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7/26/2019 Introduction to Spectrum Sensing
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KITUniversity of the State of Baden-Wuerttemberg andNational Research Center of the Helmholtz Association
COMMUNICATIONS ENGINEERING LAB (CEL)
www.kit.edu
Cognitive Radio for Dynamic Spectrum AccessVision Meets RealityFriedrich Jondral
LStelcom SummitLichtenau, July 4, 2012
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Communications Engineering Lab (CEL)2 10.07.2012 Prof. Dr.rer.nat. Friedrich Jondral
Cognitive Radio (CR)
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Communications Engineering Lab (CEL)3 10.07.2012 Prof. Dr.rer.nat. Friedrich Jondral
Immediate Urgent Normal
ACT
OutsideWorld
NewStates
PriorStates
GenerateAlternatives
Evaluate
Alternatives
ORIENT
Establish Priority
Receive a MessageRead Buttons
Send a Message Initiate Process(es)
Register toCurrent Time
Pre-ProcessParse
Save Global States
Allocate Resources
Set Display
Infer on ContextHierarchie
Joseph Mitola III: CognitiveRadioAn Integrated AgentArchitecture for SoftwareDefined Radio. KTHStockholm, 2000
CR: Vision
OBSERVE
DECIDE
LEARN PLAN
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CR: Definition
Cognitive Radiois an intelligent wireless communication system that isaware of its surrounding environment(i.e. its outside world), and uses themethodology of understanding-by-building to learn from the environmentand adapt its internal states to statistical variations in the incoming RFstimuli 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;- efficient utilization of the radio spectrum.
Simon Haykin: Cognitive Radio: Brain-Empowered Wireless Communications.IEEE J. Select. Areas in Comm., vol. 23, no. 2, 2005, pp. 201-220
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Reality
Prof. Dr.rer.nat. Friedrich Jondral
CRis not a revolution in radio communications, it is merely the way ahead to
more automationand adaptation
in finding the optimum frequency and in using the optimum transmission power
With these properties
higher spectrum efficiency lower costsand more environmental acceptability
are achieved.
The CR paradigm makes sense only in networks.
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Meaning of "Spectrum"
A material quantity that may be partitioned
or an immaterial medium
that may be accessed
without regulation?
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Spectrum Utilization
M. McHenry: NSF Spectrum Occupancy Measurements.
The Shared Spectrum Company, Tech. Rep., 2005,http://sharedspectrum.com/?sectio=nsf_measurements
Fundamental Statement:Even in crowded frequency regions not more then 15 percent of the(theoretical) capacity is actually used.
However:A hundred percent usageof the transmission resourceis utopistic (interferences)
But: Struggling is promising.
Photo: The Shared Spectrum Company
http://sharedspectrum.com/?sectio=nsf_measurementshttp://sharedspectrum.com/?sectio=nsf_measurements7/26/2019 Introduction to Spectrum Sensing
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Dynamic Spectrum Access (DAS)
Dynamic Spectrum Access
Dynamic
Exclusiv Use Model
Hierarchical
Access Model
Open Sharing Model
(SpectrumCommons Model)
Spectrum
PropertyRights
Dynamic
SpectrumAllocation
Spectrum
Underlay(Ultra WideBand)
SpectrumOverlay
(OpportunisticSpectrumAccess)
from: Qing Zhao, Brian M. Sadler: A Survey of Dynamic Spectrum Access.IEEE Signal Processing Magazine, May 2007, pp. 79 - 89
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DSA: Questions
What is the meaning of Spectrum Access?
To enhance the efficiency in the usage of spectrum (briefly: spectralefficiency) in a specific geographic region, CRs access spectrum holesleft by the licensed users system (primary users) as secondary users.
I.e.: Spectrum Access happens in time, frequency, and space.
What is the meaning of Dynamic?
Nobody knows
On which scale is DSA based upon? Milliseconds, seconds, minutes,? Change in primary users behavior?
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Dynamic / Detection Time
DynamicDetection
Time
Burst
TV White Space
high short
low long
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Time/Frequency Plane
GSM 1800
No. of Channels: 374
Bandwidth: 270 kHzDistance: 200 kHz
Burst Duration: 0.577 ms
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Energy Detector
s(t) Transmitter Signal
u(t) Baseband Representation of s(t)
r(t) Received Signal
v(t) Baseband Representation of r(t)
T Duration of s(t)
Radio Frontend Decision |v(t)|2dtT
0
r(t)
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Matched Filter Detector
s(t) Transmitter Signal
u(t) Baseband Representation of s(t)
r(t) Received Signal
v(t) Baseband Representation of r(t)
T Duration of s(t)
Radio Frontend Decision v(t)u(T-t) dtT
0
r(t)
u(t)
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Pattern Recognition Detector
s(t) Transmitter Signal
u(t) Baseband Representation of s(t)
r(t) Received Signal
v(t) Baseband Representation of r(t)
T Duration of s(t)
Radio Frontend DecisionFeature
Extraction
r(t)
u(t)
PatternRecognition
FeatureExtraction
. . .
.
.
.
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Signal Detection
Prof. Dr.rer.nat. Friedrich Jondral
DetectorA Priori
Knowledge
Detection Time/Computational
ComplexityApplicability Robustness
Energy Nothing low universal high
MatchedFilter
Signal medium specific medium
PatternRecognition
SignalFeatures
high highly specific low
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Energy Detector
Detection Time: AWGNFalse Alarm Rate: 10-4
Detection Probability: b(2: normalized noise variance)
b =0.9999n
b =0.999 b =0.99 2SNR[dB]
111 93 74 2 -3
56 47 37 1 0
28 24 19 1/2 3
14 12 10 1/4 6
7 6 5 1/8 9
4 3 3 1/16 122 2 2 1/32 15
2 2 2 1/32 15
1 1/37 15.7
1 1/47 16.7
1 1/56 17.5
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Energy Detector
D = duration for one scan over the 374 channels of GSM 1800
false alarm rate: 10-4
detection probability: 0.999
SNR: 9 dB
Monitoring of the GSM band on burst basis by one scanning energy detector with
false alarm rate 10-4and detection probability 0.999 at an SNR of 9 dB isimpossible!
And:What about the power needed in the mobile radio for permanent scanningand detection?
D = 6 x No. of Channels x = 6 x 374 x s = 8.31 ms1
Bandwidth1
270000
D = =14.4 bursts8.310.577
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Proposed Solution 1
Prof. Dr.rer.nat. Friedrich Jondral
Distributed Detection
For networks with access point:Timo Wei: OFDM-basiertes Spectrum Pooling. Dissertation, Forschungsberichte aus dem Institut frNachrichtentechnik der Universitt Karlsruhe (TH), Band 13, Karlsruhe 2004
For ad hoc networks:Ulrich Berhold: Dynamic Spectrum Access Using OFDM-based Overlay Systems. Dissertation,Forschungsberichte aus dem Institut fr Nachrichtentechnik der Universitt Karlsruhe (TH), Band 21,Karlsruhe 2009
MAC frame MAC frame MAC frame
detectionphase
boostingphase
broadcastphase
P P
2 ms
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Distributed Detection and Boosting
Prof. Dr.rer.nat. Friedrich Jondral
With Access Point Ad Hoc
b) Boosting and Collection
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Proposed Solution 2
Prof. Dr.rer.nat. Friedrich Jondral
Off-line Sensing, Data Base Query, and Instantaneous Measurement
During idle times The radio senses all potential transmission channels1) The sensing results for each channel, together with the time of the day when
the sensing took place, are stored in a data base in order to establish channel
utilization statistics depending on time and frequency
When a communications request occurs1. The radio queries the data base for a channel that is idle with highest
probability at the current time of the day and that has not been sensed yet2. The radio instantaneously senses the chosen channel
3. If the channel is idle, the radio starts operation.If not, it goes back to 1.
1)The power problem for this remains unsolved.
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Data Base Query
16:05
16:10
16:15
16:20
Time Channel Utilization Statistics
16:17
Channel No. Priority
1 22 5
3 4
4 5
5 1
6 3
1 2 3 5 64
1 2 3 5 64
1 2 3 5 64
1 2 3 5 64
.
.
.
.
.
.
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Dontforget
Prof. Dr.rer.nat. Friedrich Jondral
Coordination
A channel idle at station A must not be idle at station B (agreement necessary).
Continuous SensingAs long as a SU station is active, it must permanently sense its channel (look
through).
Automated Frequency ChangeIf a PU signal is detected on the currently used channel, communication partnersmust identify a new usable frequency and jointly switch to it.
Hidden Stations
Multicast / Broadcast
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Summary
Prof. Dr.rer.nat. Friedrich Jondral
As of July 18, 2012 there are
8 847 papers on Cognitive Radio, 9 554 papers on Spectrum Sensing, and 2 635 papers on Dynamic Spectrum Accesslisted in the IEEE Xplore Digital Library.Many of them do not observe any constraints imposed by physics.
All notionsthat we use in communications need to be well defined.
Detection time depends on SNR, false alarm rate, detection probability, andfurther conditions imposed by wave propagation.
CRand DSAbear high potential for theoretical and practical research work.
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