01 CR Concept - Project-Benefit · Userhierarchyin cognitiveradio networks •Theclassification...

Cognitive RadioConcept

Cognitive Radio, KTiOS, DEET, FTN, UNS

Main references:

• [1] Ezio Biglieri, Andrea J. Goldsmith, Larry J. Greenstein, Narayan B. Mandayam, H. Vincent Poor: Principles of Cognitive Radio, Cambridge University Press 2013

• [2] Bruce Fette: Cognitive Radio Technology, 2nd Ed, Academic Press, 2009


Cognitive radio ‐ Introduction

Motivation:• exploiting underused spectrum,

• Measurements suggest that much of the spectrum is lightly used so a very significant expansion in the ‘effective’ amount of spectrum available for personal communications.

• intelligent service management,• terminal convergence.


Motivation: Spectrum UnderutilizationGovernance/Regulation/Policy• Spectrum ‐ one of the most important resources radio communications (RC).

• Spectrum utilization is regulated to protect intended services from harmful interference.

• Traditional spectrum governance: static long‐term exclusivity of spectrum use in large geographic areas, often based on the radio technologies employed at the timeof decision making [1].

• Until recently spectrum regulatory bodies such as the Federal Communications Commission (FCC) in the US or the European Telecommunications Standards Institute (ETSI) in Europe have always allocated spectrum frequency blocks for specific uses, and assigned licenses for these blocks to specific groups orcompanies [1].


Motivation: Spectrum UnderutilizationSpectrum utilization studies• Examples of underutilization [1]:

• During the high demand periods(political convention held in 2004 in New York City) only about 13% of the spectrum opportunities were utilized.

• Measurement on radio frequency bands from 30 MHz to 3 GHz, collected during 2009 in a dense suburb of Washington DC revealed a number of bands with low spectrum occupancy.


Motivation: Spectrum UnderutilizationProposed solution: opportunistic spectrum use• Early motivation for cognitive radio technology: accomplish opportunistic spectrum use toalleviate the artificial scarcity of prime spectrum [1].

• If successful, this technology could revolutionize the way spectrum is allocated worldwide.

• Among other benefits, it would yield added bandwidth to support the demand for higher‐quality and higher‐data‐rate wireless products and services well into the future [1].


Motivation: increased traffic

• Cisco report:• laptops and netbooks will continue to generate a disproportionate amount of traffic,

• new device categories such as machine‐to‐machine and tablets will begin to account for a significant portion of the traffic by 2015.

• Explosive growth of wireless communications devices: from about 1 billion devices in 2005 to about 10 billion devices in 2010 with projections of about 100 billion devices by 2020 [1].


Biglieri et al: Principles of Cognitive Radio, Cambridge University Press 2013

Agile radioCognitive Radio


Cognitive radio ‐ Introduction

• The basic concept: a device arriving in a new environment, would ‘understand’ the usage of the radio spectrum and adapt its behavior accordingly.

• Cognitive radios can:• recognize the available systemsaround them, and

• adjust their frequencies, waveforms and protocols to access those systems efficiently.


Cognitive cycle: Observing, Learning, Reasoning, Acting• The human cycle, as described by CharlesSanders Peirce.

• Similar cycles occur in everyaspect of life, includingscience.


The Cogniteive CycleJohn F. Sowa2015

Implementing the Cycles

• An open‐endedvariety of methodsfor learning andreasoning.

The Cogniteive CycleJohn F. Sowa2015


Cognition and Agility in Radio Communications• Conceptually, CRs include multiple domains of knowledge,model‐based reasoning and negotiation.

• The knowledge and reasoningcan include different radioaspects such as RF bands, air interfaces, protocols, and spatial and temporal patterns that moderate the use of the radio spectrum [1].

• Important feature that differentiates cognitive radios from normal radios is their agility in [1]:• Spectrum: discovery of availablespectrum and opportunistic transmission

• Tehnology: single radio device across various access technologies

• Protocol: dynamicallyreconfigurable protocol stackdepending on the interactingdevices


Cognition and Agility in Radio Communications [1]• CR with listed agility enableenterance into society of radios.

• Extending cognitive behavior to networks of radios that mimic human behavior in civilized society.

• Study of cognitive radio networks may requireinterdisciplinary approaches that include cognitive and neurosciences, economics, and sociology.

• Such interdisciplinarymethodologies can be applied in modeling the behavior and dynamics of complex networks with cognitive radios.


Cognitive Radio: SDR+DSA

• Cognitive radio networks basically extend the software defined radio(SDR) framework to thedevelopment of dynamic spectrum access (DSA) algorithms that exploit temporal and spatial variability in the spectrum via [1]: • (a) initial cooperative neighbor discovery and association;

• (b) spectrum quality estimation and opportunity identification; and

• (c) radio bearer management.

• These, in turn, imply a framework that senses neighborhood conditions to identify spectrumopportunities for communication by building an awareness of spectrum policy, local network policy, and the capability of local nodes (including noncooperative or legacy nodes) [1].


Dynamic Spectrum Access and Spectrum Awareness [2]

• Sensing local spectrum utilization either through a dedicated sensor or by using a configured SDR receiver channel:• characteristics of the legacy signals provided by federated sensors

• time‐division of a channel betweentransmit and monitor functions

• Primary consideration is noninterference with other spectral uses:• By estimating the other uses and monitoring for interference, two CRs may rendezvous at an unoccupied “channel”

• Sensor technology utilized for spectrum awareness should be of high quality to mitigate the hidden node problem


Fette: Cognitive Radio Technology, 2nd Ed, Academic Press, 2009

Dynamic Spectrum Access and Spectrum Awareness• Avoidance the legacy signal [2]:

1. fixed bandwidth waveform, adaptation of the center frequency,

2. variable bandwidth signal, such as a direct‐sequence spread‐spectrum waveform, where the chip rate is adapted and the center frequency is adapted,

3. water‐filling method to populate a subset of the carriers in an OFDM waveform,

4. a direct‐sequence spread‐spectrum waveform that underlies the legacy signals,

5. frequency hopping into only unoccupied channels.



Cognitive cycle of Cognitive Radio


Tadić et al: , Principi tehnologije kognitivnog radija, Telekomunikacije, No. 1, Apr, 2008

Cognitive Radio Fundamental Issues

• The fundamental issues that need to be addressed include[1]:• constructing propagation models for such networks,

• devising efficient algorithms for spectrum sensing,

• fostering mechanisms forspectrum coexistence , as well as

• understanding the information theoretic limits of such networks.


Dynamic Spectrum AccessRadio Spectrum Policy


Dynamic Spectrum Access

• opposite of the current static spectrum management policy


Zhao et al: , A Survey of Dynamic Spectrum Access, IEEE Signal Processing Magazine, Vol. 24 , Issue 3 , May 2007

Hierarchical Access Model

• Hierarchical Access Model:• open licensed spectrum to secondary users (SUs) while limiting the interference perceived by primary users (PUs ‐licensees)

• spectrum underlay (below the noise floor of primary users, e.g. UWB) and spectrum overlay (restriction on when and where SU may transmit) approaches


Zhao et al: A Survey of Dynamic Spectrum Access,IEEE Signal Processing Magazine, Vol. 24 , Issue 3 , May 2007

User hierarchy in cognitive radio networks

• The classification of users (andassociated rights) is based on theownership (license) of spectrum across users.

• The incumbent (licensed) users occupying the spectrum are referred to as primary users.

• the users with cognitive radios desirous of opportunistic use of the spectrum are usually referred to as the secondary users.

• The secondary users communicate either with infrastructure or other secondary users without interfering with the active primary users.

• An example of this hierarchy relates to operation of cognitive‐radio‐enabled secondary users in the TV bands.


Usage scenarios for cognitive radio

• Cognitive radio network can operate in different modes:• interweave, • overlay, and • underlay

• In interweave mode the secondary users to be able to detect (sense), with very high probability, the primary user transmissions in the network. The temporary space–time–frequency void in thetransmission of primary users is referred to as a spectrum hole or a white space [1].


Opportunistic Spectrum Access:interweave mode • The occupancy of N channels, allocated to primary system,follows a Markov process with 2N states.• state is availability (idle or busy) of each channel.

• In the secondary network users seek spectrum opportunities in these N channels independently.

• The transition probabilities of theunderlying Markov process are known or have been learned bysecondary users.

• In each slot, a secondary user chooses a channel to sense and decides whether to access based on imperfect sensing outcomes. • Accessing an idle channel leads to bit delivery, and accessing a busy channel results in a collision with primary users


Cognitive radio: hidden terminal problem

• A cognitive radio user might make a measurement and not spot any activity on a piece of spectrum.• Problems:

• there might be a shadowed legitimate user of that spectrum,

• cognitive receiver can be less sensitive than the legitimate receiver

• difficult locating of other terminals to transmit directly to

• Solutions:• ‘beaconing’ (by legitimate spectrum‐owner) to indicate free spectrum,• Dedicated base stations for

spectrum monitoring may be too expensive.

• ‘broadcasting white space’: frequency reuse at a much lower power level


Webb: Wireless Communications ‐ The Future, John Wiley & Sons, 2007.

Cognitive radio: hidden terminal problem

• A cognitive radio user might make a measurement and not spot any activity on a piece of spectrum.• Problems:

• there might be a shadowed legitimate user of that spectrum,

• cognitive receiver can be less sensitive than the legitimate receiver

• difficult locating of other terminals to transmit directly to

• Solutions:• ‘beaconing’ (by legitimate spectrum‐owner) to indicate free spectrum,• Dedicated base stations for

spectrum monitoring may be too expensive.

• ‘broadcasting white space’: frequency reuse at a much lower power level


Usage scenarios for cognitive radio: overlay mode [1]• In the overlaymode, the secondary user needs to know the channel between the primary transmitter and the primary and secondary receivers as well as the channelbetween the secondary transmitter and the primary receiver. • With the channel knowledge of both the primary and secondary users, the secondary user can then chooseappropriate transmission strategies so that the communication in the secondary network causes least interference to the primary network.

• This mode requires advancedoperation, highly sophisticated radio and associated architecture and poses many challenges.


Identification of spectrum opportunity

• If A and B can communicate successfully while limiting the interference to PUs below a prescribed level determined by the regulatory policy. • receiver B will not be affected by primary transmitters, and

• transmitter A will not interfere with primary receivers


Zhao et al: A Survey of Dynamic Spectrum Access,IEEE Signal Processing Magazine, Vol. 24 , Issue 3 , May 2007

Cognitive radio as tool forspectrum governance [1]• Wireless ecosystems require efficient and decentralized spectrum sharing in extremely dense populations of wireless devices, embedded and otherwise.

• Cognitive radio technology can be a cornerstone for successful spectrum sharing in these situations. Such radio nodes could sense the usage of radio spectrum across a wide range of frequencies and then make decisions about how to transmit.

• These decisions may be as simple as frequency band selection, or they may be considerably more complex, involving transmitter waveform design, modulation and coding formats, and even cooperation methods.

• The power of this transforming radio technology is even a point ofagreement between the two sides of the contentious spectrum debate among regulators,economists, and engineers over spectrum policy


EU Radio Spectrum Policy‐ Emerging concepts ‐• Wireless Access Policy for Electronic Communications Services (WAPECS): practical steps towards more flexible spectrum use in the near future.• identifying specific spectrum bands where regulatory restrictions can be lifted to introduce competition: including competition between different radio infrastructures.

• A total of 1350 MHz of bandwidth has been identified as a first set of bands in which legal restrictions could be re‐examined to permit more flexible usage. The bands are currently used by a variety of broadcasting, mobile and information technology sectors.

• 470‐862 MHz: used for broadcasting today; • 880‐915 MHz / 925‐960 MHz as well as

1710‐1785 MHz / 1805‐1880 MHz: these bands form the 900/1800 network for GSM mobile services today;

• 1900‐1980 MHz / 2010‐2025 MHz / 2110‐2170 MHz: these bands are used for third generation (3G) mobile services (IMT‐2000/UMTS) today;

• 2500‐2690 MHz (the 2.6 GHz band): this band (still to be licensed) is intended for use by 3G mobile services (IMT‐2000/UMTS);

• 3.4‐3.8 GHz: this band is used for broadband connections to customers; it is also intensively used for satellite communications in Russia and some African countries.


Cognitive Radio (CR)

• CR is a context‐aware intelligent radio potentially capable of autonomous reconfiguration by learning from and adapting to the communication environment• built on a software radio platform

• Software‐defined radio (SDR) is a multiband radio that supports multiple air interfaces and protocols and is reconfigurable through software run on DSP or general‐purpose microprocessors.


Cognitive radio: perspective

• Webb: “cognitive radio will not be able to deliver on the promise of providing interference‐free usage of under‐utilised spectrum and will struggle to find an application where its more expensive handsets can be justified”.


Applications of cognitive radio


White spaces [1]

• The most common application of cognitive radio is in the TV white spaces, where cognitive‐radio‐enabled secondary users opportunistically utilize the unused spectrum without interfering with primary incumbents of spectrum, namely TV transmitters.

• Cognitive radio devices can also form a secondary network in such bands where all secondaryusers are required to detect white spaces or spectrum holes.


„Data Boost“ in Cellular Systems [1]

• CR is used to opportunistically offload traffic to white spaces.

• Overlay mesh network of white space hot‐spots can carry non‐real‐time or delay tolerant data like mail, content, file transfer, etc. The hot‐spots can operate either in the licensed orunlicensed band. • Off‐loading delay tolerant data helps operators to meet QoS requirements of delay sensitive traffic like voice, streaming video, etc.

• User handsets should support dual‐mode: having capability to transmit in the cellular band as well as in white spaces.

• This is an example of the interweave paradigm of cognitive radio operation.

Cognitive Radio, KTiOS, DEET, FTN, UNS Biglieri et al: Principles of Cognitive Radio, Cambridge University Press 2013

Distribution and backhaul [1]

• Cognitive‐radio‐enabled white space networks can be used as a backhaul and distributionnetwork

• Backhauling is done by a wireless router at each home, by routing on the white space backhaul network.



Cognitive digital home [1]• Wireless technologies (Bluetooth, Infrared, and WiFi) are not designed to operate in consonance with the other technologies and are a cause of interference for the receivers that are not part of their network.

• Hence, a central controller that resolves the contention and oversees the coexistence of the networks is required.

• Fig. 1.4 shows a cognitive digital home thatoperate on white spaces in unlicensed bands to carry control information between devices.

• A genie node acts as a central controller to coordinate the operation of these devices such that the number of contentions and collisions is reduced.



Long range vehicle‐to‐vehicle network [1]

• Vehicles with a white space radio capabilities can form a peer‐to‐peer ad hoc network along with fixed access points that provide backhaul capabilities.

• White space communication could supplement the short rangecommunications infrastructure. The white space network can be used for traffic alerts, geographic applications services, peer‐to‐peer content, etc.

• They can also serve as a high capacity emergency back up network.

• Developed functionality can be integrated into emerging intelligent transport systems infrastructure and smart highways.



Authentication Applications [2]

• A cognitive radio can learn the identity of its user(s). Authentication applications can prevent unauthorized people from using the CR or the network functions available to the CR.

• Enhanced security may be exploited by the military for classified communications or by commercial vendors for fraud prevention.



Standardization activities in cognitive radio


Standardization activities in cognitive radioFCC [1]• May 2004: standardization activities for defining the air interface using white spaces started after the US Federal Communications Commission (FCC) issued an NRPM (Notice of proposed rule making). • In response to the FCC proposal, the IEEE 802.22

Working Group (WG) was formed to define a standardized air interface based on cognitive radios.

• IEEE 802.22 standard is one of the earliest standardization efforts to define the MAC and PHY for opportunistic use of the television bands on a non‐interfering basis:

• It specifies a MAC that dynamically adapts to the changes in the environment.

• The standard requires sensing the spectrum to detect the presence or absence of incumbent primary transmitters in the locality of the cognitive radio.

• November 2008: FCC issued a report “Second report and order and memorandum opinion and order” to adopt rules to allow unlicensed radio transmitters to operate in TV white spaces. • Significant amount of spectrum is made available

for new and innovative products and services, including broadband data and other services for businesses and consumers.

• Strong opposition from TV broadcasters.• Mandatory requirements:

• devices must consult a database constructed by the FCC to determine which channels are available for use at a given location, and also

• monitor the spectrum locally once every minute to confirm that no legacy wireless microphones, video assist devices, or other emitters are present. If a single transmission is detected, the device may not transmit anywhere within the entire 6 MHz channel in which the transmission was received.


Standardization activities in cognitive radioFCC [1]• September 2010: FCC released a “Second Memorandum Opinion and Order” that finalized the rules for using unused TV bands for unlicensed wireless devices.• The new rules removed mandatory sensing requirements, which greatly facilitates the use of the spectrum with geolocation‐based channel allocation.


Standardization activities in cognitive radioIEEE [1]• Some of the other IEEE standards related to white space networks are as follows.

• IEEE 802.11af Working Group (WG) defines changes to the IEEE 802.11 PHY and MAC for channel access and coexistence in TV White Spaces (TVWS).

• P1900 working group of the IEEE DySPANStandards Committee defines standards for new methods of dynamic spectrum access including radio transmission interference and for coordination of wireless technologies including network management and information sharing among networks deploying different wireless technologies.

• IEEE SCC41 standardization committee was formed with the intention of checking whether reusing the IEEE 802 PHY/MAC is optimal for white space operation and to estimate how far the performance of the system could benefit from a tailored PHY/MAC system.

• IEEE 802.19 focuses on developing standards for coexistence between wireless standards of unlicensed devices. • The Task Group IEEE 802.19.1 focuses on the coexistence in the TVWS.


Standardization activities in cognitive radioITU [1]• The International Telecommunication Union (ITU) has the following study groups that discuss cognitive radio networks.

• ITU‐R Study Group 1 on Spectrum Management: dynamic spectrum issues was covered by working part 1B.

• ITU‐R Study Group 5 on Terrestrial Services: working part 5A has described the potential application of cognitive radio systems in the land mobile service. • It covers the technical and operational characteristics of cognitive radio systems, including potential benefits, challenges, deployment scenarios and their impact on the use of spectrum from a technical perspective.

• ITU‐R Study Group 5: working party 5D has started work on “Cognitive Radio Systems Specific to IMT Systems.” The scope of this work is to consider the inclusion of CRS into the IMT family of technologies.


Standardization activities in cognitive radioECC/CEPT [1]• European Communications Committee (ECC), an autonomous committee within the European Conference of Postal and Telecommunications Administrations (CEPT),has a special Task Group working on operation of cognitive radio systems in the white spaces of the frequency band 470–790 MHz.

• QoSMOS (Quality of service and mobility driven cognitive radio systems) is a pan‐European FP7 project (2010‐13) with 15organizations coming together to develop a framework for Cognitive Radio systems and to develop and prove critical technologies using a testbed. • The initial focus is on opportunistic use of radio

spectrum, with an early example being TV White Spaces.

• End‐to‐End Efficiency (E3) project (2008‐09) , is German Large Scale Integrating Project (IP) aimed at integrating cognitive wireless systems in the Beyond 3G (B3G) world, evolving current heterogeneous wireless system infrastructures into an integrated, scalable, and efficiently managed B3G cognitive system framework.


Prototyping


• One of the major cognitive radio networking testbeds is the cognitive‐radio enabled ORBIT radio grid testbed at the Wireless Information Networks Laboratory (WINLAB) at Rutgers University.

• The large‐scale radio grid emulator shown in Fig. 1.15 consists of an array of 20 × 20 open‐access programmable nodes each with multiple 802.11a, b, g, or other (Bluetooth, Zigbee, GNU/USRP, WARP, and WINLAB WINC2R Cognitive Radio) radio cards.


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Prototyping: WINLAB‐ORBIT [1]

• The radio nodes are connected to an array of backend servers over a switched Ethernet network, with separate physical interfaces for data, management, and control.

• Users of the grid log into an experiment management server which executes experiments involving network topologies and protocol software specified using an ns2‐like scripting language.

• Interference sources and spectrum monitoring equipment are also integrated into the radio grid. • A radio mapping algorithm that uses controllable

noise sources spaced across the grid to emulate the effect of physical distance allows mapping real‐world wireless network scenarios to specific nodes in the grid.


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Prototyping: WINLAB‐ORBIT [1]

Prototyping: DARPA XG program [1]

• DARPA Next Generation (XG) Communications program is among the earliest and most comprehensive cognitive radio prototyping efforts. It was motivated by the need to support the long‐term projected spectrum demand for military, civilian, government, and commercial wireless applications which is expected to significantly strain the limits of current static spectrum allocations.

• Program was targeting at least an order of magnitude improvement in spectrum utilization by providing access to underutilized spectrum for next‐generation military and commercial networks.

• XG studies have focused on designing techniques: to sense spectrum in real time, characterize the spectrum, react through dynamic waveforms, and adapt to changes in order to dramatically improve the efficiency of current allocations.

• The XG program is also involved in developing the architectural framework, protocol design, and building prototypes for dynamic spectrum access networks.


Prototyping: WiNC2R [1]

• Yet another cognitive radio prototype is the WiNC2R system. The architecture of the WiNC2R system is shown in Fig. 1.16.

• It is a flexible wireless platform that supports a range of cognitive radio network scenarios from autonomous agile radios to spectrum sharing systems. The platform design has the ability to support multiple MAC protocols, and the capability to switch protocols on‐the‐fly within a frame time boundary.



Prototyping: Academia [1]WARP• Rice University’sWireless Open‐Access Research Platform (WARP) is a scalable and extensible programmable wireless platform to prototype advanced wireless networks.

• Xilinx FPGAs are used to enable programmability of both physical and network layer protocols on a single platform, which is both deployable and observable at all layers.

• WARP opens both hardware and software needed to research, build, and prototype next generation wireless networks. This enables a community of researchers to pool their ideas in undertaking clean‐slate prototype networks.

KUAR• The KUAR (Kansas University Agile Radio) is a portable and flexible software radio architecture that enables advanced research in dynamic spectrum access and cognitive radios.

• Other wireless testbeds in the academic community that focus on software defined radio are:• the wireless networking research testbed in the

University of California at Riverside, • the cognitive radio research testbed in University

of California, Los Angeles, and • the Cognitive Radio Network Testbed (CORNET)

in Virginia Tech.


Prototyping: Industry [1]KNOWS• The KNOWS (Kognitiv Networking Over White Spaces)

project at Microsoft Research is a prototyping effort of sensing in white spaces and is an example of cognitive radio prototyping in research labs. Such efforts help in showing the proof of‐ concept of new ideas, later leading to commercialization.

• KNOWS is a hardware– software platform that includes a spectrum‐aware MAC and algorithms to deal with spectrum fragmentation.

• The hardware implementation comprises a dual‐mode scanner radio for detecting white spaces, and a reconfigurable radio for subsequent data communications.

• base stations where deployed on two different buildings within the Microsoft campus in Redmond, Washington, that operate over the white spaces, and provide coverage to nearly all of campus.

• Mobile client is deployed on a Microsoft shuttle. It bridges packets from white spaces to WiFi within the shuttle, thereby providing Internet connectivity to existing laptops.

• As part of the deployment, they have also built a research prototype of a white space database.

NRC Research• Another notable initiative in the industry is the cognitive

radio research at Nokia Research Center (NRC) at Helsinki, Finland. Cognitive radio research in NRC is focused on methods for flexible spectrum use, devising novel ways of sensing the radio environment and location, designing distributed networks that intelligently cooperate and building low power flexible implementation of wireless in mobile devices.


01 CR Concept - Project-Benefit · Userhierarchyin cognitiveradio networks •Theclassification...

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