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SDRs Grow As Flexible Communications Devices

June 15, 2011
While it was initially pushed by the militarys need for interoperable radios, the use of software-defined-radio (SDR) technology has become widespread enough to reach hobbyist and amateur radio markets.

Software-defined radio (SDR) technology is entrenched in many military applications, but has also made its mark in commercial applications, notably in amateur-radio and short-wave-radio markets. The radio approach, which employs digital signal processing (DSP) in place of functions formerly handled by analog hardware, offers the potential for flexible interoperability among many different existing radio platforms as well as the capability of defining and changing (when necessary) custom waveforms to maintain high levels of security in tactical communications.

SDR technology owes much to the funding of the US Department of Defense's (DOD's) Joint Tactical Radio System (JTRS) program and its various components, including portable Ground Mobile Radio (GMR) designs for the US Army. The basic idea for JTRS radios is to provide critical communications for all joint forces operations and, through software programming, work with new waveforms and emulate current force radios for communications with existing tactical radios.

Funding continues to be active for JTRS and SDR technology. Earlier this year, BAE Systems announced that it had received a $9.4 million contract for its Link-16 Software In-Service Support (SwISS) for JTRS. Work will include technical support, enhancements, maintenance, and upgrades to the JTRS Link-16 waveform software. The total program value could reach $24.3 million if all options are exercised.

Around the same time, Scalable Network Technologies (SNT) was awarded an independent SBIR Phase III Basic Indefinite Delivery/Indefinite Quantity (ID/IQ) from the Joint Program Executive Office for the Joint Tactical Radio System (JPEO JTRS). The contract has an estimated value of $11 million. It is in support of the JTRS Network Emulator, a virtual laboratory that allows real-time emulation of large-scale (as many as thousands of radios) communications networks with different types of waveforms.

Also earlier this year, Lockheed Martin and its Airborne & Maritime/Fixed Station Joint Tactical Radio System (AMF JTRS) team, with support from Boeing, demonstrated the use of its SDR-based JTRS radio system onboard an AH-64D Apache (Block III architecture) helicopter. The test involved transmitting data and video from the helicopter to ground-based radios. Lockheed Martin's AMF JTRS is a secure, multi-band, multimode radio network capable of providing joint forces with simultaneous voice, data, and video communications. During the demonstration, held at Boeing's Mesa, AZ facility, the AMF JTRS team integrated an AMF JTRS Small Airborne Joint Tactical Radio enabled with the Wideband Networking Waveform (WNW) onto an Apache helicopter. The AMF JTRS was then used to transmit live streaming video and real-time situation awareness data from the Apache's onboard infrared camera to multiple ground-based radios.

In terms of the radios themselves, Harris Corp. has long contributed to tactical radio technology with both analog and digital designs. In fact, the firm's experience with SDR technology dates back to the production of its RF-5000 radio in 1988. Many of the company's SDR platforms use the Software Communication Architecture (SCA) infrastructure specifications developed for JTRS radio communications. The FALCON II radios represent one of Harris's more popular SDR-based tactical radios, with over 15,000 of the radios in the field.

And companies perhaps better known for other products, such as test equipment stalwart Rohde & Schwarz, also contribute to the growth of the technology with their own SDR products, including the R&S M3TR SDRs. These radios (see figure) include the R&S MR300xH/U manpack transceiver, with frequency ranges of 1.5 to 108 MHz or 25 to 512 MHz, developed for all aspects of tactical communications. These multi-band, multimode radios can operate with a wide range of waveforms, and feature embedded 256-b key communications security (COMSEC) protection.

These manpack radios can deliver transmit power levels to 150 W through HF (1.5 to 29.9 MHz), to 50 W through VHF (30 to 107.9 MHz), and to 50 W through UHF (108 to 512 MHz). They feature integrated Global Positioning System (GPS) receivers and position-reporting capabilities and a removable front panel for flexibility.

Another company associated with test that also offers an SDR solution is National Instruments. The firm's SDR system is based on a PXI Express platform, using the NI PXIe-5641R Rio transceiver which operates from 9 kHz to 2.7 GHz with a 20-MHz real-time bandwidth.

Although SDR technology tends to be most associated with military tactical radios, the technology is spreading quickly in commercial circles, notably in amateur radio designs and in short-wave radios. The families of radios from FlexRadio Systems, for instance, have been developed with SDR technology for amateur radio use.

As an example, the FLEX-3000 radio system features a 96-kHz receive bandwidth and greater than 90 dB dynamic range. It incorporates 24-b analog-to-digital converters (ADCs) and digital-to-analog converters (DACs), with all receive and transmit filtering performed in the digital realm, by means of DSP.

In terms of components, a number of suppliers offer support for integrating their digital components into DR architectures. Texas Instruments, for example, offers a complete SDR block diagram (using their components in key places) online at docs/solution/folders/print/357.html.

National Semiconductor offers high-speed 12-b ADCs for use in SDRs, along with a good amount of on-site technical support for developing SDR designs. And Altera, a member of the Software Defined Radio Forum, offers high-performance Stratix FPGAs to perform the digital IF and baseband processing in SDRs. (Information on the SDR Forum can now be found on the Wireless Innovation Forum).

On the software end of SDR development, GNU Radio offers a free software development toolkit to develop the processing blocks of an SDR for use with low-cost RF hardware. And Green Hills Software provides its royalty-free INTEGRITY realtime operating system (RTOS), certified to the latest IEEE POSIX.1-2003 specification for use in SCA-compliant SDR platform development.

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