Description
In response to the operator's commands, the cognitive engine is capable of configuring radio-system parameters. These parameters include " waveform, protocol, 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.", 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". 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.History
The concept of cognitive radio was first proposed by Joseph Mitola III in a seminar at KTH Royal Institute of Technology in Stockholm in 1998 and published in an article by Mitola and Gerald Q. Maguire, Jr. in 1999. It was a novel approach in wireless communications, which Mitola later described as:The point in which wirelessCognitive radio is considered as a goal towards which a software-defined radio platform should evolve: a fully reconfigurable wireless transceiver which automatically adapts its communication parameters to network and user demands. Traditional regulatory structures have been built for an analog model and are not optimized for cognitive radio. Regulatory bodies in the world (including thepersonal digital assistant A personal digital assistant (PDA) is a multi-purpose mobile device which functions as a personal information manager. Following a boom in the 1990s and 2000s, PDAs were mostly displaced by the widespread adoption of more highly capable smar ...s (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.
Terminology
Depending on transmission and reception parameters, there are two main types of cognitive radio: * ''Full Cognitive Radio'' (Mitola radio), in which every possible parameter observable by a wireless node (or network) is considered. * ''Spectrum-Sensing Cognitive Radio'', in which only the radio-frequency spectrum is considered. Other types are dependent on parts of the spectrum available for cognitive radio: * ''Licensed-Band Cognitive Radio'', capable of using bands assigned to licensed users (except for unlicensed bands, such as the U-NII band or the ISM band). The IEEE 802.22 working group is developing a standard for wireless regional area network (WRAN), which will operate on unused television channels, also known as TV white spaces. * ''Unlicensed-Band Cognitive Radio'', which can only utilize unlicensed parts of the radio frequency (RF) spectrum. One such system is described in the IEEE 802.15 Task Group 2 specifications, which focus on the coexistence of IEEE 802.11 andTechnology
Although cognitive radio was initially thought of as a software-defined radio extension (full cognitive radio), most 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. Filling free RF bands adaptively, using OFDMA, is a possible approach. Timo A. Weiss and Friedrich K. Jondral of theFunctions
The main functions of cognitive radios are: * ''Power Control'': Power control is usually used for spectrum sharing CR systems to maximize the capacity of secondary users with interference power constraints to protect the primary users. * ''Spectrum sensing'': Detecting unused spectrum and sharing it, without harmful interference to other users; an important requirement of the cognitive-radio network is to sense empty spectrum. Detecting primary users is the most efficient way to detect empty spectrum. Spectrum-sensing techniques may be grouped 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 proposed approaches to transmitter detection: *** Matched filter detection *** Energy detection: Energy detection is a spectrum sensing method that detects the presence/absence of a signal just by measuring the received signal power. This signal detection approach is quite easy and convenient for practical implementation. To implement energy detector, however, noise variance information is required. It has been shown that an imperfect knowledge of the noise power (noise uncertainty) may lead to the phenomenon of the SNR wall, which is a SNR level below which the energy detector can not reliably detect any transmitted signal even increasing the observation time. ItA. Mariani, A. Giorgetti, and M. ChianiIntelligent antenna (IA)
An intelligent antenna (or smart antenna) is an antenna technology that uses spatial beam-formation and spatial coding to cancel interference; however, applications are emerging for extension to intelligent multiple or cooperative-antenna arrays for application to complex communication environments. Cognitive radio, by comparison, allows user terminals to sense whether a portion of the spectrum is being used in order to share spectrum with neighbor users. The following table compares the two: Note that both techniques can be combined as illustrated in many contemporary transmission scenarios. Cooperative MIMO (CO-MIMO) combines both techniques.Applications
Cognitive Radio (CR) can sense its environment and, without the intervention of the user, can adapt to the user's communications needs while conforming to FCC rules in the United States. In theory, the amount of spectrum is infinite; practically, for propagation and other reasons it is finite because of the desirability of certain spectrum portions. Assigned spectrum is far from being fully utilized, and efficient spectrum use 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, and can temporarily use it without interfering with the transmissions of other users. According to Bruce Fette, "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". Examples of applications include: * The application of CR networks to emergency and public safety communications by utilizing white space * The potential of CR networks for executing dynamic spectrum access (DSA) * Application of CR networks to military action such as chemical biological radiological and nuclear attack detection and investigation, command control, obtaining information of battle damage evaluations, battlefield surveillance, intelligence assistance, and targeting. *They are also proven to be helpful in establishing Medical Body Area Networks which can be utilized in omnipresent patient monitoring that aids in immediately notifying the doctors regarding vital information of patients such as sugar level, blood pressure, blood oxygen and electrocardiogram (ECG), etc. This gives the additional advantage of reducing the risk of infections and also increases the patient's mobility. * Cognitive radio is practical also to wireless sensor networks, where packet relaying can take place using primary and secondary queues to forward packets without delays and with minimum power consumption.Simulation of CR networks
At present, modeling & simulation is the only paradigm which allows the simulation of complex behavior in a given environment's cognitive radio networks. Network simulators like OPNET, NetSim, MATLAB and ns2 can be used to simulate a cognitive radio network. CogNS is an open-source NS2-based simulation framework for cognitive radio networks. Areas of research using network simulators include: # Spectrum sensing & incumbent detection # Spectrum allocation # Measurement and/or modeling of spectrum usage # Efficiency of spectrum utilization Network Simulator 3 (ns-3) is also a viable option for simulating CR.M. A. Shattal, A. Wisniewska, B. Khan, A. Al-Fuqaha and K. Dombrowski, "From Channel Selection to Strategy Selection: Enhancing VANETs Using Socially-Inspired Foraging and Deference Strategies," in IEEE Transactions on Vehicular Technology, vol. 67, no. 9, pp. 8919–8933, Sept. 2018. doi: 10.1109/TVT.2018.2853580 URL: https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=8403998&isnumber=8466982 ns-3 can be also used to emulate and experiment CR networks with the aid from commodity hardware like Atheros WiFi devices.Future plans
The 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 a Notice of Proposed Rule Making which would allow unlicensed radios to operate in the TV-broadcast bands. The IEEE 802.22 working group, formed in November 2004, is tasked with 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. To comply with later FCC regulations on unlicensed utilization of TV spectrum, the IEEE 802.22 has defined interfaces to the mandatory TV White Space Database in order to avoid interference to incumbent services. Although spectrum geolocation databases allow reducing the receiver complexity, and interference probability, for instance from sensing errors or hidden nodes, this comes at the cost of a lower spectrum utilization efficiency as the databases can not capture a fine-grained quantification of spectrum utilization and are not updated in real-time. Collaborative sensing, and distributed spectrum management based on artificial intelligence could contribute in the future towards a better balance between spectrum utilization efficiency and interference mitigation.See also
* Channel allocation schemes * Channel-dependent scheduling * Cognitive network * LTE Advanced * Network Simulator * OFDMA * Radio resource management (RRM) * White spaces (radio) * White spaces (database) * Software-defined radioReferences
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