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Cognitive Radio Networks and Dynamic Spectrum Access

2.1    Introduction

Two fundamental trends have jointly led to cognitive radio (CR) technology. The first one is the gradually increasing utilization of adaptation techniques in the transmitter/receiver design—for example, channel estimation, power control, adaptive modulation, and many other forms of adapting the radio unit parameters in response to stimulus from the surrounding environment. This trend coincided with the emergence of the concept of software-defined radio (SDR) as a communication unit that has most of its functionalities performed in software. In other words, SDR is a radio unit that is capable of easily supporting different technologies, standards, and environmental ...

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