Berkeley NEST Wireless OEP 901 Progress and Plans

1
Berkeley NEST Wireless OEP9/01 Progress and
Plans

• David Culler
• Eric Brewer Dave Wagner
• Shankar Sastry Kris Pister
• University of California, Berkeley

2
Outline

• OEP v1 requirements
• OEP v1 hardware design
• Key OEP Software Developments
• experience at scale
• network programming
• robust bcast/multicast action
• large-scale simulator
• Working across abstractions
• signal strength info
• time synchronization support
• power-efficient wake up
• Plans

3
Design Requirements

• Deliver complete kits in Jan 02
• More storage,
• More storage,
• More ...
• More communication bandwidth
• More capability available to sensor boards
• stable voltage reference
• retain cubic inch form factor and AA/year power
  budget
• allow opportunities for new approaches
• time synchronization
• other algorithms

4
Major features

• 16x program memory size (128 KB)
• 8x data memory size (4 KB)
• 16x secondary storage (512 KB)
• 5x radio bandwidth (50 Kb/s)
• 6 ADC channels available
• Same processor performance
• Allows for external SRAM expansion
• Provides sub microsecond RF synchronization
  primitive
• Provides unique serial IDs
• On-board DC booster
• Remains Compatible with Rene Hardware and current
  tool chain

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In a nutshell

• Atmel ATMEGA103
• 4 Mhz 8-bit CPU
• 128KB Instruction Memory
• 4KB RAM
• 4 Mbit flash (AT45DB041B)
• SPI interface
• 1-4 uj/bit r/w
• RFM TR1000 radio
• 50 kb/s
• Network programming
• Same 51-pin connector
• Analog compare interrupts
• Same tool chain

Cost-effective power source
2xAA form factor
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Microcontroller

• Conducted extensive comparison of alternatives
• narrowed list based on availability and design
  size
• Deep study of prime candidates
• ATmega 163 same pinout as 8535, 2x mem, reprog
• ARM Thumb greater perf, poor integration, slow
  radio
• TI MSP340 Low power, HW , 2-buffered SPI tx,
  no gcc
• ATMEGA 103 storage!, integration, compatibility
• Selected Atmel ATMEGA103
• 4 Mhz 8-bit CPU
• 128KB Instruction Memory (16x increase from Rene)
• 4KB RAM (8x increase from Rene)
• Compatible with Rene CPU and tools
• able to support high bandwidth radio techniques
• Re-programmable over Radio or Connector

7
Radio

• Retained RFM TR1000 916 Mhz radio
• Developed circuit able to operate in OOK (10
  kb/s) to ASK (115 kb/s) mode
• smaller prate resistor, race-conditional
  work-around
• pwidth res. tied to vcc to push to maximum sample
  rate
• decrease baseband capacitor to increase RF
  sensitivity
• Design SPI-based circuit to drive radio at full
  speed
• current bit-level edge detect on 10 kb/s preamble
• analog comparator to find high speed edge
• SPI synch. serializer to drive/receive bits
• resynch on every byte
• full speed on TI MSP, 50 kb/s on ATMEGA
• Improved Digitally controlled TX strength DS1804
  
• 1 ft to 300 ft transmission range, 100 steps
• Input timing capture /- .5 us on RX pin.
• Receive signal strength detector
• software integration

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Network Programming and Storage

• ATMEGA103 in-circuit, but external reprog.
• retain secondary co-processor
• AT90LS2343 only small device with internal clock
  and in-circuit programming
• 4 Mbit flash (AT45DB041B)
• Store code images, Sensor Readings and
  Calibration tables
• 16x increase in prog. mem too large for EEPROM
  solution
• forced to use FLASH option
• SPI Protocol instead of I2C!
• radio is using HW SPI support
• Novel multiplexing of 6 I/O pins on 2343 to drive
  7 signals to interface to Flash SPI and 103
• relies on remembering a previous control bit

9
Power

• Developed Energy-harvesting design with solar
  cells, superCaps, and DC booster
• Built components for Intel power regulator board
• Studied wake-up transients
• Incorporated On-board Voltage Regulation
  (Maxim1678)
• Boost Converter provides stable 3V supply
• Stabilizes RF performance
• Allows variety of power sources
• Can run on batteries down to 1.1 V
• Incorporated power supply sensor
• Can measure battery health
• used to adjust wake-up threshold for unregulated
  design
• added line to disable vcc to pot
• reduce standby current

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Timing, Identity, and Output

• Retain Dual Oscillator Design
• High Accuracy 32.768 crystal for real-time
  measurement and synchronization
• 4 MHz oscillator
• developed design with resonator
• required software recalibration
• Electronic 64-bit serial number (DS2401)
• one-wire protocol
• 3 LEDs

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Expansion Capabilities

• Backwards compatible to existing sensor boards
• eliminated i2c-2 (was for EEPROM, which is now
  ext. SPI)
• eliminated UART2
• added two analog compare lines
• added five interrupt lines (were unknown)
• added two PWM lines
• 6 ADC channels
• 10 bits/sample
• 10K samples/second
• I2C Expansion Bus (i2c-1)
• SPI Expansion Bus
• 8 Digital I/O or Power Control Lines (was 4)
• Can connect external SRAM for CPU data memory (up
  to 64KB)
• lose most sensor capability
• address lines share with lowest priority devices
  (LEDS, Flash ctrl)
• still allows radio, flash, and programming

12
Sensor Board

• Light
• Temperature
• 2D Accelerometer
• Acoustic threshold detector

13
Why not ARM Thumb ?

• CPU switch requires establishing a new tool chain
  (compiler, linker, programmer) that would be
  untested
• Peripheral support around Atmel AT91 does not
  allow for high bit rate RF communication
• Power consumption of high clock rates is still
  prohibitively high
• Very interesting to pursue in integrated core
  design
• see SYCHIP (arm thumb gps)

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Why Not Faster/Different Radio?

• RFM TR1000 is the lowest power RF Transceiver on
  the market
• High speed radios usually come with digital
  protocol logic forcing users into set
  communication regimes
• Raw interface to the RF transmission allows for
  exploration of new communication paradigms
  (Proximity Mode and Sleep)

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Key TinyOS developments

• Initial visualization
• Network programming
• RF Localization support
• Robust command broadcast
• Aggregation
• Query by schema
• Calibration
• Breaking boundaries
• power efficient wake up
• robust sample-based proximity

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Testing at Scale

• In collaboration with Intel produced 1,000
  compressed node
• size of quarter, stack 4 high with battery
• used ATMEGA 163 (2x rene)
• Stressed software components, manufacturing,
  testing
• Goal was live demonstration of network discovery
  in realistic setting
• many people in a large space

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Network programming

• Suite of handlers to support NP
• start new program upload
• write fragment i to 2nd store (EEPROM) incl.
  checksum
• read fragment map i
• initiate reload
• including verification
• Boot loader on little guy
• transfers complete, check-summed fragment set to
  main controller
• reset
• Demonstrated up 113 nodes in single cell mode
• Multihop version preliminary operation
• disseminate fragments
• aggregate verifications
• Integrated into generic_comm

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Ad Hoc MCAST Radio Cells
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ad hoc MCAST
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Multihop Network Topology
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Robust network command mcast

• Higher-level middleware component
• rooted at any node
• novel primitives
• squelch retransmission
• amorphous mcast
• many applications
• discovery, act, acquire data
• Huge potential redundancy at scale
• traditional elect and maintain cluster heads
• alternative probabilistic forwarding
• Many factors influence propagation dynamics
• early retransmit have many children
• fast, turbulent wavefront
• later collisions reduce redundancy

if (new mcast) then take action retransmit
modified request
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Example
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Surge II viz sensor field network
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Aggregation

• process data across set of nodes within the
  network
• vector logical, sum, ave, median, percentile, ...
• Dynamic physical structure
• View as time series aggregation rooted at a node
• Each level pushes request deeper then streams
  partial results
• Often can allow child to push result to multiple
  parents

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Query by schema

• Nodes contain schema of what data they contain
• id, hw config, version, temp, light, ...
• Can request the schema
• Can request elements of schema
• Requests may be one time, periodic, on threshold,
  ...

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TOSSIM

• Discrete event simulation for large sensor
  networks
• Provides implementation of hardware abstractions
• Individual rf modulation events, sensor events,
  clock events
• existing applications work
• Exploits TinyOS event driven structure
• host emulation down to HW abstraction
• redefine TOS macros and scheduler
• Allows debugging of distributed algorithms
• Proper execution verified up to 1000 motes
• Currently Static error-free connection topology

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TOSSIM Performance

• Executing for 10 seconds of virtual time

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Power Efficient Wake up

• minimize listening in communicating event to many
  nodes
• via messages
• must transmit for 1.e x sleep interval
• may have to wait (actively) for n neighbors
• receiver must lock onto message, may get many
• for all nodes awake after lt 2 rounds
• listen 1 sec with 8 sec asleep, 16 sec announce
• via sampling base-band tone
• detect any send
• does not matter that rx 0
• short listen
• 200 us listen with 4 sec sleep, 10 sec announce
• density independent

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Sample-based Proximity Count

• minimize listening in communicating small amount
  of data to many nodes
• extend tone approach with sampling
• sequence of events, each node transmits with
  known probability
• infer count based on frequency of null events
• density independent

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Challenge Application Series

• Sensing and Updates of the Environment in
  Response to Events and Queries.
• monitor the environment of a building and use
  this to instigate control actions such as
  lighting, HVAC, air-conditioning, alarms, locks,
  isolation, etc.
• monitor and protect space from environmental
  attack
• Distributed Map Building
• classic art gallery problem is provably hard
• many agents with simple proximity sensors to
  detect obstacles
• exchange info gt dense collaborative map building
• Pursuit Evasion Games
• combination of map building and intent
  determination by both teams using networks of
  motes with possible information attacks and
  mis-information from the two teams

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Component Challenge localization

• given
• graph of localized measurements Cij
• and locations of certain marker nodes Pi
  xi,yi,zi
• to within some tolerance
• compute locations of remaining nodes using the
  communication available among the nodes
• gt distributed constraint solving
• goodness metrics
• location estimation error
• size and shape of marker set
• complexity (time, proc, communication, energy)
• robustness
• rate of convergence
• variations
• small subset of more powerful nodes with more comm

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RF localization support

• RFM baseband output provided to ADC
• Signal strength component collects samples
• computes average over well-define preamble
• traditional solution would build HW integration
  circuit
• Provided to application components as part of
  packet envelope
• accessible to packet handler
• Signal strength control to change cell size
• Preliminary studies of range of localization
  algorithms

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Closing the loop more

• detect and track plume
• moving node
• moving light/hot region
• network actively adapts to expend energy sensing
  in region surrounding plume
• actively adapts to convey packets through rest of
  network
• time synchronization
• correlate multiple readings
• orchestrate multihop transfer schedule

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Component challenge time synch

• Synchronize local clocks to specified tolerance
• Need means of verifying success
• use high precision clocks at edges and fast
  network between
• Novel system support
• to communicate over the radio, transmitter and
  receive are synchronized to fraction of a bit
• - .5 us
• can timestamp particular bit in message to this
  accuracy
• gt message carries info on time and place of
  origin

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Conclusions

• HW platform development on schedule
• SW platform exercised in many distinct dimensions
• Demonstrates possibility of working across
  traditional layers in distributed system
• Novel algorithmic basis
• Formulating well-define subproblems for
  determination of best of breed algorithms