AN/PRC-117F Special Operations Forces radio has applications for digital divisions and beyond

by David Fiedler

Evolving conventional-operations doctrine requires that the coordinated combat power of a joint-service combined-arms team be brought to bear on any substantial enemy. Army force-structure constraints dictate that the Army component of this force will depend on automated command-and-control systems to remain mobile and yet capable of concentrating its combat power at the critical time and place on the battlefield.

This concept was demonstrated with success during the recent Force and Division XXI advanced warfighting experiments. The AWEs demonstrated that within the combined-arms ground force, vital information (voice, data, video and imagery) needs to travel over distances that could vary from a few feet to thousands of miles. From a tactical-communications perspective, this means adaptive tactical-radio operations using many modulation modes and frequency bands are required to service emerging automated C2 systems. This same equipment also needs to maintain backwards compatibility with communications equipment which support existing systems that will remain in the force for many years to come.

In my opinion, the AWEs demonstrated the current generation of tactical-radio equipment (single-channel ground and airborne radio system, enhanced position-location reporting system, Spitfire, etc.) lack capacity and aren’t adaptive enough to meet these requirements. Current equipment supports only particular communications modes and is restricted to comparatively narrow frequency bands. Crossband digital communications with this equipment is difficult and requires a different radio for each radio-frequency band used. These limits detract from tactical operations and degrade C2 efforts, as well as joint and combined interoperability, because each service component traditionally operates in its own assigned frequency band using its own unique waveforms.

Also, the recent AWEs showed this generation of equipment is severely stressed in terms of data rate (speed), data performance (error rates), mutual-interference characteristics and transmission distance when used to support the tactical-internetting and data-transmission requirements created by deployment of automated systems into the tactical force.

Faced with problems similar to the "big Army," the Special Operations Forces community is outpacing us by moving to an adaptable, more modern, more capable and rapidly available family of tactical radios. Nomenclatured AN/PRC-117F (photo below), the SOF radio is a multiprocessor-based, fully digital, software-controlled, voice and data transceiver that goes a long way in meeting current and future tactical-radio communications requirements for an automated information-based tactical Army. Unlike any other radio available, the AN/PRC-117F radio family can be assembled into manpack, vehicular, marine craft and base-station configurations suitable for operation in a multiband, multimode, triservice, civil-military environment.

AN/PRC-117 compared to current equipment AN/PRC-117F, right, could replace all current radio equipment, left, according to the author.

AN/PRC-117F capabilities

The AN/PRC-117F SOF radio family is designed to act as the transmission means for a range of command, control and communications input devices (both digital data and analog) that have Army application far beyond SOF units alone. These include standard audio (voice) communications via a handset; line-level audio-data devices such as the handheld data terminals found in SOF, military intelligence, field artillery and other units; analog teletype modems; C2 digital data-terminal equipment as found in the Army battle-command systems; personal computers; electronic-mail systems, video systems, fax and more. The radio itself can operate across both the very high frequency and ultra-high frequency military tactical-frequency bands using either line-of-sight modes or satellite propagation media for beyond-line-of-sight communications. Encryption is internal to the radio and is implemented in both hardware and software.

Thanks to microprocessor design, digital signal processing and software control, AN/PRC-117F is actually the equivalent of many current radios in one manpack or vehicle-mounted box. This greatly reduces the space, weight, power and support requirements for both individual fighting platforms and tactical-operations centers. This also greatly reduces cosite interference problems and, if used properly, can reduce the number of tactical-radio nets required to support a digitally equipped fighting force. The following characteristics of AN/PRC-117F details why this family of equipment is so attractive to use as a transmission means – not only in SOF, but also in heavily automated units such as the first digitized division, first digitized corps, joint contingency force, strike force and other applications.

FREQUENCY RANGE 30-512 MEGAHERTZ. This frequency range covers not only the "standard" Army tactical (30-88 mHz) band but also covers the frequency bands and modulation modes commonly used by the Air Force, Navy and Coast Guard for operations, air-traffic control, tactical data links and maritime uses. This makes AN/PRC-117F ideal for use as a "liaison radio" or "gateway" between service components using different waveforms for joint ground sea and air operations. Also, AN/PRC-117F’s frequency range and waveform modes are compatible with civil and public-service frequency bands commonly used by non-Defense Department local, state, federal and foreign agencies. This makes AN/PRC-117F the only multifunction radio now in the inventory capable of performing multiple service and civil-military operations from a single package.

Further, from the digitized-Army C2 perspective, the extended frequency range will allow frequency managers to better deal with the horrendous cosite interference and frequency-management problems at our current and projected TOCs. These problems are caused by trying to cram so many narrowband radio emitters into such a small physical space. (See "Cosite interference: Force XXI communications roadblock," Army Communicator Fall 1996 edition, Page 54.) AN/PRC-117F comes programmed for compatibility with traditional modulation modes and electronic counter-countermeasure waveforms currently installed in equipment linked with particular frequency bands (for example, SINCGARS 30-88 mHz frequency modulation and frequency-shift-keying modulation). But because the radio is processor/software-based, virtually any modulation mode or waveform available can operate in any part or across the frequency range.

MODULATION. As delivered, the radio is programmed at the factory for compatibility with current "standard" modulation characteristics segmented in the traditional RF bands:

VHF lowband (30-90 mHz) FM, FSK. This makes the radio interoperable with SINCGARS, AN/VRC- 12 family radios, AN/PRC-68, AN/PRC-126 and a host of other tactical radios of both foreign and domestic manufacture. Tactical encryption equipment such as KY-57 normally used with this equipment (not most SINCGARS) aren’t required for AN/PRC-117F since the radio has built-in communications-security and standard waveform (SINCGARS) compatibility already installed. Currently AN/PRC-117F isn’t compatible with the system-improvement program version of SINCGARS used in small quantities for the tactical Internet, but a software-generated modification is underway that will provide SIP-waveform interoperability if the waveform is adopted Armywide.
VHF high (90-225 mHz) FM, amplitude modulation, FSK, amplitude shift-keying. In this frequency band, AN/PRC-117F can be used for air-to-air, air-to-ground and ground-to-ground voice and data communications using waveforms found in this band. AN/PRC-117F is compatible with a variety of existing military aircraft and air-traffic-control radio communications, as well as military air-to-ground data-link communications, the commercial marine band, Navy/Coast Guard communications and civil police, fire and emergency-management standard radios. AN/ARC-73, AN/ARC-134 and AN/ARC-115 are but a few examples of the "standard" military equipment compatible with AN/PRC-117F in this frequency band. Because of this capability, joint and civil-military liaison for both voice and data can be accomplished in one radio by units that have AN/PRC-117F. This is particularly important to the Army National Guard because of the Guard’s large role in civil/military operations.
UHF (225-512 mHz) AM, FSK, ASK. In this frequency band, AN/PRC-117F can be used to perform air-to-air, air-to-ground, ground-to-ground, fixed or mobile radio communications missions for both voice and data modes. In this frequency band, AN/PRC-117F is compatible with ECCM-capable equipment such as AN/ARC-164 and AN/ARC-182 that can be widely found in existing triservice ground, airborne and special-mission systems.
UHF satellite communications (243-270 mHz, 292-318 mHz). In this frequency range, AN/PRC-117F is fully compatible with single-channel and demand-assigned multiple access tactical-satellite systems. The radio in this mode has full orderwire capability and can send and receive data at a rate of 64 kilobits per second in a 25-kilohertz channel or 12 kbs in a five-khz channel. Also, automatic requests for retransmission of bad data packets and COMSEC are embedded in the radio hardware and software. This key SATCOM capability gives AN/PRC-117F a feature no other standard combat-net radio has: the ability to communicate BLOS without retransmission stations from the same radio package that’s used for LOS communications.

In addition to BLOS capability, interference reduction and multiband/multimode capabilities that are very useful in CNR applications, AN/PRC-117F has many other capabilities. These capabilities make AN/PRC-117F an excellent choice for use as a data-transmission means for applications such as TI or as a point-to-point data hauler between TOCs, particularly when they’re located BLOS or are on the move. One possible architecture for this application is shown in figure below.

Improved tactical Internet connectivity Improved tactical Internet generic connectivity at brigade and below using AN/PRC-117F. Notes: doesn't show all connectivity; 1) existing 16 kbs SIP SINCGARS used at platoon and company to reduce costs; 2) area data net used for situation awareness; 3) TOC and support area connected via 64 kbs 117F link; 4) SIV connectivity supplemented by other systems (mobile-subscriber equipment); 5) SIV trunk net can be LOS (64 kbs) or SATCOM (56 kbs); 6) high-speed point-to-point links will require more 117s; 7) any 117F net can use SATCOM for wide-area coverage.

Future uses

The radio is a true marriage of radio and computer. As such, it has a true digital architecture based on an MPC860 microprocessor chip and DSP. This means hardware can be reconfigured and software reprogrammed to optimize performance without even opening the radio case.

To facilitate the radio’s use as a digital data-transmission device, RS-232, RS-422 and MIL-188-114 input/output ports are provided integral to the radio, along with synchronous and asynchronous data interfaces. This makes it very easy to interface DTE, computer workstations and networking components such as command-post routers to the radio for data-transmission applications (figure below). Most importantly, AN/PRC-117F has demonstrated data-transmission rates of 56 kbs through SATCOM and 64 kbs ground-to-ground (LOS). These rates are many times faster than current CNR equipment being used in the experimental TI.

AN/PRC-117F data interface comparison AN/PRC-117F data interface comparison.

If AN/PRC-117F replaced current equipment for the TI mission, these data rates would make data transmission among brigade and battalion TOCs and lower echelons fast enough to support lengthy database-to-database transfers. Transmission of databases, plans, orders and reports that are now difficult and time-consuming to do over tactical radios would be much faster. This would not only improve operations but would also reduce system vulnerability to enemy intercept and detection. Also, these rates will support user-desired C2 tools such as videoteleconferencing, imagery transmission, enroute mission planning and collaborative planning that aren’t practical using current lower-data-rate equipment.

AN/PRC-117F achieves transmission security through several means. As produced, it uses standard TRANSEC waveforms associated with compatible equipment operating in particular frequency bands. Specifically, in the low VHF band it uses the standard SINCGARS waveform. In the UHF frequency band it uses HaveQuick I/II waveforms, and for SATCOM it uses DAMA waveforms. This scheme was chosen to maintain backward compatibility with current radio systems’ waveforms. If desired, a pure AN/PRC-117F radio net could use any existing antijam waveform across the full frequency spectrum. Also, since the radio is software-controlled, new TRANSEC waveforms can be easily inserted into the radio via software, if desired, making equipment-hardware modification a thing of the past. In the current configuration, TRANSEC key variables are entered using standard fill devices such as the MX-18290 or the KOI-18.

COMSEC is also integral to AN/PRC-117F. In addition to being fully interoperable with SINCGARS and HaveQuick COMSEC, AN/PRC-117F also is compatible with systems using KY-57, KYV-5, KG-84C and other external encryption devices. Standard fill devices like KYK-13, KOI-18, KYX-15 and others are all that’s required to load the COMSEC variables.

In addition, AN/PRC-117F has many more features that make it extremely useful for SOF, conventional, National Guard and data/automation operations. These include:

Manpack, vehicular, marine and base-station configurations;
Built-in ECCM and COMSEC capability;
Voice/data retransmission across traditional frequency bands and waveforms;
Data rates up to 64 kbs with built-in interfaces;
Full remote-control capability (all functions);
Longer battery life due to low voltage logic design;
Multiband scanning;
100-channel presets each for fixed frequency, ECCM, DAMA;
Manpack weight is 10 pounds (without battery, antenna, handset);
Optional Global Positioning System interface for navigation and time signals;
Meets MIL-STD-810E environmental requirements;
Software-reprogrammable to accommodate evolving waveforms, ECCM, COMSEC, signal processing and modulation techniques; and
Dual antennas for optimal performance (30-512 mHz).

The AN/PRC-117F family is designed to provide the SOF user with the most advanced tactical communications technology available in a single package. Due to a microprocessor-based, software-controlled design, the radio can be tailored to fit any unconventional, conventional or data/automation mission requirements. Using AN/PRC-117F technology also makes the equipment more user-friendly and cost-effective when compared to current "standard" equipment.

From the larger Army perspective, if used as a data-communications device for applications such as TI, AN/PRC-117F offers multiple advantages. These include higher data rates, improved cosite interference characteristics and BLOS transmission capabilities no other CNR offers in a single software-programmable package. When used in more traditional tactical modes, this technology will enhance communications effectiveness by providing interoperability with legacy waveforms from all military services, plus the capability to perform the civil/military support mission not available in current equipment.

Most importantly, AN/PRC-117F provides a platform for advanced and evolving high-performance waveform insertion through software, not hardware. This means that as systems evolve, the costly production of new equipment or modification of existing hardware won’t be required – an important factor in our cost-constrained environment.

Planned system improvements already under construction include expanding into the high-frequency band (two-30 mHz), plus embedded modem and COMSEC compatibility with existing HF systems; creating compatibility with the SINCGARS SIP waveform used in the current experimental TI; and introducing the next generation of DAMA, SATCOM and high-data-rate HF waveforms.

Conclusions

The communicators at SOF have made an intelligent decision by selecting AN/PRC-117F for their use. The equipment provides a great advance in filling the Armywide requirement for a multiband, multimode, multifunction radio that has been needed for far too long. Characteristic of SOF aggressiveness, they’ve procured and placed into operation a true tactical, fully digital radio far ahead of other Army components. Also, the multiprocessor DSP-based design will ensure modifications and improvements can be implemented through software, thus keeping the equipment easily modernized to the maximum extent possible for years to come.

The emerging digital-information-based Army would do well to follow SOF’s lead and also use this equipment for a multitude of C2 roles within the Army’s divisions and corps. As we approach the reality of Army XXI and FDD, the need for AN/PRC-117F as a data-transmission device has become more and more apparent as the weaknesses of current tactical radios are revealed in strike, light and mounted experimental environments. AN/PRC-117F – with just its current capabilities – can do much to repair the tactical-communications weaknesses identified in the experiments conducted over the last four years. At the same time, wide use of the software-programmable AN/PRC-117F in Army XXI will position tactical communications so the leap to Army 2010 and beyond will be far less painful than past radical changes in tactical-communications technology. The Signal Regiment needs to fully consider the opportunity the SOF community has created for the rest of the Army before we go much further down the road we’re currently on.

Retired LTC Fiedler is employed as an engineer and special assistant to the project manager, operational tactical data systems, Fort Monmouth, N.J. He has served in Army, Army Reserve and Army National Guard Signal, infantry and armor units and as a Department of the Army civilian engineer since 1971. He holds degrees in both physics and engineering and an advanced degree in industrial management. He is the author of many articles in the fields of combat communications and electronic warfare.

Acronym QuickScan
AM – amplitude modulation
ASK – amplitude shift-keying
AWE – advanced warfighting experiment
BLOS – beyond-line-of-sight
C2 – command and control
CNR – combat-net radio
COMSEC – communications security
DAMA – demand-assigned multiple access
DSP – digital signal processing
DTE – data-terminal equipment
ECCM – electronic counter-countermeasure
FDD – first digitized division
FM – frequency modulation
FSK – frequency shift-keying
HF – high frequency
Kbs – kilobits per second
Khz – kilohertz
LOS – line-of-sight
MHz – megahertz
RF – radio frequency
SATCOM – satellite communications
SINCGARS – single-channel ground and airborne radio system
SIP – system-improvement program
SOF – Special Operations Forces
TI – tactical Internet
TOC – tactical-operations center
TRANSEC – transmission security
UHF – ultra-high frequency
VHF – very high frequency
Legend for diagrams
INC – Internet controller
Radio icon – AN/PRC-117F
R – router
S – SINCGARS SIP
SAT – SATCOM
SIV – systems-integration van
TMG – tactical multinet gateway

dividing rule

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04/04/12

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