What you’ll learn:
- Why multiple mmWave channels will be needed to address future cellular network expansion.
- Migration challenges in the first commercial deployments above 100 GHz.
In an era where the world is still grappling with the potential of 5G, the leap to 6G presents both exciting opportunities and considerable unknowns. While 6G remains largely uncharted territory, the experiences garnered from earlier technological advances provide a strong foundation for overcoming the complexities of this migration.
The next phase of 5G and future 6G include targets of achieving wireless xHaul data rates of 100 Gb/s. Currently, the highest capacity xHaul links operate at around 25 Gb/s.
Although mmWave and E-band, 71 to 86 GHz, have delivered major leaps forward with data rates in excess of 10 Gb/s, a different approach involving multiple mmWave channels will be needed to reach future targets. Therefore, we will likely see the aggregation of different frequency bands, with the next target bands—W and D—pushing beyond the 100-GHz mark.
W- and D-Band frequencies
A clear advantage of W- and D-band frequencies lies in the significantly wider bandwidths they offer compared to lower-frequency bands. This broader spectrum is critical as data demand continues to surge, driven by the proliferation of connected devices and the increasing complexity of data-intensive applications. W-band frequencies—92 to 114.5 GHz—and D-band frequencies—130 to 175 GHz—provide vast, contiguous blocks of spectrum, which are essential for supporting the high data rates required by modern communication networks.
These high-frequency bands are particularly well-suited for xHaul networks, which integrate fronthaul and backhaul connections to create a more efficient and flexible system architecture. By using these bands, networks can achieve lower latency and higher throughput, ensuring a more responsive and reliable user experience.
Specifically, D-band offers even greater bandwidth capabilities, potentially up to 4X that of lower-frequency bands. This expanded capacity is crucial for future-proofing networks against the exponential growth in data traffic.
D-band's ability to handle such high bandwidths facilitates enhanced performance and capacity, which is vital for supporting data-intensive applications such as augmented reality (AR), virtual reality (VR) and the Internet of Things (IoT). These applications demand robust and high-speed connections to function effectively, and D-band's superior bandwidth ensures that network performance remains optimal even under heavy load.
Migration Challenges with W- and D-Bands
These bands are pivotal as they’re expected to see the first commercial deployments above 100 GHz, marking a significant milestone in the journey toward ultra-high-frequency communications. Crucially, manufacturing processes for W-band are still compatible with existing methods, albeit pushing the boundaries of current manufacturing tolerances.
Such an alignment allows for a smoother transition into higher-frequency operations without necessitating a complete overhaul of established manufacturing infrastructures. As a result, it accelerates the time-to-market for new technologies in this band.
However, the progression into D-band presents a more complex scenario. Research in this area is advancing well, with available semiconductor processes in indium phosphide (InP) delivering the necessary power for high-frequency operations, though it’s currently reliant on costly boutique processes. The cost factor remains a critical hurdle that needs addressing to enable full commercial deployment.
Moreover, integration challenges are more pronounced in D-band. Traditional wire bonds are unfeasible at these frequencies, necessitating the adoption of alternative interconnect technologies such as flip-chip, waveguide interfaces, or hot vias. These technologies are essential not only for performance, but also for their potential scalability in volume manufacturing—a key factor for the commercial viability of telecommunications infrastructure in D-band.
While significant progress in the W- and D-bands outlines these promising short-term and mid-term advances in telecommunications, looking further into the future presents even more complex challenges, particularly when considering the design and manufacturing of devices capable of operating at 300-GHz frequencies.
Non-Terrestrial Needs
On Earth, networks operate within the relatively familiar confines of our atmosphere, where distance limitations are measured in kilometers and power requirements are readily met. In contrast, communication distances in space balloon into thousands of kilometers, necessitating solutions that can punch through the void with greater power while also remaining energy efficient.
Platforms like satellites and balloons become new transmission towers, imposing tight weight and size constraints on the equipment they carry. And the harsh reality of space adds an extra layer of complexity, with components needing to withstand the unforgiving onslaught of radiation. Satellites and high-altitude platforms, which must contend with the formidable constraints of gravity, require components that strike a delicate balance between power and minimal weight.
This imperative for lightweight, yet powerful, components has spurred significant innovation in materials science and engineering. For example, advanced composites and alloys are increasingly employed to reduce weight without compromising structural integrity or performance.
Engineers also focus on optimizing the design of these components to ensure they consume less power. The power efficiency not only reduces the size and weight of the power supply units, but also extends the operational lifespan of the satellites and balloons, too.
The move to miniaturization is key here, where the goal is to compress the capabilities of conventional equipment into increasingly compact forms. This involves leveraging advanced materials, designing sophisticated heat-dissipation mechanisms, and employing innovative packaging techniques—all of which are essential in creating components that are both lightweight and highly functional.
As for safeguarding against space radiation, engineers must employ a multilayered defense strategy that goes beyond traditional protection methods. This includes the use of specialized components and shielding materials designed to absorb or deflect high-energy particles.
Such materials are often lightweight yet robust, tailored to add minimal weight while providing maximum protection. In addition, the implementation of redundant circuitry is a key strategy, where multiple copies of essential components are included; if one fails due to radiation, others can take over.
Fault-tolerant designs also play a crucial role. Systems are built to detect and correct errors autonomously, enabling them to continue functioning even when some damage occurs.
Semiconductor Technology for High Frequencies
One of the primary hurdles currently facing manufacturers is the underlying semiconductor technology required to achieve the necessary high frequencies. At these frequencies, semiconductors become a critical focal point in the overall design. Each semiconductor material has unique properties that can support the critical design requirements.
At lower frequencies, a mix of performance and cost often leads to the integration of several individual semiconductors. For higher frequencies, the aim will be to integrate as much of the functionality as possible into a single chip, to minimize interconnects and the related problems outlined above.
It’s therefore likely that much of the integration will be in the form of a silicon chip. However, the high-performance elements, such as the power amplifier and LNA, must remain in a compound semiconductor material to maintain the required performance. For W-band, existing semiconductor technologies are being stretched to their limits, but they’re still within achievable tolerances. This includes precise placement tolerances, wire bonding, and machining accuracy.
For instance, in W-band applications, maintaining signal integrity requires high precision in component placement and interconnects to ensure minimal signal loss and optimal performance. The D-band, though, presents more significant challenges. Currently, commercially viable semiconductor technologies for D-band aren’t yet fully developed. While boutique processes are capable of handling D-band frequencies, these aren’t suitable for high-volume commercial applications due to their high costs and limited scalability.
This means that widespread adoption of D-band frequencies may still be several years away, pending advances in semiconductor manufacturing technologies. That said, a significant development in Filtronic’s mmWave technology involves the use of high-power, solid-state power amplifiers (SSPAs).
Traditionally, the compound semiconductor gallium arsenide (GaAs) has been used within mmWave SSPAs due to its long history and established performance. However, even at higher frequencies, such as those above 40 GHz, gallium nitride (GaN) is now becoming more prevalent. GaN offers better power density and efficiency, allowing for more power output from the same surface area. Not only does that help make devices more compact, but it also extends the range of signal transmission.
While advances in the realm of 6G technology are still unfolding, the insights gained from achieving high performance and efficiency with 5G provide a crucial roadmap for future innovations. Designing solutions for 6G frequencies is conceivable, but achieving scalable production for such high frequencies continues to be an ambitious goal—more a vision for the future than a reality of today.
