Keysight’s chief technologist on the path to 6G

As the industry progresses towards 6G, there are significant technical, business, and even geopolitical challenges that need to be overcome. What will it take for the industry to get there?

Balaji Raghothaman: Fundamentally, AI has been a huge inflection. Whether we like it or not, it’s happening, and AI traffic dominates everywhere. It is inevitable that it’s happening for wireless traffic as well. Today, AI traffic originates from phones, but five or seven years from now, you’d have smart glasses, body sensors, and robots. That will fundamentally change what the network is used for and there’s both opportunity and danger in that.

In 4G and the early days of 5G, there was the rise of the app economy, and somehow telcos ended up as just the pipe while others took value. The same thing may happen with 6G if telcos are not careful – that they’re just the pipe delivering AI traffic, and value is captured by someone else. Some forward-thinking operators are looking at concepts like AI-RAN [radio access network], where they share server resources to deliver RAN traffic and run AI workloads, creating new business cases.

From a technical perspective, there has been a lot of talk about using terahertz bandwidth for 6G, but those frequencies have very short propagation distances. What are the implications for infrastructure build-out?

Raghothaman: Early on, when people started talking about 6G, sub-terahertz was a big topic. There was a lot of investigation, but as you said, the range is very limited, and they are expensive to deploy. As we’ve come closer to 6G becoming a reality, the interest has dwindled. There’s very little appetite – and no discussion in 3GPP – right now on sub-terahertz. The focus is generally on existing frequency range [FR] bands: FR1, FR2 and FR3.

Globally, there is consensus among operators that they would like to deploy 6G with the same footprint as FR1 bands – like the existing 5G C-band [around 3.3 GHz to 4.2 GHz] – on FR3 [about 7 GHz to 24 GHz] bands. It’s a doubling of frequency, so the propagation loss is higher and coverage is lower.

The only way to reclaim coverage parity with FR1 is to use more antennas to create beamforming gain. In 5G, we talk about a maximum of 64 or 128 antennas. FR3 will most likely have 256, 512 or more antennas. That’s a big technology challenge. You have to design new radios without going over power budgets. There’s a danger that the energy-per-bit goes up when deploying on FR3, so creating more efficient power amplifiers and RF [radio frequency] front-ends is a major area of innovation.

How will these spectrum and antenna challenges impact end-user devices, particularly with constraints on battery life and physical space?

Raghothaman: The device at the edge still needs to reach the base station, which makes for an incredibly challenging design. Device makers can’t just remove old radios; they have to maintain legacy support while adding new ones. Real estate on phones is already limited.

Traditionally, you certify a device based on static behaviour. But if an AI-driven device changes its behaviour over time, how do you certify it? If it’s a drone equipped with a 6G modem flying around, how is that regulated?

If you think a phone is challenging, think about smart glasses. There is virtually no real estate. We talk to engineers at companies like Meta, and they have to make decisions on every nanometre of space – whether to use it for battery power, processing, or transmitting. It’s a good problem to have because it drives innovation, but it is a major engineering hurdle.

With 6G, there’s also a push to integrate the technology with NTNs like satellite communications. What are the interoperability challenges?

Raghothaman: First, there are spectrum coexistence issues. There are areas where NTN coincides with terrestrial spectrum, and decisions have to be made on how they will coexist – you cannot necessarily shut off the terrestrial base station when a satellite flies over.

The other big challenge is about speed. A satellite moves at thousands of kilometres per hour, whereas a person is moving at three kilometres per hour relative to a terrestrial base station. This discrepancy, along with massive delays and Doppler effects, creates a big strain on the baseband receiver.

But satellites are the only way you are going to get close to 100% coverage. In areas like the vast jungles of Indonesia or Malaysia, it’s simply not economically viable for a commercial operator to maintain a terrestrial tower.

And will we see a greater need for space-based datacentres with 6G?

Raghothaman: Satellite has two different kinds of implementations: one is pass-through which only relays signals, and the other is regenerative, which processes data. Because satellite delays are inherently long, you want to do AI inferencing as close to the edge as possible to deliver a good user experience. Putting a datacentre on a regenerative satellite makes sense. The real question is maintenance. You can climb a cell tower to fix a terrestrial antenna, but you can’t easily send a shuttle to space. This is why testing and validation are important to monitor satellites and predict when they might fail so a replacement launch can be scheduled.

Let's talk about enterprise use cases. What sorts of enterprise applications will 6G enable that might finally move the needle?

Raghothaman: With every generation of mobile technology, there’s a big push towards enterprise solutions, and in the end, enterprises figure out that Wi-Fi is just easy. Deployment ease is a big issue. For IT managers, Wi-Fi is plug-and-play. 3GPP base stations are not like that.

The other issue is that cellular network planning has traditionally been very outdoor-focused, hoping the signal penetrates indoors. But now, we finally have the tools available with ray tracing and digital twins. Because we have building plans and material information, every building can have a geometric digital twin.

Once you have that digital twin, you can use AI-powered network optimisation to arrive at a highly optimised, site-specific network design. The network can learn based on local usage patterns and dynamically tweak parameters. If the cellular guys do not figure out how to do indoor networks properly, they will lose out on a big portion of the enterprise market to Wi-Fi.

What about network sensing? Could that drive new enterprise value, such as with self-driving vehicles in logistics or robotics?

Raghothaman: Integrated sensing and communication is a big focus for 3GPP, but we have to be very careful. With 5G, we created all these great expectations of new use cases. I remember remote surgery was a major use case, but it didn’t really happen. We don’t want sensing to become that thing that fails and causes people to lose faith in the technology.

Sensing is full of hard technical problems. Depending on the frequency you use, what is the resolution? Can you tell the difference between a bird and a drone? Those things still need to be proven. But everyone is excited about it because operators are looking for new ways to monetise beyond flat-rate subscriptions. If you can provide a service to a building owner or city government – whether that’s drone detection, elder care fall detection, or sensing a sag in a bridge – that is a whole new revenue stream.

Finally, what does the regulatory landscape look like? When you mix AI, 6G, and autonomous devices, how are regulators adapting?

Raghothaman: Traditional regulatory work around spectrum harmonisation and terrestrial/satellite coexistence is ongoing. We are working hard to ensure we don’t repeat the issues where 5G deployments interfered with older aircraft radar altimeters.

But AI introduces entirely new regulatory questions. I represent Keysight on the FCC’s [Federal Communications Commission] technology advisory council in the US, where we are looking at what AI means for wireless networks. Traditionally, you certify a device based on static behaviour. But if an AI-driven device changes its behaviour over time, how do you certify it? If it’s a drone equipped with a 6G modem flying around, how is that regulated?

The appetite for regulation varies – lower in the US, higher in Europe – but AI regulation is inevitably going to collide with telecom regulation in the 6G era. Our role at Keysight is to provide the measurement, data, and evidence so the industry can safely navigate wherever that landscape goes.