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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: (33)(0)4 38 78 51 59, E-Mail:firstname.lastname@example.org 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. Benoit Denis, CEA/LETI STMicroelectronics
M26 L03 M22 M21 M24 M16 M19 M14 M29 M23 M13 M20 M30 L08 M18 M17 M12 M25 M11 L02 L07 L10 L09 M27 L01 L06 M15 M28 L04 UWB Localization Techniques Benoît DENIS email@example.com Fusing Accurate Positioning Capabilities and Digital Communications Benoit Denis, CEA/LETI STMicroelectronics
TOF Estimation Request 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 Benoit Denis, CEA/LETI STMicroelectronics
Main Limitations / Impact of Clock Drift on Perceived Time 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…) Benoit Denis, CEA/LETI STMicroelectronics
Transmitting to DEV PNC’s TOF Estimate RefPNC PNC’s TOF Estimate RefDEV T2’ T1 PNC TOF TOF TOF DEV T1’ T2 Receiving PNC’s TOF Estimate DEV’s TOF Estimate Request (Medium Access) Beacon Detection Acknowledgement 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 DEV’s Time Offset (propagation delay from PNC) PicoNet Synchronization MCTA (Slotted Aloha) Benoit Denis, CEA/LETI STMicroelectronics
TOF Estimation Request Isochronous 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 Benoit Denis, CEA/LETI STMicroelectronics
DEV-A’s Estimate of TCA TAB TCA DEV-C’s Estimate of TBC DEV-B’s Estimate of TAB TBC Ex : DEV2DEV Ranging in the 802.15.3 Scenario MAC resources for a single DEV2DEV OWR TransactionGuaranteed Time Slots in the CTA can be used between isochronous DEVs (i.e. with common reference start times) DEV-A RefPNC+Ts RefPNC+ 2Ts RefPNC DEV-B DEV-A DEV-B DEV-C Slot 1 Slot 2 Slot 3 CTA Benoit Denis, CEA/LETI STMicroelectronics
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 Benoit Denis, CEA/LETI STMicroelectronics
Anchor 2 (xA2,yA2) Anchor 1 (xA1,yA1) Mobile (xm,ym) Anchor 3 (xA3,yA3) Estimated Position Measurements Positioning from TOA 3 anchors with known positions (at least) are required to retrieve a 2D-position from 3 TOAs Specific Positioning Algorithms Benoit Denis, CEA/LETI STMicroelectronics
Info T2 Isochronous Info T3 Info T3 TOAEstimation TDOAEstimation Info T2 Time Difference Of Arrival (TDOA) & One Way Ranging (OWR) TDOAEstimation Mobile TX TOAEstimation 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 Benoit Denis, CEA/LETI STMicroelectronics
Anchor 3 (xA3,yA3) Anchor 2 (xA2,yA2) Mobile (xm,ym) Measurements Anchor 1 (xA1,yA1) Estimated Position 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 Benoit Denis, CEA/LETI STMicroelectronics
Tag Tag Tag Asynchronous Tags to be localized Tag Tag Tag 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 Benoit Denis, CEA/LETI STMicroelectronics
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 Benoit Denis, CEA/LETI STMicroelectronics
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 Benoit Denis, CEA/LETI STMicroelectronics