Spread-spectrum A spread-spectrum transmission offers three main advantages over a fixed-frequency transmission: Spread-spectrum signals are highly resistant to narrowband interference.
Description[ edit ] In response to the operator's commands, the cognitive engine is capable of configuring radio-system parameters. These parameters include " waveformprotocol, operating frequency, and networking". This functions as an autonomous unit in the communications environment, exchanging information about the environment with the networks it accesses and other cognitive radios CRs.
A CR "monitors its own performance continuously", in addition to "reading the radio's outputs"; it then uses this information to "determine the RF environment, channel conditions, link performance, etc.
Some "smart radio" proposals combine wireless mesh network —dynamically changing the path messages take between two given nodes using cooperative diversity ; cognitive radio—dynamically changing the frequency band used by messages between two consecutive nodes on the path; and software-defined radio —dynamically changing the protocol used by message between two consecutive nodes.
Snider, Lawrence Lessig, David Weinberger[ citation needed ], and others say that low power "smart" radio is inherently superior to standard broadcast radio.
It was a novel approach in wireless communications, which Mitola later described as: The point in which wireless personal 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.
Traditional regulatory structures have been built for an analog model and are not optimized for cognitive radio. Regulatory bodies in the world including the Federal Communications Commission in the United States and Ofcom in the United Kingdom as well as different independent measurement campaigns found that most radio frequency spectrum was inefficiently utilized.
Independent studies performed in some countries confirmed that observation, and concluded that spectrum utilization depends on time and place. Moreover, fixed spectrum allocation prevents rarely used frequencies those assigned to specific services from being used, even when any unlicensed users would not cause noticeable interference to the assigned service.
Regulatory bodies in the world have been considering whether to allow unlicensed users in licensed bands if they would not cause any interference to licensed users. These initiatives have focused cognitive-radio research on dynamic spectrum access.
The first cognitive radio wireless regional area network standard, IEEE This standard uses geolocation and spectrum sensing for spectral awareness.
Geolocation combines with a database of licensed transmitters in the area to identify available channels for use by the cognitive radio network. Spectrum sensing observes the spectrum and identifies occupied channels.
This white space is unused television channels in the geolocated areas. However, cognitive radio cannot occupy the same unused space all the time. As spectrum availability changes, the network adapts to prevent interference with licensed transmissions. Full Cognitive Radio Mitola radioin which every possible parameter observable by a wireless node or network is considered.
Other types are dependent on parts of the spectrum available for cognitive radio: Process by which a cognitive-radio user changes its frequency of operation. Cognitive-radio networks aim to use the spectrum in a dynamic manner by allowing radio terminals to operate in the best available frequency band, maintaining seamless communication requirements during transitions to better spectrum.
Spectrum sharing cognitive radio networks allow cognitive radio users to share the spectrum bands of the licensed-band users. However, the cognitive radio users have to restrict their transmit power so that the interference caused to the licensed-band users is kept below a certain threshold. Based on the detection results, cognitive radio users decide their transmission strategies.
If the licensed users are not using the bands, cognitive radio users will transmit over those bands. If the licensed users are using the bands, cognitive radio users share the spectrum bands with the licensed users by restricting their transmit power. Database-enabled Spectrum Sharing,   ,: The white space database contain algorithms, mathematical models and local regulations to predict the spectrum utilization in a geographical area and to infer on the risk of interference posed to incumbent services by a cognitive radio user accessing the shared spectrum.
If the white space database judges that destructive interference to incumbents will happen, the cognitive radio user is denied access to the shared spectrum.
Technology[ edit ] Although cognitive radio was initially thought of as a software-defined radio extension full cognitive radiomost research work focuses on spectrum-sensing cognitive radio particularly in the TV bands. The chief problem in spectrum-sensing cognitive radio is designing high-quality spectrum-sensing devices and algorithms for exchanging spectrum-sensing data between nodes.
It has been shown that a simple energy detector cannot guarantee the accurate detection of signal presence,  calling for more sophisticated spectrum sensing techniques and requiring information about spectrum sensing to be regularly exchanged between nodes.
Increasing the number of cooperating sensing nodes decreases the probability of false detection. Weiss and Friedrich K. Jondral of the University of Karlsruhe proposed a spectrum pooling system, in which free bands sensed by nodes were immediately filled by OFDMA subbands.
Applications of spectrum-sensing cognitive radio include emergency-network and WLAN higher throughput and transmission -distance extensions.Compounding the confusion is the use of the broad term cognitive radio as a synonym for dynamic spectrum access.
As an initial attempt at unifying the terminology, the taxonomy of dynamic spectrum. Cognitive radio and dynamic spectrum access systems are effective ways of using radio spectrum which is a scarce source.
Cognitive radio applications changed the paradigm for the wireless communications systems in the past decades. Besides that, different communications systems and wireless.
The standard approaches for dynamic spectrum access involve a procedure referred to as spectrumsensing, in which secondary radios examine a frequency band for pri- mary radio activity prior to initiating communications on the band.
The Digital Single Market strategy aims to open up digital opportunities for people and business and enhance Europe's position as a world leader in the digital economy.
for spectrum sensing are presented in Section III, while spectrum sharing is studied in Section IV. Simulation results are provided in Section V, followed by concluding remarks in Section VI.
II. SYSTEM MODEL A. Network Architecture We consider a cognitive radio network which composes of two types of users: the primary users (PUs) and secondary users (SUs). Cognitive Radio for Dynamic Spectrum Access Qing Zhao University of California at Davis A Taxonomy of Dynamic Spectrum Access (Zhao&SadlerSPM).