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

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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 Control

Only spatial supportHard to control

CryptographyComputationally expensive Difficult for fluid networks

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Our Approach Pure communication-based

Leverage fountain code Include two key components

TurfCode: for temporal information controlTurfBurst: 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

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Thank you!