Wireless Assisted GPS
Personal Location for GSM and GSM
Evolution
Presented By: Anchal Sharma (CS/04/99)
On
: 21/04/2003
Seminar O/C : Mr.Sanjoy Das
(Lecturer CSED)
Introduction
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Wireless Assisted GPS (WAG)
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Definition
How it operates
GSM Standards-Based Messaging
Requirements
WAG Performance
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WAG
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Wireless Assisted GPS (WAG)
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
Definition
How it operates
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Wireless
Assisted
GPS
Information is
obtained from the
wireless
infrastructure,
wireless handset, or
via wireless
messages from a
Location Server.
This information is
called assistance
information, and it is
used by the WAG
receiver
The assistance
information received,
or derived from, the
wireless network is
used to “aid” the
WAG receiver by
providing data that
would normally be
derived by
timeconsuming
demodulation of
GPS satellite signals
– demodulation is
difficult and
sometimes
impossible in certain
common wireless
environments.
A proven system for
world-wide
positioning and
navigation used for
personal,
commercial,
business, and
government
applications.
Commercial
implementations
have been in place
for close to 10
years, though the
system has been in
place over 20
years
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WAG Architecture
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Why WAG ?
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Very rapid acquisition--100 to 1000 times faster than
conventional GPS.
Extremely fast positioning in almost all conditions
Operation in difficult environments (blocked signals,
fading, etc.)
Very sensitive for given acquisition time
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Can withstand >20 dB signal attenuation due to building
blockage, etc.
Works indoors
Excellent accuracy/reliability through cooperation
between MS client and server
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Why WAG? (Cont…)
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A single server supports roaming across different
networks and different geographies
Other than one Server, no special infrastructure
equipment is needed
Accuracy of WAG supports emergency services and
enables a much larger number of location service
applications
Cost of implementation decreases over time as
handset integration increases
WAG can be combined with other terrestrial
radiolocation methodologies
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How it Works?
WAG receiver obtains aiding data from the
server and/or extracts key information from the
wireless network
 Using this aiding data, WAG receiver processes
small amounts of GPS satellite signals
 Then…
MS-Assisted: Sends data to Server for position
calculation
MS-Based: Calculates position in the handset
WAG splits the workload into a very efficient,
quick, and accurate client/server structure
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Client/Server Structure
μ=μ0 (v-us)/(v-uo)
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GSM Standards-Based Messaging
Requirements
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GSM Architecture
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Existing Technologies

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Cell – ID
 Locates user in a sector at most.
 Easy to implement
 Low cost
 Low accuracy
E-OTD
 Can’t be used in WCDMA (specific to GSM/GPRS)
 High costs involved due to additional LUs
 Accuracy better than Cell-Id
OTDOA
 Used only in WCDMA
 Cost between Cell-Id and EOTD
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Cell-Id
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E-OTD
Enhanced Observed Time Difference
3 ΔT
Measurements
to measure
distance.
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OTDOA
Observed Time Difference of Arrival
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WCDMA version of EOTD
Little Cheaper than EOTD due to LU
implementation only at Base Stations.
Uses RTT
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LBS Architecture on GSM/GPRS
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WAG Implementation on WCDMA
Stand-alone Assisted-GPS SMLC
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GSM LCS Methodologies
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Two Mobile Station Location Methodologies
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MS-Assisted = Location Computation in Network
MS-Based = Location Computation in MS
Two Location Transaction Modes
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Broadcast mode
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Periodic Short Message Service Cell Broadcast (SMSCB) on
Broadcast Control Channel (BCCH)
Point-to-Point messaging mode (request/response)
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Standalone Dedicated Control Channel (SDCCH) in idle mode
Fast Associated Control Channel (FACCH) in dedicated mode
Slow Associated Control Channel (SACCH) in dedicated
mode
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GSM Point-to-Point Mode
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GPS Assistance Data Element provides
several information elements
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Reference Time (optional)
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GPS Time Assistance information (optional)
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Nominal size - 3 bytes per satellite
Produces ~3dB sensitivity improvement
Allows LMU-independent GPS time dissemination
Reference Location (optional)
DGPS Corrections (optional)
Navigation Message Bits (optional)
Acquisition Assistance (optional)
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GSM Broadcast Mode
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Broadcast SMSCB messages with four data
elements
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Reference Time (mandatory)
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GSM Time (optional)
GPS Time (mandatory)
Reference Location (mandatory)
Differential (DGPS) Corrections (optional)
Navigation Message Bits (optional)
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Produces ~3 dB additional sensitivity improvement
Allows LMU-independent GPS time dissemination capability
Incremental means for Navigation Model update
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Reduces requirements for point-to-point messages
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Scenario1: GSM Broadcast
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Handset listens to broadcast messages to
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Receive navigation message bits for GPS SVs (satellites
in view)
Acquire one or more GPS SVs
Determine/maintain GPS time
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Software-based method utilizing navigation message bits
Incrementally update Navigation Model
Ready for location requests from user or network
Supports MS-based or MS-assisted solutions
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Scenario2: Point-to-Point Mode
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Handset is powered on
Scenario 1 operation commenced
Location request initiated by user or network
Resident GPS assistance data evaluated
If data insufficient, point-to-point mode
entered
Required assistance data requested/received
Required location request performed
Transition back to Scenario 1
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MS Assisted Sample GSM Call Flow
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MS Based GSM Call Flow
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WAG Performance
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WAG Performance Expectations
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High Performance
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High Sensitivity (inside, urban canyons, etc.)
Rapid First Fix (<8 seconds from cold start)
Accuracy suitable for location services (5-50m)
Roaming
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Across geographies
Maintain accuracies
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Global Validation
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Conclusion
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Cell-ID meets cost objectives, supports roaming, but provides generally
poor performance and poor ROI,
E-OTD provides good performance, but has severe roaming limitations,
is expensive, is limited to GSM networks and provides poor ROI,
OTDOA provides average performance, but has severe roaming
limitations, is expensive, is limited to WCDMA networks and provides
poor ROI,
A-GPS provides very good performance, is relatively inexpensive,
supports roaming, can be used on all networks and provides good ROI,
A-GPS hybrid combinations of A-GPS + Cell-ID provide very good
performance, support roaming, optimize yield, minimize the cost of the
hybrid implementation and provide ROI on par with A-GPS solutions,
A-GPS hybrid combinations with spot deployments of E-OTD or
OTDOA are also viable, but the complexity and cost of these
implementations increases over the A-GPS + Cell-ID hybrid because of
the need for LMUs in the network to support E-OTD/OTDOA, which can
decrease the ROI.
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Hybrid Technology
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References
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Andrew S. Tenenbaum, Computer Networks.
http://isi.edu
Location Based Services, A Strategic Analysis of Wireless Technologies, Markets, and
Trends; Frank Viquez, AnnaLee Dragon, Tim Archdeacon; Allied Business Intelligence; 1Q,
2001
Ready or Not, Mobile Location Technology is Here!; Allen Nogee; Cahners In-Stat Group;
March 2001
European Wireless Location Services; Jake Sanders, Jamie Moss, Stephan Beckert; The
Strategis Group; March 2000
Synchronous vs. Asynchronous Deployment of WCDMA – Effect on Communication
System Performance; QUALCOMM; publish date September 2001
GSM Mobile Location Systems; Omnipoint Technologies, Inc.; Document #0710009-00B,
1999
Determining Location Using Wireless Networks; Gunter W. Hein, Bernd Eissfeller, Jon O.
Winkel, and Veit Oehler; GPS World; March 2001
Synergies Between Satellite Navigation and Location Services of Terrestrial Mobile
Communication, Gunter W. Hein, Bernd Eissfeller, Jon O. Winkel, and Veit Oehler; Institute
of Navigation; September 2000 Conference Proceedings, September 2000.
http://www.fcc.gov/e911 ; FCC mandate for Docket 94-102
http://gullfoss2.fcc.gov/cgi-bin/websql/prod/ecfs/comsrch_v2.hts ; Carrier Filings on
performance relative to FCC mandate 94-102
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Thank You
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