Opening the FR3 Band: opportunities and challenges

It goes without saying that there are several challenges with the implementation of the FR3 band. Having spoken about the bright side of the FR3 band, many questions remain unanswered. For instance, “What technological advancements will be required to make the most of the FR3 band for 6G communications?“ or “How will the FR3 band be allocated among different applications while avoiding interference with existing services? ». This section aims to respond to these questions as well as the general challenges that this band presents.

In January 2023, the « Upper Midband Software Defined Radio Workshop Report » [6] highlighted the importance of technological and policy advancements for the effective use of the FR3 band over the next decade. The report acknowledged that, while reasonably wide, the FR3 band will likely be shared due to the large number of users. Paolo Testolina, a postdoctoral research fellow at Northeastern University’s Institute for the Wireless IoT (Internet of Things), agrees with this statement in the article, stating that “spectrum sharing will be key in this band.” [4]

But what do we mean by this?

Sharing the spectrum means that different users, services, or technologies will need to share the available frequency spectrum to maximize its usage while avoiding interference. Traditionally, a frequency band is exclusively assigned to a single operator or service. Spectrum sharing allows multiple entities to coexist in the same band, improving efficiency and flexibility. The Federal Communications Commission Technical Advisory Committee (FCC TAC) has a paper that gathers the current allocations and uses in the 7.125–24 GHz band, both for the US case and the rest of the world. [16]  Together with their 6G working paper [17], they emphasize that it is indeed necessary to use segments of the FR3 band if we want to cover the increasing demands for data. The problem is that some of these segments are already in use (as mentioned before, parts of the FR3 band are used by satellite internet and military communications). There are different mechanisms to share the spectrum, namely licensed spectrum access (LSA) or dynamic spectrum sharing (DSA). However, rather than diving into the details of each, the key takeaway is that multiple different actors will need to share the spectrum when implementing the FR3. 

The authors in [14] very well detail the main challenges when deploying cellular networks in this band, including spectrum sharing. This work presents a highly valuable contribution to the studies of the FR3 band, and the challenges proposed next will be based on their contributions.

With spectrum sharing comes the prior step of spectrum sensing. This is detecting who is using the spectrum. Unlike mmWave (FR2), where the spectrum was largely unoccupied before deployment, some users occupy parts of the FR3 band today (again, by satellite internet and military communications). This makes spectrum coexistence a major challenge, requiring advanced sensing mechanisms to detect and avoid interferences.

FR3 occupies a broad frequency range (unlike traditional cellular bands that cover only a small percentage of the carrier frequency). According to [14], another major challenge is to adapt the current RF Front ends so that they are capable of sensing and  dynamically exploiting large bandwidths while optimizing directional transmissions (adjusting the transmission of a signal to improve its tx-rx performance)

They also state that given the shared nature of FR3, protection against jammers and signal disruption is crucial. Techniques mentioned before, such as advanced sensing, or others, such as spatial adaptability, will be key in ensuring reliable communications, particularly for critical 6G infrastructure. [14]