1. UWB Localization Techniques
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Benoît DENIS CEA LETI DSIS/SSIT/AST
Fusing Accurate Positioning Capabilities and Digital Communications

2. Prescribed Protocol Delay and/or Processing Time
Time Of Arrival (TOA) & Two Way Ranging (TWR) To T1
Terminal A TX/RX
Asynchronous
Terminal B RX/TX
TOF
TReply
TOF
TOF Estimation
Cooperative Ranging
Terminal A
Prescribed Protocol Delay and/or Processing Time
Request
TOF Estimation
Answer
Terminal B

3. Time Of Arrival (TOA) & Two Way Ranging (TWR)
Main Limitations / Impact of Clock Drift on Perceived Time
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…)

4. Request (Medium Access)
Ex : DEV2PNC Ranging in the Scenario
MAC ressources for a double DEV2PNC TWR Transaction
Beacon synchronization (PNC2DEV)
Association procedure in MCTA slots
DEV-C
DEV-A
Imm-ACK or Dly-ACK (PNC2DEV) & Association Request (DEV2PNC)
Time stamp (fixed retransmission times T’)
DEV-B
Relative clock drift DEV / PNC available
PNC
Correction of DEV’s Time Offset (propagation delay from PNC)
Acknowledgement
Transmiting to DEV PNC’s TOF Estimate
TOF
DEV’s TOF Estimate
Receiving PNC’s TOF Estimate
TOF
PNC
DEV
RefDEV
RefPNC
T1’ T1
Beacon Detection
TOF
Request (Medium Access)
T2’ T2
PNC’s TOF Estimate
PicoNet Synchronization
MCTA (Slotted Aloha)

5. 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
TOF Estimation
Terminal A
Request
TOF Estimation
Terminal B
Isochronous

6. Ex : DEV2DEV Ranging in the 802.15.3 Scenario
MAC ressources 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-C
DEV-A
RefPNC+Ts
TCA
DEV-A’s Estimate of TCA
RefPNC+ 2Ts
RefPNC
DEV-B
PNC
TAB
DEV-B’s Estimate of TAB
TBC
DEV-C’s Estimate of TBC
DEV-A
DEV-B
DEV-C
Slot 1
Slot 2
Slot 3
CTA

7. Time Of Arrival (TOA) & One Way Ranging (OWR)
Main Limitations / Impact of 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 (prior phase synchronization)
Requirements
Achieving fine synchronization between terminals prior to ranging

8. Positioning from TOA
Mobile (xm,ym)
Anchor 2 (xA2,yA2)
Anchor 3 (xA3,yA3)
Anchor 1 (xA1,yA1)
3 anchors with known positions (at least) are required to retrieve a 2D-position from 3 TOAs
Measurements
Estimated Position

9. Time Difference Of Arrival (TDOA) & One Way Ranging (OWR)
TDOA Estimation
Mobile TX
TOA Estimation To
Anchor 1
TOF,1
Anchor 1 RX
Info T3
Info T2
Isochronous
Info T2
Info T3 T1
TOF,2
Anchor 2 RX
Mobile T2
TOF,3
Anchor 3 RX
Anchor 2
Anchor 3 T3
Passive Location
Isochronous
TOA Estimation
TDOA Estimation

10. Positioning from TDOA
Mobile
Anchor 1
Anchor 2
Anchor 3
3 anchors with known positions (at least) are required to find a 2D-position from a couple of TDOAs
Measurements
Estimated Position

11. Ex. of Existing Embodiment for TDOA/OWR based Systems
EX: MSSI’s 3-D PAL System
Serial Data Link + Timing Ref Clock
RF RX & Timing Pulse Processor
RF RX & Timing Pulse Processor
Tag
Asynchronous Tags to be localized
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

12. Received Signal Strength Indicator (RSSI)
Power Strenght 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

13. AOA could be an alternative solution to TOA/TDOA in the UWB Context
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 nodes are sufficient for 2D-positioning
But
UWB Arrays Antennas technology is 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
AOA requires highly coherent receivers