Aggressive Synchronous Transmissions with In-network Processing Beshr Al Nahas Olaf Landsiedel

Goals Try a strategy other than Glossy Capture-based in-network processing Top 3 solutions in 2017, and top 2 this year Low-power wireless communication Flexible: self-forming networks without planning Fault Tolerant: cope with node and link failures Agnostic to communication patterns: One-to-one, one-to-many, many-to-one, many-to-many

Concurrent Wireless Transmissions (of different data) B A C ✔ ✖ Timing: 160us, 3dB Receive stronger signal of concurrent transmissions Preambles overlap: 802.15.4 @2.4GHz: 5 bytes = 160 µs Threshold: roughly 3dB Known as: Capture Effect

Concept Nodes transmit concurrently On receive Capture effect: rx with high probability On receive Process & merge local & received data Transmit if new Feedback: assists convergence All: progress flags to support flow Sinks: ACK flags to ensure delivery Aggressive: retransmit until all sinks acknowledge reception All-to-all communication Synchronous transmissions + in-network processing + capture-effect F D S2 S1 Introduce each figure, axis To CTP and LWB on Twist (90 nodes) Sources Destination Relay F S2 S1 D

Example Scenario F D S2 S1 Network: four nodes Packet: Progress Ack S1 Two sources S1, S2 Forwarder F Destination D Packet: Four progress bits: one for each node Two ACK bits: A1, A2 one for each source Set by the destination Progress Ack S1 F D S2 A1 A2

Example Scenario Progress Ack S1 F D S2 A1 A2 X - X X S1 F D S2 Slot 1 Flag not set TX Success TX Failure X Flag set Flag changed Progress Ack S1 F D S2 A1 A2   X - X  X   S1 F D S2 Slot 1 Slot 2 Slot 3 Slot 4 Slot 5 Slot 6 Slot 7 Slot 8 Node merges flags Destination ack S1

Example Scenario Progress Ack S1 F D S2 A1 A2 X - X X S1 F D S2 Slot 1 Flag not set TX Success TX Failure X Flag set Flag changed Progress Ack S1 F D S2 A1 A2   X - X  X   S1 F D S2 Slot 1 Slot 2 Slot 3 Slot 4 Slot 5 Slot 6 Slot 7 Slot 8 S1 F D S2 Progress flags only: Risk missing data

Reflections: Capture-based vs. Glossy Glossy-based solutions outperform Short slots (0.7 ms) Rx-tx-tx-tx policy  more retransmissions Constructive interference Top 3 solutions in 2017, and top 2 this year

Reflections: Capture-based vs. Glossy Capture-based solution penalizes weak links Longer slots to fit flags & processing (2.6 ms)  less retransmissions RX iff RSSI > noise-sum + 3dB High interference  weak / border-line links Multiple senders with different data  add to noise  break weak links Unlike constructive interference

Questions?? F D S2 S1 Progress Ack S1 F D S2 A1 A2 Beshr Al Nahas Introduce each figure, axis To CTP and LWB on Twist (90 nodes) Beshr Al Nahas Olaf Landsiedel

Low level details Save power: fine-grain duty-cycling Combat interference: hop channel [1] A2: Network-wide Consensus Utilizing the Capture Effect in Low-power Wireless Networks, Beshr Al Nahas, et al, In SenSys’17.