the progress of tactical radios from legacy systems to cognitive radios

IEEE Communications Magazine • October 201350 0163-6804/13/$25.00 © 2013 IEEE

INTRODUCTION

Before automobiles were in use, military radios,which were very large in size, were carried bymules and wagons. Hardware was based onmicrometer spark gap, followed by various mag-netic, electrolytic, and crystal detectors, thenvacuum tubes, then solid-state, leading to theVietnam War era of radios which used:• VHF band divided to: Armour/Infantry/

Artillery• HF for long distance (over the horizon)• UHF for air-to-air and air-to-ground com-

municationsThe drive for technological advancement

during the Cold War furthered the developmentof many critical defense technologies. The suc-cess of Soviet jammers has pushed the U.S.Department of Defense (DoD) to fund thedevelopment of a new generation of radios thatcan resist jamming. The U.S. defense industry

introduced direct-sequence spread-spectrum(DSSS) in a mix with time-division multipleaccess (TDMA) and frequency hopping in ageneration of radios that can be consideredahead of its time. DSSS modulation enabledthese radios to resist jammers and detect signalsat low signal-to-noise ratio (SNR). This articlepresents the Link-16 radio, using the Joint Tac-tical Information Distribution System (JTIDS)for network communications, as an example oflegacy systems that have anti-jamming capabili-ties, mobility at high speed, and long rangesbetween nodes.

The Link-16 generation of radios startedas non-IP radios and rel ied on the use ofstatic resource allocations (i.e., a radio termi-nal is assigned its frequency hopping patternand TDMA slot al location through a con-troller). They support a predetermined num-ber of users per subnet, and they cannot beupgraded without hardware upgrades. Thesoftware defined radio (SDR)-based pro-grams adapted by the U.S. DoD used thesoftware communications architecture (SCA)as the core of their design. These radios canbe considered conventional radios with addedsoftware architecture, reconfigurability, easy-to-upgrade design, and so on. One can con-sider cognitive radios (which are still evolvingtoday) as SDRs with intelligence, awareness,learning and observations. Figure 1 demon-strates this progression concept.

Reference [1] provides more details abouteach of these three technological leaps of tacti-cal radios. This article highlights the main fea-tures of each type using a benchmark system/waveform to demonstrate the technologicaladvances associated with each radio type. Ipresent the Links-16/JTIDS system as thebenchmark of legacy radios. This article dedi-cates a section to the Wideband NetworkingWaveform (WNW) as an example of softwarewaveforms that can be downloaded into differ-ent SDR platforms. WNW was developed asan IP-based waveform with mobile ad hoc net-working (MANET) capabilities. This articlegives a brief description of cognitive radios asthe generation of radios that is still evolvingand presents some known characteristics ofthe wireless network after next (WNAN) radioas an example of cognitive tactical radios.Finally, the article gives a summary of thistutorial.

ABSTRACT

This article gives a tutorial about some criti-cal milestones regarding the journey of tacticalradios from legacy systems to cognitive radios.Although tactical radios have been in use forover 100 years, this tutorial focuses on the post-Vietnam War radios and uses examples from theU.S. Department of Defense major acquisitionprograms. The article considers legacy radios tobe the generation of radios that was initiated bythe U.S. Department of Defense in the 1970sthat had spread-spectrum and frequency-hop-ping capabilities to resist jamming. The Link-16system is covered in this article as a benchmarkfor legacy radios. Two major technological leapscame after these legacy radios. First was thesoftware defined radios initiative, which broughtabout the ability to develop waveforms entirelyin software in the absence of a defined hardwareplatform. As a result, different waveforms can beported into the same hardware platform. Thisarticle presents the Wideband Networking Wave-form, which is a complex waveform developedunder a U.S. Department of Defense program,as a software-based waveform that can be down-loaded into different hardware platforms. Thenext technological leap came with cognitiveradios, which have the ability to sense their envi-ronments and adapt intelligently to the dynamicsof the war theatre.

MILITARY COMMUNICATIONS

George F. Elmasry, DSCI

The Progress of Tactical Radios fromLegacy Systems to Cognitive Radios

ELMASRY_LAYOUT_Layout 1 9/27/13 10:34 AM Page 50

IEEE Communications Magazine • October 2013 51

LINK-16/JTIDS: A LEGACY SYSTEM

Link-16 is a sophisticated wireless tactical datasystem that supports time-critical robust radiocommunications and is integrated into manyplatforms, including fast movers. Link-16 sup-ports voice, free text, and variable format mes-sages. It is a complex system that deploysTDMA, DSSS, and frequency-division multipleaccess (FDMA) with frequency hoppingschemes.

Link-16 was conceived before the standard-ization of the protocol stack layers and the cre-ation of the Internet Protocol (IP). The corenetwork radio functionalities of this system (weare focused on the JTIDS system in this article)are in the physical and data link layers. It isimportant to note that Link-16/JTIDS’s equiva-lent of the medium access control (MAC) layer(where the apportionment of physical layerresources is handled) is done in the planningphase. That is, the air interface resources arestatically allocated. Each Link-16 terminal isassigned a set of time blocks. Instead of MACframes and IP packets, a block of 75 bits (knownas J-words) is used for transmitting and receivingdata over the Link-16 net.

Link-16 uses wide spectrum in the UHF Lxband, between 960 and 1215 MHz. Dividing thisspectrum band, Link-16/JTIDS implementationuses 51 frequencies between 969 and 1206 MHzin order to create frequency hopping capabili-ties. Figure 2 details the slot structure of Link-16/JTIDS. The left side of the figure illustratesthe 127 different possible nets in Link-16 (hori-zontal rings numbered 0–126, with net 127 rep-resenting a stacked net), with the vertical axisrepresenting the FDMA dimension of the slotstructure (each of these nets has its own fre-quency hopping pattern). The top right of thefigure demonstrates how a single ring (net)employs TDMA, creating 98,304 time slots dur-ing a period of 768 s. The bottom right part ofthe figure shows how separate nets can worksimultaneously, while a unique hopping patternis assigned to each terminal in the net. Thesefigures are taken from [2].

The slot structure shown in Fig. 2 creates acombination FDMA and TDMA time slot struc-ture. The structure is split into 12.8 min (768 s)epochs. Each epoch contains three sets of timeslots (i.e., sets A, B, and C) numbered from 0 to32,767. A, B, and C are used as a numbering

scheme such that time slots can be numberedA0, B0, C0, A1, B1, C1, .. A32,767, B32,767,C32,767. Each time slot is 7.8125 ms and consistsof a train of pulses each of 6.4 ms duration sepa-rated by an interval of 6.6 ms.

The use of frequency hopping createsresilience against jamming. In addition, the useof DSSS modulation makes it possible to detecta signal at low SNR. Jammers that work on aspecific frequency can be mitigated by frequencyhopping, and jammers that spread their spec-trum will be combated by DSSS modulation anderror correction. In Link-16/JTIDS, hoppingoccurs within the same time slot, approximately600 times per time slot. Tactical radios startingfrom this legacy generation rely on fast hoppingas a core part of their design.

The use of two types of encryption security,transmission security (TSEC) and message secu-rity (MSEC), provide excellent multilayereddefense.1 An enemy attempting to listen to aLink-16 signal has to zero in on the hopping pat-tern, decode the TSEC, and decipher the MSECcode (among other evasive techniques) in orderto get useful information.

Link-16/JTIDS used an elaborate error detec-tion and error correction technique consideringthat its design was done in the 1970s (see [2, 3]for more details). Link-16/JTIDS was the firstimplementation outside of the space program thatused concatenated coding and Reed-Solomon(RS) coding with interleaving. The later versionsof Link-16/JTIDS introduced soft decisiondemodulation and used RS codes with erasure,increasing the error resilience of the waveform.Orthogonal 32-chip cyclic code shift keying(CCSK) was also adapted in later versions [3].

One should appreciate the extent of the tech-nological advancement made with the develop-ment of this radio system, which started in the1970s. Other than the U.S. National Aeronauticsand Space Administration (NASA) space pro-gram, Link-16 was the first project to use con-catenated codes. The combination of FDMA,TDMA, DSSS, and different modes of interac-tion created such exceptional communicationcapabilities for fast movers (e.g., fighter jets)that it remains unmatched. The Link-16/JTIDSsystem guaranteed communication betweenfighter jets, traveling at speeds up to Mach threeand at distances up to 500 km in the presence ofjamming. This was truly an astounding accom-plishment.

1 Link-16 references usethe terms TSEC andMSEC. The more widelyused terms in militarycommunications refer-ences are TRANSEC andCOMSEC for transmis-sion security and commu-nications security.

Figure 1. The evolution of tactical radios as three generations.

Conventional radio

• Traditional RF and baseband design• Supports a fixed number of users• Not reconfigurable after deployment• Specific uses defined at the time of the design• Not upgradable

Software radio

• Supports variable numbers of users• Supports variable protocols and interfaces• Highly configurable• Provide variable range of QoS• Software upgradable

Cognitive radio

• Can create a new waveform on its own• Can negotiate new interfaces• Adjust operations to meet the QoS required by application given signal environments• Internal, collaborative and software upgrades

The Link-16/JTIDS

system guaranteed

communication

between fighter jets,

traveling at speeds

up to Mach three

and at distances up

to 500 km in the

presence of jam-

ming. This was truly

an astounding

accomplishment.


IEEE Communications Magazine • October 201352

Link-16 is not the only successful non-IP sys-tem, although it is the best of its generation. TheU.S. Army maintains widespread usage of theEnhanced Position Location Reporting System(EPLRS), which has excellent anti-jammingcapabilities. The newer generation of EPLRS isIP-capable through a gateway with a fully capa-ble IP router that can represent each node in thenon-IP net with an IP address to the IP core net-work. The U.S. Army also utilizes the SingleChannel Ground and Airborne Radio System(SINCGARS) [1].

WIDEBAND NETWORKINGWAVEFORM: A SOFTWARE-BASED

WAVEFORM

The WNW protocol stack is introduced in Fig. 3.The plain text IP layer gives the radio user accessto an IP port into which applications can beplugged. One can also form an entire plain textIP LAN utilizing this IP port. The High Assur-ance Internet Protocol Encryption (HAIPE) [4]encryption layer uses an embedded processor forencryption that can adhere to multiple versionsof HAIPE standards.2 A WNW node can sup-port multiple security enclaves (multiple plain

text subnets), where the HAIPE embedded pro-cessor handles more than one parallel imple-mentation of HAIPE in order to support thesemultiple security enclaves that are entirely sepa-rated (implemented over separate hardwarecomponents). Each security enclave maintains aplain text IP layer and an application IP port.This is necessary for some platforms that requireclassified and unclassified applications that mustremain separate. Cross-layer signaling (CLS) is avital aspect of the WNW design. The mobileInternet (MI), mobile data link (MDL), and sig-nal-in-space (SiS) layers have an excellent CLSdesign, as detailed below [5].

The U.S. DoD sponsored the development ofdifferent software-based waveforms with IP-based capabilities in conjunction with the WNW,such as the soldier radio waveform (SRW). Also,the U.S. DoD adapted another class of IP-basedwaveforms with dynamic resource allocation thatare designed for the long-haul connectivitybetween gateway routers of reach-back networknodes. Two known waveforms from this class arethe high-band networking waveform (HNW)3

and the network-centric waveform (NCW) [6],which is a satellite communications on-the-movewaveform. The WNW is considered the mostcomplex software-based waveform sponsored bythe U.S. DoD.

Figure 2. Link-16 static resource allocation and the creation of nets [2].

Multiple nets

Time slice Time slot

NetNumber

0

1

2

47

48

49

50

123

124

125

126

Net 3Net 2Net 1Net 0

Stacked netair control

Net 3

Net 1

Time slot

WF

16/5

A-0

8M-

Time slot

A-3

2766

A-3

2767

A-0 A-1 B-1

C-1

B-0

C-0B-

3276

6

B-32

767

C-3

2767

C-3

2766

Single net

A-3

2766

A-3

2767

A-0 A-1 B-

1 C-1

B-0

C-0B-

3276

6

B-32

767

C-3

2767

C-3

2766

2 HAIPE standards aredecided by the U.S.National Security Agency(NSA).

3 Most of the details of thiswaveform are owned by theHarris Corporation.

4 With high mobility, linkstates change very frequent-ly. Standard OSPF couldconsume all availablebandwidth as the numberof nodes in a subnetincreases.

5 The GIG is a U.S. gov-ernment IP-based networkof networks that can carrydifferent classifications ofdata for tactical andstrategic purposes. (Youcan conceptualize it as theU.S. government versionof the Internet)



CIPHER TEXT IP LLAYER

The WNW cipher text IP layer maintains excep-tional implementation of CLS with the mobileInternet (MI) layer below. With this CLS, linkstate updates (LSUs) are not discovered by thecipher text IP layer; rather, the Open ShortestPath First (OSPF) protocol is altered, creating aprotocol called Radio OSPF (ROSPF). ROSPFthen allows for an increase in the number ofnodes in a single subnet and prevents the over-flooding of the limited physical layer resourceswith LSUs.4 The cipher text IP layer has an Eth-ernet IP port (marked GIG port in Fig. 3), whichallows the WNW subnet to communicate seam-lessly with other networks of the global informa-tion grid (GIG)5 at the cipher text side (to createseamless encrypted core IP flow). The ciphertext IP layer is capable of running OSPF overthe GIG port and running ROSPF over theradio stack layer. It can also build route tablesfor internal routing in the WNW subnet andexternal routing over the GIG port.

THE MI LAYERThe WNW MI layer is responsible for theMANET networking (connectivity at the IPlayer). It maintains a multi-level link state rout-ing topology of the WNW subnet. The MIensures that the waveform maintains a connect-ed topology that can be dynamically mapped tothe routing table for IP delivery. IP gatewayselection is also managed by the MI layer. Inaddition, the MI layer controls data flow, pre-vents buffer overflow at the lower layers andimplements multilevel queuing to ensure thewaveform meets tactical quality of service (QoS)requirements.

THE MDL LAYER ARCHITECTUREThe WNW MDL layer implements Unifying SlotAssignment Protocol (USAP), which supportsmultihop broadcast of packets and controls thesubnet topology. Conflict resolution of TDMAslot assignment and reconfiguring slot assignment(per traffic demand of each node) become achallenging problem. USAP heuristically assignsthe optimum number of TDMA slots to eachneighboring node and coordinates the activationof these slots to prevent collision. USAP is tiedto the heuristics of the higher layers of the proto-col stack.6 CLS between the MI, MDL, and SiSlayers considers traffic demand (from the upperlayers), and the link condition (from the lowerlayers) to influence slot allocation. The mannerby which USAP functions at each node affectsthe heuristics of the upper stack layers. This isreferred to as convergence of the stack layers.

The MDL layer plays a major role in flowcontrol, topology control, creating fault-toleranttopology, and minimizing the number of hopsbetween communicating nodes. Topology con-trol, and its relation to TDMA slot allocation, isdetailed in [1]. Channel resources (TDMA slots)are reused spatially and concentrated in thenodes that are best positioned to relieve conges-tion. The MDL layer provides unicast and broad-cast coverage through the allocation of TDMAslots.7 The MDL layer also allows selected nodesto bridge between channels.

CLS allows each node to respond to thechanges provided by the SiS layer; these changesrefer to volatility in measurements, and reflectsignal strength and symbol error rate. The MDLlayer uses this information to continuously opti-mize the use of the physical layer resources.

COGNITIVE RADIOS AND THEWNAN WAVEFORM

There are plenty of references on cognitiveradios since it is a research area shared by thecommercial and tactical wireless communicationsresearch communities. The commercial side ofthis research area has made strides in oppor-tunistic spectrum utilization and creating cogni-tive radio architecture [7]. The defense industryside of this research area is concerned aboutpolicies, since operationally one cannot leave acognitive radio subnet to make decisions that arenot aligned with the entire war theatre plan.

The field of producing hardware for cognitiveradios is still evolving. There are some availablehardware and software platforms such as theGNU8 radio, which is a free software signal pro-cessing toolkit. GNU is rich with capabilities thatallow its users to experiment with manipulatingand using the electromagnetic spectrum. One ofthe basic design concepts of GNU is to allow itsusers to use a single generic radio hardware unit.This hardware can be used to feed complex cog-nitive radio formations into the powerful GNUsignal processing software. The GNU radio

6 The term unifying wasselected because the pro-tocol is tied to the upperstack layers. It also refersto the protocol’s flexibilityin serving many differentheuristics, with a commonlower level mechanism.

7 Some MANET MAClayers can allocate someslots to be shared betweennetwork nodes in a carriersense multiple access(CSMA)-like protocol(contention slots). How-ever, the WNW waveformimplementation of USAPdoes not use contentionslots.

8 GNU started as project atMIT for free softwarewhich initiated an operat-ing system called GNU(“GNU” is a recursiveacronym which stands for“GNU's Not Unix”). GNUradio is a toolkit of GNU.

Figure 3. The WNW waveform protocol stack layers.

Applications

IP portPlain text (red)

IP layer

HAIPE

GIG IP port

OSPFCipher text (black)

IP layer

Mobile Internet (MI)layer

Mobile data link(MDL) layer

Signal-in-space(SiS) layer

ROSPF



toolkit also utilizes the universal software radioperipheral (USRP), which is a computer-basedtransceiver with powerful analog-to-digital anddigital-to-analog converters with circuitry tointerface with a host computer. The USRP inter-faces with several transmitters and receivers cov-ering frequency bands from 0 to 5.9 GHz.

CONCEPTUALIZING COGNITIVE RADIOSI have reviewed CLS with the WNW radio. Youcan see how the channel parameters play a majorrole in ensuring that the higher-layer protocolsadapt to the changes in the physical layer param-eters. Let us compare CLS to the simplest con-cept of cognitive radio settings (CRSs).

Cognitive radios have CLS, as shown in Fig.4. In addition to CLS from the physical layer tothe cognitive engine, the radio metrics are alsosent to the cognitive engine (e.g., spectrum sens-ing metrics). The cognitive engine generatesoptimum parameters for the radio, which includechanging the actual software modules (e.g.,change the modulation type) and possibly creat-ing new software components based on knowl-edge of the surrounding environments. Please beaware that some cognitive radio references usethe term radio loosely. The physical layer issometimes referred to as the radio. Referencesthat focus on cognitive algorithms conceptualizea cognitive radio as having three main compo-nents: a radio or physical layer, a MAC layerwith a cognitive engine as its focus, and operat-ing environments (OEs), as indicated on theright of Fig. 4.

COGNITIVE RADIO SETTING PARAMETERSWith CLS, one can see a myriad of parametersbeing used by the radio to adapt to the dynamicenvironment. With CRSs, the cognitive enginedeals with even more parameters from the physi-cal layer, MAC layer, and radio OEs to include: • From the physical layer, the radio metrics

can include received signal parameters suchas power, angle of arrival, delay spreading,Doppler spreading, and fading patterns.The radio metrics can also include noiseparameters and interference power. Note

that with waveforms such as WNW, thephysical layer can communicate parameterssuch as power, Doppler spreading, andsome noise parameters; with CRSs, a largerset of parameters is communicated fromthe physical layer to the cognitive engine.

• From the MAC layer, the cognitive enginedeals with issues such as frame error rate,transmission data rate, multiple accessoptions, and channel slot allocation. Thecognitive engine addresses how the MAClayer selects frame types, changes framesize, and implements compression andencryption. It also influences how the MAClayer performs error control coding andinterleaving.

• From the radio operating environment, thecognitive engine may deal with its own nodetransmitting power, power consumptionrate, spreading type, spreading code, andmodulation type (including symbol rate,carrier frequency, antenna diversity, dynam-ic range, etc.) in order to adapt the node tothe changes in its surroundings. The cogni-tive engine also considers its own nodecomputational power, battery life, and CPUallocation for ensuring proper use of thenode’s internal resources.

THE COGNITIVE ENGINEThis is the most challenging part of cognitiveradio. The challenge becomes how to architecttrue cognitive radios with cognitive engines orintelligent agents that perform cognition tasks.These agents must be intelligent, in the sensethat they can make accurate and consistent deci-sions. The agents must be able to collect infor-mation from surrounding environments andprocess this information with low overhead com-putation and without excessive battery consump-tion. These cognitive engines need to beadaptable to the dynamic environment and capa-ble of making the optimal decisions to meet theapplications’ needs, given the available spectrumresources.

There have been initiatives to base the cogni-tive engine design on approaches that rangefrom machine learning, such as neural networks,to generic statistical-based algorithms. The useof game theory for interactive decision makingbetween the different cognitive engines in a net-work has been studied extensively in the litera-ture. The concept of using some form ofcentralized control in a cognitive network, wherenodal interest can be overridden by the networkinterest, is more applicable to the tactical use ofcognitive radios. The use of policy-based net-work management (PBNM) or a policy engine tocontrol the behavior of a cognitive network isalso of great interest to the tactical applicationsof cognitive radios. Please refer to [1, Ch. 7 andreferences therein] for more details regardingcognitive radio.

Virginia Tech proposed the software architec-ture demonstrated in Fig. 5, showing the cogni-tive engine with different modules and differentinterfaces to other radio components. In Fig. 5,note the four main components: radio, radiointerface, user interface, and a cognitive systemmodule or cognitive engine. Notice the impor-

Figure 4. Cross-layer signaling and cognitive radio settings.

CLCRS

Radio RXRadio Metrics

Cognitiveengine

Radio/physicallayer

MAC layer

MACOEOperating

environments

Radio TX

Radio settings parameters

ELMASRY_LAYOUT_Layout 1 9/27/13 10:34 AM 4


tance of the policy and security models with thecognitive engine interface design, which is rele-vant to the use of cognitive radios in tacticalenvironments.

With this architecture, the cognitive enginehas the following main components:• Resource monitor component: Continuously

feeds the radio metrics through the cogni-tive engine-radio interface application pro-gramming interface (API).

• Wireless system genetic algorithm (WSGA)component: Implements the approach usedto adapt the radio to the changing environ-ment.

• Evolver component: Enables the cognitiveengine to control the search space by limit-ing the number of generations, crossoverrates, mutation rates, fitness evaluations,and so on. Especially with tactical environ-ments, the cognitive engine cannot be leftto evolve without boundary. In commercialapplications, the evolution process is con-trolled to ensure legal and regulatory com-pliance. In tactical applications, theevolution process must be contained byoperational needs and policies.

• Decision maker component: Feeds theWSGA with initial settings, WSGA param-eters, objectives and weights. The settings

are referred to by genetic algorithm devel-opers as the initial chromosomes, whereevery radio parameter is represented by agene.

• Knowledge base component: Contains capa-bilities such as short term memory, longterm memory, WSGA parameter set, andregulatory information.

THE WNAN RADIOThe commercial world has created cognitive-radio-based standardizations such as IEEE802.11K, in which the access point regulateschannel access based on intelligent spectrumsensing. Also, IEEE 802.22 has excellent detailson opportunistic spectrum based on fast sensingof TV channels spectrum to create the wirelessregional area network (WRAN). In the tacticalworld, the WNAN radio can be considered atactical cognitive radio that was sponsored bythe U.S. Defense Advanced Research ProjectsAgency (DARPA)9 strategic technology office.The WNAN waveform implementation has thefollowing characteristics:• It implements dynamic spectrum access with

strict policies to meet tactical needs. Notethat spectrum sensing and dynamic spec-trum access are the most mature aspects ofcognitive radios today.

9 The Internet started as aDARPA project.

Figure 5. Software architecture of a cognitive radio showing 1) cognitive engine focus; 2) policies and security interfaces relevant to tac-tical radios.

Cognitive engine-radio interface

Radio

API

Modeling system

WMS

Policy model

User model

Security

Resource monitor

Evolver

Cognitive system module

Cognitive engine controller

Decision maker

Knowledge base

Userinterface

Policies,preferences,and securityinterfaces

Channelprobe

Cog

niti

ve e

ngin

e-us

er in

terf

ace

WSGA

ELMASRY_LAYOUT_Layout 1 9/27/13 4:37 PM Page 55


• It forms a network with densely deployedlow-cost wireless nodes, and adaptive net-work layers that mitigate the shortcomingsof any individual nodes by leveraging theirrich interconnection.

• A WNAN node can be built at low cost andhas multichannel, spectrum-agile, multiple-input multiple-output (MIMO)-capablewireless access. It is built with inexpensiveradio frequency (RF) circuit technology.

• The WNAN waveform is considered disrup-tion-tolerant networking since it is designedsuch that nodes store packets temporarilyduring link outages.

• The WNAN waveform stack can sit underthe IP layer, allowing the use of standard IPapplications.

• The waveform has cloud computing con-cepts such as content-based access — that is,users query the network to find information— situational awareness (SA) informationcan be automatically pre-placed around thenetwork.

• The waveform implements multicast voicewith QoS. That is, bandwidth can bereserved for a voice call group.

• The waveform design considers energy sav-ing portability. That is, protocols aredesigned such that when the waveform isported into a small hardware platform, thewaveform can optimize for energy conser-vation. This feature is essential for sensorsthat are required to operate for long timeswithout replacement of the sensors or theirbatteries.

THE FUTURE OF COGNITIVE TACTICAL RADIOSIt is hard to predict the impact cognitive radioswill have on tactical communications. The U.S.Department of Defense realizes the drawback ofSDR. It also realizes the time and fiscal invest-ment it took to realize SDR. Cognitive radiosstill need significant research before they can bewidely used in tactical environments; we are noteven at the point where we can accurately modelthe decision processes, the learning processes,and so on. Moreover, we have yet to know whathardware support cognitive radios require. Whilethe U.S. Federal Communications Commission(FCC) and the equivalent agencies around theworld can regulate dynamic spectrum access forthe commercial application of cognitive radio [8-9], in tactical applications, we have regulatoryconcerns: we are not dealing with just the FCC.In war time, there is no guarantee that regula-tors will agree. Also, military-operations-focusedstakeholders are concerned about the loss ofcontrol over a deployed tactical cognitive radiosubnet: a deployed group of radios may haveundesirable adaptations.

SUMMARYThis article reviews three major developmentalmilestones of tactical radios within the last fourdecades, showing benchmark technologicaladvances with legacy radios, SDRs, and cognitiveradios. We review legacy radios, showing howthey had breakthroughs in combating jamming

and eavesdropping, but were static in nature,and their early designs were before the IP proto-col stack was known. We also review SDRs,which made it possible to develop software-based platform-independent waveforms that canbe downloaded to different hardware platforms.The U.S. DoD sponsored the development ofsoftware waveforms for SDRs that are IP-basedwith excellent MANET capabilities, dynamicresource allocation, and outstanding CLS foroptimizing the use of the scarce air interfaceresources in highly mobile and dynamic environ-ments. This article presents the WNW as anexample of the software-based waveforms thatwere sponsored by the U.S. DoD. We cover cog-nitive radios, which are starting to emerge withintelligent capabilities, allowing the radio termi-nal and the subnet to morph itself and adapt totactical theatre dynamics. Cognitive radio use inthe tactical theatre comes with great concernsregarding the level of autonomy with which theycan be allowed to operate and emphasizes theimportance of policies to ensure cognitive radiosoperate as intended. The future battle space willbe crowded with unmanned aerial, ground, andspace vehicles that will necessitate the extensiveuse of cognitive radios and drive great advancesin cognitive radios.

REFERENCES[1] G. F. Elmasry, Tactical Wireless Communications and

Networks, Design Concepts and Challenges, Wiley, Oct.2012.

[2] Northrop Grumman Corp., Understanding Link-16: AGuidebook for New Users, Sept. 2001.

[3] C.-H. Kao, Performance Analysis of a JTIDS/Link-16 TypeWaveform Transmitted over Slow, Flat Nakagami Fad-ing Channels in the Presence of Narrowband Interfer-ence, Ph.D. dissertation, Naval Post Graduate School,Dec. 2008.

[4] U.S. NSA, “High Assurance Internet Protocol EncryptorInteroperability Specification,” v. 3.1.0, Dec. 31, 2006.

[5] “Wideband Networking Waveform (WNW) System Seg-ment Specification,” spec. no. AJ01120, Boeing, 12Feb. 2003.

[6] J. Wiss and R. Gupta, “The WIN-T MF-TDMA Mesh Net-work Centric Waveform,” Proc. IEEE MILCOM 2007.

[7] J. Mitola, Cognitive Radio Architecture, in CognitiveNetworks: Towards Self-Aware Networks, Q. H. Mah-moud, Ed., Wiley, 2007.

[8] FCC, “Notice of Proposed Rulemaking and Order: Facili-tating Opportunities for Flexible, Efficient, and ReliableSpectrum Use Employing Cognitive Radio Technolo-gies,” ET Docket No. 03-108, Feb. 2005.

[9] M. Marcus, “Unlicensed Cognitive Sharing of TV Spec-trum: The Controversy at the Federal CommunicationsCommission,” IEEE Commun. Mag., vol. 43, no. 5,2005, pp. 24–25.

BIOGRAPHYGEORGE F. ELMASRY [SM] ([email protected]) received hisB.Sc. in electrical engineering from Alexandria University,Egypt, and his M.S. and Ph.D. degrees in electrical andcomputer engineering from the New Jersey Institute ofTechnology. He has been with DSCI since 2006 supportingvarious military communications programs. Before DSCI, hewas with General Dynamics C4S in the Warfighter Informa-tion Network-Tactical (WIN-T) group. Prior to GeneralDynamics, he worked for Lucent Technologies in the Wire-less Networks Wideband CDMA group. His research inter-ests are in the areas of wireless networking, ARQ, jointsource and channel coding, and multidimensional inter-leaving, in which he has over 50 publications and patents.He is the sole author of Tactical Wireless Communicationsand Networks: Design Concepts and Challenges (Wiley,2012).

Cognitive radios use

in the tactical theatre

comes with great

concerns regarding

the level of

autonomy in which

they can be allowed

to operate and

emphasizing the

importance of

policies to ensure

cognitive radios

operate as intended.


the progress of tactical radios from legacy systems to cognitive radios

Documents