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Positioning Techniques in 3G Networks
Pushpika Wijesinghe
Independent Study Presentation
Supervisor:Prof (Mrs.) Dileeka Dias
Outline
• 3G mobile Networks
– 3G Standards
– Basic Network Architecture
• Positioning Parameters in 3G networks
• Positioning Techniques in 3G networks
3G Mobile Networks• Intended to provide Global Mobility
Source: http:// www.ccpu.com
3G standardsIMT-2000
WCDMA(UTRA FDD)
TD-CDMA(UTRA TDD)
Cdma2000(multi-carrier)
UWC 136(Single-carrier)
DECT(Frequency Time)
3GPP 3GPP2
UWCC
ETSI DEC
T
Paired spectrum
Unpaired spectrum
UMTS
Basic Network Architecture
Source: http:// www.ccpu.com
To Access Network
Core Network ..
Core Network
To PSTN Network
To Packet Network
SGSN GGSN
MSC GMSC
AuC HLR EIR
PS Domain
CS Domain
Positioning Parameters
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
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
• 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
SFN-SFN observed time difference
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
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
NodeB with directional antenna
Positioning Techniques
Positioning Techniques
Positioning Techniques
Cell ID Based Methods
OTDOA with Enhancements
Database Correlation Method
Pilot Correlation Method
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
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)
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)
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
N
i i
N
ii xg
PxfxF1
1
1
2
)(1)()(
)()( xfxg ii
0)()()( 22 yyxxdxf iiii
Location Estimation:
- Location estimation is done according to the following recursion
- Continue until the following condition is fulfilled, for a defined threshold
Cell ID + RTT (Round Trip Time)
)(1 kxkk xFxx
txF kx )(
Cell ID + RTT (Round Trip Time)
• Some simulation results for urban & suburban areas (by Jakub Borkowski & Jukka Lempiainen)
Topology Urban Suburban
67% 95% 67% 95%6-sector / 650 75 m 200 m 50 m 150 m
6-sector / 330 60 m 220 m 55m 170 m
Cell ID + Reference Signal Power Budget (RSPB)
•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
OTDOA method with Enhancements
• 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
Standard OTDOA Method
Source:
[3] 3GPP TS 25.215:
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 MSDrawbacks• Hearability Problem Serving NodeB drowns the signals
from distant NodeBsSolution• Get the assistance of secondary services
OTDOA method with Enhancements
OTDOA method with Enhancements
• 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)
Use of Idle Periods in Down Link (IPDL)
OTDOA method with EnhancementsUse 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
OTDOA method with EnhancementsTime 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
Time Aligned IPDL (TA-IPDL) Method
Area 67 % error 90 % rms error
Rural 8 m 6 mSub urban 6 m 5 mUrban-B 44 m 39 mUrban -A 95 m 83 m
Bad Urban 218 m 193 m
- Simulation Results (TSG-RAN Working Group 1)
OTDOA method with Enhancements
• 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
Use of Cumulative Virtual blanking (CVB)
Source:
[12] http://www.3gpp.org/ftp/tsg_ran/TSG_RAN/RP-020372.pdf
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
Use of Cumulative Virtual blanking (CVB)
• 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
Features
Use of Cumulative Virtual blanking (CVB)
Some preliminary results obtained through trials in
several sites of a UMTS network (TSG-RAN Group)
Site Time Error
1 16:26 22.8 m
2 16:43 27.6 m
3 17:11 16.9 m
4 17:13 5.7 m
5 17:16 26.2 m
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
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”
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
Database Correlation Method (DCM)
• Some simulation results in urban UMTS network in comparison
with OTDOA method -(by Suvi Ahonen & Heikiki Laitinen)
67 % 95%
DCM 25 m 140 m
OTDOA 97 m 620 m
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.
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
Pilot Correlation MethodLocation 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
Ni
iNi
iiLMS mSS 2)(
Pilot Correlation MethodAdvantages• 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
Pilot Correlation Method• Some results obtained in real network conditions in an
urban UMTS network in Finland….
Test Route
67 % 95 %
Route -1 70 m 130 mRoute -2 90 m 195 mRoute -3 90 m 180 m
- By Jakub Borkowski & Jukka Lempiainen
Other Positioning Techniques
• Positioning Element OTDOA method
• Angle of Arrival Method
• Uplink Time Difference of Arrival Method
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
References[1] http://www.three-g.net/3g_standards.html (accessed on 15.05.2007 10.30
a.m)[2] Sumit Kasera, Nishit Narang, “3G Networks Architecture, Protocols and
Procedures”, Tata McGraw-Hill Professional Networking Series.[3] 3GPP TS 25.215: Universal Mobile Telecommunications System (UMTS);
Physical layer; Measurements (FDD), version 7.1.0 Release 7.[4] WCDMA RNP and RNO Training material, Part I and Part II, Huawei
Technologies Company limited.[5] 3GPP TS 25.305, “UMTS; UE positioning in Universal Terrestrial Radio
Access Network (UTRAN); Stage 2,” ver. 7.1.0, Rel. 7, http://www.3gpp.org.
[6] Jakub Borkowski , Jukka Lempi¨ainen, “Practical Network-Based Techniques for Mobile Positioning in UMTS”, Institute of Communications Engineering, Tampere University of Technology, Finland.
[7] J. Borkowski, J. Niemel¨a, and J. Lempi¨ainen, “Performance of Cell ID+RTT hybrid positioning method for UMTS radio networks,” in Proceedings of the 5th European Wireless Conference, pp. 487–492, Barcelona, Spain, February 2004.
[8] S. Ahonen and H. Laitinen, “Database correlation method for UMTS location,” in Proceedings of the 57th IEEE Vehicular Technology Conference, vol. 4, pp. 2696–2700, Jeju, South Korea, April 2003.
[9] J. Borkowski and J. Lempi¨ainen, “Pilot correlation method for urban UMTS networks,” in Proceedings of the 11th European Wireless Conference, vol. 2, pp. 465–469, Nicosia, Cyprus, April 2005.
[10] 3GPP TSG-RAN WG1 doc. No R1-99b79, “Time Aligned IP-DL positioning technique,” 1999, http://www.3gpp.org/ftp/ tsg ran/WG1 RL1/TSGR1 07/Docs/Pdfs/R1-99b79.pdf.
[11] 3GPP TSG-RAN WG1 doc. No R1-00-1186, “Initial Simulation Results of the OTDOA-PE positioning method,” 2000, http://www.3gpp.org/ftp/tsg ran/WG1 RL1/TSGR1 16/Docs/ PDFs/R1-00-1186.pdf.
References
[12] 3GPP TSG-RAN Meeting No. 16, TSG RP-020372, “Software blanking for OTDOA positioning”, June 2002, Marco Island, Florida, USA,
[13] P. J. Duffett-Smith, M. D. Macnaughtan, “Precise UE Positioning in UMTS Using Cumulative Virtual Blanking,”, 3G Mobile Communication Technologies, May 2002, Conference Publication No.489.
[14] Lames J, Caffery Jr, Gordon L.Stuber, Georgia lnstitute of Technology, “Overview of Radiolocation in CDMA Cellular Systems”, IEEE Communications Magazine, April 1998.
[15] Jakub Borkowski, Jarno Niemelia, Jukka Lempiainen, “ Location Techniques for UMTS Radio Netwroks”, Presentation of Reasearch Activities, Institute of Coommunications Engineering, Tampere university of Technology, Tampere, Finland.
[16] Jakub Borkowski , Jukka Lempiäinen, “Novel mobile-based location techniques for UMTS”, Institute of Communications Engineering, Tampere University of Technology, Tampere, Finland.
References
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