Fifth-generation (5G) cellular offers many advantages for military and government communications. By speeding data rates and boosting bandwidth, it paves the way for new military as well as commercial applications. Examples include high-definition video, such as three-dimensional or augmented reality; ultra-reliable, low-latency communications; and massive machine-type communications. For aerospace defense, improvements in such applications promise enhancements in areas ranging from intelligence, surveillance, and reconnaissance (ISR) through command and control (C2) and supply chain/procurement. However, concerns remain over the risks of shared spectrum between 5G and other applications.
Issues could arise due to the sharing of spectrum in the U.S. between the 3.1-3.5 GHz Federal and non-Federal radio location services, explains Raymond Shen, Director of 5G and Spectrum Solutions for Keysight’s Government and Aerospace Defense solutions group. In that case, the Federal services have the primary allocation. Similarly, both the C-band and extended C-band are used for fixed satellite services in addition to 5G. Potential conflicts may arise between 5G and radar/satellite allocations—a problem known as coexistence.
What Is Coexistence?
In this case, two or more signals have the right to occupy the spectrum in question. Usually, however, one has priority. In coexistence conditions, radar will typically take priority. 5G then must shut off or move off frequency, according to Shen. For satellite systems, the risks from 5G interference are more severe. Satellite ground stations have very sensitive front ends. As a result, receiver front ends are highly susceptible to external interference, which could arise from 5G base stations.
Currently, Shen notes that the 5G operating bands are grouped into frequency ranges 1 (sub 6 GHz) and 2 (around 28 or 39 GHz, also known as millimeter wave). Many new operating bands are being allocated for 5G, with more expected in the future. The bulk of new trials and initial deployments focus on the 3.6 to 3.8 GHz and 26 to 27.5 GHz bands. Immediately, when considering the use of these bands for 5G, overlaps arise in the possible satellite downlink frequency range of ground stations from 3.4 to 4.2 GHz. Potential conflicts also arise in uplinks from 27.5 to 29.5 GHz and fixed satellite service (FSS) downlinks from 37.5 to 40 GHz.
Some of these coexistence issues are unique to the U.S. According to “National Security Implications of Fifth Generation (5G) Mobile Technologies” from the Congressional Research Service, “Although Department of Defense (DOD) uses certain millimeter-wave frequencies for high-profile military applications such as Advanced Extremely High Frequency satellites that provide assured global communications for U.S. forces, it extensively uses sub-6 frequencies—leaving less sub-6 availability in the United States than in other countries. The Defense Innovation Board (DIB) advised DOD to consider sharing sub-6 spectrum to facilitate the build-out of 5G networks and the development of 5G technologies used in the sub-6 band.”
The near-term solution to these challenges is greater spectrum sharing, which makes coexistence issues a more likely risk. To learn more about the potential impact of coexistence on radar and satellite systems, register for our free Keysight University course taught by Raymond Shen: Coexistence of 5G with Radar and Satellite