2.5 Regulatory Issues of Cognitive Access 29 All of this is generally quite controversial. The incumbents will seek the max- imum level of protection and hence seek out situations where the hidden node problem or other signal modification issues are most extreme. Even setting an appropriate level of probability of interference occurring can be fraught with diffi- culties. Many other rules are also needed, including the maximum in-band power, the out-of-band power limits, the bandwidth, whether transmit power control is required, the periodicity of sensing and so on. These tend to be simpler to set because they are mostly parameters that regulators address for every band or technology they consider. 2.5.3 Regulatory Implications of Different Methods of Cognition To date, three broad techniques for identifying whether bands are free from use have been suggested. These are sensing, beacons, and geolocation, which impor- tantly can be used discretely or in combination to effect the desired level of confidence in the attainment of a low-interference environment. Here the text will not seek to compare their efficiency, only their regulatory implications. The implications of sensing has already been mentioned: that the regulator needs to determine the appropriate device sensitivity.