As 5G becomes commercially available, several countries have begun exploring the transformative potential of 6G. This next-generation technology is anticipated to support a wide range of future applications, including extended reality (XR), digital twins, autonomous driving, and smart homes. These advanced services will place unprecedented demands on data rates, energy consumption, mobility, and positioning accuracy. For example, 6G is expected to achieve peak data rates up to 50 times higher and sensing accuracy improvements up to 20 times greater than current 5G standards. However, meeting these ambitious targets with traditional microwave frequencies and established modulation techniques like OFDM/SC-FDE may prove quite challenging. In this context, initial efforts have been made to develop new modulation techniques from a physical-layer perspective, with the goal of meeting the diverse performance requirements needed for 6G networks.

Thus, as we edge closer to the rollout of sixth generation (6G) wireless networks, the quest for faster, more reliable, and more efficient communication technologies is intensifying. One of the critical areas driving this innovation is digital modulation techniques, which are essential for optimizing how data is transmitted over the airwaves, and recent advances are setting the stage for revolutionary improvements in 6G networks. For instance, to achieve terabits per second (Tbps) data rates, it may be necessary to utilize terahertz (THz) frequencies and beyond due to the limited spectrum available at microwave frequencies. Despite offering ultra-wide bandwidth and carrier frequencies exceeding 100 GHz, THz frequencies present significant challenges, including severe path loss, frequency-selective fading, and pronounced Doppler shifts, particularly at high mobility. These issues render existing modulation formats inadequate, prompting the development of new modulation schemes designed to improve resilience in such challenging channel conditions. Examples include orthogonal time frequency space (OTFS), orthogonal delay-Doppler division multiplexing (ODDM), orthogonal chirp division multiplexing (OCDM), and affine frequency division multiplexing (AFDM).

The Role of Digital Modulation in 6G

Digital modulation involves altering a carrier signal's properties—such as amplitude, frequency, or phase to encode data. In the context of 6G, which promises unprecedented data rates, ultra-low latency, and massive connectivity, advanced modulation techniques are crucial for meeting these demands.

Key Advances in Digital Modulation for 6G

       1.    Higher-Order Modulation Schemes

The development of higher-order modulation schemes is a significant trend in the 6G wireless networks. While 4G LTE predominantly uses 64-QAM (Quadrature Amplitude Modulation), 5G has pushed the envelope with 256-QAM. There has been increased focus of researchers on exploring even higher-order schemes such as 1024-QAM and beyond for 6G. 1024-QAM allows for a 25% increase in data rates for Wi-Fi 6 (802.11ax) access points and devices. By modulating both the phase and amplitude of the radio waves, this technology enhances spectral efficiency, enabling more data to be transmitted with each signal. These advanced schemes enable higher data rates by increasing the number of bits per symbol transmitted, but they also come with challenges in terms of signal-to-noise ratio and error performance.

       2.    Orthogonal Time Frequency Space (OTFS) Modulation

OTFS modulation is an innovative approach that enhances robustness against Doppler shifts and multipath fading—common issues in high-speed and mobile environments. OTFS, when combined with equalization, transforms the fading and time-varying wireless channel encountered by modulated signals like OFDM into a time-independent channel with a nearly constant complex channel gain for all symbols. This means that transmitter adaptation is unnecessary. By fully exploiting channel diversity, OTFS simplifies system operation and enhances performance, especially in scenarios involving high Doppler shifts, short packets, and large antenna arrays. Unlike traditional modulation schemes that rely on time-frequency resources, OTFS transforms the signal into an orthogonal basis that is more resilient to time and frequency variations. This is particularly beneficial for the high-speed mobility and diverse environments anticipated in 6G networks.

       3.    Non-Orthogonal Multiple Access (NOMA)

Non-Orthogonal Multiple Access (NOMA) is a key technology for improving spectrum efficiency and user connectivity in 6G. NOMA is proposed as an alternative to traditional orthogonal multiple access (OMA) because it enhances user capacity, bandwidth efficiency, and minimizes downtime. The core concept of NOMA is to enable multiple users to transmit signals concurrently within the same bandwidth block. Combining NOMA with MEC (Multi-access Edge Computing) has emerged as an effective approach for efficient transmission and processing across numerous devices. By using NOMA, multiple clients can simultaneously offload their computational tasks to an edge server, thereby boosting computational power and overall efficiency. NOMA stands out as one of the most promising electromagnetic transmission techniques for the next generation of mobile communication. It provides several significant enhancements over traditional orthogonal frequency division multiple access (OFDMA).

Recent advancements include the integration of NOMA with advanced modulation techniques like power-domain NOMA and code-domain NOMA, which promise to significantly boost the capacity and connectivity of 6G networks. NOMA maintains user fairness and diverse quality of service through flexible power allocation between strong and weak users. By allocating more power to users with weaker signals, NOMA enhances cell-edge throughput, thereby improving the overall user experience.

      4.     Machine Learning-Enhanced Modulation

Machine Learning (ML) plays a very important role in realizing and optimizing 6G network applications and it is gradually making its mark on digital modulation through adaptive modulation schemes that can dynamically adjust based on channel conditions and network load. With the use of ML algorithms, 6G systems can optimize modulation parameters in real-time, and hence improve both efficiency and performance. Techniques such as reinforcement learning, and deep neural networks are being explored to predict optimal modulation strategies and enhance error correction.

Combining machine learning estimators, such as CNN with Autoregressive Network (ARN) for predicting Channel State Information (CSI) and RNN for channel forecasting, can enhance performance in massive MIMO systems with channel aging characteristics. Results indicate that this proposed model improves prediction accuracy and user throughput gains in both low and high mobility scenarios.

       5.    Polarization-Domain Modulation

Polarization-domain modulation leverages the polarization properties of electromagnetic waves to encode information. This technique provides increased data rates and spectral efficiency by utilizing both the amplitude and polarization states of the carrier signal. With advancements in polarization-sensitive materials and detection techniques, this method is becoming more feasible for 6G systems.

The polarization-resolved, wire-gate structure enables the device to respond distinctively to terahertz waves with different polarizations, allowing it to modulate terahertz waves according to their polarization.

The preparation method is straightforward and cost-effective, making it ideal for 6G communication devices. It allows for large-scale production with high precision.

The integration of SPPs, polarization resolution, and ultra-fast response, coupled with precise fabrication and high-volume production capabilities, makes it highly suitable for applications such as 6G communication encoders.

       6.    Terahertz (THz) Communication Modulation

As 6G explores the use of terahertz frequencies (100 GHz to 10 THz), new modulation techniques are being developed to handle these high frequencies. THz communication requires novel modulation schemes that can cope with the unique challenges of ultra-high-frequency signals, including increased free-space loss and atmospheric absorption. Researchers are investigating THz-specific modulation techniques to achieve high data rates and extended range for 6G.

THz communication primarily relies on THz modulation and demodulation technologies, THz detection and reception methods, and THz generation techniques. Efficient use of modulators can significantly reduce the complexity, cost, and size of THz systems, making modulation technology a key area of research in THz communication. Signal modulation involves using a modulation signal to control one or more parameters (such as amplitude or phase) of the carrier signal. Recently, a variety of THz modulators utilizing different materials and structures have been developed to achieve high modulation depth, rapid modulation speed, and broad modulation bandwidth.

Challenges and Future Directions

Although these advancements are promising, several challenges remain. High-order modulation schemes require precise signal processing and error correction to maintain performance in noisy environments. OTFS and NOMA introduce complexity in both design and implementation. Machine learning-enhanced approaches necessitate robust training data and real-time processing capabilities. Polarization-domain and THz modulation techniques need further research to optimize their practicality and efficiency.

Pros & Cons of Digital Modulation in 6G

Pros of Digital Modulation in 6G

Greater Spectral Efficiency:

Digital modulation techniques, such as 64-QAM or higher, enable the transmission of more bits per symbol, significantly increasing the data rate and spectral efficiency. This leads to more efficient use of the available bandwidth, which is crucial for the high data rate demands of 6G.

Improved Error Detection and Correction:

Digital modulation techniques often incorporate advanced error detection and correction schemes, enhancing the reliability of data transmission. This enhances the overall communication quality, and thereby limiting errors and ensuring more accurate transmission of data.

Flexibility and Adaptability:

Digital modulation is useful in dynamic adjustment of modulation schemes based on channel conditions and user requirements. This adaptability supports various use cases and helps in optimizing performance across different scenarios, such as high mobility or varying signal conditions.

Compatibility with Modern Processing Techniques:

Digital modulation is well-suited for integration with modern digital signal processing techniques. This compatibility facilitates advanced features such as beamforming, spatial multiplexing, and advanced MIMO (Multiple Input Multiple Output) configurations, which are integral to 6G.

Better Security:

Digital modulation techniques are able to incorporate encryption and secure key management within the transmission process. This improves the security of communications, which is increasingly important in the context of 6G's vast and varied applications.

Cons of Digital Modulation in 6G

Complexity in Design:

Advanced digital modulation schemes can make both the transmitter and receiver designs complex and this complexity can lead to higher costs and challenges in system implementation and maintenance.

Increased Consumption of Power:

More sophisticated digital modulation techniques often require more power for processing and signal processing tasks. This can be a concern, particularly in mobile and battery-operated devices.

Latency Issues:

The processing involved in digital modulation can introduce additional latency and this latency might affect real-time applications and services that are sensitive to delay, such as autonomous driving or augmented reality.

Bandwidth Requirements:

Some digital modulation schemes may require larger bandwidths to achieve high data rates. This can be a limitation in frequency bands where bandwidth is constrained, affecting overall system efficiency.

Signal Degradation:

High-order digital modulation schemes can be more prone to signal degradation caused by noise, interference, and channel impairments. This susceptibility can impact the overall signal quality and reliability, especially in challenging environments.

According to TechSci Research report “6G Market – Global Industry Size, Share, Trends, Opportunity, and Forecast, 2018–2035, Segmented By Component (Hardware, Software, Services), By Communication Infrastructure (Wireless, Fixed), By Application (Multisensory XR Applications, Connected Robotics and Autonomous Systems (CRAS), Wireless Brain-Computer Interactions (BCI), Digital Twins, Smart Cities, Internet of Everything (IoE), Blockchain and DLT, and Others), By End User (Government, Consumer, Industrial, and Enterprise), By Region,” Global 6G Market is expected to thrive during the forecast period 2024-2035. The market growth is driven by growing demand for 6G communication across industries and the emphasis on low latency networks for applications.

Factors Driving the Global 6G Market:

1.Increased Demand for Faster Speeds and Lower Latency

One of the primary drivers for the market growth is the increased demand for higher data speeds and ultra-low latency. 6G is expected to provide speeds up to 100 times faster than 5G, with latency reduced to just a few microseconds. This will support applications which require real-time responses, such as autonomous vehicles, augmented reality (AR), virtual reality (VR), and advanced robotics.

2. Better Connectivity and Network Capacity

There is an increasing demand for networks that can handle massive amounts of data and connect a broader range of devices seamlessly with the growing number of connected devices. 6G promises to expand network capacity and connectivity, accommodating the proliferation of Internet of Things (IoT) devices and smart infrastructure.

3. Technological Advancements in the Sector

Technological advancements such as artificial intelligence (AI), machine learning (ML), and advanced antenna systems (like terahertz frequencies) are driving the 6G market. These technologies enable more efficient spectrum use, improved signal processing, and enhanced network management, all of which are important for the deployment of 6G networks.

4. Innovation in Use Cases

6G technology is expected to enable new applications and business models that were previously impractical or impossible. The demand for 6G is driven by innovations such as holographic communication, advanced telepresence, and immersive experiences. The potential for creating entirely new industries or transforming existing one’s further fuels investment and research in 6G.

5. Enhanced Economic Growth and Investment

The pursuit of 6G technology is closely linked to economic growth. Governments and private sector players are investing heavily in research and development (R&D) to secure a competitive advantage in the global market. Also, national and regional strategies aimed at leading in the future technology also drive investment in 6G research and related infrastructure.

6. Government Initiatives and Policies

Several initiatives and government policies play a major role in advancing 6G technology. Many countries are developing national strategies and funding programs to support the research, development, and deployment of 6G networks. These policies often include public-private partnerships and collaborative research initiatives.

7. Global Competition and Collaboration

The global race to develop and implement 6G technology involves intense competition among countries and companies. As leading global economies ramp up their research and development (R&D) efforts for 6G, governments, businesses, and academic institutions across various countries are intensifying their investments in 6G technology research. At the same time, there is a significant amount of international collaboration in standards development and research. This dynamic environment accelerates innovation and drives the growth of the 6G market.

China is actively advancing 6G technology in collaboration with numerous international companies and organizations. Foreign experts believe that international cooperation in this field is crucial.

8. Consumer Experience and Expectations

With consumers becoming accustomed to increasingly advanced digital experiences, there is a growing expectation for seamless and high-quality connectivity. Meeting these expectations is important and drives the demand for next-generation networks like 6G, which promise to deliver superior performance and user experiences.

9. Infrastructure Development

For the realization of 6G networks the development of new infrastructure, including the deployment of new cell sites and the upgrading of existing ones is essential. Moreover, investments in infrastructure and advancements in technologies, such as advanced fiber optics and satellite communication, further boost the growth of the 6G market.

However, 6G access infrastructure has limitations in supporting underwater services and communications. First, efficiently addressing the persistent issue of continuous wireless transmission across water-air surfaces is challenging due to signal reflection problems. Second, the uncertainty, instability, and high absorbency of underwater environments pose significant obstacles to deploying wireless network infrastructure. Third, human activities in aquatic environments are constrained, limiting the effectiveness of exceptional services in these areas.

10. Environmental and Sustainability Goals

6G technology also aims to address environmental and sustainability concerns. The development of energy-efficient technologies and sustainable practices in network deployment is becoming increasingly important. As the global focus shifts towards greener technologies, 6G is expected to play a role in supporting these sustainability goals.

Incorporating environmental sustainability principles into the design and operation of 6G is essential for the telecom industry to achieve Net Zero emissions. Although achieving Net Zero is the primary goal, sustainability KPIs are crucial for assessing the effectiveness of strategies and technologies aimed at developing inherently sustainable 6G systems.

Every decision, whether it involves selecting energy-efficient technologies during 6G standardization, choosing eco-friendly suppliers, minimizing environmental impact through measurable trade-offs in design choices before deployment, or adopting sustainable business practices, plays a crucial role in the collective effort towards a more sustainable future.

Conclusion:

In summary, the Global 6G Market is being driven by a combination of technological advancements, growing demand for faster and more reliable connectivity, and significant investments from both the public and private sectors. As 6G technology continues to evolve, it will likely open new avenues for innovation and transformation across various industries and applications.

The evolution of digital modulation techniques is a cornerstone of 6G technology. As researchers and engineers continue to push the boundaries, we can expect to see a new generation of modulation schemes that will redefine the limits of wireless communication. From higher-order schemes and OTFS to machine learning-enhanced methods and THz communication, these advancements are not just incremental improvements but transformative innovations that will shape the future of global connectivity.