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

2. 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

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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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.