Www.cs.helsinki.fi Overview of Cognitive Radio Basics and Spectrum Sensing CN-S2013 Faculty of Science Department of Computer Science1 Jan.29, 2013 Suzan

www.cs.helsinki.fi

Overview of Cognitive Radio Basics and Spectrum Sensing

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Faculty of ScienceDepartment of Computer Science 1

Jan.29, 2013

Suzan Bayhan

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Cognitive radio: What, why, and how

Spectrum Sensing: Basics and challenges

Summary of Today’s Class

2Faculty of ScienceDepartment of Computer Science

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Joseph Mitola III and Gerald Q. Maguire, Jr. (KTH, Sweden), Aug.1999 IEEE Personal Communications, Cognitive Radio: Making Software Radios More PersonalSimon Haykin, Feb. 2005, IEEE Journal on Selected Areas in Communications, Cognitive Radio: Brain-Empowered Wireless Communications

“an intelligent wireless communication system that is aware of its environment and uses the methodology of understanding-by-building to learn from the environment and adapt to statistical variations in the input stimuli, with two primary objectives in mind: (1) highly reliable communication whenever and wherever needed; (2) efficient utilization of the radio spectrum”

Cognitive Radio: Definition and History


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Cisco Report: http://www.cisco.com/en/US/solutions/collateral/ns341/ns525/ns537/ns705/ns827/white_paper_c11-520862.html

Wireless data consumption increases (from Cisco’s report)

4

By 2012, the number of mobile-connected devices will exceed the world's population.

http://www.cisco.com/en/US/solutions/collateral/ns341/ns525/ns537/ns705/ns827/white_paper_c11-520862.html

http://www.cisco.com/en/US/solutions/collateral/ns341/ns525/ns537/ns705/ns827/white_paper_c11-520862.html

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Radio spectrum: 3kHz to 300 GHz

The use of radio spectrum for communication dates back to

How is the wireless spectrum is managed?


Image from http://kids.britannica.com/elementary/art-87886/Guglielmo-Marconi-is-pictured-with-his-telegraph-equipment

1895: Guglielmo Marconi, radio signal transmission using telegraph codes over 1,25 mile distance

Static Spectrum Access

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Use of Radio Frequencies in Finland (www.ficora.fi)

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License for a large region, usually country-wide

Large chunk of licensed spectrum (expensive licenses)

Barriers to new ideas

Prohibited spectrum access by unlicensed users

ISM bands are unlicensed WLAN bands at 2.4 GHz, 5 GHz

Temporary short range licenses

Shortcomings of current spectrum management


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The Finnish Communications Regulatory Authority (FICORA)

International Telecommunication Union (ITU)

European Telecommunications Standards Institute (ETSI)

Radio Spectrum Use in Finland


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Ficora allocates spectrum in Finland


How much is this frequency? Calculate the fee for frequency!

http://www.ficora.fi/en/index/luvat/taajuusmaksut/laskentakaavatjakertoimet.html

You can check from this document:

http://www.ficora.fi/attachments/englantiav/673vb43bJ/TJTen_20042012.pdf

You can find radio spectrum regulations in Finland here:

http://www.ficora.fi/en/index/palvelut/palvelutaiheittain/radiotaajuudet.html

http://www.ficora.fi/en/index/luvat/taajuusmaksut/laskentakaavatjakertoimet.html

http://www.ficora.fi/attachments/englantiav/673vb43bJ/TJTen_20042012.pdf

http://www.ficora.fi/en/index/palvelut/palvelutaiheittain/radiotaajuudet.html

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Spectrum Measurements


Image from RWTH http://www.inets.rwth-aachen.de/static-spectrum.html

Image from http://www.cmpe.boun.edu.tr/WiCo/doku.php?id=research#cognitive_radio

Measurement campaigns have shown that there is plenty of unused spectrum!

Working time vs. night time usage

City-center to suburb usage

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Cognitive Radio (CR)


There is a huge demand for spectrum, but there is unused spectrum Radio spectrum is inefficiently used.

Change in ownership; a resource is owned by the one who uses it. Sharing for sustainability.

Static spectrum management since 1900s.

Imagine a world with no-lane-changing.

Smarter schemes: Dynamic spectrum access (DSA)

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Primary User, Secondary User

Licensed, primary, incumbent, higher-priority user: PU

Secondary, cognitive, unlicensed user: SU, CR

Spectrum hole, white space, white spectrum, idle frequency/channel/band

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Hardware: Static, once designed at the factory, never changed

SDR: Reconfigurable radio (e.g. operation frequency, modulation type)

Multiple standards

Multiple bands

Software Defined Radio (SDR)


SDR is the building block of the CR.

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How does cognitive radio work?


SPECTRUM SENSING

Cognitive Cycle

Image from http://pgcoaching.nl

http://pgcoaching.nl/

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Reading Material:

- T. Yucek and H. Arslan A survey of spectrum sensing algorithms for cognitive radio applications, IEEE Communications Surveys and Tutorials, vol. 11, no. 1, pp. 116-130, 2009. - Ghasemi, Amir, and Elvino S. Sousa. Spectrum sensing in cognitive radio networks: requirements, challenges and design trade-offs. IEEE Communications Magazine, 46.4 (2008): 32-39.

Spectrum Sensing Reading Material


http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=4796930

http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=4796930

http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=4481338&tag=1

http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=4481338&tag=1

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What is spectrum sensing?


Time

Time1- Sense:There is PU

2- Sense: IDLE3- Sense: PUPU collision: Interference or harmful interference

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1- Sense for vacating the band if PU arrives. CR must not harm PUs

2- Sense for finding unused spectrum

How to measure quality of sensing?

•Probability of detection (Pd) Higher is better

•Probability of false alarm (Pf) Lower is better

Spectrum Sensing


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Various aspects of spectrum sensing


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Sensing: PHY and MAC Layer Issues

PHY SensingSpectrum Sensor at PHY

MAC SensingSensing and access strategy

CR SENSING DESIGN = SENSOR + SENSING STRATEGY + ACCESS

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Energy Detector: Measures the energy received on a primary band during an observation interval and declares a white space if the measured energy is less than a properly set threshold. (2) Do not differentiate PU and CR signals (3) Low complexityWaveform-based Sensing: (1) Preambles, midambles can be used to detect PU signals. (2) Short measurement time; Susceptible to synchronization errorsMatch Filtering MF: (1) If transmitted signal is known, test using filters. (2) Dedicated circuitry for each primary licenseeRadio Identification: Identifying the transmission technologies used by PUs, channel bandwidth, coverage etc.Cyclostationary: PU signal differentiated from noise

PHY Sensing


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Energy Detector:Binary Hypothesis Test


H0: The frequency is idle, there is no PU signalH1: The frequency is occupied, there is PU signalw(n): Noise, s(n): PU signal, y(n): Measured signal, N number of

samples

H0 or H1?

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Effect of Signal to Noise Ratio (SNR)


Decibel: 10log10(P2/P1)

Generally, sensing performance increases under increasing SNR.

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Comparison of Sensing Schemes


1. Energy Detector2. Waveform-based Sensing3. Match Filtering4. Radio Identification5. Cyclostationary

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Types of Spectrum Sensing


Proactive

Reactive

Local

Cooperative

Distributed Centralized

In-band

Out-of-band

Synchronious

Asynchronious

SequentialParallel

SPECTRUM SENSING

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Parallel

Sequential

Proactive

Reactive

Local

Cooperative

Centralized

Distributed

Synchronous

Asynchron.

In-band

Out-of-band

Sense channels 1 to N at the same time (parallel) requires N sensing device!

If there are N frequency channels

Sequential: Sense channels one by one. Which order? May take too long to find an empty channel.

Parallel vs. Sequential Sensing

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Proactive

Reactive

Local

Cooperative

Centralized

Distributed

Synchronous

Asynchron.

In-band

Out-of-band

Parallel

Sequential Proactive Sensing:CR senses even if it will not transmit immediately, e.g. periodic sensing.

Trade-offcollected information about the channels vs. sensing cost

Reactive Sensing:CR senses only if it will transmit or receive

Energy-efficient, time to find an idle channel may be longer than Proactive Sensing.

Proactive vs. Reactive Sensing

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Proactive

Reactive

Local

Cooperative

Centralized

Distributed

Synchronous

Asynchron.

In-band

Out-of-band

Parallel

Sequential Local Sensing:Each CR senses itself and uses its sensing data to give a decision on channel state, i.e. idle or busyWhat if hidden node or bad channel conditions?

Cooperative Sensing:CR shares its sensing data with others and utilize the sensing outcomes of others to give a decision

Robust to sensing errors due to hidden node or fading channels.

Cost of cooperation?

Cooperative vs. Non-cooperative Sensing

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Cooperative Sensing


More robust to sensing errors.

Hidden node problem

PU is hidden to the CR. CR’s transmission will result in interference at the PU receiver.

Cooperate with this user!

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Proactive

Reactive

Local

Cooperative

Centralized

Distributed

Synchronous

Asynchron.

In-band

Out-of-band

Parallel

SequentialCentralizedA Central Manager (BS or AP) collects CR sensing data and makes a decision on channel state, i.e. idle or busyCost of transmission sensing data? What if the Central Manager fails? Single

Point of Failure.

Distributed (Decentralized)Each CR makes decision itself.

Centralized vs. Distributed Sensing

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Centralized/Distributed Cooperative Sensing


Decision Fusion Center

Increased sensing reliability at the expense of increased communication overhead

How to communicate: Common control channels (CCC)

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Decision Fusion: How to decide?


Yes, there is PU

No, it is IDLE

Yes Yes No

How to decide? (DECISION FUSION LOGIC) AND OR MAJORITY K-of-N

Soft or Hard Decision Combining: Yes or No answers (0-1), or Received Signal Strength

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Number of Cooperating Users vs. Sensing Time

11 April 2012Faculty of ScienceDepartment of Computer Science 32

Amir Ghasemi and Elvino S. Sousa, Spectrum Sensing in Cognitive Radio Networks: Requirements,Challenges and Design Trade-offs

Cooperation overhead generally increases with the number of cooperating

Optimal number of cooperating users

Single CR or 5 CRs

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Proactive

Reactive

Local

Cooperative

Centralized

Distributed

Synchronous

Asynchron.

In-band

Out-of-band

Parallel

SequentialSynchronousAll CRs have the same sensing schedule to sense a channel.

How to synchronize?Stop transmission and sense the medium.

AsynchronousEach CR has its own schedule to sense a channel.

If other CRs are transmitting while this CR is sensing, how to distinguish between SU and PU signal.

Synchronous vs. Asynchronous Sensing

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Proactive

Reactive

Local

Cooperative

Centralized

Distributed

Synchronous

Asynchron.

In-band

Out-of-band

Parallel

Sequential In-bandCR senses the channel that it is already transmitting- To detect if a PU appears

Out-of-bandCR senses channels other than the channel it is in

To find other spectrum holes To find another channel to switch since a PU has

already appeared.

In-band vs. Out-of-band Sensing

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Hardware requirements: High speed processing units (DSPs or FPGAs) performing

computationally demanding signal processing tasks with relatively low delay.

Operation in a wide spectrum range

Sensing-Transmission Tradeoff

Security: a selfish or malicious user can modify its air interface to mimic a primary user.

Challenges of Spectrum Sensing


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Static spectrum access is cumbersome!

CR facilitates unused spectrum to be used opportunistically.

Spectrum sensing facilitates discovery of unoccupied spectrum.

The spectrum sensing can be designed considering various criteria at MAC and PHY layer.

The longer is the sensing duration, generally the higher is the sensing reliability.

Cooperation increases sensing performance but has higher overhead.

Summary


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References


T. Yucek and H. Arslan, A survey of spectrum sensing algorithms for cognitive radio applications, IEEE Communications Surveys and Tutorials, vol. 11, no. 1, pp. 116-130, 2009.

Ghasemi, Amir, and Elvino S. Sousa. Spectrum sensing in cognitive radio networks: requirements, challenges and design trade-offs. IEEE Communications Magazine, 46.4 (2008): 32-39.

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Questions?


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Self-Study: Make sure you know all the terms below

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Primary User Secondary User Cognitive Radio Spectrum Hole Spectrum Sensing Harmful Interference SNR Cooperative Sensing Dynamic Spectrum Access Static Spectrum Access Spectrum Underutilization Sensing-transmission trade-off Decision fusion logic

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Presentation Schedule


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Next week

2-Minute Madness Session: In two minutes present your topic’s basic idea, questions, etc! Only 2 minutes.


Documents

Www.cs.helsinki.fi Overview of Cognitive Radio Basics and Spectrum Sensing CN-S2013 Faculty of Science Department of Computer Science1 Jan.29, 2013 Suzan