Jan M. Rabaey

1
Ultra-low power and ultra-low costwireless
sensor nodes An integrated perspective

• Jan M. Rabaey
• EECS Dept.
• Univ. of California, Berkeley

2
PicoRadios - The Original Mission

• Meso-scale low-cost radios for ubiquitous
  wireless data acquisition that
• are fully integrated
• Size smaller than 1 cm3
• minimize power/energy dissipation
• Limiting power dissipation to 100 mW
  enables energy scavenging
• and form self-configuring ad-hoc networks
  containing 100s to 1000s of nodes

Still valid, but pushing the limits ever further
3
The Incredibly Shrinking Radio
PA Test
LNATest
TX1
Passive Test Structures

• Technology 0.13 mm CMOS combined with
  off-chip FBARs
• Carrier frequency 1.9 GHz
• 0 dBm OOK
• Two Channels
• Channel Spacing 50MHz
• 40 kbps/channel
• Total area lt 8 mm2

Diff Osc
Receiver
4 mm
Env Det Test
TX2
RF Amp Test
4
Wireless Sensor Network Protocol Processor

Technology 0.13µ CMOS
Chip Size 3mm x 2.75mm 8.2 mm2
Transistor Count 3.2M
Gate Count 62.5K gates
Clocks Freqs 16MHz(Main), 1MHz(BB)
On Chip memory 68Kbytes
Core Supply Voltages 1V(High) 0.3V(Low)
On_Power lt 1 mW
Standby Power mWs
Integrates all digital protocol and applications
functions ofwireless sensor node
In fab (Jan 04)
Runs reliable and energy-optimizedprotocol stack
(from application level down)
5
The Road towards a First Integrated PicoNode
Digital Network Processor
Flash Storage
20MHz Clock Source
Board Design In Process
Powertrain
Solar Cell
Voltage Supply
Voltage Supply
Voltage Supply
Sensor1
Sensor2
RF Transceiver
PrgThresh0
PrgThresh1
Tx0
Tx2
User Interface
OOK Receiver
OOK Transmitter
SIF sensor interface
6
Energy-Scavenging becoming a Reality

• Demonstrate a self contained 1.9GHz transmitter -
  powered only by Solar Vibrational scavenged
  energy
• Push integration limits - limited by dimensions
  of solar cell

Front
Front
regulator
cap
Tx COB
7
Perspectives Where are we heading?

• Extrapolating towards the future how far can we
  push cost, size, and power?
• Ultra-dense sensor networks (smart surfaces)
  enabled by sub 10 mW nodes.
• Cutting RF power by at least another factor of 5
  (if not more)
• Pushing the boundaries on voltage scaling
• Focus on the application perspective
• A Service-based Application Interface for Sensor
  Networks
• Focus on issues such as portability, universality
  , scalability, and ad-hoc deployment

8
An Application Perspective to Sensor Networks
A plethora of implementation strategies emerging,
some of them being translated into standards
TinyOs/TinyDB

• The juggernaut is rolling but is it the right
  approach?
• Bottom-up definition without perspective on
  interoperability and portability
• Little reflection on how this translates into
  applications

9
A Quest A Universal Application Interface (AI)
for Sensor Networks

• Supports essential services such as queries,
  commands, time synchronization, localization, and
  concepts repository
• Similar in concept to the socket interface in the
  internet
• Provides a single point for providing
  interoperability
• Independent of implementation architecture and
  hardware platform
• Allows for alternative PHY, MAC, and Network
  approaches and keeps the door open for innovation

10
SNSP Status (joint project with GSRC (ASV) and
TU Berlin)

• White paper completed and in feedback gathering
  mode (http//bwrc.eecs.berkeley.edu/research/picor
  adio/...)
• Very positive support so far (both from industry
  and academia)
• Next targets
• Further evolve document (start working group)
• Demonstrate feasibility by implementation on at
  least two test beds
• Address number of issues left open for research
  (e.g. implementation approaches for naming,
  synchronization, localization, and concept
  repository services)
• Currently in process of acquiring funding (NSF,
  European Commission, CEC, )

11
Extrapolation of the low-power theme Ultra-dense
sensor networks

• How to get nodes substantially smaller and
  cheaper (real mm3 nodes) get them closer, use
  lots of them, and make their energy consumption
  absolutely minimal (this is lt 10 mW).
• Smart surfaces plane wings, smart construction
  materials, intelligent walls
• How to get there? Go absolutely non-traditional!
• Use non-tuned mostly passive radios center
  carrier frequency randomly distributed
• Use statistical distribution to ensure reliable
  data propagation

12
On the RoadReducing RF power by another factor
of 5

• Providing gain at minimal current The
  Super-regenerative Receiver

Back from fab any day
13
Realizing sub-50 mW receivers
Example sub-threshold RF oscillatorusing
integrated LCs (in fab)
Simulated Performance
Supply voltage 0.5 1.2V
Current consumption 150µA
Oscillation frequency 1.5GHz
Differential output swing 150mV (Vdd500mV)
Phase noise -100dBc/Hz _at_1MHz offset
Next step mostly untuned radios and lots of
them Combine with purely statistical routing (in
collaboration with Kannan)
14
Ultra-Low Voltage (ULV) Digital Design

• Aggressive voltage scaling the premier way of
  reducing power consumption Performance not an
  issue
• Our goals design at 250 mV or below
• Challenges
• Wide variation in gate performance due to
  variability of thresholds and device dimensions
• Sensitivity to dynamic errors due to noise and
  particle-caused upsets (soft errors)
• ? Explore circuit and architecture techniques
  that deal with performance variations and are
  (somewhat) resilient to errors!

Idea Self-adapting approach to ULV Status
White paper