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On Modeling Low-Power Wireless Protocols Based On Synchronous Packet Transmissions

On Modeling Low-Power Wireless Protocols Based On Synchronous Packet Transmissions . Marco Zimmerling , Federico Ferrari, Luca Mottola * , Lothar Thiele ETH Zurich * Politecnico di Milano and SICS Swedish ICT. TexPoint fonts used in EMF.

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On Modeling Low-Power Wireless Protocols Based On Synchronous Packet Transmissions

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  1. On Modeling Low-Power Wireless Protocols Based On Synchronous Packet Transmissions Marco Zimmerling, Federico Ferrari, Luca Mottola*, Lothar Thiele ETH Zurich *Politecnicodi Milano and SICS Swedish ICT TexPoint fonts used in EMF. Read the TexPoint manual before you delete this box.: AAAAAAA

  2. Motivation Accurate mathematical models of low-power wireless protocols are important • Understanding (e.g., trade-offs, parameters) • Verification • System design (e.g., node placement, power sources) • Prediction and adaptation at runtime But traditional link-based multi-hop protocolsare intricate and difficult to model (e.g., ZigBee)

  3. Motivation Highly dynamic network topology due to: • Volatile low-power wireless links • Node mobility, failures Traditional protocols maintain substantial network state that governs their operation (e.g., link qualities) • Distributed across nodes • Concurrent, uncontrolled updates

  4. Motivation Highly dynamic network topology due to: • Volatile low-power wireless links • Node mobility, failures Traditional protocols maintain substantial network state that governs their operation (e.g., link qualities) • Distributed across nodes • Concurrent, uncontrolled updates Modeling often stops at the link layer, where interactions are single-hopinsufficient!

  5. Example: End-to-End Delivery Devise a model of the packet delivery rate (PDR) observed at the sink PDR = f()

  6. Example: End-to-End Delivery wake-up times one-hop A Media Access B Radio Driver = network state A: wake-up times PDR = f( , …) B: time

  7. Example: End-to-End Delivery one-hop/ end-to-end link qualities Tree Routing wake-up times one-hop A Media Access 0.9 B Radio Driver 0.7 = network state wake-up times PDR = f( , , …) link qualities

  8. Example: End-to-End Delivery one-hop/ end-to-end link qualities Tree Routing wake-up times one-hop A Media Access B Radio Driver = network state wake-up times PDR = f( , , …) link qualities

  9. Example: End-to-End Delivery Application end-to-end queue sizes Reliable Transport one-hop/ end-to-end link qualities Tree Routing one-hop A wake-up times Media Access B Radio Driver = network state wake-up times PDR = f( , , , …) link qualities queue sizes

  10. Example: End-to-End Delivery Application end-to-end queue sizes Reliable Transport one-hop/ end-to-end Continuously changing link qualities Tree Routing one-hop A wake-up times Media Access B Radio Driver = network state wake-up times PDR = f( , , , …) link qualities queue sizes

  11. Example: End-to-End Delivery Application end-to-end queue sizes Reliable Transport one-hop/ end-to-end Continuously changing link qualities Tree Routing one-hop A wake-up times Media Access 0.8 B Radio Driver 0.95 = network state wake-up times PDR = f( , , , …) link qualities queue sizes

  12. Example: End-to-End Delivery Application end-to-end queue sizes Reliable Transport one-hop/ end-to-end Continuously changing link qualities Tree Routing one-hop A wake-up times Media Access 0.8 B Radio Driver 0.95 = network state Protocols abstract the unreliable wireless channel as point-to-point links major reason for complexity

  13. Synchronous Transmissions (ST) Multiple nodes send simultaneously to the same receiver, as opposed to pairwise link-based transmissions (LT) R R

  14. Synchronous Transmissions (ST) Enabled by IEEE 802.15.4 physical-layer phenomena: • Power (and delay) capture  different/identical packets • Constructive baseband interference  identical packets Several recent protocols exploit ST for various purposes: • A-MAC [SenSys 10]: contention resolution • Glossy [IPSN 11]: network flooding • Splash [NSDI 13]: code updates • CAOS [SenSys 13]: all-to-all communication

  15. Synchronous Transmissions (ST) Enabled by IEEE 802.15.4 physical-layer phenomena: • Power (and delay) capture  different/identical packets • Constructive baseband interference  identical packets Several recent protocols exploit ST for various purposes: • A-MAC [SenSys 10]: contention resolution • Glossy [IPSN 11]: network flooding • Splash [NSDI 13]: code updates • CAOS [SenSys 13]: all-to-all communication ST enable efficient and reliable multi-hop protocols with very little network state

  16. Open Question Do ST also enable simple yet accurate modeling?

  17. Modeling Trade-Off Space High Tree Routing Accuracy of Models Radio Driver Low Low High Modeling Scope

  18. Modeling Trade-Off Space 2-7 % error Zimmerling et al. [IPSN 12] Link layer Polastre et al. [SenSys 04] High Buettner et al. [SenSys 06] Tree Routing Challen et al. [MobiSys 10] Accuracy of Models Park et al. [IPSN 10] Radio Driver Langendoen & Meier [TOSN 10] Low Low High Modeling Scope

  19. Modeling Trade-Off Space 2-7 % error Zimmerling et al. [IPSN 12] Full stack Link layer Polastre et al. [SenSys 04] High Buettner et al. [SenSys 06] Tree Routing Challen et al. [MobiSys 10] Accuracy of Models Park et al. [IPSN 10] Bruneo et al. [PE 12] Radio Driver Gelenbe et al. [TOSN 07] Langendoen & Meier [TOSN 10] Guenther et al. [UKPEW 12] Low Low High Modeling Scope

  20. Modeling Trade-Off Space 2-7 % error 0.25 % error Zimmerling et al. [IPSN 12] Full stack Link layer Polastre et al. [SenSys 04] Our work High Buettner et al. [SenSys 06] Tree Routing Challen et al. [MobiSys 10] Accuracy of Models Park et al. [IPSN 10] Bruneo et al. [PE 12] Radio Driver Gelenbe et al. [TOSN 07] Langendoen & Meier [TOSN 10] Guenther et al. [UKPEW 12] Low Low High Modeling Scope

  21. Outline Validity of the Bernoulli assumption to ST vs LT Modeling an ST-based multi-hop protocol Model validation through real-world experiments

  22. Outline Validity of the Bernoulli assumption to ST vs LT Modeling an ST-based multi-hop protocol Model validation through real-world experiments

  23. Bernoulli Assumption Intended receiver of a sequence of packets observes a sequence of i.i.d. Bernoulli trials • Success (packet received) with probability p • Failure (packet lost) with probability 1 – p Empirical studies showed that this assumption is not always valid to LT (esp. when packets are close in time) S R S S Receptions/losses are independent over time

  24. Bernoulli Assumption Intended receiver of a sequence of packets observes a sequence of i.i.d. Bernoulli trials • Success (packet received) with probability p • Failure (packet lost) with probability 1 – p Empirical studies have shown that this assumption is not always valid to LT S R S S Receptions/losses are independent over time What about ST?

  25. Methodology Glossy [IPSN 11] leverages ST for efficient and reliable network flooding

  26. Methodology Glossy [IPSN 11] leverages ST for efficient and reliable network flooding

  27. Methodology Glossy [IPSN 11] leverages ST for efficient and reliable network flooding

  28. Methodology Glossy [IPSN 11] leverages ST for efficient and reliable network flooding

  29. Methodology Glossy [IPSN 11] leverages ST for efficient and reliable network flooding

  30. Methodology 139-node testbed at NUS 20-byte packets at 20 ms IPI

  31. Methodology 139-nodetestbed at NUS 20-byte packets at 20 ms IPI ST-Type: how protocols perceive Glossy • 70 equally distributed nodes • 50,000 Glossy floods each • Remaining 138 nodes log

  32. Methodology 139-nodetestbed at NUS 20-byte packets at 20 ms IPI ST-Type: how protocols perceive Glossy • 70 equally distributed nodes • 50,000 Glossy floods each • Remaining 138 nodes log LT-Type: how protocols perceive LT • All 139 nodes • 50,000 broadcasts each • Nodes within radio range log

  33. Methodology 139-nodetestbed at NUS 20-byte packets at 20 ms IPI ST-Type: how protocols perceive Glossy • 70 equally distributed nodes • 50,000 Glossy floods each • Remaining 138 nodes log LT-Type: how protocols perceive LT • All 139 nodes • 50,000 broadcasts each • Nodes within radio range log Tx power: 0 dBm (max) and -15 dBm (lowest possible)

  34. Methodology 139-nodetestbed at NUS 20-byte packets at 20 ms IPI ST-Type: how protocols perceive Glossy • 70 equally distributed nodes • 50,000 Glossy floods each • Remaining 138 nodes log LT-Type: how protocols perceive LT • All 139 nodes • 50,000 broadcasts each • Nodes within radio range log Tx power: 0 dBm (max) and -15 dBm (lowest possible) Collected >1,200,000,000 packet reception events

  35. Trace Analysis • Represent every trace as a discrete-time binary time series {xi}nof length n = 50,000: 010011100111110011101010… • Keep only weakly stationary time series, using two empirical tests for non-constant mean/variance • Check the validity of the Bernoulli assumption, using a statistical test based on the sample autocorrelation

  36. Bernoulli Results 200 1000 1010111110111101100110111111101111101110110001111111001111011101011111000111110100111101011001100110

  37. Bernoulli Results 0.5 0.03 0.1 200 1000

  38. Bernoulli Results 40.0 14.5 2.6 0.5 0.03 0.1 200 1000

  39. Bernoulli Results 40.0 34.6 14.5 14.1 8.7 4.0 2.5 2.6 0.5 0.3 0.03 0.1 200 1000

  40. Bernoulli Results 40.0 34.6 14.5 14.1 8.7 4.0 2.5 2.6 0.5 0.3 0.03 0.1 The Bernoulli assumption is highly valid to ST and significantly more valid to ST than to LT

  41. Outline Validity of the Bernoulli assumption to ST vs LT Modeling an ST-based multi-hop protocol Model validation through real-world experiments

  42. Low-Power Wireless Bus (LWB) LWB [SenSys 12] uses only ST for communication • Turns a multi-hop network into a “virtual” single-hop network, similar to a shared bus Centralizedscheduling • A controllernode orchestrates all communication LWB controller multi-hop network Glossy floods shared bus

  43. Low-Power Wireless Bus (LWB) LWB [SenSys 12] uses only ST for communication • Turns a multi-hop network into a “virtual” single-hop network, similar to a shared bus Centralizedscheduling • A controllernode orchestrates all communication LWB controller multi-hop network Glossy floods shared bus Does the validity of the Bernoulli assumption to ST help devise a simple yet accurate energy model of LWB?

  44. Schedule-Driven Operation A single event − the reception of schedules from the controller − drives the operation of all LWB nodes Communication rounds … schedule data data data

  45. Finite-State Machine = schedule received = schedule missed

  46. Finite-State Machine The Bernoulli assumption allows us to characterize schedule receptions through a single parameter p = schedule received = schedule missed

  47. Discrete-Time Markov Chain 1-p p 1-p p p 1-p 1-p 1-p p 1-p p p p p p p 1-p 1-p 1-p 1-p p p 1-p = schedule received, with probability p = schedule missed, with probability 1-p

  48. Energy Model Stationary distribution of the DTMC gives the frequency of visits to each state in the long run for a given p Combined with the well-defined cost of each state, we get the long-term expected energy cost of a LWB node 0 0.5 1 Stationary distribution 0 0.2 0.4 0.6 0.8 1 Probability of receiving a schedule p

  49. Outline Validity of the Bernoulli assumption to ST vs LT Modeling an ST-based multi-hop protocol Model validation through real-world experiments

  50. Model Validation 30-node testbed at ETH Zurich 15-byte payload at 6 sec IPI Tx power: odBm (max) Estimate several model parameters at runtime, such as: Measure energy consumption using established software-based methods number of received schedules p= number of expected schedules

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