The presence of autonomous vehicles and weaponry in the military is set to grow at a significant rate, spurred by funding from the Department of Defense (DOD) in recent years. In 2021, the Pentagon received $7.5 billion to fund unmanned systems across the Air Force, Army and Navy.1 Generally speaking, these are positive innovations that help the U.S. keep pace with the military advancement of other world powers, such as Russia and China, but they are not without significant risks to national security if the communication infrastructure supporting them is insufficient.
Unmanned vehicles and weapons rely heavily on continuous real-time communication, in addition to radar/LiDAR, as well as other passive sensors that are deployed without human involvement. Operational integrity is at risk if there is any communication failure or adversarial intervention based on emission profiles. Even autonomous mission-oriented apparatus that does not emit information, for the sole purpose of avoiding detection, relies on receiving signals. While always important, communication has never been on the “hot seat” quite like it is now when it determines whether our autonomous defenses work reliably. Figure 1 shows a portion of the U.S. Naval fleet, a military domain containing some of the biggest sensor platforms in existence.
Exacerbating the issue are the high frequency RF signals that provide the low latency, high bandwidth communication necessary for automation. High frequencies tend to be less resilient and more easily disrupted by outside elements, of which there are many in military environments. This article examines the state of military communications and why radio frequency over fiber (RFoF) is important to safeguard autonomous military systems.
MILITARY COMMUNICATION AT A GLANCE
Military communication relies on a wide spectrum of RF bands, each serving specific purposes tailored to the demands of modern warfare. The choice of RF bands varies depending on factors such as geographic location, technology availability and operational requirements. What follows is a general overview of key RF bands used in military communication and their typical applications:
Ultra-High and Very High Frequency (UHF/VHF) Bands
The UHF (300 MHz to 3 GHz) and VHF (30 to 300 MHz) bands, often associated with “walkie-talkie” style communication, are essential for ground troops, vehicles and aircraft. VHF radios excel in line-of-sight communication over open terrain, providing reliable voice and data transmission. In contrast, UHF radios are preferable in congested or urban environments due to their shorter wavelengths and better signal penetration capabilities. UHF satellite communication facilitates secure and encrypted data transmission among military units, including ground stations, ships and aircraft.
L-Band (1 to 2 GHz)
L-Band is used for satellite communications, GPS and certain radar systems, offering a versatile spectrum for military applications. The ability of L-Band networks to penetrate atmospheric conditions and foliage enhances utility in scenarios where communication resilience is crucial. This makes it suitable for military command and control, intelligence gathering and communication of strategic information.
S-Band (2 to 4 GHz)
S-Band frequencies support long-range surveillance and tracking radars, as well as select satellite communication systems. Some overlap exists with Wi-Fi and cellular bands, as well as certain GPS applications.
C-Band (4 to 8 GHz)
C-Band is a versatile frequency range employed in radar systems, satellite communications and various weather radar applications. It offers a balanced compromise between the need for high-resolution and atmospheric penetration.
X-Band (8 to 12 GHz)
Military radar systems rely on X-Band for tasks like target identification, tracking and missile guidance. This band provides exceptional resolution and accuracy to improve situational awareness.
Ku-Band (12 to 18 GHz) and Ka-Band (26.5 to 40 GHz)
These higher frequency bands are crucial for military satellite communications, offering enhanced data transfer rates compared to lower frequencies. Ku-Band is widely used for communication between different U.S. military units.
While these RF bands are arguably the most common, frequency allocations and standards in military communication can vary globally and evolve with technological advancements. Additionally, classified or encrypted communication further complicates the disclosure of precise frequency bands and their applications.
THE BALANCING ACT OF DIGITAL AND ANALOG COMMUNICATIONS
The military has relied on communications since its inception. Even with network evolution, at the heart of contemporary military communications lies the fact that the nature of transportation over RF bands is analog. The receiver of the signal must have a wide dynamic range, so even systems deploying down-converters must have an analog transport section.
Digital communication systems are celebrated for their precision and reliability, boasting error correction capabilities, adaptability to various data types and better spectral efficiency. However, converting RF signals into digital formats introduces certain complexities. These conversions can lead to latency and jitter, along with creating vulnerabilities such as unauthorized interception, commonly known as “listening,” by nefarious actors.
In contrast, analog technology is the primary medium for propagating signals through the air. Autonomous non-tethered military platforms, such as drones and unmanned aircraft, rely on analog components for receiving and transmitting signals. Since there is no need for conversion between endpoints and the transport medium, there is less latency and it drastically reduces the chance of detection. While cabled communication via fiber or CAT cables is principally digital, coaxial and waveguide transport is almost always analog. Each technology has its strengths and weaknesses, making their combination essential for effective and secure communication.
A persistent concern in military communication is the potential detection of electromagnetic radiation by adversaries. To enhance survivability, military strategists often opt for remote antennas, distancing them from sensitive command centers or main platforms. For instance, an unmanned ship may house its processing and command center below deck while needing to communicate with remote antennas on its exterior. This practice creates a foundation for resiliency, as it reduces the risk of mission failure due to antenna damage or compromise. It is also the reason that RFoF is so critical for autonomous military systems.