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XMesh Low-Power MAC Features

XMesh Low-Power MAC Features. Objectives: Motivation Overall Power Usage Profile General Low-Power Approach Network Wide Synchronization Mica2 Implementation MicaZ Implementation Interface and Usage Labs Low-power MAC Low-power XMesh. Motivation – Mote Energy Consumption.

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XMesh Low-Power MAC Features

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  1. XMesh Low-Power MAC Features Objectives: Motivation Overall Power Usage Profile General Low-Power Approach Network Wide Synchronization Mica2 Implementation MicaZ Implementation Interface and Usage Labs Low-power MAC Low-power XMesh WSN Training: XMesh Route Cntrl - Low Power

  2. Motivation – Mote Energy Consumption How much power do motes consume? Combined Total: 20 mA to 30 mA *8 MHz cpu clock, 32 khz oscillator on WSN Training: XMesh Route Cntrl - Low Power

  3. Motivation – Battery How long will motes last on 2 AA alkaline* batteries? * Note: Alkaline cells are not the only battery, but their wide availability and price point makes them a standard by which to measure performance WSN Training: XMesh Route Cntrl - Low Power

  4. Motivation – Typical Application Requirements • Many sensor network applications require battery powered motes with life times greater than one year. • Most sensor network applications have very low data rates that do not require continuous processor or network activity. • Our low power strategy implemented in the MAC layer • Power cycles the radio while maintaining communication with neighboring nodes. WSN Training: XMesh Route Cntrl - Low Power

  5. Motivation -- Estimating Average Current • Sleep • The system is in this state approximately 95% of the time. • Timer0: • This timer service is always running • For the MICAz this timer wakes every 230 msec for 400 µsec, increments a counter, and goes back to sleep • During this time the processor is using 8 mA of current. • Measure Sensor • Specific to sensor board • Affected by sensor power requirements, number and type of sensors, sample time and rate • Transmit Data • This occurs at intervals dependent on the sensor system requirements. • Without a low-power radio strategy the Mote will only last a few days (as seen in the previous slide) • We can improve battery life with a better strategy. WSN Training: XMesh Route Cntrl - Low Power

  6. Measured averaged current including health packets: 309 µA 50 msec idle to acquire sensor data Sensor power on Sensor Measure Interval Xmit data Timer Service 8 mA Current Draw of a Mote in Various Modes WSN Training: XMesh Route Cntrl - Low Power

  7. XMesh Low-Power MAC Features Objectives: Motivation General Low-Power Approach Network Wide Synchronization Mica2 Implementation MicaZ Implementation Interface and Usage Labs Low-power MAC Low-power XMesh WSN Training: XMesh Route Cntrl - Low Power

  8. General Strategy – Receiver Radio On Listening Device 1 Fixed Period Radio On Listening Device 2 (time) Fixed Period WSN Training: XMesh Route Cntrl - Low Power

  9. General Strategy – Receiver (text version) • Every node when not transmitting will periodically power on their radio in receive mode for short durations. • This period is known and fixed through out the network. WSN Training: XMesh Route Cntrl - Low Power

  10. General Strategy – Sender Radio Listen Receives wakes up & packet Device 1 (Receiver) Fixed Period Transmit data Transmit wake up Device 2 (Sender) (time) Fixed Period WSN Training: XMesh Route Cntrl - Low Power

  11. General Strategy – Sender (text version) • Before transmitting any data packets, a node will send a long wake up sequence which spans the duration of the fixed listening period first. • Any receiving node that hears the wake up sequence will keep listening until the data packet is received. Otherwise the listening node will power down the transceiver. WSN Training: XMesh Route Cntrl - Low Power

  12. XMesh Low-Power MAC Features Objectives Motivation General Low-Power Approach Network Wide Synchronization Mica2 Implementation MicaZ Implementation Interface and Usage Labs Low-power MAC Low-power XMesh WSN Training: XMesh Route Cntrl - Low Power

  13. General Strategy – Synchronized Radio Listen Receives wakes up & packet Device 1 Fixed Period Transmit data Transmit short wake up Device 2 (time) Fixed Period WSN Training: XMesh Route Cntrl - Low Power

  14. General Strategy – Synchronized (text) • If we then synchronize every node to sniff and send at the same time through out the network, then we do not always need to send a long wake up sequence. • We can shorten the wakeup sequence to within the synchronization accuracy and only send synchronization messages with long preamble. WSN Training: XMesh Route Cntrl - Low Power

  15. Network Wide Sync – Components • Disseminate time synchronization packets • Establish hierarchy graph • Propagating time stamps • Compensate for oscillator skew/drift over time WSN Training: XMesh Route Cntrl - Low Power

  16. Network Wide Sync – Disseminate Time Source (Base) 1 Hop Nodes 2 Hop Nodes 3 Hop Nodes Note: Arrows indicate transmitter and receiver of time synchronization broadcasts with long wakeup WSN Training: XMesh Route Cntrl - Low Power

  17. Network Wide Sync – Disseminate (text) • Time synchronization messages are disseminated through out the network as local broadcasts. • Every node in the network will periodically send out time synchronization messages. • Every time synchronization message is sent with a long wake up sequence to ensure that every node hears the message. WSN Training: XMesh Route Cntrl - Low Power

  18. Network Wide Sync – Authority Time Source (Base) Authority = 0 1 Hop Nodes Authority >= 2 2 Hop Nodes Authority >= 4 3 Hop Nodes Authority >= 6 WSN Training: XMesh Route Cntrl - Low Power

  19. Network Wide Sync – Authority (text) • Every time synchronization update message contains an authority value in addition to a time stamp. • The authority value of the base station is always 0. No other node may have authority equal to 0. • When a node accepts a time stamp in a time update, the Node will also adopt the authority level + 2. • Nodes will only accept time updates with an authority level lower than the authority level of the node. • Since time updates are infrequent, oscillator drift over time is tracked to improve accuracy. WSN Training: XMesh Route Cntrl - Low Power

  20. Propagating Time Stamps Time Stamp Taken. Inserted into Paylaod Time Sync packet queued for transmission Start Preamble / Wakeup Sequence Transmission Start of Packet Payload Queueing Delay Backoff Preamble + Wakeup Sequence Start Symbol Packet Transmission Transit Delay RX IDLE / SLEEP SYNC Packet Reception New Time = Time Stamp + Transit Delay WSN Training: XMesh Route Cntrl - Low Power

  21. interface RadioCoordinator { /** * This event indicates that the start symbol has been detected * and its offset */ async event void startSymbol(uint8_t bitsPerBlock, uint8_t offset, TOS_MsgPtr msgBuff); /** * This event indicates that another byte of the current packet has been rxd */ async event void byte(TOS_MsgPtr msg, uint8_t byteCount); /** * Signals the start of processing of a new block by the radio. This * event is signaled regardless of the state of the radio. This * function is currently used to aid radio-based time synchronization. */ async event void blockTimer(); } RadioCoordinator is used for time stamping Low level MAC features generate interrupts through the RadioCoordinator interface when packet transmissions are initiated. In this way time stamps can be taken without the ambiguity cause by undetermined delay in the stack. nesC Interface – RadioCoordinator WSN Training: XMesh Route Cntrl - Low Power

  22. Compensate For Oscillator Skew/Drift Over Time TimeSource = Skew * TimeRemote + RemoveOffset • The worest case skew between any 2 nodes over temperature will not exceed 50ppm. • Typical skew between nodes is usually < 10ppm. • Over a 10 minute interval, worest case drift will be 6 to 30 ms. • Essentially every node synchronizes to the base station, the drift caused by the crystal can be track and eliminated via the forum above. WSN Training: XMesh Route Cntrl - Low Power

  23. XMesh Low-Power MAC Features Objectives Motivation General Low-Power Approach Network Wide Synchronization Mica2 Implementation MicaZ Implementation Interface and Usage Labs Low-power MAC Low-power XMesh WSN Training: XMesh Route Cntrl - Low Power

  24. Implementation • The wake sequence is implemented differently between the MICA2 and MICAz platforms. • The MICA2 platform uses a byte radio • The wake up sequence is implemented by increasing the preamble of the data packet. • The MICAz platform uses a packet based radio • The length of packets is fixed • Long preambles are implemented as series of small packets WSN Training: XMesh Route Cntrl - Low Power

  25. MICA2 Implementation – Unsynchronized time 125 ms 125 ms 125 ms 125 ms Sender data preamble Receiver data Receiver data WSN Training: XMesh Route Cntrl - Low Power

  26. MICA2 Implementation – Unsynchronized (text) • Long Preamble: • Every data packet will be sent with an extended preamble as the wake up sequence. • In this example the preamble length is 140 ms. • Algorithm: • Wake up 8 times per second • Sniff radio channel • If preamble, receive data • If clear, send if needed, else sleep WSN Training: XMesh Route Cntrl - Low Power

  27. MICA2 Implementation – Synchronized time 125 ms 125 ms 125 ms 125 ms Sender data preamble Receiver data Receiver data WSN Training: XMesh Route Cntrl - Low Power

  28. MICA2 Implementation – Synchronized (text) • Algorithm • Every node in the network synchronizes to sniff and send at the same moments • In this example it is every 125 msec. • Senders and receivers are synchronized so data packets do not need long preambles. WSN Training: XMesh Route Cntrl - Low Power

  29. MICA2 Implementation – Synchronized time 125 ms 125 ms 125 ms 125 ms Sender data preamble Receiver data Receiver data WSN Training: XMesh Route Cntrl - Low Power

  30. MICA2 Implementation – Sniff Timing Fast Channel check: 140 µsec WSN Training: XMesh Route Cntrl - Low Power

  31. MICA2 Implementation – Sniff Current Draw WSN Training: XMesh Route Cntrl - Low Power

  32. MICA2 Implementation -- Performance • Testbed: 20 MICA2 • Majority of the nodes 2 hops from the base station • Estimated battery lifetime • 1.2 years @ 3-minute reporting intervals • Battery life depends on type of sensor(s) attached to node. WSN Training: XMesh Route Cntrl - Low Power

  33. τ MICAz Implementation -- Unsynchronized Sender τ Receiver Transmit Wakeup packet sequence Link Lvl Ack Sniff for activity Transmit data packet Rx Wake Up + Data Packets Rx Link Lvl Ack WSN Training: XMesh Route Cntrl - Low Power

  34. MICAz Implementation -- Text • Long Preamble: • Every data packet will be sent with a wake up sequence composed of a series of short packets. • In this example the sequence length is 135 ms. • Algorithm: • Wake up 8 times per second • Sniff radio channel • If any packets detected, receive data • If clear, send if needed, else sleep WSN Training: XMesh Route Cntrl - Low Power

  35. MICAz Implementation – Sniff Current Draw WSN Training: XMesh Route Cntrl - Low Power

  36. MICAz Implementation • Moteworks 2.0 • Only asynchronous low power available for MICAz • Synchronized version available in MW 2.2 • Estimated battery lifetime • 400 A @ 8 sniffs per second and no traffic • 700 A @ one sensor sample and send per 3 minutes • ~4 month on two AA alkaline cells • Battery life depends on type of sensor(s) attached to node. WSN Training: XMesh Route Cntrl - Low Power

  37. Lab on Low-Power MAC Applications: CountSend CountReceive WSN Training: XMesh Route Cntrl - Low Power

  38. Lab – Part 1: Low Power MAC • Background • The low power features of XMesh is implemented in the MAC layer. • It is thus possible to enable low power in applications that do not use a networking layer. • In this lab we will compile two programs, CountSend and CountReceive to use a low-power MAC. • File Location • CountSend: Moteworks/apps/general/CountSend • CountRecv: Moteworks/apps/general/CountReceive • Notes • This lab requires two Motes • We recommended that you enable low power is via the route,lp flag at compile time for both applications • The following examples assumes a MIB510 on COM1 therefore adjust as necessary WSN Training: XMesh Route Cntrl - Low Power

  39. Example for MICAz being flashed on a MIB520 Example for MICA2 being flashed on a MIB520 Lab Step 1: High Power MAC Compile & Flash After flashing is done, remove Mote 1 and attach Mote 2 to MIB $ cd /opt/Moteworks/apps/general/CountSend $ make micaz route,hp install mib520,COM<#> $ cd /opt/Moteworks/apps/general/CountReceive $make micaz route,hp install mib520,COM<#> After flashing is done, remove Mote 1 and attach Mote 2 to MIB $ cd /opt/Moteworks/apps/general/CountSend $ make mica2 route,hp install mib520,COM<#> $ cd /opt/Moteworks/apps/general/CountReceive $ make mica2 route,hp install mib520,COM<#> But use the appropriate <programmer> and COM port# or IP Address WSN Training: XMesh Route Cntrl - Low Power

  40. Example for MICAz being flashed on a MIB520 Example for MICA2 being flashed on a MIB520 Lab Step 2: Low Power MAC Compile & Flash After flashing is done, remove Mote 1 and attach Mote 2 to MIB $ cd /opt/Moteworks/apps/general/CountSend $ make micaz route,lp install mib520,COM<#> $ cd /opt/Moteworks/apps/general/CountReceive $make micaz route,lp install mib520,COM<#> After flashing is done, remove Mote 1 and attach Mote 2 to MIB $ cd /opt/Moteworks/apps/general/CountSend $ make mica2 route,lp install mib520,COM<#> $ cd /opt/Moteworks/apps/general/CountReceive $ make mica2 route,lp install mib520,COM<#> But use the appropriate <programmer> and COM port# or IP Address WSN Training: XMesh Route Cntrl - Low Power

  41. Lab Notes: Low Power Enabling an XMesh App • Usage • The low power feature can be enable in any XMesh-enabled application in the same manner. • Go to any application that is XMesh enabled and use the route,lp flag during compilation. • For instance, try it with MyApp_Mesh • Notes • The low power feature is meant for applications that run at low duty cycles • There is always a trade off between sampling rate, duty cycle, and power. • For example is not feasible to expect a high sampling data rate and high duty cycle application to last very long running solely on batteries. WSN Training: XMesh Route Cntrl - Low Power

  42. Q & A WSN Training: XMesh Route Cntrl - Low Power

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