In the past, spectrum around 3.5 GHz has been typically allocated for fixed wireless broadband applications, as well as satellite. It has been unwanted by most large mobile operators and so has often been sold for low prices. All that has now changed. Of course, the official global bands for 5G will not be assigned until the World Radio Conference in 2019, but in the meantime, consensus is building in many regions around a few ‘pioneer bands’.
Although a lot of hype surrounds those in the high frequency millimeter wave (mmWave) ranges, there are issues of design complexity, short range and cost, and the need to grapple with emerging technologies like Massive MIMO.
Those will be solved over time, but for the foreseeable future, the most immediately valuable spectrum is the C-band, despite conflicts with satellite incumbents in some parts of the band and some regions. In many areas, there is significant 3.5 GHz capacity available. China’s support for early deployment in the band will be significant in driving an early equipment and device ecosystem – essential for the economics of early roll-out.
So the UK’s auction is timely, adding 150 MHz of spectrum in this range to the potential 5G capability, to add to existing 3.5 GHz licences held by Three UK (courtesy of its acquisition of UK Broadband). The new spectrum is technology neutral, and UK Broadband had already deployed TD-LTE – but had also discussed 5G roadmaps and use cases. Back in 2015, for instance, it shared its views on 5G readiness for a report by the Spectrum Policy Forum, led by Real Wireless.
Then, it said that UKB had “a roadmap to expand LTE and introduce new ‘5G’ technologies. It aims to more than double its capacity by 2020 using next generation 3GPP advances such as massive MIMO, massive carrier aggregation, 80 MHz channels and LTE in 5 GHz.”
This is one example of how the ecosystem to enable advanced 5G usage in C-band spectrum has been building up, in the UK and elsewhere, for several years now. So once the new airwaves are acquired and made available, the winning operators will have a strong opportunity to deploy 5G quickly, and with sufficient capacity to support new quality of service for existing and new use cases.
The band is well suited to densification, because it has high capacity but limited range. The same is even more true of higher frequency, mmWave bands (Ofcom has identified 26 GHz as a 5G ‘pioneer band’), but these are less well understood for cellular technologies, and will present greater technical challenges to deploy cost-effectively. Their very short range means that they will require a new grid of sites, while 3.5 GHz 5G could reuse many of the operators’ current sites, for initial roll-outs at least, before MNOs move on to more extreme levels of density, based on new infrastructure such as street lights.
New technologies are making the C-band progressively more useful and efficient for 5G. One example is Uplink Decoupling (called Uplink Sharing by 3GPP), which allows downlink and uplink to run on separate bands, making midband spectrum more usable and efficient. While downlink coverage can be enhanced with techniques like Massive MIMO, uplink is constrained by the transmission capabilities and low power of end user devices. With decoupling, downlink and uplink do not have to be associated with the same base station, and uplink can take place in lower bands, using less power to achieve a long distance.
This technique enables MNOs to extend their coverage when deploying 5G in higher bands such as the C-band or even mmWave, which have limited range and so can add significant cost to achieving wide area coverage. It will be standardized in 3GPP Release 15, the first set of 5G specifications, and will appear in the second phase of those specs, due in April 2018.
Huawei and EE recently conducted a trial in London at the ExCel conference center, using the C-band for downlink and the 1.8 GHz band for uplink on a pre-standard 5G test network. Vodafone has conducted a similar test in its 5G test network in Milan and said uplink coverage was increased 10-fold.