Cognitive Radio and Dynamic Spectrum

Software-Defined Radios (SDR) were initially defined so as to facilitate changing the characteristics and capabilities of a radio interface simply through reprogramming. Its evolution, Cognitive Radio (CR), was one where the programmability of the SDR can be made over-the-air and on-the-fly. What is more, however, is that a CR had sufficient processing capability to autonomously understand and react to various elements of the radio's context of operation [8]. Among other things, these characteristics include identifying whether the current spectrum band of operation is the best spectrum available for the radio's active communication, and whether there are bands that are available and, for example, would offer greater bandwidth or better transmission quality. For CR to perform, it requires more than simply identifying whether or not a particular spectrum band is busy – rather, it becomes important that the radio recognizes what entity is utilizing that spectrum, and know for how long will this utilization will take place.

Such distinction is greatly important, especially in light of recent international cooperation between the different Telecommunications Regulatory Authorities (TRA) of the different countries and the ITU-R. These cooperations are at spectrum harmonization, refarming and reallocation. In addition, many countries now recognize primary and secondary users for certain bands, allowing for cooperative arrangements and coexistences between the different spectrum users, both licensed and unlicensed. It thus becomes possible for a secondary user to utilize spectrum “holes” or “empty spots” in a primary user's band or, depending on the band and mode of communication, for both primary and secondary users to operate in the same band [9]. Such cognition, however, is not limited to licensed bands. Bluetooth, for example, is already instilled with adaptability so as to overcome from other devices in the ISM band such as WiFi network elements or microwaves.