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In achieving the data rates required by 6G the most important part of the wireless signal processing enabling terahertz communications is likely to be the digital baseband. This article explores the developments in this area needed to address this.
Over the past 30 years, wireless technology has made tremendous leaps. Devices have become much smaller and are nearly ubiquitous. Dropped calls have become a thing of the past, while high-definition video routinely streams to our devices on demand. While we’re aware of the beneficial technological evolutions that have taken place, the most transformational innovations are often those that users can’t see because they take place behind the scenes, at the most foundational levels.
As we look to the next decade of 5G and 6G evolution, several emerging use cases will require data rates and bandwidth previously unimaginable, which means focus is now turning to terahertz (THz) communications as a means to achieving this goal. But there are technological challenges the leap to THz communications presents—and one of the most complex is digital baseband processing.
Understanding the baseband
As the component where all wireless signal processing functions are computed, the digital baseband processor is the most computationally intensive part of a wireless system. Within the overall baseband chain, encoding and decoding processes are the most complex blocks that are found in almost every wireless system. To unlock the ultra-high data rates and high-frequency radio communications integral to 5G and future 6G technologies, it is vital to tackle the development of ultra-fast encoding and decoding for the baseband chipset, also known as channel coding, or forward-error-correction (FEC) technology.
Figure 1. 5G requirements vs B5G (beyond 5G)requirements in FEC for various use-cases, including ultra-high speed communications (Tbps), ultra-low-latency communications. The EPIC project is aimed at delivering the B5G requirements. (Image Source: InterDigital)
And just how fast is ultra-fast? Think faster than 100 Gbps—a hundred times faster than today’s 5G speeds. These terabyte-approaching speeds can only be achieved at ultra-high frequencies exceeding 100 GHz and above. This far surpasses the highest frequency millimeter wave spectrum in commercial use today.
When examining the baseband components present in every cellular system, the channel coding, or encoder/decoder block in the baseband chipset (or baseband system-on-a-chip) represents the most complex and power-hungry part of the baseband—consuming nearly 40 percent of the baseband chip’s entire power use.
Channel coding is complex by nature and requires a significant number of computations that ultimately drive power consumption. This dynamic has existed since the dawn of digital cellular, from 2G systems processing voice and text communications up to future 6G networks that will enable advanced immersive video experiences.
Using our history to look ahead, Moore’s Law suggests that the telecommunications industry will double the number of transistors on a silicon chip every 18-24 months. This law has held true since the 1970s, but current realities have stagnated the trend, which makes it increasingly difficult to support 5G’s massive increases in computing horsepower demands with silicon scaling alone.
To achieve the data rates required by 5G and 6G, the foundations of Moore’s Law are no longer sufficient and require new innovations.
A key piece of the puzzle
When it comes to THz communications, FEC technology will be a key piece of the puzzle, as it allows the transmitter and receiver to detect and correct transmission errors, while using advanced channel coding algorithms to achieve processing efficiency and higher throughput.
Funded by the European Commission’s Horizon 2020 program, the Enabling Practical Wireless Tb/s Communications with Next Generation Channel Coding (EPIC) project [epic-h2020.eu] has developed (FEC) technology using all three major channel code families—LDPC codes, Turbo codes, and Polar codes—to meet the performance requirements of terabits per second (Tb/s) technologies for 6G.
Figure 2. Real-time demonstration of novel Polar Code decoder technology achieving 200Gbps on FPGA. (Image Source: InterDigital)
The project also addresses another pressing issue within THz communications. Future THz networks will require a higher densification of cellular nodes than previous generations. While 5G’s millimeter wave technology requires macrocells and microcells to be deployed every 50-100 meters, 6G’s THz bands communications will depend on nanocells deployed around every 10 meters or so, because higher frequencies are less favorable for long-distance signal propagation.
This structural change represents a major redesign of cellular systems, extending beyond simply requiring higher data throughput to needing increased network-level computations to manage vast networks of nanocells. These THz nanocells will require very specific antennas, radio units and generators, but a huge part of the computational burden will remain on the baseband chipset. The research championed in the EPIC project demonstrated the ground-breaking potential of this solution.
Figure 3. Virtual silicon design of novel Polar Code technologies achieving 500Gbps in 28nm nodes. (Image Source: InterDigital)
The future of THz communications
The question on everyone’s mind is: where does this take us? Among the emerging use cases being explored for 6G, one of the most exciting is XR communications: the concept of truly real-time, immersive mixed reality communications technology.
The immersivity of this technology would make it much more computationally intensive than today’s videoconferencing technologies and require specialized hardware like wearable devices or multi-camera arrays to be realized. Unless a new Einstein discovers a fundamental change in the underlying laws of physics, a most feasible way to enable this vision is through joint hardware-algorithm development concept also demonstrated by the EPIC project.
This is an exciting time for beyond 5G research. Historically, algorithmic development and hardware development have been treated as two separate disciplines with different trajectories. The wireless industry primarily focused on creating standards for wireless algorithms and evolutions, while the development and evolution of hardware was seemingly secured by the “natural” improvement in silicon performance supported by Moore’s Law.
But even Moore admitted that his law wouldn’t increase infinitely, and even predicted the current slow down our industry is in. The EPIC project represents a pioneering approach in the context of 5G and beyond physical layer design where the algorithms and the hardware were researched and developed together. What’s more, EPIC not only developed the underlying algorithmic models, but it also successfully showcased a physical demonstration in a real-world environment.
While the future of wireless might not be clear, it is certain it will be fast, and THz communications will be key to bringing the 6G future to bear.
Onur Sahin is a senior manager at InterDigital [interdigital.com], a technologist with over ten years’ experience primarily in telecommunications and wireless systems. His current work is focused on 5G and beyond 5G technology creation, project management, and pre-standards research and development, particularly in the areas of radio access networks, link level algorithms, low-power learning modules and internet of things (IoT).
- EU funds development of secure low power embedded processors [embedded.com]
- 5G and GaN: Future innovations [embedded.com]
- 5G and GaN: Understanding sub-6Ghz Massive MIMO infrastructure [embedded.com]
- How to place two or more antennas in one design [embedded.com]