At Fieldfisher's recent telecoms update conference, I spoke of what I believe to be the key necessities for the next generation mobile network, and described the 'seven pillars' for 5G development (maximising data rates; minimising latency; speed of mobility; seamless transition between technologies and at cell boundaries; spectral efficiency; maximising simultaneous connections; and lowering cost and energy consumption per unit of data). The network of the future is expected to be all about quality of experience for the user, driven by the media consumption habits of users, and shaped by the appearance of new technologies. This article describes some of the challenges faced by network operators and regulators, and explores some of the possible solutions.
Many of you, like me, will only just be getting used to the convenience and ease in connecting to the internet that the 4G network provides. Despite the occasional 'not-spot', I've really been impressed by the blindingly fast connection speeds (when compared to 3G networks). It therefore may seem a little strange to be writing about the network of the future but, even as we adapt to the technology now appearing in stores, a contender for the ‘next big thing’ for our connected society appears on the horizon - commonly (and perhaps not unsurprisingly) referred to as ‘5G’.
Although we have only recently seen the full-scale rollout of 4G in the UK, there are a number of technologies that demand (or will soon demand) functionality that existing and planned 4G infrastructures will be unable to meet. 5G does not describe a particular technology, nor does it yet comprise particular standards - it is therefore something of a moving target. What we can say, is that it seems likely to be heavily application driven; defined by the demands of future technologies set against the limitations of the current wireless infrastructure to meet those demands.
Networks are becoming more user-centric
To my mind, it will be the media consumption habits of users that drive the development of the network of the future, and the appearance of new technologies that will shape it. Researchers at the 5G Innovation Centre set up at the University of Surrey suggest that, whereas previous networks were operator-oriented, the next network will be fully focused on users and their needs. For many of us the 4G network meets current needs in terms of high speed and low latency, which seem to be the current focus of the consumer market. New applications are being developed all the time however, and are expected to dictate the requirements of any new network specification.
Darko Ratkaj of the European Broadcasting Union recently spoke about media services in the context of 5G, considering in particular how broadcasters may use the new network. He highlighted that whilst linear radio and television are still the core proposition for most broadcasters, there are now a multitude of options which are not bound by channel schedules and channel concepts, available in high quality formats supported by digital technologies. Audio-visual media is currently delivered to audiences via various broadcast networks such as digital terrestrial television (DTT), satellite, and cable; and also via broadband (internet protocol) through both fixed networks and existing mobile infrastructure. Mr Ratkaj suggests that that there will be no single network to rule them all, as none of these delivery methods will be accessible to all users at all times. 5G will therefore need to work alongside the other delivery methods to effectively serve all possible audiences. Even so, a four-fold increase in mobile data traffic in the five years to 2018 was predicted in a recent report to Ofcom due to an expectation of considerable medium term growth in video and television consumption.
I see the network of the future being about quality of experience for the user. To meet the demands of new applications and technologies, the network of the future will need to provide for incredible bit rates and low latency across a wide geographical area. It will need to ensure great service in crowds by providing large bandwidth in regions of high-demand, as well as ensuring that the best experience follows the user as they move. As bandwidth-hungry applications such as ultra-high-definition video and virtual reality are set to rise, the ability to transition these high data-rate/low-latency data streams seamlessly between transmitters as users move will be key to positive user experiences.
The new network must be smart, reliable, robust, and context aware. It will need to be smart, in that it must dynamically alter its behaviour to deliver a level of service suitable to each individual user’s requirements. Data components of transmissions have become more and more important over the last few years overtaking the voice elements in mobile telecommunications, and will change further to become more machine-centric as the ‘Internet of Things’ develops. The Internet of Things envisages a wide variety and massive number of wireless-enabled devices communicating both with us, and with each other. These will have an equally wide variety of different networking requirements. For example:
- an embedded sensor periodically reporting on the status of critical infrastructure will need access to a reliable, robust and resilient network, but perhaps only with very low bandwidth requirements;
- mobile control will likely require sub-millisecond latencies;
- vehicle-to-vehicle applications will need seamless movement; so data rates at cell boundaries must be sufficient together with fast and effective transitioning between cells (figures of under 10 milliseconds have been suggested for switching between radio access technologies); and
- ultra high definition (UHD) video services will require high bitrates and low latency, but not necessarily all the time.
Context-aware networking will be essential to enable the efficient servicing of the huge range of networked devices expected to be introduced over the coming years. There will eventually be a staggering number of devices accessing the network – tens and even hundreds of billions – and it must therefore be flexible to cope with varying demand. As the quantity of data increases the network must become both more energy efficient and more cost efficient. If there is a thousand-fold increase in the amount of data transmitted, then there must also be a thousand-fold reduction in energy use and cost per bit to keep it both sustainable and affordable.
Overcoming the hurdles of user centricity
Widening use cases for mobile connectivity leaves us with a number of technical hurdles that will need to be addressed before devices and networks can meet a 5G standard suitable to the needs of the user. In particular, networks must have the capability to support massive capacity and connectivity, for a diverse set of users and applications, using non-contiguous spectrum flexibly for different deployment scenarios. The technical challenges can broadly be condensed down into seven pillars which can broadly be described as:
- achieving the maximum data rates possible to give the sensation of unlimited speeds;
- minimising latency so that information is available as soon as it is required;
- speed of mobility, so that the network works effectively whilst the user is travelling;
- good data rates at cell boundaries and seamless transition between cells, to give a ubiquitous network;
- spectral efficiency, to maximise the potential of the airwaves;
- maximising the possible number of simultaneous connections, to ensure great service in crowds; and
- lowering the cost and energy requirement per unit of data, to keep it affordable and sustainable even with a thousand-fold increase in consumption.
A number of approaches have already been proposed that have the potential to assist in overcoming the technical challenges, and I have outlined a few below.
One possible solution to bandwidth challenges might be ‘Massive MIMO’ and 'Miniaturised MIMO'. Multiple-antenna technology is becoming mature for wireless communications and has already been incorporated into wireless broadband standards such as LTE and Wi-Fi. Multiple Input Multiple Output (MIMO) uses several antennae because the more a transceiver has, the greater the possible signal paths. This gives better performance in terms of data rate and link reliability. Massive MIMO would use hundreds or thousands of antennae, bringing huge improvements in throughput, energy efficiency, and resistance to interference. The downside of this will be the increased complexity of the hardware, and the complexity and energy consumption of signal processing. Other challenges that will need to be overcome include making high numbers of low-cost low-precision components work effectively together, resource allocation, reducing internal power consumption, and finding new deployment scenarios. Miniaturised MIMO would involve the miniaturisation of current MIMO technology allowing MIMO transceivers to be used in greater numbers.
Terminal-side development will also be required so that data processing components in mobile handsets and connected devices can quickly and efficiently handle the flow of data without draining the power supply. Battery technology will also need to evolve.
The use of advanced waveforms for carrier signals, and innovative encoding and modulation methods, could assist in making systems more spectrally efficient. In modern wireless networks upload and download channels tend to be given different spectrum allocations so that there is no interference between the channels. If the same allocation of spectrum could be used for both upload and download, then spectrum capacity could theoretically be doubled. Self-interference remains a big hurdle to overcome before this technology can be implemented however, although both analogue and digital techniques have been used to reduce interference. The potential gains if these techniques were to be further developed are certainly of interest, and this interest might drive more funds into the development of this technology.
Predicted bottlenecks in capacity (number of users) and bandwidth (data volume per user) could be addressed by using other parts of the electromagnetic spectrum for broadcast. Today, mobile networks predominantly use spectrum in the sub-3GHz band. In the future, 5G could use spectrum in the 10-30 GHz and 30-300 GHz ranges where there are large chunks of continuous spectrum available for use. Whilst these high frequencies are attenuated to a greater extent as they travel through air and obstacles (and therefore have a shorter range), they may be more suitable for urban environments with a high density of wireless devices where range is not an issue. Higher frequency transmissions may also be used to complement lower frequencies when in sufficient proximity to other networks, with lower frequencies being used to provide the core service. If the network can structured as a 'smart network', that is able to self-organise within these various spectrum blocks based on current and anticipated demand, then the available bandwidth can be used more efficiently.
The European Commission would like to see 1.2GHz of bandwidth to be allocated to 5G – which would include both licensed spectrum and shared spectrum. In particular, it intends to recycle the 700MHz band which is currently used in the mobile industry and for digital terrestrial television broadcasting, and this process is already beginning in the United Kingdom. Also proposed are:
- spectrum sharing in the 2.3GHz band, facilitated by an appropriate legal framework;
- harmonisation within the 3.4GHz band, and the European Commission intends this to be discussed at future World Radio Conferences; and
- the use of higher frequency regions of the spectrum, and in particular the 60-80GHz band, which could be a serious candidate for some close proximity applications.
Another development, which might assist in building a ubiquitous network, is the implementation of a virtualised radio access network. Legacy and current infrastructures provide coverage and capacity using a fixed allocation of resources. This means that systematic over-provisioning would be needed in order to meet peak demand at any given time and location using the same method of resource allocation. Radio access network virtualization, configurable by software, would provide a method of sharing the physical radio infrastructure in the same way as physical storage and processing hardware are currently shared in cloud computing. This would allow the simultaneous use of several different networks and easy handover between them. Through the use of virtualisation, the existing wireless networks (such as GSM, HSPA, LTE, and Wi-Fi) could all be integrated into the new 5G standard, meaning that existing network coverage could be leveraged.
After around eighteen months of discussion within the 5G Public-Private Partnership (the association set up at the end of 2013 between the European Commission and representatives from industry and research), Europe set out its vision for the new network at the Mobile World Congress 2015. In particular, it set out a number of key drivers and principles for 5G as follows - 5G will:
- "provide an order of magnitude improvement in performance in the areas of more capacity, lower latency, more mobility, more accuracy of terminal location, increased reliability and availability";
- "ensure user experience continuity in challenging situations such as high mobility (e.g. in trains), very dense or sparsely populated areas, and journeys covered by heterogeneous technologies" (e.g., by effective switching between different radio access technologies and at cell boundaries);
- "be a key enabler for the Internet of Things by providing a platform to connect a massive number of sensors, rendering devices and actuators with stringent energy and transmission constraints"; and
- support "mission critical services requiring very high reliability, global coverage and/or very low latency";
- have enhanced spectral efficiency to "enable 5G systems to consume a fraction of the energy that a 4G mobile networks consumes today for delivering the same amount of transmitted data", and "will allow costs to be dramatically reduced".
This is a useful statement of intent for 5G, and reinforces and restates our existing understanding of the requirements.
What I have seen and heard so far has indicated the growing importance of the user and use cases as the determining factors shaping expectations for the 5G network. The key however, is likely to be the extent to which infrastructure and handset technology can develop, within the necessary timescale, to allow the network to grow to fulfil those expectations. For that, we will have to wait and see.
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