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Full-Duplex Tactical Informationand Electronic Warfare Systems

Karel Parlin, Taneli Riihonen, Vincent Le Nir, Mark Bowyer, Thomas Ranstrom,Erik Axell, Borje Asp, Robert Ulman, Matthias Tschauner, and Marc Adrat

Abstract—Electromagnetic spectrum is a scarceresource becoming increasingly congested as in-formation technologies advance. This is particu-larly concerning in the military domain, wherefrequencies are contested for by both CIS andEW systems. The success of NATO activitiesnecessitate mission-critical communications withincreasing throughput, hidden from enemy sig-nals intelligence, robust against electronic attacks,and compatible with host EW tasks. In response,the NATO STO IST-175 research task group isworking on the disruptive concept of FD radiotechnology to address those challenges. MilitaryFD radios promise to increase the spectral effi-ciency and robustness of CIS and improve theperformance of EW tasks through simultaneousoperation and multifunctionality.

INTRODUCTIONTactical communication and information sys-

tems (CIS) utilize electromagnetic (EM) spec-trum for sharing voice and data between battleunits. At the same time, electronic warfare(EW) systems aim at achieving superiority inuse of the same EM spectrum. Inevitably, CISand EW affect each other, and consequently,both disciplines of military operation can ben-efit from coordinated use. This is especiallyevident as bandwidth requirements for CISgrow hand in hand with other battlefield tech-nological advancements and congestion of EMspectrum becomes increasingly problematic.

Consequently, military radios must use spec-trum efficiently to fulfill the communicationneeds without compromising reliability require-ments [1]. Thus, the outcome of future militaryoperations will depend on information servicesbeing provided with increased data throughput,strict timing requirements, robustness againstadversarial EW, and compatibility with hostEW systems. However, in practice compati-bility between CIS and EW systems is oftendifficult to achieve because both may requireto operate on the same frequency bands. Thisis, for instance, almost always true when con-sidering compatibility between interrelated EWtasks such as signals intelligence and jamming.

Karel Parlin is with Rantelon; Taneli Riihonen is withTampere University; Vincent Le Nir is with the BelgianRoyal Military Academy; Mark Bowyer is with AirbusDefence & Space; Thomas Ranstrom, Erik Axell, andBorje Asp are with the Swedish Defence Research Agency(FOI); Robert Ulman is with the US Army Research Office;Matthias Tschauner and Marc Adrat are with FraunhoferFKIE.

Similarly to most radio technology, CIS andEW technology have evolved into their currentstate with the assumption that same-frequencysimultaneous transmit and receive (SF-STAR)operation, also referred to as in-band full-duplex (FD) operation, is intractable. This tech-nological limitation is a significant contributorto spectral congestion problems and ineffec-tiveness to carry out simultaneous CIS andEW tasks. However, recent research is forcinga paradigm shift as this assumption is beingoverturned by FD radios [2].

In the civilian domain, many challenges re-lated to FD radios have already been solvedand the technology is seriously being consid-ered for inclusion in next generation wirelesscommunication standards [3]. However, currentsolutions cannot be directly adopted for the mil-itary domain because of significantly differentoperational conditions like lower carrier fre-quencies, higher transmit powers, and narrowerbandwidths. Overcoming these challenges andtaking advantage of this paradigm shift in themilitary domain can result in technologicalsuperiority in the battlefield over conventionalhalf-duplex (HD) radio technology as illustratedin Fig. 1.

As testament to that, the NATO Scienceand Technology Organization (STO) IST-175research task group (RTG), which succeedsIST-ET-101 exploratory team [4], is workingon introducing FD radio technology into themilitary domain, in order to enhance both CISand EW applications. The RTG’s aim is to firstoutline the specific applications and use casesfor FD technology in the electronic battlefieldand subsequently to solve some of the military-specific challenges related to implementing FDradios for those applications. In this article, wedescribe the scenarios focused on and capabil-ities developed within the RTG.

FULL-DUPLEX RADIO TECHNOLOGYTo date, most radio technology (civilian and

military) is of HD type, meaning that simulta-neous transmission and reception on the samefrequency is impossible. This is because whena radio is transmitting a signal, it inevitablyreaches the same radio’s receiver, as illustratedin Fig. 2, causing self-interference (SI) thatdrowns out any signals-of-interest transmittedby other distant radios. Until recently, this lim-itation was considered too ambitious to over-come, and has therefore been circumventedand hidden from the user by employing ei-ther frequency-division duplex (FDD) or time-

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Radioshield

Relay

Com

m.

SI

Detection

Jamming

SI

Hidden node

Two-waycommunication

Remotecontrol

Adaptivepower control

Securekey exchange

Mixedinterception

SI

SI

Figure 1. Conceptual use of military FD radios in the battlefield for enhanced CIS and EW.

division duplex (TDD) operation in almost ev-ery wireless application. Thus, different fre-quencies or time slots are used for transmissionand reception.

The principal difference in FD radios com-pared to HD radios is addition of SI can-cellation methods, shown in Fig. 2, to sup-press different types of SI that inevitably leakinto the receiver path. Ideally, SI would becancelled digitally, however, because of thedynamic range limitations in analog-to-digitalconversion, digital cancellation needs to be ac-companied by analog methods [3]. The analogcanceller typically needs to be designed fora specific carrier frequency and it delays andfilters a copy of the transmitted signal so thatthe copy is in opposite phase to the SI, thussuppressing the SI. The digital canceller isfrequency agnostic and works under similarprinciples as the analog canceller, addition-ally modelling nonlinearities that affect the SI.Altogether, both stages prevent powerful SIfrom overpowering the typically weak receivedsignal-of-interest. Current state-of-the-art FDradio prototypes, including those that have beendeveloped by RTG members, achieve SI can-cellation in excess of 100 dB [4] and providereasonable communication conditions in non-military wireless applications [3]. The most ob-vious advantage of FD radios is to double thecapacity in a point-to-point communication— which alone is a significant advantage overFDD and TDD operating modes.

For large wireless networks, such as tacticalmobile ad hoc networks (MANETs) [5], theadvantages of FD operation can be equallyinfluential. Although FD operation inherently

increases interference within a network asthe number of simultaneous transmissions in-creases, the overall throughput of an FD net-work is improved compared to an HD network,so long as sufficient SI cancellation is providedand a medium access control protocol designedfor FD operation is used [6].

Throughput is not the only aspect improvedby FD operation in wireless networks. Tac-tical MANETs are expected to provide com-pletely self-forming, self-healing, and decen-tralized platforms for tactical units to joinand leave swiftly; particularly in highly time-varying topologies, typical where battlefieldinfrastructure is lacking or inaccessible dueto rapid deployment [1]. Such MANETs facenumerous challenges, including cognitive spec-trum usage, relaying, and hidden nodes, whichall can be addressed with FD operation.

When considering EW aspects, consequencesof FD radio technology can result in an equiv-alent of a wireless superpower, especially asFDD and TDD have severe limitations for manyEW tasks, such as detection and neutralisa-tion [7]. The former, FDD, is almost neverconsidered for combined detection and neutral-isation, because that would mean detecting andneutralising on different frequencies. When sig-nals of interest fall into either frequency range,only one of two outcomes can arise — detectionwithout neutralisation or neutralisation withoutdetection, neither of which is desirable.

Therefore, TDD is typically used, forcinga trade-off between situational awareness andneutralisation efficiency. By dividing detectionand neutralisation operations in time, situationalawareness and neutralisation efficiency depend

Circulatorleakage

Antennamismatch

Near fieldreflections

–Analog

canceller

Σ+ Low-noise

amplifier

Power amplifier

–Digital

canceller

DAC

Σ+

ADC

Figure 2. General architecture of FD radios, with passive, analog, and digital cancellation of SI. Digital-to-analog converteris abbreviated as DAC and analog-to-digital converter as ADC.

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on the portion of time spent in either state.This is where the FD radio technology excels— it removes that trade-off and opens theway for combining different EW tasks on thesame frequency simultaneously. Furthermore,EW tasks can be combined with CIS, introduc-ing EW capabilities to devices that are classi-cally used only for communications. Thus, FDradio technology is a key enabling technol-ogy to develop multifunction military radioscombining CIS and EW functions, which haslong been coveted by defence forces [8].

One such case is jamming and signals in-telligence, where by using HD radio technol-ogy, it is impossible to simultaneously achievecontinuous jamming efficiency and situationalawareness. Thus, neutralising hostile wirelesscommunications is often approached in an all ornothing way, through jamming the entire enemyfrequency band. This is a robust approach giventhe limitations of modern HD radio technol-ogy. However, it requires a lot of power tocover large frequency bands and is also likelyto damage friendly communications within thecovered frequency bands.

Alternatively, with FD radios, jamming en-ergy can be directed on demand to target onlythe radio frequency (RF) communications usedby the enemy, hence making sure that collateraldamage is minimized. This is possible becauseFD technology allows simultaneous jamming,analysis of jamming effectiveness, and to senseif the jammed signal changes its operationmode. Consequently, jamming can be adaptedto be more effective and focus only on themalicious RF systems. Not only do FD radiosgive an advantage to defensive technologies,they also benefit attack-minded applications,which itself is motivation not to forgo this radiosuperpower.

ENHANCED COMMUNICATION ANDINFORMATION SYSTEMS

Within the first of its two demonstratorgroups, the RTG is working towards apply-ing the FD radio technology for augmentingCIS. When enhancing tactical CIS, the aimis similar to civilian FD applications. In bothcases the objective is, ideally, to double spectralefficiency. This is a significant advantage overconventional HD radio technology, especiallywhen considering how congested and limitedmilitary spectrum allocations are.

The main differences between the militaryand civilian domains arise in frequency bandsused and battlefield operating conditions. Manymilitary communication systems operate at ei-ther high frequency (HF), very high frequency(VHF), or low ultra high frequency (UHF)band, with higher powers and narrower band-widths than typical in high UHF band, wherethe FD radio technology has so far mostly beendemonstrated to be feasible with lower powersand comparatively wider bandwidths.

While 100 dB of SI cancellation is consid-ered sufficient for many civilian applications, amilitary FD radio needs to provide additional50 dB or more of SI cancellation. Due to the

lower carrier frequency, the analog cancellercircuit needs delay lines in the order of metersof electrical wavelength leading to challenges incompact design. Furthermore, with respect totypical tactical communication scenarios, fastanalog canceller tuning is needed. However,due to the narrow signal bandwidth, the SIestimation can only be provided at very lowrates, which subsequently leads to degraded SIcancellation.

Aside from these challenges, the improve-ment in wireless network throughput resultingfrom FD operation may fall short of ideal dueto the typically asymmetrical data flow, imper-fect SI cancellation, and increased inter-nodeinterference. Nevertheless, as discussed next,FD radio technology has potential to improveseveral other aspects of CIS networks, whichin turn can enhance situational awareness andnetwork security.

COGNITIVE RADIO NETWORKS

One of the most promising technologiesconsidered for coping with the limited natureof RF spectrum is dynamic spectrum sharingthrough cognitive radio (CR). The fundamentalidea behind CR is to opportunistically shareRF spectrum as opposed to operating withinpredetermined frequency and time spaces. Thisallows better use of spectral resources basedon operational needs. However, CR relies firstand foremost on having an overview of thespectrum usage before deciding to use anyspectrum areas. It is also beneficial to retainthat overview during transmissions, in orderto continue learning from the environment andkeep adapting to it, e.g., to detect multi-accesscollisions or adversarial intervention.

It has been shown that FD-enhanced CRoffers higher throughput, higher probability ofdetection and reduced sensing time, all of whichempowers CIS [6], [9]. In tactical scenarios, CRexpands beyond just dynamic spectrum sharingas CRs can work around adversarial electronicattacks, especially when enhanced with FDcapabilities. For example, FD enables swift andadaptive power control to lower the probabilityof detection, or enables to detect a jammingattack from an adversary, while simultaneouslytransmitting tactical communications to an allyon the same frequency channel [10]. Successfuldetection of electronic attacks enables the radioto take appropriate countermeasures against theattacks, e.g., switching the channel frequency.A combination of cognitive and FD capabilitiesenables truly multifunctional military radioscapable of efficient fusion between CIS and EWbased on operational needs.

Moreover, cognition is often envisioned tobecome a capability of the network, not justbeing limited to the individual radio. As such,a CR network can build local knowledge aboutenvironment (spectral and topological) to reachoverall network goals. In military applications,cognitive networking capabilities are especiallyof interest as a mechanism for intelligentlyadapting to the dynamics of the theater of warand coping with the temporal nature of tactical

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networks [11]. Through cross-layer manage-ment and information exchange between alllayers of the OSI protocol stack, the spectruminformation gathered by an FD-enhanced CRcould be propagated throughout the adaptivetactical network to improve resilience, lowerprobability of detection, and increase through-put of tactical end-to-end communications.

RELAYING

Information flow from data sources to con-sumers in the modern battlefield is crucial to thesuccess of military operations. However, in thehostile environments where military networkstypically operate, provision of robust and de-pendable connections is a significant challenge.The entirety of CIS systems is often complex,consisting of scattered networks across the bat-tlefield from tactical edge networks (TENs) tothe theater of war. In order to tackle thoseissues, self-organizing and information-centricnetworking paradigms have been recently pro-posed [12]. Further, integral to self-organizingand information-centric networking is the useof relays, sometimes referred to as gateways,between the different scattered networks. Tradi-tionally, using conventional HD radios, relayingis achieved by TDD or FDD, where the relayhas receive and transmit time slots or frequencychannels.

Compared to HD relays, FD operationpromises to increase relaying channel capacity,as a single frequency channel is used simulta-neously for receiving and forwarding [6]. Addi-tionally, FD radio technology enables relays toseamlessly combine legacy CIS networks andsystems that are not designed to work withrelays specifically. That is because FD is a moretransparent option than HD, in the sense thatFD relaying does not introduce timing nor fre-quency constraints imposed by the use of TDDor FDD. As such, FD relays, including airbornerelays for beyond line-of-sight coverage [13],could be used to extend the operational range ofCIS networks as illustrated in Fig. 3. However,as with most FD applications, residual SI be-comes the performance limiting factor and thefull extent of the advantages of using FD overHD in relaying depend on the SI cancellationperformance.

SISI

Ground-basedFD relay

AirborneFD relay

CIS network coverageExtended CIS network coverage

Figure 3. Tactical FD relays can seamlessly extend thecoverage of CIS networks.

In hostile environments, FD relays can playan important role in delivering robustness andphysical security. Instead of simultaneous re-ception and transmission, tactical relays withFD capabilities can monitor for adversarial in-terference while at the same time transmittinginformation to allies or receive informationfrom allies while simultaneously interferingwith its reception by adversarial intelligence.In the first case, interference awareness canaid self-organization within tactical networks.In the second case, simultaneous reception andjamming can create an FD radio shield over theTEN and prevent adversaries from interceptingthe host forces’ communications or locatingunits within the TEN. Should the operationalscenario require, FD relays can effortlesslybecome amplify-and-forward eavesdropping re-lays for carrying out signals intelligence onapproaching adversaries.

OUT-OF-BAND INTERFERENCE

As with in-band SI, radio systems that useclosely located frequencies may also, due toout-of-band (OOB) emission, suffer from stronginterference when transmission and receptionoccur simultaneously. This problem is partic-ularly prevalent when radios are co-locatedon the same platform and subject to limitedphysical separation [8]. The lack of space dueto co-siting may equate to poor EM isolationbetween radios, which results in appreciableinterference even when OOB emission require-ments are met. This issue is especially promi-nent in military applications, where it can havea significant negative effect on robustness tointerference, communication range, as well asfrequency allocation.

When co-located radios are treated like anFD transceiver, the transmitted signal can beforwarded to receiving radios on the platform.Each radio can then perform interference can-cellation in their respective spectrum, reducingOOB interference. Though additional hardwareis necessary, implementation of such OOB in-terference cancellation can be done withoutintroducing complex scheduling, or requiringadditional time or frequency resources [14].Consequently, removing OOB interference cansignificantly boost both robustness of radios onthe same platform as well as enable functionalcommunications in situations where this waspreviously not possible. Furthermore, cancella-tion of OOB interference can enable integratingmultiple RF tasks simultaneously onto a singleplatform, which is of significant interest in themilitary domain and has been pursued throughprograms such as the Advanced MultifunctionRadio Frequency Concept and Integrated Top-side [8]. For example, radar, EW operations,and communications could be integrated into amultifunction radio with shared aperture.

NATO NARROWBAND WAVEFORM

In general, FD radio technology is waveformagnostic, meaning that the type of waveformused does not affect the capability to transmit

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and receive simultaneously on the same fre-quency. Yet, some properties of a waveform(e.g., bandwidth, crest factor, and frequencyhopping) do have an impact on the complexityand performance of an FD radio. Furthermore,in order to take advantage of FD radios in multi-hop configuration, networking protocols need totake FD capabilities into account [3]. As such,the NATO Narrowband Waveform (NBWF) isa prominent candidate to benefit from FD radiotechnology. It is a modern combat-net radiostandard that includes both the waveform andnetworking capabilities, with the aim to en-hance interoperability among NATO forces inmultinational missions.

The standardization of NBWF covers thethree lowest layers of the OSI networkingmodel: physical, data link, and network layers.On physical layer, the NBWF employs con-tinuous phase modulation (CPM) for spectralefficiency, where the constant envelope prop-erty allows transmitter power amplifiers (PAs)to operate near saturation, improving energyefficiency. The same properties that make CPMspectral and energy efficient are also expectedto result in efficient SI cancellation. On dataand network link layers, NBWF is designedfor limited link capacity and harsh interferenceenvironments, employing crosslayer link met-rics to manage interference and link qualityissues. Those characteristics and capabilities areessential to managing residual SI and inter-nodeinterference in FD-capable radio networks.

The NBWF is essentially a single-channelMANET, offering several transmission modes,supporting occupied bandwidths of 25 kHz and50 kHz, and providing data throughput from20 kpbs up to 82 kbps. The design allowsradios to adapt waveform and power parametersto achieve the desired quality-of-service with-out wasting resources. Similarly to a generalMANET, a multi-hop NBWF network suffersfrom the hidden node problem, degrading aNBWF network’s throughput. Fortunately FDoperation is a promising candidate to solve thehidden node challenge [3]. The RTG membershave been studying, implementing, and demon-strating FD radio technology using the NBWFas an example tactical waveform. The resultsof RTG’s multinational demonstrator provide aproof of concept for increasing spectral effi-ciency of the NBWF through FD radio tech-nology [4].

ENHANCED ELECTRONIC WARFAREIn parallel with CIS enhancement efforts,

the RTG is working towards applying FD ra-dio technology for EW tasks. Specifically forcounter-drone purposes as drones pose an in-creasingly large threat and RF-based counter-drone methods are prominent [15]. In FD oper-ation mode, a counter-drone node can simulta-neously interfere with various RF systems usedby a drone and itself receive those signals unin-terrupted. The interference creates an invisibleEM dome, a so called FD radio shield, aroundthe FD node as illustrated in Fig. 4. Interferingcould, in this case, mean either jamming or

spoofing, and the concept of FD radio shieldhas already been shown feasible in a laboratoryenvironment by the RTG for, e.g., disablingdrone remote control (RC) links by jammingwhile simultaneously detecting the same [10].

GROUND-BASED RADIO SHIELD

A ground-based FD radio shield (either mo-bile or stationary) can be used to prevent:

• drones from communicating within theswarm while at the same time monitor-ing the swarms’ attempts to communi-cate within itself — this allows simulta-neously preventing the swarm (even anautonomous swarm) from operating as acoherent unit (as communications withinthe swarm are essential for the functioningthereof) and to track drones by their RFfingerprints (classify and locate individualdrones).

• ground station from directing the droneswarm while at the same time intercept-ing command and control signals — thismeans that within the radio shield, theswarm is completely cut off from its op-erator, but the FD node can still observe(classify and locate) the ground controlstation.

• drones inside the swarm from deter-mining their geographical position us-ing global navigation satellite systems(GNSSs) while at the same time retainingthe FD node’s own access to GNSS —the swarm can not determine its positionusing GNSS but the FD node can, whichis essential in case of a mobile FD node.

• drones from positioning each other insidethe swarm using RF-based methods (two-way ranging or radar-based positioning)while at the same time detecting thoseefforts — the ability to position each otherwithin the swarm is essential for the op-eration of a swarm and without this, theswarm becomes paralyzed, yet with FDcapabilities those positioning attempts canstill be detected.

On the other hand, a ground-based FD radioshield also facilitates:

• locating drones while simultaneously jam-ming their RC links and other RF systemsby using joint radar and jamming wave-forms — FD radio technology can become

FDradio shield

FD node

Figure 4. Defensive FD radio shield — simultaneouslyrestricting unauthorized drones access to the defendedairspace and monitoring the RF spectrum (detection, classi-fication, and locating of drones and their control stations).

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a key enabler for multifunction militaryradios and RF convergence that have forlong been coveted by armed forces [8].

• controlling an allied drone (or droneswarm) from the ground station while atthe same time simultaneously sensing forenemy drone’s RC signals and electronicattacks within the same frequency bandthat is used for allied drone RC.

AERIAL RADIO SHIELD

Another, more proactive, option is to use FDradios for countering drones as illustrated inFig. 5. Instead of using a ground-based FDradio shield, a drone itself could be equippedwith FD capabilities, allowing to

• interfere with the entire RF spectrum(ground control, inter-drone communica-tions, two-way-ranging, radar) used by amalicious swarm, while itself retaining theability to communicate with its controlstation — when the host drone operateson the same frequency as the adversarialdrones, FD technology is needed so thatthe host drone can transmit interferenceand receive commands at the same time.

• transmit spoofed GNSS signals while itselfreceiving the actual ones — this could beused to direct the malicious swarm awayfrom its target, although successful GNSSspoofing itself can be expected to be ahighly complicated task.

• jam from air, which can be much more en-ergy efficient than jamming from ground,especially if the drone can get close to theswarm — this is a considerable advantageof FD radio technology as this would si-multaneously paralyze the swarm but alsocomplicate localization of allied forces onthe ground by the enemy (that is typicallya high priority).

• use the drone for scouting (e.g., transmit-ting aerial video feed) while at the sametime detecting for frequency usage on thesame frequencies by adversarial drones.

FULL-DUPLEX ADVERSARIES

It is also relevant to consider, how FD ca-pabilities in the hands of adversaries affect the

FD drone

Figure 5. Disruptive FD drone — simultaneously operatingon and jamming the same frequencies that are used by theadversarial drones.

electronic battlefield. When facing two adver-sarial HD nodes that utilize FDD for com-munication, as is quite typical for drones, ajammer needs to target both the uplink andthe downlink frequency channels to completelycut the communication link. In the case oftwo adversarial FD nodes, only one commonfrequency channel needs to be targeted. Onthe other hand, if the enemy is using FD linkbetween two nodes, e.g., for operating a drone,then radiolocating the nodes or eavesdroppingon the communication link can be complicateddue to the mixed reception of the two signals.As a result, adversarial FD communicationscan become an easier target compared to HDcommunications when intentionally interferingbut a tougher target when monitoring.

But of course the adversary is not limitedto applying FD only for communications. Theadversary can combine its communications withEW operations or simply combine different EWoperations as proposed throughout this articleso far. In this case, when the host is limitedto HD capabilities, the FD benefits will simplywork for adversary’s advantage. When bothteams use FD capabilities, the playing fieldbecomes increasingly complex. For example,when the adversary is using FD radios toenhance physical layer security and preventthe host from eavesdropping, the host couldcounter-strike with simultaneous jamming andeavesdropping to pressure the adversary intoincreasing communication transmission powers.

COGNITIVE AND MULTIFUNCTIONALELECTRONIC WARFARE SYSTEMS

The aspects considered in this section aremade possible by FD radios or FD radio tech-nology significantly improves on the perfor-mance that can be achieved when comparedto conventional HD radio technology. This isone of the next steps in radio evolution thatwill enable the growing list of requirementsthat modern EW faces in congested spectrumenvironments. However, the advantages to EWapplications extend beyond the counter-dronecontext, which is the main focus of the RTG’ssecond demonstrator group and was describedin detail above.

Much more widely, the importance of EWas a whole is on the rise as EM spectrum isrecognised as a key operational environment.Classically, all EW tasks have been separatedfrom CIS functions to large extent, so thatEW operations do not interfere with the host’sCIS [8]. Similarly to the simultaneous combi-nation of different counter-drone aspects, theadvent of FD radios enables that paradigm toshift. As a result, and in the future, many of theCIS tasks can be combined with EW tasks toenhance both aspects. Broadly, these combina-tions mean either simultaneous communicationand jamming, interception and communication,or interception and jamming [7]. Such combina-tions enhance CIS and EW with an added layerof physical security or perception of spectralenvironment.

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CONCLUSIONSResearch into FD radio technology has

progressed in strides over the recent decadewith mostly civilian/commercial applications inmind. However, the technology is yet to makeits way into standardized networks and it isevident that in order to take advantage of theFD concept in CIS and EW systems, muchwork still lays ahead. Specifically operating fre-quency ranges and SI cancellation levels mustbe extended to satisfy the wide requirements setby military radio equipment.

The NATO STO IST-175 RTG is working onovercoming these challenges to take advantageof the FD concept and enhance both CIS andEW systems. In this article, we have discussedthe military specific challenges of FD radiosand outlined the most promising applicationsfor FD enhancement in the defence domain. Asa result of FD operation, the spectral congestionissue within CIS can be alleviated, compatibil-ity with EW equipment improved, and robust-ness against EW attacks enhanced. Moreover,FD enables truly multifunctional military radiosthat can simultaneously carry out both CIS andEW functions.

ACKNOWLEDGMENT

The research work leading to this article wassupported in part by the Estonian Ministry ofDefence, in part by the Academy of Finland, inpart by the Finnish Scientific Advisory Boardfor Defence, as well as in part by the EDADefence Innovation Prize.

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BIOGRAPHIES

KAREL PARLIN (karel.parlin@rantelon.ee) received hisM.Sc. degree in electrical engineering from Tallinn Uni-versity of Technology, Estonia, in 2017. He is an engineerat Rantelon in Tallinn, Estonia.

TANELI RIIHONEN [S’06, M’14] (taneli.riihonen@tuni.fi)received his D.Sc. degree in electrical engineering fromAalto University, Finland, in 2014. He is a tenure-trackassistant professor at Tampere University, Finland.

VINCENT LE NIR (vincent.lenir@rma.ac.be) received hisPh.D. degree in electronics from the National Institute ofApplied Sciences, France, in 2004. He is a senior researcherat the Royal Military Academy in Brussels, Belgium.

MARK BOWYER (mark.bowyer@airbus.com) received hisPh.D. in solid state electronics from the University of Kent,United Kingdom, in 1993. He is a senior expert in securecommunications at Airbus Defence & Space in Portsmouth,United Kingdom.

THOMAS RANSTROM (jranstrom@usf.edu) received hisM.Sc. degree in electrical engineering from LinkopingUniversity, Sweden, in 2018. He is a research engineer atthe Swedish Defence Research Agency (FOI) in Linkoping,Sweden and a Ph.D. student at the University of SouthFlorida in Tampa, United States.

ERIK AXELL (erik.axell@foi.se) received his Ph.D. de-gree in communication systems from Linkoping University,Sweden, in 2012. He is a senior scientist at the SwedishDefence Research Agency (FOI) in Linkoping, Sweden.

BORJE ASP (borje.asp@foi.se) is a research director at theSwedish Defence Research Agency (FOI) in Linkoping,Sweden.

ROBERT ULMAN (robert.j.ulman.civ@mail.mil) receivedhis Ph.D. degree in electrical engineering from the Univer-sity of Maryland, United States, in 1997. He is a programmanager at the US Army Research Office in Triangle Park,North Carolina, United States.

MATTHIAS TSCHAUNER (matthias.tschauner@fkie.fraun-hofer.de) received his Dipl.-Ing. degree in electrical engi-neering from RWTH Aachen University, Germany, in 2011.He is a research assistant at Fraunhofer FKIE in Wachtberg,Germany.

MARC ADRAT (marc.adrat@fkie.fraunhofer.de) receivedhis Dr.-Ing. degree in electrical engineering from RWTHAachen University, Germany, in 2003. He is the head ofthe SDR research group at Fraunhofer FKIE in Wachtberg,Germany.