Harmony: Content Resolution for Smart Devices using ...cs752/papers/acoustic-001-slides.pdfHARMONY...
Transcript of Harmony: Content Resolution for Smart Devices using ...cs752/papers/acoustic-001-slides.pdfHARMONY...
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HARMONY: CONTENT RESOLUTION FOR SMART DEVICES USING ACOUSTIC CHANNEL
BY MOSTAFA UDDIN AND DR TAMER NADEEM
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WI-FI NETWORKS
•74% of smartphones data goes through Wi-Fi
• Low/free cost and high throughput
•Enhancing Wi-Fi network performance and functionalities
is very essential to support the widespread use of smart
devices
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HARMONY
•2 main operations
• Contention Resolution over the acoustic channel
• Data transmissions over the Wi-Fi channel
i. selecting a single node
ii. Selecting multiple nodes
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HARMONY DESIGN
Simplistic Overview
• Two contending nodes
• Acoustic tone with
random frequency
• Nodes receives each
others acoustic tones
• Contention resolution
• Lowest frequency =
Winner Node A
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HARMONY DESIGN
• Winning Node A triggers data transmission after DIFS waiting period
• Node B disables transmission
• Harmony saves time by running node selection process over the acoustic
channel
• Assumptions- all nodes can hear each other (no hidden nodes) and network
saturated (all nodes have enough data to transmit)
• Frequency band 16kHz to 21 kHz (12 kHz is the high limit for background
noise, human conversations, and music players)
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THREE CONTENDING NODES
• Randomly Chosen tones 10,12, 5
• All nodes hear the other acoustic
tones
• Node C Wins, waits DIFS period
and transmits
• Other nodes disable transmission
• Next round A, B decrease by 5 and
node C selects new random tone
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HARMONY DESIGN
•Wi-Fi interface controlled by acoustic interface thru a
shared flag variable
•Flag- enable or disabled to control data transmission from
the Wi-Fi driver buffer
•Node C transmits its data and clears the shared flag upon
completion
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CHALLENGES
•Propagation delay of acoustic signals cause contention
resolution operation to happen over a long duration
• Inefficient to run contention resolution operation for every
transmission
•Possible solution? Allow selected node to transmit batch of
packets over single transmission
•But is this fair? Are there inefficiencies?
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SOLUTION TO CHALLENGE
•Select multiple nodes instead of a single node without
additional delays
•Pipelining the two main operations of Harmony
- Contention resolution over acoustic channel
- Data transmission over Wi-Fi channel
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SELECTING MULTIPLE NODES
• Basic Example with 2
consecutive epoch periods,
n and n + 1
• Nodes A and B transmit data
in epoch n (selected to
transmit in epoch n - 1)
• Node C and D selected in
epoch n to transmit data over
epoch n + 1
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SELECTING MULTIPLE NODES
• Thus pipelining the action of selecting nodes over acoustic channel with the data transmissions
over the Wi-Fi channel
• Note: Epoch time is fixed based on propagation time, duration acoustic tone, and
computational time for detecting the acoustic frequency
• During each epoch period n, nodes A, B, C and D generate its own acoustic tone
corresponding to randomly selected tone number
• Each hears each others tones
• Node C and D have the 1st and 2nd ranking tones, they will transmit during epoch n +1
• A and B update their tone numbers subtracting tone 7 (2nd ranked tone)
• C and D select new random tone numbers for epoch n + 1
• Since A and C have the 1st and 2nd ranked tones, they will transmit during n + 2
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MULTIPLE NODES SELECTION CHALLENGES
• Collision- 2 nodes generate the same acoustic tone with the same tone number
• Ambiguity between nodes
• If node B generates an acoustic tone corresponding to tone number 7
similar to node D
• Data transmissions collide over Wi-Fi channel
• Node D generates an acoustic tone corresponding to tone number 5
similar to node C
• No ambiguity but collision over Wi-Fi channel
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MULTI-NODE SELECTION SOLUTIONS
• Acoustic Tone Design
• Collision Detection
• Frequency Set F
• Double Rounds of Multiple-Node Selections
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MULTI-NODE SELECTION SOLUTION
• Acoustic tone design considering
• Length of the tone
• Shape of the tone
• Collision Detection- occurs when a node hears an acoustic tone with an
identical tone number to its own tone number
• Scenario 1- two tones are not overlapped in time
• Scenario 2- the tones are overlapped in time
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MULTI-NODE SELECTION SOLUTION
• Frequency Set F- the larger the number of frequencies in frequency set F, the
less the probability of the conceding nodes to select the same tone number.
• 26 available frequencies to choose from
• Double Rounds of Multiple-Node Selections- run a second round of random
tones generation for only the set of nodes that are selected in the first round if
a collision is detected.
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IMPLEMENTATION
• Acoustic Interface - 2 layers
• A-PHY layer
• A-MAC layer
• Components implemented by function pointer API
• Codec Driver
• Platform Driver
•Machine Driver
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HARMONY CONCLUSION
• New contention resolution scheme Harmony
• Addresses the overhead of current Wi-Fi backoff scheme
• Leverages cross-interface framework Acoustic-WiFi
• Harmony evaluated using small scale testbed and large scale
simulation
• Several research challenges still open for future work