Driven by the increasing demand for radio spectrum bands, it is now becoming extremely hard to find vacant bands to deploy new value added services. Spectrum shortage results from the spectrum management policy rather than from the physical scarcity of usable frequencies. Dynamic Spectrum Access (DSA) is proposed as an emerging solution to optimally use the radio resources. DSA allows secondary (unlicensed) Cognitive Radio (CR) users to access the spectrum, avoiding harmful interference with primary (licensed) users. The CR technology is a context intelligent radio capable of autonomous reconfiguration. Spectrum sensing is the enabling technology that allows cognitive radios to detect free bands (spectrum holes) and opportunistically access the radio spectrum. This paper presents an overview about the major spectrum sensing strategies, discussing some related fundamental issues and solutions. In particular, some relevant patents about this topic are discussed as well as detection strategies, current challenges and future solutions.
Keywords: Cognitive radio, dynamic spectrum access, primary detection, spectrum holes, spectrum sensing, Receiver Detection, Interference Based Detection, Transmitter Detection, Matched Filter Detection, Energy Detection