GeoLENs™ GSM Location Methods:

A-GPS based positioning

Hybrid A-GPS Positioning

Assisted-GPS (A-GPS) is a handset-based mobile locating method fundamentally based on GPS locating technology but functionally distributed between the mobile and a centralized server. Mobiles must be specially equipped to receive GPS signals from multiple GPS satellites in order to make measurements of the signals from GPS satellites and relay this information or their calculated position through the mobile network to the SMLC/SAS/SLP software (iSAS: Control Plane, SUPL: User Plane implementations). In cases where the mobile does not compute its own location from GPS data, the SMLC/SAS/SLP uses GPS data relayed from the target mobile to compute the mobile's position. Once determined, the position can be sent to a gateway mobile location center (GMLC) or SUPL Location Platform (SLP) for distribution to the application that originated the location request. A-GPS is a supplemental form of GPS whereby GPS satellite position data is sent from the SMLC/SAS/SLP through the mobile network to the mobile to assist the mobile in determining which GPS satellites it should attempt to acquire. This supplemental data is intended to:

• Speed the mobile's satellite signal acquisition process.
• Increase the mobile's ability to receive signals from the target GPS satellites.

A-GPS is intended to reduce latency and improve other location performance when a mobile's view of GPS satellites is obscured. That can occur when the caller is in a building, in a vehicle, or in an "urban canyon." Although A-GPS does improve overall locating performance, accuracy, latency, and yield performance can be subject to degradation if a mobile's view of GPS satellites is obscured.

 TA/NMR Positioning

• Timing Advance (TA) is an existing GSM parameter conceived to avoid overlapping of bursts transmitted by several Mobile Stations (MSs) in the same cell
• For positioning purposes the TA is an estimate of the absolute distance between MS and serving BTS
• Statistical TA information can be used to adapt to different environments
• By combining TA with the coordinates of the serving BTS and eventually with orientation and angular width of the serving sector, the MS position can be estimated

Cell ID Positioning

Allows basic location services to be deployed using existing handsets and network capabilities and kick start market interest and revenues.

• Cell sector location coordinates passed to the application
• Can be accomplished using a standalone Gateway Mobile Location Center (GMLC) that connects to MSC and HLR using ATI
• SMLC based when deployed
• Can be configured to provide mid point of the cell if desired

Uplink Time Difference of Arrival – U-TDOA

UTDOA takes timing measurements of standard handset RF procedures (uplink).  It calculates the difference in the time of arrival of the RF signal between multiple pairs of Location Measurement Units (LMUs) .  The differences in arrival time determine hyperbolic curves between receivers of where the mobile could be.  The location is then estimated by the best intersection of the multiple hyperbolic curves.

LMUs may also be equipped with antennae capable of providing angle of arrival measurements (AoA) which can augment timing measurements where coverage or DOP is poor.

Multiple Range Estimation Locator—MREL

MREL (Multiple Range Estimation Location) is the next generation of location technology used with Andrew’s Location Measurement Units (LMUs). MREL and U-TDOA use different techniques to determine the location of a mobile.  MREL exploits features in the newer digital signaling protocols to produce location results in areas U-TDOA cannot.  For example, MREL requires only two sensor sites instead of U-TDOA’s three, which is particularly important in rural or highway corridors where only two sensor sites might be available.

MREL makes innovative use of the feedback loop that exists between a mobile and a base station to determine the actual time that the mobile transmits a signal of interest.  MREL then uses the transmission time and the time of arrival of the signal at a sensor site to determine a circular range ring, where the mobile could be located, around each sensor site.  The location is then estimated by the best intersection of the multiple range-rings.  

Conversely, U-TDOA calculates the difference in the time of arrival of the mobile signal between multiple pairs of receivers.  The differences in arrival time determine hyperbolic curves between receivers of where the mobile could be.  The location is then estimated by the best intersection of the multiple hyperbolic curves.

Unlike U-TDOA, MREL is not dependent on time differences of arrival of a signal at multiple sensor sites.  MREL uses absolute times of transmission and arrival.  Because MREL does not rely on differences, it is able to generate a range ring for each sensor site and has the ability to generate accurate location information with just two sensor sites.  U-TDOA cannot generate accurate location information with anything less than three sensor sites.

Testing shows that in a comprehensive set of environments, MREL offers a high accuracy location capability in areas where A-GPS and U-TDOA may fail.  MREL coupled with the other location technologies available in GeoLENs provides the most comprehensive and competitive location solution on the market today, both for LBS and E911 applications.

User Plane Location (SUPL) Solutions

For User Plane (SUPL) location in GSM networks, please refer to Andrew’s SUPL Location Platform (SLP).

GeoLENs™ GSM System Features:
SMLC (Serving Mobile Location Center)

• Provides overall positioning coordination, and interacts with MS, MSC, BSC and various positioning methodologies when necessary
• Control Plane Location
• Triggers A-GPS measurements for higher accuracy and interfaces to A-GPS Reference Network data feed
• Supports MS-Based and MS-Assisted A-GPS for GSM/GPRS/EDGE, iDEN
• Applies handset-based and network-based locating methods including A-GPS, Timing Advance/Network Measurement Reports, Cell/Sector ID
• Interfaces with operator network to extract measurement data required for position calculation processes
• Can be combined with GMLC, SAS, SLP, etc. on single equipment platform

GMLC (Gateway Mobile Location Center)

• Controls and authenticates requests for a subscriber’s location from applications
• Coordinates transformation of position    information into latitude and longitude that is handed off to an application or PSAP
• Interfaces to MSC and HLR to query for Cell ID positioning, allowing for cost-effective low  accuracy solution
• Interfaces to Public Safety Answering Points (PSAPs) or other Emergency/Public Safety Authorities for E911, E112, etc.
• Supports standards-based interfaces

                - 3GPP/GSM Le interface

               - Mobile Location Protocol (MLP) for location services and European E112                  emergency interface

                - J-STD-036 for E911 Phase 2 in the U.S.

• Can be combined with SMLC, SAS, SLP, etc. on single equipment platform