Uplink decoupling and Chinese allocations drive momentum into C-band

The industry’s eyes are firmly on the C-band spectrum between 3.4 GHz and 4.2 GHz as an early source of new spectrum for 5G. 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 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 readily available – often assigned, but underused, for fixed wireless services, which means that, regulator willing, it could be extended to mobile services and reallocated without expensive auctions.

The C-band is the most common band identified by national regulators for 5G, which may present a fait accompli to WRC-19. China has been spearheading this, and some European regulators are planning assignments or sales – the UK’s has been postponed because of legal wrangling between BT and Three, but France’s Arcep is planning to sell part of the 3.4 GHz band next year.

New technologies are making the C-band more useful and efficient for 5G. In a new report, ABI Research points to one of those, Uplink Decoupling, saying:  “C-band, with the support of new technologies, including Uplink Decoupling, will likely be the dominant 5G spectrum band, since it allows operators to deploy 5G on an existing network grid, rather than spend significantly on new cell sites.”

Uplink Decoupling, which allows downlink and uplink to run on separate bands, was demonstrated by two European operators in recent weeks, both working with Huawei. This makes higher band 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.

Called Uplink Sharing by 3GPP, the 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.

Huawei and EE 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.

Meanwhile, Vodafone Italy conducted a similar demo on a pre-standard 5G test network in Milan, using an unspecified “high frequency band” for downlink and a low frequency band for uplink.

Compared to using the same band for both, the MNO said uplink coverage increased by 10 times by combining the high capacity of high frequency spectrum and the strong propagation of low bands.

Francisco Martin, head of radio product for Vodafone Group, said: “This test of pre-standard 5G uplink and downlink decoupling will help us to deploy the technology efficiently to support our customers as soon as we launch services.”

Yang Chaobin, president of Huawei’s 5G product line, said: “In the 5G era, the available bands for operators will increase, and the coverage of higher bands such as C-band will become a major barrier to deployment. To solve this problem, networks need to make use of multiband coordination to eliminate higher band coverage bottleneck and improve user experience.”

Uplink Decoupling will be used in combination with other techniques – such as Massive MIMO, and full duplex – to boost the performance of future networks and overcome the limitations of some spectrum bands, as the availability of midband spectrum, which offers a fine balance of coverage and capacity, dries up.

Driving further momentum into the C-band, China’s Ministry of Industry and Information Technology (MIIT) has officially reserved the 3.3-3.6 GHz and 4.8-5 GHz bands for 5G services, and is likely to add 3.6-4.2 GHz, according to Jefferies analysts, who also believe MIIT is getting ready to allocate 700 MHz and some mmWave airwaves. The MIIT previously issued a request for opinions about high frequency spectrum.

The Jefferies analysts are particularly interested in China Unicom’s recent reorganization, which led to several industrial and webscale partners taking stakes in the operator – implicitly to secure influence over how its 5G network is developed to support industrial and IoT services optimally.

Analysts Edison Lee and Timothy Chau wrote in a client note: “We continue to believe that the most sensible, and the most likely, solution is for SAPPRFT [the broadcast agency] to take a stake in Unicom and in return allow Unicom to use the 700 MHz spectrum.” Or the MIIT might make available spectrum at 1 GHz or 2.5 GHz to Unicom for 5G services.

“Assuming Unicom will obtain allocation at 2.5 GHz, and China Mobile will be given 4.8 GHz-5.0 GHz for 5G services, the much lower frequencies for Unicom will still give it a significant cost advantage to allow it to achieve a healthy ROIC at a much smaller scale (e.g.20%-25% market share),” they wrote. “We expect the government will continue to offer asymmetric regulations to boost the competitive position of Unicom in 5G.”