Tuesday, June 2, 2009



[Here is an article on Cognitive Radio compiled by my students Shijesh, Sibil, Shyju and John by browsing the internet, books and journals]

The Radio Spectrum – that segment of the electromagnetic continuum comprising the radio-frequency range – accommodates myriad communications devices today.

As the Radio Spectrum gets is gets more and more crowded and available frequencies become scarce the evolution of Cognitive Radio may be able to optimally manage the available spectrum.

The use of radio frequency bands has been regulated in most countries through the process of spectrum allocation in which the use of a particular frequency band is restricted to the license holders of the band. Within this framework, spectrum has often been viewed as a scarce resource in high demand. However, various studies carried out have suggested that most licensed spectrums are often under-utilized with large spectral holes at different places at different times.

Cognitive Radio (CR) systems have been proposed as a possible solution to the spectrum crisis. The idea is to detect times when a specific licensed band is not used at a particular place and use that band for transmission without causing any significant interference to the transmissions of the license holder. Built on the foundation of the Software Defined Radio (SDR), Cognitive Radios will learn and autonomously perform “cognitive” functions as a form of intelligence that comes from their ability to be defined and upgraded using software.

To examine the concept of cognitive radio consider the example.

Let’s say you walk into an empty cafĂ© called Spectrum. Since all of the tables are available, you position yourself at the best one and settle down for a meal. [Let’s assume all tables have four seats and you occupy one seat].

A few minutes later, another person comes in and sits on a seat at another vacant table.

Soon, if all the tables are full [but there are a few vacant seats on some tables], a new patron must negotiate with someone already at a table to be allowed to share the table. [Maybe she may request you to let her occupy the vacant chair at your table, and you may agree].

This process of negotiation is the concept behind a technology called Cognitive Radio, a way to share and optimally utilize unused spectrum. Cognitive Radio is sometimes called Smart Radio because it senses its environment and reacts to it.

The present paucity of radio spectrum is primarily due to the cost and performance limits of legacy hardware established during the past century. Traditionally, radios were hardwired to operate at a particular power and frequency, and once a station was assigned a frequency, no other station could use it. Over the years, as engineers built radios in cheaper and smaller packages, it became possible to build intelligence into them, making the idea of sharing frequencies possible.

Engineers are now working to bring flexible operating intelligence to future radios, cell phones and other wireless communications devices. During the coming decade, cognitive radio technology should enable nearly any wireless system to locate and link to any locally available unused radio spectrum to best serve the consumer. Employing adaptive software, these smart devices could reconfigure their communications functions to meet the demands of the transmission network or the user.

Cognitive Radio will intelligently know, by sensing, adapting and learning, what to do based on prior experiential knowledge, by building an internal database that defines how to best operate in different places and at specific times of day.

As Cognitive Radios send and receive signals, they will nimbly leap and bound in and out of free bands as required, avoiding those that are already in use. This lightning-fast channel jumping will permit cognitive radio systems to transmit voice and data streams at reasonable speeds.

This efficient use of existing Radio Frequency resources will alleviate spectrum-availability traffic jams and wireless communications may become far more dependable, convenient and, perhaps, considerably economical than it is today. Indeed, if Cognitive Radio technology progresses as its developers hope the airwaves will never be the same again.





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