spectrum management and cognitive radio fine secondo anno... · operation of cognitive radio...

Spectrum Management and

Cognitive RadioAlessandro Guidotti

Tutor: Prof. Giovanni Emanuele Corazza, University of Bologna, DEIS

Co-Tutor: Ing. Guido Riva, Fondazione Ugo Bordoni

The spectrum scarcity problem

• The ever increasing spectrum demand for new wireless

communication systems cannot be satisfied anymore,

thus leading to an overall “spectrum scarcity” perception

The Command &

Control static spectrum

allocation method is

completely ineffective

• Possible solutions:

– Releasing frequency bands thanks to novel and more efficient

transmission techniques (e.g. DVB-T)

– Allowing smart devices to dynamically access licensed bands

Research activity

• The digital switch-over process is releasing some very valuable bands that can

be reallocated to other services

– WRC-07 allocated the 790-862 MHz band to mobile services starting from June

2015, and allowed EU countries to utilize this allocation before 2015 subject to

technical coordination with neighbouring countries

• New interference issues:

– Co-channel interference between neighbouring countries/regions, one of them using

this band for mobile service and the other one for broadcast television

– Adjacent channel interference within a given territory

DVB-T

470 MHz

Mobile

& DVB-T

790 MHz 862 MHz

Research activity

• White Space: “part of the spectrum available for radiocommunication

application at a given time in a given geographical area on a non-interfering /

non-protected basis with regard to other services with a higher priority” [CEPT]

• CR: “a radio in which communications systems are aware of their environment

and internal state and can make decisions about their operating behaviour

based on that information and predefined objectives” [IEEE]

• Several technological challenges must be overcomeSpectrum Sensing

Spectrum Management

Spectrum Mobility

DVB-T

470 MHz

Mobile

& DVB-T

790 MHz 862 MHz

Research activity

• CEPT SE43 “Technical and operational requirements for the possible

operation of cognitive radio systems in the „White Space‟ of the frequency

band 470-790 MHz”

– Hidden Node Problem

– Amount of spectrum potentially available as White Space

– Geolocation Database

• Collaboration with CREAT-NET, NET&SERV Dept., Trento:

– Cooperative and distributed energy detection

– Cognitive Satellite Terrestrial Radios (54-862 MHz & 3.1-10.6 GHz bands)

DVB-T

470 MHz

Mobile

& DVB-T

790 MHz 862 MHz

Hidden Node Problem

1path

2path

3path

• Path1: rooftop mounted DTT receiver in LOS

condition with respect to the DTT TX

• Path2: CR attempting to detect the DTT

signal at street level, shielded by the

surrounding buildings

• Path3: the CR could erroneously conclude

that the specific DTT channel is available and

hence it might cause harmful interference to

the DTT receiver

• Hidden Node Margin: difference between filed strengths received at the location of

the CR and the DTT receiving antenna

• Methodology 1: Ray Tracing simulations performed in several environments and

validated against measurements

• Methodology 2: analytical study based on Recommendation ITU-R P.1546

Gsha

CR

med

DTT

med EEHNM )50,50()50,50( )()(

Hidden Node Problem

UK Ofcom

results

90% of test

points

95% of test

points

99% of test

points

Densely

Urban

18.5 dB 22.4 dB 29.2 dB

Urban 28.1 dB 30.2 dB 32.5 dB

Rural 14.9 dB 15.6 dB 16.6 dB

•M.Barbiroli, C.Carciofi, A.Guidotti, D.Guiducci, “Evaluation and analysis of the Hidden Node Margin for Cognitive Radio

System operation in a real scenario,” submitted to EuCAP2011

•Italian Contribution to SE43, “Calculation of the Hidden Node Margin in a real Italian Scenario”, August 2010

4km2 area with

1765 test points

Simulation Parameters – M1:

• Frequency = 690 MHz

• Bandwidth = 8 MHz

• ERP TV = 81.11 dBm

• Distance = 3.4 – 4.7 km

SE43 single-device sensing threshold range: [-91,-165] dBm

HNM for DTT Service Protection

Urban environment

+24.7=44.46 dB

Cooperative Energy Detection

• The energy detector performs the detection of the signal by comparing

the energy of the received signal with a predefined threshold

• Single-device energy detector is extremely simple from a computational

point of view, but the performance are highly susceptible to noise and

fast/slow fading

• Possible solution: let several devices cooperate among them in order to

increase the detection performance

Pre-filter A/D (1/N)*ΣN| |2>

<X+

)(ts

)(tn )(th

)(tx iE

1

0

H

H


Fusion

Center

DTT

Transmitter

• Cooperative spectrum sensing with p-

out-of-L rule: if at least p CRs among

the L cooperating devices detect the

primary signal, then the fusion center

concludes that the channel is

occupied

• Simulations are performed on AWGN,

Rayleigh and Lognormal channels

• Performance evaluation: Prob{H0|H0} vs Prob{H1|H1}


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Probability of Correct Secondary User Authorization

Pro

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Theoretical ROC [L=6 - SNR=-3 dB - N=2]

p=1

p=2

p=3

p=4

p=5

p=6

Single-Device

• W.Zhang (ICC‟2008) computed the

optimal value of p

– When Pd and Pf have the same

order, popt≈L/2

– When Pf<<Pd, popt≈1 (OR rule)

– When Pf>>Pd, popt≈L (AND rule)


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1


Pro

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Theoretical ROC [L=6 - SNR=-3 dB - N=2]

p=1

p=2

p=3

p=4

p=5

p=6

Single-Device

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1


Pro

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ROC on Lognormal Channel [L=6 - SNR=-3 dB - N=2]

Single-Device

p=1

p=3

p=6

• W.Zhang (ICC‟2008) computed the

optimal value of p

– When Pd and Pf have the same

order, popt≈L/2

– When Pf<<Pd, popt≈1 (OR rule)

– When Pf>>Pd, popt≈L (AND rule)

• There is a significant gain obtained thanks to cooperation among CRs

• With higher values of L the performance improve, but the gain is less evident for

increasing L

• The problem is the traffic overhead due to the sensing report to the Fusion Center (higher

for large values of L, of course)

• A possible solution could be an hybrid cooperative/distributed architecture (under study)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1


Pro

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ROC on Rayleigh Channel [L=6 - SNR=-3 dB - N=2]

Single-Device

p=1

p=3

p=6

Cognitive Satellite Terrestrial Radios

• The future satellite ground terminals need to

integrate and coexist with the spectrally

crowded terrestrial wireless systems

• The cognitive functionalities are proposed for

satellite uplink and terrestrial transmissions

• The satellite downlink cannot adopt such

capabilities due to many practical limitations in

the controlling satellite transmissions










• Application

– Satellite-802.22 for WRAN (54-862 MHz)

– Satellite-UWB for PANs (3.1-10.6 GHz)










• Application

– Satellite-802.22 for WRAN (54-862 MHz)

– Satellite-UWB for PANs (3.1-10.6 GHz)

• 3D-spatial domain frequency reuse: since the

satellite is seen under a high elevation angle

(depending on the latitude), proper design of

the antenna radiation pattern can allow to

reduce mutual interference


• Simulations were performed with an energy detection sensing

• Due to the directional gain pattern of the parabolic antenna, the Terrestrial Transmitter

detection performance becomes worse when reduces

• For the same reason, the detection performance becomes worse for increasing values of

θ

• On the one hand, the TT detection becomes harder for increasing θ or decreasing , but

on the other hand in such cases the directional antennas interfere less with the TT

•S.Kandeepan, L.De Nardis, M.-G. Di Benedetto, A.Guidotti, G.E.Corazza, “Cognitive Satellite Terrestrial

Radios,” to appear in GLOBECOM2010

LTE / DVB-T interference

• The digital switch-over process is releasing some very valuable bands that can be

reallocated to other services

– WRC-07 allocated the 790-862 MHz band to mobile services starting from June 2015, and

allowed EU countries to utilize this allocation before 2015 subject to technical coordination

with neighbouring countries

• We performed a study of the co-channel interference problem, proposing a

methodology to take into account the mutual interference between a LTE mobile

network and a DVB-T system• Monte Carlo simulations (100 iterations)

– Aggregated interference from 42 LTE BSs

towards 200 Yagi receiving antennas

– Interference from a DVB-T transmitter towards

42 LTE BSs (uplink)

• Performance evaluation

– DVB-T: an acceptable guard distance was

defined as the distance between the two

networks such that <1% of performance

degradation is obtained

– LTE: uplink average throughput reduction

•A.Guidotti, D.Guiducci, M.Barbiroli, C.Carciofi, P.Grazioso, “Coexistence and mutual interference between

mobile and broadcasting systems,” submitted to VTC Spring 2011


• Please note that Link Adaptation behaviour was taken into account

• The effect of the 42 BSs has been evaluated for several distances between the DVB-

T coverage area edge and the mobile area center

• The guard distances are the distance such that the DVB-T system suffers less than

1% of coverage degradation

• Deploying the LTE system at the computed guard distance, the effect of the DVB-T

transmitter on this network has thus been evaluated


• There might be situations where more interest is focused on the protection of the

mobile service

• The proposed performance parameter to be evaluated is the reduction in the

throughput provided to the users

• Having defined the maximum acceptable throughput reduction (e.g. 10%), the DVB-T

system parameters that guarantee the protection of the mobile service can be easily

identified

Further work

• The dependence of the Hidden Node Margin values on the

geometrical properties of the scenario (e.g. street orientation and

width) is currently under study

• The performance of the Cooperative Energy Detection is being

evaluated in correlated lognormal channels, as well as the

implementation of the hybrid cooperative/distributed architecture

• The analysis of adjacent channel interference between mobile and

broadcasting services still has to be analyzed

• Analytical characterization of the interference originated by a CR

network on a primary network will be analyzed using stochastic

geometry (6 months visit at SUPELEC, Paris)

Bibliography• M.Barbiroli, C.Carciofi, A.Guidotti, D.Guiducci, “Evaluation and analysis of the

Hidden Node Margin for Cognitive Radio System operation in a real scenario,”

submitted to EuCAP2011

• Italian Contribution to SE43, “Calculation of the Hidden Node Margin in a real

Italian Scenario”, August 2010

• Italian Contribution to SE43, “Estimate of the amount of spectrum available as

White Space in north west of Italy”, January 2010

• S.Kandeepan, L.De Nardis, M.-G. Di Benedetto, A.Guidotti, G.E.Corazza,

“Cognitive Satellite Terrestrial Radios,” to appear in GLOBECOM2010

• A.Guidotti, D.Guiducci, M.Barbiroli, C.Carciofi, P.Grazioso, “Coexistence and

mutual interference between mobile and broadcasting systems,” submitted to

VTC Spring 2011

• Italian Contribution to SE43, “Translation of the information provided to the

geolocation database into elements of authorization to the WSD,” SE43, August

2010

• Italian Contribution to CPG PT-D, “WRC-12 – AI 1.17 – Broadcasting vs mobile:

theoretical analysis of mutual interference”

THANK YOU!

spectrum management and cognitive radio fine secondo anno... · operation of cognitive radio...

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