Infrastructure Focus Clouds the Blue-Sky View for 6G

The 35-year history of digital cellular standards has followed a predictable trajectory since the 3G Partnership Project took the lead in standards development. As soon as one generation of standard reached draft form in 3GPP, it was time to speculate about the next generation, even if the barest framework of the next generation was still years away. The speculation has led to hype and nonsense in 4G and 5G, but for the still-nascent 6G, the decade of the 2020s may be too murky for even the best crystal balls to penetrate.

Uncertainty about 6G comes from two sources. First, with “handset fatigue” dampening end users’ enthusiasm for continual upgrades to new smartphone models, the standard will be defined almost solely by upgrades to infrastructure. The soft-function trends of software-defined networking (SDN) and network function virtualization (NFV) will drive base station and remote radio head development. That could make the feature sets of soft switches and SDN controllers seem downright squishy.

The second source is regional and political. China’s massive investments in backbone networks for 5G/6G could put engineers from Chinese OEMs and service providers solidly in the driver’s seat within international standards bodies like IEEE within the next decade. When engineers from Huawei, ZTE, and other Chinese companies accelerated involvement in 4G/5G, their practical contributions to areas such as narrowband internet of things (IoT) were benign, if not downright beneficial. But as China envisions a more centrally controlled wireless network for 6G, the protocols for ad-hoc subnets and “just right” bandwidth may look far different from what engineers at U.S. and European OEMs might propose.

Some trends in infrastructure look like no-brainers. The lower costs of soft functionality, for one, appear to make SDN/NFV a foregone conclusion for future network switches and base stations.

Yet foregone conclusions can turn out to be anything but. Scaled granularity from small cell to picocell to femtocell was the presumptive natural path for 5G, but the architectural model of widely proliferated femtocells hasn’t found the expected degree of market reality. Users and service providers tolerated a coarser granularity at the neighborhood and single-building levels because it was cheaper to deploy than a cell in every living room.

Similarly, ad hoc networks characterized by dial-up bandwidth on demand would seem to be a given for 6G, but unexpected market demands or shifts could change those expectations.

NOT SO FAST

The irony in launching a 6G discussion in 2018 is that only the first round of 5G standards, known to 3GPP as Release 15, is in draft stages of definition. At a minimum, additional standards packaged as Releases 16 and 17 will be debated through the middle of the next decade, and many analysts expect even more releases for 5G. That could push early implementations of 6G out to 2030 or beyond.

In the meantime, interest in 5G deployments is flagging for three reasons that should have been obvious.

First, the rise of 160-MHz channels and 4 × 4 multiple-input, multiple-output (MIMO) antennas promises theoretical data rates of up to 10 Gbits/second, translating to several hundred Mbits/s at the handset. Sounds great, but service providers have been polling users on the cost versus benefits of such upgrades, and their findings cast doubt on whether such speeds are necessary for traditional smartphones.

The second 5G goal is serving mission-critical applications requiring low latency, fault tolerance, fast failover, and ultra-high reliability. First-responder radio networks obviously can use such a feature set, but will the users of police and medical-radio subnets be willing to underwrite the primary costs of 5G deployment?

The final goal for 5G, IoT and autonomous-vehicle connectivity, has the opposite problem. Networks must support tens of thousands of low-data-rate nodes. Work on special networks such as Long-Term Evolution (LTE) Category 0 has been robust, but industrial and automotive networks cannot shoulder the deployment costs of 5G.

The deployment conundrum of 5G, seen from service providers’ perspective, is bad enough in bands below 3 GHz. For the most flexible sub-3-GHz services, carriers will need to provision a variety of small cells, including pico- and femtocells — an approach that attracted few users and lost money when it was tried in 2010–2015. Newer services, such as millimeter-wave long-distance offerings in the 11-GHz band, will require even more dedicated equipment, which might pull in new businesses — but only if the new commercial users emulate the diversity of military millimeter-wave users.

Some service providers have elected to focus on a subset of available bands. Verizon, for instance, has put most of its investment behind the 28-GHz and 39-GHz bands and called them 5G. But there have been no auctions yet for the 11 GHz of new spectrum that the U.S. Federal Communications Commission (FCC) defined two years ago for blocks at 28, 37, and 39 GHz. A new FCC-defined band at 64 to 71 GHz is even fuzzier, dwelling in a nascent state in which the blocks are not yet fully characterized.

It’s no wonder that users and carriers alike scratch their heads when network equipment vendors boast about the promises of 5G.

Even in markets that seem a sure bet, such as vehicle-to-vehicle (V2X) communications, existing LTE networks must compete with a slate of IEEE-based standards and proprietary offerings. Qualcomm and Huawei are promoting Cellular V2X (C-V2X) as a derivative of LTE Direct, the autonomous long-distance device-to-device (D2D) protocol introduced in 3GPP Release 12. But C-V2X must compete with automotive networks based on IEEE 802.11p, a Wi-Fi derivative for cars. The reality has deflated V2X cheerleaders’ early predictions of a $40 billion market for V2X services in 2020 and a component and hardware market reaching $36 billion in 2025. Such market fragmentation will likely repeat itself in other vertical domains.

BUILD IT AND THEY WILL COME?

Many broad areas were deliberately left out of 5G standards development, such as the integration of terrestrial cellular networks with satellite communications, the definition of ultra-dense cellular networks with ad-hoc joining features, more complex reconfigurable hardware following SDN/NFV models, and full immersion in wearable communication devices. From the standpoint of practical bandwidth, 6G proponents are talking about speeds of 1 to 100 Gbits/s for end users, along with multi-user MIMO element scaling to thousands of antenna nodes.

Those feature sets are of immediate interest in the infrastructure equipment and network testing segments because backbone networks will require new switching and transmission. In virtually all instances, however, such services will need to be “sold” to both service providers and end users, as usage cases are still in their infancy.

Some proponents suggest that 6G will primarily serve the IoT/V2X market. While the number of nodes will dwarf those in traditional cellular communications, we are back to the problem of low-bandwidth users subsidizing a network defined for high-bandwidth advantage, which cannot be realized through a primarily IoT focus. If 5G Release 16 and beyond is still blue-sky territory, then 6G may well occupy the realm of speculative fiction.

Because nonsense never stops, blue-sky analysts already are talking about 7G networks, which would enable “space roaming” (central Internet Protocol nodes communicating with multiple satellite networks), and even 8G, which has not yet been defined beyond “ultra-high-fidelity” immersion networks. But it is important to remember that 3GPP just released the core 5G radio protocols and IP network-layer translations in October, and it has yet to define true 6G programs. As for 7G and 8G, those proposals exist only in some singularity-based world defined by followers of Ray Kurzweil. ■