Cognitive Radios

A Cognitive Radio (CR), as defined by the researchers at Virginia Polytechnic Institute and State University, is “a software defined radio with a cognitive engine brain”.^[1]

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Description

In response to the operator’s commands, the cognitive engine is capable of configuring the radio system parameters. These parameters include “waveform, protocol, operating frequency, and networking”.^[2] It functions as an autonomous unit in the communication environment and frequently exchanges information about the environment with the networks it is able to access as well as with other CRs (Wipro Technologies, 2002).^[3] A CR “monitors its own performance continuously, in addition to “reading the radio’s outputs”; it then uses this information to “determine the RF environment, channel conditions, link performance, etc.”, and adjusts the “radio’s settings to deliver the required quality of service subject to an appropriate combination of user requirements, operational limitations, and regulatory constraints”. These processes have been described as “reading the radio’s meters and turning the radio’s knobs”. ^[4]

Practical application

CR can sense its environment and without the intervention of the user can adapt to the users communication needs while conforming to FCC rules. Conceptually, the amount of spectrum is infinite, practically for propagation and other reasons; it is finite because of the desirability of certain portions of the band. Even the spectrum which is assigned is far from being 100% utilized, hence efficient use of the spectrum is a growing concern. CR offers a solution to this problem. A CR can intelligently detect whether any portion of the spectrum is in use or not, and can temporarily latch into or out of it without interfering with the transmissions of other users thereby efficiently utilizing spectrum. According to Dr.Bruce Fette (2004), “Some of the radio’s other cognitive abilities include determining its location, sensing spectrum use by neighboring devices, changing frequency, adjusting output power or even altering transmission parameters and characteristics. All of these capabilities, and others yet to be realized, will provide wireless spectrum users with the ability to adapt to real-time spectrum conditions, offering regulators, licenses and the general public flexible, efficient and comprehensive use of the spectrum”.^[5]

The future of CR

The phenomenal success of the unlicensed band in accommodating a range of wireless devices and services has led the FCC to consider opening further bands for unlicensed use. In contrast, the licensed bands are underutilized due to static frequency allocation. Realizing that CR technology has the potential to exploit the inefficiently utilized licensed bands without causing interference to incumbent users; the FCC released the Notice of Proposed Rule Making to allow unlicensed radios to operate in the TV broadcast bands. The IEEE 802.22 working group formed in November/2004 is equipped with the task of defining the air interface standard for Wireless Regional Area Networks based on CR sensing for the operation of unlicensed devices in the spectrum allocated to TV service.^[6]

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