Overview of Radiolocation in CDMA Cellular Systems - PowerPoint PPT Presentation

About This Presentation
Title:

Overview of Radiolocation in CDMA Cellular Systems

Description:

Georgia Institute of Technology. Radiolocation. Measures parameters of radio signals that travel between an MS and a set of fixed transceivers. ... – PowerPoint PPT presentation

Number of Views:43
Avg rating:3.0/5.0
Slides: 17
Provided by: spr75
Category:

less

Transcript and Presenter's Notes

Title: Overview of Radiolocation in CDMA Cellular Systems


1
Overview of Radiolocation in CDMA Cellular Systems
  • James J. Caffery, Jr.
  • Gordon L. Stuber
  • Georgia Institute of Technology

2
Radiolocation
  • Measures parameters of radio signals that travel
    between an MS and a set of fixed transceivers.
  • Can be implemented in two ways
  • The MS calculates its own position eg. in GPS
  • The BSs relay signals to a central site for
    processing.
  • Advantage no modifications required in the MS
    handset.

3
Applications of Wireless Location
  • E-911
  • Location-sensitive billing
  • Fraud detection
  • Cellular system design and resource management
  • Fleet management and intelligent transportation
    systems (ITS)

4
Accuracy Requirements
  • Application-specific
  • E-911 Location accuracy to within 125m
  • Fleet management and ITS services Knowledge of
    general vicinity will do.
  • Methods
  • Cellular network as proximity location system
  • Signal strength, AOA and TOA
  • Monitoring handoffs

5
Radiolocation Methods
  • Based on signal strength, angle of arrival (AOA),
    or time of arrival (TOA) measurements, or their
    combinations.
  • This article only considers the case where the
    signal measurements are made at the BSs.

6
Signal Strength
  • Uses a known mathematical model describing the
    path loss attenuation with distance.
  • The MS lies on a circle centered at the BS.
    Location of the MS can be determined by using
    multiple BSs.
  • Problems Errors due to multipath and shadowing

7
Angle of Arrival (AOA)
  • Estimate the MS location by measuring the AOAs of
    a signal from an MS at several BSs.
  • Problems Accuracy diminishes with increasing
    distance between the MS and BS.
  • Useful for macrocells, may be impractical for
    microcells.

8
  • The scattering model for propagation in
    macrocells.
  • The MS is a distance d from the BS and is
    surrounded by a scattering ring of radius a.

9
Time-Based Systems
  • TOA - Estimate the TOAs of a signal transmitted
    by the MS and received at multiple BSs. The MSs
    position is given by the intersection of the
    circles.
  • TDOA Estimate the time differences of arrival
    (TDOAs) of a signal received at multiple pairs of
    BSs. The MSs position is given by the
    intersection of the hyperbolae.

10
Time-Based Systems (contd.)
  • Problems
  • Require high-resolution timing measurements
  • LOS propagation conditions are necessary to to
    achieve high accuracy
  • Requires synchronization at three or more BSs

11
TDOA
12
Performance of TOA vs. AOA
  • Performance of the TOA and AOA location methods
    for a varying number of BSs and scatterer radii
    in macrocells.
  • Solid lines denote results for TOA, dashed lines
    results for AOA.

13
Sources of Error
  • Multipath
  • Effects of reflected signals associated with
    signal propagation
  • NLOS
  • Signal arriving from at the BS from the MS is
    reflected or diffracted, and takes a longer path
    than the direct path.
  • Multiple Access Interference
  • Co-channel interference

14
The near-far effect
15
Conclusion
  • Radiolocation fits naturally with wireless
    networks.
  • It would allow location determination with
    existing handsets without modification, but might
    need considerable modification on the network
    side.
  • TOA or TDOA most appropriate for high accuracy
    signal strength measurements for low accuracy.
  • Need for techniques to mitigate multipath and
    NLOS propagation and multiple access
    interference.

16
The End.Thank you!
Write a Comment
User Comments (0)
About PowerShow.com