ECET 581

1. ECET 581 Wireless Sensor Networks Infrastructure Establishment November 28, 2006 Fall 2006 http://www.etcs.ipfw.edu/~lin References: **Ch 4 Infrastructure Establishment of the book: "Wireless Sensor Networks - An Information Processing Approach," by Feng Zhao and Leonidas Guibas, from Morgan Kaufmann/Elsevier inc, 2004 ** Ch 9 Network Position and Synchronization Services and Ch 10 Energy Management of the book: Principles of Embedded Networked System Design, by Gregory and William Kaiser, from Cambridge University Press **TMote Sky Web site: www.moteiv.com WSN Mote- MCU & Sensor Hardware

2. Infrastructure Establishment • Topology Control • Clustering • Time Synchronization • Clock and Communication Delays • Interval Methods • Reference Broadcasts • Localization and Localization Services • Ranging Techniques • Range-based Localization Algorithms • Location Services WSN Mote- MCU & Sensor Hardware

3. Topology Control • Applications • Military surveillance • Emergency response • Scientific exploration • Neighborhood Discovery • Execute a neighbor-nodes discovering protocol • Topology Discovery – build routing path • Radio power of the nodes • Local topography • Other conditions • Issues • Setup radio range to minimize energy usage • Remains connected and satisfies other desirable communication properties • Determines CTR (critical transmitting range) WSN Mote- MCU & Sensor Hardware

4. Topology Control • Determines CTR (critical transmitting range) • Geometric Random Graph (GRM) Theory • Related Issues • Link Quality Indicator – LQI (packet reception ratio) • Received Signal Strength Indicator - RSSI • Coverage range • Optimal transmit power adjustment (transmission power control) • Adaptive transmitting range control (models, temporal and LQI, RSSI) • CC1000/CC2420 RF Radio Hardware: Transmitter/Receiver, dBm) WSN Mote- MCU & Sensor Hardware

5. RF Transceivers • TI-Chipcon • CC1000 • CC2420 WSN Mote- MCU & Sensor Hardware

6. Tmote Sky - RSSI values • Ref: http://www.moteiv.com/community/Reading_RSSI_values_from_Tmote_Sky • Read a incoming packet and store the signal strength in the • TOS_Msg structure • Read the signal in the absence of the incoming packets • Noise • Source interference : 802.11 networks, Microwave ovens WSN Mote- MCU & Sensor Hardware

7. Tmote Sky - RSSI values • Modifying CC2420RadioC.nc implementation { ... components new CC2420ResourceC() as CmdRSSI; ... CC2420ControlM.CmdRSSI -> CmdRSSI; } WSN Mote- MCU & Sensor Hardware

8. Tmote Sky - RSSI values • Modifying CC2420ControlM.nc to provide extra ADC interface • Use an additional Resource provides { ... interface ADC as RSSI; ... } uses { ... interface ResourceCmd as CmdRSSI; ... } WSN Mote- MCU & Sensor Hardware

9. Tmote Sky - RSSI values implementation { ... async command result_t RSSI.getData() { call CmdRSSI.deferRequest(); return SUCCESS; } event void CmdRSSI.granted(uint8_t rh) { uint16_t data; data = call HPLChipcon.read(rh, CC2420_RSSI); call CmdRSSI.release(); data += 0x7f; data &= 0x00ff; signal RSSI.dataReady(data); } async command result_t RSSI.getContinuousData() { return FALSE; } WSN Mote- MCU & Sensor Hardware

10. Power Management Issues • TMote Sky Typical Operating Conditions WSN Mote- MCU & Sensor Hardware

11. Power Management Issues • A pair of AA batteries – 2400 mA-hours of capacity • Mote’s Current: • Sleeping – 21 µA • Active – 23 mA • Sampling period Td = 30 sec, 4 sec active time • Battery Life Life = 2400/(4/Td)*23 +((Td-4)/Td)*0.21) = 738 hr, or 30 days WSN Mote- MCU & Sensor Hardware

12. Radio Transmit Power and Frequency – CC2420 • Ref: http://www.moteiv.com/community/Change_radio_transmit_power_and_frequency • Change frequency at compile time • Valid channels - 11 to 26 • Default channel – 11 • Env Variable setup: Export CC2420_CHANNEL=12 • Makefile inclusion: CC2420_CHANNEL=12 • Change transmit power at compile time • Preprocessor Directive: CC2420_DEF_RFPOWER • CFLAGS = -DCC2420_DEF_RFPOWER=x make mote • Power Index x: 1 through 31 • 1 == -25 dBm • 31 == 0 dBm WSN Mote- MCU & Sensor Hardware

13. Radio Transmit Power and Frequency – CC2420 • Change power or frequency at run time • Command result_t TunePreset(uint8_t rh, uint8_t channel); • Command result_t TSetRFPower(uint8_t rh, uint8_t power); • rh options • RESOURCE_NONE: for automatic resource scheduling • CC2420ResourceC component • channel • One of the valid 802.15.4 present channel: 11 – 26 • Freq = 2405 + 5(k-11) MHz, k = 11, 12, .., 26 • Power: 1 to 31 WSN Mote- MCU & Sensor Hardware

14. Clustering • Manual/Self-organizing • Support routing and data aggregation • Hierarchical structures • Multiple clusters • Cluster heads (higher ID nodes – Unique ID) • Gateways – cluster nodes • Long range communication – Cluster heads • Fault tolerance • Within a Cluster • Simple protocol for • Broadcasting • Routing • Time or frequency division multiplexing can be reused across the non-overlapping clusters • Monitoring nodes health WSN Mote- MCU & Sensor Hardware

15. Time Synchronization • Time Synchronization • Issues: • Time-based sensor reading (moving objects) • Ultrasonic, radio signals • Detection time comparison? Accuracy, sync. • Inter-node distance estimation • Local/global clock synchronization methods WSN Mote- MCU & Sensor Hardware

16. Time Synchronization (cont.) • Clock and Communication Delays • Hardware clock • Perfect clock - dC(t)/dt = 1 • Skewed clock – drifted due to temperature, humidity, etc [ 1- δ ≤ dC(t)/dt ≤ 1+ δ; δ≈10-6] • Latency in the Channel • Send time • Access time • Propagation time • Receive time WSN Mote- MCU & Sensor Hardware

17. Time Synchronization (cont.) • Move clock reading around the network and perform temporal comparisons • Intervals between events duration • Event times -> Time Intervals (mapping) • Time stamps – real time • Time differences • Temporal reasoning (more important than the exact time) • 1- δi ≤ ΔCi/Δt ≤ 1+ δi • ΔCi – local duration • Time in sender • Time in receiver WSN Mote- MCU & Sensor Hardware

18. Time Synchronization (cont.) • Interval Methods – Time Sync Protocol • Low-overhead • Scalable with network size changes • Can accommodate topology changes • Short-lived connection WSN Mote- MCU & Sensor Hardware

19. Tmote Sky – Measure Elapse Time • Elapse time: time between events • LocalTime interface • 3 basic time precisions: Components • CounterMilliC - Millisecond • Counter32khzC - 30 µs (32 kHz) • CounterMicroC - Microsecond WSN Mote- MCU & Sensor Hardware

20. Tmote Sky – Measure Elapse Time • LocalTime interface interface LocalTime<precision_tag> { async command uint32_t get(); } • Example Code: configuration MyAppC { { implementation { components MyAppP; components CounterMilliC; MyAppP.LocalTime -> CounterMilliC; } WSN Mote- MCU & Sensor Hardware

21. Tmote Sky – Measure Elapse Time • Example Code: module MyAppP { uses interface LocalTime<TMilli>; } implementation { task void some_task() { // ... t = call LocalTime.get(); // ... } } WSN Mote- MCU & Sensor Hardware

22. Time Synchronization – Reference Broadcast System (RBS) • Major Sources of Time Sync. Errors • Send time – clock propagation through node OS and radio transmitter • Access time – due to multiple access protocol • Propagation time - due to transmission through the multihop physical medium, queuing delays caused by congestion • Receive time – receive path in the radio and variable delays in interrupting the OS WSN Mote- MCU & Sensor Hardware

23. Time Synchronization – Reference Broadcast System (RBS) • Problems with time comparison protocols • Long delays/Multihop routes • Mapping time become useless • Assume that all radios are within range of a single transmitter, many of these delays are mitigated • Reference Broadcasts Protocol – Objectives of Tim Sync • Reduce delays and delay uncertainty • Establish the relative time among different clocks, while allowing the individual clocks to run freely WSN Mote- MCU & Sensor Hardware

24. Time Synchronization – Reference Broadcast System (RBS) • Sender • Send a sync reference packet (message) • The send and access times – unknown and variable, but are the same for every radio that hears any particular message broadcast • Negligible propagation time for single radio hop • Receivers • Receive the same the packet • Record TOA in their own time frame • Receive time • The only significant source of error • Due to the variability among the receivers • A sequence of broadcasts – reduce error • Exchange info among themselves • Receiver know the relative to each other, rather than to the broadcasting node WSN Mote- MCU & Sensor Hardware

25. Time Synchronization – Reference Broadcast System (RBS) • Sender • Send a sync reference packet (message) • The send and access times – unknown and variable, but are the same for every radio that hears any particular message broadcast • Negligible propagation time for single radio hop • Receivers • Receive the same the packet • Record TOA in their own time frame • Receive time • The only significant source of error • Due to the variability among the receivers • A sequence of broadcasts – reduce error • Exchange info among themselves • Receiver know the relative to each other, rather than to the broadcasting node WSN Mote- MCU & Sensor Hardware

26. Localization and Localization Services • Provide info about the world – highly localized in space and/or time • Applications • Static nodes • Mobile nodes • Location and time info • Target tracking • Habitat monitoring • How about the addition of GPS? • Landmark nodes • Outside only WSN Mote- MCU & Sensor Hardware

27. Localization and Localization Services (cont.) • Ranging Techniques • Received Signal Strength (RSS) – RF signal estimation • Distance estimation • Send/Receive Power calculation • Source signal strength, attenuated laws, RSS • Square law (not linear) – received power and distance relationship • TOA (Time of Arrival) • Time measurement (sender -> receiver) • Synchronized sender and receiver time • TDOA (Time Difference of Arrival) at two receivers • Estimate the difference in distances between the two receivers and the sender WSN Mote- MCU & Sensor Hardware

28. Localization and Localization Services (cont.) • Range-based Localization Algorithms • Location Services WSN Mote- MCU & Sensor Hardware