otdoa user plane location support.pdf

OTDOA User Plane Location Support

USER DESCRIPTION

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Copyright

Ericsson AB 2011. All rights reserved. No part of this document may bereproduced in any form without the written permission of the copyright owner.

Disclaimer

The contents of this document are subject to revision without notice due tocontinued progress in methodology, design and manufacturing. Ericsson shallhave no liability for any error or damage of any kind resulting from the useof this document.

Trademark List

All trademarks mentioned herein are the property of their respective owners.These are shown in the document Trademark Information.

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Contents

Contents

1 Introduction 11.1 Basic Characteristics 11.2 Benefits 21.3 Additional Information 2

2 Feature Operation 32.1 Network Requirements 32.2 Feature Operation Sequence Diagram 3

3 Parameters 73.1 Introduced Parameters 73.2 Affected Parameters 8

4 Network Impact 94.1 Capacity 9

5 Associated Features and Affected Functions 115.1 Prerequisite Features 115.2 Affected Features 115.3 Related Features 115.4 Affected System Functions 11

6 Performance 136.1 KPIs 136.2 Counters 136.3 Events 13

7 O&M Information 157.1 Feature Activation Steps 15

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Introduction

1 Introduction

This document describes the Observed Time Difference of Arrival (OTDOA)User Plane Location Support feature and its main benefits and impacts in theLTE RAN.

The OTDOA User Plane Location Support feature enables the operator toconfigure the Positioning Reference Signals (PRS) that form the basis for theOTDOA method defined in 3GPP (introduced in 3GPP release 9). The operatordetermines the periodicity of the radio frames containing PRS and the numberof sub-frames transmitting PRS for each transmit occasion. A sequence ofsub-frames (1, 2, 4, or 6) transmitting PRS is referred to as a PRS occasion.To minimize the interference in the positioning reference signal sub-frame, noother data is scheduled in those sub-frames. These sub-frames are thereforereferred to as Low Interference Sub-frames (LIS).The User Equipment (UE) measures PRSs from multiple E-UTRAN Node B(eNodeB) and along with geographical information of the eNodeB positions andtheir relative downlink timing, an estimate of the UE position can be established.

The feature also enables the eNodeB to provide precise cell frame timing tothe Operations Support System Radio and Core (OSS-RC), from where thepositioning node can retrieve this information. The positioning node is in theuser plane architecture called Secure User Plane Location Platform (SLP).Knowledge of cell timing by the positioning node is a prerequisite for theOTDOA method.

This section provides a brief description of why it is important to configure thefeature correctly and have the optimal parameter settings.

In the sub-frames where the PRS signals are transmitted (LIS), no user data isscheduled. This means that some of the downlink cell capacity is lost. Capacityloss depends on the periodicity of the PRS frames, the number of sub-frames ineach PRS occasion and the number of downlink sub-frames per radio frame. Inthe worst case, with a periodicity of 160 ms and all downlink sub-frames usedfor PRS signaling, the downlink capacity loss will be 6.25%. A more typicalscenario with a periodicity of 1280 ms and four out of six downlink sub-framesused for PRS will give a loss of only 0.52%.

1.1 Basic CharacteristicsThis section describes the basic characteristics of the feature.

Feature Identity

TDD: FAJ 221 0986, OTDOA User Plane Location Support

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Replaces: N/A

Dependencies

This feature requires the following RAN features to be active:

Clock Source over GPS, part of LTE Basic

This feature affects no other features.

1.2 BenefitsThis section describes the benefits of this feature.

The OTDOA method provides sufficient positioning accuracy (50200 m) toserve as a fallback method for the Assisted GPS (A-GPS) method and enablesthe operator to comply with the Federal Communications Commission (FCC)phase 2 accuracy requirements on positioning of emergency calls.

In standalone, it can serve as the positioning method for a wide variety ofcommercial services based on UE location.

1.3 Additional InformationThis section provides a reference or link to other sources of information whichmay provide useful background information in regards to the feature.

More information about this feature and related topics can be found in thefollowing documentation:

Radio Network Configuration

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Feature Operation

2 Feature Operation

This section describes the OTDOA User Plane Location Support feature inmore detail, including network configuration requirements and operation flows.

2.1 Network RequirementsThe following must be fulfilled at feature activation:

The eNodeBs must be synchronized using clock source over GPS with timeand phase synchronization.

2.2 Feature Operation Sequence DiagramIn a cell where the OTDOA User Plane Location Support feature is activated,the PRSs are broadcast in accordance with the configuration decided by theoperator. Parameter details can be found in Section 3 on page 7.

2.2.1 PRS Configuration

Since transmission of System Information Block type 1 (SIB1) data can occurevery 20 ms, there are a large number of combinations for PRS and NPRS thatcause PRS sub-frames to collide with SIB1. To prevent this from happening,a non-collision check is made before the cell is brought into service (beforecell is unlocked). Should a collision occur with the current parameter setting,the configuration is aborted, the cell remains in the locked state and an errormessage is sent to the operator. Collisions with other SIB messages are notchecked since those messages are much less frequent than SIB1.

For operator convenience, a special parameter input mode is provided whichassures a non-collision configuration. This mode is entered if the operatoruses the MOM parameter prsPeriod to set the periodicity of the PRS (andleaves the MOM parameter prsConfigIndex untouched).The current release of LTE supports two selectable uplink-downlink allocationconfigurations. A fixed value for PRS sub-frame offset (the starting pointof the PRS sub-frames relative sub-frame number zero, SFN0) is used foreach uplink-downlink allocation configuration. For uplink-downlink allocationconfiguration 1, the value 14 is used for noConsecutiveSubframes = 1 or 2,while 9 is used for noConsecutiveSubframes = 4 or 6. For uplink-downlinkallocation configuration 2, the value 13 is used for all cases.

Figure 1 shows example configurations where collisions are avoided. The PRSperiod = 160 ms and number of consecutive sub-frames = 4. The fixed values

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for PRS sub-frame offset are 9 for uplink-downlink configuration 1 (a) and 13for configuration 2 (b) respectively.

L0000458A

SIB1

PRS subframe, even transmit occasion

PRS subframe, odd transmit occasion

D: Downlink subframe

Radio frame #0 Radio frame #1 Radio frame #16 Radio frame #17

U: Uplink subframe

S: Special subframe

D S U U D D S U U D D S U U D D S U U D

D S U D D D S U D D D S U D D D S U D D

D S U U D D S U U D D S U U D D S U U D

D S U D D D S U D D D S U D D D S U D D

(a)

(b)

PRS TPRS

PRS TPRS

Figure 1 Example of PRS Configuration Avoiding Collisions forUplink-Downlink Configurations 1 and 2

For a two-antenna configuration, PRS is transmitted from one antenna at thetime. The same antenna is used for the entire PRS occasion but between PRSoccasions the antenna is changed. PRS occasions transmitted using antenna 0are referred to as even PRS occasions and PRS occasions transmitted usingantenna 1 are referred to as odd PRS occasions.

2.2.2 LIS

If the data region in a PRS sub-frame contains Physical Downlink SharedChannel (PDSCH) data, the accuracy of the estimated UE position isdecreased due to increased interference. Therefore, no scheduling of PDSCHtransmissions in PRS sub-frames is done, which also reduces the impact ofOTDOA on the scheduler. This will as already mentioned have a slight negativeimpact on the capacity of the cell.

2.2.3 Power Scaling

Power scaling of PRS depends on whether the eNodeB is configured for oneor two cell-specific TX antenna ports. Since PRS is only transmitted from oneantenna (for each transmit occasion in case of two cell-specific TX antennaports), the following scaling of the amplitude applies to PRS:APRS = Na*AreferenceSince the only values for Na are 1 and 2, the scaling when two antennas areused will result in a doubling of the power of the PRS resource elements on theantenna where PRS is transmitted.

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Feature Operation

2.2.4 Mapping to Resource Elements

Mapping to resource elements for one or two antennas is shown in Figure 2.

L0000325A

PRS

l=0

Even-numbered slots Odd-numbered slots

6 0 6

Figure 2 Mapping of PRS for One or Two Antenna Ports

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Parameters

3 Parameters

This section describes parameters introduced by the OTDOA User PlaneLocation Support feature and parameters affected by activating the feature.

3.1 Introduced ParametersTable 1, Table 2, Table 3, and Table 4 describe the parameters introduced byMOs in the feature. Generic cell parameters also used by this feature canbe found in Radio Network.

Table 1 PRS Configuration Parameters in MO EUtranCellTDDParameter Description

noConsecutiveSubframes Number of consecutive downlink sub-frames with positioningreference signals as defined in 3GPP TS 36.211Values define 1, 2, 4, or 6 consecutive sub-frames.

prsConfigIndex PRS index value for the cell defines the periodicity of the PRSoccasions and the PRS sub-frame offset, as defined in 3GPP TS36.211

The value -1 (default) means that this parameter will not be usedfor setting the PRS period and parameter prsSubframeOffset.Instead, the prsPeriod parameter must be used to directly setthe PRS period while the prsSubframeOffset parameter set bythe system guarantees non-collision with SIB1.

prsConfigIndexMapped Holds the resulting value for parameter prsConfigIndexIf the prsPeriod parameter is used by the operator,prsConfigIndexMapped parameter is set by the system. Ifthe prsConfigIndex parameter is used by the operator, theprsConfigIndexMapped parameter is a copy of the enteredvalue.

prsPeriod Period of PRS occasionsValid periods include 160 ms, 320 ms, 640 ms, and 1,280 ms.

Table 2 Cell Geographical Parameters in MO EUtranCellTDDParameter Description

altitude Altitude of the transmitter antenna in meters above the WGS84reference ellipsoid

Use positive and negative values to denote height and depth.

confidence Percentage of confidence that the target device is within theellipsoid defined by the three axes of uncertainty: semi-major,semi-minor, and altitude

eutranCellCoverage Models the cell coverage area used for UE positioningThe cell coverage area is defined by the cell bearing, cell openingangle, and cell radius. Cell opening angle = 0 implies omni cell.

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Parameter DescriptioneutranCellPolygon Models the manageable characteristics for the cell polygon used

for UE positioningEach polygon corner is described by a latitude and longitudepair. Each polygon corner is represented with one position inthe sequence. The other configured polygon corners follow insequence. tAt least three corners must be configured in a polygonwhen the function is active or used. The points must be connectedin the order that they are given. The last point is connected tothe first point.

latitude Degree of latitude of the transmitter antenna position

longitude Degree of longitude of the transmitter antenna position

uncertAltitude Uncertainty altitude (h) expressed in meters is derived from theuncertainty altitude (k) by h = 45*((1.025)^k - 1)

uncertSemiMajor Semi-major axis of uncertaintyThe uncertainty (r) is derived from the uncertainty code (k) by: r =10 * ((1.1^k) - 1).

uncertSemiMinor Semi-minor axis of uncertaintyThe uncertainty (r) is derived from the uncertainty code (k) by: r =10 * ((1.1^k) - 1).

Table 3 Cell Timing Parameters in MO EUtranCellTDDParameter Description

gpsTimeSFN0DecimalSecond Fractional part of the GPS time for the most recent occurrence ofSFN = 0 in the cell

gpsTimeSFN0Seconds Integer part of the GPS time for the most recent occurrence ofSFN=0 in the cell

Table 4 Feature Activation Parameters in MO EUtranCellTDDParameter Description

otdoaSuplActive Indicates whether the OTDOA User Plane Location Supportfeature is ACTIVATED or DEACTIVATED in the cell

3.2 Affected ParametersThe implementation of this feature affects no parameters.

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Network Impact

4 Network Impact

This section describes how the OTDOA User Plane Location Support featureimpacts the network functions and capabilities.

4.1 CapacityThe non-transmission of user data in the sub-frames where the PRS signalsare transmitted results in a somewhat reduced capacity in the cells wherepositioning is activated. The capacity loss will be in the range 0.13% to 6.25%,corresponding to the lowest and highest frequency possible of PRS sub-frametransmission. A typical scenario with a periodicity of 1,280 ms and four out ofsix downlink sub-frames used for PRS will give a loss of 0.52%.

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Associated Features and Affected Functions

5 Associated Features and AffectedFunctions

This section describes how the OTDOA User Plane Location Support featureaffects other features and functions.

5.1 Prerequisite FeaturesTable 5 Prerequisite Features

Feature Description

Clock Source over GPS Synchronizes the system clock of the RBS to an absolute timewith sufficient accuracy

5.2 Affected FeaturesThis feature affects no other feature.

5.3 Related FeaturesThis feature is not related to any other feature.

5.4 Affected System FunctionsThis feature affects no system functions.

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Performance

6 Performance

This section describes performance indicators, counters, and events associatedwith the OTDOA User Plane Location Support feature.

6.1 KPIsThis feature has no associated Key Performance Indicators (KPIs).

6.2 CountersThis feature has no directly associated counters.

6.3 EventsThis feature has no associated events.

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O&M Information

7 O&M Information

This section provides Operation and Maintenance (O&M) information for theOTDOA User Plane Location Support feature.

7.1 Feature Activation StepsThis section describes the main process steps for feature activation.

7.1.1 Entering Cell Parameters

The first step in the activation is to enter the cell parameters needed for locationsupport. These parameters are defined in the EUtranCellFDD MOs. Iflocation support is defined for a new cell, some generic cell parameters mustbe entered as well. Information on the generic parameters can be found inRadio Network.

The parameters can be grouped as follows:

Cell identification parameters (if this is a new cell) Cell frequency and cell power parameters (if this is a new cell) PRS configuration parameters

Cell geographical parameters

Cell timing parameters

Feature activation parameter on cell level

7.1.2 Lock and Unlock Cell

To put the parameters (entered in the previous step) into effect, the cell mustbe manually locked and unlocked. The cell parameters above can also beentered when the cell is in the locked state and the parameters will then takeeffect when the cell is unlocked. Here take effect means that the PositioningReference Signals (PRSs) are transmitted in accordance with the parametervalues set in the previous step. Scheduling of user data is stopped in thosesub-frames where PRS is transmitted.

When unlocking the cell, the GPS time stamp for the latest occurrence ofSub-frame Number Zero (SFN0) is retrieved and the corresponding read-onlyManaged Objects Model (MOM) parameters are set by the eNodeB. TheseMOM parameters are updated whenever a change of synchronization statetakes place in the cell.

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Note: The time stamp is written into two MOM parameters, one for theinteger part (gpsTimeSFN0Seconds) and one for the fractional part(gpsTimeSFN0DecimalSecond). The unit of the fractional part is2^(-32) second.

7.1.3 Unlock Cells Fails Due to Erroneous Parameter Setting

When the operator uses the MOM parameter prsConfigIndex to set the PRSperiod and PRS sub-frame offset, the eNodeB checks that this setting does notcause a collision in the air between the PRS signals and the SIB1 message.If there is a collision, the cell does not become active and the operator musttry another setting before trying to unlock the cell. An alarm is issued that inthe Additional text will state Parameter setting not supported: prs This isinterpreted as Current PRS setting will cause collision with SIB1 and is thusnot acceptable, try another PRS setting.

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toc1 Introduction1.1 Basic CharacteristicsDependencies1.2 Benefits1.3 Additional Information

2 Feature Operation2.1 Network Requirements2.2 Feature Operation Sequence Diagram2.2.1 PRS Configuration2.2.2 LIS2.2.3 Power Scaling2.2.4 Mapping to Resource Elements

3 Parameters3.1 Introduced Parameters3.2 Affected Parameters

4 Network Impact4.1 Capacity

5 Associated Features and Affected Functions5.1 Prerequisite Features5.2 Affected Features5.3 Related Features5.4 Affected System Functions

6 Performance 6.1 KPIs6.2 Counters6.3 Events

7 O&M Information7.1 Feature Activation Steps7.1.1 Entering Cell Parameters7.1.2 Lock and Unlock Cell7.1.3 Unlock Cells Fails Due to Erroneous Parameter Setting

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