Cognitive Radio

Cognitive Radio is an intelligent wireless communication system that is aware of its surrounding environment 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 parameters in real-time. [1]

Cognitive radio is a paradigm for wireless communication in which either network or wireless node itself changes particular transmission or reception parameters to execute its tasks efficiently. This parameter alteration is based on observations of several factors from external and internal cognitive radio environment, such as radio frequency spectrum, user behavior, and network state.[2]

The driving force behind cognitive radio technology is attributed to the lack of enough radio spectrum to accommodate for the increasing need of spectrum for high data rate communication. Imagine what happens as more devices go wireless -- not just laptops, or cell phones, but sensor networks that monitor everything from temperature in office buildings to moisture in cornfields, radio frequency ID tags that track merchandise at the local supermarket, devices that monitor nursing-home patients. 

All these gadgets have to share a finite and increasingly crowded amount of radio spectrum. But as anyone who has twirled a radio dial knows, not every channel in every band is always in use. In fact, the Federal Communications Commission (FCC) – the spectrum controlling body of the US – has determined that, in some locations or at some times of day, 70 percent of the allocated spectrum may be sitting idle.

Fig. 1. TV band occupancy over time and frequency at some particular instance

There are two major subsystems in a cognitive radio; a cognitive unit that makes decisions based on various inputs and a flexible software defined radio (SDR) unit whose operating software provides a range of possible operating modes. A separate spectrum sensing subsystem is also often included in the architectural of a cognitive radio to measure the signal environment to determine the presence of other services or users. It is important to note that these subsystems do not necessarily define a single piece of equipment, but may instead incorporate components that are spread across an entire network. As a result, cognitive radio is often referred to as a cognitive radio system or a cognitive network.

The cognitive unit is further separated into two parts as shown in the block diagram below. The first labeled the “cognitive engine” tries to find a solution or optimize a performance goal based on inputs received defining the radio’s current internal state and operating environment. The second engine is the “policy engine” and is used to ensure that the solution provided by the “cognitive engine” is in compliance with regulatory rules and other policies external to the radio.

Fig. 1. Cognitive radio concept architecture

References: 1. S. Haykin, “Cognitive Radio,”JSAC 2005

       2. http://en.wikipedia.org/wiki/Cognitive_radio.