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

others 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

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

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