Cognitive' radios the next step for SDR

The future of two-way radio communication lies in the ability to use a single device to communicate as a network with other types of devices, maximize the use of limited bandwidth and harness the power of flexible and adaptive software-based protocols. That future, the cognitive radio, is drawing ever closer thanks to software-defined radio technology.

Such radios will learn and autonomously perform "cognitive" functions, thanks to a form of intelligence that comes from their ability to be defined and upgraded using software. Software-defined radio (SDR) is the foundation upon which the cognitive radio will be built.

The term SDR was coined by Joe Mitola, chief scientist at the Defense Advanced Research Projects Agency, who saw a graduation of technologies that began with the hardware-defined radio and evolved into the digital radio and the software-defined radio, in which all applications can be configured by software. The Software-Defined Radio Forum has been working with this technology for several years and similarly defines SDRs as radios in which the software defines all the radio waveform properties and applications. Furthermore, an SDR is reprogrammable and may be upgraded in the field with new capabilities.

Harmonious integration
One of the SDR Forum's functions is to define the standards by which those upgrades can be performed so that new technology can be harmoniously integrated into the radio after it has been sold, without completely replacing all the previous software functionality. This will allow equipment developers-and, eventually, users-to enhance the capabilities of their equipment.

SDR technology standardizes the architecture and supports a wide variety of modulation strategies, access strategies and protocols as well as higher-level systems protocols such as trunk radio, satellite communications systems and even wireless access. The U.S. military has embraced the properties and characteristics of SDR technology by way of the Joint Tactical Radio System initiative, which will bring communications interoperability to each of the armed services across their platforms.

Earlier this year, General Dynamics Decision Systems demonstrated prototypes of "small-form-fit" SDRs that can fulfill multiple military communications functions and are tiny enough to integrate into miniature robotic devices or body electronics worn by soldiers. The demonstration emphasized that SDR technology can improve interoperability among military services and coalition partners, and solve bandwidth problems while reducing the number of radios required to accomplish these objectives.

Several software-defined radios are available today. In 2000, the U.S. Navy selected General Dynamics to develop the Digital Modular Radio, the first true SDR. The DMR's four-channel, full-duplex design provides essentially four radios in one.

The cognitive radio, a name also coined by Darpa's Mitola, is the next step and builds on SDR technology. Cognitive-radio technology represents an SDR with not only the ability to adapt to spectrum availability and to protocols and waveforms, but also the capability to learn waveforms and protocols, to adapt to local spectral activity and to learn the current needs of its user.

Cognitive-radio technology enables the radio itself to learn, allowing it to perform such cognitive functions as identifying and using empty spectrum to communicate more efficiently. Cognitive radios will sense and adapt their behavior according to the environment in which they operate. Once you have a device in which the software implements the protocols programmed for it, the radio can become smart and alert and can negotiate with its environment. In one potential commercial application, a cognitive radio learns about various services of interest to its user by being aware of its user's activities. It knows how to find those services and knows the likelihood that some services will be of interest to its user (the subscriber) in the immediate area.

For example, a cognitive radio could be aware of a Bluetooth network and what is available and of interest to its user within the Bluetooth service zone. It could also be aware of what's available in wireless-LAN range, cell phone range and so on. In one of Mitola's favorite examples, a cognitive radio notifies its user that a bookstore down the street has a rare book the user wants and tells the user how to find the store.

How does a cognitive radio get that smart? The defense community refers to a process called the OODA Loop: observe, orient, decide and act. This is similar to the process a human performs as he or she goes about deciding what to do in a particular situation. Those concepts can be extended to include planning and learning in the cognition cycle.

The cognitive radio may do many of these kinds of things. It may observe and orient itself to the spectrum environment, and decide and act on certain functions. Academic, industrial and government research will synthesize new protocols, etiquette and technologies in the form of software that is integrated into the cognitive radio. Software-defined radios and cognitive radios must use etiquette in order to know when it is appropriate to interact and how to interact with the environment.

Demonstrations of cognitive-radio techniques will be performed in both the commercial and research areas within the next three to five years. Spectrum rental transaction could be one such experiment that would prove the technology's value. I anticipate the SDR Forum and other standards activities will bring this technology to standardization within the next five to seven years. The SDR products and technology are a reality today.

SDRs with cognitive capabilities have the ability to implement protocols beyond traditional communications techniques. Knowledge and information transfer can be achieved with cognitive radios as the underlying technology enabler.

Bruce Fette is chief scientist at General Dynamics Decision Systems (Scottsdale, Ariz.).