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Cognitive Radio: Smart Use of Radio Spectrum

Miguel López-Benítez

Department of Electrical Engineering and Electronics

University of Liverpool, United Kingdom

[email protected]

www.lopezbenitez.es

Tokyo University of Agriculture and Technology, Tokyo, Japan, 16 January 2018

mailto:[email protected]



http://www.lopezbenitez.es/

Contents

• Introduction

• Cognitive radio

• Cognitive functions

• Applications

• Conclusion

16 January 2018 Tokyo University of Agriculture and Technology

– 2 –

Contents

• Introduction

• Cognitive radio


• Applications

• Conclusion

– 3 – 16 January 2018 Tokyo University of Agriculture and Technology

Introduction

• Spectrum management:

– Allocation: Frequency bands Services

– Assignment: Frequency bands Operators

• Fixed spectrum management:

– Spectrum bands are allocated/assigned statically

– Exclusive use licence

– In use since early days of radio communications

– Easy avoidance of interference

– Usable spectrum has already been allocated


The UK Frequency Allocation Table

– 5 –

http://www.ofcom.org.uk/static/spectrum/fat.html




Is spectrum exhausted?

• Spectrum usage is concentrated on certain portions

• A significant amount of spectrum remains unused

• Inefficient spectrum usage!

– 6 –

Source: M. López-Benítez et al., “Spectral occupation measurements and blind standard recognition sensor for cognitive radio networks,” Proc. 4th Int’l. Conf. Cognitive Radio Oriented Wireless Networks and Comms. (CrownCom 2009), Hannover, Germany, June 22-24, 2009.


Fixed vs. Dynamic spectrum access

• Fixed spectrum management:

– Easy avoidance of interference

– Inefficient usage of spectrum!

– Inability to roll out new radio technologies and services!

• Solution? Dynamic Spectrum Access:

– 7 –

Source: M. López-Benítez, “Spectrum usage models for the analysis, design and simulation of cognitive radio networks,” PhD Thesis, Department of Signal Theory and Communications, Technical University of Catalonia, Barcelona, Spain, July 2011.


Opportunistic spectrum access

– 8 –

• Analogy:

– Spectrum = Motorway

– Band = Lane

– Interference = Collision

• Concepts: – Primary user (w/ licence) High priority

• Police car, ambulance car, etc.

– Secondary user (w/o licence) Low priority

• Regular car



• Time domain OSA:

– 10 –

P P P S S S

Spectrum hole or white space



• Time domain vs. Space domain OSA:

– 11 –

Time domain OSA Space domain OSA



• Advantages of DSA/OSA:

– Higher spectrum efficiency

– Several systems can coexist in the same spectrum: • Roll-out of new radio technologies, services, networks…

• Reduced cost of spectrum (i.e., inexpensive services for the end-user)

• Drawbacks:

– Concept is simple in theory, but challenging in practice.

– Need for a more sophisticated, smart technology:

Cognitive radio


Contents

• Introduction

• Cognitive radio


• Applications

• Conclusion


Cognitive radio

• J. Mitola: “Radio etiquette is the set of RF bands, air interfaces, protocols, and spatial and temporal patterns that moderate the use of radio spectrum. Cognitive radio extends the software radio with radio-domain model-based reasoning about such etiquettes.”

• S. Haykin: “Cognitive radio is an intelligent wireless communication system that is aware of its surrounding environment (i.e. its outside world), and uses the methodology of understanding-by-building to learn from the environment and adapt its internal states to statistical variations in the incoming RF stimuli by making corresponding changes in certain operating parameters (e.g. transmit power, carrier-frequency and modulation strategy) in real-time, with two primary objectives in mind: highly reliable communications whenever and wherever needed and efficient utilization of the radio spectrum.”

• F. K. Jondral: “A CR is an SDR that additionally senses its environment, tracks changes, and reacts upon its findings. A CR is an autonomous unit in a communications environment that frequently exchanges information with the networks it is able to access as well as with other CRs.”


Cognitive radio


Cognitive radio

• Main features:

– Cognitive capability: Senses RF environment and learns about it. • Activity of licensed users

• Temporal and spatial variations of environment

• Identifies portions of unused spectrum

• Selects the best spectrum and transmission parameters

– Reconfigurability: Adapts operating parameters accordingly. • Frequency of operation

• Modulation

• Transmission power

• Communication protocol


Cognitive radio as OSA enabler

• Cognitive radio is the key enabling technology for DSA / OSA!


Contents

• Introduction

• Cognitive radio


• Applications

• Conclusion


Cognitive radio functions

• Functions of a CR system: – Spectrum awareness: Identify free portions of the spectrum and detect the

presence of licensed users when a user operates in a licensed band.

– Spectrum selection: Select the best available spectrum.

– Spectrum sharing: Coordinate access to this channel with other users.

– Spectrum mobility: Vacate the channel when a licensed user is detected and smoothly move the transmission to another channel with minimal disruption.

– 19 –

Source: M. López-Benítez, “Cognitive radio”, Chapter 13 in Heterogeneous cellular networks: Theory, simulation and deployment, CUP 2013.


Spectrum awareness

• Spectrum awareness: Identify free portions of the spectrum and detect the presence of licensed users when a user operates in a licensed band.

• Methods:

– Beacon signals

– Geolocation databases

– Spectrum sensing


Spectrum awareness (beacon signals)

• Beacon signals:

– Primary transmitters broadcast “beacon” signals: • Spectrum usage, power, coverage, etc.

– Secondary users tune and decode the signal.


Spectrum awareness (beacon signals)

• Pros and cons of beacon signals:

– Perfect information

– Requires agreement primary-secondary

– Changes in legacy systems (technical & economical problems)


Spectrum awareness (databases)

• Databases:

– Regional DB contains relevant info • Spectrum usage, TX location, frequency, power, coverage, etc.

– Geolocation needed (GPS)


Spectrum awareness (databases)

• Pros and cons of databases:

– Perfect / accurate information

– Relies on external system (technical, admin & legal problems)

– Need for geolocation in DSA/CR terminals (cost, location accuracy, etc.)

– Database updating rate: not suitable for dynamic bands


Spectrum awareness (spectrum sensing)

• Spectrum sensing:

– Sample primary signal and determine ON/OFF state by means of signal processing methods: • Matched filter detection

• Energy detection

• Feature detection (cyclo-stationarity, pilots)

• Covariance based detection



– 26 –

CR user 1

Primary transmitter

Primary receiver

No interaction between CR users and primary Tx/Rx

CR users must rely on locally sensed signals to infer

primary user activity

Channels found occupied by CR user (licensed bands 1 and

2) are now avoided during communication between CRs

CR user 2

Licensed band 1

Licensed band 2



• Pros and cons of spectrum sensing:

– Does not rely on an external system

– No changes to primary (legacy) system (simple, inexpensive)

– Suitable for dynamic spectrum bands

– Inaccurate information (spectrum sensing errors)



• Problems of spectrum sensing:

Hidden node problem (receiver uncertainty)

Primary Base-station

Primary

transmitter

range

Primary user

CR transmitter

range Interference

CR user

Cannot

detect the

transmitter



• Problems of spectrum sensing:

– 29 –

CR

transmitter

range

Primary transmitter

CR user

Primary

transmitter

range

Primary user

Interference

Hidden node problem (shadowing/fading)

Cooperation



• Solution to problems of spectrum sensing:

– 30 –

Primary user

Primary transmitter

Multi-path fading

Weak signals are received due to the multi-path fading may not detect the primary user

Shadowing

Cannot detect the primary user due to the obstacles

Detects the primary user correctly

By exchanging their sensing information, CR

users can detect the primary user under fading

and shadowing environments

CR user 2

CR user 3

CR user 1

BUSY

IDLE

IDLE

BUSY BUSY



• Non-cooperative sensing: – CR users detect primary signal independently through local observations.

• Cooperative sensing: – CR users share their local observations to collectively detect primary signal.


Spectrum awareness


Spectrum selection

• Spectrum selection: Select the best available spectrum.

• Classification:

– Spectrum analysis

– Spectrum decision


Spectrum selection

• Spectrum analysis: – Characterise spectrum holes based on certain metrics.

• RF metrics:

– Frequency

– Bandwidth

– Interference

– Emission limits

• Activity metrics

– Duty cycle

– Other statistics

• Spectrum decision: – Select the most

convenient spectrum

– 34 –

8

6

4

0

2 Primary

user

Primary user CR user CR user

No PU: SU can transmit with max power

PU: SU must reduce power

4

0

2

Transmission range

Received power


Spectrum sharing

• Spectrum sharing: Coordinate access to this channel with other users.

• Classification methods: • Architecture: centralised vs. distributed.

• Behaviour: cooperative vs. non-cooperative.

• Scope: intra-network vs. inter-network.

– 35 –

P P P S S S S1 S2 S3 S1 S3


Spectrum mobility

• Spectrum mobility: Vacate the channel when a licensed user is detected and smoothly move the transmission to another channel with minimal disruption.


Spectrum mobility

– 37 –

CR user B

Occupied by primary users

CR user A

Idle spectrum band

Spectrum

handover CR user A

CR user B


Cognitive radio functions

• Functions of a CR system:


Contents

• Introduction

• Cognitive radio


• Applications

• Conclusion


Applications: Rural broadband

– 40 –

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TV transmitter • IEEE 802.22:

– Broadband access in rural areas.

– Using TV channels (6-7-8 MHz).

– Coverage: 33km (100 km max).


Applications: Rural broadband


Applications: Public safety


Applications: Broadband mobile comms

– 43 –

• Mobile communication systems face a serious problem:

– Capacity has doubled every 5 years

– Traffic level has doubled every year!


Applications: Broadband mobile comms


Contents

• Introduction

• Cognitive radio


• Applications

• Conclusion


Conclusion

• Spectrum problem: – Spectrum use is not efficient nowadays

• Spectrum bands are allocated… • …but not fully exploited

– Spectrum demand increases constantly

• Solution: dynamic / opportunistic use of spectrum

– Increases spectrum efficiency. – Enables roll-out of new services at lower costs.

• Key enabling technology: Cognitive radio

– Senses the radio environment and learns about it – Reconfigures and adapts dynamically to the operating conditions

• Important technical problems and challenges to be overcome

• Important applications in future wireless communication systems


The End


Further reading

M. López-Benítez, “Cognitive radio”, Chapter 13 in Heterogeneous cellular networks: Theory, simulation and deployment,

Cambridge University Press, 2013


…for your attention!

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