{Editor’s Note: This article was contributed by Dr. Brett Walkenhorst, director of R&D and business development at Silvus Technologies. Dr. Walkenhorst discusses how commercial waveforms and technologies and the development of Low Probability of Interception/Low Probability of Detection (LPI/LPD) waveforms. and anti-jam capabilities are integrated into the field. Read Dr. Walkenhort’s article below.}
Although invisible to the eye, the airwaves above today’s battlefields are often as congested as the terrain beneath them. The US military gains a major strategic advantage by using the electromagnetic spectrum for communications, but transmissions from commercial and military radio frequency systems are sucking up our precious bandwidth.
The spectrum is not only congested, but contested. Adversaries are constantly struggling to disrupt or damage our communications, whether by denying us access to the spectrum through electronic attack or passively detecting and geolocating our systems. Whether the spectrum is congested or contested, however, the consequences are the same: the lives of US forces are at risk and key tactical or strategic information may be compromised.
But recent developments in advanced radio networks give our soldiers greater access to secure, stable and covert communications in future conflicts.
DARPA planted the seeds of mobile ad-hoc network (MANET) radios in the 1970s, while other companies and research subsequently helped make the technology feasible. Thus MANET systems like the one offered by Silvus Technologies became available to the US military. It provided a robust multi-antenna software-defined radio platform that hosted an OFDM-based waveform called Mobile Networked MIMO (MN-MIMO). MIMO processing greatly improves throughput, reliability and range.
MIMO processing helped create a set of critical new or improved radio features: anti-jamming (AJ), low probability of interception (LPI), and low probability of detection (LPD). These features ensure that radios cut through the noise of congested and contested environments while remaining stealthy. The development of these technologies will lead to huge advances on the battlefield in the next few years.
Anti-Jam
With their MIMO arrays, radios like the StreamCaster are able to eliminate interference by pointing a null at a jammer. This happens through an additional software module called MANET-Interference Cancellation (MAN-IC). The MAN-IC listens to the spatial signature of a jamming signal, then calculates a set of antenna weights that reset that spatial signature. This method has proven to be extremely powerful, giving up to 30 dB of constant attenuation in field trials. The module also has the secondary benefit of improving LPI/LPD performance. By using a friendly masking signal, radios can operate on the same frequencies by resetting the friendly “jamming” signal. The friendly signal overpowers the much weaker communication signals of these radios, hiding those weaker signals from the enemy.
Another module, called MANET-Interference Avoidance (MAN-IA), allows military radios to avoid interference by hopping to a different frequency band. The system monitors multiple frequencies in different bands using the MIMO degrees of freedom available in radios. After radios detect a jamming signal, each radio independently selects the next best channel. The regrouping algorithm ensures that all radios converge on a common frequency in less than one second.
Low Probability of Interception/Detection (LPI/LPD)
In a MANET, radios typically operate at maximum power to ensure high throughput and high network efficiency. But this leads to sub-optimal LPI/LPD performance as the higher power is more easily detected by adversaries. This led to the development of a module called MANET-Power Control (MAN-PC), which minimizes the transmit power of the radio while maintaining the desired throughput. Field tests show a 70 percent reduction in the distance to the detector before the signal is detected.
Working within the U.S. Army’s Secure Communications for Manned and Unmanned Teams (PCM), Silvus recently developed a new physical layer waveform. Although the details of this waveform are confidential, field tests have shown that it significantly improves LPI/LPD performance.
next steps
Each of the modules described here offers advantages in the AJ/LPI/LPD space. Until now, they have largely operated in isolation. Abilities will now be able to work together. Since the technologies share some goals, their operation must be adjusted so that they do not conflict with each other. The settings also ensure that the radio selects the best mode or combination of modes for the best possible performance. To this end, next in the works is a machine learning algorithm to control the selection and operation of the different modes while optimizing the throughput, reliability and performance of the LPI/LPD in various hostile environments.
As much as advanced weapons and well-thought-out strategy, our military relies on clear, unobstructed and reliable radio communications. The expectations and needs of warfighters described above are shaping the future of radio communications in the modern battlespace. Machine learning combined with advanced signal processing will enable robust, covert communications that keep us ahead of those who seek to harm us.
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