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5 August 2019

In its quest for optimal 5G spectrum, AT&T is testing in the 4.4-5 GHz band

The US operators, and the FCC, have made a virtue out of necessity by taking some creative approaches to address their shortage of optimal 5G spectrum. While the 3.5 GHz C-band is the primary new spectrum band in which most first-phase 5G networks are being rolled out, in the USA, this is occupied by federal and other incumbents.

With the US operators lacking access to significant amounts of spectrum in this band, they will be denied the economies of scale of a global ecosystem, and AT&T and Verizon will be at a disadvantage to Sprint (and T-Mobile, assuming they merge), which has midband spectrum in 2.5 GHz. This is driving interest in alternative options, preferably in the midband, and possibly including the 4.4-5 GHz frequencies. These are the upper portion of the C-Band in the USA (the lower range is what most regions are using in 5G, with various subsets of the frequencies from 3.4 GHz to 4.2 GHz).

The fact that 3.5 GHz is not open in the USA has led various innovations already, but each comes with compromises in terms of the operators’ 5G business cases. The regulator has created the innovative, if politically fraught, three-tiered access system for the CBRS portion of the C-Band (3550-3700 MHz); but while that sets important precedents for spectrum sharing and opens up more unlicensed capacity for cellular, that shared section will not be addressable with 5G until standards for 5G-Unlicensed are agreed next year.

The licensed portion of the band will give operators some midband spectrum which could be used for 5G, but will be allocated in small chunks for relatively short terms (three years), which means other players such as private operators may gain some of the licences, and there will be limited capacity.

The situation in the C-Band has led to the MNOs moving up or down the spectrum so that they do not have to delay their first 5G build-outs because of a spectrum shortage. Verizon, AT&T and T-Mobile all have deployments in millimeter wave bands and TMO is also building out in 600 MHz.

But the fact remains that the midband spectrum is optimal for the first stage of 5G, when most operators are looking to add targeted capacity while keeping the LTE network for coverage (and holding on to the LTE core). Using mmWave spectrum for this purpose delivers the capacity but is far more challenging in terms of engineering, propagation and device ecosystem, and if these bands have to be used at scale, rather than for highly targeted hotzones, the costs will be extortionate.

Only Sprint has the advantage of large amounts of midband spectrum – not in 3.5 GHz, but over 120 MHz in the 2.5 GHz band, which it uses for TD-LTE. It scored a major victory when this band was approved as an official ITU/3GPP 5G band too, which means it can deploy 5G in unused portions of its spectrum, and over time, refarm the portions which currently support LTE too.

Assuming the merger with T-Mobile is approved, the combined company will have a huge spectrum advantage over Verizon and AT&T in terms of deployable spectrum which delivers the coveted combination of high capacity with mainstream devices and engineering; plus TMO’s dominant position in the 600 MHz band will support affordable wide area coverage, providing the flexibility to move away from 4G whenever the business case suits.

This will accelerate the efforts of AT&T and Verizon to enhance their own spectrum position, especially with Dish harnessing its new infrastructure MVNO agreement, and large amounts of unbuilt spectrum, to become the new fourth MNO; and with the cablecos ramping up their wireless efforts too.

AT&T is testing 5G equipment in Austin, Texas under an experimental licence in the 4.4-5 GHz band, which is called the n79 band in the 5G definitions. AT&T is conducting its tests until the end of September and says, in its application for the licence, that it “seeks to further validate system design and operation in the sub-6 GHz band for certain applications and use cases”.

The use cases it lists include all the broad categories targeted for 5G or 4G/5G networks, including “LNC (LTE-NR Coexistence), V2X (Vehicle to vehicle/others), URLLC (Ultra-Reliable Low Latency Communication), mMTC (massive Machine Type Communications), and eMBB (enhanced Mobile BroadBand)”. It also notes “IAB (Integrated Access and Backhaul)” – many operators are looking to use the high bandwidth of 5G midband or high frequency spectrum to support both backhaul and access in the same spectrum, especially for small cells and locations which lack fiber access.

AT&T is also planning to start its mobile 5G roll-out in its 700 MHz band next year along with further mmWave deployments in 39 GHz. The 700 MHz roll-out will take place alongside its 4G 700 MHz build-out for the FirstNet public safety system. AT&T has also been involved in discussions about using the area of the C-Band which sit above CBRS – 3.7GHz to 4.2GHz – for 5G. This is an international effort so this could become a globally harmonized band in time, but this is subject to reaching a workable arrangement with the satellite industry which occupies some of these frequencies (see separate item).