CR may demonstrate most of the properties this information for its own purposes, such as utilization of shown, but is not required to be absolutely repar- open channels on a non-interference basis. Methods for ameterizable. Note that the industry consensus is that measuring spectrum occupancy are discussed in commonly a CR is not required to be an SDR, even though it may available literature. demonstrate most of the properties of an SDR. However, A simple sensor resembles a spectrum analyzer. The there is also consensus that the most likely path for differences are in quality and speed. The CR application development of CRs is through enabling SDR technology. must consider the quality of the sensor in setting parameters such as maximum time to vacate a channel upon use by an incumbent signal. It ingests a band of 2.4b.5 Available technologies interest and processes it to detect the presence of signals above the noise floor. The threshold of energy at which for CRs occupancy is declared is a critical parameter. The detected energy is a function of the instantaneous power, in- The increased availability of SDR platforms is spurring stantaneous bandwidth, and duty cycle. An unpredictable developments in CR. The necessary characteristics of duty cycle is expected. Spectrum occupancy is spatially an SDR required to implement a practical CR are excess variant, time variant, and subject to observational block- computing resources, controllability of the system op- age (e.g., deep fading may yield a poor observation). erating parameters, affordability, and usable software Therefore, a distributed approach to spectrum sensing is development environments including standardized ap- recommended. plication programming interfaces (APIs). This section The primary problem associated with spectrum discusses some additional technologies that are driving awareness is the hidden node problem. A lurking receiver CR. Even though this is not a comprehensive list of (the best example is a television (TV) set) may be driving technologies