Cognitive Radio Survey

Spectrum Sensing and Allocation Techniques for Cognitive Radios Farrukh Javed F-05-020/07-UET - PHD-CASE-CP-40

Sequence of Presentation  Section I – Cognitive Radios  Introduction  Next generation networks  Cognitive radios

 Section II – Spectrum Sensing  Transmitter detection  Cooperative detection  Interference based detection  Spectrum sensing challenges

 Section III – Spectrum Allocation  Spectrum analysis  Spectrum decision

 Section IV – Future of Cognitive Radios  Conclusion

Cognitive Radios Cognitive Radios Section – I

Motivation for Cognitive Radios

Spectrum Scarcity [1]

Motivation for Cognitive Radios

Spectrum Utilisation [1]

COGNITIVE RADIOS

Motivation for Cognitive Radios Measured Spectrum Occupancy Averaged over Six Locations PLM, Amateur, others: 30-54 MHz TV 2-6, RC: 54-88 MHz Air traffic Control, Aero Nav: 108-138 MHz Fixed Mobile, Amateur, others:138-174 MHz TV 7-13: 174-216 MHz Maritime Mobile, Amateur, others: 216-225 MHz Fixed Mobile, Aero, others: 225-406 MHz Amateur, Fixed, Mobile, Radiolocation, 406-470 MHz TV 14-20: 470-512 MHz TV 21-36: 512-608 MHz TV 37-51: 608-698 MHz TV 52-69: 698-806 MHz Cell phone and SMR: 806-902 MHz Unlicensed: 902-928 MHz Paging, SMS, Fixed, BX Aux, and FMS: 928-906 MHz IFF, TACAN, GPS, others: 960-1240 MHz Amateur: 1240-1300 MHz Aero Radar, Military: 1300-1400 MHz Space/Satellite, Fixed Mobile, Telemetry: 1400-1525 MHz Mobile Satellite, GPS, Meteorologicial: 1525-1710 MHz Fixed, Fixed Mobile: 1710-1850 MHz PCS, Asyn, Iso: 1850-1990 MHz TV Aux: 1990-2110 MHz Common Carriers, Private, MDS: 2110-2200 MHz Space Operation, Fixed: 2200-2300 MHz Amateur, WCS, DARS: 2300-2360 MHz Telemetry: 2360-2390 MHz U-PCS, ISM (Unlicensed): 2390-2500 MHz ITFS, MMDS: 2500-2686 MHz Surveillance Radar: 2686-2900 MHz 0.0%

25.0%

50.0%

75.0%

100.0%

Spectrum Occupancy

Spectrum Concentration [2]

COGNITIVE RADIOS

Cognition  Oxford English Dictionary definition of

“cognition” as “The action or faculty of knowing taken in its widest sense, including sensation, perception, conception, etc., as distinguished from feeling and volition”  Encyclopedia Encarta defines “cognition” as “To acquire knowledge by use of reasoning, intuition or perception”  Encyclopedia of computer Sciences gives a three point computational view of “cognition” as “1. Mental state and processes intervene between input stimuli and output responses 2. The mental state and processes are described by algorithms

Cognitive Radio  Joseph Mitola introduced the idea of Cognitive Radio

in 2000 as “Situation in which wireless nodes and related networks are sufficiently computationally intelligent about radio resources and related computer to computer communication to detect the user communication needs as a function of user context and to provide the resources most required”  Simon Haykin explains the concept in six key words  Awareness  Intelligent  Learning  Adaptability  Reliability  Efficiency

 An intelligent radio capable of adapting itself to best

Operating Principal of CR Overlay CRs utilise the concept of spectrum

holes Underlay CRs use the concept of interference temperature

Overlay Cognitive Radios

Time

COGNITIVE RADIOS

Interference temperature model

 Interference temperature TI is specified in Kelvin and is defined

as

where PI (fc , B) is the average interference power in Watts centered at fc, covering bandwidth B measured in Hertz. Boltzmann's constant k is 1.38 x 10-23  Any Un-licensed transmission must not violate the interference temperature limit at the licensed receivers. Mi is a fractional value between 0 and 1, representing a multiplicative attenuation due to fading and path loss between the unlicensed transmitter and the licensed receiver.

 The TL is to be decided by regulatory authority such as FCC or

Underlay Cognitive Radios

Interference Temperature Model [10]

SPECTRUM

Interference Temperature Level

Interference temperature is the maximum

RF interference acceptable at a receiving antenna

Basic Characteristics of Cognitive Radios Cognitive Capability Re-configurability

COGNITIVE RADIOS

Cognitive Capability Cognitive Cycle Spectrum Sensing Spectrum Allocation Spectrum Analysis Spectrum Decision

Cognitive cycle [3]

Re - Configurability Operating Frequency Modulation Scheme Transmission Power Communication Technology Directivity of Transmission

Next Generation Networks Introduction Protocol Layers and Cognitive Radio

Functionalities

xG Network Functionalities [3]

COGNITIVE RADIOS

Spectrum Sensing Spectrum Sensing Section – II

Spectrum Sensing Techniques

SPECTRUM

Transmitter Detection Introduction Techniques Matched Filter Detection Energy Detection Cyclo – Stationary Feature Detection

SPECTRUM

Introduction Opportunities Commonly Used High Processing Gain

Challenges

Transmitter Detection

Matched Filter Detection

Matched Filter Bound A priori knowledge of transmission is required

SPECTRUM

Introduction Opportunities

Transmitter Detection

Energy Detection

Easy implementation Multi path and fading channel studies carried

out

Challenges Critical selection of threshold Susceptible to noise power variations Communication type identification not

possible Reduced flexibility SPECTRUM

Introduction Opportunities

Transmitter Detection

Cyclo – Stationary Feature Detection

Robust against un-certain noise powers Transmitter information is not required

Neural network application has been found

very feasible Challenges

Computationally complex Transmission type identification is not possible Reduced flexibility

SPECTRUM

Receiver Un-certainty Shadowing Un-certainty

(a) Receiver Uncertainty (b) Shadowing Uncertainty [3]

SPECTRUM

Transmitter Detection

Transmitter Detection Un – Certainties

Cooperative Detection Introduction Centralised Detection Distributed Detection

Cooperative Detection Opportunities No receiver or shadowing un-certainties Effects of degrading factors mitigated Primary User’ interference reduced

Cooperative Detection Challenges Implementation Complexity Constrained Resources Primary user un-certainty un-resolved

SPECTRUM

Interference Based Detection

Interference Temperature Model [10]

SPECTRUM

Opportunities and Challenges of Interference Based Detection Opportunities Focus on primary receiver rather than primary

transmitter Frequency parameters of choice can be utilised Challenge Receiver temperature detection Due to interference power constraints, the

underlay techniques can only be employed for short range communications

SPECTRUM

Few Generalised Spectrum Sensing Challenges Multi user environment Interference temperature measurement Speed of detection etc.

SPECTRUM

Spectrum Allocation Spectrum Allocation Section – III

Spectrum Allocation

SPECTRU M

Spectrum Analysis Channel capacity Primary user related information xG user information

SPECTRU M

Channel Capacity Wireless Link Layer Link Layer Delay Noise Info

Spectrum Analysis

Path Loss

User Related Information (Primary and xG Users) Holding Time User Transmission Parameters

Spectrum Analysis

Interference

Spectrum Analysis Challenges and Opportunities

Spectrum Analysis

Challenges

Heterogeneous Spectrum Sensing Non Cooperative Primary and xG users Varying Transmission Parameters Real Time Analysis Delays in Processing

Opportunities

Spectrum Decision Spectrum management Spectrum mobility Spectrum sharing User related info

SPECTRU M

Spectrum Management Decision Model Multiple Spectrum decision Reduced Transmission Power Cooperation with reconfiguration Heterogeneous Spectrum

SPECTRU M

Spectrum Mobility  Introduction  Challenges Latency Suitable Algorithm Appearance of a Primary User Vertical and Inter-Cell Handoff Scheme Suitable Threshold for Handoff Spectrum Mobility in Time Domain Spectrum Mobility in Space

 Opportunities Prioritised White Space Soft and Hard Handoff SPECTRU M

Spectrum Sharing  Architecture Based Classification Centralised or Distributed Challenges and Opportunities

 Access Behaviour Classification

Cooperative and Non-cooperative Sharing Challenges and Opportunities

 Access Technology Classification

Overlay and Underlay Techniques Challenges and Opportunities

 Generalised Spectrum Sharing Challenges Common control Channel Dynamic radio range Spectrum Unit

SPECTRU M

Future of Cognitive Radios Future of Cognitive Radios Section IV

Cognitive Radio Advantages  All of the benefits of software defined radio  Improved link performance  Adapt away from bad channels  Increase data rate on good channels  Improved spectrum utilization  Fill in unused spectrum  Move away from over occupied spectrum  New business propositions  High speed internet in rural areas  High data rate application networks (e.g., Video-

conferencing)  Significant interest from FCC, DoD  Possible use in TV band refarming

Cognitive Radio Drawbacks  All the software radio drawbacks  Significant research to realize  Information collection and modeling  Decision processes  Learning processes  Hardware support  Regulatory concerns  Loss of control  Fear of undesirable adaptations  Need some way to ensure that adaptations yield

desirable networks

How can CR improve spectrum utilization? Allocate the frequency usage in a network Assist secondary markets with frequency

use, implemented by mutual agreements Negotiate frequency use between users Provide automated frequency coordination Enable unlicensed users when spectrum not in use Overcome incompatibilities among existing communication services

Potential Applications of CR Leased networks Military usage Emergency situations Mesh networks Licensed user may enhance its performance Improving UWB transmission by avoiding

NBI

Jeffery H Reed and Wills G Worcester

Conclusion Conclusion Spectrum Sensing and Allocation Techniques for Cognitive Radios