turfcast: a service for controlling information dissemination in wireless networks xinfeng li, jin...
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TurfCast: A Service for Controlling Information Dissemination in Wireless Networks
Xinfeng Li, Jin Teng, Boying Zhang, Adam Champion and Dong Xuan
IEEE Infocom2012
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Information Dissemination with TurfCast
0/1 information dissemination over both temporal AND spatial domain
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Outline TurfCast Applications TurfCast Key Components
TurfCodeTurfBurst
Implementation and Evaluations Conclusion
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TurfCast Applications Electronic Proximity Advertising
Reward Loyal Customers with Special Promotions
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TurfCast Applications (Cont’d) Mobile Social Networking
Publishes personal information in a temporal/spatial bounded location
Location VerificationGenerates physical presence proofs for users
in proximity in an automatic manner
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Possible Approaches For TurfCast
Power ControlOnly spatial support
Hard to control
CryptographyComputationally expensive
Difficult for fluid networks
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Our Approach Pure communication-based
Leverage fountain code
Include two key componentsTurfCode: for temporal information control
TurfBurst: for spatial information control
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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
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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
K: number of packets for correct decoding
Fountain Codes cannot be directly used for TurfCast
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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
m’=Sm c=Bm’
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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
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Nested 0-1 Fountain Codes For multiple level of TurfCast, we need nested 0-1
fountain codes.
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TurfBurst
Use the Shannon bounds to achieve spatial turfs.
Users at different locations have different capability of receiving informationUsers 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
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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
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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
A Quick Recap of Our Solutions
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TurfCast: Multi-level Priority Information
Dissemination
TurfCode:Temporal Control
TurfBurst:Spatial Control
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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
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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.
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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.
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Final Remarks TurfCast concept
0-1 CommunicationsEnable new applications
Temporal and Spatial information control based on 0-1 fountain codesTurfCode for temporal controlTurfBurst for spatial control
