LTE Positioning Technology for Mobile Devices: TEsT .../media/White Papers/Mobile/LTE_Test... · SPIRENT WhITE PAPER • 2 LTE Positioning Technology for Mobile Devices: Test Challenges

LTE Positioning Technology for Mobile Devices:

TEsT ChaLLEngEs anD soLuTionsFebruary 2012

Rev. A 02/12

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LTE Positioning Technology for Mobile Devices: Test Challenges and solutions

SPIRENT WhITE PAPER • i

CoNTENTSIntroduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

overview of LTE Positioning Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

Three Positioning Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Three Positioning Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

SUPL 2.0 Expands from LTE to GSM/GRPS, WCDMA, and CDMA . . . . . . . 3

Challenges of LTE Positioning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

Five Test Challenge Categories. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Antenna Performance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Ensuring Receiver Performance and Measurement Accuracy . . . . . . . . . 6

Verifying Reliable Protocol Exchange. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

End-to-End Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Performance in Real World Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

overcoming Challenges of LTE Positioning . . . . . . . . . . . . . . . . . . . . . . . 10

Standardized Testing for LTE Positioning . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

3GPP Minimum Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3GPP Signaling Conformance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

oMA SUPL 2.0 Enabler Tests (ETS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

CTIA A-GPS oTA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

operator Acceptance Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

R&D Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

Antenna Performance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Ensuring Receiver Performance and Measurement Accuracy . . . . . . . . 15

Verifying Reliable Protocol Exchange. . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

End-to-End Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Performance in Real World Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . 17

The Future of LTE Positioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

Spirent offerings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20

LTE Positioning Technology for Mobile Devices: Test Challenges and Solutions

1 • SPIRENT WhITE PAPER

INTRoDUCTIoN

The rapid rise in popularity of Location Based Services (LBS), as well as the FCC’s E911

mandate in the US which requires location (with certain accuracy limits) of emergency

callers to be provided, is driving the wireless industry to evolve the positioning

technologies that enable these services. With the rollout of LTE comes a new focus on

enabling E911 and LBS performance on these networks, along with the need to provide

a seamless transition between positioning services on LTE and 2G/3G networks. New

enhancements are being introduced which are critical to enabling E911 requirements to

be met by LTE networks, and they bring the mobile industry one step closer to accurate

location everywhere, the key enabler for truly mainstream LBS adoption.

Current LTE standards support three independent positioning techniques: Assisted

Global Navigation Satellite Systems (A-GNSS), observed Time Difference of Arrival

(oTDoA), and Enhanced Cell ID (ECID). There is new protocol for LTE called LPP (LTE

Positioning Protocol), although SUPL 2.0 (Secure User Plane Location) remains a key

user plane protocol for enabling LBS and E911 on some networks, with its support for

techniques such as WiFi positioning.

So by the end of 2012, most new LTE devices coming to market will likely be expected to

support satellite and cellular-based positioning technologies, together with techniques

such WiFi positioning and in some cases sensor-based capabilities. They will also

need to support the multiple protocols that enable positioning over LTE, WCDMA, GSM/

GPRS and/or CDMA networks. All this leads to greatly increased complexity and testing

challenges for chipset and device manufacturers.

This white paper discusses the challenges associated with deploying LTE positioning

in mobile devices, with a special focus on test methods that can be employed to

accelerate development and ensure the highest levels of positioning performance.

This white paper discusses the challenges associated with deploying LTE positioning in mobile devices, with a special focus on test methods that can be employed to accelerate development and ensure the highest levels of positioning performance.

SPIRENT WhITE PAPER • 2


oVERVIEW oF LTE PoSITIoNING TEChNoLoGy

Mobile devices that support all of the positioning technologies and features defined

in 3GPP Release 9 will offer effective and efficient positioning performance, but the

complexity associated with this technology presents a major challenge to those looking

launch LTE-enabled mobile devices. This section presents a very brief overview of LTE

Positioning Technology. More detailed information can be found in Spirent’s companion

white paper.1

Three Positioning Technologies

The LTE specifications in 3GPP Release 9 include three major handset based positioning

technologies: ECiD, a-gnss, and Downlink oTDoa (DL-oTDoa). ECID and DL-oTDoA are

cellular network-based technologies that depend on UE signal level measurements from

one or more base stations (eNodeBs) for position calculation. A-GNSS has historically

consisted of support for A-GPS, but support for A-GLoNASS is increasingly included as

well. A typical LTE mobile device that is intended to reach the market at the end of 2012

can be expected to support ECID, A-GNSS (A-GPS+A-GLoNASS), and oTDoA.

Three Positioning Methods

LTE positioning protocol (LPP) is used to exchange positioning information with the

network positioning entities and supports ECID, A-GNSS, and oTDoA technologies. LPP

is similar to protocols such as RRC, RRLP, and IS-801 which are already deployed in 2G

and 3G networks.2 LTE Positioning can be deployed using LPP control plane, LPP user

plane via suPL 2.0, or RRLP user plane via suPL 2.0. If RRLP is used, then positioning

will be limited to A-GNSS, as ECID and oTDoA information cannot be exchanged with

this protocol. Since individual operators may support one, two, or all three of these

methods, it is imperative that mobile devices support all methods.

1 For more information, please see “An overview of LTE Positioning” white paper on www.spirent.com.2 For more information, please see “Secure User Plane Location 2.0 Reference Guide” and the two webinars

“Unleash the Business Potential of LBS over LTE Using SUPL 2.0” and “SUPL 2.0 Conformance Requirements for LTE” on www.spirent.com.

LTE PosiTioning TEChnoLogiEs anD PRoToCoLs

ECID, A-GNSS, OTDOA

LPP, RRLP SUPL 2.0



SUPL 2.0 Expands from LTE to GSM/GRPS, WCDMA, and CDMA

In cases where SUPL 2.0 protocol is supported for user plane positioning in LTE, then

support for SUPL 2.0 over one or more 2G/3G technologies is also likely to be required.

This is advantageous for network operators because it provides one common user plane

protocol that can be used across all air interface technologies. For a “world phone”

device that supports GSM/GPRS, WCDMA, CDMA, and LTE, SUPL 2.0 would need to be

supported on all air interfaces, with IS-801, RRLP, and LPP as the underlying positioning

protocol.

As you can see from this very short overview of LTE Positioning Technology (and the

subsequent 2G/3G technologies that are required as a result), there are many new

challenges associated with LTE Positioning in mobile devices. The remainder of this

white paper breaks down the individual challenges likely to emerge as a result of

developing LTE Positioning. It also reviews both standardized and R&D test methods

intended to ensure the challenges are overcome long before devices get into the hands

of consumers.

ChALLENGES oF LTE PoSITIoNING

By the end of 2012, most LTE mobile devices are likely to support all of the following:

• A-GPS, A-GLoNASS, ECID, and oTDoA technologies (some will also support WiFi Positioning and sensor-based navigation capabilities)

• LTE Positioning: LPP Control Plane, LPP User Plane via SUPL 2.0, and RRLP User Plane via SUPL 2.0 (A-GNSS only)

• WCDMA Positioning: RRC Control Plane, RRLP User Plane via SUPL 1.0, and RRLP User Plane via SUPL 2.0

• GSM/GPRS Positioning: RRLP Control Plane, RRLP User Plane via SUPL 1.0, and RRLP User Plane via SUPL 2.0

• CDMA Positioning: IS-801 Control Plane and IS-801 User Plane via SUPL 2.0

While some of these options will be enabled or disabled to suit specific operator needs,

this still represents a major challenge for the chipset and device manufacturers, who

need to support all the different technologies and protocol combinations.

This white paper focuses on LTE Positioning, as many of the 2G and 3G challenges are

not new (with the exception of SUPL 2.0 support). It also focuses on challenges from

the perspective of testing in the lab, using a controlled environment to analyze and

replicate issues.



ExaMPLE: LTE PosiTioning TEsT ChaLLEngEs

Five Test Challenge Categories

The challenge of testing LTE positioning can be broken down into five categories:

1. Antenna Performance

2. Ensuring Receiver Performance and

Measurement Accuracy

3. Verifying Reliable Protocol Exchange

4. End-to-End Performance

(e.g. Location Accuracy, Response Time, yield)

5. Performance in Real World Conditions

The following figure illustrates how these five test challenges map to the 7-layer

implementation stack.

1

2

34

5



Antenna Performance

LTE introduces MIMo, which makes use of more than one antenna on the UE, and the

performance of this antenna configuration will affect oTDoA performance. The same

principle applies to the GNSS antenna. Factors including interference concerns, form

factor, orientation and antenna placement must be taken into account during the

design phase in order to ensure optimal performance. Devices with the best performing

receivers can be crippled if antennas and/or device form factors cause signal reception

issues. With more and more radios and operating bands supported by already small

mobile device form factors, these tradeoffs can represent a tremendous challenge to

optimize.

ExaMPLE: gPs oTa Performance in Presence of LTE signal interference

• GPS signals in L1 band (1575 Mhz) may suffer interference from strong LTE signals

• Second harmonic of LTE Band 13 in LTE band

• LTE Band 24 is adjacent channel to GPS L1

• Radiated oTA testing is the ideal method for determining impact



Ensuring Receiver Performance and Measurement Accuracy

Making accurate measurements under realistic conditions is the foundation of

positioning performance in GNSS and LTE receivers. if devices are unable to make

accurate measurements, or if accuracy degrades in challenging but realistic conditions,

then positioning performance will be an issue. For LTE Positioning, four types of

receiver performance issues must be characterized:

1. a-gnss Receiver Performance: A-GNSS (likely A-GPS + A-GLoNASS) receivers must be

tested under a variety of challenging GNSS conditions, such as low satellite levels/visibility,

multi-GNSS, poor hDoP, etc. Sensitivity must also be characterized, as this plays an

important role in the availability of A-GNSS positioning in the real world.

2. oTDoa Receiver Performance: This depends heavily on Reference Signal Time Difference

(RSTD) measurement accuracy. This is directly related to Positioning Reference Signal

(PRS) acquisition, which can be difficult under challenging conditions such as fading,

variable BW, and cell timing offset. To work well in the real world, PRS acquisition and RSTD

measurements must be both accurate and reliable.

3. ECiD: ECID relies on estimating distance between the UE and eNodeB based on Round Trip

Time (RTT). The key measurement for determining RT is Timing Advance, and mobile devices

must report their measured receive-transmit time difference to serving eNodeB’s for Type 1

Timing Advance measurements (as defined in Release 9). The accuracy of this measurement

will impact the accuracy of the position calculation.

4. hybrid a-gnss+oTDoa Receiver Performance: Some devices will support hybrid A-GNSS/

oTDoA positioning to improve the performance of positioning when only 1 to 3 GNSS

satellites can be received. By combining oTDoA and A-GNSS measurements, a “hybrid”

position fix can be calculated. For this to work, the receiver must be able to acquire both

PRS and satellite signals (Multi-GNSS) simultaneously and accurately.

ExaMPLE: PRs acquisition and RsTD Measurement

• PRS acquisition is critical for determining accurate RSTD measurements which impacts oTDoA positioning performance

• PRS acquisition can be impacted by eNodeB antenna placement and physical location, PRS configuration parameters and relative signal strengths of serving vs. reference eNodeB

• Characterizing RSTD measurement accuracy with different patterns is very important

PRs Muting Pattern from Three LTE CellsReference enodeB #1

Reference enodeB #2

serving enodeB



Verifying Reliable Protocol Exchange

Assuming that GNSS, ECID, and oTDoA are validated, the next challenge is ensuring

that positioning information is reliably exchanged between the mobile device and

network entities through the various positioning protocols. Protocols such as LPP

and SUPL 2.0 are used to exchange assistance data from the network, receiver

measurements from the mobile device, and other positioning-related information. As

mentioned previously, LTE network operators are supporting both control plane and

user plane signaling, meaning that both need to be exhaustively testing to ensure

reliability in the real world.

1. Control Plane LPP: LPP uses procedures (a single action, such as requesting assistance

data) which are further grouped into transactions. Multiple procedures can be active at the

same time. In addition, signal measurements and/or position information can be returned

for multiple positioning technologies. This leads to extremely complex call flows.

2. user Plane suPL 2.0 (with LPP or RRLP): SUPL 2.0 has a vast and rich feature set which,

while offering advantages, can also complicate use cases. Along with complex SUPL call

flows (such as in geographic triggers and batch reporting), the underlying LPP call flows

must be studied for proper adherence to protocol. Link layer issues such as TCP/TLS errors

and packet bearer setup further complicate scenarios.

ExaMPLE: area Event Trigger

suPL 2.0 supports triggers based on entering (or leaving) a predefined geographic area.

1. LPP call flow required for positioning session

2. Must handle TCP/IP connection release or reconnect while waiting for trigger

3. Position accuracy of trigger is very important

4. UE must handle many back-to-back sessions

12

3

4



End-to-End Performance (e.g. Location Accuracy, Response Time, yield)

End-to-End testing refers to overall system performance, including positioning

accuracy and response time (also known as Time-to-first-fix, or TTff.) Even if receiver

performance and protocol reliability have been verified, there is no guarantee that

end-to-end performance will be acceptable. There are many factors and trade-offs

associated with optimizing accuracy, response time, and yield. For example, optimizing

for accuracy may come at the expense of response time, and vice versa. Furthermore,

LTE Positioning requires optimizing across several different positioning modes: A-GNSS,

oTDoA, ECID, and optionally oTDoA + A-GNSS hybrid. All of these technologies need to

be blended together to optimize performance in the real world. Because so many trade-

offs exist, this can be quite challenging.

ExaMPLE: oTDoa and oTDoa+a-gnss Position Calculation

End-to-end performance helps compare accuracy response time and yield

1. Four+ GNSS satellites likely to produce best accuracy

2. Four LTE base stations likely to outperform three LTE base stations for oTDoA positioning

3. hybrid GNSS oTDoA likely to produce the best yield (availability) although at the expense of accuracy (vs. GNSS)

vs.

vs.

vs.

1

2

3



Performance in Real World Conditions

Real world conditions encountered by the UE due to its signal environment make all

aspects of the positioning session challenging. Everything from signal acquisition to

reliable delivery of protocol messages is affected. Mobility scenarios, such as circuit

switched fall back to legacy networks, LTE inter-frequency handovers, etc. add to the

challenge. Real world performance is the most important metric for determining end

user satisfaction and adherence to the fCC mandate for E911. The following categories

of real world conditions can impact performance and should be considered when

implementing LTE Positioning:

• Multipath: Both GNSS and LTE measurements can be affected by multipath and fading, which are extremely common in the real world.

• signal obscuration: GNSS measurements can be greatly impacted by obscuration of signals from the sky. This is common in indoor environments, areas with dense trees, and urban areas with high buildings.

• interference: LTE deployments can result in GNSS interference becoming a larger issue for mobile devices. In some cases (Band 13), the 2nd harmonic of LTE spectrum is located right in the middle of the GNSS L1 band. In other cases (Band 24), spectrum is directly adjacent to the GNSS L1 band. Both present potential challenges and real world performance issues for mobile devices that support GNSS positioning.

• service interaction: Mobile devices such as smartphones are obviously capable of running many different services at the same time. For example, it is common to be talking on the phone while downloading email and using a location based service. Just because these services operate well in isolation does not mean they will work well together within the constraints of a mobile device platform.

• handovers and Mobility: Mobile devices are, by definition, made to move with their users. Since most LTE Positioning techniques depend on communication with network servers, it is imperative that this communication works reliably when handovers are occurring, within networks and between networks. Inter-RAT handovers (e.g. LTE to WCDMA handover) can be particularly problematic.

• Circuit switched fallback: Many early LTE deployments are making use of a feature called Circuit Switched Fallback, which allows data to be carried over LTE while voice calls fall back to 3G infrastructure, meaning that E911 calls will be placed on 3G networks. Since safety of life is at stake, it is very important to ensure that positioning sessions for E911 work well when a LTE mobile device falls back to 3G.



overcoming Challenges of LTE Positioning

While the opportunities for improved location performance and the applications it

enables are very exciting, it should be clear from the preceding sections that optimal

performance is far from easy to maintain. an important part of any development

program for LTE Positioning technology has to be an associated test strategy, which is

generally a mix of the following methodologies:

1. Field Testing, or testing with commercial infrastructure in the lab

2. Standards-based testing using test equipment, including specific tests required for

network operator acceptance

3. Lab-based R&D testing using test equipment

While field testing is likely to be a part of every LTE Positioning test strategy, it can be

costly to send people into the field to analyze performance. When problems are found,

it can be challenging to replicate the conditions precisely, which makes it hard to verify

that problems have been fixed.

Overcoming all of the challenges of LTE Positioning requires a comprehensive test strategy that includes both industry-standard and R&D test methods. This white paper explores all types of standardized tests and provides guidance on R&D testing that will provide a good return on investment.

ExaMPLE: Positioning during LTE to WCDMa or CDMa handover, or LTE-LTE inter-frequency handover

• LTE cells are interspersed among 3G and 2G cells, so inter-RAT mobility is common

• In the future, VoLTE E911 calls (and associated positioning sessions) will need to work reliably during inter-RAT handovers



STANDARDIzED TESTING FoR LTE PoSITIoNING

Considering that so many industries rely on GPS and other positioning and navigation

technologies, it is surprising that only the mobile device community has established

clear testing standards. Following the precedent set by standardization for 2G and

3G positioning, LTE Positioning minimum performance (end-to-end performance) and

signaling conformance (protocol compliance) test plans have been published by both

3gPP and the open Mobile alliance (oMa). This section presents a comprehensive

overview of these standards.

In addition to 3GPP and oMA test standards, several network operators around the

world have already defined, and continue to define, their own unique acceptance test

requirements for LTE Positioning in mobile devices. Many of these test requirements

hold devices to a higher performance bar, as network operators are highly motivated

to catch potential field issues before devices are launched. While some of these test

requirements start to look more like R&D performance tests, for the purposes of this

discussion they will be considered standardized tests, so long as there is a clear test

plan with agreed upon “pass/fail” performance metrics.

3GPP Minimum Performance

Test standards for LTE control plane positioning are covered under TS 37.571. Part 1

covers minimum performance of A-GNSS, oTDoA and ECID. The minimum performance

tests are similar to TS 34.171 and TS 34.1723 that measure A-GNSS performance on

UMTS networks. however, the LTE Positioning standard goes beyond just A-GNSS

to also include tests for ECID and oTDoA. The key focus of the test specification is

to characterize the minimum performance of the UE using each major positioning

technique. for a-gnss, analysis is based on a final position calculation, and for oTDoa

and ECiD, analysis is based on reporting of RsTD and cell measurements. Generally,

the signaling environment used in the tests is close to ideal with high power levels and

low multipath.

3 TS 34.171 and TS 34.172 have recently been added to TS 37.571 so that all location-related tests standards can be accessed from the same test specification.

TEsT CasEs

a-gnss• Nominal Accuracy• Sensitivity • Dynamic Range• Multipath • Moving Scenario

ECiD• Reporting of

Receive – transmit difference in

• TDD Mode• FDD Mode

oTDoa• RSTD

Measurement Reporting Delay

TesT Modes• UE- Assisted• UE-Based

TesT Modes• UE- Assisted

TesT Modes• UE- Assisted



3GPP Signaling Conformance

Signaling conformance cases are covered in 37.571 Part 2, and are similar to TS 34.123

and TS 51.0104 for UMTS and GSM networks. The key aim is to verify the use of LPP

under different call flows, including notification and privacy, position capability

transfer, error handling, assistance data delivery and position measurement. In

addition to these, Circuit Switched Fall Back (CSFB) is tested; this technique is used

when location is not supported by the E-UTRAN. When positioning is required, the

network redirects the position request to be handled by the E-UTRAN. The key aim of

the protocol cases is to ensure that messaging is correct. Signaling conditions are close

to ideal and horizontal accuracy is not a consideration.

oMA SUPL 2.0 Enabler Tests (ETS)

In addition to TS 37.571, the oMA SUPL 2.0 ETS describes a series of protocol cases.

SUPL 2.0 is independent of the air interface, and the enabler tests are defined for

multiple interfaces and positioning protocols. LTE is supported over both RRLP and

LPP protocol. Key SUPL 2.0 test cases of great commercial relevance are Area Event

Triggers and Periodic reporting. In these, both the SUPL call flow and the underlying

LPP call flow are tested. The entire specification has more than a 100 test cases, most

of which are applicable to LTE. As the primary focus of these cases is to test the SUPL

2.0 protocol, signaling conditions are close to ideal, with limited focus on accuracy

analysis. The main positioning technique of interest is A-GNSS, but there are a few test

cases covering ECID and oTDoA as well.

CTIA A-GPS oTA

Antenna testing for A-GPS oTA is standardized for UMTS, GSM and CDMA in the CTIA’s

3.1 version of the Test Plan for Mobile Station over The Air Performance. This test

plan formalizes the industry-standard method of measuring antenna performance in

a controlled radiated environment known as an anechoic chamber. Tests are defined

for measuring gPs antenna pattern, total isotropic sensitivity (Tis), and inter-channel

degradation (iCD)5. Looking ahead, the CTIA is planning to adopt a similar methodology

for testing A-GPS antenna performance on devices supporting LTE. The 3.2 version of

the CTIA’s test plan containing this enhancement is likely to be released during 2012.

4 The location-related portions of TS 34.123 and TS 51.010 have also been added to TS 37.571 so that all location-related tests standards can be accessed from the same test specification.

5 More information on GPS oTA testing can be found in Spirent’s “A-GPS over-the-Air Test Method” white paper on www.spirent.com.



operator Acceptance Testing

Apart from standards based testing, operators often define their own test plans.

Certain complex call flows are encountered in E-UTRAN deployments that may become

“trouble spots” for some aspects of positioning. These are generally scenarios involving

service interaction, difficult GPS or cellular conditions, or mobility scenarios. operators

may also be interested in specific positioning call flows (such as hybrid oTDoA +

A-GNSS). Much of operator acceptance testing revolves around performance and

R&D scenarios, which are organized as handset conformance requirements. These

acceptance test cases are crucial in helping operators compare handset performance

and are often key factors in influencing device selection.

R&D TESTING

Standardized tests ensure minimum UE positioning performance. The scenarios

generally assume ideal GNSS conditions and the variety of cellular conditions is limited.

While these tests are a good approach to ensuring the minimum functioning of the UE,

there are many important real-world scenarios that are not covered by any standard

tests.

in order to ensure end user satisfaction, it is important to test a variety of scenarios

and call flows that are beyond the scope of the standardized tests. For the purposes

of this white paper, all these non-standard test methods are grouped as “R&D Testing”.

The scope of R&D testing can become extremely expansive if every positioning function

is considered, but the most critical R&D test methods for LTE Positioning can be

grouped into the same categories as previously discussed in the Test Methods section:

1. Antenna Performance

2. Receiver Performance and Measurement Accuracy

3. Reliable Protocol Exchange

4. End-to-End Performance (e.g. Location Accuracy, Response Time, yield)

5. Performance in Real World Conditions



Antenna Performance

The CTIA test plan currently covers 2G and 3G A-GPS and Cellular oTA testing, and LTE

A-GPS/Cellular oTA is expected to be added in 2012. once defined, there are still

many antenna test considerations for R&D that are not covered by the standard. Key

examples include “quick” antenna performance analysis and A-GNSS LTE interference

testing.

Test time is a very important factor for R&D. Fast antenna characterization allows for

rapid prototyping and analysis of various designs. The CTIA procedure dictates very

specific conditions and parameters, and the tests will typically take 2-4 hours as a

result. For fast A-GPS antenna analysis, tests can be performed using modified test

parameters that speed up test time. This may come at the expense of accuracy or

reliability, but this is often an acceptable tradeoff when prototyping antennas.

LTE interference with GPS is an increasing concern in the industry. Prime examples are

Band 13 LTE signals which have a 2nd harmonic that lies directly in the GNSS L1 band

and Band 24 signals which are directly adjacent to the GNSS L1 band. oTA antenna

tests are the best way to characterize this interference, but standardized methods are

not sufficient to do this. As a result, multiple industry groups (to which Spirent was

an active contributor) have created test methods to characterize mobile device GPS

performance in the presence of these types of LTE interference sources.6

RECoMMEnDED TEsTs

• “Quick” oTA tests to analyze antenna performance in 15 minutes or less using modified test parameters

• A-GPS antenna performance in presence of Band 13 (2nd harmonic) and 24 (adjacent channel) LTE signals

• A-GPS+A-GLoNASS antenna sensitivity characterization

6 http://j.mp/FCCLightSquaredReport



Verifying Reliable Protocol Exchange

The LPP control plane signaling conformance tests defined in 3GPP 37.571-2 and

the user plane oMA SUPL 2.0 (w/ LPP or RRLP) ETS signaling test cases provide a

very comprehensive set of tests for ensuring major features work correctly. however,

real world scenarios will inevitably differ from the ones specified. To fully ensure

positioning session reliability, important protocol interactions must be thoroughly

tested beyond the standardized tests.

RECoMMEnDED TEsTs

RECoMMEnDED TEsTs

• Reliability of repeated LTE SUPL 2.0 positioning sessions

• Area Event triggers with complex LPP call flows, including multiple procedures and reporting of signal information using multiple positioning technologies

• Priority handling when multiple SUPL sessions happen at the same time

• User plane to Control Plane fallback (over LPP)

• Adversarial scenarios where network response is not as expected (especially important)

• oTDoA measurement accuracy with 2, 3 and 4 cells

• Simulating eNodeB synchronization errors and varying PRS offsets

• oTDoA measurement accuracy with varying PRS bandwidth and muting patterns

• A-GNSS measurement accuracy with realistic hDoP, multipath, obscuration mask, and satellite configurations

Ensuring Receiver Performance and Measurement Accuracy

Some basic receiver performance and measurement accuracy tests exist in 37.571 for

A-GNSS, ECID, and oTDoA, although all are performed under very basic and benign

conditions. To ensure performance in the real world, measurement accuracy must be

analyzed under a range of gnss and LTE channel conditions.



End-to-End Performance (e.g. Location Accuracy, Response Time, yield)

Complete end-to-end performance tests that measure the location accuracy,

response time, and yield are very important because they map directly to the

end-user experience. TS 37.575 does specify some basic end-to-end tests for

A-GNSS (not oTDoA or ECID), but the specification only applies to control plane LPP

implementations. Since most deployments will include user plane implementations

using LPP and/or RRLP, it is very important to test LTE User Plane (SUPL 2.0) end-to-end

performance.

The same is true for oTDoA, where only measurement accuracy tests are included in

the standards-based tests. To understand how well oTDoA really performs, end-to-end

tests that include a position calculation are required. Additionally, mobile devices will

return both GNSS and oTDoA measurements via LPP, and it is important to understand

how good the location accuracy can be in a variety of scenarios where one or the other

may not be completely available. In some cases, oTDoA and GNSS measurements can

be combined—in much the same way that AFLT and GPS measurements are combined

on some CDMA networks—to facilitate a hybrid position fix. This holds great potential,

but lab testing is essential to ensure it delivers the improved accuracy and availability

that is required.

RECoMMEnDED TEsTs

• LTE A-GNSS User Plane (SUPL 2.0) positioning performance (sensitivity, nominal accuracy, dynamic range, multipath, dynamic motion, …) for both RRLP and LPP

• oTDoA positioning performance (including position calculation) in realistic conditions

• SUPL 2.0 session positioning performance comparison (accuracy and response time) of cold start vs. warm start vs. hot start scenarios

• Accuracy of target area based triggers for geofencing applications



Performance in Real World Conditions

Performance in real world conditions is not covered by 3GPP or oMA standards. Some

operator requirements exist, but this type of testing is largely left unspecified. in the

real world, there are some very common scenarios that produce the greatest number of

issues in positioning performance. These include positioning sessions during mobility

and handover scenarios, positioning sessions in indoors or deep urban environments,

and positioning sessions taking place while other services are also running on a devices

(voice calls, data sessions, SMS, etc.). Testing these scenarios in the field can be

difficult because conditions are never the same. Fortunately, it is possible to simulate

these scenarios in the lab, and doing so allows the most common real-world issues to

be identified and worked through in a repeatable and representative environment.

ThE FUTURE oF LTE PoSITIoNING

Many new location technologies and protocols have been discussed in this white paper,

and everything discussed so far is likely to be developed and deployed in handsets by

the end of 2012. As we have come to expect, there will be more. Implementation and

deployment dates for these new features are unclear, but it is certain that they will be

coming in the next few years:

• oMa LPPe 1.07: The oMA is extending the LPP protocol defined by 3GPP in LPPe

Release 1.0. This protocol adds support for higher accuracy GNSS methods, emerging

network-based positioning techniques, and device-to-device positioning and

assistance data transfer.

• oMa LPPe 1.1: LPPe 1.1 is currently under development by the oMA as a

continuation of LPPe 1.0 in order to add the capability of broadcasting assistance

data, in addition to using point-to-point delivery. This will significantly reduce the

data-transfer load on the cellular network.

RECoMMEnDED

• Positioning session during LTE inter-frequency and LTE-3G (UMTS or CDMA) inter-RAT handovers, including change of positioning protocol (LPP, RRLP, IS-801)

• SUPL 2.0 persistence when radio link failures occur

• Interaction of multiple services (voice, data, SMS, location, etc.)

• Replicate field test points in the lab using advanced simulation and replay capabilities

7 http://www.openmobilealliance.org/Technical/release_program/LPPe_v1_0.aspx



SPIRENT oFFERINGS

Spirent is a global leader in location technology testing. Its 8100 and CS8 families of

solutions address both standards-based and R&D testing. The core test functionality

is delivered by the Location Technology System (LTS) for UMTS and LTE devices and

Position Location Test System (PLTS) for CDMA devices. Complete coverage for both

control plane and user plane positioning test standards is available. The LTS and PLTS

integrate Spirent’s market-leading GNSS simulators with multi-cell-capable cellular

network emulators. The systems support all major location protocols, and the LTS is

validated by the Global Certification Forum (GCF) and PCS Type Certification Review

Board (PTCRB) for conformance testing.

In addition to its conformance offerings, the LTS features an array of configurable

features for design verification or operator acceptance testing where flexibility in test

case configuration and test parameters is required. The test software features an easy-

to-use GUI that allows for quick test configurability and powerful test automation.

Results include raw measurement display, graphs, and decoding of all positioning

related messages exchanged over the air.

The CS8 solutions with their powerful, flexible interactive test capabilities, and

rapid configuration that requires little or no scripting, are intended for developers of

positioning capabilities in mobile devices or chipsets.

• suPL 2.1: SUPL 2.1 is currently under development by the oMA as a continuation of

SUPL 2.0 in order to add the capability to use a “Discovered SLP (D-SLP)”. A D-SLP

can be considered as a smaller, geographically localized SLP.

• oMa suPL 3.08: Version 3.0 of the SUPL protocol adds various functional

enhancements, including improved location for IP calls, improved location

performance, triggered location enhancements, improved indoor accuracy, SET to SET

location, authentication enhancements, privacy enhancements, additional access

networks, and support for extended location information.

• a-gnss + Wifi + network-Based + sensor hybrid Positioning9: In addition to the

oTDoA+A-GNSS hybrid positioning discussed in this white paper, there is a trend

towards blending additional positioning technologies in order to offer an accurate

location in all environments where mobile devices are used. WiFi Positioning and

Sensor-augmentation (e.g. accelerometers, barometers, magnetometers) are among

the most promising candidates, in addition to other network-based technologies

beyond just oTDoA and ECID.

8 http://www.openmobilealliance.org/Technical/release_program/supl_V3_0.aspx9 http://www.gpsworld.com/Wireless/expert-advice-getting-accurate-everywhere-location-12540



ExaMPLE: sPiREnT LTE TEsT CaPaBiLiTy

LTE/WCDMA/CDMA SUPL 2.0 ETS User Plane (LPP, RRLP, and IS-801): Testing conformance to the oMA’s SUPL 2.0 ETS specification is automated with Spirent’s series of SUPL 2.0 ETS protocol conformance test packages. Each suite of tests can be tested using a CDMA, GPRS, WCDMA, or LTE air interface, and RRLP, IS-801, and LPP positioning protocols are supported on applicable air interfaces. Please refer to Spirent’s “Secure User Plane Location (SUPL) 2.0 Reference Guide” for more information.

LTE SUPL 2.0 Positioning Performance: Spirent’s TestDrive LTS software includes a test for analyzing positioning performance metrics such as location accuracy, response time, and yield—much like a standardized minimum performance test with additional flexibility for testing beyond the standards. This test allows for the selection of a LTE air interface and SUPL 2.0/RRLP positioning protocol. Using this test, the end-to-end positioning performance of LTE devices can be analyzed. In addition, measurement accuracy metrics and protocol logs are recorded for root-cause analysis when performance issues occur.

oTDoA Measurement Accuracy: Testing a device’s ability to accurately measure oTDoA RSTD via PRS acquisition is easy with Spirent’s oTDoA measurement accuracy tests (based on 3GPP test specifications). SUPL 2.0/LPP positioning protocols are used to obtain RSTD measurements from UE, and accuracy is compared to actual time difference. Using this test, performance vs. PRS and LTE channel configuration can be analyzed.



SUMMARy

It should be clear from this white paper that, with the advent of LTE and requirements

for E911 and LBS on LTE networks, chipset and device manufacturers face greatly

increased complexity from the need to support an increasing number of location

technologies and protocols in their devices. In addition to the three major positioning

technologies specified for LTE (ECID, A-GNSS, and oTDoA), devices will also need

to support the three positioning methods (LPP control plane, LPP user plane via

SUPL 2.0 and RRLP user plane via SUPL 2.0), as well as the multiple protocols that

enable positioning over WCDMA, GSM/GPRS and/or CDMA networks. With this added

complexity comes a greatly increased testing need in order to ensure devices will

exhibit robust positioning performance after commercial deployment.

Standards-based testing for minimum performance, signaling conformance, SUPL

2.0 and A-GPS oTA play an important role in establishing the baseline positioning

capability of a device. however, with their ideal GNSS conditions and narrow range of

cellular conditions they are of very limited value in determining real-world performance.

To achieve this, it is important to test a variety of scenarios and call flows beyond the

scope of the standardized tests in areas that include antenna performance, receiver

performance and measurement accuracy, protocol exchange reliability, end-to-end

performance and performance in real world conditions. Although the device acceptance

test plans of some leading network operators go beyond the minimum requirements

of the standards, very few other test methodologies or test plans have been made

available, so this white paper included a comprehensive set of recommended tests for

each of the areas listed above.

With its global leadership and acknowledged expertise in location technology testing,

Spirent is well positioned to provide solutions that address all the areas required

to ensure the positioning performance of an LTE device, from standards-based

conformance to operator acceptance to oTA and R&D testing.

Documents

LTE Positioning Technology for Mobile Devices: TEsT .../media/White Papers/Mobile/LTE_Test... · SPIRENT WhITE PAPER • 2 LTE Positioning Technology for Mobile Devices: Test Challenges