In Chapter 2, we defined cognitive radios as software-defined radios with built-in cognition and intelligence. A distinctive feature of intelligence is the ability to apply and reason with knowledge. We saw in Chapter 2 that a cognitive radio acquires spectrum knowledge through a process called spectrum sensing. Simply possessing knowledge, however, is not intelligence. An intelligent cognitive radio must be able to use the accumulated knowledge to make better decisions. This is called reasoning.

It is not hard to see how the need for reasoning arises in the operation of a cognitive radio. Indeed, the spectrum sensing problem itself will require the cognitive radio to decide which spectrum band or channel to sense at any given time. While a fixed protocol or random guessing can be alternative ways of making these selections, they certainly do not sound very intelligent. Instead, we expect that a cognitive radio uses the spectrum knowledge it had gained in selecting a particular spectrum band or a channel for sensing. Hence, the cognitive radio must be able to reason based on knowledge it has about the spectrum environment which band may be worth sensing in order to meet its performance objectives. Similarly, cognitive radios need to make decisions on how to perform actual communications based on its knowledge of spectrum environment and the user performance objectives. Knowledge is not perfect. Hence, in its reasoning, a cognitive ...

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