The Battle for Spectrum
By Major Christopher S. Tsirlis, U.S. Marine Corps

The Marine Corps is always looking for innovative ways to manipulate the battle space. One of the biggest challenges for Marine communicators is dealing with radio frequency (RF) spectrum. RF spectrum is a commodity in finite supply, heavily regulated both in and outside the United States. All Marines who use communication devices are users of RF spectrum whether they know it or not, and all successful tactical communications must be cognizant of it.

Military communications equipment, civilian cellular infrastructure, and countless other technologies, specifically anything with an RF emitter, must compete for available spectrum to operate. Entire government and commercial enterprises are built around proper spectrum allocations. Entire technologies rely on the enforcement and regulation of access. In the United States alone it is intensely congested.

For the Department of Defense, specific RF spectrum areas are allocated for military use only. Unfortunately, certain areas that are permitted inside the United States are not allowed in other countries. Often, and with increasing frequency, the U.S. military is not permitted to transmit on desired frequencies while outside the continental United States because this would interfere with host nations’ communications infrastructures. For legacy and future communication systems, this requires enormous capital investment to redesign tactical communications equipment - in some cases resulting in the loss of capability altogether.

Military communications fall at every point on the RF spectrum range. For example, submarines may use very low frequency (VLF) to communicate while submerged to receive radio navigation information. Most tactical radio commuideations use HF, VHF, and UHF frequencies. Almost all wideband satellite communications use super high frequency and extremely high frequency.

Certain areas of the RF spectrum have characteristics that make one type of communications technology more advantageous than others. Technology has advanced in so many ways that manipulating the finite space has spurred many different modulation techniques to pack more information in a given radio signal. Some of the most common and basic modulation techniques are amplitude modulation (AM) and frequency modulation (FM), which are used by your car stereo. More sophisticated techniques, such as code-division multiple access and time-division multiple access, allow for several devices to operate over one radio channel, much like today’s cellular phones. All RF devices have modems to manipulate the signals transmitted or received by a like device.

With the proliferation of communications devices on battlefields worldwide, the RF spectrum is becoming saturated and has made military operations more challenging to conduct. Spectrum truly is a zero-sum gain. Advances in technology are now being stymied, because larger chunks of the RF spectrum are required to pass larger amounts of bandwidth desired by military operations. The Marine Corps, along with other services, have entire military occupational specialties dedicated the issues of spectrum allocation, and their jobs are getting tougher as technology marches on.

Why RF Spectrum Counts
According to the Department of the Navy Budget Estimates for Fiscal Year 2009, the Marine Corps invested more than $1.6 billion in the past three years to upgrade and expand its communications equipment. This expansion is undoubtedly a combat multiplier for Marines conducting home-station training and combat operations abroad. The result of these actions is a better-postured, capable force for the next several years. However, some of the unintended consequences of this investment will be thousands more transmitters populating an already saturated RF spectrum space, which is already the Wild West in many respects.

Operations Iraqi Freedom and Enduring Freedom introduced several new technologies that were rapidly deployed to meet Marines’ needs in combat. Many were quickly procured and assembled by commercial vendors without regard to existing commercial or military communication frequency assignments. As a result, large investments in these technologies have gone to waste. They cannot programmatically be sustained because of the frequency ranges in which they operate. The problem extends beyond tactical communications and affects future investments in new technologies that offer many of the attributes that will be required by tomorrow’s Marines. Quite simply, there may not be enough available RF spectrum in the frequency ranges required to pursue significant advances in technology.

Meeting the Challenge
Fortunately, there are entities that recognize the DOD’s problem. More efficient use of radio spectrum is paramount when exploring new communications technologies for the Corps. Adopting technologies that creatively exploit spectrum and allow users to establish software-defined, policybased radio configurations to manipulate RF spectrum are available to the DOD today.

For example, not everyone transmits on all frequencies at the exactly same time. Many users may be geographically separated and transmitting at different power outputs that limit or negate the ability to inadvertently jam or interfere with others. If this is the case, then the capacity to use spectrum that is not currently being used, based on policy, can be established to make more efficient use of it.

The Defense Advanced Research Agency (DARPA) has developed a technology called Next Generation (XG), which uses cognitive radios that alter transmit parameters based on several variables. XG has been shown to greatly increase the efficient use of spectrum and allow users to set rules for any given spectrum environment. This is especially useful for urban areas where radio frequencies become overcrowded and interference happens most often. Simply, Marines could move into any operating environment with spectrum-policy presets established on their tactical radios that would only operate on frequencies not in use or where there is no known interference. Once a radio device transmits on a frequency used by tactical units, the radios would quickly sense a disruption in the RF environment and switch to another frequency not currently in use. Since all countries manage their spectrum allocations differently, Marines could avoid problems and not worry about receiving host-nation approvals to transmit in a particular spectrum space.

Another attribute of this technology is its inability to jam or intentionally interrupt such transmissions. An adversary most likely cannot direct enough energy on enough channels long enough to keep up with spectrum-sensing equipment. Most important, XG technology could greatly mitigate our ability to jam ourselves with the wide deployment of counter radio-controlled LED electronic warfare jammers on most tactical wheeled vehicles.

Most of the Marine Corps’ ground tactical radios can transmit from 3MHz to 512MHz. At first glance this would appear to be a large chunk of the spectrum. Unfortunately, internationally many countries have different frequency assignments in these areas, a fact that often interferes with our tactical radio assets. At the further end of the RF spectrum, many high-bandwidth data applications require frequency ranges in the gigahertz range, which host countries use for commercial infrastructure, and thus negates many of the broadband tactical assets we currently rely on. Using policy-based cognitive equipment would better ensure tactical communications are established and maintained without interference.

Squeezing More Out of Nothing
Ordinarily, once a piece of spectrum is being used, it can’t be used by anyone else. If it is not in use, there is a form of technology to pursue that may take advantage of this. We usually want to avoid interference in communications. There may be a way to develop technology to address spectrum interference by transmitting and receiving a signal simultaneously on a preoccupied channel without negatively affecting both power and timing controls, effectively using the interference to boost or strengthen a desired signal, thus manipulating the spectrum to fit our needs.

Our dependence on radios, satellites, unmanned aerial vehicles, and other RF emitting devices continues to increase, and where and how these technologies transmit is important for every Marine who relies on them. Our current investments must actively support new ways to manipulate this finite resource. The creative use of spectrum should guide all future procurements of tactical communications equipment. As Marines, we must understand how to successfully operate in every battle space. RF spectrum is another one we cannot avoid.

About the Author
Major Tsirlis is the operations officer for 8th Communication Battalion, Second Marine Headquarters Group, Second Marine Expeditionary Force, Camp Lejeune. He has more than 22 years of service.

Reprinted from Proceedings with permission; Copyright © 2012 U.S. Naval Institute www.usni.org.

U.S. Marine Corps

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