Instantiation of the TADIL-A Waveforminto a Software Programmable Tactical Intelligence Terminal

by

Ernie FrankeRaytheon Systems Company

St. Petersburg, FL 33733

TActical Digital Information Link-A (TADIL-A) is usedfor situational awareness dissemination to thewarfighter at both HF and UHF. With the recentaddition of TADIL-A to the Joint Tactical Terminal(JTT) Operational Requirements Document (ORD), itserved as a test for demonstrating the ability toinstantiate a legacy broadcast waveform into a softwarere-programmable, digital tactical intelligence terminal.Software resident in a field-proven TADIL-A DataTerminal Set (DTS) was re-written in Higher OrderLanguage to provide operation for both HF and UHF.

I. The Joint Tactical Terminal (JTT)

Meeting the warfighter’s need for timely, secure, tacticalintelligence and targeting information, the Joint TacticalTerminal (JTT) [1] provides a high-performance,software-programmable radio, with modular functionalitythat is both backward and forward compatible with themigration of the Integrated Broadcast Service (IBS). TheJTT program provided the first truly scaleable, flexible,open-architecture, software digital radio to bringintegrated tactical and intelligence broadcasts into the nextmillennium. The JTT provides critical data links to battlemanagers, intelligence centers, air defenders, fire supportelements, and aviation nodes across all services andaboard airborne, sea-going, subsurface and ground mobilemission platforms. The JTT allows each warfightingCommanders-in-Chief (CINC), Army, Air Force, Navy,Marine Corps, Special Operations Forces (SOF) and otheragency users to exploit the current IBS intelligencenetworks: TRIXS, TIBS, TDDS, TADIXS-B and 5/25kHz DAMA. In addition, the JTT supports the evolvingIBS broadcast architecture, including changes to messageformats and transmission protocols. With the recentaddition of TActical Digital Information Link-A (TADIL-A)/Link-11 to the JTT Operational RequirementsDocument (ORD) [2], it serves as a test for theinstantiation of a legacy intelligence broadcast. Link-11 isthe NATO designation (STANAG 5511) of TADIL-A.This paper describes the program for implementing theTADIL-A/Link-11, receive-only capability into the familyof JTT terminals. Transmit functionality will be addedlater.

Figure 1: The JTT can support up to 12 receivechannels, while simultaneously operating full-duplex on4 transmit channels. ………………………….

The JTT places prime importance on flexibility, scaleability,portability, interoperability, and adoption of widely-accepted (commercial), open (published) standards. JTT isflexible, in that it meets the variable demands of thewarfighter through the ability to exercise multi-mode, multi-channel, multi-mission roles. It is responsive to the IBSORD because it can both interoperate with currentwaveforms and accommodate a migration to a commonwaveform, protocol, or data format, and can accept newwaveforms. It is responsive to change using “plug and play”technology insertion. It is scaleable with a choice in thenumber of transmit and receive channels or scaleable withinthe family of terminals.

II. Open Systems Architecture (OSA)

Future tactical intelligence terminals will be comprised of afamily of radios that share common interchangeableHardware (HW) and Software (SW) components (modules)to simplify management and support. An open-systemarchitecture focuses on modularity by function with thedevelopment of a library of common HW and SW modules,cutting across current radio equipment types to enable anatural progression of module improvements withtechnology advances (technology insertion). The functionalflow of processing in a radio terminal conforms to a generalstandard, as shown in Figure 2.

0-7803-5538-5/99/$10.00 (c) 1999 IEEE

The tactical intelligence terminal is naturally divided intothree major segments: Radio, INFOrmation SECurity(INFOSEC) and Message Processing. Each segmentperforms a function that can easily be re-programmed toalter the HW or SW functionality. The radio segment, forinstance, can be commanded to any frequency within theoperating band. It also performs an antenna matrixselection to connect the proper antenna to the correctchannel. The radio segment also handles black-side, linkprocessing such as frequency hopping or spreading, blockand differential coding, interleaving and modulation. TheINFOSEC segment includes both the CommunicationsSecurity (COMSEC) and Transmission Security(TRANSEC). COMSEC is the encryption of the messagedata, while TRANSEC is the modulation overlay on thetransmitted signal. The INFOSEC segment bridges theblack and the red buses with INFOSEC cryptography. Thered-side (classified) message processing segment performsmessage filtering and formatting, video compression,correlation, while providing a user interface via aGraphical User Interface (GUI), serial bus or Client-Service application for a Man-Machine Interface (MMI).

Technological transparency is characterized by standardizedmodular functions, independent of waveform (network) orpackaging. The modules use widely-accepted, non-proprietary interfaces that interconnect core designs througha tailored adapter that enables portability to alternateembodiments, effectively creating a bus-independentarchitecture. The software may then be placed into a libraryof re-usable components. Modular-granularity is a trade-offbetween the ability to perform Pre-Planned ProductImprovement (P3I) and to minimize Life-Cycle Cost (LCC).Each module has comprehensive functional descriptions andwell-know/understood interfaces. This allows third-partyvendors to spin-on their specific areas of expertise.…………………….JTT software is written in a High-Order Language (HOL),allowing it to be transportable across a family of widely-used commercial processors. By developing the TADIL-Asoftware in an HOL (C for the DSP), it can be easily re-compiled to host it on a new processor. As processor speedssteadily increase, the software is simply re-hosted on thelatest version in the backwards-compatible family ofprocessors.

Multi-FrequencyBand Filtering

Frequency TranslationFrequency HoppingAntenna Interface

Power Amplifier

Multi-ModeMod/DemodInterleave/

De-InterleaveFEC

Preamble

COMSECTRANSECEncryptionDecryption

II/O BufferingTDP Interface

Black-Side Control/Data Bus Red-Side Control/Data Bus

RF Segment INFOSEC Segment

ProgrammableI/O

ProgrammableProcessor

ProgrammableINFOSEC

ProgrammableModem

ProgrammableRF Front-End

Control/StatusCorrelation

Fitlering/FormattingNetwork Processing

Digitized MapsBuilt-In Test

Message Processing Segment

T/R Switching

EthernetMIL-STD-1553

EIA-232/422

Figure 2: Segmenting the terminal by function with well-defined interfaces ensures that technology insertion may be isolated to the single module.

III. TADIL-A Network Operation

TADIL-A/Link-11 employs netted communicationtechniques with a standard message format for exchangingdigital information among airborne, land-based andmaritime tactical data systems to any area of the world, asshown in Figure 3. TADIL-A supports an extensive range ofmissions including wide-area monitoring, tacticalIndications and Warning (I&W), Over-the-Horizon (OTH)targeting, and intelligence. TADIL-A is used by a number ofintelligence platforms that conduct Signal Intelligence(SIGINT) data collection including CommunicationsIntelligence (COMINT) and Electronic Intelligence(ELINT). TADIL-A data communications operate both in

the High-Frequency (HF) and in the Ultra-High Frequency(UHF) bands. When operating in the HF band (2 to 30MHz) the ground wave can deliver ranges up to 300 nauticalmiles (nm), with a sky wave range of 1,000 nm. UHF (225to 400 MHz) operation provides gapless, omnidirectionalLine-of-Sight (LOS) coverage to approximately 20 to 30 nmship-to-ship or 150 nm ship-to-air, depending on aircraftaltitude. In addition, UHF Satellite Communications(SATCOM) operation (292 to 390 MHz uplink / 243 to 270MHz downlink) is available for Beyond Line-of-Sight(BLOS) operation using FLTSAT and UFO UHF satellites.

0-7803-5538-5/99/$10.00 (c) 1999 IEEE

Figure 3: Multi-service TADIL-A networks initiate with the first capable Net Control Station (NCS) arriving in theatre.

In addition to the standard intelligence broadcasts such asTIBS, TDDS and TADIXS-B, which are received over UHFSATellite COMmunications (SATCOM), aircraft have adesire to receive TADIL-A over HF or UHF SATCOM forlong-range planning and over UHF LOS for in-theatreupdates. Today’s forces must be ready to respond to a crisisat almost any point at any distance. The time from take-offto time over-target or objective can be as much as 12 to 15hours. The ability of the Air Mobility Command (AMC),

Figure 4, to accomplish their mission can be dramaticallyimpacted by changes in the objective area while forces areenroute. The JTT provides the means to receive informationrelevant to conditions in the objective area while enrouteand over the destination as symbology is overlaid ontostored images and charts, indicating parameters and lethalityranges in two and three dimensional representation. GPS isused for centering data on their own platform or on an offsetreference point.

C-5 Galaxy KC-135 Stratotanker

Figure 4: The Air Mobility Command (AMC) requires situational awareness updates enroute to their destination.

TADIL-A is a secure digital data link that operates in a RollCall mode under control of a Net Control Station (NCS),with the rest of the platforms designated as pickets. Sincethe HF band was the first application of TADIL-A,waveform selection depended heavily on compatibility withexisting signals. Thus a waveform having the same framelength as radio teletype (75 baud) and using multi-toneaudio to replicate voice was chosen. After sending aninterrogation message, the NCS waits 15 frames (0.2 sec) fora response from other platforms. If a response is notreceived, then the NCS continues with the operation of the

Network. Since the TADIL-A net is typically operatedaround a 300 nm radius HF and 30 nm for UHF LOS, shipsand aircraft have plenty of time to respond to the NCSinterrogation. When TADIL-A is operated through asatellite, the NCS would not receive a response, since round-trip delay is approximately 0.25 seconds. Thus SATCOMoperation requires a change in link protocol. The NCS isoperator-selectable to extend its allowable response up to250 frames (3.33 sec.) in one-frame increments. Special timegating is also incorporated to inhibit the signal received viathe echo.

E-2C Hawkeye

P-3C Maritime Patrol EP-3 Story Teller RC-135 Rivet Joint

EA-6B Prowler

TAOM/MCE

Patriot MissileAEGIS DD/DDG/CG

CV/LHA/LHD

EC-130ABCCC

E-3 AWACSES-3 Viking

CVN/LHA/LHD

USMC & USAFTAOM/MCE

EC-130ABCCC

KC-10 Extender

C-130 Hercules

C-141 Starlifter

C-17 Globemaster III

AEGIS DD/DDG/CG/CGN

0-7803-5538-5/99/$10.00 (c) 1999 IEEE

There are many different TADIL-A equipmentconfigurations aboard each platform, however they alwaysconsist of the following units: the Tactical Data System(TDS) or computer, the cryptographic device (KG-40) orcrypto, the Data Terminal Set (DTS) or modem, and the HFor UHF radios as shown in Figure 5. TDS computers supplytactical digital information to net participants, and retrieveand process incoming tactical digital information receivedfrom net participants. The software executing in the TDScomputer performs many other functions in addition tomaintaining the tactical database. It manages the displays,performs interim updates of track locations, responds tooperator entries and inquiries, and controls all peripheralinput and output data. Maritime platforms utilize a NavalTDS (NTDS) with a parallel interface, while airborneplatforms utilize the Airborne TDS (ATDS), with itscorresponding serial interface.

Figure 5: Actual functions may be combined or embeddedin software to form the TADIL-A system.

The TDS computer accepts operator entries, such as the DataLink Reference Point (DLRP), Participating Unit (PU)identification, track block data, and various filter selectionmodes. After information is received, it is correlated, ormatched with information already in the database. Forcedgridlock is the process of adjusting the local tactical grid ofeach unit to that of the DLRP, thereby gridlocking all units.

The interface between the TDS computer and the DTS iscontrolled by the DTS. The KG-40 cryptographic deviceoperates between the TDS and the DTS, providingCOMmunications SECurity (COMSEC) for each 24-bit wordof tactical data that flows through the system. The JTT usesan embedded HAYFIELD cryptographic device for receive-only capability. Future expansion to add transmit capabilitieswill be available with the advent of the CORNFIELD or theAdvanced INFOSEC Module (AIM) crypto device.

The DTS serves as both a Modulator/Demodulator (Modem)and as a Link Protocol controller. The DTS encodes TDSdata into multi-tone audio for HF and UHF LOS andgenerates and recognizes protocol signals that control theoperation of the net. HF operation uses Single Sideband

(SSB) suppressed carrier techniques for either Upper (USB),Lower (LSB), or Independent (ISB) sidebands for frequencydiversity. UHF LOS operation use Frequency Modulation(FM) techniques, as shown in Table I. The DTS converts theTDS binary data stream into Shaped Binary Phase-ShiftKeying (SBPSK) for UHF SATCOM. Efficient use of 5 kHz(narrowband) SATCOM channels requires the selection ofdata rates and modulation waveforms that make maximumuse of the available channel bandwidth, without causinginterference to adjacent channel users. Using shaped,constant-amplitude vector modulation of 2400 bps SBPSK,adjacent channel emissions are contained to allow SATCOMusers to operate at a 10 kHz channel spacing [3].

The receiving DTS makes corrections to the receivedmessage using a Hamming Error Detection and Correction(EDAC) technique. Each data word is 24 bits, plus 6 controlbits added for parity check. If one bit is in error, the controlbits can determine which bit is in error and correct it.

There are five modes of DTS operation: Net Synchronization(NS) to establish initial communication by the NCStransmitting preamble frames; Net Test (NT) for connectivitychecks using a known test pattern and for setting line levels;Roll Call (RC) for the normal mode of operating the net; andShort Broadcast (SBC) and Broadcast (BC), where a picketor NCS will broadcast its information once (SBC) orcontinuously (BC). In the normal RC mode of operation, oneplatform is the NCS, with the rest of the platforms designatedas pickets. The NCS will begin net operation by broadcastinga short message known as an interrogation. Each picket willrespond with a message. All participants will hear each picketreply. During the next round, the NCS will address eachpicket in sequence. When all of the pickets have broadcasttheir data, the NCS will broadcast its own data to completeone cycle of the net, with no operator intervention required.

The UHF LOS signal is downconverted and demodulatedfrom FM to multi-tone audio in the JTT receiver. Presentlythe HF receiver is external to the JTT. With the advent ofmulti-band modules, such as the 2 MHz to 2 GHz receiverfrom the Digital Modular Radio (DMR), even this functionwill be embedded in the tactical terminal. At this point theUHF LOS or the HF data information is extracted from theDE-QPSK signal.

For UHF LOS and HF, the modem processes a 16-tonewaveform, in which 15 of the tones are differentially-encoded, quadrature phase shift-keyed (DE-QPSK)modulated. The tones are spaced every 110 Hz beginningwith a single unmodulated 605 Hz tone for used for Dopplercorrection. Since each tone of the DE-QPSK signal containstwo bits of information, the modem output contains 30 bits ofdata per 75 bps baud. The frame interval (either 13.33 or 22msec) coincides with phase shifts to yield either a 2250 or1364 bps (normal or slow) modulation rate.

RADIOSYSTEM(HF/UHF)

D ATATERMINALSET ( DTS)

CRYPTODEVICE(KG-40)

SENSORSAND

WEAPONS

TACTICALDATA

SYSTEM(TDS)

DISPLAYSYSTEM

0-7803-5538-5/99/$10.00 (c) 1999 IEEE

Each TADIL-A message consists of a preamble, a start code,data and a stop code. The preamble is the first five frames ofevery transmission, consisting of two audio tones. The 605Hz tone is used for Doppler correction, while the 2915 Hztone is alternately shifted to provide frame sync. Doppler

correction maintains stability to 75 Hz, with 3.5 Hz/sec oftracking. HF Doppler correction operates independently onboth sidebands and is operator selectable betweenLSB/USB/Diversity.

Table I: Comparison of HF, UHF LOS and UHF SATCOM TADIL-A modes and rates.

Mode Information Rate Modem I/O Modulation Military StandardHF 1364 or 2250 bps Multi-tone AM: USB/LSB/ISB MIL-STD-188-203-1A

UHF LOS 1364 or 2250 bps Multi-tone FM: +20 kHz pk deviation MIL-STD-188-203-1AUHF SATCOM 2400 bps Binary SBPSK, 5 kHz channel MIL-STD-188-181

Figure 6: Instantiation of the TADIL-A waveform touches each of the functional segments of the tactical terminal.

IV. Hardware vs. Software Approach

Instantiation of the TADIL-A waveform presented a choicebetween using an existing, dedicated VME, single-boardmodule solution (hardware solution) and importing asoftware module into universal Modem and Black Processormodules (software solution). The trade study clearly showedthat the modular software approach was the preferredmethod for adding the TADIL-A function to a re-programmable tactical terminal. The terminal would beeasier to upgrade, since it is re-programmable through asoftware download. The terminal reliability would beimproved, due to the decrease in overall hardware andpower consumption. The terminal has more expansioncapability using the vacant slot. A dedicated TADIL-Amodem represents a dedicated “slice” concept, as opposedto a modem that is “personalized” to a TADIL-A DTSduring configuration of a channel.

The assembly code from a field-proven DTS was re-writteninto the high-order language (HOL) of "C" for hosting themodem function on the TMS320C6201 Digital SignalProcessor (DSP) fixed-point device in the Joint TacticalTerminal. The highly-efficient C compiler enables users toprogram in C language, offering up to 80% code cycleefficiency compared to hand-coded assembly, resulting in afaster time-to-market for the end user.

V. Conclusions

Instantiation of the TADIL-A/Link-11 broadcast waveformhas been performed on a software, re-programmable tacticalintelligence terminal by re-hosting a software module into are-programmable modem, black-side processor andembedded cryptographic device. … …….

VI. References

[1] S. Kostek and E. Franke, “Joint Tactical Terminal andCommon Integrated Broadcast Service - Modules(JTT/CIBS-M),” IEEE MILCOM 98, C6.6, October 1998,Boston, MA, pp. 112-118.

[2] Operational Requirements Document (ORD) for theJoint Tactical Terminal (JTT) and Common IntegratedBroadcast Service–Modules (CIBS-M), 13 September1996.

[3] E. Franke, “UHF SATCOM Downlink Interference forthe Mobile Platform,” IEEE MILCOM 96, October 1996,McLean, VA, pp. 22 – 28.

….

UHF (LOS or SATCOM) Joint Tactical Terminal (JTT)

RF/IF Modem Link COMSEC Red TDS Protocol I/O

Multi-tone TADIL-A, KG-40 Algorithnm, Serial, (HF, UHF LOS) /Link-11 Crypto Bypass Ethernet

PSK (UHF SATCOM)

HF

HF Radio

0-7803-5538-5/99/$10.00 (c) 1999 IEEE