The landscape, however, is much different in the high-frequency bands, usually known as the millimeter wave (mmW). The channels are much wider, reaching even 250MHz and multiples thereof in some bands (such as E-band), providing the needed capacity for 5G access and backhauling. In general, the mmW can request a wide availability of spectrum, which is a prerequisite for both access and backhaul. More antennas can be used (ranging from 4, 16 or even 32), resulting into beamforming that as it advances to shorter wavelengths allows for smaller antennas (including arrays needed for beamforming and beamsteering). Antenna directivity is much better in high frequencies, allowing a high spectral reuse factor. High-frequency radios can widely be used today and demand will continue to grow, especially for E-Band (80GHz) in dense areas where high capacity is needed. ACG anticipates that the momentum for E-Band will continue and will be preferred for new 5G (by 2020 or earlier) deployments technologies. (One in five links could be E-band in 2020.)
Regulation is the main enabler for high-frequency solutions adoption because by applying different licensing models it could encourage better use of spectrum, weighing in factors such as frequency bands, geographic region, and local microwave hop density. Ericsson recently described the multiband booster method, which could maximize spectrum efficiency, add new technologies that can exploit unused spectrum, and upgrade the capacity of microwave backhaul networks up to tenfold. This is a great option that has been used for years from other leading vendors as well but in most cases is still restricted by regulation.
Introducing and allowing wider channels in less deployed areas would further encourage the use of multiband solutions. Leo Macciotta, Huawei’s Senior Marketing Manager, highlights that “the challenges in capacity and latency requirements posed by LTE-A and in the future 5G make this kind of equipment the best and most cost-efficient choice for a future-proof deployment. Continuous investments in component, system and antenna technology provide a clear and dependable road map of improvement in performance such that we are confident that E-band will become one of the key building blocks of the future front- and back-haul networks for 5G and beyond.”
For access, most vendors could offer high modulation, wider channels, and multiple antennas (MIMO). The capacity offer varies between 2 and 4 Gbps full duplex, although some vendors are testing solutions in the lab that could go up to 10 Gbps in a range of a few kilometers. The MIMO types used today in most cases are 2x2 and 4x4 but could increase much higher along the 5G spec. This is not the case for backhaul; although the MIMO feature is offered, there is no real demand yet, but that might change beyond 2020.
E-band has recently come into mainstream use for mobile backhaul, allowing capacities of up to 10 Gbps over link lengths up to several km (even more than 10 km when bundled with lower frequency bearers) and is currently shipping in volume. Regarding backhauling, Yigal Leiba, co-founder and CTO of Siklu, mentioned that “a capacity of 2 Gbps could be enough today and possibly for the next 2 years for Mobile Operators and specifically for network aggregation layers and major Macro Base Stations backhauling, while 1Gbps street level backhaul could serve effectively Small Cells.” Looking to the future, the industry shares a vision of using frequencies above 100 GHz, as they will enable capacities in the 40 Gbps range over hop distances of about a kilometer but mostly for access. Regarding 5G and backhaul, there is already pressure, and leading vendors and major Tier 1 operators are worried that backhaul requirements may not be kept in the right considerations.
Tying the whole industry ecosystem together is the ETSI mWT (Millimetre Wave Transport) ISG, a common forum for component, subsystem and system manufacturers, telecommunications operators, and regulator. The forum promotes understanding and acceptance of mmW worldwide. With endorsements from such respected groups the future of these technologies looks promising.
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