been better, faster, and cheaper than the previous generation, but not to the degree that was initially hoped for.

In this sense, 5G is not altogether different from prior generations; however, the gap between hope and reality is even greater than usual, especially in the policy domain. Every possible policy measure is claimed to be necessary to the success of 5G (and we sometimes see this claimed for opposite policy positions). Since nobody can say with certainty today what 5G will be, nobody can refute these claims.

Successive generations of technology have purported to provide a single view of all networks, and to enable all network services to compete with all other network services. Claims along these lines have been advanced for ISDN, for Open Systems Interconnection (OSI) protocols, for ATM, and for the NGN IMS. Alas, none of these have brought us to the promised network nirvana.

There are lessons that we can take from this history:

  • The initial degree of corporate or government support for a technology or standard does not uniquely determine the degree to which it will ultimately be accepted by the marketplace. IP protocols initially had scant corporate or government support, while OSI protocols enjoyed seemingly universal acclaim … but who won? Few readers today will even remember what OSI protocols were.
  • What a technology is capable of does not uniquely determine how it will be used. The electronic communication value chain is comprised of many mutually competing firms … and that is a good thing! The actual deployments will be determined by business needs – technology is an enabler, but it alone is not dispositive.
  • Dystopian forecasts likewise need to be taken with a grain of salt. Claims that it might not be possible to support more than one 5G deployment in a European Member State assume that a huge number of cells would be required. With a hybrid design, however, this might not be the case, especially when one takes into account the possibility to share base station locations, antennas, and perhaps back-haul facilities among competitors.

There are many factors that could delay or impede 5G deployment, even if business and technical circumstances are otherwise favourable, such as:

  • Possible inability of the technology to converge to a single, interoperable standard.
  • Delays in assignment or re-farming of the required spectrum resources (for instance in the 700 MHz or 3400-3800 MHz bands.
  • Challenges in deploying base stations and in obtaining fibre-based backhaul to them, especially where large numbers are needed in dense areas. This may be less of an issue for deployments in the 700 MHz, where existing locations designed with 800 MHz in mind are widespread. This risk is compounded by delays in transposition and implementation of the Cost Reduction Directive, where infringement actions are pending against most of the Member States.

Claims regarding 5G today are surely over-blown; nonetheless, we should expect significant benefits.

-J. SCOTT MARCUS

Bruegel.org

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