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Positioning Techniques in 3G Networks

Positioning Techniques in 3G Networks

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Positioning Techniques in 3G Networks

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  1. Positioning Techniques in 3G Networks Independent Study Presentation

  2. Outline • 3G mobile Networks • 3G Standards • Basic Network Architecture • Positioning Parameters in 3G networks • Positioning Techniques in 3G networks

  3. 3G Mobile Networks • Intended to provide Global Mobility Source: http:// www.ccpu.com

  4. IMT-2000 Paired spectrum Unpaired spectrum ETSI DECT UWCC 3GPP 3GPP2 UMTS WCDMA (UTRA FDD) TD-CDMA (UTRA TDD) Cdma2000 (multi-carrier) UWC 136 (Single-carrier) DECT (Frequency Time) 3G standards

  5. Basic Network Architecture Source: http:// www.ccpu.com

  6. AuC HLR Core Network .. Core Network PS Domain To Packet Network SGSN GGSN To Access Network EIR MSC GMSC To PSTN Network CS Domain

  7. PositioningParameters

  8. Received Signal Code Power (RSCP) • Received power on one code measured on the Common Pilot Channel (CPICH) • A downlink measurement, carried out by the UE • Can be obtained in idle mode and active mode

  9. Received Signal Strength (RSS) • The received wide band power, including thermal noise and noise generated in the receiver • RSSI describes the downlink interference level at the UE side • Measurable by the UE • Can be measured in active mode only

  10. SFN-SFN observed time difference • Time Difference of System Frame Numbers (SFN) between Two cells TCPICHRxj – TCPICHRxi TCPICHRxj - Time when the UE receives one Primary CPICH slot from cell j TCPICHRxi - Time when the UE receives the Primary CPICH slot from cell i that is closest in time to TCPICHRxj • Measured in idle mode or active mode by the UE

  11. Round Trip Time (RTT) • Corresponds to the Timing Advance Parameter in GSM RTT = TRX – TTX TTX - Time of transmission of the beginning of a downlink DPCH frame to a UE TRX - Time of reception of the beginning (the first detected path, in time) of the corresponding uplink DPCCH frame from the UE • Measurements are possible on Downlink DPCH transmitted from NodeB and Uplink DPDCH received in the same NodeB • Measured in active mode only

  12. NodeB with directional antenna Angle of Arrival (AoA) • Arrival angle of the signals from the mobile station at several NodeBs • Special antenna arrays should be equipped at the NodeBs

  13. Positioning Techniques

  14. Positioning Techniques

  15. Cell ID Based Method • Simplest method • MS position is estimated with the knowledge of serving NodeB • Position can be indicated as: • Cell Identity of the serving cell • Service Area Identity • Location co-ordinates the serving cell • Accuracy of the estimation depends on the coverage area of the cells

  16. Enhancements to Cell ID • Wide range of enhancements for the Cell ID based method • Cell ID + RTT (Round Trip Time) • Cell ID + Reference Signal Power Budget • Cell ID + RSCP (Received Signal Code Power)

  17. Cell ID + RTT (Round Trip Time) • Identical to Cell ID+TA (Timing Advance) method in GSM • Accuracy of RTT measurements in UMTS is significantly higher (36m) • RTT is used to calculate the distance from the NodeB to MS using propagation models • Performance can be enhanced by incorporating the RTT measurements from all Node Bs in the Active Set • Accurate RTT measurements through Forced Hand Over (FHO)

  18. Cell ID + RTT (Round Trip Time) Location Estimation: • Constrained least-square (LS) optimization for estimating the position (by Jakub Borkowski & Jukka Lempiainen) • Assume an initial position (Geographical mean of hearable NodeBs) • Minimize the function F(x) x = column matrix consisting the coordinates of the MS (x,y). P = A Positive Scalar

  19. Cell ID + RTT (Round Trip Time) Location Estimation: - Location estimation is done according to the following recursion - Continue until the following condition is fulfilled, for a defined threshold

  20. Cell ID + RTT (Round Trip Time) • Some simulation results for urban & suburban areas (by Jakub Borkowski & Jukka Lempiainen)

  21. Coverage area of a cell can be determined by using RSPB • RSPB gives information about • - Node B transmitted power • - Isotropic path loss • - Coverage threshold at coverage area border for a given location probability • - Cell radius for indoor and outdoor coverage • SRNC may compare the received power levels with the power budget to accurately position the UE Cell ID + Reference Signal Power Budget (RSPB)

  22. OTDOA method with Enhancements Standard OTDOA Method • Relative timing offset of the CPICH associated with different Node Bs are used • Each OTDOA measurement describes a line of constant difference (a hyperbola) along which the MS may be located • MS's position is determined by the intersection of hyperbolas for at least three pairs of Node Bs Source: [3] 3GPP TS 25.215:

  23. Standard OTDOA method Features • The accuracy depends on the precision of the timing measurements • Timing synchronizations of different NodeBs is essential • Best results are when the Node Bs equally around the MS Drawbacks • Hearability Problem  Serving NodeB drowns the signals from distant NodeBs Solution • Get the assistance of secondary services  OTDOA method with Enhancements

  24. OTDOA method with Enhancements Use of Idle Periods in Down Link (IPDL) • In UMTS NodeB transmissions are synchronously ceased for a short period of time - Idle Period • Terminal can measure neighbor NodeBs during Idle Periods • Maximizes the hearability of distant pilots • Two techniques • Standard IPDL • Time Aligned IPDL (TA-IPDL)

  25. OTDOA method with Enhancements Use of Idle Periods in Down Link (IPDL) Standard IPDL - Pseudo random idle slots Time Aligned IPDL (TA_IPDL) - Time Aligned Idle Slots Source: [10] 3GPP TSG-RAN WG1 doc

  26. OTDOA method with Enhancements Time Aligned IPDL (TA-IPDL) Method • During the ‘common’ idle period each node B transmits a signal ONLY useful for location estimation, randomly, pseudo-randomly or periodically • OTDOA of these common pilots is measured in the MS for different Node Bs • Positioning is done as in the standard OTDOA algorithm • Drawbacks • added complexity to the network operation • reduced communication efficiency

  27. Time Aligned IPDL (TA-IPDL) Method - Simulation Results (TSG-RAN Working Group 1)

  28. OTDOA method with Enhancements Use of Cumulative Virtual blanking (CVB) • Uses virtual blanking of the Node B downlink signals in the software domain based on the principles of interference cancellation • Significantly enhances hearability than in IPDL, using signal processing techniques Source: [12]http://www.3gpp.org/ftp/tsg_ran/TSG_RAN/RP-020372.pdf

  29. Use of Cumulative Virtual blanking (CVB) • Downlink signal are measured simultaneously at the handset and at Node Bs • Handset – Received signal snapshots • NodeB - Time co-incident snapshots of the transmitted signals • Measurements are transferred to the location server • Location server extracts the OTD of weaker NodeBs’ signals by attenuating the interfering signals one by one • Multiple Node B signals are blanked allowing weaker ones to be measured • Positioning is done using standard OTDOA algorithm

  30. Use of Cumulative Virtual blanking (CVB) Features • No impact on downlink capacity • Median number of hearable Node Bs for CVB is roughly double that for IPDL • Much more robust in the presence of multipath • Operational complexity is reduced compared with IPDL

  31. Use of Cumulative Virtual blanking (CVB) Some preliminary results obtained through trials in several sites of a UMTS network(TSG-RAN Group)

  32. Database Correlation Method (DCM) • Based on a pre-measured database of location dependent variable • DCM in UMTS utilizes Power Delay Profile (PDP) of locations (GSM used RSSI) • An entry of the database consists of: • location coordinates (Lat, Lon) • serving Node ID • Power delay profile from that Node

  33. Database Correlation Method (DCM) • In location estimation PDP from the serving NodeB is correlated with the PDPs stored in the database • The point with the highest correlation coefficient is chosen as the location estimate • RTT measurement from same NodeB is used to limit the number of correlation points Source: [8]. “Database correlation method for UMTS location”

  34. Database Correlation Method (DCM) • Advantages • Avoids problems related to Multipath Propagation • Drawbacks • Delay Profile Measurements are not standardized in 3GPP, thus requiring software changes at the MS • Reporting of such measurements to the location server in the network is also not standardized • Higher cost in creating database

  35. Database Correlation Method (DCM) • Some simulation results in urban UMTS network in comparison with OTDOA method -(by Suvi Ahonen & Heikiki Laitinen)

  36. Pilot Correlation Method • Based on a database with pre-measured samples of Received Signal Code Power (RSCP) Measurements of visible Pilots • Database Preparation • Area is divided into small regions (positioning regions) • Size of the region depends on the desired accuracy • For each positioning region, the most probable Common Pilot Channels’ RSCP measurements are stored.

  37. Pilot Correlation Method Database Preparation • An entry of the database contains: • The positioning region • Visible Common Pilot Channels • RSCP of each pilot • Can be created automatically from log files of the measurement tool

  38. Pilot Correlation Method Location Estimation • Measured RSCP of visible pilots are compared with all samples stored in the database • Least Square Method is applied for comparison Si – Value of the ith field of the stored sample mi – Value of the ith field of the measurement N - Number of fields in the vector • Estimated location  coordinates of the middle point of the position region having smallest SLMS

  39. Pilot Correlation Method Advantages • An entirely network-based approach and doesn’t require any hardware or software modifications in the MS • Deployment costs are minimized by the use of standardized measurements and procedures • Since the database can be created automatically using the log files of the measurement tool, no additional effort is needed in database formation

  40. Pilot Correlation Method • Some results obtained in real network conditions in an urban UMTS network in Finland…. - By Jakub Borkowski & Jukka Lempiainen

  41. Other Positioning Techniques • Positioning Element OTDOA method • Angle of Arrival Method • Uplink Time Difference of Arrival Method

  42. Summary • 3G Mobile Networks • Positioning Parameters in 3G Networks • Positioning Techniques • Enhancements to Cell ID based methods • Time based methods • OTDOA methods and enhancements • Database Correlation method • Pilot Correlation method

  43. Thank You

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