Higher frequencies bring more complexity to every part of the network, from tiny antennas to powerful base station processors.
6G is expected to bring data speeds that enable highly integrated and responsive technology in smartphones, homes, cities, and autonomous vehicles, but realizing that goal will require a lot more work.
There will be many more antennas everywhere, embedded in infrastructure around town, in base stations, edge-devices, and everything in between. They will be sending and receiving many more signals at different speeds and wavelengths, including some that are much more susceptible to interference.
Physically, these new antennas will be much less visible than today’s giant cell towers. “You could build them into lamp posts,” said Shawn Carpenter, program director for 5G/6G at Ansys, now part of Synopsys. “There are several companies that have been developing a combination streetlight and Wi-Fi repeater, or streetlight and cellular repeater system that just screws right into the bolt socket, so you don’t really even see it. The towers are as large as they are because they have to carry the lowest frequency bands, which give you the longest coverage, and those are for public safety features and functions. When you call 911 on your phone, it’s more than likely accessing one of the lowest bands that necessitate the use of the largest antennas. That will have to be in place, but those antennas don’t have to be directional, and you don’t need as many of them.”
Moving from 3G through to 6G means antennas must have multi-band capabilities, because lower LTE bands need to be accommodated as well as some of the new bands. “Once government agencies have coordinated the spectrum, manufacturers have to dig in and say, ‘Oh, boy, we’ve been designing antennas for 3.5 to 4 gigahertz,’” Carpenter said. “Now we’ve got to design antennas for 7, 10, 12 GHz.’ It’s going to be a complete redesign of the antenna system.”
Different frequencies have to be addressed and fit into the same form factor, so that the operator doesn’t have to spend a lot more money building new towers or renting new towers. “Hopefully you can get it all to fit in a package that still sits on that same tower but can operate over more bands and wider bands. What goes into the antenna technology now for base stations is quite a bit more complex than it used to be,” he noted.
For small edge devices, such as a phone, higher frequencies use smaller antennas, but there are more of them. There could be as many as 16 antennas for millimeter wave bands, and that’s just for the handset.
“A handset will have to be ready to operate worldwide and be able to address maybe 10 bands, and it’s going to be quite a design challenge for the folks doing that now,” Carpenter said. “If you have higher dielectric property materials, that enables you to shrink the size of the antenna because the wavelength size in these exotic materials becomes even smaller. We’ve evolved our ability to develop antennas that fit inside the form factor of the case. We can now print planar antennas, or we can fold them around conveniently. We can use parts of the substrate, or the carrier substrate inside of, for example, the mobile device, to print the phones or print the antennas into the system, and then we’ve come up with circuitry that can tune the antenna for us, make it resonant. This isn’t particularly critical when you’re receiving signals. Receive antennas are not that sensitive. You do want to pay attention to how you design them, but when you’re transmitting, that’s when antennas have to be very efficient in radiating what you’ve given them, or what they radiate will be proportional on their physical size.”
Antennas also can be tuned through a technique known as “aperture tuning, which improves antenna efficiency by shifting the natural resonance of an antenna to the required frequency band of operation,” according to an Infineon application note. “This reduces stress on the antenna-driving hardware on the transmitter side (Tx) and increases sensitivity on the receiver side (Rx). Aperture tuning also allows antennas to communicate on multiple bands simultaneously to support carrier aggregation.” Another option is antenna impedance matching which is carried out at the antenna feed point and “helps to maximize signal transmission between RF Front-End (RFFE) and the antenna by compensating for frequency and environmental effects.”
Beam-steering antennas also will be required to direct radiated energy from the base station antenna array to the end-user while overcoming the higher path losses that occur at these frequencies, according to a Cadence white paper. “Fortunately, the shorter wavelength translates into smaller antennas, which, in turn, drives more IC-based antenna array solutions. Monolithic microwave IC (MMIC) and RFIC design will play an important role in future beam-steering technologies for 5G systems operating at mmWave frequencies. As wireless communications systems evolve, smaller devices with better performance will be required that incorporate multi-technology-based module designs with different IC and printed circuit board (PCB) process technologies.”
Another antenna challenge is cross-coupling, due to the need for more antennas in a smaller space. “We need very good simulation models to predict if there is some coupling between the antennas, and also antenna to the package,” said Andy Heinig, head of department for efficient electronics at Fraunhofer IIS’ Engineering of Adaptive Systems Division. “You really must be careful of this behavior for the different antennas, and the influence of one antenna on another.”
6G is going to be a much finer meshed configuration of the antennas, and there are a lot of issues there with the wavelengths. “The real challenges are in the electromagnetics of the whole thing said Marc Swinnen, director of product marketing at Ansys. “HFSS (high-frequency structure simulation) can model edge nodes in an extensive system and assess them for signal integrity, power integrity, thermal integrity, structural integrity, antenna systems, and large system deployment.”
In today’s 5G systems, edge compute nodes are constructed with 5G NR mmWave and sub-6 GHz wireless connection capabilities built-in, with WiFi, Bluetooth, and GPS combined with a complex microserver. 6G will include all of this and more.
One advantage of 5G/6G’s increased number of antennas is spacial agility. “One of the beautiful things they’ve been developing with 5G technology is this ability to give every user their own special spotlight from the base station,” said Carpenter. “As you move around, you get your own private beam, because they’re coding it into your signal with the baseband processor. That takes a lot of bespoke silicon, because you can’t just buy an off-the-shelf chip to do that sort of thing. An Ericsson or a Huawei or a Nokia or other designer would have to roll out chips that do this really heavy processing, because you’ve got to figure out what the beam weights are for every user, and update that periodically as that user moves through a really interactive environment. They’re probably going to raise the number of antenna elements in that array because they’ve already got a baseline size for the face of the base station antenna. And they’ll say, ‘Hey, we’re used to using antennas this size, so when we go to higher frequencies, we could add more elements in there.’ If we add more elements, we get a lot more agility. We can squeeze that user’s power into a tighter beam with an electrically larger array. And if we can then get the processing on silicon to process every subscriber signal uniquely, then we can give them all their own little spotlight as they move around, and focus that energy on them, minimize the interference to other subscribers in the field, minimize subscribers to other base stations, and then we can raise the bandwidth that every one of those subscribers gets.’ And now you could stream 15 cat videos simultaneously in high definition.”
In the future, antennas may even have radar ability, but that also could create problems with antenna integration, said Fraunhofer’s Heinig. “The requirements for the antennas are a bit different between radar and communication. For sure, we have beamforming in both cases. But how do you form the beam?”
Chip design and edge AI compute challenges
6G is going to put a lot of pressure on devices due to its much higher data speeds. “There’s a lot of research going on with regard to new spectrum for 6G, because it is going to have probably 4 to 10 times more bandwidth than 5G,” said Ron Squiers, solution networking specialist at Siemens EDA. “We’re talking about a terabit per second device instead of a 20 gigabit per second device. There are extensions in mobility for, instead of 400 kilometers per hour, we’re going to achieve 500 to 600 kilometers per hour. These are all set out in the IMT 2030 objectives document for 6G, and you’ll see these things being attacked individually in the various 3GPP Release Standards Working Group through the next 5 to 10 years.”
While consumer applications will continue to evolve, the scalable and unpredictable part of 6G is going to be on the physical AI, said Mung Chiang, president of Purdue University and recipient of the 2025 IEEE Founders Medal for his leadership and research in communication networks and its applications. “For AI interacting with agriculture, transportation, and manufacturing, or Industry 4.0 robotics and automation, 6G is going to be driving all the other verticals. It’s not just a consumer electronics thing. It’s going to be like electricity — the foundation of all modern technologies and verticals of applications. To get there, you need much better latency and responsiveness. Not just higher throughput — peak throughput, average throughput, worst-case throughput, whatever it is you use as the metric. How responsive can you be, because you can only put in stable control loops and feedback in real-time decisioning and actioning if you have reliable and low latency in responding. That’s where the prevalent edge compute is going to kick to allow you to say, ‘I may not get it perfectly accurate, but I can get it, say, as a learning or inference action, before it’s too late.’ It will be good enough when it’s still in time. That’s why edge compute has many advantages. One is latency reduction and jitter reduction.”
6G will likely compound existing 5G design challenges, which affect every device in the network, according to Cadence. Among them:
Base stations will be taking on a lot of the heavy lifting when it comes to AI and they will need mixed chip architectures. “You’re going to need a variety of processing types at that access point that are going to have different architectures that will be suitable and necessary for the wide range of tasks that people are going to apply there,” said Ansys’ Carpenter. “AI/ML is one of them, but there’s a whole lot going on.”
Custom chips also will be needed. “Some of the machine use cases will be very low power,” said Purdue’s Chiang. “Some will need to be very responsive in terms of the kind of memory chips and the power of logic chips needed. Some are going to be operating different bands, and therefore you need new kinds of analog/mixed signal front-end chips.”
For 6G edge devices, it remains to be seen if companies can design chips that tick all the boxes. “I’m not sure if there’s one single answer that gives you everything you desire — low power, high performance, high bandwidth, small form factor — everything,” Chiang said. “But you’re going to have a suite you may customize. You may get different types of choices within that range of choices. It’s going to be a mix of GPUs, TPUs, and so on, and customization will be useful. They will have to work together because the proliferation of edge devices and the continuum from the cloud to the edge — the whole fog — is going to give you so many different configurations. There’s no one size fits all.”
Fig. 1: 6G technical focus areas by protocol layer and technical readiness. Source: Purdue University
Companies can target multiple markets by enabling one network, such as 3G, 4G, or 5G, on the base die, and then have a second die for high-end products that offers 6G and more powerful AI, said Hezi Saar, executive director of product management for mobile, automotive and consumer IP at Synopsys, and chair of the MIPI Alliance. “One vendor says, ‘I’m going after the feature phone market as well as the high-end smartphone market. How do I go about it? If it’s 2nm, it will cost me millions of dollars to go for it.’ So they may decide to do a base monolithic chip that can go to a feature phone. It has enough capability — let’s say, three cameras, one medium range display, a modem that doesn’t need to go to 6G, just 5G, the storage is limited, so it fits the price point that they’re going to go after with multi-die in mind. This means they can use that base and then add an AI accelerator, so now it can do more AI. With this additional chip that has additional I/Os, or higher storage capacity, or higher DDR connectivity for the computing, higher connectivity to the modem, now it becomes a high-end engine. It’s multi-die, and it can go after that market.”
Other companies will focus on next-gen Wi-Fi, Bluetooth, and Zigbee chips and leave 5G/6G to the established players. “The cellular market is dominated by very strong incumbents, like Qualcomm and a few others,” said Ananda Roy, senior product manager for low-power edge AI at Synaptics. “There has to be a big change for them to select new vendors, and there is relatively lower opportunity for new players. We want to be very focused on the IoT technologies as opposed to a more infrastructure side of things, which is 5G/6G baseband technologies.”
GaAs, GaN, Si and other needed developments
Network operators and radio manufacturers will need to manage a much higher data capability at the same total cost, necessitating a significant reduction in the cost per bit. This can be achieved by combining frequency bands in one radio unit; employing wider frequency bands to reduce the number of required radios; reducing the size and weight of radios to lower tower rental costs; and reducing the consumed energy per radio to lower operator energy bills. Breaking these requirements down for 5G radios, the RF power amplifiers (PAs) need to support higher frequencies, significantly wider instantaneous bandwidths, and high efficiency over a wide back-off range. These radios also must be capable of being linearized at levels below 50 dBc with digital predistortion. The semiconductor technologies capable of delivering those targets at a commercially viable price position are RF GaN-on-SiC (gallium nitride on silicon carbide) and RF GaN-on-Si (GaN grown on a Si substrate), according to Infineon.
The need for GaN is also widely discussed. An antenna array the size of your palm may cover one side of a radiohead module with beam-steering RFICs, transceivers, and PAs driving them from the reverse side of the PCB. Such compact high-frequency modules demand technology-aware design platforms that support discrete and embedded RF component design and system integration with in-design electromagnetic (EM) and thermal analysis, RF circuit simulation, and workflow support for co-design of ICs, IC packages, and modules with GaAs [gallium arsenide], GaN, and Si technologies.
Recent 6G developments:
As indicated by the Nordic/Omnispace/Gatehouse Satcom 5G trial mentioned above, satellites are set to be a key part of the 6G revolution. An example is shown below.
Fig. 2: Direct satellite connectivity to end user devices. Source: Purdue University 6G Global Roadmap Taxonomy Report
Conclusion
By 2030, Purdue’s Chiang expects edge compute and dispersive AI to be more prevalent, along with different kinds of chip customizations, protocols, users, and use cases. “When we get there, people may say, ‘We missed 5G. It took 6G to get there.’ Other people may say, ‘I’ll give 5G credit where credit is due. 5G started that transition.’ It just took a little longer for other things to mature — the business case and economics, the user experience, and a regulatory environment. If we’re talking about physical objects, it’s one thing if you miss a byte on your Netflix streaming. It’s another if you miss a byte on physical objects. What matters most is that technology will continue to evolve.”
Related Reading
6G Line-Of-Sight Repeaters, Dots, And Reflections
Private networks and city-wide simulations show how 6G providers will reach edge devices via repeaters, small cell radios, and reflections.
6G Rollout Will Be A Patchwork At First
Spectrum allocation, infrastructure development, and varying use cases will affect when and where this technology rolls out.
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We don’t need 6g we need to finish building out the 5g mmWave network otherwise it will only make phones more expensive for everyone with benefits only a few people