UWB Localization Techniques

1
Project IEEE P802.15 Working Group for Wireless
Personal Area Networks (WPANs) Submission Title
UWB Localization Techniques Date Submitted 10
August 2004 Source Benoit Denis Company
CEA/LETI, STMicroelectronics Address 17 rue des
Martyrs, F 38054 Grenoble cedex 9, FRANCE
(CEA/LETI) 39 ch. du Champ des
Filles CH - 1228 Plan-les-Ouates, SWITZERLAND
(STMicroelectronics) Voice(33)(0)4 38 78 58 11,
FAX [phone], E-Maildenisbe_at_chartreu
se.cea.fr Re TG4a Ranging Subcommittee
Time-of-Arrival Algorithms Abstract This
document describes classical UWB TOA ranging /
localization algorithms Purpose In support of
TG4a Ranging Subcommittee work. Notice This
document has been prepared to assist the IEEE
P802.15. It is offered as a basis for discussion
and is not binding on the contributing
individual(s) or organization(s). The material in
this document is subject to change in form and
content after further study. The contributor(s)
reserve(s) the right to add, amend or withdraw
material contained herein. Release The
contributor acknowledges and accepts that this
contribution becomes the property of IEEE and may
be made publicly available by P802.15.
2
UWB Localization Techniques
Benoît DENIS
benoit.denis_at_cea.fr
Fusing Accurate Positioning Capabilities and
Digital Communications
3
Time Of Arrival (TOA) Two Way Ranging (TWR)
T1
To
Terminal A TX/RX
Terminal B RX/TX
TOF
TOF
TReply
Terminal A
Prescribed Protocol Delay and/or Processing Time
Terminal B
4
Time Of Arrival (TOA) Two Way Ranging (TWR)
Is the frequency offset relative to the nominal
ideal frequency

• Range estimation is affected by
• Relative clock drift between A and B
• Clock accuracy in A and B
• Prescribed response delay

• Relaxing constraints on clock accuracy by
• Performing fine drift estimation/compensation
• Benefiting from cooperative transactions
  (estimated clock ratios)
• Adjusting protocol durations (time stamp)

5
Ex DEV2PNC Ranging in the 802.15.3 Scenario
MAC resources for a double DEV2PNC TWR Transaction

• Beacon synchronization (PNC2DEV)

DEV-C
DEV-A

• Association procedure in MCTA slots

Imm-ACK or Dly-ACK (PNC2DEV) Association
Request (DEV2PNC)

• Time stamp (fixed retransmission times T)

DEV-B
PNC

• Relative clock drift DEV / PNC available

• Correction of DEVs Time Offset (propagation
  delay from PNC)

PicoNet Synchronization
MCTA (Slotted Aloha)
6
Time Of Arrival (TOA) One Way Ranging (OWR)
If Terminals are synchronized to a common clock,
direct OWR can be used for Ranging
To
T1
Terminal A TX
Isochronous
Terminal B RX
TOF
Terminal A
TOF Estimation
Terminal B
7
Ex DEV2DEV Ranging in the 802.15.3 Scenario
MAC resources for a single DEV2DEV OWR
Transaction Guaranteed Time Slots in the CTA can
be used between isochronous DEVs (i.e. with
common reference start times)
DEV-A
RefPNCTs
RefPNC 2Ts
RefPNC
DEV-B
DEV-A
DEV-B
DEV-C
Slot 1
Slot 2
Slot 3
CTA
8
Time Of Arrival (TOA) One Way Ranging (OWR)
Main Limitations / Impact of Synchronization and
Clock Drifts on Perceived Time
Is the frequency offset relative to the nominal
ideal frequency

• Range estimation is affected by
• Clock accuracy
• Uncertainty on the reference start times
  (synchronization)

• Requirements
• Achieving fine synchronization between terminals
  prior to ranging

9
Positioning from TOA
3 anchors with known positions (at least) are
required to retrieve a 2D-position from 3 TOAs
Specific Positioning Algorithms
10
Time Difference Of Arrival (TDOA) One Way
Ranging (OWR)
TDOA Estimation
Mobile TX
TOA Estimation
To
TOF,1
Anchor 1
Anchor 1 RX
T1
TOF,2
Anchor 2 RX
T2
Mobile
TOF,3
Anchor 3 RX
Anchor 2
T3
Anchor 3
Passive Location
Isochronous
11
Positioning from TDOA
3 anchors with known positions (at least) are
required to find a 2D-position from a couple of
TDOAs
Specific Positioning Algorithms
12
Ex. of Possible Embodiment for TDOA/OWR based
Systems
Serial Data Link Timing Ref Clock
RF RX Timing Pulse Processor
RF RX Timing Pulse Processor
RF RX Timing Pulse Processor
Known Fixed Locations
RF RX Timing Pulse Processor
Base Control Unit
Short Transmitted Packets Asynchronous TX Tags
Infrequent Packet Collisions
13
Received Signal Strength Indicator (RSSI)

• Power Strength could be an alternative solution
  to TOA/TDOA in the UWB Context
• Lower requirements in terms of synchronization
  and clock precision

• But
• RSSI requires precise channel behavioral model
• RSSI is sensitive to channel inconstancy and
  non-stationarity
• RSSI does not benefit from UWB high resolution

14
Angle Of Arrival (AOA)

• AOA could be an alternative solution to TOA/TDOA
  in the UWB Context
• Lower requirements in terms of synchronization
  and clock precision
• Two anchors are sufficient for 2D-positioning

• But
• UWB Arrays Antennas technology may be not mature
• AOA requires precise calibration at anchor nodes
• Cost increases with size and size may not be
  reduced
• The number of elements in the array highly
  depends on the radio environment