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 1 st and 2 nd ranking tones, they will transmit during epoch n +1 • A and B update their tone numbers subtracting tone 7 (2 nd ranked tone) • C and D select new random tone numbers for epoch n + 1 • Since A and C have the 1 st and 2 nd 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
Recommend
More recommend
