TurfCast : A Service for Controlling Information Dissemination in Wireless Networks

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

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

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

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

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

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

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

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

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 Fountain Codes cannot be directly used for TurfCast K: number of packets for correct decoding

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 c=Bm’ m’=Sm

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

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

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

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

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 TurfBurst TurfCode

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

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

19. Evaluations (Temporal) 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) 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

22. Thank you!