new directions in cognitive radio and spectrum sharing
TRANSCRIPT
New directions in cognitive radio and spectrumsharing
Anant Sahaipresenting joint work with:
Danijela Cabric Mubaraq Mishra Rahul TandraArash Parsa Amin Gohari Kristen Woyach
George Atia Saligrama Venkatesh
BWRC and Wireless Foundations CenterU.C. Berkeley
Major support from the National Science Foundation
IEEE Workshop on Networking Technologies for SDR Networks
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 1 / 40
Spectrum, spectrum, everywhere, but . . .
Available spectrum looks scarce.
Measurements suggest the allocated spectrum is vastly underutilized.
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 2 / 40
Examine the problem from first principles
What is the deep reason for the existing waste?
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 3 / 40
Examine the problem from first principles
What is the deep reason for the existing waste?3R’s: Rate,Reliability, andRobustness
◮ Rate and Reliability: our usual focus⋆ Fighting ergodic uncertainty⋆ Shannon capacity limits⋆ Error correcting codes
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 3 / 40
Examine the problem from first principles
What is the deep reason for the existing waste?3R’s: Rate,Reliability, andRobustness
◮ Rate and Reliability: our usual focus⋆ Fighting ergodic uncertainty⋆ Shannon capacity limits⋆ Error correcting codes
◮ Robustness: the rest⋆ “Outage” within a system⋆ Coexistence with other systems⋆ Traditional approach: static guard bands (“frequency plans”)
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 3 / 40
Examine the problem from first principles
What is the deep reason for the existing waste?3R’s: Rate,Reliability, andRobustness
◮ Rate and Reliability: our usual focus⋆ Fighting ergodic uncertainty⋆ Shannon capacity limits⋆ Error correcting codes
◮ Robustness: the rest⋆ “Outage” within a system⋆ Coexistence with other systems⋆ Traditional approach: static guard bands (“frequency plans”)
Separation of time and space scales◮ Years/decades: frequency planning◮ ms/minutes: actual use
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 3 / 40
Examine the problem from first principles
What is the deep reason for the existing waste?3R’s: Rate,Reliability, andRobustness
◮ Rate and Reliability: our usual focus⋆ Fighting ergodic uncertainty⋆ Shannon capacity limits⋆ Error correcting codes
◮ Robustness: the rest⋆ “Outage” within a system⋆ Coexistence with other systems⋆ Traditional approach: static guard bands (“frequency plans”)
Separation of time and space scales◮ Years/decades: frequency planning◮ ms/minutes: actual use
In the future, technical solutions must bridge these scales!Rethinkrobustness architecture to enable rate/reliability gains.
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 3 / 40
The basic policy alternatives for sharing
A new comprehensive commons — eliminate legacy users entirely.
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 4 / 40
The basic policy alternatives for sharing
A new comprehensive commons — eliminate legacy users entirely.
Eliminate some legacy users and reallocate their spectrum.
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 4 / 40
The basic policy alternatives for sharing
A new comprehensive commons — eliminate legacy users entirely.
Eliminate some legacy users and reallocate their spectrum.Preserve some priority for “primary users”
Interference management is Interference management notprimary’s responsibility primary’s responsibility
Secondary has permission Markets UWBSecondary must take care Denials Opportunistic
Current ultra-wideband: blanket permission◮ “Speak softly, but use a wideband”◮ Energy limited regime — works because most bands are not used
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 4 / 40
The basic policy alternatives for sharing
A new comprehensive commons — eliminate legacy users entirely.
Eliminate some legacy users and reallocate their spectrum.Preserve some priority for “primary users”
Interference management is Interference management notprimary’s responsibility primary’s responsibility
Secondary has permission Markets UWBSecondary must take care Denials Opportunistic
Current ultra-wideband: blanket permission◮ “Speak softly, but use a wideband”◮ Energy limited regime — works because most bands are not used◮ Not future-proof!
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 4 / 40
The basic policy alternatives for sharing
A new comprehensive commons — eliminate legacy users entirely.
Eliminate some legacy users and reallocate their spectrum.Preserve some priority for “primary users”
Interference management is Interference management notprimary’s responsibility primary’s responsibility
Secondary has permission Markets UWBSecondary must take care Denials Opportunistic
Current ultra-wideband: blanket permission◮ “Speak softly, but use a wideband”◮ Energy limited regime — works because most bands are not used◮ Not future-proof!
Even future “licensed” systems will likely haveopportunisticfeatures.
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 4 / 40
Layering revisited
PHY
MAC
Regulatory
Application
Networking
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 5 / 40
Outline
MotivationSpectrum sensing: uncertainty is key challenge
◮ Single-detector sensitivity◮ Overhead-oriented metrics◮ Cooperation and multiband sensing
Technical questions in regulation◮ A simple model ofa posteriori enforcement◮ Do you know who I am?
Conclusions
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 6 / 40
Sensing the primary’s presence
fc+W/2fc−W/2
UnknownActivity
UnknownActivityBand of Interest
Spectrum picture
Look for the primary in the ‘band of interest’Within band model:
◮ Primary signal:X(t)◮ Background and receiver noise:W(t)
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 7 / 40
Impact of uncertainty: energy detector
Actual noise power,σ
2a ∈ [ 1
ασ
2n, ασ
2n]
If
P + σ2a ≤ ασ
2n
⇒ P ≤α
2 − 1α
σ2n
Energy detector fails to detectthe signal
UncertaintyZone
Signalpresent
TargetSensitivity
σ 2nα
σ 2n1/α ����������������������
����������������������
}Impossible
Noise power
Test statistic
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 8 / 40
SNR wall for energy detector
−40 −35 −30 −25 −20 −15 −10 −5 00
2
4
6
8
10
12
14
Nominal SNR
log 10
N
x = 0.1 dBx = 0.001 dB x = 1 dB
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 9 / 40
SNR wall for energy detector
0 0.5 1 1.5 2 2.5 3−14
−12
−10
−8
−6
−4
−2
0
2Position of SNR wall for radiometer
Noise uncertainty x (in dB)
SN
Rw
all (
in d
B)
−3.3 dB
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 9 / 40
Primary structure vs environmental uncertainty
Primary Detector Key Uncertainty
Constellation any Noise distributionPilot coherent Phase-coherence timePilot any Noise color
Pulse-shape cyclostationary Delay-coherence time
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 10 / 40
Primary structure vs environmental uncertainty
fc+W/2fc−W/2
UnknownActivity
UnknownActivity
Pilot tone
Spectrum picture
Band of Interest
Primary Detector Key Uncertainty
Constellation any Noise distributionPilot coherent Phase-coherence timePilot any Noise color
Pulse-shape cyclostationary Delay-coherence time
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 10 / 40
Primary structure vs environmental uncertainty
UnknownActivity
Pilot
tone
−W/2fc f
c+W/2
Noise +Interferencelevel
MeasurementZone
UnknownActivity Band of Interest
}Primary Detector Key Uncertainty
Constellation any Noise distributionPilot coherent Phase-coherence timePilot any Noise color
Pulse-shape cyclostationary Delay-coherence time
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 10 / 40
Primary structure vs environmental uncertainty
X(t)
t
Primary Detector Key Uncertainty
Constellation any Noise distributionPilot coherent Phase-coherence timePilot any Noise color
Pulse-shape cyclostationary Delay-coherence time
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 10 / 40
Primary structure vs environmental uncertainty
T (Y )1 T (Y )2 T (Y )3 T (Y )4 T (Y )
5
H ( f )1 H ( f )
3H ( f )4H ( f )2 H ( f )
5
t
Primary Detector Key Uncertainty
Constellation any Noise distributionPilot coherent Phase-coherence timePilot any Noise color
Pulse-shape cyclostationary Delay-coherence time
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 10 / 40
Detector robustness with coherence time
100
101
102
103
104
105
106
−60
−50
−40
−30
−20
−10
0
10
20
Coherence time, Nc samples
SN
R (i
n dB
)Location of SNR wall for various detectors
Modified feature detectorEnergy detectorPilot detector, 10% pilot powerCompletely known signal
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 11 / 40
Are we just being paranoid?
Experimental validationUsed BEE2 and 2.4 GHz radio front-ends
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 12 / 40
Are we just being paranoid?
Experimental validationUsed BEE2 and 2.4 GHz radio front-ends
Noise levels move around over a day.
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 12 / 40
Are we just being paranoid?
Experimental validationUsed BEE2 and 2.4 GHz radio front-ends
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 12 / 40
Are we just being paranoid?
Experimental validationUsed BEE2 and 2.4 GHz radio front-ends
The spectral correlation function shows spectral redundancy in a transformeddomain.
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 12 / 40
Are we just being paranoid?
Experimental validationUsed BEE2 and 2.4 GHz radio front-ends
But this redundancy is blurred away by fast fading.
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 12 / 40
Outline
MotivationSpectrum sensing: uncertainty is key challenge
◮ Single-detector sensitivity◮ Overhead-oriented metrics◮ Cooperation and multiband sensing
Technical questions in regulation◮ A simple model ofa posteriori enforcement◮ Do you know who I am?
Conclusions
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 13 / 40
How to model the requirement of safety
ON ON
Consider time-domain
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 14 / 40
How to model the requirement of safety
ONSense
Use Band ON
Consider time-domain
Can sense a whitespace and use it.
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 14 / 40
How to model the requirement of safety
ONSense
Use BandInterference
safe again
Consider time-domain
Can sense a whitespace and use it.
Some interference unavoidable.
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 14 / 40
How to model the requirement of safety
ONSense
Use BandInterference
safe again
Consider time-domain
Can sense a whitespace and use it.
Some interference unavoidable.
Otherwisefear of return makes it impossible to recover.
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 14 / 40
Consider strong primary transmitters
A
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 16 / 40
Define a protected radius
B
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 16 / 40
Mice can get close...
B
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 16 / 40
But keep the lions far away!
B
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 16 / 40
Fading
������
������
���� ��������������
������
0 5 10 15 20 25 30−50
−40
−30
−20
−10
0
10
20
30
40
50Maximum power for secondary transmitter
SNR margin ψ at secondary receiver (dB)
Max
sec
onda
ry p
ower
(dB
W)
No shadowing10 dB shadowing
10 dB
If you hear a weak signal, are you far away, or just locally faded?
The possibility of 10 dB of fading results in a 10 dB shift of the requireddetection margin
How to choose X dB of fading margin?
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 17 / 40
The spatial equivalents�������������������������������������������� ����������(a)
(b)
Occupied Spectrum Hole Recovered Spectrum
time
TX 1
TX 2
TX 3
r p
r p
r p
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 18 / 40
What are we giving up?
���� ��������������
������
������
������
Safe, but might be faded(fading uncertainty)
Will recover using diversity.
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 19 / 40
What are we giving up?
���� ��������������
������
������
������
Safe, but might be faded(fading uncertainty)
Will recover using diversity.
Lights on, but no one home(receiver uncertainty)
Could be recovered using denials.But not worth it.
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 19 / 40
What are we giving up?
���� ��������������
������
������
������
Safe, but might be faded(fading uncertainty)
Will recover using diversity.
Lights on, but no one home(receiver uncertainty)
Could be recovered using denials.But not worth it.
Safe, but not shadowed enough(symmetry uncertainty)Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 19 / 40
Example Distribution of Primary Users
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 20 / 40
Performance: Weighted Probability of Area Recovered
WPAR =
∫ ∞
rn
w(r)PFH(r) rdr
PFH(r) is the probability of finding a spectrum hole at distancer fromprimary.w(r) is a weighting function satisfying
∫ ∞
rnw(r) r dr = 1.
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 21 / 40
Performance: Weighted Probability of Area Recovered
WPAR =
∫ ∞
rn
w(r)PFH(r) rdr
PFH(r) is the probability of finding a spectrum hole at distancer fromprimary.w(r) is a weighting function satisfying
∫ ∞
rnw(r) r dr = 1.
◮ More people are likely to be close to city centers
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 21 / 40
Performance: Weighted Probability of Area Recovered
WPAR =
∫ ∞
rn
w(r)PFH(r) rdr
PFH(r) is the probability of finding a spectrum hole at distancer fromprimary.w(r) is a weighting function satisfying
∫ ∞
rnw(r) r dr = 1.
◮ More people are likely to be close to city centers◮ After enough distance, a new primary might exist.
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 21 / 40
Performance: Weighted Probability of Area Recovered
WPAR =
∫ ∞
rn
w(r)PFH(r) rdr
PFH(r) is the probability of finding a spectrum hole at distancer fromprimary.w(r) is a weighting function satisfying
∫ ∞
rnw(r) r dr = 1.
◮ More people are likely to be close to city centers◮ After enough distance, a new primary might exist.
e.g. exponential:w(r) = K exp(−κr)
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 21 / 40
What should the safety metric be?
Key issue: incentives and trust
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 22 / 40
What should the safety metric be?
Key issue: incentives and trust◮ Probability of interference depends on the model.
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 22 / 40
What should the safety metric be?
Key issue: incentives and trust◮ Probability of interference depends on the model.◮ Primary does not andshould not trust full model for:
⋆ Noise distribution
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 22 / 40
What should the safety metric be?
Key issue: incentives and trust◮ Probability of interference depends on the model.◮ Primary does not andshould not trust full model for:
⋆ Noise distribution⋆ Secondary deployment assumptions
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 22 / 40
What should the safety metric be?
Key issue: incentives and trust◮ Probability of interference depends on the model.◮ Primary does not andshould not trust full model for:
⋆ Noise distribution⋆ Secondary deployment assumptions⋆ Fading distribution
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 22 / 40
What should the safety metric be?
Key issue: incentives and trust◮ Probability of interference depends on the model.◮ Primary does not andshould not trust full model for:
⋆ Noise distribution⋆ Secondary deployment assumptions⋆ Fading distribution
This fear must by accounted for:
FHI = sup0≤r≤rn
supFr∈Fr
PFr(D = 0|ractual = r)
whereFr is the uncertain distribution underlying algorithmD.
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 22 / 40
The story so far in these metrics
10−4
10−3
10−2
10−1
100
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1Single Detector Performance
Wei
gh
ted
Pro
bab
ility
of
Fal
se A
larm
(W
PA
R)
Fear of Harmful Interference (FHI
)
Perfect detector, Number of Samples (N) = ∞Complete knowledge, Number of Samples (N) = 100Single Quantile knowledge, Number of Samples (N) = 100
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 23 / 40
The story so far in these metrics
102
103
104
105
106
107
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Gains from increasing the number of samples (FHI
= .1)
Wei
gh
ted
Pro
bab
ility
of
Are
a R
cove
red
(W
PA
R)
Number of samples (N)
Perfect detectorComplete knowledgeSingle quantile knowledge
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 23 / 40
The story so far in these metrics
v
r n
Area never recoverd
Area recovered
No Noise uncertainty
v
r n
With Noise uncertainty
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 23 / 40
The story so far in these metrics
10−4
10−3
10−2
10−1
100
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Fear of harmful interference (FHI
)
Wei
ghte
d P
roba
bilit
y of
Are
a R
ecov
ered
(W
PA
R)
Radiometer with noise uncertainty
No noise uncertainty (x=0)
1 dB noise uncertainty (x =1)
0.1 dB noise uncertainty (x=0.1)
0.01 dB noise uncertainty (x=0.01)
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 23 / 40
Outline
MotivationSpectrum sensing: uncertainty is key challenge
◮ Single-detector sensitivity◮ Overhead-oriented metrics◮ Cooperation and multiband sensing
Technical questions in regulation◮ A simple model ofa posteriori enforcement◮ Do you know who I am?
Conclusions
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 24 / 40
Spatial domain: How can cooperation help?
It lessens the required detector performanceRough Analogy: Deck of cards wherered
cards signify bad fades.
Probability that I get aredcard: VeryHigh (50%)!
Probability that all users getredcards: Very Low
���������
���������
���� ����������������
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 25 / 40
Spatial domain: How can cooperation help?
It lessens the required detector performanceRough Analogy: Deck of cards wherered
cards signify bad fades.
Probability that I get aredcard: VeryHigh (50%)!
Probability that all users getredcards: Very Low
���������
���������
���� ����������������
Multipath varies significantly on the scale ofλ
4 (10cm at 800MHz).Shadowing varies significantly on the scale 20-500m
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 25 / 40
Spatial domain: How can cooperation help?
It lessens the required detector performanceRough Analogy: Deck of cards wherered
cards signify bad fades.
Probability that I get aredcard: VeryHigh (50%)!
Probability that all users getredcards: Very Low
���������
���������
���� ����������������
Multipath varies significantly on the scale ofλ
4 (10cm at 800MHz).Shadowing varies significantly on the scale 20-500m
Close enough to be relevant, far enough to be independent.
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 25 / 40
Spatial domain: How can cooperation help?
It lessens the required detector performanceRough Analogy: Deck of cards wherered
cards signify bad fades.
Probability that I get aredcard: VeryHigh (50%)!
Probability that all users getredcards: Very Low
���������
���������
���� ����������������
Multipath varies significantly on the scale ofλ
4 (10cm at 800MHz).Shadowing varies significantly on the scale 20-500m
Close enough to be relevant, far enough to be independent.
It also increases robustness to the fading model.
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 25 / 40
Does cooperation really work?
Experimental validation
Used BEE2 and 2.4 GHz radio front-ends
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 26 / 40
Does cooperation really work?
Experimental validation
Used BEE2 and 2.4 GHz radio front-ends
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 26 / 40
Time-domain: How can cooperation help?
Interference diversity!
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 27 / 40
Cooperation story in correct metrics
10−4
10−3
10−2
10−1
100
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Wei
ghte
d P
roba
bilit
y of
Are
a R
ecov
ered
(W
PA
R)
Fear of Harmful Interference (FHI
)
ML cooperation
ML rule, 5 users (M=5)ML rule, 4 users (M=4)ML rule, 3 users (M=3)ML rule, 2 users (M=2)ML rule, 1 user (M=1)
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 28 / 40
Cooperation story in correct metrics
100
101
102
103
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Wei
ghte
d P
roba
bilit
y of
Are
a R
ecov
ered
(W
PA
R)
Number of cooperating radios (M)
Multi−user cooperation: ML vs OR rule (FHI
= 10−2)
ML rule with complete knowledgeOR ruleOR rule with bounded single−quantile knowledgeML rule with single quantile knowledge
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 28 / 40
Cooperation story in correct metrics
10−4
10−3
10−2
10−1
100
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Wei
ghte
d P
roba
bilit
y of
Are
a R
ecov
ered
(W
PA
R)
Fear of Harmful Interference (FHI
)
Two user (M=10) ML detector with varying correlation uncertainty
ρ
max =0
ρmax
=0.5
ρmax
=0.8
ρmax
=1
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 28 / 40
Multiband detection: hope for the future
10−4
10−3
10−2
10−1
100
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Target PHI
Wei
ghte
d P
FH
Impact of GPS
Single radioSingle radio with GPS
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 29 / 40
Multiband detection: hope for the future
10−5
10−4
10−3
10−2
10−1
100
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Target PHI
Wei
ghte
d P
FH
MAP Cooperation with GPS
1 radio with GPS2 radios with GPS3 radios with GPS4 radios with GPS5 radios with GPS
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 29 / 40
Multiband detection: hope for the future
Tower - A
Tower - B
r A
r B
r n
2r n + D
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 29 / 40
Multiband detection: hope for the future
CR #2
CR #1 Tower A
Primary 1 Primary 2
Global Shadowing (S A )
Global Shadowing (S B )
Local Shadowing (L 2 )
Local Shadowing (L 1 )
Tower B Primary 3 Primary 4
Multipath (M 21 , M 22 , M 23 , M 24 )
Multipath (M 11, M 12 , M 13 , M 14 )
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 29 / 40
Multiband detection: hope for the future
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10.65
0.7
0.75
0.8
0.85
0.9
0.95
1
Pro
babi
lity
of F
indi
ng a
Hol
e (P
FH
)
Normalized distance from tower A (r/rn)
Multiband, 1 radioSingleband, 1 radioMultiband, 2 radiosSingleband, 2 radios
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 29 / 40
Outline
MotivationSpectrum sensing: uncertainty is key challenge
◮ Single-detector sensitivity◮ Overhead-oriented metrics◮ Cooperation and multiband sensing
Technical questions in regulation◮ A simple model ofa posteriori enforcement◮ Do you know who I am?
Conclusions
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 30 / 40
The regulatory challenge
Part-15-style device-certification would be great◮ Easy to enforce◮ Easy to generalize to single-user sensing
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 31 / 40
The regulatory challenge
Part-15-style device-certification would be great◮ Easy to enforce◮ Easy to generalize to single-user sensing◮ Terrible for QoS
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 31 / 40
The regulatory challenge
Part-15-style device-certification would be great◮ Easy to enforce◮ Easy to generalize to single-user sensing◮ Terrible for QoS
Could attempta priori certification of cooperative algorithms
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 31 / 40
The regulatory challenge
Part-15-style device-certification would be great◮ Easy to enforce◮ Easy to generalize to single-user sensing◮ Terrible for QoS
Could attempta priori certification of cooperative algorithms◮ Undecidability? (Need a proof of cooperative correctness)
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 31 / 40
The regulatory challenge
Part-15-style device-certification would be great◮ Easy to enforce◮ Easy to generalize to single-user sensing◮ Terrible for QoS
Could attempta priori certification of cooperative algorithms◮ Undecidability? (Need a proof of cooperative correctness)◮ Pick “one true algorithm” and approve it: evolvability problems
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 31 / 40
The regulatory challenge
Part-15-style device-certification would be great◮ Easy to enforce◮ Easy to generalize to single-user sensing◮ Terrible for QoS
Could attempta priori certification of cooperative algorithms◮ Undecidability? (Need a proof of cooperative correctness)◮ Pick “one true algorithm” and approve it: evolvability problems◮ Squeezes out innovation: return of “beauty contest”
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 31 / 40
The regulatory challenge
Part-15-style device-certification would be great◮ Easy to enforce◮ Easy to generalize to single-user sensing◮ Terrible for QoS
Could attempta priori certification of cooperative algorithms◮ Undecidability? (Need a proof of cooperative correctness)◮ Pick “one true algorithm” and approve it: evolvability problems◮ Squeezes out innovation: return of “beauty contest”◮ Draconian Digital Restrictions Management
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 31 / 40
The regulatory challenge
Part-15-style device-certification would be great◮ Easy to enforce◮ Easy to generalize to single-user sensing◮ Terrible for QoS
Could attempta priori certification of cooperative algorithms◮ Undecidability? (Need a proof of cooperative correctness)◮ Pick “one true algorithm” and approve it: evolvability problems◮ Squeezes out innovation: return of “beauty contest”◮ Draconian Digital Restrictions Management
Shift to somea posteriori enforcement
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 31 / 40
The regulatory challenge
Part-15-style device-certification would be great◮ Easy to enforce◮ Easy to generalize to single-user sensing◮ Terrible for QoS
Could attempta priori certification of cooperative algorithms◮ Undecidability? (Need a proof of cooperative correctness)◮ Pick “one true algorithm” and approve it: evolvability problems◮ Squeezes out innovation: return of “beauty contest”◮ Draconian Digital Restrictions Management
Shift to somea posteriori enforcement◮ Ideas already present in Coase ’59 and de Vany ’69.◮ Users incur liability for harmful interference and are punished
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 31 / 40
A toy model
TX No TX
S2: Wait S
1: FA
S3: Illegal TX S
0: Legal TX
S4: Pen. Box S
5: Pen. Box
Primary Use
Secondary Use
p
q
S0
S0
S1 S
1S
2S
2
S3
S3
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 32 / 40
A toy model
00.25
0.50.75
1
00.25
0.50.75
10
0.25
0.5
0.75
1
pP(Pri TX)
Uto
tal
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 32 / 40
A toy model
00.25
0.50.75
1
00.25
0.50.75
10
0.25
0.5
0.75
1
pP(Pri TX)
p chea
t
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 32 / 40
A toy model
00.25
0.50.75
1
00.25
0.50.75
10
0.25
0.5
0.75
1
pP(Pri TX)
Uco
llide
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 32 / 40
A toy model
00.25
0.50.75
1
00.25
0.50.75
10
0.250.5
0.751
pP(Pri TX)
p chea
t
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 32 / 40
A toy model
TX No TX
S2: Wait S
1: FA
S3: Illegal TX S
0: Legal TX
S4: Pen. Box S
5: Pen. Box
Primary Use
Secondary Use
p
q
S0
S0
S1 S
1S
2S
2
S3
S3
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 32 / 40
A toy model
00.25
0.50.75
1
0
0.25
0.5
0.75
10
0.25
0.5
0.75
1
pP(Pri TX)
p chea
t
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 32 / 40
A toy model
0 0.25 0.5 0.75 10
0.25
0.5
0.75
1P
(Pri
TX
)
p
β = 1.5β = 1.4β = 1.3β = 1.2β = 1.1A
B
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 32 / 40
A toy model
0 0.2 0.4 0.6 0.8 10
1
2
3
4
5
ppen
β
pcatch
= .2
pcatch
= .4
pcatch
= .6
pcatch
= 1
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 32 / 40
A toy model
00.25
0.50.75
1
00.25
0.50.75
10
0.25
0.5
0.75
1
pP(Pri TX)
Uto
tal
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 32 / 40
A toy model
TX No TX
S2: Wait S
1: FA
S3: Illegal TX S
0: Legal TX
S4: Pen. Box S
5: Pen. Box
Primary Use
Secondary Use
p
q
S0
S0
S1 S
1S
2S
2
S3
S3
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 32 / 40
A toy model
0 0.2 0.4 0.6 0.8 10
2
4
6
8
10
12
14
pwrong
β
pcatch
= 0.2
pcatch
= 0.4
pcatch
= 0.6
pcatch
= 0.8
pcatch
= 1
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 32 / 40
Outline
MotivationSpectrum sensing: uncertainty is key challenge
◮ Single-detector sensitivity◮ Overhead-oriented metrics◮ Cooperation and multiband sensing
Technical questions in regulation◮ A simple model ofa posteriori enforcement◮ Do you know who I am?
Conclusions
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 33 / 40
Wireless + anonymity: a serious problem
Faulhaber’s “Hit and run radios” vs Hatfield’s “Spectrum trolls”
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 34 / 40
Wireless + anonymity: a serious problem
Faulhaber’s “Hit and run radios” vs Hatfield’s “Spectrum trolls”What can we do about identity?
◮ PHY-Layer Identity
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 34 / 40
Wireless + anonymity: a serious problem
Faulhaber’s “Hit and run radios” vs Hatfield’s “Spectrum trolls”What can we do about identity?
◮ PHY-Layer Identity⋆ Easy to think about: just transmit your name⋆ Obvious overhead: power in identity
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 34 / 40
Wireless + anonymity: a serious problem
Faulhaber’s “Hit and run radios” vs Hatfield’s “Spectrum trolls”What can we do about identity?
◮ PHY-Layer Identity⋆ Easy to think about: just transmit your name⋆ Obvious overhead: power in identity⋆ Removes flexibility
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 34 / 40
Wireless + anonymity: a serious problem
Faulhaber’s “Hit and run radios” vs Hatfield’s “Spectrum trolls”What can we do about identity?
◮ PHY-Layer Identity⋆ Easy to think about: just transmit your name⋆ Obvious overhead: power in identity⋆ Removes flexibility⋆ Nonobvious catastrophic performance degradation for multiuser techniques.
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 34 / 40
Wireless + anonymity: a serious problem
Faulhaber’s “Hit and run radios” vs Hatfield’s “Spectrum trolls”What can we do about identity?
◮ PHY-Layer Identity⋆ Easy to think about: just transmit your name⋆ Obvious overhead: power in identity⋆ Removes flexibility⋆ Nonobvious catastrophic performance degradation for multiuser techniques.⋆ Doesn’t help with Trolls
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 34 / 40
Wireless + anonymity: a serious problem
Faulhaber’s “Hit and run radios” vs Hatfield’s “Spectrum trolls”What can we do about identity?
◮ PHY-Layer Identity⋆ Easy to think about: just transmit your name⋆ Obvious overhead: power in identity⋆ Removes flexibility⋆ Nonobvious catastrophic performance degradation for multiuser techniques.⋆ Doesn’t help with Trolls
◮ MAC-Layer Identity
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 34 / 40
Wireless + anonymity: a serious problem
Faulhaber’s “Hit and run radios” vs Hatfield’s “Spectrum trolls”What can we do about identity?
◮ PHY-Layer Identity⋆ Easy to think about: just transmit your name⋆ Obvious overhead: power in identity⋆ Removes flexibility⋆ Nonobvious catastrophic performance degradation for multiuser techniques.⋆ Doesn’t help with Trolls
◮ MAC-Layer Identity⋆ A signature that shows up in the pattern of interference
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 34 / 40
Wireless + anonymity: a serious problem
Faulhaber’s “Hit and run radios” vs Hatfield’s “Spectrum trolls”What can we do about identity?
◮ PHY-Layer Identity⋆ Easy to think about: just transmit your name⋆ Obvious overhead: power in identity⋆ Removes flexibility⋆ Nonobvious catastrophic performance degradation for multiuser techniques.⋆ Doesn’t help with Trolls
◮ MAC-Layer Identity⋆ A signature that shows up in the pattern of interference⋆ What is the overhead?
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 34 / 40
Trollsbane: No harm, no foul
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 35 / 40
Trollsbane: No harm, no foul
0.1 0.12 0.14 0.16 0.18 0.2 0.22 0.24 0.26 0.28 0.30.75
0.8
0.85
0.9
0.95
1
∆=θ1−θ
0
Util
izat
ion
(1−
γ)
PF=15%, P
M=10%, T=280 slots
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 35 / 40
Identity through superimposed codes
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 36 / 40
Identity through superimposed codes
0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.910
1
102
103
104
105
106
Utilization (p)
Tim
e to
Con
vict
ion
(Tc)
in s
lots
Information Theoretic LBRandom Coding UB found from UD codes propertiesRandom Coding UB found from the bipartite graph
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 36 / 40
Identity through superimposed codes
102
103
104
105
106
107
108
109
102
103
104
105
106
Total Number of Systems (N)
Tim
e to
Con
vict
ion
T c in s
lots
Random Coding Upper BoundInformation Theoretic Lower Bound
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 36 / 40
Outline
MotivationSpectrum sensing: uncertainty is key challenge
◮ Single-detector sensitivity◮ Overhead-oriented metrics◮ Cooperation and multiband sensing
Technical questions in regulation◮ A simple model ofa posteriori enforcement◮ Do you know who I am?
Conclusions
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 37 / 40
Decouple sensor network and communication network
Interference management is Interference management notprimary’s responsibility primary’s responsibility
Secondary has permission Markets Spectrum MonitorsSecondary must take care Denials Opportunistic
Purely opportunistic useis harder than it looks.
Cooperation is just another word for “infrastructure”
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 38 / 40
Decouple sensor network and communication network
Interference management is Interference management notprimary’s responsibility primary’s responsibility
Secondary has permission Markets Spectrum MonitorsSecondary must take care Denials Opportunistic
Purely opportunistic useis harder than it looks.
Cooperation is just another word for “infrastructure”Dedicatedsensor-networkinfrastructure
◮ Assume network nodes know where they are◮ Assume large spatial extent beyond primary user scale◮ Construct primary usage map on slower time-scale
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 38 / 40
Decouple sensor network and communication network
Interference management is Interference management notprimary’s responsibility primary’s responsibility
Secondary has permission Markets Spectrum MonitorsSecondary must take care Denials Opportunistic
Purely opportunistic useis harder than it looks.
Cooperation is just another word for “infrastructure”Dedicatedsensor-networkinfrastructure
◮ Assume network nodes know where they are◮ Assume large spatial extent beyond primary user scale◮ Construct primary usage map on slower time-scale
Coordinate secondary radios by giving explicit permission.
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 38 / 40
“Disneyland” vs “Yosemite”
Owner controls access topreserve QoS
“Band-managers” own the bandand leases it out to users.
Monopoly
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 39 / 40
“Disneyland” vs “Yosemite”
Owner controls access topreserve QoS
“Band-managers” own the bandand leases it out to users.
Monopoly
Public owns and sets broadguidelines for use
Unlicensed users are on theirown.
Competition
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 39 / 40
“Disneyland” vs “Yosemite”
Owner controls access topreserve QoS
“Band-managers” own the bandand leases it out to users.
Monopoly
Public owns and sets broadguidelines for use
Unlicensed users are on theirown.
Competition
“Spectrum tour guide” can coordinate users without owning bands.
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 39 / 40
Speculation: who benefits from cognitive radio?
Conventional answer: new entrants and other small players denied accessto spectrum by the existing regime.
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 40 / 40
Speculation: who benefits from cognitive radio?
Conventional answer: new entrants and other small players denied accessto spectrum by the existing regime.
Sounds familiar: Rhetoric around the Internet boom in the 90s. . .
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 40 / 40
Speculation: who benefits from cognitive radio?
Conventional answer: new entrants and other small players denied accessto spectrum by the existing regime.
Sounds familiar: Rhetoric around the Internet boom in the 90s. . .But what actually happened?
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 40 / 40
Speculation: who benefits from cognitive radio?
Conventional answer: new entrants and other small players denied accessto spectrum by the existing regime.
Sounds familiar: Rhetoric around the Internet boom in the 90s. . .But what actually happened?
◮ Many smaller niche applications were enabled.
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 40 / 40
Speculation: who benefits from cognitive radio?
Conventional answer: new entrants and other small players denied accessto spectrum by the existing regime.
Sounds familiar: Rhetoric around the Internet boom in the 90s. . .But what actually happened?
◮ Many smaller niche applications were enabled.◮ But big players got bigger — used the new technology tocut costs and
further exploit economies of scale.
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 40 / 40
Speculation: who benefits from cognitive radio?
Conventional answer: new entrants and other small players denied accessto spectrum by the existing regime.
Observation:carriers are users of spectrum, not mere holders.
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 40 / 40
Speculation: who benefits from cognitive radio?
Conventional answer: new entrants and other small players denied accessto spectrum by the existing regime.
Observation:carriers are users of spectrum, not mere holders.Why pay for spectrum when you could just take it?
◮ Achieve ubiquitous coverage through opportunistic use!◮ Pay only when truly scarce.
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 40 / 40
Speculation: who benefits from cognitive radio?
Conventional answer: new entrants and other small players denied accessto spectrum by the existing regime.
Observation:carriers are users of spectrum, not mere holders.Why pay for spectrum when you could just take it?
◮ Achieve ubiquitous coverage through opportunistic use!◮ Pay only when truly scarce.
Carriers can build and update the sensor network infrastructure.
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 40 / 40
Speculation: who benefits from cognitive radio?
Conventional answer: new entrants and other small players denied accessto spectrum by the existing regime.
Observation:carriers are users of spectrum, not mere holders.Why pay for spectrum when you could just take it?
◮ Achieve ubiquitous coverage through opportunistic use!◮ Pay only when truly scarce.
Carriers can build and update the sensor network infrastructure.
Cheap devices will win out over more expensive ones.
Anant Sahai (UC Berkeley) Cognitive Sharing 6/15/2008 40 / 40