Reconfigurable Antennas for Cognitive Radio: Classification and Reconfiguration Techniques – Examples and Case of a Frequency Reconfigurable PIFA Antenna System Using a Microcontroller

Cognitive Radio And Reconfigurable Antennas

The development and rapid evolution of wireless technologies have led to a high demand in terms of spectral resources. The charter frequency allocation of the U.S. regulatory agency, the Federal Communications Commission (FCC) shows that most frequency bands are occupied by various applications. The radio spectrum is now become a rare resource and crowded, at least by regulation. Conversely, recent studies by the FCC (2002) also showed that the use of allocated frequencies varied widely, from 15% to 85%, depending on geographic areas and times of day.

In this context, the cognitive radio is an emerging technology in wireless access, to significantly improve the utilization of radio spectrum by allowing access opportunistically. Mitola (1999, 2000) introduces the concept of cognitive radio which defines it as a conscious radio system environment, capable of modifying its behavior to follow complex strategies. After the FCC (2003) approved this concept by redefining with slight variations. The idea of cognitive radio is to have a system that can interact with its radio environment in order to adapt, to detect free frequencies and exploit. More generally, a cognitive radio is a radio system that operates according to the following scheme: observation (measurement), decision (selecting a configuration), execution (reconfiguration), learning (cognition). This cognitive cycle is realized in parallel with the main function of the system, that is to say the communication. In radio opportunist, one of the applications of cognitive radio, the cycle is as follows:

Observation: information about the occupancy status of the spectrum; Decision: Depending on the information gathered, the radio selects a free frequency band for further communication; Execution: radio changes its configuration (transmit and receive parameters) in order to use the new frequency band; Learning: radio considers all these observations and decisions to anticipate, predict correct view.