Embedded Avionics, Military

SDR Takes Flight

By By Charlotte Adams | February 1, 2013
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Left to right, the Harris Airborne Multiband Radio (HAMR), the Harris Small Secure Data Link (SSDL) and the Rockwell Collins Gen5 ARC-210 Software-Defined Radio.

After a prolonged and costly gestation, software-defined radio (SDR) technology is gaining ground. Airborne tactical networking radios, data links and relays based on SDR architectures are being fielded today. New procurements are brewing in the United States and elsewhere, and SDR has gone from concept to reality.

A SDR is like a computer with a radio frequency (RF) front-end. Functions that previously were hard-wired, such as modulation/demodulation and encoding/decoding, are now programmable, said Lee Pucker, CEO of the Wireless Innovation Forum, an industry standards group.

“All modern radios are SDR,” says one military program manager. The technology is “becoming the standard by which we launch all new developments,” agrees Troy Brunk, Rockwell Collins’ acting vice president and general manager for communications and navigation. But whether SDR technology has reached the off-the-shelf procurement level remains to be seen. The U.S. Army’s new Small Airborne Networking Radio (SANR) NDI (non-developmental item) program will test that view. 

Rockwell Collins in January said it completed the first installation of the ARC-210 Gen5 radio on an HH-60G Combat Search and Rescue (CSAR) helicopter for the U.S. Air Force Air National Guard (ANG).

The way has not been smooth. The mammoth Joint Tactical Radio System (JTRS) development program reportedly consumed $15 billion over 15 years with only a 50 percent success rate. The survivors are the MIDS JTRS airborne data link — for Multifunctional Information Distribution System — and the Handheld Manpack Small Form Fit (HMS) radios. Gone are the Ground Mobile Radio (GMR) and the Airborne Maritime Fixed (station) (AMF) contracts, although the AMF moniker remains with new programs. The current small tactical airborne networking SDR, Rockwell Collins’ fifth-generation ARC-210, was developed with about $33 million in funding from the Naval Air Systems Command (NAVAIR) outside of the JTRS program.

Part of SDR’s allure is its promise to reduce life-cycle costs, compared with conventional radios. If additional capability is needed once the radio has been shipped, and that capability can, for the most part, be added via software, then it could be less expensive in the long run, explains Tom Waters, NAVAIR’s ARC-210 team lead. “If we’re maintaining [RF] hardware that doesn’t change, it’s easier — the logistics footprint is minimized.”

Another advantage is increased operational flexibility, says Mark Robey, product manager for the Army’s SANR program. For example, if a mission requires a two-channel radio to run the Soldier Radio Waveform (SRW) on both channels, instead of two different waveforms, such changes can be made in the field.

ARC-210 Reinvents Itself

The Navy is buying the generation-five (Gen5) Rockwell Collins’ ARC-210 radio, redesigned as an SDR. Between 750 to 1,000 of the new radios have been delivered and a handful have been fielded, Waters says. Gen5 platforms include variants of the V-22, H-60, H-1, H-53 and E-2. (The Air Force also buys off the Navy contract.) The SDR now ships with the HaveQuick, Demand Assigned Multiple Access (DAMA) SATCOM and Single Channel Ground and Airborne Radio System (SINCGARS) software waveforms.

Perhaps the Gen5’s biggest benefit is the radio “fits in the same spot in the aircraft,” Waters says. It uses the same mounting and interfaces and exactly the same connectors as prior generations of the product. The interfaces and form factor were defined a long time ago and would be very disruptive to change. The difference is that “all waveforms in the Gen5 radio are software-defined.”

“It’s 100 percent backward-compatible,” Brunk says. “All functionality that’s ever existed before, we retained. The same size, weight and power, identical connectors and pinouts.” There are still spare connectors, and now there is an Ethernet port.

The ARC-210 program currently is working to incorporate the Integrated Waveform (IW) into the new radios. Billed as “DAMA [SATCOM] on steroids,” with improved connectivity and greater user access, IW is expected to be fielded in Gen5 radios this year.

Data Link: MIDS JTRS, a four-channel SDR produced by Data Link Solutions (DLS), is being fielded on F/A-18E/Fs. (DLS is a joint venture between Rockwell Collins and BAE Systems.) The current MIDS JTRS radio operates the Link 16 software waveform. The spare channels could be used for Link 16 enhancements as well as the Tactical Targeting Network Technology, (TTNT) waveform, Brunk says. Rockwell Collins hopes to be under contract to put TTNT into the radio in the second quarter of 2013 and to be fielding it by the FY 2015 timeframe.

SANR and SALT: SANR, a new Army program, seeks an essentially off-the-shelf, two-channel radio for Apache AH-64D Block III, Black Hawk UH-60M/L, Chinook CH-47F and Kiowa Warrior OH-58F helicopters. SANR comes under the AMF umbrella as the successor to the AMF two-channel Small Airborne (SA) radio, which aimed to replace conventional single-channel radios like the ARC-210 but was eventually terminated over schedule and cost concerns. SANR would fill an urgent need — the service views the airborne node as critical, Robey says.

SANR scales back the requirements of its predecessor. The SA two-channel SDR was expected to run dozens of waveforms, including the Wideband Networking Waveform (WNW), SRW, Mobile User Objective System (MUOS), VHF/UHF Line of Sight and Link 16 waveforms — two of them simultaneously if need be. For now the Army has split off SA’s prior Link 16 requirement into a separate two-channel SDR, the Small Airborne Link 16 Terminal (SALT), aimed just at the Apache fleet.

SANR, by contrast, focuses on the waveforms that are required immediately. The Army wants to be able to operate the SINCGARS and SRW waveforms simultaneously, and run a “mid-tier” waveform such as the WNW. Contract award is expected in FY 2014, and as many as 7,000 radios could be procured over a 12-year period.

SANR’s NDI approach reflects the thinking that “there’s been enough money out there in industry [for] there to be something … ready to go,” Robey says. Replies to a July 2012 RFI were encouraging, with a lot of the candidates well within the required dimensions, a tough challenge. The Army understands some products would have to go through certification for airborne use, but SANR is not a development program, he says.

Among the candidates for SALT and SANR is Harris’ Small Tactical Terminal (STT). The company has sold more than 100 STTs, and they are flying on multiple airborne platforms today, says Ed Zoiss, vice president of programs for Harris’ C4ISR business. The dual-channel radio can operate VHF/UHF and Link 16 simultaneously or run two channels of VHF/UHF, and can function as a VHF/UHF relay. “It fits squarely into the SALT domain,” Zoiss says.

Although SALT is looking for a Link 16 SDR for the Apache, the Army also is putting some STTs on the Apache, according to Zoiss. Data from the test and evaluation of these units probably will be used by the service to formulate how they go forward, he thinks.

There would be advantages to having an integrated solution like STT for the Apaches, and the SALT procurement has gone back and forth on the issue, Zoiss says. Having Link 16 and VHF/UHF radios in one box would simplify integration — with one chassis, one power supply and one set of connectors. The company is positioning the Harris Airborne Multiband Radio (HAMR) for the SANR buy. HAMR is the “back half” of the STT, with two channels of VHF/UHF. HAMR has not been fielded yet, but it is a “simple matter” to remove the Link 16 unit from the current configuration, Zoiss says.

General Dynamics sees an opportunity for its small form fit (SFF) “B,” a two-channel HMS radio, in the SANR program. The radios already are planned for the Shadow UAV program as communications repeaters for the ground network, says Joe Miller, director of business development and strategy for General Dynamics’ C4 Systems.

Because the SFF-B is intended for embedded in applications, it “has really lined up well with SANR requirements,” Miller says. Airworthiness certification for use on helicopters is not that great a bar, he says, because the radio is not flight-critical equipment.

The Gen5 ARC-210 radio could also fit this space even though it is a single-channel radio, Brunk says. It can do cross-banding and transmit/receives over a second receive path built into the radio.

SDR Challenges

The No. 1 hardware challenge for SDR is size, weight and power (SWAP). SDR architectures dissipate a lot of heat and the availability of cooling on an aircraft is limited. Antennas are also a limiting factor since size depends on frequency. And analog-to-digital conversion is not as close to the antenna is designers would like.

But software is more of an issue, says Vik Patel, CEO of Datasoft, a developer of SDR technology and waveform-building tools. Software has a tendency to expand to consume the processor it runs on, and battery life depends on software efficiency. Also network monitoring and spectrum management issues have to be resolved, he says.

There are also security challenges about information that could be leaked if the network was tapped into. The size of the pipes, the accessibility of information to multiple nodes and the kind of data sent over the networks “is still under a lot of scrutiny,” says Brunk of Rockwell Collins.

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