The term cognitive radio, coined by Dr. Joseph Mitola, refers to "a radio frequency transmitter/receiver that is designed to intelligently detect whether a particular segment of the radio spectrum is currently in use, and to jump into (and out of, if necessary) the temporarily-unused spectrum very rapidly, without interfering with the transmission of other authorized users."
Cognitive radio promises to make future wireless communication devices â€œsmarter.â€ A device with cognitive radio capability could survey the electromagnetic spectrum, find the channels in use and those that are free, share this knowledge with nearby devices, and then select the best channel to use based on data throughput, signal strength, government regulations, and other factors.
Cordeiro, a senior researcher and project leader with Philips Research in Briarcliff Manor, N.Y, is seeking commercial applications for cognitive radio and establishing Philipsâ€™s relationships with academia and industry. Heâ€™s also a participant in the IEEE 802.22 Working Group developing standards for wireless broadband services operating at frequencies originally allocated for TV broadcast. The new services had to be designed to not interfere with the TV channels, and thatâ€™s why cognitive radios are necessary. Theyâ€™ll monitor the spectrum and use only idle channels.
To demonstrate such a control scheme, Cordeiroâ€™s team put together a prototype consisting of one computer streaming video to another. The researchers then activated equipment that simulates a TV stationâ€™s transmitter, generating a signal at the same frequency as computerâ€“computer video. Ordinarily, the interference would disturb the streaming video.
â€œBut because the computers are equipped with cognitive radios,â€ Cordeiro says, â€œthey rapidly detect the presence of the TV signal and seamlessly jump to another channel, without interrupting the video transmission.â€
With a range of 30 kilometers, the IEEE 802.22 technology may one day bring Internet and voice service to rural areas, disaster-stricken zones, and regions where wired infrastructure is scarce. One place Cordeiro hopes the technology will make an impact is Brazil, where less than 10 percent of households have broadband Internet access.
The idea of cognitive radio was first presented officially in an article by Joseph Mitola III and Gerald Q. Maguire, Jr. It was a novel approach in wireless communications that Mitola later described as:
The point in which wireless personal digital assistants (PDAs) and the related networks are sufficiently computationally intelligent about radio resources and related computer-to-computer communications to detect user communications needs as a function of use context, and to provide radio resources and wireless services most appropriate to those needs.
It was thought of as an ideal goal towards which a software-defined radio platform should evolve: a fully reconfigurable wireless black-box that automatically changes its communication variables in response to network and user demands.
Regulatory bodies in various countries (including the Federal Communications Commission in the United States) found that most of the Radio frequency spectrum was inefficiently utilized. For example, cellular network bands are overloaded in most parts of the world, but amateur radio and paging frequencies are not. Independent studies performed in some countries confirmed that observation and concluded that spectrum utilization depends strongly on time and place. Moreover, fixed spectrum allocation prevents rarely used frequencies (those assigned to specific services) from being used by unlicensed users, even when their transmissions would not interfere at all with the assigned service. This was the reason for allowing unlicensed users to utilize licensed bands whenever it would not cause any interference (by avoiding them whenever legitimate user presence is sensed). This paradigm for wireless communication is known as Cognitive Radio.
Depending on the set of parameters taken into account in deciding on transmission and reception changes, and for historical reasons, we can distinguish certain types of cognitive radio. The main two are:
â€¢ Full Cognitive Radio ("Mitola radio"): in which every possible parameter observable by a wireless node or network is taken into account.
â€¢ Spectrum Sensing Cognitive Radio: in which only the radio frequency spectrum is considered.
Also, depending on the parts of the spectrum available for cognitive radio, we can distinguish:
â€¢ Licensed Band Cognitive Radio: in which cognitive radio is capable of using bands assigned to licensed users, apart from unlicensed bands, such as UNII band or ISM band. One such system is described in the IEEE 802.15 Task group 2 specification.
â€¢ Unlicensed Band Cognitive Radio: which can only utilize unlicensed parts of radio frequency spectrum. An example of Unlicensed Band Cognitive Radio is IEEE 802.19.
Although cognitive radio was initially thought of as a software-defined radio extension (Full Cognitive Radio), most of the research work is currently focusing on Spectrum Sensing Cognitive Radio, particularly in the TV bands. The essential problem of Spectrum Sensing Cognitive Radio is in designing high quality spectrum sensing devices and algorithms for exchanging spectrum sensing data between nodes. It has been shown that a simple energy detector cannot guarantee the accurate detection of signal presence, calling for more sophisticated spectrum sensing techniques and requiring information about spectrum sensing to be exchanged between nodes regularly. Increasing the number of cooperating sensing nodes decreases the probability of false detection.
Filling free radio frequency bands adaptively (OFDM) seems to be the ideal approach. In fact, Timo A. Weiss and Friedrich K. Jondral of the University of Karlsruhe proposed a Spectrum Pooling system in which free bands sensed by nodes were immediately filled by OFDM subbands.
Applications of Spectrum Sensing Cognitive Radio include emergency networks and WLAN higher throughput and transmission distance extensions.
The main functions of Cognitive Radios are:
o Spectrum Sensing: detecting the unused spectrum and sharing it without harmful interference with other users, it is an important requirement of the Cognitive radio network to sense spectrum holes, detecting primary users is the most efficient way to detect spectrum holes. Spectrum sensing techniques can be classified into three categories:
o Transmitter detection: cognitive radios must have the capability to determine if a signal from a primary transmitter is locally present in a certain spectrum, there are several approaches proposed:
- matched filter detection
- energy detection
- cyclostationary feature detection
o Cooperative detection: refers to spectrum sensing methods where information from multiple Cognitive radio users are incorporated for primary user detection.
o Interference based detection.
o Spectrum Management: Capturing the best available spectrum to meet user communication requirements. Cognitive radios should decide on the best spectrum band to meet the Quality of service requirements over all available spectrum bands, therefore spectrum management functions are required for Cognitive radios, these management functions can be classified as:
- spectrum analysis
- spectrum decision
o Spectrum Mobility: is defined as the process when a cognitive radio user exchanges its frequency of operation. Cognitive radio networks target to use the spectrum in a dynamic manner by allowing the radio terminals to operate in the best available frequency band, maintaining seamless communication requirements during the transition to better spectrum
o Spectrum Sharing: providing the fair spectrum scheduling method, one of the major challenges in open spectrum usage is the spectrum sharing. It can be regarded to be similar to generic media access control MAC problems in existing systems
Three obstacles to cognitive radio
Cognitive radio (CR) is the next step in the evolution of software-defined radio (SDR). It takes SDR's ability to adapt to changing communications protocols and frequency bands and adds a new dimension: the ability to perceive the world around it and learn from experience.
FCC Commissioner Jonathan Adelstein says, "Cognitive radio technologies offer the potential for even more innovation that can spur our nation's productivity and our citizens' safety."
To the military this means radios that can adapt to the needs of any branch of the service, in any country, across time. To emergency and public-service providers this means spectrum sharing, while maintaining their priority. For the consumer it means a cell phone that can "tell" them, in real time, what the traffic conditions are ahead, where the nearest gas station is, and even how the surrounding terrain was formed.
It is a powerful vision of the future, which brings with it attendant challenges. The advent of CR engenders a quantum leap for policy makers and users alike. The concept of radio that can "learn" is a fundamental change in the perception of radio and the rules that govern it. In addition, the technology to create this new usage means a substantial overhaul of the way we do telephony today.
To realize the full potential of cognitive radio, there are hurdles to overcome. These include: the FCC development of policies that address and enforce the process and rules governing how frequencies and waveforms are selected and approved for use by cognitive equipment; software flexibility that can interface with policy updates; and functional interaction in the real world.
Development of policies
The first actionable challenge to development of CR lies with the Federal Communications Commission and related international governing bodies in developing policies governing cognitive radio. The two primary considerations are the language and protocols for initial interfacing with software and compliance/validation for existing instruments as policies change across time.
May 2003, marked the FCC's first public recognition of CR as a way to dramatically improve the efficiency of spectrum use. One of its first steps was a notice of proposed rule making and request for comment on "how rules and enforcement policies should address possible regulatory concerns posed by authorizing spectrum access based on a radio frequency (RF) device's ability to reliably gather and process real-time information about its environment or on the ability of device and/or users to cooperatively negotiate for spectrum access."
In response, a number of groups formed to provide feedback to the FCC. The National Science Foundation is studying and holding a number of interactive meetings with interested participants.
The newly formed Software Defined Radio Forum (SDRF) is taking a leadership role in exploring the questions that will help the FCC define policy. The SDRF is actively organizing people to begin to ask the right questions, defining interfaces and holding technical conferences.
Legacy spectrum holders are weighing in with their concerns about losing their spectrum. Internationally, the European and Asian communities are moving forward to develop their own policies, hoping there will be efforts to harmonize these policies among Europe, Asia and the Americas.
This need for national and international standards and policies is not theoretical, but urgently practical. Without it there can be no software development, and software is the very heart of CR.
Fundamentally, CR will have computational models of itself, its user, the uses it is put to, the networks available and its environment. Formulating standards in which waveform software has well-defined interfaces will not only make it feasible, but will in fact spur cooperation among developers of software.
As development moves forward, the greatest difficulty will be creating for an unknown future. As cognitive radios are placed in service, they will comply with prevailing operating rules of engagement. But on both the national and international fronts, policy will necessarily be fluid, adapting to changing needs, users, borders and technological advancements and challenges. It will be no small task to develop software agile enough to anticipate, accommodate and adapt to these unknown changes.
Current software development includes cellular waveform software, specifying what kind of waveform is needed to communicate in a particular application. But it must now expand into the kind of software that multimode radios can use to implement more than one waveform type. In addition, networking software needs to be developed that allows CR to participate in more than one network.
Other software development in the United States, principally through the Department of Defense and in academia, is in the early experimental stages.
Meanwhile, in Europe the E2R research program took a brisk approach and is studying end-to-end reconfigurability. This could effectively position them to control the intellectual property of CR. If the United States wants leadership in software development it may be necessary to set a more aggressive pace in software development.
The third and final hurdle for cognitive radio is real-life functionality. Cognitive radio will be required to interface with ever-expanding networks.
When the dream of cognitive radio melds into our highly mobile lives, it will be necessary to exhibit maximum flexibility and cognition to access shared spectrum on an opportunistic basis. For example, a construction foreman who stops at Starbucks on his way to the job site will need to see the color of the roofing that is being delivered to the site, and then find real-time alternatives to freeway congestion. When he gets to the site he'll need to e-mail the latest blueprint revisions to his home office, through the least expensive network. If he accidentally loses his phone, he needs it to call him and tell him where he lost it. And do this while sending and receiving phone calls and e-mails.
Currently there are few, if any, standardized protocols that lay the groundwork for this functionality.
As the appetite and need for services grows, networks are proliferating. In the defense community alone there are perhaps hundreds of different waveforms and networks made of those waveforms. Government networks are growing, including metro-area networks. In the commercial community there are Wi-Fi, WiMax, and Bluetooth networks. Add to these satellite networks based on Iridium that are capable of voice and data transmission.
The question now becomes: with so many points of entry and networks, each with their own services, how will CR be able to interface with the proliferation? The challenge then is to write software that is smart enough to choose the optimal network that fits the radio operator's requirements today and tomorrow.
Additionally, networks must be able to announce their availability. This network intelligence and access is integral to the CR's cognitive power.
We have difficult and complex questions facing us in the next decade. In addition to the pressing need to develop standards and policies, we face the daunting challenge of developing software that can imbue CR with the ability to reason, establish situational awareness and adapt to changing conditions in both policies and functionality.
By focusing time, energy and resources into both policies and software, we can realize the full potential of cognitive radio and its ability to maximize use of the spectrum while delivering ever-expanding services both here and around the world.