Software Defined Radio Use Case for Aerospace & Defense

From time to time, disruptive technologies emerge that revolutionize existing systems and processes across various industries. One such technology is software-defined radio (SDR), an RF communication technology that is used for countless applications in numerous industries.

This article discusses the use of SDRs in defense applications. Defense applications encompass a wide range of use cases such as radar, military missile guidance, tactical radios, unmanned vehicle control, electronic warfare, and satellite communications. Figure 1 illustrates some of these examples.

Radio Communication Demands of the Defence Industry

One of the major applications of radio communication in defense is actual communication, ie., the exchange of messages. Radios are used to carry out missions, provide command and control, and generally exchange messages among various segments of the military on all levels. Communication is required between the military authorities, infrastructure, stations, vehicles & aircraft, warfighter information network-tactical (WIN-T) platforms, unmanned vehicles, intelligence units, troops, and several other military entities. These entities continually exchange information in a wide spectrum of operations, including attack, defense, intelligence, reconnaissance, and search & rescue. For all these exchanges, communication is carried out using transceiver radios over various frequencies, depending on the operation.

Figure 1: Modern defense radio communications are shown.

Modern defense communications are also employed in streaming real-time video and audio data over a network. This process is broadly applied in military surveillance, intelligence, reconnaissance, and situation awareness. High-efficiency video coding (HVEC) plays a significant role in making these operations possible. HVEC is a video compression standard that offers high data compression at sustained high resolutions, allowing large amounts of audiovisual data to be compressed for low-latency transfer. Depending on the operation, IP streaming, line-of-sight, or satellite communication technologies may be used.

GNSS (Global Navigation Satellite Systems) play crucial geolocation, tracking, and navigation roles in defense. A GNSS is a radio-based system that employs satellite constellations to determine the position of an entity on earth accurately. One of the many uses of GNSS in the military is precise geolocation. These systems enable users to accurately locate enemy positions, friendly facilities, and other areas of interest. They also make it possible to identify the position of troops for operations such as search and rescue, providing backup or medical assistance, and mission planning. GNSS also serve in projectile and unmanned vehicle guidance. Another vital use of GNSS in the military is navigation. This includes land, sea, air, and subsea-based navigation. These systems are especially necessary when navigating through unfamiliar or hostile territory.

Increasingly complex wireless protocols have led to increasing electronic warfare sophistication. This brings us to yet another defence application of radio systems: electronic warfare and signal intelligence. Signal jamming, interference, intrusion, and interception are some of the attacks that can be carried out against RF systems. These cyberwarfare attacks can be prevented using advanced RF solutions, such as RF shielding and frequency hopping. Furthermore, there is signal intelligence, an aspect of electronic warfare that has vast applications. In signal intelligence, signals from known and suspected hostile sources are intercepted for analysis and data extraction.

Other applications of radio communication systems in defense include radar detection, data communication, and remote monitoring and control.

A close analysis of these military applications will reveal that they each involve various forms of radio technology. For example, intelligence involves satellites, GNSS, and radar systems, while other operations involve all of the radio systems discussed.

With so many defense applications by different militaries around the world, there is the possibility of over congestion in radio bands. International Telecommunication Union (ITU) radio regulations explicitly make provision for military uses of the radio spectrum. Further allowance is provided for exceptional cases. This allowance is extended to the North Atlantic Treaty Organization (NATO). NATO further regulates and harmonizes radio frequency usage among member countries through the NATO joint civil frequency agreement (NJFA).

There are various defense waveforms currently employed in military applications. Some of these are as follows:

The European Secure Software-defined Radio (ESSOR) Military high data waveform (HDR WF); Commercial SATCOM waveforms: this includes bandwidth-on-demand MF-TDMA military waveform (a point-to-point highly efficient FDMA waveform) and Frequency Hopping Spread Spectrum (FHSS) waveforms; and tactical data links: Link 16, IDM, Link 22, JREAP, SADL, Link 11 and VMF, etc.

Direct-sequence spread spectrum (DSSS) and Gaussian-based waveforms: these are very attractive modulation techniques for military communication systems, mainly due to their resistance to interference and low probability of detection.

In addition to these, there are dense mesh network comms such as NATO STANAG (standardization agreement) signals. Figure 2 contains some STANAG waveform spectrums.

Figure 2: STANAG waveforms are regulated by NATO.

Important Radio Communication Parameters and Capabilities

There are certain requirements that RF devices for defense must meet and capabilities they must have, to be suitable for use in defense applications.

A significant number of military operations involve different levels of mobility. In such operations, the SWaP (Size, Weight, and Power) of the radio device are crucial considerations. Radio devices are often required to be compact, light-weight, and have low power consumption. Note that SWaP requirements will vary depending on where the radio is deployed, but low SWaP is always preferred.

Another essential requirement of radio devices used in defense is versatility and interoperability. As we've seen, there is a wide range of military operations that are carried out in different bands, with different waveforms and using different radio configurations. Multiple operations may need to be performed at one location over a period, sometimes simultaneously. However, it is impractical to have different radio devices for each operation. This is why it is essential for defense radio systems to be capable of producing multiple waveforms and operating over multiple bands & in multi-modes.

Furthermore, military data is very often extremely sensitive and there can be severe implications from it landing in the wrong hands. However, during transmission, data is susceptible to interception. This makes it vital for the transmitting and receiving radios to have advanced cyber security capabilities and electronic countermeasures such as ECM detection, pulse compression, frequency hopping, sidelobe blank, and radiation homing.

SDRs for the Defence

There are various types of radio devices that may be employed in defense. However, none of these meet the high requirements that are vital in defense as sufficiently as SDRs. Their inherent capabilities align with the highly technical radio demands of defense.

SDR is a radio communication device that performs certain radio tasks, such as signal modulation, demodulation, and processing, using software instead of hardware as in traditional systems. SDRs contain a radio front end (RFE) and digital backend. The RFE contains the receive (Rx) and transmit (Tx) functions, to handle signals over a large tuning range on multiple independent Tx and Rx channels with dedicated DACs/ADCs. Per Vices offers the highest- bandwidth SDR available with up to 3 GHz of instantaneous bandwidth.

An SDR's digital backend contains an FGPA with on-board DSP capabilities for modulation, demodulation, upconverting, downconverting, signal processing, and data transfer, as well as configurable and upgradeable capabilities for the latest radio protocols, DSP algorithms, etc. SDRs are often used with host systems for further signal processing and man-machine interfacing.

Legacy systems are still widely used in military and defense but are slowly phasing out as they don't meet the rising technology demands that the far more efficient and functional SDRs are capable of.

Most legacy and enduring radio platforms are non-digital and operate on analog infrastructure. Such platforms offer consistency of design and maintainability at the expense of improved performance over time. While SDRs offer the best of both worlds and are becoming the standard in modern defense comms, certain legacy systems are still mission-critical. In such scenarios, SDRs can be seamlessly integrated into these existing systems. These devices are very easy to integrate into legacy defense comms systems and are able to reduce the amount and complexity components in the system due to the capability of an SDR to embed various components in software (waveform storage, modulation, encryption, downconverting/upconverting, etc).

SDRs meet the various hardware requirements of defense systems. One of these is easy connection to other hardware such as antennas and amplifiers. Also, as earlier stated, military operations usually involve various simultaneous radio communication processes. These processes usually take place over different frequencies. SDRs have MIMO capabilities (Multiple Input Multiple Output) via multiple radio chains. This means that a single SDR can be used to perform all the processes involved in an operation or even different operations simultaneously. SDR is capable of simultaneous transmission and reception on two separate bands. One band can be used to support local mission communications, and another to relay the communications of other missions across the network.

Furthermore, SDRs possess frequency and phase stability capabilities. This is an important aspect of a radar system and provides phase coherency across multiple radio chains.

SDRs also have a high-frequency tuning range. This is required for channel spacing, wide band tuning, and to support communication over the various bands used in defense communications. In addition, SDRs have jamming and interference prevention capabilities necessary for electronic warfare and to ensure channels remain unobstructed. They also have low noise figure/high sensitivity, required to ensure you can pick up weak signals.

Massive amounts of data usually need to be transferred in military operations. This requires communication systems to have high data throughput. Again, this requirement is met by advanced SDRs with quad 40 Gbps qSFP+ ports, upgradeable to 100 Gbps.

SDRs also meet digital backend requirements for defense. High-performance SDRs use FPGA and DSP resources to perform extremely fast and parallel computations and handle the huge amount of data using high-performance network interface cards and 100GBASE-R qSFP+ transceivers.

They are able to provide customized encryption/cryptography of secure data, perform compression, and encode/decode data for videos, voice, images, etc. Figure 3 shows a representation of the architecture used for encrypting audio. These capabilities ensure efficient and extremely secure data transmission. SDRs are also capable of modulation/demodulation of transmitted/received signals as well as digital down-conversion (DDC) and digital up-conversion (DUC) using CORDIC based mixers.

Figure 3: FPGA Basic Architecture of Secure/Encrypted Voice is shown.

As an example, it’s possible to use a software-enabled noisy channel avoidance algorithm in an SDR, which always reverts to a known good frequency. Instead of continually searching for clear frequencies, this algorithm increases the frequency-hopping synchronization probability in high noise and jamming conditions.

In addition to these characteristics, SDRs also offer adaptability. In traditional systems, each radio operation requires dedicated systems. SDRs, on the other hand, are extremely versatile and can reconfigure, whenever necessary, using simple software updates.

SDRs improve interoperability in tactical communications as different radios can use the same waveforms, bands, or carrier frequency. This means that one can reuse the same software developed for communications on different radios. Software is also behind other beneficial SDR characteristics such as compatibility and upgradability, ensuring that these devices are always up-to-date with the latest technologies.

Recent developments in SDRs for defense include programs that aim to increase the advancement and adoption of SDR in defense. One of such programs is European Secure Software Defined Radio (ESSOR) by OCCAR (Organisation Conjointe de Coopération en matière d'Armement / Organization for Joint Armament Co-operation).

According to OCCAR, "The main scope of this project is to provide architecture of Software Defined Radio (SDR) for military purposes and a military High Data Waveform (HDR WF) compliant with such architecture, thus offering the normative referential required for development and production of software radios in Europe. In addition, the project will deliver guidelines which are related to the validation and verification of waveform portability and platform re-configurability, setting up a common security basis to increase interoperability between European Forces."

Conclusion

SDR is fast becoming the go-to solution for radio systems in defense and various other industries.

Per Vices has extensive experience in designing, developing and building highly advanced SDRs for numerous uses in military and defence, scientific research and industry applications.

Click here to browse Per Vices SDR products listed on everything RF.