Evolving radio technology: SDR to cognitive radio

History

October 09, 2013

Sally Cole

Senior Editor

Military embedded systems

Software-defined radio is no longer just a military technology, having evolved beyond the now-defunct Joint Tactical Radio System (JTRS) program, it can be found in commercial and defense applications around the world and is essentially a solved problem. Meanwhile, a major remaining challenge is the limited amount of available spectrum. Dynamic spectrum management is needed to navigate what’s left, and cognitive radio is seen as the technology that will make this possible.

Software-defined radio (SDR) technology is thriving in defense and commercial applications despite the demise of its patron, the Department of Defense (DoD) JTRS program. SDR devices are in the hands of today’s warfighters not only through certain JTRS successes, but also through various non-developable item (NDI) programs and independent development by companies such as Harris Corp. in Melbourne, Florida. To see also : 85 Patents Granted for Week of Feb. 8 » Dallas Innovates. New SDR products continue to be developed and an upgrade to the Software Communication Architecture (SCA) is forthcoming. Yet, challenges still remain for users and designers of SDR solutions – especially the impending spectrum shortage that will likely force a shift to cognitive radio.

Software defined radio is a solved problem

Most radios in the world today, including telephones, are based on SDR technology because some level of physical baseband processing is done on a digital signal processor (DSP), which is a programmable device.

“The key to software-defined radio is really the ability to reprogram the radio to change its functionality,” explains Lee Pucker, CEO of the Wireless Innovation Forum, a nonprofit international industry association focused on radio communications and systems worldwide and based in Reston, Virginia (www.wirelessinnovation.org).

The definition of SDR, developed by the Wireless Innovation Forum in conjunction with the IEEE, is “a radio in which some or all of the physical layer functions are software programmable”.

A key distinction is that there is no connection between SDR and radio frequency (RF), meaning it can be SDR and only be able to transmit in one band, according to Manuel Um, vice president of marketing for Coherent Logix, a supplier of high-performance processors that to enable the next generation of software-defined systems in Austin, Texas. Uhm also serves as Chief Marketing Officer and Treasurer of the Wireless Innovation Forum. “Many people confuse SDR with a radio that can receive or transmit anywhere in the wideband spectrum, which is not true,” points out Um. “What it really means is that the actual processing of the master tape, or part of it, is done in software.”

JTRS and its SDR targets

Like so many wireless technologies, SDR was originally developed by the military. This is not new technology; the military has been working with it for over 20 years and was the first to field it through their JTRS program. Most military systems around the world operate with JTRS-like systems that define SDR as the way forward for all radios. A big impetus behind JTRS was the ability for warfighters to reduce the number of radios they had to carry. The AN/PRC-154 Rifleman radio from General Dynamics C4Systems in Phoenix, Arizona is an example of a successful dismantled radio that came out of the JTRS program. It transmits voice and data simultaneously using the Soldier Radio Waveform (SRW) (see Figure 1).

Figure 1: The AN/PRC-154 Rifleman radio from General Dynamics emerged from the JTRS program and transmits voice and data simultaneously using the Soldier Radio Waveform (SRW).

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“A typical communications soldier on the battlefield today might carry between 20 to 30 radios because you need different radios to talk to different services and forces,” Wm says. “Each of these radios is like a brick, so imagine running around Afghanistan with 20 to 30 of these bricks on your back… it’s ridiculous.” Another driver was the drive to save costs. “If the radio waveform is software-defined, in theory you can easily port the waveform to next-generation radios using next-generation processors that are higher performance and lower power,” Wm explains.

Although DOD and US government agencies funded the initial development of the JTRS, they have, for all intents and purposes, now canceled the program – having achieved their goals. “Going forward, they’re not funding development, they’re funding the purchase of radios. They are still spending money to buy existing SDRs that have been developed under JTRS, but only off-the-shelf,” notes Wm.

A recent example of spending on off-the-shelf SDRs is a $38 million order placed by Harris Corp. to provide tactical radios to expand the deployment of wideband tactical communications in the US Air Force. The Air Force is using Harris’ Falcon III AN/PRC-117G multiband backpack and AN/PRC-152A multiband handheld tactical radio systems to accelerate the deployment of JTRS broadband network capabilities for para-rescue, combat communications and other Air Force personnel. While this type of investment will continue, in the future, if companies want to provide new features or waveforms, they will likely have to fund them themselves.

Development of SDR: Software Communication Architecture 4.0

While SDR devices are becoming more widely used on the battlefield and in law enforcement such as Falcon radios, the enabling technology behind SDR – Software Communications Architecture (SCA) – is currently undergoing a revision called “SCA 4.0”. The SCA is the key component of any SDR as it enables reconfiguration of the SDR. This is the middleware that allows the radio waveforms to be designed in the software.

SCA 4.0 takes this concept a step further by allowing users to tailor SCA components to specific applications. It will be “more modular and allow you to select parts of the SCA to use for a specific program,” explains Pucker. “One of its capabilities is dynamically allowing you to tune and break waveforms.” By taking a more modular approach, you can remove parts of the SCA that you don’t use and “shrink the footprint to create something that’s more easy to instantiate a specific kind of radio platform,” says Pucker. “Allows more a la carte SCA options than the comprehensive previous versions.”

Cognitive radio: The next frontier

Beyond SDR remains the challenge of the limited amount of spectrum available. Industry experts see cognitive radio as a solution to this problem.

“Cognitive radio is the next frontier,” says Um. “It adds dynamic spectrum access capability to SDR, which means you can still change the type of waveform processing the radio does, but now add a wideband RF front end and you have a radio with the intelligence to scan across a wide bandwidth of the spectrum to identify “holes” in the spectrum and transmit through them.

Why would you want this opportunity? It is a well-established fact that the traditional licensed spectrum model is not sustainable going forward. “At some point, we’re going to have to move to spectrum sharing to maximize our use, or else we’re going to run out of spectrum — that’s inevitable,” Um says.

Cognitive radio will have implications for everyone, including the military, which may end up losing or sharing spectrum in the future. The military uses dedicated spectrum, as do public safety and mobile operators. Whatever decisions are made in the regulatory environment will have a huge impact on all of these markets.

The scope of this problem also extends much further, as one of the battlegrounds is the ultra-high frequency (UHF) spectrum (~500 to 700 MHz) used by broadcasters. This is a very desirable spectrum as this frequency tends to propagate further and pass through walls – providing much better radio performance than shorter wavelengths. Today, television broadcasters own this highly coveted spectrum surrounded by buffer strips or open channels between television channels, also known as television white space. As we have moved from an analog world to a digital one, these open channels are no longer needed.

To share spectrum on these open channels, cognitive radio technology is an obvious solution. If the military needs to move within spectrum, for example, cognitive radio will allow them to adapt to changes without having to replace radios, according to Uhm. “It makes sense to use cognitive radios that can change and move within different spectrum bands, rather than replacing them with fixed-function radios that can become obsolete again in a few years,” he explains. “This is an issue that the defense industry is aware of because it could have significant implications for them – not only within the military communications market, but some of the spectrum in question is also used by military radars.”

The military radar spectrum is ~3 GHz, which also falls within the range of commercial services. If this range of spectrum is opened up in the future, an entire swath of military radar may need to switch to another frequency.

The bottom line is that regardless of what happens in the regulatory environment with spectrum sharing, “moving forward, we’re going to start seeing more cognitive radio capabilities and dynamic spectrum access added to SDR capabilities,” Pucker says.

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