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Secrecy Capacity Scaling of Large-Scale
Cognitive Networks
Yitao Chen1, Jinbei Zhang1, Xinbing Wang1,
Xiaohua Tian1, Weijie Wu1, Fan Fu2, Chee Wei Tan3
1 Dept. of Electronic Engineering, Shanghai Jiao Tong University
2 Dept. of Computer Science and Engineering, Shanghai Jiao Tong University
3 Dept. of Computer Science, City University of Hong Kong
Outline
 Introduction
 Network Model and Definition
 Independent Eavesdroppers
 Colluding Eavesdroppers
 Conclusion
2
Motivations
 Security is a major concern in wireless networks
Mobile Payment
Privacy
Virtual Property
Military Communication
3
Motivations
 Cryptographic methods
 Key distribution
 Rapid growth of
computation power
 Improvement on
decoding technology
 Physical Layer Security
 Assume eavesdroppers
have infinite computation
power
 Require the intended
receiver should have a
stronger channel than
eavesdroppers
 Provable security
capacity
C   log(1  SNR )  log(1  SNRe ) 

4
Related works
 Secrecy capacity in large-scale networks
 Guard zone [9]
 Artificial noise + Fading gain (CSI needed) [8]
 Using artificial noise generated by receivers to suppress
eavesdroppers’ channel quality [11]
Cited from [8]
[9] O. Koyluoglu, E. Koksal, E. Gammel, “On Secrecy Capacity Scaling in Wireless
Networks”, IEEE Trans. Inform. Theory, May 2012.
[8] S. Vasudevan, D. Goeckel and D. Towsley, “Security-capacity Trade-off in Large Wireless
Networks using Keyless Secrecy,” in Proc. ACM MobiHoc, Chicago, Illinois, USA, Sept. 2010.
[11] J. Zhang, L. Fu, X. Wang, “Asymptotic analysis on secrecy capacity in large-scale
wireless networks,” in IEEE/ACM Trans. Netw., Feb. 2014.
5
Motivations
 Limited spectrum resources and CR networks
 Key questions:
 What is the impact of security in cognitive networks?
 What is the performance we can achieve?
6
Outline
 Introduction
 Network Model and Definition
 Independent Eavesdroppers
 Colluding Eavesdroppers
 Conclusion
7
Network Model and Definition – I/III
 Network Area: a  ×  square
 Legitimate Nodes
  primary users { } ,  secondary users { }
 I.I.D
 Self-interference cancelation [17] adopted
 CSI unknown
 Eavesdroppers
  () eavesdroppers
 Location positions unknown
 CSI unknown
Cited from [17]
[17] J. I. Choiy, M. Jainy, K. Srinivasany, P. Levis and S. Katti, “Achieving Single Channel,
Full Duplex Wireless Communication”, in ACM Mobicom’10, Chicago, USA, Sept. 2010. 8
Network Model and Definition – II/III
 Random permutation traffic, no cross network traffic
 Communication Model
 Physical Model: Primary user i transmits to primary user j
Interference from other primary TXs
Interference from secondary TXs
Interference from other primary RXs
Interference from secondary TXs
 Define the physical model for secondary users and eavesdroppers
similarly.
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Network Model and Definition – III/III
 Definition of Per Hop Secrecy Throughput:
 Independent eavesdropper
 Colluding eavesdroppers
 Definition of Asymptotic Capacity
  = Θ(()), if
 Similarly, we can define the asymptotic per-node capacity for the
secondary network
10
Outline
 Introduction
 Network Model and Definition
 Independent Eavesdroppers
 Colluding Eavesdroppers
 Conclusion
11
Independent Eavesdroppers
 Physical Feasibility of Security
 Primary Networks

 ≥ 
and
Successful transmission

 ≤ 
No eavesdropper can
decode the message
 Secondary Networks


≥  and


≤ 
 < min{ ,  }
 Operation Rules:
• Primary users disregard secondary users;
• Secondary users should affect primary users little.
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Independent Eavesdroppers
 Intuitive
 Primary Networks




Concurrent Transmission Range
Secrecy Capacity
 Secondary Networks


Unknown
? Good or bad for primary nodes
? Good or bad for eavesdroppers
 Depend on SUs’ locations
13
Independent Eavesdroppers
 Primary T-R pair (node i to node j)
•
For other primary transmitter k and receiver l

 ≥ 

 ≤ 
•
For other secondary transmitter k and receiver l
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Independent Eavesdroppers
 Scheduling scheme
 Cell Partition Round-Robin Scheduling:
• Tessellate the network into cells.
• Different cells take turn to transmit.
• Secondary users can transmit in non-occupied cells with the
guarantee of affecting primary transmissions little.
Figure: Simple 9-TDMA
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Independent Eavesdroppers
Routing scheme
 Highway System
– Draining Phase
– Highway Phase
– Delivery Phase
Bottleneck: Highway Phase (nodes need to relay packets for others)
 Distance of primary T-R pairs is 1.
 Distance of primary concurrent transmission range is Θ(1).
 Secrecy Capacity is Θ( 1/) for primary network.
 Secrecy Capacity is Θ( 1/m) for secondary network.
No order cost comparing to the scenario without security concern!
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Outline
 Introduction
 Network Model and Definition
 Independent Eavesdroppers
 Colluding Eavesdroppers
 Difference with previous case
 Conclusion
17
Colluding Eavesdroppers
 SINR of Colluding Eavesdroppers
– maximum ratio combining of SINR
Bound the SINR of eavesdroppers:
 Disjoint rings with same size.
 Eavesdroppers in the same ring has a
similar SINR.
 Artificial noise + Path loss gain +
Cooperation
18
Colluding Eavesdroppers
Choice of Concurrent Transmission Range k
k , artificial noise , throughput
k , SINR of eavesdroppers , security
 
  = log 1 +
0 +  

≥ log(1 +
≥
≥
 1+ 2 +1
)
0 +7′  +    −

7′′  1 +

7   −
when choosing  = Θ
−
( 

2  + 1
1

−
) and 7 is a constant.
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Colluding Eavesdroppers
 Result comparison
Cooperation in cognitive networks helps to increase secrecy
capacity, compared to stand-alone networks [11].
[11] J. Zhang, L. Fu, X. Wang, “Asymptotic analysis on secrecy capacity in large-scale
wireless networks,” to appear in IEEE/ACM Trans. Netw., 2013.
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Outline
 Introduction
 Network Model and Definition
 Independent Eavesdroppers’ Case
 Colluding Eavesdroppers’ Case
 Conclusion
21
Conclusion
 In this paper, we study physical layer security in cognitive
networks.
 Our scheme adopting self-interference cancellation is very
efficient.
 Cooperation between secondary network and primary
network in CR networks can help to strengthen physical
layer security.
22
Thank you !

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