Supplemental Material on

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Supplemental Material on

• Lectures 12, 13, 14

2
Source Laurent Chalard, Didier Hélal,
Gian-Mario Maggio, Yinqwei Qiu,Lucille
Verbaere-Rouault, Armin Wellig, Julien Zory
STMicroelectronics, Geneva, Switzerland
Implementation challenges of UWB for sensor
networks

• UWB4SN 2005 workshop on UWB for Sensor Networks
  , EPFL 2005

3
A problem under constraints
Market understanding
Complete mote solution
Competitive advantage
Innovative WSN solutions
Standard compliancy
STs technology compatibility
4
Major Limitations to Global Wireless Sensor
Adoption
Ease/install
Reliability
Interference
Battery
Cost
Interoperability
Security
Bit rate
No need
Size
Source ON-World 2004
5
Application requirementsexpressed at IEEE
802.15.4a
Low data rate does not mean simple !
ranging with accuracy inside 5 of range
6
Regulation

• No harmonization done by ITU-R so far
• EC final decision in March 2006
• Low data rate is still under discussions
• duty cycle
• Minimum average burst repetition period over an
  hour
• 1 sec
• Minimum instantaneous burst repetition period
  over 1 second
• 30 to 200ms
• emission level limitation
• -41.3dBm/MHz or -45dBm/MHz

7
Standardization (1)

• Standards has exhibited limitations up to know
  for wireless sensor network applications
• 802.15.4 poor reliability
• Zigbee too complex
• WiFi too expensive
• BT limited in number of nodes
• Now appear 3 different alternate PHY options in
  IEEE 802.15.4a
• Low-band UWB DC-960MHz
• Chirp Spread Spectrum 2.4GHz ISM band
• High band UWB 3.1-10.6GHz

8
Standardization (2)

• IEEE 802.15.4a status
• Band plan defined
• PRF will be a multiple of 7.21875MHz
• Perfect Balanced Ternary Sequences (PBTS) of
  length 31 and 127 have been agreed.
• All systems should support a mandatory
  non-coherent mode
• Still 6 Forward Error Correction proposals (Super
  Orthogonal Codes, Convolutional codes)

9
Mote Complete Solution

• Fully integrated wireless sensor devices
• Small lt 1cm3 (System-in-Package )
• Cheap lt1 (low cost electronics)
• Low power lt10mW peak
• Operate from energy scavenging lt100uW average

10
STMicroelectronics ASTareas of work in WSN

• 802.15.4 / ZigBee (PHY, MAC and networking
  protocol)
• UWB Physical Layer
• Localization enabled networking
• Target is convergence !

11
Synchronization (1)

• Context
• Inaccurate reference clocks (typ. gtgt 1ppm)
• Multi-user, asynchronous random communications
• Low SNR gt Need for pulse energy accumulation (CI
  and/or MF, etc.)
• Short pulses gt down-convert to limit processing
  speed
• Synchronization shall overcome
• Jitter (reference clock PLL)
• Drift between motes clocks (frequency offset)
• Noise
• Interferences
• multi-user
• Mobility
• etc.

12
Synchronization (2)

• A few illustrative numbers
• Coherency time of a 500MHz pulse is in the order
  of 100ps
• Preamble duration is between 1us and 33us
• Possible drift due to oscillator's accuracy
• Over 1us, 10ppm to 10ps, 40ppm to 40ps
• Over 33us, 10ppm to 330ps, 40ppm to 1.32ns
• Hence a few design challenges
• Acquisition/detection
• How to coherently accumulate energy?
• How to estimate frequency drift, so as to relax
  tracking requirements?
• Tracking
• How to do it on a non-continuous signal?
• How to do it with minimum complexity?

13
Symmetric Double Sided-Two Way Ranging
(SDS -TWR)
Device A
Device B
Device B
Time of flight
TOF
TReplyB gtgt TOF
TRoundA
reply time
TOF
TOF
TReplyA ? TReplyB
TRoundB ? TReplyB
TOF
(IEEE 802.15.4a Nanotron)