Viet Nguyen, Vice President, 5G Americas (July 2024) – As our digital world grows, so does the need for more bandwidth. Enter spectrum sharing—a concept that promises to revolutionize how we manage and utilize wireless frequencies. However, this innovation comes with its own set of challenges. In 5G Americas’ latest briefing paper entitled “Spectrum Sharing: Challenges and Opportunities” we explore the intricacies of spectrum sharing, highlighting both the opportunities and the hurdles it presents.
Licensed spectrum has been the backbone of cellular networks, providing the dedicated frequencies necessary for reliable and high-performance mobile services. This model has enabled networks to scale effectively and meet growing traffic demands, but the insatiable appetite for data means we need more spectrum than ever. With North American mobile data demand projected to grow at approximately 21 percent annually through 2029, wireless operators are locked in a race to effectively double the capacity of their networks every 3.5 years. To address this, regulatory authorities have reallocated and repacked spectrum bands to provide the necessary resources, ensuring that each generation of cellular technology has the bandwidth it needs to thrive.
Licensed full-power commercial spectrum model still provides the best, most optimal solution for delivering wireless cellular service. However, finding spectrum suitable for commercial licensed uses, particularly in the mid-bands, have become an acute and chronic challenge, particularly for the United States. Indeed, the United States ranks 13th out of 15 leading nations when it comes to the amount of commercially available licensed mid-band spectrum. Over the years, 5G Americas has highlighted the need for licensed mid-band spectrum for 5G in numerous white papers.
“5G Americas supports the 7.125 to 15.35 GHz spectrum range, especially below 10 GHz, for licensed mobile operations for its balance in capacity and coverage. Opening bands in this range involves exploring relocations and sharing strategies.”
— Aleksandar Damnjanovic, Principal Engineer/Manager at Qualcomm Technologies Inc
Unlicensed spectrum, on the other hand, has traditionally been the domain of Wi-Fi, allowing for widespread connectivity in homes and offices. Here, the United States leads the world in the amount of available unlicensed mid-band spectrum it offers. As our reliance on wireless internet grows, so does the demand for more unlicensed spectrum to support higher data rates and new applications. This model has proven essential for delivering high-speed internet access in environments where licensed spectrum isn’t feasible. However, unlicensed spectrum typically does not allow for full power use, which can provide some limitations to coverage – particularly for mobile uses.
Shared spectrum models are a potentially innovative approach to making the most of available spectrum by enabling multiple users to access the same frequencies. These models can involve either the same technology or multiple technologies sharing the airwaves, facilitated by advanced coordination systems. This approach enhances spectral efficiency and helps to alleviate the pressure on existing spectrum resources.
Dynamic Spectrum Sharing (DSS) is such an innovative approach in the world of wireless communication. DSS allows different users to dynamically share the same frequency bands, minimizing interference and maximizing efficiency. Here, we must take care to clearly distinguish the difference between Dynamic Spectrum Sharing (DSS), a specification established by the Third Generation Partnership Project (3GPP) to allow operators to use the same frequency while transitioning their users from 4G LTE to 5G versus the broader general idea of dynamic spectrum sharing. The latter can be particularly relevant for bands like 3.1-3.45 GHz, where commercial services must coexist with incumbent users such as defense systems.
The benefits of spectrum sharing also come with significant challenges. One example is the Citizens Broadband Radio Service (CBRS) in the 3.5 GHz band. CBRS employs a centralized Spectrum Access System (SAS) to manage frequency access, ensuring that devices operate without interfering with incumbent systems. This model blends licensed and unlicensed access, creating a flexible and efficient sharing environment that benefits both commercial users and incumbents. Yet, even this successful model highlights several obstacles inherent in spectrum sharing.
Spectrum sharing introduces numerous technical hurdles. Shared systems require coordination protocols, which consume bandwidth that could otherwise be used for data transmission. Power limitations to prevent interference can also impact network capacity, necessitating denser networks and higher costs. Another significant challenge is access uncertainty. In a dynamic sharing environment, spectrum might not always be available when needed, potentially degrading the quality of service. Additionally, reliance on sensors to detect incumbent activity can lead to conservative restrictions on spectrum usage.
Regulation is another critical area. Spectrum sharing requires a flexible regulatory framework that can adapt to changing usage patterns and ensure fair access for all parties. This includes developing accurate spectrum inventories to identify underutilized frequencies and creating incentives for spectrum holders to share or repurpose their bands. Ensuring that these regulations keep pace with technological advancements is crucial, but it is also a complex and ongoing task.
From an economic perspective, motivating existing spectrum holders to facilitate sharing is tricky. Financial incentives, accurate valuation of shared spectrum, and managing the administrative and technical costs of shared access are all complex issues that need to be addressed. Encouraging spectrum holders to share or repurpose their bands requires well-designed incentive mechanisms. These might include financial benefits, priority access arrangements, or other forms of compensation that make sharing an attractive option.
To navigate these challenges, we need strategic approaches that balance the needs of all stakeholders. Simplifying sharing frameworks is crucial. Whenever possible, opting for the simplest form of spectrum sharing reduces complexity and makes implementation easier. For example, static or semi-static sharing models might be more practical than fully dynamic systems, especially in the early stages. Regulatory flexibility is also essential. Regulators must create frameworks that can adapt to new technologies and changing usage patterns. This includes allowing for high-power operations to maximize coverage and capacity and setting performance benchmarks to ensure efficient use of shared spectrum.
Investing in advanced technologies and infrastructure is another key strategy. This includes developing sophisticated sensing systems to accurately detect incumbent activity and creating robust coordination mechanisms to manage shared access effectively. Additionally, developing incentive mechanisms is vital. Encouraging spectrum holders to share or repurpose their bands requires well-designed incentive mechanisms. These might include financial benefits, priority access arrangements, or other forms of compensation that make sharing an attractive option.
Spectrum sharing represents an interesting path forward for meeting the ever-increasing demand for wireless communication. By leveraging advanced technologies and creating flexible regulatory frameworks, we can maximize the utility of available spectrum and ensure that both legacy users and new entrants can coexist harmoniously. As we continue to explore and refine these models, spectrum sharing will play a pivotal role in shaping the future of wireless connectivity, keeping us connected in an increasingly digital world.
With these strategies in place, we can navigate the complexities of spectrum sharing and unlock its full potential, ensuring that our wireless networks remain robust, efficient, and capable of supporting the next generation of mobile services.
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