1. TurfCast: A Service for Controlling Information Dissemination in Wireless Networks Xinfeng Li, Jin Teng, Boying Zhang, Adam Champion and Dong Xuan IEEE Infocom2012

2. Information Dissemination 2

3. Information Dissemination with TurfCast 3 0/1 information dissemination over both temporal AND spatial domain

4. Outline TurfCast Applications TurfCast Key Components  TurfCode  TurfBurst Implementation and Evaluations Conclusion 4

5. TurfCast Applications Electronic Proximity Advertising  Reward Loyal Customers with Special Promotions 5

6. TurfCast Applications (Cont’d) Mobile Social Networking  Publishes personal information in a temporal/spatial bounded location Location Verification  Generates physical presence proofs for users in proximity in an automatic manner 6

7. Possible Approaches For TurfCast Power Control  Only spatial support  Hard to control Cryptography  Computationally expensive  Difficult for fluid networks 7

8. Our Approach Pure communication-based  Leverage fountain code Include two key components  TurfCode: for temporal information control  TurfBurst: for spatial information control 8

9. TurfCode A new type of nested 0-1 fountain code.  To achieve temporal turfs Fountain code:  Streams of packets coded from raw information Linear combination of message chunks  Whenever enough packets are received, decoding is possible  Like collecting water from a fountain to fill a cup  Statistically more water drops, more information 9

10. Premature Decoding of Fountain Codes A fraction of information can be decoded even if the number of received packets does not reach the correct decoding threshold 10 K: number of packets for correct decoding Fountain Codes cannot be directly used for TurfCast

11. 0-1 Fountain Codes We add a new scrambling precoding layer  To ensure that any linear combination of the received packets cannot reveal any block before intended decoding 11 m’=Sm c=Bm’

12. Scrambling Matrix Design m’=Sm  Not conventional bit-wise XOR operation. We have proved that scrambling with bit-wise XOR operation cannot be safe.  We use real numerical additions The matrix S is designed to be a trilinear matrix  Easy to guarantee that a trilinear matrix is reversible For decoding, we need the matrix to be reversible  We can randomly pick the diagonal elements A small change in the diagonal matrix can result in a total different m’  These diagonal elements are the key to de-scramble the message A hacker must guess all diagonal elements correctly to get any information 12

13. Nested 0-1 Fountain Codes For multiple level of TurfCast, we need nested 0-1 fountain codes. 13

14. TurfBurst Use the Shannon bounds to achieve spatial turfs. Users at different locations have different capability of receiving information  Users far away gets lower Signal to Noise Ratio (SNR), and hence lower information amount according to the Shannon bound  With lower information amount, the user is able to decode less information 14

15. TurfBurst Design TurfBurst needs special attention when designed  Boundary not so sharp as the noise is probabilistic.  Need larger difference between layers to accommodate the noise. However, in many scenarios, we have barriers that drastically reduce the SNR, which is to our advantage.  E.g., Room Walls 15

16. TurfCast Put Together Messages of several different priorities to be sent.  Each priority level has distinctive requirement, i.e., when the message should be received and how far  Messages with lower priority cannot be received before those with higher priority. Need to design meta-blocks based on TurfCode and TurfBurst to achieve this 16 TurfBurst TurfCode

17. A Quick Recap of Our Solutions 17 TurfCast: Multi-level Priority Information Dissemination TurfCode: Temporal Control TurfBurst: Spatial Control

18. Implementation On laptops and Android Smartphones Receiver side: Laptop using aircrack-ng for MAC level packet sniffing in WiFi. Sender side:  Laptop : Use aircrack-ng for MAC level packet injection.  Nexus S: Socket programming on the TCP/IP level 18

19. Evaluations (Temporal) 19 User can get Layer 1 message in around 5-10 seconds But to get Layer 2 messages, they need to linger around 10 seconds longer To get Layer 3 messages, they need to stay still longer.

20. Evaluations (Spatial) 20 Users within the inner circle can get Layer 3 messages Users between circle 1 and 2 gets significantly less Layer 3 messages The farthest users receives little Layer 3 information.

21. Final Remarks TurfCast concept  0-1 Communications  Enable new applications Temporal and Spatial information control based on 0-1 fountain codes  TurfCode for temporal control  TurfBurst for spatial control 21

22. 22 Thank you!