Gain early access to 5G capabilities
The emerging demands on 5G are far more comprehensive than previous generations. As a result, the 5G solution is likely to require a mixture of technologies. The key to 5G will be less a matter of creating a new cellular protocol than the culmination of a process of technological integration that will see the alignment of protocols developed for the telecommunication and local-area networking (LAN) environments, making it possible to take advantage of technologies already available. These can provide key elements of the 5G feature set particularly for situations where the upgrades to cellular communications are most needed: in the high-density, urban environment.
Bandwidth challenges are at their most extreme in the urban environment where the bulk of users will expect to be able to transfer data at high speed. Telecommunications companies are budgeting for downlink speeds on the order of hundreds of megabits, even gigabits per second for urban users.
One of the options being explored for urban communications is to make use of the millimetre-wave (mm-wave) RF spectrum between 10 GHz and 100 GHz. This area of spectrum is not only under-utilised but offers key advantages for high-density, high-speed digital communications. Spectrum in this region offers opportunities for channels with much higher bandwidths than are available in the sub-5 GHz region employed for 2G, 3G and 4G. Bandwidth of up to 9 GHz has already been allocated for the 60 GHz range for use by the WiGig wireless LAN standard.
Frequencies in the mm-wave region have shorter range than those used for cellular. Oxygen and water absorption are stronger, which restricts their use for longer-distance communications. The signals are also more directional in nature.
In the high-density urban environment, absorption not only becomes far less of an issue, the combination of absorption and the directivity of the signals become key advantages. In the urban environment, even macrocells may be deployed with spacing as low as half a kilometre. Microcells and increasingly important picocells use tighter geographical spacing – from 200m down to as little as 10m – that is highly compatible with mm-wave signals. The increased atmospheric absorption helps reduce the overlap between individual cells.
As basestations can be deployed close to each other, this maximises the use of backhaul links to the internet to allow for the high capacities envisaged for 5G-enabled applications such as high-definition video and gaming on the move.
An apparent requirement for line-of-sight communications is also less onerous that it at first appears. Research has shown that sufficient levels of reflection from hard surfaces, such as the walls of buildings, can greatly extend the number of situations in which outdoor mm-wave equipment can be used to transfer high-bandwidth data.
Multiple-input, multiple-output (MIMO) antenna arrays provide additional means to exploit the directivity of mm-wave signals. With ten or more antennas on a mobile device – massive MIMO – it is possible to exploit multipath reflections with beamforming techniques to increase the effective data rate between the mobile and the base station. A further key advantage of using massive MIMO is that it can provide impressive gains in energy efficiency compared to a single-antenna structure.
As antenna size is inversely proportional to frequency, mm-wave signals operating at 60 GHz (5 mm wavelength) or above can take advantage of more antenna elements per unit area than those working at lower frequencies, such as the 28 GHz and 38 GHz-centred bands that have been investigated for early 5G systems. This can more than compensate for the losses through absorption as frequency increases, particularly when energy efficiency is taken into account.
Operation at frequencies above 60 GHz is also being explored in research labs. But their use in any practical 5G system remains some way into the future. Even if those frequencies are found to offer acceptable performance, there are still significant frequency harmonization, standardization, and regulatory obstacles to be overcome. 5G cellular technologies able to exploit mm-wave technologies are unlikely to be available commercially before 2020 at the very earliest.
Such obstacles have already been overcome by the WiGig standard based around the internationally licensed exempt 60 GHz band. Numerous semiconductor and product vendors are working on solutions for WiGig, primarily for indoor use as a way of greatly boosting the transmit speeds of WiFi networks – in effect providing the capability of Gigabit Ethernet without the inconvenience of cabling. Pre-certified WiGig products are available today and mass market deployment is expected to ramp from 2016.
WiGig also has a number of features that suit it to use not just as a pre-5G technology for high-speed communications in the urban environment but for long-term use within the 5G framework. WiGig is a low-latency protocol, with round-trip delays through the media-access channel of hundreds of microseconds – far below the 1ms latency demanded of 5G. Through its alignment with the existing WiFi standards, WiGig can easily be incorporated into the framework being developed for 5G.
The vision for 5G is to use heterogeneous networking (het-net), combining cellular and wireless LAN protocols, to maximise effective bandwidth and switching between these systems based on channel availability at the local level. The het-net approach is so important to the evolution of 5G that support for it is already being built into upgrades for the existing 4G infrastructure. These upgrades allow for seamless switching between the LTE channels used for 4G and WiFi. Adding the mm-wave capabilities of WiGig to this infrastructure allows for a massive upgrade to short-range datarates, both indoor and outdoor, long before the standards for 5G are complete. But long-term integration with the 5G standard set is all but inevitable.
As WiGig and 60 GHz communication R&D is already well advanced – and Blu Wireless has been central to much of this advancement – it makes sense for manufacturers with an eye on the evolution of 5G to fully embrace WiGig. Any mm-wave frequencies selected for 5G cellular will be used in combination with 60 GHz, providing even higher aggregate bandwidths for users. But, by working on 60 GHz and WiGig equipment vendors can take advantage of a head start on 5G and be confident that the work will still fill into the final 5G landscape.
Blu Wireless designs and licenses silicon IP for 60 GHz and other mm wave applications.
The author, Mark Barrett is the CMO at Blu Wireless Technology.
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