prospects and challenges for spectrum sharing by cognitive ...sahai/presentations/harvard09.pdfanant...
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Prospects and challenges for spectrum sharing bycognitive radios
Anant Sahaipresenting joint work with students:
Mubaraq Mishra Rahul Tandra Kristen Woyachalong with my BU Collaborators:
George Atia Venkatesh Saligrama
BWRC and Wireless Foundations CenterU.C. Berkeley
Boston University
Support from the National Science Foundation, C2IT, and Sumitomo
Harvard EE Seminar
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Spectrum, spectrum, everywhere, but . . .
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Outline
How much usable white-space is there?How can we understand sensing?
Light-handed regulation: identity
Light-handed regulation: deterrence
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How much white-space is there in a single band?
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Consider channel 39 . . .
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The pollution perspective: 15dB above noise
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The pollution perspective: 10dB above noise
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The pollution perspective: 5dB above noise
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5dB above noise with -35dB spillover from next door
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5dB above noise with -45dB spillover from next door
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5dB above noise with -55dB spillover from next door
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The protection perspective
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The protection perspective: 4W
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The protection perspective: 20W
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The protection perspective: 100kW
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The protection perspective: 1MW
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How much to protect? 0.1dB margin
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How much to protect? 1.0dB margin
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How much to protect? 10dB margin
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How much to protect? 1.0dB margin vs 5db pollution
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How much to protect? 1dB margin with adjacent
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Can we sense these holes?
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Can we sense these holes? 90%
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Can we sense these holes? 99%
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Can we sense these holes? FCC rules
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How much white-space is there across bands?
0 5 10 15 20 25 30 35 40 45 500
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Number of channels recovered
CC
DF
Actually available by area
Actually available by population
−114dBm
rule by area
−114dBm
rule by population
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. . . If we account for adjacent-channel effects?
0 5 10 15 20 25 30 35 40 45 500
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Number of channels recovered
CC
DF
Actually available by area
Actually available by population
−114dBm
rule by area−114dB
m rule
by population
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How much white-space is there across bands?
0 5 10 15 20 25 30 35 40 45 500
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Number of channels recovered
CC
DF
Actually available by area
Actually available by population
−114dBm
rule by area
−114dBm
rule by population
0 5 10 15 20 25 30 35 40 45 500
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Number of channels recovered
CC
DF
Actually available by area
Actually available by population
−114dBm
rule by area−114dB
m rule
by population
Detection Scheme/RuleBy Area By Population
LVHF HVHF LUHF HUHF LVHF HVHF LUHF HUHF2,5,6 7-13 14-51 52-69 2,5,6 7-13 14-51 52-69
Pollution (5dB,45dB adj.) 1.6 1.63 15.6 15.8 1.62 0.729 6.63 14.8Geolocation 1.52 2.86 22.3 16.2 1.69 2.09 14.8 15.8Geolocation with adj. 1.24 1.63 14.1 14.6 1.25 0.703 5.36 13.1Sense -114dBm 0.985 0.409 7.7 13.8 1.13 0.167 2.57 13.6-114dBm,-110dBm adj. 0.515 0.0635 2.63 9.83 0.576 0.008 0.284 8.87
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. . . If we vary the allowed power?
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What is the underlying public policy tradeoff?
.1 1 100
5
10
15
20
25
30
35
40
45
Margin (dB)
Ave
rage
num
ber
of c
hann
els
per
user
White space use: actual population density
White space use:
Broadcast use:
uniform population density
Broadcast use: actual population density
uniform population density
15dB, actual population density
15dB, uniform population density
10dB, uniform population density
10dB, actual population density
5dB, uniform population density
5dB, actual population densityWhite space use: protection & pollution
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What is the underlying public policy tradeoff?
0.1 1 101
10
100
1000
Margin (dB)
Peo
ple
gain
ed v
ersu
s pe
rson
lost
Cumulative gain−loss, uniform population density
Cumulative gain−loss, actual population density
Instantaneous gain−loss, uniform population density
Instantaneous gain−loss, actual population density
ActualPop. Density15dB10dBfor 5dB pollution rule
Achievable margins
Achievable margins
for 5dB pollution rule 10dB 15dBUniformPop.Density
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Outline
How much usable white-space is there?
How can we understand sensing?Light-handed regulation: identity
Light-handed regulation: deterrence
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What are the right metrics for sensing?
WPAR =∫ ∞
rn
PFH(r) w(r) rdr
PFH(r): probability of finding a spectrum hole at distance r.
w(r): weighting function satisfying∫∞
rnw(r) r dr = 1.
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What are the right metrics for sensing?
WPAR =∫ ∞
rn
PFH(r) w(r) rdr
FHI = sup0≤r≤rn
supFr∈Fr
PFr(D = 0|ractual = r)
where Fr is the uncertainty about the distribution Fr underlying algorithm D.Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 11 / 1
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Single-user sensing
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Single-user sensing: finite samples
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Single-user sensing: SNR Walls
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Cooperation
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Cooperation
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Cooperation
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Outline
How much usable white-space is there?
How can we understand sensing?Light-handed regulation: identity
I Prior work:F Faulhaber ’05F Hall, Barbeau, Kranakis ’03F Brik, Banerjee, Gruteser, Oh ’08F Rasmussen and Capkun ’07F Rozovsky and Kumar ’01
Light-handed regulation: deterrence
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Identity through taboos
Network IDUser ID
× Device IDTX Identity: Band 1
TX Identity: Band 2
TX Identity: Band 3
. . .Cannot transmit
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Single secondary user case
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Single secondary user case
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Multiple Users: cooperation and/or “framing”
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Multiple Users: noise-free non-strategic case
Min
imum
enf
orce
men
t ove
rhea
d
Number of users
Catch coalition of 4
Catch coalition of 3
Catch coalition of 2
0.1
0.2
0.3
0.4
0.5
02 73 65410 1010 101010
Time steps until conviction = 3000
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Multiple Users: coalitions and overhead
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Noisy-case: An equal-rate MAC-framework
Identifying Culprits MAC channelN Distinguishable Secondary Users N Distinct messages
K Coalition size K different usersTc Time-to-identification Codeword length Tc
γ Taboo-fraction γ average cost-constraint on codewordsUsers may/may-not cheat/interfere MAC channel model
limTc→∞
log NTc≤ min
k≤K
I(Xk1; Y|XK
k+1)k
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Outline
How much usable white-space is there?
How can we understand sensing?
Light-handed regulation: identityLight-handed regulation: deterrence
I Prior work:F Rose, Ulukus, Yates ’01F Popescu and Rose ’04F Etkin and Tse ’05F Huang, Berry, Honig ’04F Xu, Kamat, Trappe ’06
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Single-band model
False Alarm
Legal TX
SecondaryTX No TX
No Cheat
Cheat
False Alarm
Legal TX
Primary
Cognitive
Jail
Pcatch
Ppen
p1
q1
Ptx = q/(q+p)
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Single-band model
00.25
0.50.75
1
00.25
0.50.7510
0.25
0.5
0.75
1
pPtx
Pcheat
Always cheat
Never cheat
Pcatch = 1Ppen = 0.6
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Single-band model
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10
1
2
3
4
5
6
7
8
9
10
Ppen
β =
pai
n of
jail
Pcatch = 0.1
0.2
0.4
0.60.8
1
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Multiple-bands: need to have something to lose
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Multiple-bands: need to have something to lose
TX No TX
No Cheat
Cheat
False Alarm
Legal TX
q
SecondaryTX No TX
No Cheat
Cheat
False Alarm
Legal TX
Primary
Cognitive
Band 1Band 2
Band 3
Band B
Global Jail
Pcatch
Pcatch
Primary
Ppen
p1
q1
pN
qN
Ptx = q/(q+p)
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Multiple-bands: need to have something to lose
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10
1
2
3
4
5
6
7
8
9
10
β =
hom
e ba
nds
requ
ired
to in
cent
iviz
e no
che
atin
g
Ppen
B = 1
B = 3
B = 5
B = 7
B = 9
Pcatch = 1
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The problem of false convictions
TX No TX
No Cheat
Cheat
False Alarm
Legal TX
q
SecondaryTX No TX
No Cheat
Cheat
False Alarm
Legal TX
Primary
Cognitive
Band 1Band 2
Band 3
Band B
Global Jail
Pcatch
Pcatch
PrimaryPwrong
Pwrong
Ppen
p1
q1
pN
qN
Ptx = q/(q+p)
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The problem of false convictions
Pcatch = 1Pcatch = 0.5
Pcatch = 0.1Ppe
n
0
1
0.5Pwrong0.1 0.2 0.3 0.4
0.5
B = 3
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The problem of false convictions
Pcatch = 1Pcatch = 0.5
Pcatch = 0.1Ppe
n
0
1
0.5Pwrong0.1 0.2 0.3 0.4
0.5
B = 3
Ppe
n
0.5
10
1
01 2 6 84
Expansion
Pcatch = 0.1
Pcatch = 0.5
Pcatch = 1
Pwrong = 0.03
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The “overhead” needed for bandwidth expansion
30
1
2
10 20
3
Expansion
0
0
1
0
0.5
Utility
Fraction of time in jail Ptx = 0.55Pcatch = 1
Pwrong = 0.03
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The “overhead” needed for bandwidth expansion
Exp
ansi
on
0
40
20
30
10
Overhead0.1 0.2 0.3 0.4 0.5
Pwrong = 0.01
Pwrong = 0.06
Pwrong = 0.1
Pwrong = 0.035
Pwrong = .02
Pwrong = 0.001
MaximalExpansion
Ptx = 0.55Pcatch = 1
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The “overhead” needed for bandwidth expansion
0 0.1 0.2 0.3 0.4 0.50
10
20
30
40
Overhead
Expansion
Pcatch = 1
0.8
0.6
0.4
0.2
0.1
Ptx = 0.55Pwrong = 0.02
MaximalExpansion
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Conclusion: Freedom isn’t free
Interference management is Interference management notprimary’s responsibility primary’s responsibility
Secondary has permission Markets UWB/Spectrum MonitorsSecondary must take care Denials Opportunistic
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References on www.eecs.berkeley.edu/∼sahai/
“How much white space is there?”
“What is a spectrum hole and what does it take to recognize one?”
“A technical perspective on light-handed regulation for cognitive radios”
“Cognitive Radios for Spectrum Sharing”
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