Panda: Neighbor Discovery on a Power Harvesting Budget. Robert Margolies, Guy Grebla, Tingjun Chen, Dan Rubenstein, Gil Zussman

Transcription

1 Panda: Neighbor Discovery on a Power Harvesting Budget Robert Margolies, Guy Grebla, Tingjun Chen, Dan Rubenstein, Gil Zussman

2 The Internet of Tags Small energetically self-reliant tags Enabling technologies Ø Energy harvesting with lightweight components Ø Low power wireless communications Ø Energy adaptive algorithms Smart Buildings Monitoring of Objects Searching Objects: Where are my keys?

3 An Example Application Boxes equipped with small tags Ø Harvest light energy Ø Communicate within short range Ø Exchange IDs (Dewey Decimal System) A box whose ID is significantly different from its neighbors is identified (e.g., flashing an LED) Related Works o o o Locating misplaced boxes in a warehouse Margolies et. al. Energy-harvesting active networked tags (EnHANTs). ACM. Trans. Sens. Netw Liu et. al. Ambient backscatter: wireless communication out of thin air Proc. ACM SIGCOMM Wang, Katabi. Dude, where s my card? RFID positioning... Proc. ACM SIGCOMM Microcontroller Energy Storage Solar cell Energy Harvesting Source (Light) Wireless Transceiver

4 Panda: A Neighbor Discovery Protocol Neighbor discovery is key to searching and monitoring applications Perpetual neighbor monitoring last forever Extremely limited energy budget: tags can only be active for small periods of time Achieving and maintaining coordination is difficult We design, analyze, and experimentally evaluate the Panda protocol, which maximizes the rate of neighbor discovery under a power budget

5 Outline Introduction and Motivation Prototype Description Model and Objective Panda Protocol o Description o Analysis and Optimization o Panda-Dynamic Experimental Evaluations Conclusions

6 Prototype Description Prototype based on the TI ez430-rf2500-seh Powered by Sanyo AM 85 solar cell Energy stored in a capacitor Low-power MSP430 Microcontroller implements neighbor discovery protocol Power Connector CC2500 Transceiver sends neighbor discovery messages - R. Margolies, M. Gorlatova, J. Sarik, G. Stanje, J. Zhu, P. Miller, M. Szczodrak, B. Vigraham, L. Carloni, P. Kinget, I. Kymissis, G. Zussman, "Energy Harvesting Active Networked Tags (EnHANTs): Prototyping and Experimentation," ACM Transactions on Sensor Networks, vol., no. 4, pp. 62:-62.27, Nov. 205.

7 Powered harvested at average rate of P b (mw) Model Neighbor discovery protocol to exchange ID messages of length (ms) M Power Connector Objective: Maximize the neighbor discovery rate, while maintaining energy neutrality CC2500 Transceiver can be in 3 states: Sleeping ( P s 0 mw ) Listen ( P rpt mw) Transmit ( mw )

8 Model and Related Work Our Goal: Develop a protocol that maximizes the rate of neighbor discovery Subject to energy neutrality: power consumed matches power harvested Related work o Attempts to minimize the worst-case discovery latency o Duty cycle constraint, instead of a power budget o Does not incorporate radio power consumption o Probabilistic Protocol: Birthday o Deterministic Protocol: Searchlight - M. Bakht, M. Trower, and R. H. Kravets, Searchlight: Won t you be my neighbor? in Proc. ACM MobiCom 2, Aug M. J. McGlynn and S. A. Borbash, Birthday protocols for low energy deployment and flexible neighbor discovery in ad hoc wireless networks, in Proc. of ACM MobiHoc 0, Oct. 200.

9 Panda Protocol Description If discovery message received Configuration Parameters After exp. duration with rate λ If no message received after ` Sleep Listen Transmit After transmitting message of length M

10 Panda Protocol: Configuration Goal: Select the exponential sleep rate,, and listen duration,, to maximize discovery Rate,. Panda: designed for environments with homogenous nodes o N nodes arranged in a clique topology (no packet errors) o All nodes are homogenous with a power budget of P b o The number of nodes,, is known a-priori N Panda Dynamic (Panda-D) ` U

11 Panda Protocol: Discovery Rate Node Node 2 Node 3 Node 4 Node 5 Node 6 Sleep Listen Tx 2 3 l M N r N t Time Expected Renewal Duration, N + l + M Discovery Rate (U) = Expected Number of Discoveries Expected Length of Renewal = E[ N r ] = (N )( e l ) + l + M N

12 Panda Protocol: Power Consumption Sleep Sleep Listen Tx Sleep Parameter Cost P t (mw) P r (mw) M(ms) 0.92 C sr (µj) C rs (µj) 3.48 C ts (µj) 4.83

13 Panda Protocol: Power Consumption Node Node 2 Node 3 Node 4 Node 5 Node 6 Sleep Listen Tx l 3 2 M N r N t Expected Renewal Duration, Expected power consumption for a node in Expected power consumption for a node in Pr(n 2 N r)(energy to listen for + M) Expected power consumption for all other nodes Pr(n /2 N t [ N r ) 0=0 Time N + ` + M N t Pr(n 2 N t)(energy to listen for l and transmit for M) N r

14 Panda Protocol: Power Consumption Expected Renewal Duration, N Expected power consumption for a node = Node Node 2 Node 3 Node 4 Node 5 Node 6 Sleep Listen Tx l 3 2 M N r N t Time + ` + M Pr(n 2 N t)(energy to listen for l and transmit for M) + Pr(n 2 N r)(energy to listen for + M) + Pr(n /2 N t [ N r ) 0=0

15 where Panda Protocol: Configuration Select the exponential sleep rate,, and listen duration, `, to maximize discovery Rate, U, max,l U = (N )( e l ) + l + M = s.t. apple P b N N (C sr + P r l + P t M + C ts )+ N N ( e l )(C sr + P r ( e l e l + M)+C rs ) N + l + M Nonconvex l Numerical approximation solution Derive an analytical upperbound approximation: U A U using the e x x for x 0, and e x x for x 0.

16 Panda Protocol: Configuration Panda is numerically shown to achieve 94+% of the optimal discovery rate, while obeying energy neutrality Numerical approximation solution Derive an analytical upperbound, approximation: Where U A apple U apple U U A U, using the e x x for x 0, and e x x for x 0.

17 Panda - Dynamic Relax the homogeneity assumptions Adjust the node sleep duration based on power harvesting feedback from the capacitor voltage Average Sleep Duration (ms) At center of voltage range (3.8V), behavior is equivalent to Panda Capacitor Voltage (V)

18 Experimental Performance Evaluation: Setup Light Control System + Solar Cells MSP430 Microcontroller CC2500 Transceiver Energy Storage Capacitor Listening Node connected to PC

19 Experimental Performance Evaluation: Power Consumption Energy neutrality is demonstrated by the oscillation within the limits of the storage of the capacitor

20 Experimental Performance Evaluation: Discovery Rate N = 5 Discovery rate improves with number of nodes and power budget. Experimental accuracy over 98%.

21 CDF of Discovery Latency Experimental Performance Evaluation: Comparison to Related Works N = 5 P b = 0.5mW P b = 0.3mW P b = 0.5mW Time (min) Outperform average discovery rates for related protocols by 2-3x, while maintaining beker 99 th quantile latency.

22 Panda-D Performance Evaluation 4 nodes configured with Panda-D with varying light levels 0.5 mw 0.08 mw 0.23 mw 0.3 mw * Line widths represent the discovery rate on each link

23 Conclusions Objective: maximize the average discovery rate for energy harvesting nodes subject to a power budget Designed, analyzed, and evaluated the Panda protocol Experimental discovery rates are within 2% of theoretical estimates, demonstrating the practicality of the model Outperforms related work with a discovery rate that is up 3x higher Panda-D is able to adapt to scenarios with non-homogenous power harvesting