6G aims to achieve a wide range of goals and requires a wide range of technologies. Similar to 5G, there is no single technology that defines 6G. The foundation laid by the previous generation serves as the starting point for the new generation. However, as a distinct new generation, 6G frees itself from previous generations, including 5G, by introducing new concepts. Among them, new spectrum technology will help the industry fully cover his 6G.
Harness the new spectrum
Looking back, every generation of mobile phone technology seeks to take advantage of new spectrum. 6G is no exception, as new use cases emerge and the demand for high-speed data increases. As a result, 6G will need to deliver much higher data throughput than his 5G, making millimeter wave (mmWave) bands very attractive.
New frequency bands being considered for 6G include 100 GHz and 300 GHz, known as sub-terahertz (sub-THz) bands. There is also interest in the upper midband (spectrum between 7 GHz and 24 GHz) due to lower propagation losses compared to sub-THz bands, especially between 7 GHz and 15 GHz frequencies.
However, this spectrum has regulatory challenges and is used by various parties such as governments and satellite service providers. However, some bands could potentially be used for mobile communications by implementing more advanced spectrum sharing techniques. Figure 1 Here is an overview of the frequencies allocated for mobile and wireless access within this spectrum.
Figure 1 Overview of frequency allocation for mobile and fixed wireless access in the upper midband.Source: International Telecommunication Union, Radio Regulations, 2020
Although these frequencies are used for a variety of non-cellular applications, channel sounding is required to characterize the use of this spectrum in 6G and ensure that it provides benefits to targeted 6G applications.
The 7-24 GHz spectrum is a key focus area of RAN Working Group 1 (RAN1) within the 3rd Generation Partnership Project (3GPP) for Release 19. Release 19 will be completed in late 2025 and will accelerate the transition from 5G to 6G. .
Scaling with ultra-massive MIMO
Over time, wireless standards have continued to evolve to maximize the available bandwidth in various frequency bands. Multiple-input multiple-output (MIMO) and massive MIMO technologies were key enhancements in wireless systems that had a major impact on 5G. MIMO has significantly improved performance by combining multiple transmitters and receivers and beamforming information to the user using constructive and destructive interference.
6G can improve this further. MIMO is expected to scale to thousands of antennas to provide higher data rates to users. Data rates are expected to increase from 1 Gigabit per second to hundreds of Gigabits per second. Ultra-massive MIMO enables hyper-local coverage even in dynamic environments. The localization accuracy goal for 6G is 1 centimeter, which is significantly higher than 5G’s 1 meter.
Interacting with signals to improve coverage and security
Reconfigurable Intelligent Surfaces (RIS) also represent an important development for 6G. This technology is currently the focus of discussions at 3GPP and the European Telecommunications Standards Institute (ETSI).
The use of high frequency spectrum is essential to achieving greater data throughput, but this spectrum is susceptible to interference. RIS technology plays a key role in addressing this challenge, helping mmWave and sub-THz signals overcome high free-space path loss and high-frequency spectrum interference.
RIS is a flat, two-dimensional structure consisting of three or more layers. The top layer consists of multiple passive elements that reflect and refract the input signal, allowing data packets to avoid large physical obstacles such as buildings, as shown in the diagram. Figure 2.
Figure 2 RIS is a two-dimensional, multilayer structure, with the top layer consisting of a series of passive elements that reflect/refract the received signal, allowing the sub-THz signals used in 6G to successfully pass around large objects. These elements can be programmed to control the phase shift of the signal into a narrow beam directed at a specific location.Source: RIS TECH Alliance, March 2023
Engineers can program elements in real time to control phase shifts, allowing the RIS to reflect signals to specific locations in a narrow beam. RIS has the ability to interact with source signals to increase signal strength, reduce interference, extend signal range, and improve security in dense multi-user environments or multi-cell networks.
Transition to full duplex
Wireless engineers have been trying for years to enable simultaneous transmission and reception of signals in order to increase the capacity of wireless channels step-wise. Wireless systems typically use only one antenna to send and receive signals. Therefore, the local transmitter must be stopped or transmitted on a different frequency during reception so that weak signals from distant transmitters can be received.
Duplex communication requires two separate radio channels, or the division of the capacity of a single channel, with the advent of in-band full duplex (IBFD) technology currently under study in 3GPP Release 18. That’s changing. IBFD uses arrays. Various techniques for avoiding self-interference allow receivers to maintain high levels of sensitivity while transmitters operate simultaneously on the same channel.
Introducing AI/ML-driven waveforms
New waveforms are another exciting development for 6G. Despite its widespread use in cellular communications, the signal flatness of orthogonal frequency division multiplexing (OFDM) poses challenges for wideband signals in radio frequency amplifiers. Additionally, the integration of communication and sensing into a single system, known as Joint Communications and Sensing (JCAS), also requires waveforms that can effectively accommodate both types of signals.
Recent developments in AI and machine learning (ML) provide an opportunity to reinvent the physical layer (PHY) waveforms used in 6G. Integrating AI and ML into the physical layer enables adaptive modulation, which has the potential to improve the power efficiency of communication systems while increasing security. Figure 3 shows how the physical layer will evolve to include ML for 6G.
Figure 3 Migration to an ML-based physical layer for 6G is proposed to enhance both transmitter and receiver power efficiency and security. Source: IEEE Communications Magazine, May 2021.
Towards complete coverage
6G is reshaping the communications landscape and advancing cellular technology to have a meaningful impact on society. The 6G standard is currently in its early stages, with the first release expected to be Release 20, but research on various aspects is in full swing. These efforts drive the development of standards.
Predicting future network demands and which applications will prevail is a big challenge, but new spectrum technologies are one of the key areas the industry needs to focus on for 6G. With new spectral bands, ultra-high-capacity MIMO, reconfigurable intelligent surfaces, full-duplex communication, and AI/ML-driven waveforms, 6G provides users with complete coverage.
Jessy Cavazos is a member of Keysight’s Industrial Solutions Marketing team.
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