1 / 24

Strawman : Resolving Collisions in Bursty Low-Power Wireless Networks

Strawman : Resolving Collisions in Bursty Low-Power Wireless Networks. Fredrik Österlind , Luca Mottola , Thiemo Voigt, Nicolas Tsiftes , Adam Dunkels Swedish Institute of Computer Science Presenter:SY. About This Paper. Strawman Contention resolution mechanism

marius
Download Presentation

Strawman : Resolving Collisions in Bursty Low-Power Wireless Networks

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Strawman: Resolving Collisions in Bursty Low-Power Wireless Networks Fredrik Österlind, Luca Mottola, Thiemo Voigt, Nicolas Tsiftes, Adam Dunkels Swedish Institute of Computer Science Presenter:SY

  2. About This Paper • Strawman • Contention resolution mechanism • Resolve collision in low-power duty-cycled networks that experience traffic bursts • Copes with hidden terminals and is designed for receiver-initiated duty-cycled protocols • Contribution • Builds upon two previous papers • Improve Strawman along several dimensions • Embed it within RI-MAC (real implementation)

  3. Background • Radio duty cycling • nodes wake up regularly • Receiver-initiated radio • Traffic Peaks • Event detection, network code update, bulk download

  4. Background Cont. • Collisions in duty-cycled networks • Hidden Terminals • RTS/CTS schemes have high overhead

  5. Mechanism and Implementation

  6. Receiver Initiate Radio • Receiver Probe • Sender Reply • Collision occur • channel activity without successfully receiving a packet S2 Probe S1 R Reply Collision S3

  7. Starwman Reply longest length Another request Send Collision request • Multi-channel operation • Initial probe at pre-determined channel • Rest of communication at the other channel Until every sender sent its data Random length Packet 7 bytes granularity (224us) Winner send data

  8. Implementation • Contiki + Tmote Sky • RI-MAC • Version 1: Strawman + multi-channel operation • Version 2: random backoff (geometric distribution) • Collision length estimation • Clear Channel Assessment (CCA) • Default threshold: -77 dBm

  9. Alleviating Channel Noise • Transmissions of COLLISION packets are synchronized • receiver knows exactly when they occur • Max COLLISION packets length is fixed • Methods • Sample right before transmission • If busy  abort • If > Max length, abort • Two consecutive Strawman rounds abort • Go to sleep, use another channel next time

  10. Evaluation

  11. Evaluation • Key findings • Collision packet length estimation is accurate • No overhead when no collisions, limited energy cost when resolving collisions • Sustain a range of different traffic loads • Able to cope with hidden terminals efficiently • Increase robustness in standard tree routing protocols

  12. Collision Lengths • Two TMote Sky: sender + receiver • COLLISION packet different length • Vary distance: 0.5m (nearby), 10m (distant, decreased TX power) Within the 7-byte granularity

  13. Collision Signal Strengths • Vary the receiver-contender distance

  14. Interference from External Noise • Two TMote Sky: 3m apart • Third TMote Sky node as interferer • Control interference • change distance between interferer-receiver

  15. Interference from Out-of-range Contenders • 3 nodes: 1 receiver and 2 contenders • One receiver kept at 0.5 m • 0 bytes payload • Another vary the distance: 0.5 to 20 m • 112 bytes payload

  16. Energy Cost of Resolving Collisions • simulate a single receiver and four contenders in Cooja • Contenders hidden to each other • 1 data packet every 4 seconds • vary the nodes’ wakeup intervals • four times per second to once every 32 seconds

  17. Different Traffic Loads • TWIST: a testbed with 100 Tmote Sky • Areceiver node probingfor data once per second • All other nodesare contenders • Data generation rate: 1 pkt/m to 2 pkt/s

  18. Goodput and Fairness

  19. Clear Channel Assessment Sensitivity • 15 DATA packets per minute • Vary the CCA threshold

  20. Reacting to Sudden Traffic Bursts • 1-hop network with 8 nodes • Measuring the resulting goodput • Always contend • Vary number of active contenders every 10s

  21. Coping with Hidden Terminals • Black Burst protocol S2 R S1

  22. Coping with Hidden Terminals • RI-Strawmanvs RI-Black Burst

  23. Multi-hop Data Collection • 82 nodes in the TWIST testbed • Multi-hop topologies (at least 4 hops) • Contiki Collect protocol • Traffic patterns • No traffic (NT) • Periodic traffic (PT): 1 pkt every 5 minutes • Bursty traffic (BT): • Instantaneously generate 1 pkt on 8 randomly-selected nodes

  24. Conclusions • Leverages synchronized packet collisions to implement efficient and fair contention resolution among hidden terminals • Implementation on real testbed • Potential weakness in noisy environment

More Related