Energy Aware Routing for PicoRadio

1. Energy Aware Routing for PicoRadio Rahul C. Shah Berkeley Wireless Research Center

2. Wireless Sensor Networks • Dominant trend in wireless industry: • More bits/sec/Hz • Wireless sensor networks offer: • More bits/$/nJ

3. PicoRadio System Design

4. Wireless Sensor Nodes – Constraints • Low Data Rates << 10 kbps • Self-configuring, maintenance-free and robust • Aggressive networking protocol stack • Redundancy in deployment • Low cost: < 1$ • Small size: < 1 cm3 • Low power/energy • Long lifetime of product requires energy-scavenging • Plausible scavenging level: < 100 W

5. Energy Scavenging

6. Practical Means of Energy Scavenging

7. Application Network Data Link Physical Protocol Stack Issues at the network layer: • Addressing • Addressing will be class based: <location, node type, sub type> • Symbolic addressing may be supported • Routing • Should route packets to the destination • Given: • Destination location • Position of self • Position of the neighbors

8. Distributed Positioning [Chris Savarese(UCB)]

9. Transfers data between network and physical layers; Maintains neighborhood info Power control, error control and access control Computes location Data Link Layer Functions Controller Sensors Actuators

10. Mostly-Sleepy MAC Layer Protocols • Receiving a bit is computationally more expensive than transmitting one (receiver has to discriminate and synchronize) • Most MAC protocols assume that the receiver is always on and listening! • Activity in sensor networks is low and random • Careful scheduling of activity pays off big time, but … has to be performed in distributed fashion

11. A Reactive PicoMAC • Truly Reactive Messaging • Power Down the Whole Data Radio • Reduce Monitoring Energy Consumption by 103 Times • Wakeup Radio will Power Up Data Radio for Data Reception • Multi-Channel Access Scheme • To Reduce Collision Rate • To Reduce Signaling Overhead (Shrink Address Space)

12. TCA RCA SCA Multi-Channel Access Scheme Channel Assignment Using Distributed GraphColoring (combined with discovery) Receiver-based ChannelAssignment: Channel code used as address [Chunlong Guo(UCB)]

13. Sleeping nodes Wake up! Communicating nodes Reactive Radio Issues • Broadcast and data communication modes must co-exist simultaneously • Sleeping nodes have to wake-up to broadcast signals, and • not to any signal leaking from surrounding communicating nodes • Broadcast signals should not disrupt data transmission

14. PicoRadio Routing Protocol

15. PicoNetwork Specifications • Density of nodes – 1 node every 1 to 20 sq. m. • Radio range – 3 to 10 m • Average bit rate per node ~ 100-500 bps • Peak bit rate per node ~ 10 kbps • Very low mobility of nodes • Loose QoS requirements: • Sensor data is redundant, so reliability is not required • Most data is delay insensitive

16. Routing Protocol Characteristics • Ensure network survivability • Low energy (communication and computation) • Tolerant and robust to topology changes • Scalable with the number of nodes • Light weight

17. Critical node as it is the only one of its type Critical node to maintain network connectivity (network issue) Network Survivability Network survivability is application-dependent – coverage may also be an issue

18. Proactive routing maintains routes to every other node in the network Regular routing updates impose large overhead Suitable for high traffic networks Reactive routing maintains routes to only those nodes which are needed Cost of finding routes is expensive since flooding is involved Good for low/medium traffic networks Proactive vs. Reactive Routing

19. Traditional Reactive Protocols • Finds the best route and then always uses that! • But that is NOT the best solution! • Energy depletion in certain nodes • Creation of hotspots in the network Dest Source

20. Sending data Source Destination Directed Diffusion† Setting up gradients Source Destination • Destination initiated • Multiple paths are kept alive †C. Intanagonwiwat, R. Govindan and D. Estrin, “Directed Diffusion: A scalable and robust communication paradigm for sensor networks”, IEEE/ACM Mobicom, 2000

21. Energy Aware Routing • Destination initiated routing • Do a directional flooding to determine various routes (based on location) • Collect energy metrics along the way • Every route has a probability of being chosen • Probability  1/energy cost • The choice of path is made locally at every node for every packet

22. Local Rule (0.75*10) + (0.25*30) = 15 nJ 10 nJ p1 = 0.75 30 nJ p2 = 0.25 Setup Phase Directional flooding Sensor Controller

23. 0.3 Sensor 0.6 0.7 Controller 1.0 0.4 1.0 Data Communication Phase Each node makes a local decision

24. What’s The Advantage? • Spread traffic over different paths; keep paths alive without redundancy • Mitigates the problem of hot-spots in the network • Has built in tolerance to nodes moving out of range or dying • Continuously check different paths

25. Energy Cost • The metric can also include: • Information about the data buffered for a neighbor • Regeneration rate of energy at a node • Correlation of data

26. Simulation Setup • Simulations done in Opnet • 76 nodes in a typical office setup • 47 light sensors • 18 temperature sensors • 7 controllers • 4 mobile nodes • Light sensors send data every 10 seconds, while the temperature data is sent every 30 seconds • Comparison with directed diffusion routing

27. Simulation Model Network model Office layout Node layout

28. Simulation Measurements • Energy used is measured: • For reception: 30 nJ/bit • For transmission: 20 nJ/bit + 1 pJ/bit/m3 • Packet sizes are ~ 256 bits • 1 hour simulation time

29. Energy Usage Comparison Diffusion Routing Energy Aware Routing Peak energy usage was ~50 mJ for 1 hour simulation

30. Normalized Energy Comparison Diffusion Routing Energy Aware Routing Energy of each node is normalized with respect to the average energy

31. Bit Rate Comparison Diffusion Routing Energy Aware Routing Peak bit rate was 250 bits/sec. Average bit rate was 110 bits/sec.

32. Network Lifetime • Nodes have fixed initial energy – 150 mJ • Measure the network lifetime until the first node dies out • Diffusion: 150 minutes • Energy Aware Routing: 216 minutes 44% increase in network lifetime

33. Funneling Algorithm Data Communication Interest Flooding [w/ Dragan Petrović (UCB)]

34. PicoRadio Implementations

35. PicoNode I Off-the-shelf fully programmable communication/computation node sensor digital power radio

36. fclock Peak Det  RF Filter LNA RF Filter fclock Peak Det  RF Filter PN3 Architecture - Rx • Two Channel • Channel Spacing ~ 50MHz • 10kbps/channel • Issues include noise suppression and isolation between RF filters • Prototype Target: 3mA @ 1V

37. OSC1 MOD1 Preamp PA Matching Network OSC2 MOD2 PN3 Architecture - Tx • Use simple modulation scheme (OOK) • Allows efficient non-linear PA • Target output power: 0dBm • Prototype Target: 4mA @ 1V

38. TX0 TX1 RX0 RX1 PN3 Cycled Receiver