Spectrum sensing

As discussed in Chapter 2, cognitive radio (CR) aims at maximizing the throughput of secondary users coexisting with primary users under a noninterference or a limitedinterference assumption. Both assumptions require the secondary user to collect cognition about the radio environment, or spectrum sensing. Here the concept of spectrum space is extended to multiple dimensions, such as time, space, frequency, and code, and sensing may include not only detecting and classifying the regions of the spectrum space that can be used by secondary users, but also determining what type of signals are occupying the spectrum, including modulation, waveform, bandwidth, carrier frequency, etc. [50]. All these operations assume that the primary user is not aware of the presence of a secondary user.