Communications/Sensor Technologies forNext Generation Urban Warfare SystemsJames Saultz, Gregory Barnett, and M arc Olivieri

Lockheed Martin Advanced Technology Laboratories, Cherry Hill, NJ1-856-792-{9818, 9895, 9892} / {jsaultz, gbarnett, molivier}@atl.lmco.com

Thomas Radovich, Albert Pergande, and Lee M irthLockheed Martin Missiles & Fire Control, Olrando, FL

1-407-356-{5343, 5169, 8036} / {thomas.v.radovich, albert.n.pergande, lee.a.mirth}@lmco.com

Renato Levy and Leonard HaynesIntelligent Automation, Inc., Rockville, MD

1-301-294-5200 / {rlevy, lhaynes}@i-a-i.com

AbstractRecent developments in emerging sensor and communicationsystems technology are presented with a focus on the specialneeds of urban warfare. The paper also offers an overview o ffuture requirements for the processing and sensor supportneeded to realize these novel system concepts.

1. INTRODUCTIONThis paper presents advanced ad-hoc networking conceptswith sensor systems that exploit the unique potential of time-based radar processing, passive W-band radiometer tech-nology for concealed weapon detection, and advanced agentbased technology for knowledge sharing across sensornetworks. Finally, the paper offers an overview of futurerequirements for the hardware and sensor support needed torealize these novel system concepts.

2. BACKGROUNDThe focus of this paper is on the challenges posed to systemsdevelopment to support the warfighters in Urban Warfare andin Homeland Security Groups. Urban environments providechallenging conditions in which unit forces must operate todetect and neutralize asymmetrical threats. A challengingaspects of this environment is the close proximity amongfriendlies, neutrals and hostiles. The Urban Warfare challengesare:

• Robust communication in networks• Use and coordination of unmanned vehicles to do

Situation Awareness• Detecting concealed weapons on citizens and intruders• Detecting snipers/threats using concepts of ad-hoc

networks of multiple sensors.

The most challenging technological issues for the systemintegrator is to create a solution that provides an architecturefor improved communications, improved detection/localiza-tion and improved network operation. The Urban Warfarechallenge is to combined emerging technologies in a systemthat improves the survivability and probability of disablingthe threat.

Advances in beyond line of sight (BLOS) and through wallsensing technologies are needed to quickly detect and identifyhostile elements so the appropriate response can minimizecasualties and collateral damage. The unit soldier needs a cleartactical picture of the entire situation to respond appro-

priately. As a result, fully networked communication capabili-ties must be shared among the units so a total and moreaccurate tactical picture can be determined.

Advances in communications technologies are needed ascurrent systems experience severe fading in the difficultmultipath conditions typically encountered during MilitaryOperation in Urban Terrain (MOUT). The recent development inadvanced RF technologies combined with the maturationprocess of emerging systems concepts for future of urbanwarfare applications has led us to investigate new combina-tions of advanced ad-hoc networking to achieve unique sensorsystems designs.

The analysis of the specific requirements imposed by the harshurban warfare environment points towards networked-basedsensing/comms systems solutions. This approach fullyexploits the unique potentials of time-based RF systems(wideband and ultra-wideband). The following examples inthis paper describe emerging radar and communicationssystem technologies and concepts that will support the urbanwarfare fighter of the 21st Century. Many of these technologiesare being researched by DARPA, CECOM and AFRL.

3. EXAMPLES OF CURRENT SYSTEMSDEVELOPMENT

3.1 The XNETDeveloped at Lockheed Martin Advanced TechnologyLaboratories (LM ATL), the eXtreme NETwork (XNET) conceptis based on the use of networked sensors across a platoon andprovides innovative solutions for this new mode of operation.The concept leverages the advantages of both spatial andspectral diversity offered by the deployment of small specialforces units or special weapons and tactics teams equippedwith radios that have very wide bandwidths. The soldiers inthe squad form an ad-hoc network of sensors/hopping nodesused for improving both sensor and communication perform-ance of the squad.

Synchronized wideband communications offer unique locat-ing capabilities among the network’s nodes. This can be usedin the sensing system for the fusion of multi-aspect angleviews of targets. The use of very wideband signals makes thesystem far more robust in the harsh multipath environmentsfound in MOUT. The concept is illustrated in Figure 1.

Figure 1. XNET Concept for an ad-hoc network of UWBsensors used to detect and identify targets in the harsh

environment of urban terrain.

1.2 RF-Sensors to Support Urban WarfareThe advanced sensing technology derived from usingcooperative and synchronized radios in ad-hoc networks leadsitself to the natural application of through the wall sensing. Amulti-suite sensor technology including stepped-frequency,Ultra Wide Band (UWB) or synthetic wideband radartechnologies for through the wall sensing have been widelyrecognized and successfully demonstrated to date.

1.2.1 Wideband TomographyThe combination of simultaneous multiple-looks in a networkof synchronized sensors offers additional gain against clutterand increases resolution. The derived spatial diversity pro-vides a more robust target recognition capability. Widebandtomography is somewhat different than synthetic aperturesystems since it eliminates the need for the “full” synthesis ofthe aperture. Very wideband waveforms enable the use ofincoherent or semi-coherent tomographic imaging methods [1]that exploit the sensing of a target from multiple view angles.Hidden Markov Models [2] for target classification is furtherenhanced when multiple target-sensor orientations areavailable [3].

1.2.2 Passive Millimeter Wave Technology for theDetection of Concealed Weapons

Alternative methods for concealed target detection are alsobeing developed. Lockheed Martin Missiles & FireControl–Orlando (LM M&FC–O) began research into thedetection of concealed weapons under the sponsorship of bothgovernment and commercial interests in the mid-90s. Initialproof-of-concept tests were developed using non-radiatingmillimeter-wave (MMW) sensors at W-Band and showed thecapability of a rudimentary passive millimeter-wave system todetect both metallic and non-metallic objects concealed underclothing for static subjects (Figure 2) [4].

Based on this initial success, the National Institute of Justice(NIJ) provided additional funding through AFRL to build abrassboard system. This system was used to demonstrate thereal-time detection of metallic and non-metallic concealedweapons on stationary and moving subjects at standoff ranges

Figure 2. Proof-of-concept experiment revealsconcealed weapon.

and behind materials such as drywall up to 40 feet away. Whileproducing useful images, initial image quality highlighted theneed for better real-time scanning techniques and improvedmillimeter-wave low noise amplifiers (LNAs). Such upgrades[5] are required to provide the resolution and sensitivityneeded for accurate detection and classification of weapons atvarying ranges for both indoor and outdoor urban warfarescenarios. The use of the system as an “anomaly” detector toaid in the detection of concealed explosive packages is alsobeing investigated.

The NIJ brassboard incorporated dual linear receiver arrays (2X 17) consisting of discrete horn antennas which collected andtransmitted signals through waveguides to individualradiometer modules. A Cassegrain system was used to form animage of the scene for scanning by the receiver array. Theprimary mirror aperature was 12 inches, which offers promisefor a compact, handheld unit. A PIN diode switch wasincorporated at the front of each module to adjust for receivergain variation by selecting between the scene and a referenceload. Behind the PIN switch, a cascade of LNAs, a filter, and asquare-law detector diode supplied signal to a video amplifier.Along with the contributing losses from the switch and theinput transition from the waveguide, the LNA noise figure wasthe primary determinant of the overall noise figure and theresultant sensitivity of the system. The NIJ brassboard [6] i sshown in Figure 3.

Figure 3. NIJ MMW camera.

1.3 Organic Platforms ApplicationsOther wideband sensing and communication packages arebeing developed for use in organic platforms. The unique

capabilities of wideband signaling combined with biomimeticsensor design has led to the development of high performance,low cost, small-size and low power systems well suited fororganic platforms. Micro-Unmanned Aerial Vehicles (UAV)and Small Unmanned Ground Vehicles are among thecandidate platforms for bio-inspired sensors. Recent efforts inthe system design of an obstacle avoidance sensor for a smallUAV resulted in a bio-inspired anti-symmetric UWB/Videofusion system based on the Barn Owl audio/visual targetqueuing bio-system (Figure 4).

Figure 4. Organic platform applications for smallsize high performance collision avoidance sensor

that are bio-inspired and based on state of theart RF UWB sensing capabilities.

4. SUPPORTING FUTURE NETWORKCAPABILITIES

4.1 Wideband Communications ThroughEnhanced Waveforms and MIMOSystems

A coherent wideband version of Multiple Input MultipleOutput (MIMO) communications is currently underdevelopment. In the harsh environment of urban terrain,multipaths create complications and this emerging technologyexploits this complexity based on sophisticated signalprocessing across synchronized nodes to reach data rates closeto Shannon’s limit [7]. This wideband MIMO technology i scurrently being developed to permit robust high data ratetransmission in urban environment even for deep fadingchannels. This technique provides superior Low Probability ofIntercept & Detection (LPI/LPD) and Anti-Jamming character-istics for the waveforms based on the Coherent Multi-Bandwaveforms developed by LM ATL.

4.2 Resource Management SupportingSystems

The coordination of radios and sensors in MOUT is crucial tooperational success. Another effort is being undertaken foroptimizing the utilization of the RF resources, including fre-quency bands, time of operation and spatial reuse. Thisresource management for RF operation in MOUT is based onemerging agent technology. This solution creates limitedoverhead (few percent of total data flow) for the distribution

and coordination of the operations of the sensor/radionetworks within a squad, platoon, or the company level.

4.3 Mobile Agent RoutingAdvanced routing protocols are needed to send informationamong the networked nodes for MOUT applications. Our ad-hoc networking techniques allow the fast deployment ofsensor networks before or at the moment of group deployment.Scaleable ad-hoc quality oriented connectivity and integratedsensor network, with in-network processing capabilities, havebeen achieved while keeping overhead and processingrequirements to a minimum.

Lockheed Martin’s partner Intelligent Automation, Incorpor-ated has developed an ad hoc mobile network system based onthe use of software agents. This Mobile Agent Routing (MAR)protocol is designed to establish and keep connections for anad-hoc mobile network, given requirements for QoS andpriority of connections. The MAR protocol is a hybrid proto-col that is both proactive and reactive.

The two main aspects that distinguish MAR from other mobilead-hoc network (MANET) protocols are that although MARkeeps a connectivity table, it assumes this information is atleast partially stale. This assumption forces MAR to introduceelements of reactivity (reactive protocols find routes uponrequest) in its routing mechanism. The second key distinctionbetween MAR and other MANET protocols is that MARproduces routes that are linked to a specific connection,instead of a specific source/destination pair. The emergentbehavior of this cost function is to naturally distribute theroutes across available links. In the MAR protocol each nodeof the network is a potential routing agent. Each of theseagents holds data structures in which they store their own viewof the network, and their current resource allocation commit-ments. Using these data structures the network agents canprocess the data packets and commands issued to them.

4.4 Increased Performance Leads toIncreased Requirements

One of the most precious commodities exploited by thesefuture systems is bandwidth. In these systems large bandwidthradios front ends, antennas, Analog to Digital Converter (ADC)and processing capabilities are required because nextgeneration systems for urban warfare need to operate over widebandwidths (probably greater than a couple of GHz).

A simple example illustrating this case is a set of 8 nettedsensor/radios used to create a tomographic image of only 5m2

area with a 5 GHz bandwidth from 64 target/sensors positionsat 16 bits precision. In this case roughly 482 Kbits of datamust be transmitted over a common channel for the fusion at acentral node for a single update. This 5 GHz bandwidth resultsin a 3cmX3cm imaging resolution. To achieve performanceacross a XNET type system a 10 Mbps data throughput must besustained across an ad-hoc network in a harsh urban environ-ment for a 20 updates per seconds. This implies that eachsensor needs to support at least a 1.25 Mbps communicationrate.

5. FUTURE ELECTRONIC AND MMICREQUIREMENTS

The large bandwidth requirements present unique challengesfor the digitizing circuitry and associated RF signal chain.

Clearly performance will bottleneck at the weakest part of thesignal chain, therefore next generation electronics mustaddress the need for increased bandwidth for widebanddirective antennas, LNA, Variable Gain Amplifiers, ADC withgood resolution and low sampling noise, Track/hold devices,filters, etc.

The MAR solution discussed in Section 4.3 is built on anagent infrastructure called CybeleTM. The CybeleTM code itselfhas small memory requirement and has been ported to a handheld Personal Digital Assistant (PDA). It is fully feasible toimplement a CybeleTM node in a custom next generationmicro-electronics IC chip.

In the case of the concealed weapon passive millimeterradiometer (see Section 3) specific hardware improvement areplanned. The LNA MMICs used in the radiometers for thisconfiguration were fabricated on 4-mil thick Gallium Arsenide(GaAs) wafers using a mature 0.1 um gate length PHEMTprocess. The noise figure for the LNA was 4 to 5 db over a 12GHz bandwidth centered at 94 GHz with a minimum gain of 15dB. For a next generation design, LM M&FC–O anticipates thesubstitution of Indium Phosphide (InP) LNAs, as well asincorporating the antennas directly into the modules toeliminate transition losses. The InP process should reduce thenoise figure to 3 dB, provide higher gain per stage, andsubstantially reduce power consumption since InP draws 30%less current. Along with improved bandwidth, this approach i sexpected to reduce the noise equivalent differentialtemperature (NEDT) to less than one degree K, sufficient forindoor concealed weapon detection applications [8].

A key to success in evolving new capabilities has beencontinued emphasis in advancing both MMIC and transceivermodule technology in collaboration with industry partners.Looking into the future, we anticipate greater levels of inte-gration at the chip and module levels to reduce parts count andimprove yields. In the ideal case, this will lead to multi-channel modules incorporating integrated single channelchips.

6. CONCLUSIONSThis paper has presented some of the recent developments inemerging sensor and communication systems technology forMOUT undertaken by Lockheed Martin and its partners. Thepaper briefly discussed the current limitations in hardware andmicro-electronics and also offered an overview of the futurerequirements needed to realize these novel system concepts.

7. ACKNOWLEDGEMENTSOur thanks to Mr. Caposell of Naval Air Systems Command forthe invitation to participate in this GOMACTECH UrbanWarfare Special Session and to Mrs. K. Griggs for facilitatingour paper submission. IAI's work on software agent-based adhoc mobile network protocols and its development of asoftware agent-based ad hoc mobile network simulator werepartially supported by U.S. Army CECOM.

8. REFERENCES[1] Olivieri, Marc, “Bio-inspired Broadband SONAR Technol-

ogy for Small UUVs,” IEEE Proceedings of OCEANS(2002).

[2] Dong, Runkle, et al, “Multi-aspect Detection of Surfaceand Shallow Buried Unexploded Ordnance via UWBSAR,” IEEE Trans. Geo. Science & Remote Sensing, 39(6)(2001).

[3] Azimi, et al, “A Biologically Inspired Adaptive Under-water Target Classification Using Multi-Aspect DecisionFeedback,” IEEE Proceedings of OCEANS (2002).

[4] Randal Olsen, et. al. “Passive Millimeterwave Imagingusing a Sparse Phased-Array Antenna,” Proceedings o fSPIE, 3064, Passive Millimeter-wave Imaging (1997).

[5] Price, S., et. al. “Compact Video Rate Passive Millimeter-Wave Imager” 23rd International Conference on Infraredand Millimeterwave (1998).

[6] Pergande, A., L. Mirth, L. Anderson “CommercializationAspects of a MMW Camera,” Proceedings of SPIE, PassiveMillimeterwave Imaging (2002).

[7] Golden, Foshini, et al, “ Detection Algorithm and InitialLaboratory Results using V-BLAST Space-TimeCommunication Architecture,” Electronic Letters, 35(1)(January, 1999).

[8] VanderLugt, A. , “Signal Detection by Complex SpatialFiltering,” IEEE Transactions on Information Theory, 10,139-145 (1964).

9. BIBLIOGRAPHIESJames Saultz has been involved in LM ATL’s signalprocessing for many years and currently is leading thebusiness development. Gregory Barnett holds an MS in EEand his research interest are radar sensing, communicationsand signal processing (member IEEE). Dr. Marc Olivieri holdsa PhD in OE with a minor in EE. His research focuses onwideband systems for sensing and communications (memberIEEE).

Thomas Radovich is currently a Director at LM M&FC-O. Mr.Radovich is responsible for developing dual-use technologiesand implementing technology spin-offs and licenses. Mr.Radovich has been recognized for technical papers andcontributions to such professional organizations as SAMPEand AIAA. Albert Pergande has an MS in EE and has beeninvolved in RF and Radar design for 23 years. Mr. Pergandehas designed and field-tested many types of radar. He holdsseveral patents in the field of Radar system design, waveformmethodologies, and components. Lee Mirth has an BS in EEwith over 40 years experience in the defense and aerospaceindustry with a focus on advanced microwave and millimeterwave components and systems. Mr. Mirth is currently theProgram Manager for the millimeter wave concealed weaponsdetection system that uses passive imaging in a standoffconfiguration to detect objects under clothing.

Dr. Leonard Hayes is founder and president of IntelligentAutomation, Incorporated. Dr. Hayes is founding chairman ofboth the IEEE Robotics and Automation Society’s StandardsCommittee, and the Robotic Industries Associated StandardsCommittee R15.04, and is active in other ongoing standardsactivities.