RESOLUTION FOR SMART DEVICES USING ACOUSTIC CHANNEL BY MOSTAFA - - PowerPoint PPT Presentation

HARMONY: CONTENT RESOLUTION FOR SMART DEVICES USING ACOUSTIC CHANNEL

BY MOSTAFA UDDIN AND DR TAMER NADEEM

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

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

HARMONY DESIGN

Simplistic Overview

• Two contending nodes
• Acoustic tone with

random frequency

• Nodes receives each
• thers acoustic tones
• Contention resolution
• Lowest frequency =

Winner Node A

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)

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

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

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?

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

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

SELECTING MULTIPLE NODES

• Thus pipelining the action of selecting nodes over acoustic channel with the data transmissions
• ver 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

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

MULTI-NODE SELECTION SOLUTIONS

• Acoustic Tone Design
• Collision Detection
• Frequency Set F
• Double Rounds of Multiple-Node Selections

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

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.

IMPLEMENTATION

• Acoustic Interface - 2 layers
• A-PHY layer
• A-MAC layer
• Components implemented by function pointer API
• Codec Driver
• Platform Driver
• Machine Driver

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