**System Aspects**

Cognitive radio is an adaptive, intelligent radio, and network technology that can automati‐ cally detect available channels in a wireless spectrum and change transmission parameters, enabling more communications to be performed concurrently. Cognitive radio is based on software radio technology where the pieces of software have replaced traditional hardware components such as amplifiers, modulators, and mixers. This way it is easy to change the operation of the radio. All that is needed is reprogramming. It can also be considered to be an

The cognitive radio needs to collect cognition about the radio environment to operate effi‐ ciently. Such a radio needs to understand if the spectrum it intends to use is free or utilized by some primary user and redistribute the available spectrum dynamically. By primary user, we mean the licensed user of the band, and correspondingly, the cognitive radios are often

A secondary user may collect information about primary user activities alone or it may coop‐ erate with other secondary users to improve the detection and estimation results. Of course for the cooperation to be possible, several secondary users must be designed so that they allow it. If cooperation between the secondary users is possible, it results in more reliable detection. This is because cooperation allows overbridging the fading and shadowing effects that are present in real‐world radio propagation by the usage of spatial diversity, which in

The first standard on cognitive radio was developed by IEEE (IEEE 802.22) and published in 2011. The standard combines a database of licensed users of the area with spectrum sensing to locate the primary users. The standard was developed for usage of unused television chan‐

The chapters of this book discuss different aspects of cognitive radio, covering a large span of the problems that have to be solved in order to build reliable systems. This is the hope of the editor that the material published in this book is useful for people who design the cognitive radio systems and for the people who research the different aspects of the exiting subject.

[1] Mitola III J, Maguire GQ, Jr. Cognitive radio: Making software radios more personal.

adaptive radio, which monitors and modifies its own performance.

termed as secondary users. This process is called spectrum sensing.

Address all correspondence to: tonu.trump@gmail.com

IEEE Personal Communications Magazine. 1999;**6**(4):13-18

turn improves the results.

4 Cognitive Radio

nels in the rural areas.

**Author details**

Virgostell OÜ, Tallinn, Estonia

Tõnu Trump

**References**
