1. Month Year
doc.: IEEE /0xxxxr0
Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: Ranging as a requirement for BAN and study on existing ranging schemes
Date Submitted: May 12, 2008
Source: Giriraj Goyal, Kiran Bynam, Ranjeet Kumar Patro, Arun Naniyat, Seung-Hoon Park, Noh-Gyoung Kang, Jaeseung Son, EunTae Won
Contact: Giriraj Goyal, Samsung Electronics
Voice: ,
Re: []
Abstract: Brief overview of existing ranging techniques
Purpose: To identify ranging as a requirement for BAN applications set and present brief study on existing ranging mechanisms.
Notice: This document has been prepared to assist the IEEE P 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 in May’08 it would be made publicly available by P 1
Page 1
Kiran Bynam, Samsung

2. Agenda Ranging applications Ranging as a Requirement criterion for BAN
Existing Ranging and localization Techniques

3. Ranging applications GPS based application Radar applications
Ship navigation
Tracking ‘search & rescue’
Inventory
Security and surveillance

4. BAN Applications requiring Ranging
Game application
Body posture detection
Tracking applications

5. Common Ranging Techniques
Time-of-Arrival (TOA)
TOA/TWR
DTOA
TOA/OWR
TDOA
Received signal strength (RSS)
Angle-of-Arrival (AOA)

6. Assumptions with ranging techniques
Direct line of sight
Static channel condition
Anchor (reference) nodes and the nodes are static when distances are measured.
Anchor nodes positions are known to each other.

7. Time Of Arrival (TOA) – 1
TOA/TWR – Two way ranging (Single packet exchange) T0 T1
time
TOF
TResponse
TOF
Dev A Transmits signal
Dev B receives the signal
Dev B Respond back to dev A
Dev A receives response from Dev B
TOF = Time of flight for signal from Dev A to Dev B
TResponse = Turnaround time for Dev B to respond back to Dev A (Prescribed Protocol Delay and/or Processing Time)
Distance (between A and B) estimation done by A

8. Time of Arrival (TOA) - 2
Range estimation with TOA/TWR is affected by :
Relative clock drift between A and B
Clock accuracy in A and B
Prescribed response delay

9. Time Of Arrival (TOA) – 3
TWR with Double packet exchange; known as DTOA (Differential Time of Arrival)
DTOA is a modification of TOA/TWR technique, to remove effects of protocol/response delay (turn around time)
Random Time Delay T0 T1
T’0
T’1
time
TOF
TResponse
TOF
TOF
TDelay = 2*TResponse
TOF
Dev A Tx signal
Dev B rx signal
Dev B Respond back to dev A
Dev A rx response from Dev B
Dev A Tx signal
Dev A rx response from Dev B
Dev B rx signal
Dev B Respond back to dev A
TOF = Time of flight for signal from Dev A to Dev B
TResponse = Turnaround time for Dev B to respond back to Dev A (Prescribed Protocol Delay and/or Processing Time)
Distance (between A and B) estimation done by A

10. Time Of Arrival (TOA) - 4
OWR – One way ranging, If Terminals are synchronized to a common clock, direct OWR can be used. T0 T1
time
TOF
Dev A* Transmits signal
Dev* B receives the signal
TOF = Time of flight for signal from Dev A to Dev B
* Device A and Device B are isochronous
Distance (between A and B) estimation done by B

11. Time Of Arrival (TOA) – 5 TOA Localization (circle geometry):
Anchor1 (x1, y1) A3
Anchor3 (x1, y1) A2
Anchor2 (x1, y1) M
Mobile Node (xm, ym)
Anchors A1, A2 & A3 are centers of circles.
Three circles will pass through one common point for a single solution.
Calculate
Algorithm for drawing circle trajectory and finding common point of intersection
Estimation
3 anchors with known positions (at least) are required to retrieve a 2D-position
4 anchors with known positions (at least) are required to retrieve a 3D-position

12. Time Of Arrival (TOA) - 6
TDOA (Time Difference of Arrival) localization is a modification of TOA localization technique T0
Mobile* Tx
time
TOF 2
Anchor 2* Rx T2
Anchor 2 sends T2 info to Anchor 1
TDOA Estimation
TOF 3
Anchor 3* Rx
Anchor 3 sends T3 info to Anchor 1 T3
TOF 1
Anchor 1* Rx T1
Mobile Node M Tx signal
Anchor 2 Rx signal
Anchor 2 Rx signal
Anchor 1 Rx signal
Reference time
Time of flight information by anchor nodes can be calculated by any of TOA method.
Example shows Time Difference by a anchor node (anchor 1) can be calculated by any reference time if TOA/OWR ranging method

13. Time Of Arrival (TOA) - 7 TDOA Localization (hyperbola geometry):
Calculate A3
Anchor3 (x1, y1)
Algorithm for drawing hyperbolic trajectory and finding point of intersection A1
Anchor1 (x1, y1) A2
Anchor2 (x1, y1) M
Mobile Node (xm, ym)
Estimate
Note: 3 anchors with known positions (at least) are required to retrieve a 2D-position
Anchors A1, A2 & A3 are Foci of Hyperbola
Hyperbolas are drawn for locus of M with
and as constant.

14. Received Signal Strength (RSS) – 1
Data link
Processing unit
Anchor/reference node
Nodes required being located
-Devices calculate ranges to their neighbors
Location is jointly estimated using collective information
Location Accuracy/ Range Extension

15. Received Signal Strength (RSS) – 2
RSS is an alternative solution to TOA/TDOA as it lowers requirements in terms of synchronization and clock precision
The Disadvantages are –
RSSI requires precise channel behavioral model
This technique is sensitive to channel inconsistency

16. Angle of Arrival (AOA)
AOA could be an alternative solution to TOA/TDOA
Lower requirements in terms of synchronization and clock precision
Two anchors are sufficient for 2D-positioning and three for 3D-positioning
AOA requires precise calibration at anchor nodes
Cost increases with size and size may not be reduced

17. Comparison chart Ranging Techniques Advantages Disadvantages TOA
Highly accurate for wide bands transmission as synchronization accuracy is high
Clock drift issue
Clock accuracy in nodes  
Clock synchronization is required
RSS
Less complexity
Effected by channel dynamics
AOA
Localization technique
Number of anchors required for 2-D and 3-D positioning are lesser than TOA technique.
Multi-path effects changes phase of a signal and can yield large positioning errors.
Requires array of antenna

18. Ranging challenges MAC role/computation complexities
Energy attenuation
Multi-path channel
Clock synchronization

19. Ranging scheme for UWB Hybrid of TOA/TDOA Accuracy of up to 3 cm
Code sequences are used for transmission
Use of CDMA to allow multiple localizers at same time in same area

20. Reference 15-04-0581-07-004a-ranging-subcommittee-final-report.doc