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)

2 Introduction Wireless Assisted GPS (WAG)  Definition  How it operates GSM Standards-Based Messaging Requirements WAG Performance

3 WAG Wireless Assisted GPS (WAG)  Definition  How it operates

4 Wireless 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 Assisted 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. GPS 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

5 WAG Architecture

6 Why WAG ? 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  Can withstand >20 dB signal attenuation due to building blockage, etc.  Works indoors Excellent accuracy/reliability through cooperation between MS client and server

7 Why WAG? (Cont…) 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

8 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

9 Client/Server Structure μ=μ 0 (v-u s )/(v-u o )

10 GSM Standards-Based Messaging Requirements

11 GSM Architecture

12 Existing Technologies 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

13 Cell-Id

14 E-OTD Enhanced Observed Time Difference 3 ΔT Measurements to measure distance.

15 OTDOA WCDMA version of EOTD Little Cheaper than EOTD due to LU implementation only at Base Stations. Uses RTT Observed Time Difference of Arrival

16 LBS Architecture on GSM/GPRS

17 WAG Implementation on WCDMA Stand-alone Assisted-GPS SMLC

18 GSM LCS Methodologies Two Mobile Station Location Methodologies  MS-Assisted = Location Computation in Network  MS-Based = Location Computation in MS Two Location Transaction Modes  Broadcast mode Periodic Short Message Service Cell Broadcast (SMSCB) on Broadcast Control Channel (BCCH)  Point-to-Point messaging mode (request/response) Standalone Dedicated Control Channel (SDCCH) in idle mode Fast Associated Control Channel (FACCH) in dedicated mode Slow Associated Control Channel (SACCH) in dedicated mode

19 GSM Point-to-Point Mode GPS Assistance Data Element provides several information elements  Reference Time (optional) GPS Time Assistance information (optional)  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)

20 GSM Broadcast Mode Broadcast SMSCB messages with four data elements  Reference Time (mandatory) GSM Time (optional) GPS Time (mandatory)  Reference Location (mandatory)  Differential (DGPS) Corrections (optional)  Navigation Message Bits (optional) Produces ~3 dB additional sensitivity improvement Allows LMU-independent GPS time dissemination capability Incremental means for Navigation Model update  Reduces requirements for point-to-point messages

21 Scenario1: GSM Broadcast Handset listens to broadcast messages to  Receive navigation message bits for GPS SVs (satellites in view)  Acquire one or more GPS SVs  Determine/maintain GPS time 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

22 Scenario2: Point-to-Point Mode 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

23 MS Assisted Sample GSM Call Flow

24 MS Based GSM Call Flow

25 WAG Performance

26 WAG Performance Expectations High Performance  High Sensitivity (inside, urban canyons, etc.)  Rapid First Fix (<8 seconds from cold start)  Accuracy suitable for location services (5-50m) Roaming  Across geographies  Maintain accuracies

27 Global Validation

28 Conclusion 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.

29 Hybrid Technology

30 References Andrew S. Tenenbaum, Computer Networks. 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 # B, 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 ; FCC mandate for Docket ; Carrier Filings on performance relative to FCC mandate

31 Thank You