Cognitive Radio

An Approach to Spectrum Management

We are all quite familiar with the enormous capacity of the universe that makes it a massive storehouse of energy from where humans have been continuously extracting assets to somehow build a human friendly world. One of them is finite and increasingly precious resource - the electromagnetic spectrum.

The radio spectrum is an entity of the electromagnetic spectrum corresponding to radio frequencies in the range of around 3 KHz to 300 GHz that help us transmit information through air. Radio spectrum enlarges the definition of natural resources to use air as a medium of communication, so like any other resource, it has a fixed capacity at any given time and the use of it by one limits the use of it by others. The dependence in radio communication in one form or the other has grown dramatically in recent years, and the growth in the number and variety of applications, many of them bandwidth hungry, and the huge expansion in user expectations place ever-increasing demands on radio spectrum.

Fixed and mobile communications, sound and television broadcasting, aviation, railway and maritime transport, defense, medical electronics, emergency services, remote control and monitoring, radio astronomy and space research, as well as many other applications, make use of radio spectrum. Because the radio spectrum offers the instantaneous and direct way of communicating across space, congestion has greatly increased abating its efficiency.

                 Congestion, here called interference results, when spectrum is overtaxed, just as pollution arises in a crowded highway or in a body of water that receives effluents. In order to avoid interference, spectrum holes need to be sensed. The under-utilization of the electromagnetic spectrum leads us to think in terms of spectrum holes, which is a band of frequencies assigned to a primary user, but, at a particular time and specific geographic location, the band is not being utilized by that user. Spectrum utilization can be used significantly by making it possible for a secondary user (who is not being serviced) to access the spectrum hole unoccupied by the primary user at the right location and time.

Cognitive radio, inclusive of software-defined radio, has been proposed as a means to promote the efficient use of spectrum by exploiting the existence of spectrum holes. Cognitive radio is a popular technology as it is based on software to define the wireless sensing techniques which further enhances the spectrum utility rate evidently. Software radio provides an ideal platform for the realization of the cognitive radio. Software radios are emerging as platforms for multiband multimode personal communication systems. Radio etiquette is the set of RF bands, air interfaces, protocols and spatial and temporal patterns that moderate the use of the radio spectrum. Cognitive radio extends the software radio with radio-domain model-based reasoning about such etiquettes. Cognitive radio enhances the flexibility of personal services through a radio knowledge representation language. This language represents the knowledge of radio etiquettes, devices, software modules, propagation, networks, user-needs, and application scenarios in a way that supports automated reasoning about the needs of the user.

The concept of cognitive radio is originated from radio sensing and learning; recognizes and allocates spectrum opportunity; realizes spectrum opportunity, and cognitive radio utilizes the intelligent sensing method to acquire the spectrum usage information and environment parameters, then chooses the most feasible network or the spectrum reconfigurable network architecture.

Cognitive radio is an intelligent wireless communication system that is aware of its surrounding environment (i.e. outside world), and uses the methodology of understanding-by-building to learn from the environment and adapt its internal states to statistical variations in the incoming RF stimuli by making corresponding changes in certain operating parameter (e.g. transmit-power, carrier-frequency, and modulation strategy) in real-time, with two primary objectives in mind:

• Highly reliable communications whenever and wherever needed.
• Efficient utilization of the radio spectrum.