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 standards

IMT-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

NodeBsNodeB 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 MS

Drawbacks

• Hearability Problem Serving NodeB drowns the signals from distant NodeBs

Solution

• 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 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

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

Time Aligned IPDL (TA-IPDL) Method

Area 67 % error 90 % rms error

Rural 8 m 6 m

Sub urban 6 m 5 m

Urban-B 44 m 39 m

Urban -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 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

Ni

iNi

iiLMS mSS 2)(

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

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 m

Route -2 90 m 195 m

Route -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

Questions?

Thank You