Progress in the development of software-defined radios (SDRs) depends upon improvements in many components and software. Nevertheless, the electronics industry has wholeheartedly embraced the challenges in enhancing SDR technology. The name accurately summarizes the mode of operation for these radios: being able to modify the performance of the hardware components via software code. But accomplishing this still requires high-performance analog and digital componentssuch as low-noise amplifiers (LNAs) and data converters, respectivelyand system-level configurations that lend themselves to interoperability between SDRs from different manufacturers. These radios typically operate in the range from 2 MHz to 2 GHz.

SDR technology is now very much a part of commercial markets, such as cellular communications networks. But the technology owes much of its growth to the on-again, off-again US military Joint Tactical Radio System (JTRS) program. This program's goal has been to replace existing analog tactical radios with some form of a universal, software-programmable radio; the challenge has been to provide communications security in addition to interoperability among different military networks.

The JTRS has been fueled by some of the largest military contractors, including Boeing's efforts on a Ground Mobile Radio (GMR) version of the JTRS network and Lockheed-Martin's work on an air-and-sea version of the JTRS radio system, known as the airborne/maritime fixed (AMF) JTRS radio. JTRS radios are based on the Software Communications Architecture (SCA), which is an open-architecture framework that defines how the hardware and software work together.

Unfortunately, delays and cost overruns by Boeing led to a cancellation of their part of the JTRS program late last year (although the contract was scheduled to end in March of 2012). Boeing was working with Northrop-Grumman, Rockwell Collins, BAE Systems, and Harris RF Communications on the development of these high-performance GMR JTRS radios. Of course, cutbacks in the Army's part of the JTRS program can be traced back to the related Future Combat Systems (FCS) program, an ambitious and expensive effort at creating technology for the soldier of the future. The FCS program was cancelled in 2009.

Some of the problems that the Department of Defense (DoD) saw with Boeing's JTRS radios were linked to trying to support a wide range of sophisticated waveforms within relatively hardware-limited radios. The US Army, for example, has developed two waveforms for these programmable radiosthe Soldier Radio Waveform (SRW) and the Wideband Networking Waveformfor reliable and secure communications.

The SRW-based radios are designed to work with 1.2-MHz bandwidth allotments, while WNW radios operate optimally with 3- or 5-MHz bandwidth allotments. But these are memory/compute-intensive waveforms; Boeing has discovered that it is difficult to cost-effectively deliver an SDR-based radio that supports all of these waveforms and networks simultaneously.

Harris RF Communications has enjoyed a great deal of success owing to its involvement in the JTRS, but also for developing its own SDR-based radios. For example, the company just received a $39 million order from the US Special Operations Command (USSOCOM) for its Falcon III AN/PRC-152A wideband handheld tactical radios (see figure). This is the initial delivery order from a $400 million indefinite-delivery, indefinite-quantity (IDIQ) contract intended to help modernize SOCOM's tactical radio inventory. The contract also covers the Falcon III AN/PRC-117G multiband manpack radios.

The flexible AN/PRC-152A radio system supports both wideband and narrowband waveforms. Harris' wideband capabilities will be provided by the firm's Networking Wideband Waveform, which has been certified by the National Security Agency (NSA) for Type-1 High Assurance Internet Protocol Encryption (HAIPE). Harris expects to receive NSA Type-1 certification for the AN/PRC-152A to also work with the JTRS SRW later this year.

In addition, Data Link Solutions (DLS), a joint venture between Rockwell Collins and BAE Systems, was recently awarded a $25.8 million contract by the Space and Naval Warfare Systems Command (SPAWAR). This order is for the First Full Production & Fielding (FP&F) of Multifunctional Information Distribution System JTRS terminals, intended for the US Navy F/A-18 E/F (Super Hornet), Navy Lab, and NAVSUP (Navy Supply). They will also be provided to the US Air Force E-8 (JSTARS), RC-135 (Rivet Joint), EC-130E (Senior Scout), EC-130H (Compass Call), Air Force Participating Test Unit, and Warner Robins Air Force Base.

The MIDS JTRS is a four-channel terminal that includes Link-16 capability with the ability to incorporate additional networking waveforms as they become available. The MIDS JTRS project is a cooperative, competitive development effort between Data Link Solutions and ViaSat.

Meanwhile, the DoD has instructed Lockheed-Martin to restructure its efforts on JTRS with an eye towards enhanced affordability. The Lockheed-Martin AMF JTRS teamwhich includes BAE Systems, General Dynamics, Northrop Grumman, and Raytheonis working as part of an initial System Development and Demonstration (SDD) contract valued at $766 million. The AMF JTRS radios are being designed for use by fixed stations, submarines, surface ships, and aircraft.

The DoD's vision of how SDRs fit into the battlefield has changed a great deal since early concepts of SDRs in the 1990s. Recently, the Army's Joint Program Executive Office for JTRS has promoted its interest in JTRS radios developing into full-fledged cognitive radio systems (see www.army.mil/articles), which would also include software-defined antennas (SDAs).

A cognitive radio can be thought of as one step beyond an SDR, using a technique called dynamic spectrum access (DSA). This allows an SDR to detect and use available bandwidth in an operating area, changing its own transmission and reception characteristics to adapt to the available spectrum. In theory, an SDR with DSA can more efficiently and effectively make use of limited spectrum than a standard radio or even a JTRS radio. JTRS cognitive radios will also need to use a technique known as spectrum fragmentation, in which large-bandwidth waveforms can be spread across available portions of bandwidth.

For Lockheed-Martin, tests of the AMF JTRS radios aboard the Army's Apache attack helicopters flying in New Mexico late last year proved encouraging for the SDR technology. A combination of voice, data, and images were communicated from a test bed AH-64 Block III Apache helicopter to ground forces using the SRW. A pre-engineering developmental airborne radio aboard the helicopter linked directly with six ground forces equipped with JTRS Handheld Manpack Small Form Fit (HMS) Rifleman Radios. The Apache provided an aerial network extension, serving as a relayfor the ground-based troops. The Apache was able to break all connections in the network and then rejoin all units in the JTRS network, without major delay or information loss.

As noted earlier, not all SDR technology is military, and commercial communications providers are quickly discovering the benefits of having software-definable wireless networks. The industry group known as the Wireless Innovation Forum, is devoted to the development of next-generation radio technologies, including SDR. Also, SDR-BR is a group of amateur radio researchers and experimenters interested in SDR.

The uses for SDR technology on the commercial side are many, with new products spanning from component to system levels. Communications equipment and service provider Alcatel-Lucent has developed its multicarrier remote radio head (MC-RRH) based on SDR and multicarrier power amplifier (MCPA) technologies. It has become a building block of the firm's converged radio access network. The MC-RRH module enables carriers to handle two different technologies simultaneously, supporting Long Term Evolution (LTE) and multiple-input, multiple-output (MIMO) technologies with a single module.

Components suppliers supporting SDR technology are many. Altera boasts lines of field-programmable gate arrays (FPGAs) for SDR applications. Texas Instruments offers analog-front-end (AFE) integrated circuits (ICs) for femtocell base stations and portable SDR applications. For example, the latter's low-power, 12-b model AFE7225 AFE integrates a dual 125-Msamples/s analog-to-digital converter (ADC) and dual 250-Msamples/s digital-to-analog converters (DACs).

For the broadcast market, Carlson Wireless recently announced RuralConnect IP, an SDR that uses "white space" bandwidth left in the VHF and UHF spectra by broadcasters to provide wireless broadband service to underserved and rural areas. Carlson Wireless, which hopes to receive US Federal Communications Commission (FCC) certification for the device, worked with database provider Spectrum Bridge and KTS Wireless to develop the radio.