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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
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 1 / 1
Spectrum, spectrum, everywhere, but . . .
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 2 / 1
Outline
How much usable white-space is there?How can we understand sensing?
Light-handed regulation: identity
Light-handed regulation: deterrence
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 3 / 1
How much white-space is there in a single band?
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 4 / 1
Consider channel 39 . . .
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 4 / 1
The pollution perspective: 15dB above noise
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 4 / 1
The pollution perspective: 10dB above noise
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 4 / 1
The pollution perspective: 5dB above noise
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 4 / 1
5dB above noise with -35dB spillover from next door
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 4 / 1
5dB above noise with -45dB spillover from next door
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 4 / 1
5dB above noise with -55dB spillover from next door
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 4 / 1
The protection perspective
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 5 / 1
The protection perspective: 4W
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 5 / 1
The protection perspective: 20W
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 5 / 1
The protection perspective: 100kW
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 5 / 1
The protection perspective: 1MW
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 5 / 1
How much to protect? 0.1dB margin
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 6 / 1
How much to protect? 1.0dB margin
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 6 / 1
How much to protect? 10dB margin
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 6 / 1
How much to protect? 1.0dB margin vs 5db pollution
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 6 / 1
How much to protect? 1dB margin with adjacent
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 6 / 1
Can we sense these holes?
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 7 / 1
Can we sense these holes? 90%
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 7 / 1
Can we sense these holes? 99%
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 7 / 1
Can we sense these holes? FCC rules
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 7 / 1
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
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 8 / 1
. . . 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
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 8 / 1
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
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 8 / 1
. . . If we vary the allowed power?
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 8 / 1
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
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 9 / 1
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
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 9 / 1
Outline
How much usable white-space is there?
How can we understand sensing?Light-handed regulation: identity
Light-handed regulation: deterrence
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 10 / 1
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.
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 11 / 1
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
Single-user sensing
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 12 / 1
Single-user sensing: finite samples
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 12 / 1
Single-user sensing: SNR Walls
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 12 / 1
Cooperation
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 13 / 1
Cooperation
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 13 / 1
Cooperation
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 13 / 1
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
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 14 / 1
Identity through taboos
Network IDUser ID
× Device IDTX Identity: Band 1
TX Identity: Band 2
TX Identity: Band 3
. . .Cannot transmit
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 15 / 1
Single secondary user case
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 16 / 1
Single secondary user case
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 16 / 1
Multiple Users: cooperation and/or “framing”
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 17 / 1
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
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 18 / 1
Multiple Users: coalitions and overhead
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 19 / 1
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
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 20 / 1
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
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 21 / 1
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)
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 22 / 1
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
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 22 / 1
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
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 22 / 1
Multiple-bands: need to have something to lose
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 23 / 1
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)
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 23 / 1
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
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 23 / 1
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)
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 24 / 1
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
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 24 / 1
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
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 24 / 1
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
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 25 / 1
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
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 25 / 1
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
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 25 / 1
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
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 26 / 1
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”
Anant Sahai (UC Berkeley) Cognitive Radio 02/19/2009 27 / 1
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