Acognitiveradiois a Kind Oftwo-Way Radiothat Automatically Changes

Acognitiveradiois a kind oftwo-way radiothat automatically changes itstransmissionorreceptionparameters, in a way where the entirewirelesscommunicationnetwork-- of which it is anode-- communicates efficiently, while avoiding interference with licensed or licensed exempt users. This alteration of parameters is based on the active monitoring of several factors in the external and internal radio environment, such asradio frequencyspectrum,userbehaviour andnetworkstate. A cognitive radio, as defined by the researchers atVirginia Polytechnic Institute and State University, is "a software defined radio with a cognitive engine brain".[1]

History

The idea ofcognitiveradio was first presented officially by Joseph Mitola III in a seminar at KTH, The Royal Institute of Technology in Stockholm, in 1998, published later in an article by Mitola and Gerald Q. Maguire, Jr in 1999.[2]It was a novel approach in wireless communications that Mitola later described as:

The point in which wirelesspersonal digital assistants(PDAs) and the related networks are sufficiently computationally intelligent about radio resources and related computer-to-computer communications to detect user communications needs as a function of use context, and to provide radio resources and wireless services most appropriate to those needs.[3]

It was thought of as an ideal goal towards which asoftware-defined radioplatform should evolve: a fully reconfigurable wirelessblack-boxthat automatically changes its communication variables in response to network and user demands.

Regulatory bodies in various countries (including theFederal Communications Commissionin the United States, andOfcomin the United Kingdom) found that most of theradio frequencyspectrum was inefficiently utilized.[4]For example,cellular networkbands are overloaded in most parts of the world, but many other frequency bands, such as military,amateur radioandpagingfrequencies are not. Independent studies performed in some countries confirmed that observation,[5][6][7]and concluded that spectrum utilization depends strongly on time and place. Moreover, fixed spectrum allocation prevents rarely used frequencies (those assigned to specific services) from being used by unlicensed users, even when their transmissions would not interfere at all with the assigned service. This was the reason for allowing unlicensed users to utilize licensed bands whenever it would not cause any interference (by avoiding them whenever legitimate user presence is sensed). This paradigm for wireless communication is known ascognitiveradio.

The first phone call over a cognitive radio network was made on Monday 11 January 2010 in Centre for Wireless Communications atUniversity of Ouluusing CWC's cognitive radio networkCRAMNET(Cognitive Radio Assisted Mobile Ad Hoc Network), that has been developed solely by CWC researchers.[8],[9]

Terminology

Depending on the set of parameters taken into account in deciding on transmission and reception changes, and for historical reasons, we can distinguish certain types of cognitive radio. The main two are:

Full Cognitive Radio("Mitola radio"): in which every possible parameter observable by a wireless node or network is taken into account.[10]
Spectrum Sensing Cognitive Radio: in which only theradio frequencyspectrum is considered.[11]

Also, depending on the parts of the spectrum available for cognitive radio, we can distinguish:

Licensed Band Cognitive Radio: in which cognitive radio is capable of using bands assigned to licensed users, apart from unlicensed bands, such asU-NIIband orISM band. TheIEEE 802.22working group is developing a standard for wireless regional area network (WRAN) which will operate in unused television channels.[12][13]
Unlicensed Band Cognitive Radio: which can only utilize unlicensed parts ofradio frequencyspectrum.[citation needed]One such system is described in theIEEE 802.15Task group 2 specification.[14]which focuses on the coexistence ofIEEE 802.11andBluetooth.[citation needed]

Technology

Although cognitive radio was initially thought of as asoftware-defined radioextension (Full Cognitive Radio), most of the research work is currently focusing on Spectrum Sensing Cognitive Radio, particularly in theTVbands. The essential problem of Spectrum Sensing Cognitive Radio is in designing high quality spectrum sensing devices and algorithms for exchanging spectrum sensing data between nodes. It has been shown[15]that a simpleenergy detectorcannot guarantee the accurate detection of signal presence, calling for more sophisticated spectrum sensing techniques and requiring information about spectrum sensing to be exchanged between nodes regularly. Increasing the number of cooperating sensing nodes decreases the probability of false detection.[16]

Filling freeradio frequencybands adaptively usingOFDMAis a possible approach. Timo A. Weiss and Friedrich K. Jondral of theUniversity of Karlsruheproposed aspectrum poolingsystem[7]in which free bands sensed by nodes were immediately filled byOFDMAsubbands.

Applications of Spectrum Sensing Cognitive Radio includeemergency networksandWLANhigherthroughputandtransmissiondistance extensions.

Evolution of Cognitive Radio toward Cognitive Networks is under process, in which Cognitivewireless mesh network(e.g. CogMesh) is considered as one of the enabling candidates aiming at realizing this paradigm change.

Main functions

The main functions of Cognitive Radios are:[17][18]

Spectrum Sensing: detecting the unused spectrum and sharing it without harmful interference with other users. It is an important requirement of the Cognitive Radio network to sense spectrum holes. Detecting primary users is the most efficient way to detect spectrum holes. Spectrum sensing techniques can be classified into three categories:
Transmitter detection: cognitive radios must have the capability to determine if a signal from a primary transmitter is locally present in a certain spectrum. There are several approaches proposed:
matched filterdetection
energy detection
cyclostationaryfeature detection
Cooperative detection: refers to spectrum sensing methods where information from multiple Cognitive radio users are incorporated for primary user detection.
Interference based detection.

Spectrum Management: capturing the best available spectrum to meet user communication requirements while not creating undue interference to other (primary) users. Cognitive radios should decide on the best spectrum band to meet theQuality of servicerequirements over all available spectrum bands, therefore spectrum management functions are required for Cognitive radios. These management functions can be classified as:
spectrum analysis
spectrum decision

The practical implementation of spectrum management functions is a very complex and multifaceted issue in itself, given that it has to address a mixture of technical and legal requirements. An example of the former is chosing appropriate sensing threshold to detect other users, while the latter is exemplified by the need to meet the rules and regulations set out forradio spectrum accessin international (ITU Radio Regulations) and national (Telecommunications Law, etc.) legislation[19][20].

Spectrum Mobility: is defined as the process when a cognitive radio user exchanges its frequency of operation. Cognitive radio networks target to use the spectrum in a dynamic manner by allowing the radio terminals to operate in the best available frequency band, maintaining seamless communication requirements during the transition to better spectrum.

Spectrum Sharing: providing the fair spectrum scheduling method. One of the major challenges in open spectrum usage is the spectrum sharing. It can be regarded to be similar to genericmedia access controlMAC problems in existing systems

Cognitive radio (CR) versus intelligent antenna (IA)

Intelligent antenna(orsmart antenna) is antenna technology using spatial beamforming and spatial coding to cancel interference; however, it requires intelligent multiple or cooperative antenna array. On the other hand, cognitive radio (CR) allows user terminals to sense whether a portion of the spectrum is being used or not, in order to share the spectrum among neighbor users. The following table compares the different points between two advanced approaches for the future wireless systems: Cognitive radio (CR) vs. Intelligent antenna (IA).

Point / Cognitive radio (CR) / Intelligent antenna (IA)
Principal goal / Open Spectrum Sharing / Ambient Spatial Reuse
Interference processing / Avoidance by spectrum sensing / Cancellation by spatial pre/post-coding
Key cost / Spectrum sensing and multi-band RF / Multiple or cooperative antenna arrays
Challenging algorithm / Spectrum management tech / Intelligent spatial beamforming/coding tech
Applied techniques / Cognitive Software Radio / Generalized Dirty-Paper and Wyner-Ziv coding
Basement approach / Orthogonal modulation / Cellular based smaller cell
Competitive technology / Ultra widebandfor the higher band utilization / Multi-sectoring (3, 6, 9, so on) for higher spatial reuse
Summary / Cognitive spectrum sharing technology / Intelligent spectrum reuse technology

Description

In response to the operator's commands, the cognitive engine is capable of configuring the radio system parameters. These parameters include "waveform, protocol, operating frequency, and networking".[21]It functions as an autonomous unit in the communication environment and frequently exchanges information about the environment with the networks it is able to access as well as with other CRs (Wipro Technologies, 2002).[21]. A CR "monitors its own performance continuously, in addition to "reading the radio's outputs"; it then uses this information to "determine theRFenvironment, channel conditions, link performance, etc.", and adjusts the "radio's settings to deliver the required quality of service subject to an appropriate combination of user requirements, operational limitations, and regulatory constraints". These processes have been described as "reading the radio's meters and turning the radio's knobs".[1]

Practical application

CR can sense its environment and without the intervention of the user can adapt to the users communication needs while conforming toFCCrules. Conceptually, the amount of spectrum is infinite, practically for propagation and other reasons it is finite because of the desirability of certain portions of the band. Even the spectrum which is assigned is far from being 100% utilized, hence efficient use of the spectrum is a growing concern. CR offers a solution to this problem. A CR can intelligently detect whether any portion of the spectrum is in use or not, and can temporarily latch into or out of it without interfering with the transmissions of other users thereby efficiently utilizing spectrum. According to Dr.BruceFette (2004), "Some of the radio's other cognitive abilities include determining its location, sensing spectrum use by neighboring devices, changing frequency, adjusting output power or even altering transmission parameters and characteristics. All of these capabilities, and others yet to be realized, will provide wireless spectrum users with the ability to adapt to real-time spectrum conditions, offering regulators, licenses and the general public flexible, efficient and comprehensive use of the spectrum".[22]

The future of CR

The phenomenal success of the unlicensed band in accommodating a range of wireless devices and services has led the FCC to consider opening further bands for unlicensed use. In contrast, the licensed bands are underutilized due to static frequency allocation. Realizing that CR technology has the potential to exploit the inefficiently utilized licensed bands without causing interference to incumbent users; the FCC released the Notice of Proposed Rule Making to allow unlicensed radios to operate in the TV broadcast bands. TheIEEE 802.22working group formed in November/2004 is equipped with the task of defining the air interface standard for Wireless Regional Area Networks based on CR sensing for the operation of unlicensed devices in the spectrum allocated to TV service.[23]