July 22, 2016

LTE Impacts on GPS

Test and Metrology Plan

July 22, 2016

Prepared by: Dr. William Young, NIST

Dr. Daniel Kuester, NIST

Dr. Adam Wunderlich, NIST

Dr. Duncan McGillivray, NIST

Mr. John Ladbury, NIST

Dr. Marc Weiss, NIST

Dr. Sheryl Genco, NASCTN

Mr. Frank Sanders, ITS

Mr. Billy Riddle, NIST
July 22, 2016

Contents

Preface ..........................................................................................................................................................4

1 Background ...........................................................................................................................................5

2 Objective ...............................................................................................................................................5

3 Scope.....................................................................................................................................................6

4 Deliverable ............................................................................................................................................7

5 Test Methods........................................................................................................................................7

5.1 Overview .......................................................................................................................................7

5.2 Parameters....................................................................................................................................8

5.2.1 Device Under Test (DUT) Population ....................................................................................8

5.2.2 Global Positioning System (GPS) Satellites.........................................................................11

5.2.3 Augmentation Signals.........................................................................................................14

5.2.4 Long Term Evolution (LTE) Signaling Scenarios...................................................................14

5.3 Setup ...........................................................................................................................................15

5.3.1 Equipment...........................................................................................................................15

5.3.2 GPS Position Testbed ..........................................................................................................17

5.3.3 GPS Time Testbed ...............................................................................................................18

5.3.4 In-Band LTE Emulation........................................................................................................20

5.3.5 Out-of-Band Emissions (OOBE) LTE Emulation ...................................................................23

5.3.6 Measurement Locations.....................................................................................................24

5.4 Tests to Establish Data Collection Timing ...................................................................................24

5.5 Tests at Swept LTE Levels............................................................................................................26

5.5.1 Study LTE In-Band Coexistence Margins.............................................................................27

5.5.2 Emulate swept range ..........................................................................................................27

5.6 Time to First Fix...........................................................................................................................28

5.7 Test Matrix ..................................................................................................................................29

6 Statistical Considerations ....................................................................................................................30

6.1 Test Population ...........................................................................................................................30

6.2 Relevant Experimental Variables and Sources of Uncertainty.....................................................30

6.3 Analysis Plan................................................................................................................................31

6.3.1 Overview .............................................................................................................................31

6.3.2 Warm-up Time Assessment.................................................................................................31

6.3.3 Quantile Estimation.............................................................................................................32
July 22, 2016

7 Outreach and Community Feedback ..................................................................................................32

8 Data Management..............................................................................................................................32

9 Project Tasks.......................................................................................................................................32

10 Safety ..............................................................................................................................................33

11 References ......................................................................................................................................34

Appendix A. Estimating In-Situ Interference Response from Anechoic Measurement Results..............35

A.1. Introduction. ...................................................................................................................................35

A.2. Goal.................................................................................................................................................35

A.3. Interference Scenarios....................................................................................................................35

A.4. Systems Engineering Approach for Interference-Effects Measurement Studies...........................37

A.5. Impacts of Sharing a Single Transmit Antenna in Anechoic Tests..................................................37

A.6. Applying the SIR to Predicted System Performance.......................................................................37

Appendix B. Specifications of Antenna and RF Front End.......................................................................39

Appendix C. Procedures for Characterization and Calibration of Conducted Signals.............................39

C.1. Instrument Calibration....................................................................................................................39

C.2. Characterization of In-Band LTE Signal Generation........................................................................41

C.3. Characterization Out-of-Band LTE Signal Generation.....................................................................46

C.4. Characterization of L1 GPS Signal Generation................................................................................48

C.5. Uncertainty .....................................................................................................................................49

Appendix D. Procedures for Characterization, Calibration, and Validation of Radiated Power .............50

D.1. Calibration of Transmit Loss to Linear Polarization ........................................................................50

D.2. Calibration of Radiated Power Levels.............................................................................................50

D.3. Validating radiated signal levels at the DUT ...................................................................................52

D.4. Uncertainty .....................................................................................................................................53

Appendix E. Procedures and Considerations for Validating Calibrations...............................................55

E.1. Intermodulation Effects between Test Signals...............................................................................55
July 22, 2016

Preface

The “LTE impacts on GPS: Test and Metrology Plan” discussed in this document is intended to ensure 

these fundamental goals:

• a transparent, well-calibrated test method

• sound and statistically-valid data retrieval and processing

• a clear path from measurement setup to data collection to processed results

• inform discussions between different interests on proper measurement requirements

In pursuit of these goals, the NASCTN team initially focused on an anechoic or semi-anechoic chamber

test environment, as such testing represents a necessary component in achieving all of the goals above. 

The content in this version of the document reflects the initial development of the anechoic or semianechoic test method, but does not incorporate insight from any preliminary chamber tests that would 

naturally solidify the test plan. Incorporation of preliminary results will occur during in the first testing 

stage.

The ability to maintain consistent test conditions and parameters that are shared between any testing 

environments greatly impacts the ability to draw strong correlations between data collected via 

different methods. Thus, direct correlation to previous test results depends on strength of the linkage 

between test conditions and parameters that are common to the methods. Comparison of results 

between this test and any other tests are outside the scope of this effort; that relationship must be 

established by additional analysis. 

The waveforms used in this testing assume some basic features of a communication system 

architecture. An important aspect of this test includes an iteration with simultaneous activity both in the 

up and downlinks of the band, which are separated in the spectrum. The LTE waveforms assume certain 

levels, resource block usage, and data transfer rates. Typical for this type of testing, the downlink signal 

is a 10 MHz LTE channel with fully-allocated resource blocks; the uplink is a 10 MHz LTE channel with 

70% resource block allocation. 

There are several key features to this document, such as Section 7 Statistical Considerations and the 

calibration procedures in Appendix C, which provide valuable discussions that are highly relevant to 

similar test methodologies. In addition, Section 5 proposes testing of timing receivers by examining the 

output timing pulse train.

The test is designed to make a reproducible measurement with as few assumptions as possible. Namely, 

our approach aims to measure the response to a given ratio of GPS and LTE power levels in the GPS 

device, while limiting the number of extraneous variables. From this measurement, it will be 

straightforward to extrapolate the results to specific choices for various factors, such as:

• Antenna patterns

• Antenna polarizations

• Propagation environment

• Angle of arrival

• Separate antennas for GPS and LTE signal transmission.

NASCTN will solicit comments about the test plan from the engineering community within federal and 

non-federal groups and entities. 
July 22, 2016

1 Background

The National Advanced Spectrum and Communications Test Network (NASCTN) was established to 

support four key functions [1]: 

• Facilitate and coordinate spectrum sharing and engineering capabilities,

• Create a trusted capability for evaluating spectrum-sharing technologies,

• Perform outreach activities to identify spectrum-related testing and modeling needs, and

• Protect proprietary, classified and sensitive information while facilitating maximum 

dissemination.

In support of these functions, this NASCTN effort focuses on potential impacts of proposed Long Term 

Evolution (LTE) activities adjacent to L1 GPS receivers in tracking and reacquisition modes. The resulting 

test methods and data are intended to provide sound and transparent technical information that can 

support the technical dialogue between affected parties. 

In January of 2011, the United States Federal Communications Commission (FCC) granted a conditional 

waiver for the operation of a terrestrial communications network in a frequency band adjacent to that 

used by the Global Positioning System (GPS). This waiver required the users of the spectrum to prove 

that their transmissions would not interfere with existing GPS receivers. The resulting four-month 

(March to June, 2011) measurement effort brought together experts from the fields of communications, 

GPS, and EMC (Electromagnetic Compatibility), referred to as a GPS Technical Working Group (TWG). 

The TWG formed sub-teams to evaluate different types of GPS receivers (e.g., aviation, cellular, general 

location and navigation, precision timing, etc.) for possible interference effects. In addition, testing was 

performed by National Space-Based Positioning, Navigation, and Timing Systems Engineering Forum 

(NPEF) in October 2011 to January 2012. These efforts, including their test plans, paved the way for 

future efforts to assess potential interference between transmitters and GPS receivers.

However, even after the TWG presented their results, consensus on the definition of what constitutes 

interference to a GPS receiver has yet to be achieved. The GPS industry prefers to define interference as 

a 1 dB change in the carrier-to-noise-density ratio (C/N0) as reported by the receiver. This implies that a 

1 dB increase to the noise floor, as measured by any receiver in a shielded or direct-wired environment, 

is considered interference. Potential users of the spectrum adjacent to the GPS bands have proposed a 

definition based on the end-user experience. To complicate matters, many modern GPS receivers do not 

readily provide or fully define Key Performance Indicators such as pseudo range error or C/N0. This 

significantly impedes future evaluations of GPS receivers by users and license holders in frequency 

bands adjacent to GPS without the assistance and cooperation from GPS manufacturers.

2 Objective

The objective of this project is to establish a test methodology to investigate the impact of LTE 

transmission on GPS receivers in tracking and reacquisition modes. This test is not a pass/fail 

determination but rather covers a range of LTE power levels to determine the impact trends.

Specifically, an emulated 10-MHz-bandwidth LTE waveform is created by fully allocating the resource 

blocks with data representative of downlink activity. The uplink LTE is created by emulating a 10 MHz 

band with approximately 70% resource block allocation. A set of select GPS devices will be tested as part 

of test validation and the collection of a subset of data. 
July 22, 2016

The testing will make use of an anechoic or semi-anechoic chamber. A representative subset of available

devices will be tested in the anechoic or semi-anechoic chamber. As several comments solicited during 

the external review process have pointed out either directly or indirectly, there are tens of millions of 

GPS devices on the market. Testing a set of devices that represents the comprehensive market in a 

statistically complete manner is not practical in the timeframe of this testing. Details and descriptions in 

this test plan would allow testing of additional devices in an equivalent manner. The testing of devices 

representing different radio architectures e.g., narrow versus broadband, will be covered. 

3 Scope

The purpose of the GPS receiver measurement project is to develop a rigorous (i.e., a repeatable, 

calibrated, and well-documented) testing methodology and collect supporting data to establish the 

impact of LTE signals on GPS devices. The test method discussed here focuses on the anechoic or semianechoic chamber setup. Specifically, LTE waveforms representing a downlink band will occupy 1526 

MHz - 1536 MHz. The bands of 1627.5 MHz - 1637.5 MHz and 1646.5 MHz - 1656.5 MHz will contain 

uplink waveforms. The order of priority for testing are the 1526 MHz - 1536 MHz downlink, the 1627.5 

MHz - 1637.5 MHz uplink, the 1646.5 MHz – 1656.5 MHz uplink, and a waveform that includes

simultaneous up and downlink activity. Time-to-first-fix (TTFF) with LTE activity in the 1526 MHz - 1536 

MHz downlink and the 1627.5 MHz - 1637.5 MHz uplink will be tested.

A key aspect in the investigation is the quality and availability of measurands such as the signal-to-noise 

ratio (SNR), C/N0, position error, pseudo range error, loss-of-lock, etc. Emphasis is on real-world 

expected LTE signals. However, where practical, the LTE signal levels will cover a range of power levels 

that may inform LTE system architecture considerations. Since the specific architecture of deployment 

(e.g. base station density and location) is not yet known, to the extent possible, the testing is performed 

in a manner that seeks to be architecture agnostic.

An important consideration in the testing is the specifics of the LTE waveform. The downlink closest to 

the GPS band is generally considered the waveform most likely to cause disruption due to its high power 

and high utilization factor. The next waveform considered critical for interference testing is the uplink 

closest to the GPS band due to out-of-band emissions (OOBE).

The pair used for testing simultaneous LTE activity is the 1526 MHz - 1536 MHz downlink and the 1627.5

MHz - 1637.5 MHz uplink. The maximum power level is not expected in both bands at the same time, 

but simultaneous activity in both the uplinks and downlinks resemble a more realistic deployment 

scenario than operation in only the uplink or downlink portions of the band. 

The categories of devices for testing include general navigation and location, high precision position, and 

high precision timing. Aviation, space-based, cellular, and DoD devices of all categories are not included. 

The test procedure may require modification to include those additional categories of devices, such as 

base station connectivity for cellular devices or verification of consistency with testing required for 

certified aviation requirements. While a device from each category mentioned above is not tested here, 

as pointed out during the feedback process and consistent with radio architectures in general, the 

previous TWG and NPEF testing appear to indicate that the basic receiver RF architecture is the 

distinguishing feature, e.g., a narrowband versus wideband receiver, in determining susceptibility to LTE 

activity outside of the GPS band. 
July 22, 2016

Precision devices will be tested with the antenna specifically designed and typically included with that 

system. Replacement antennas that may provide additional filtering and amplification are not the 

primary focus of this test. Time permitting and in cooperation with the manufacturers, such antennas 

may be considered.

The initial measurements will focus on stationary devices, with a moving satellite constellation. Testing 

with the DUT in simulated motion, which represents a useful use-case for consideration, is not included 

in these test primarily due to test time limitations. The testing does include a limited satellite exposure 

condition; there are certainly other limited satellite exposure conditions that could be tested. 

Some important test considerations are: 1) the device-under-test (DUT) may not provide a mode of 

operation that allows collection of the desired measurands; 2) an accurate radiation pattern for the DUT 

will typically be unknown; 3) the DUT is generally not a metrology-grade piece of equipment. These 

factors shall be mitigated to the extent that is practical, but will contribute to the uncertainty of the final 

results.

4 Deliverable

The output of this project will be a test methodology and measurement data from a set of GPS devices

subject to nearby LTE activity. These data will be collected for several measurands identified in the 

sections below. Statistics on the collected data will be provided as discussed in the “Statistical 

Considerations” section below. Pass/fail criteria will not be discussed nor will conclusions be drawn by 

the testing team on the data collected.

The measurement process described here is intended to focus on the LTE waveform impacts on a GPS 

DUT. In order to compare those results to a field-deployment scenario, additional processing must be 

completed. To the first order, Appendix A describes how to carry-out that extrapolation process.

A key component will be the characterization of the setup. This is important to establish the veracity of 

the data. Appendices B through D discuss parameters important to characterization of the setup and a

calibration process. Appendix E provides an analysis on intermodulation products due to the bands of 

interest.

5 Test Methods

5.1 Overview

The anechoic or semi-anechoic chamber tests utilize GPS and LTE emulation to characterize the impacts 

of LTE activity in the bands previously discussed on various devices that utilize GPS. The data on the 

ambient RF conditions and temperature will be monitored and collected as part of the test process. The 

anechoic or semi-anechoic chamber tests will include atmospheric impairments in the GPS signal 

simulation. A key consideration in the use of either an anechoic or semi-anechoic environment is the 

shielding from external RF sources and the minimization of multipath contributions.

The test methods are designed to minimize the influence on factors such as polarization mismatch and 

path loss during the testing. Those factors should be included as the measured data is extrapolated to 

in-field performance estimates. Factors that are typically considered in the extrapolation process are 

discussed in Appendix A.
July 22, 2016

5.2 Parameters

5.2.1 Device Under Test (DUT) Population

The initial targeted set of DUTs for the experiment are listed in Table 1 through Table 4. This list may be 

modified to either include additional devices or remove devices where extraction of measurands is not 

achievable. In some cases, extraction of useable data from the devices will require cooperation from the 

manufacturer. Some key features and web links are included for each of the devices. 

The highest priority devices include four general location and navigation, three precision timing, and 

four precision location devices. In addition, based on feedback, the list now includes additional high 

precision devices rather than several lower priority devices. Lower priority devices are chosen for 

considerations such as ability to access the measurands (e.g. development boards) and representation 

of common user platforms (e.g. fitness devices). Both of these latter examples represent current and 

growing uses of GPS technology. The testing will focus on the highest priority devices, with testing on 

the lower priority devices on a time permitting basis.
July 22, 2016

Table 1. General Navigation and Location devices identified for testing. Some key features relevant to testing are included.

General Location and Navigation

Unit Antenna

PC 

interface

Data 

format(s) Extra KPIs Sub-type Website

Garmin eTrex H Internal USB

Flash

NMEA

GPX

NMEA 

params Hiking https://buy.garmin.com/en-US/US/into-sports/discontinued/etrexh/prod8705.html

Garmin eTrex 30x Internal USB GPX No Hiking https://buy.garmin.com/en-US/US/into-sports/handheld/etrex30x/prod518048.html

Garmin GPSMAP 78 Internal Serial NMEA

GPX

NMEA 

params Hiking https://buy.garmin.com/en-US/US/on-the-water/handhelds-wristworn/gpsmap-78/prod63601.html

Garmin Montana 680t Internal USB GPX No Hiking https://buy.garmin.com/en-US/US/into-sports/hiking/montana680t/prod523677.html

Garmin Montana 650t Internal ? Hiking

Table 2. High precision positioning devices identified for testing.

High Precision Positioning

Unit Antenna PC Interface Data

format(s) Extra KPIs Website

Trimble NETR9

Trimble 

Zephyr 

Geodedic

Antenna 

Model 2

Ethernet

Bluetooth

Onboard

NMEA,T02, RINEX v2, 

RINEX v3, Google Earth 

KMZ

all NMEA

RINEX

http://www.trimble.com/Infrastructure/TrimbleNetR9.aspx

Leica GR50

Leica AR10,

or Leica 

AS10

Ethernet

USB

RS232

Onboard

NMEA, RINEX, MDB, 

HATANAKA, CMR, CMR+, 

RTCM BINEX

all NMEA

RINEX

http://leica-geosystems.com/products/gnss-referencenetworks/receivers/leica-gr50-and-gr30

NovAtel FlexPak 628

NovAtel 

GPS-702-

GGL

Ethernet

USB

RS232

Onboard

NMEA, RINEX, MDB, 

HATANAKA, CMR, CMR+, 

RTCM BINEX

all NMEA

RINEX

http://www.novatel.com/products/gnssreceivers/enclosures/flexpak6/

NovAtel ProPak 6

Ethernet

USB

RS232

NMEA, RINEX, MDB, 

HATANAKA, CMR, CMR+, 

RTCM BINEX

all NMEA

RINEX

http://www.novatel.com/products/gnssreceivers/enclosures/propak6/
July 22, 2016

Onboard

Table 3. Precision timing devices identified for testing

Precision Timing

Unit Antenna Accuracy Ext. Oscillator 

Support

Lock state 

indicator Website

Arbiter 1088B GPS 

Satellite Clock (40ns)

Arbiter AS0087800 

GPS Active Timing 40 ns Yes Yes http://www.arbiter.com/catalog/product/model-1088b-gpssatellite-precision-time-clock-40ns.php

MicroSemi Symmetricom 

SyncServer S650

Microsemi Kit <15ns Yes Yes

http://www.microsemi.com/products/timing-synchronizationsystems/time-frequency-distribution/network-appliancesservers/syncserver/syncserver-s650

Novatel ProPak (OEMV) GPS-703-GGG Yes

MicroSemi TimeSource 

3050

Microsemi Kit Yes Yes

http://www.microsemi.com/products/timing-synchronizationsystems/time-frequency-references/telecom-primaryreference-sources/timesource-3050
July 22, 2016

5.2.2 Global Positioning System (GPS) Satellites

The configurations for the satellite constellation are based on a nominal and limited exposure setting, 

respectively. The emulated GPS signals will include the ionospheric and tropospheric propagation 

effects, as typically included in the Spirent simulated scenarios. Details for the constellation are listed in

Table 5, with examples of the constellations shown below. Losses from the calibrated test signal 

radiation to the DUT will be verified according to Appendix D.3.

Table 4. Satellite constellation setup.

Nominal

Number of generated satellites 11

GPS L1 C/A signal for each satellite -128.5 dBm

Additional transmit signals L1C pilot, Pseudo Y, 

and M-code

Time to First Fix

Number of generated satellites 8 to 13

GPS L1 C/A signal for each satellite -128.5 dBm

Additional transmit signals L1C pilot, Pseudo Y, 

and M-code

Limited Exposure 

Number of generated satellites 8 

GPS L1 C/A signal for 1st satellite -128.5 dBm

GPS L1 C/A signal for 2nd satellite -128.5 dBm

GPS L1 C/A signal for 3rd satellite -133.5 dBm

GPS L1 C/A signal for 4th satellite -133.5 dBm

GPS L1 C/A signal for 5th satellite -138.5 dBm

GPS L1 C/A signal for 6th satellite -138.5 dBm

GPS L1 C/A signal for 7th satellite -143.5 dBm

GPS L1 C/A signal for 8th satellite -143.5 dBm

Additional transmit signals L1C pilot, Pseudo Y, 

and M-code

Augmentation signals

Two WAAS satellites, W1 and W2 -128.5 dBm

GPS constellation power levels based on hypothetical 

power available from a 0 dBi antenna in the location of the 

DUT.
DRAFT 5/3/2016

July 22, 2016

GPS emulator (Spirent GSS8000 GNSS Simulator) is configured to provide a satellite constellation with 

the following features:

• Frequency: (L1 only) 1575.42 MHz

• Stationary Location: N 31 degrees 35.893636 minutes; W 110 degrees 16.670841 minutes; 

height 1352.30m 

• Satellite elevation mask angle of 5 degrees above horizon

• WAAS augmentation signals from two geostationary satellites: W1 (Intelsat Galaxy 15) at 133 

degrees W longitude and W2 (Telesat Anik F1R) at 107 degrees, 18 seconds W longitude.

• Initial Satellite configuration corresponds to July 4, 2016 at UTC time 01:40:00 (UTC 1:40 am)

Nominal Satellite Coverage:

For a nominal satellite coverage case the power levels of all satellites is fixed (all satellites in view 

transmit the same power) to correspond to -128.5 dBm at plane of the DUT. 

During a measurement power-level dwell period (on the order of 30 mins) the simulation provides 11 

GPS L1 satellites in view. 

Figure 1. The Nominal satellite constellation. Initial GPS constellation (left), after 30mins (right). All satellites in view are 

configured to emit -128.5 dBm at the plane of the DUT assuming a 0 dBi receiving antenna.

Limited Satellite Coverage:

For a limited satellite coverage condition the number of satellites is reduced to 8 satellites at a range of 

power levels with the following constellation profile.
DRAFT 5/3/2016

July 22, 2016

Figure 2. Limited satellite constellation. Initial GPS constellation (left), after 30 mins (right). Satellites in view will have a 

distribution of power levels at the plane of the receiver assuming a 0 dBi receiving antenna.

As the LTE power levels are incremented, the constellation is advanced by approximately 24 hours. A 

modified almanac was used to obtain similar geometries between the 24 hour intervals. Each DUT is 

tested using the same series of days.
July 22, 2016

5.2.3 Augmentation Signals

The intent of the testing is to focus on the LTE impacts on GPS. When possible, the DUT will be tested 

initially without augmentation signals to ensure that the impacts can be mapped to the GPS component 

of the receiver. Augmentation signals such as Wide Area Augmentation Signals (WAAS), Real Time 

Kinematic (RTK) solutions (e.g., signals from a secondary receiver), will be included as needed. Other 

navigation satellite constellations such as Galileo and Glonass are not considered and are not included in 

the GNSS simulation.

5.2.4 Long Term Evolution (LTE) Signaling Scenarios

The LTE waveforms emulated for signaling in these tests will be generic because the architecture of the 

proposed LTE system is not known to authors of this test plan. Emulated LTE waveforms and power 

levels will be chosen to mirror those in a few key scenarios relevant to the topic under study:

1. LTE Downlink (base station transmission) only, radiated toward a GPS L1 receiver,

2. LTE Uplink (User Equipment (UE) transmission) only, radiated in close physical proximity to a 

GPS L1 receiver,

3. Dual LTE uplink and LTE downlink activity - 1 and 2 (above) superimposed. For example, the 

downlink will be attenuated by 96 dB from maximum power (representing a free-space path loss 

of approximately one km) and the uplink will be stepped through a range of power levels. 

The LTE uplink and downlink frequency bands are each 10 MHz allocations as specified in Table 6. The 

LTE downlink band at 1670 MHz-1680 MHz will not be generated during test since a cavity filter is not 

currently available with this passband.

Table 5. Up and downlink frequencies.

Number LTE Link 

Direction

LTE Band

(MHz)

1 Downlink 1526 - 1536

2 Uplink-1 1627.5 - 1637.5

3 Uplink-2 1646.5 - 1656.5

Not Tested Downlink 1670 - 1680 

Waveforms will be designed to match the emissions masks under consideration in [8]. These emission 

masks specify effective isotropic radiated power (EIRP) power spectral density (PSD) limitations or LTE 

UEs and base stations. They are illustrated by Figure 3 in relation to GPS L1 and LTE operating bands 

under consideration.
July 22, 2016

Figure 3. Proposed in-band and out-of-band LTE emission masks under study near the radio navigation satellite service (RNSS) 

allocation used by GPS L1.

5.3 Setup

5.3.1 Equipment

The nominal equipment needed to conduct these measurements are listed in Table 7. Substitute 

equipment that meets the necessary performance criteria may be used. The final report will include the 

actual equipment used during the testing.

Either a semi-anechoic or a fully anechoic chamber is appropriate for the test setup described here. The 

key considerations are the RF shielding from outside signals and the control of multipath contributions, 

i.e., reflections inside the chamber, at the location of the DUT. In addition, in a semi-anechoic chamber, 

the reflection off the floor, i.e., the “ground bounce”, should have minimal contribution at the DUT 

location. If necessary, adding RF absorber on the floor between the transmitting antenna and the DUT 

will help attenuate any floor reflections. D.4 describes the calibration process for ensuring the correct 

radiated power at the DUT and for verifying minimal multipath contribution at the DUT.
July 22, 2016

Table 6. Equipment for anechoic or semi-anechoic chamber testing.

Item Example 

Manufacturer

Part Number

Manufacturer Specification Quantity

GPS emulator Spirent

GSS8000

(Provided by EPG) 1

LTE emulator Rohde Schwarz

SMW200A (or similar)

With LTE emulation option 2

Isolator Fairview Microwave

SFI1020 (or similar)

1- 2 GHz

Isolation > 19 dB

2

LTE amplifier Varian Med S/N: 6459 

TWTA: VZL6941K1

1-2 GHz, 20 W 1

LTE amplifier EMPOWER Model: 2170-

00

1000-3000 MHz, 1000 W 1

Programmable 

attenuator

Mini-Circuits

RCDAT-6000-110 (or 

similar)

0.25 dB steps; 0.3 dB uncertainty 5

LTE downlink inband OOB 

rejection filter

Custom 

S/N: 1103007 Model 

Name: 

RMC1531B10M01

1560 MHz-1610 MHz 1

Duplexer Anatech 1542-1643D296 Separates an input into separate channels - LTE 

downlink bands and uplink bands 

2

Antenna (RHCP for 

anechoic or semianechoic chamber)

ETS-Lindgren

3102 

RHCP conical log spiral

Nominal 1 GHz-10 GHz; use gain calibration @ 3m

1

Antenna 

(validation horn)

ETS Lindgren

3115 (or similar)

Nominal 1 GHz-18 GHz; use gain calibration @ 10m 1

Spectrum Analyzer Rhode and Schwartz 

FSW26 ID: 

1312.8000K26-103545-

UQ

2 Hz -26.5 GHz 1

Network Analyzer Agilent 8753ES 30 KHz – 3 GHz 1

Signal generator 

for LTE OOB 

emission

Rhode and Schwartz 

SMBV100A 

9k kHz – 3.2 GHz, Requires ARB capability 1

Time Interval 

Counter

Keysight Technologies

53220A (or similar)

Single shot resolution 100 ps 1

Temperature 

monitor

Pyle Digital 

Hygrometer/Thermo

meter USB DataLogger PTHDL170

-40 to 221° F 1

Band Pass Filter K&L 4CP120-

1651.7/E10.3-O/O 

Custom OOBE filters 1 

Band Pass Filter K&L 4CP120-

1632.7/E10.3-O/O

Custom OOBE filters 1 
July 22, 2016

Air Dielectric 

Hybrid Coupler

H-3-CPUSE-N-Ai6 698-2700 MHz 3

High Power 

Amplifier

Minicircuits ZHL-4W422+500 to 4200 MHz, 4W, 1

Precision Timing Cable Web Link Length

FSJ1-50A, HELIAX® Superflexible Low Density Foam 

Coaxial Cable, corrugated copper, 1/4 in, black PE 

jacket

http://www.commscope.com/catalog

/andrew/product_details.aspx?id=13

42

53.4 m

LDF2-50, HELIAX® Low Density Foam Coaxial Cable, 

corrugated copper, 3/8 in, black PE jacket

http://www.commscope.com/catalog

/wireless/product_details.aspx?id=13

51

55 m

5.3.2 GPS Position Testbed

The position tests investigate how the LTE waveform impacts the GPS receiver’s ability to provide 

accurate position. Figure 4 depicts the setup in the anechoic or semi-anechoic chamber that provides 

the GPS environment and the LTE waveform. Some of the key features are the addition of out-of-band

emission (OOBE) noise and the custom OOBE filter on the downlink signal. The test process is to setup 

the desired GPS constellation state, and then follow the process depicted in Figure 10. The inclusion of 

augmentation signals such as WAAS and RTK will be included as necessary. It is important to recognize 

that these tests are focusing on the change in the baseline due to the LTE activity, not on the precise 

locations. The DUT will be reset to operate under the same conditions during LTE activity as the during 

the establishment of the baseline.

The test setup depicts a single antenna radiating both the GPS and LTE signal. This setup will need to be 

checked carefully to ensure proper isolation between the two signal paths. The calibration process 

(Appendix C) will ensure that proper isolation is maintained, and that the cable and coupler losses and 

antenna gain and polarization factors (e.g. circular versus linear) are accounted for in the setup. The 

purpose for using a single antenna rather than two separate antennas is to remove potential orientation 

bias between the transmitting antennas and the DUT, and thus reduce the uncertainty in the ratio of LTE 

to GPS power received by the DUT. In post analysis, factors such as antenna mismatches and path loss 

can be included to relate the measurements to deployment scenarios.

Adequate isolation between channels is necessary to ensure that coupled signals between signal paths 

do not cause problems. This needs to be verified experimentally before testing begins. If the isolation 

provided by coaxial paths and large attenuation levels is not sufficient, additional isolators can be added 

to the testbed. When possible, isolators will be removed in order to minimize the number of devices in 

the signal chain and maximize flatness across the wide 1526 MHz – 1680 MHz operating band.
July 22, 2016

If proper isolation in the LTE and GPS signal paths is not achievable with a single antenna, then a two 

antenna setup will be used, with separate signal paths for the LTE and GPS waveforms. The same 

calibration process will be required as the use of two antennas by no means ensures the isolation 

between the signal paths. In addition, care must be taken to minimize the impacts of antenna coupling

on the antenna patterns. A primary drawback to using two antennas is the increased uncertainty in the 

power ratio of the LTE and GPS signals received by the DUT antenna.`

Figure 4. Setup for position measurements in the anechoic or semi-anechoic chamber.

5.3.3 GPS Time Testbed

Timing variations can be greatly influenced by the GPS receiver, antenna, and receiver-to-antenna cable

individually, and impedance matching among them. Hence it is important to measure them as a 

combined unit. The cable length also contributes to timing variations, and a length should be chosen 

that maximizes these variations [2].
July 22, 2016

Each GPS satellite transmits its own version of UTC with errors in the transmitted values as well as due 

to the propagation medium. Timing receivers all produce a 1 PPS to realize the best estimate of UTC, 

and many can also provide data that give the individual satellite UTC values as offsets from the 1 PPS 

out. 

Figure 5 illustrates the test setup for timing tests. Some additional considerations for the calibration and 

measurement process from the position test are discussed below

First, the time accuracy of the receiver is first measured without an LTE signal. This should be done with 

minimal filtering by an oscillator in the receiver. The test focuses on the performance of the antenna, 

cable, and receiver system, not the ability of an oscillator to filter these. For example, a rubidium (Rb) or 

cesium (Cs) atomic frequency standard could greatly slow the appearance of any bias, but could not stop 

it. The calibration continues until the variations in UTC from the receiver stabilize. 

Second, during the test, LTE signals are introduced in the adjacent band at minimal power levels, then 

stepped up until the receiver loses lock. This is the process shown in Figure 10. Timing data are stored to 

allow determination of UTC accuracy and stability for the 1 PPS and, if available for each individual 

satellite. 
July 22, 2016

Figure 5 Setup for precision timing tests in the anechoic or semi-anechoic chamber.

5.3.4 In-Band LTE Emulation

The LTE in-band downlink (base station transmission) signaling will be synthesized for all tests at the full 

10 MHz frequency allocation and full resource block allocation.

The uplink interference signal is meant to represent a single LTE UE uploading streaming video to a base 

station over a weak link. The data load is a pseudo-random binary sequence. There are two candidate 

channel configurations: 1) a single 10 MHz wide channel filling the full allocation, consisting of 50 

available resource blocks (RBs), and 2) two 5 MHz channels to fill a full allocation, each consisting of 25

available RBs. The base station compensates for the weak link with fair scheduling, limiting the number 
July 22, 2016

of RBs allocated to our UE. For each channel configuration, we assume a relatively large 70% RB

allocation (35 RBs for the single 10 MHz channel, or 18 RBs for each 5 MHz channel). The UE 

compensates for the weak link by transmitting the quadrature phase-shift keying (QPSK) at its maximum 

allowed EIRP following Figure 3. Proposed in-band and out-of-band LTE emission masks under study . 

Resource blocks are distributed by Type-2 PUSCH frequency hopping, resulting in an RB allocation time 

plan as illustrated in Figure 6 and a spectrum like that in Figure 7. This uplink corresponds with 7 Mbps

maximum data rate.

Figure 6. Example LTE uplink resource block allocation
July 22, 2016

Figure 7. Example PSD measurement of a 10 MHz LTE uplink

The LTE in-band waveforms used in testing will also include scenarios that include both uplink and 

downlink activity. In the dual link configuration, the waveform shall depend on the results from testing 

up and downlink bands individually. The pair combination will include activity closest to the GPS band. 

The scenario represents a GPS unit located near is a fully-allocated downlink signal from a base station 

while a UE is also sending data to another base station on an uplink. These data will provide insight into 

the acceptable density of UE and base station nodes on GPS.

In-band LTE signals in the test system will be filtered to help ensure that the OOBE levels (section 5.3.5)

are determined by synthesized noise and not the spectral “skirts” of the LTE waveform synthesizer. A 

commercial, off-the-shelf (COTS) duplexer in the test system will isolate the LTE uplink and LTE downlink 

frequencies, and help limit OOBE from the in-band generation path.

The OOBE of the LTE synthesizer will be minimized (potentially with the help of added filtering) to 

ensure that in-band and OOBE signals are controlled by their designated signal paths. Roll-off of the inband LTE downlink path will be achieved in part with a cavity filter, which is taken to be representative 

of a practical deployment. The LTE uplink path specifies OOBE in the GPS L1 band at 98 dB below the inband level. Cavity filtering is not generally practical for deployable UEs, but may be used in the emulated 

path to ensure that uplink OOBE spectral density is strongly dominated by the OOBE signal path.

A key consideration in the testing process is the expected physical separation between the UE and the 

GPS receiver. The LTE emissions masks are defined at the LTE systems, but the risk of interference is 

determined by the LTE level at a GPS receiver. The relationship between these is an attenuation level 

determined by the propagation environment; meaningful use cases need to be considered carefully to 
July 22, 2016

determine a reasonable range of attenuation levels for test. In the anechoic or semi-anechoic

environment, this attenuation can be translated to range with the Friis transmission equation.

In the LTE uplink, the UE radiator is assumed mobile, and a proximity of less than 1 meter is possible in a 

deployment. Tests can gauge the equivalent response of a DUT at different distance in an anechoic or 

semi-anechoic chamber by adjusting the transmit power. Figure 1 shows the path loss due to separation 

distance. Intuitively, a test run with the DUT separated from the transmit antenna by 3 m needs to 

transmit extra power to determine the response of the DUT at a separation distance 0.5 m. This power 

correction in Figure 8 below shows the path loss due to separation distance. This path loss must be 

taken into consideration when determining power levels at the DUT. Actual losses from the calibrated 

test signal radiation to the DUT in the test will be verified according to Appendix D.3.

Figure 8. Path loss calculations based on the Friis transmission equation. 

5.3.5 Out-of-Band Emissions (OOBE) LTE Emulation

Out-of-band emissions (OOBE) are critical aspects of the LTE uplink and LTE downlink spectrum masks

that need to be fully emulated to support testing across a wide range of power levels (or equivalently 

various separation distances). These waveforms will be synthesized in a separate instrument from the 

in-band emissions, then added to in-band emissions with a combiner.

Wideband LTE OOBE waveform generators are not known to be commercially available to the authors of 

this test plan, and therefore not expected to be feasible for testing. As a surrogate, OOBE transmit 

signaling will be additive white Gaussian noise (AWGN) filtered to meet the OOBE emission limit masks

of Figure 3. Signal levels will be calibrated as discussed in Appendices B.3 and C.2, respectively, and 

validated according to the procedure in Appendix C.3.
July 22, 2016

The waveforms will be predesigned to last for several seconds and uploaded as the baseband 

modulation input to signal generator. The I/Q waveforms will be circular AWGN in baseband with 

bandwidth of 109 MHz centered at 1595.5 MHz (1541 MHz – 1650 MHz), filtered to match the emissions 

mask. Because there are separate uplink and downlink emissions masks, OOBE noise will need to be 

generated for each and summed together in baseband.

5.3.6 Measurement Locations

The testing will take place at the National Test Systems (NTS) facility in Longmont, CO. The facility

utilized will be a 10-meter, semi-anechoic chamber. 

5.4 Tests to Establish Data Collection Timing

The primary measurement protocol requires stepping through a range of power levels and collecting

data from the DUT at each level. The amount of data collected at each LTE power level is based on 

establishment of steady state conditions, as described in the Statistical Considerations section below.

Power level increments are determined by an initial investigation of the DUT behavior and the eventual 

maximum power level sought. 

The process for establishing the time needed to collect sufficient data at each step is shown below. The 

first part, shown in Figure 9, is to capture a relatively long time series of data with no LTE signal activity. 

Offline processing is used to determine the time for stability, ts. During the portion of the test that 

includes LTE activity, an additional amount of time, tmeas, is added for the collection of data after 

reaching steady state. The total of the two times is called the capture time, tc . As depicted in Figure 10, 

at each LTE power level, data are captured for a time duration of tc . 
July 22, 2016

Figure 9. Process to establish data collection time for the DUT.
July 22, 2016

5.5 Tests at Swept LTE Levels

We propose here two approaches of swept LTE power levels to study the impact of LTE waveforms on 

GPS receivers. While either test pattern may produce results that are useful for coexistence analysis, 

they are inherently linked when considering practical deployments. The first approach assumes a fixed 

Figure 10. Process to increment LTE power for a specific waveform and collect data from the DUT.
July 22, 2016

physical distance between the LTE signal and the DUT and will be given preference in the testing. The 

second approach assumes that the physical distance between the LTE source and the GPS device varies 

over a range. If time permits, both types of testing will be performed.

5.5.1 Study LTE In-Band Coexistence Margins

This test fixes the power level of the out-of-band emission while varying the power level of the in-band 

emission as in Figure 11. The out-of-band emission power-spectral density is fixed to that of Figure 3, 

whereas the in-band emission is variable. In stepping through the power levels, the victim receiver is 

stressed with the maximum admissible out-of-band emission for specified distance (e.g. 3-meter 

separation) and observations inform on susceptibility to additional LTE in-band power. This test method 

evaluates the validity of the proposed emission mask shape, as well as gives LTE infrastructure designers 

guidelines on maximum in-band power levels while preserving the currently proposed out-of-band 

emission limits. 

Figure 11. The in-band and out-of-band emission and the waveform mask for in-band LTE coexistence margin testing. Here, LTE 

out-of-band emission is held constant while LTE in-band emission is varied.

5.5.2 Emulate swept range

This test sweeps a path loss value that is approximately constant across the entire 1526 MHz - 1680 MHz

range. This emulates slow fading path loss between LTE transmitter and the GPS receiver. This scenario 

assumes changes in the fading channel between the DUT and the LTE transmitter due to factors such as 

changes in physical separation distances between the DUT and the LTE transmitter. The spectral shape

in

-

ban

dem

issi

o

n

out-of-band

emission

Mask
July 22, 2016

of the emission mask (the ratio between in-band to out-of-band emission) of the LTE waveform is 

preserved, and simply shifted up and down.

Figure 12. The in-band and out-of-band emission and the waveform mask for swept range emulation. The same losses apply to 

both in-band and out-of-band emissions.

This test aligns closely with propagation analysis through the Friis transmission equation. This, coupled 

with assumptions about noise levels inside the GPS receiver, connect transmitter and victim path loss 

and LTE impact on GPS receivers. The result may be to inform on spectral emission mask tolerances, LTE 

infrastructure design decisions, and to consider operating characteristics of GPS devices at various 

separation distances from LTE emitters near GPS L1.

5.6 Time to First Fix 

Time to first fix (TTFF) is the measure of the time a DUT takes to reacquire GPS lock after loss of signal 

through either a warm start or a cold start. In the warm start case, GPS signal is terminated for treaq

seconds and then reintroduced. For a cold start, the GPS signal is held constant, however the DUT is sent 

a command to initialize a cold start as per manufacturer specification. It is important that treaq be chosen 

such that the DUT will have sufficient time to acquire or reacquire a lock on the GPS signal. Note that 

treaq is not necessarily equal to ts discussed above.

The TTFF is being conducted in a nominal GPS satellite constellation and a fixed LTE power level, where 

the exact LTE power level will be determined during the Phase 1 testing of the devices. TTFF will be first 

tested with a downlink LTE waveform and subsequently an uplink LTE waveform. The warm/cold start 

cycling is performed a sufficient numbers of times to obtain sufficient data for meaningful statistical

analysis.

The warm start sequence is described below: 

1) GPS signal is turned on to nominal power level;

2) LTE signal is turned on to specific power level;

3) The DUT is started up and data collection begins;

4) After treaq seconds the GPS signal is attenuated such that the DUT loses lock;

5) Wait for treaq seconds;

6) Reintroduce GPS signal;

7) Repeat steps 4 – 6 until sufficient number of reacquisitions are achieved;

in

-b

an

d

e

m

is

si

on

out-of-band

emission

Mask
July 22, 2016

8) Stop data collection and turn off DUT.

Cold start sequence is described below: 

1) GPS signal is turned on;

2) LTE signal is turned on;

3) The DUT is started up and data collection begins;

4) After treaq the cold-start command is sent to the DUT;

5) Wait for treaq seconds;

6) Repeat steps 4 – 6 until sufficient number of reacquisitions are achieved;

7) Stop data collection and turn off DUT.

5.7 Test Matrix

The table below lists the test phases. The satellite constellations are described in Section 5.2.2. An initial 

stepped LTE power test will determine the delta between LTE power steps. The time spent at each 

power step will be long enough to collect sufficient data for the accompanying the data analysis 

discussed below. 

Table 7. Matrix for the three phases of testing. The satellite constellation descriptions are provided in Table 5 and the uplink and 

downlink frequencies are given in Table 6. The stepped LTE is described in Section 5.5.

Phase 1

# Device Satellite 

Constellation

LTE Waveform LTE 

Power

Downlink Uplink1Uplink2Downlink 

+ uplink1

1 Garmin GPSMAP 78 Nominal x x x x Stepped

2 Garmin 2 Etrex 30x Nominal x x x x Stepped

3 Garmin 3 Montana 680T Nominal x x x x Stepped

4 Garmin 4 Etrex H Nominal x x x x Stepped

5 Trimble NetR9 Nominal x x x x Stepped

6 Leica GR30 Nominal x x x x Stepped

7 NovAtel Propak 6 Nominal x x x x Stepped

8 NovAtel FlexPak 628 Nominal x x x x Stepped

9 Arbiter Timing Nominal x x x x Stepped

10 MicroSemi Symmetricom 

SyncServer S650

Nominal x x x x Stepped

11 MicroSemi TimeSource 

3050

Nominal x x x x Stepped

Phase 2 Time to First Fix (TTFF)

1 Garmin GPSMAP 78 Nominal x x Fixed

2 Garmin 2 Etrex 30x Nominal x x Fixed

3 Garmin 3 Montana 680T Nominal x x Fixed

4 Garmin 4 Etrex H Nominal x x Fixed

5 Trimble NetR9 Nominal x x Fixed

6 Leica GR30 Nominal x x Fixed

7 NovAtel Propak 6 Nominal x x Fixed
July 22, 2016

8 NovAtel FlexPak 628 Nominal x x Fixed

9 Arbiter Timing Nominal x x Fixed

10 MicroSemi Symmetricom 

SyncServer S650

Nominal x x Fixed

11 MicroSemi TimeSource 

3050

Nominal x x Fixed

Phase 3 Limited Exposure

1 Garmin GPSMAP 78 Limited x x Stepped

2 Garmin 2 Etrex 30x Limited x x Stepped

3 Garmin 3 Montana 680T Limited x x Stepped

4 Garmin 4 Etrex H Limited x x Stepped

5 Trimble NetR9 Limited x x Stepped

6 Leica GR30 Limited x x Stepped

7 NovAtel Propak 6 Limited x x Stepped

8 NovAtel FlexPak 628 Limited x x Stepped

9 Arbiter Timing Limited x x Stepped

10 MicroSemi Symmetricom 

SyncServer S650

Limited x x Stepped

11 MicroSemi TimeSource 

3050

Limited x x Stepped

6 Statistical Considerations

6.1 Test Population

GPS devices from the following categories will be tested:

• general location and navigation

• high precision

• timing

A detailed enumeration of the GPS devices under test is provided in Table 1 through Table 4. To keep 

the test time and cost manageable, only a single unit of each device will be tested. 

Although the sample of test devices will be stratified according to category, it will not be randomized 

within each category. Therefore, there is a risk of selection bias in the test results. In addition, because 

only one unit of each device will be tested, variations in off-the-shelf performance will not be included in 

the test results. For these reasons, the conclusions that can be drawn from this test will be limited to the 

specific set of devices under test, and will not be rigorously generalizable to the population of all 

devices. 

6.2 Relevant Experimental Variables and Sources of Uncertainty

• Response variables: GPS lock (binary outcome), once GPS lock is achieved, available device outputs, 

such as position, time, pseudo-range values, C/N0, etc. will be recorded at regularly- spaced time 

intervals. Also, for a limited number of conditions, time to first fix (TTFF) will be evaluated. Note 

that the response variables will be device dependent. 

• Controlled variables: 
July 22, 2016

o GPS emulator parameters: number of satellites, satellite constellation, satellite signal-power 

levels, impairments (atmospheric effects, Doppler shift, multipath effects, satellite clock, 

and ephemeris errors)

o LTE emulator parameters: transmission band, power level, and resource block allocation

o Device position and orientation, start-up conditions, availability of augmentation, and 

indoor environmental conditions

• Uncontrolled variables: receiver antenna orientation (for embedded antennas), start-up device state 

(for devices without an accessible reset option) 

• Sources of uncertainty: variations in LTE and GPS signal strength, structure of LTE signals, satellite 

constellation, GPS signal impairments, GPS processing algorithm, start-up device state, receiver 

antenna orientation, and indoor environmental conditions

6.3 Analysis Plan 

6.3.1 Overview

The analysis aims to compare the steady-state distribution of each device output with LTE interference 

to the steady-state distribution of the device output without LTE interference (the “baseline”). Key 

steps of the analysis are as follows:

• Each time-series is first processed by estimating a warm-up period, which includes transients 

due to start-up or sudden changes in conditions. Subsequent analysis discards data from the 

warm-up period. 

• Steady-state distributions are compared by evaluating quantiles, e.g., median, 90th and 95th

percentiles, capturing differences in both typical and extreme behavior

6.3.2 Warm-up Time Assessment

The analysis of device outputs is predicated on the assumption that the device is operating in a steadystate condition. Non-steady-state behavior is expected at start-up or when the device is experiences a 

sudden change in conditions. Since the GPS simulator will be set-up so as to minimize sudden changes 

in the satellite constellation, transient effects are expected to be present only when the device is first 

exposed to a new test condition. 

The time at which transients are negligible, called the warm-up time, will be estimated with the 

approach of Alexopoulos et al.[3]. This procedure starts by dividing the time-series into non-overlapping 

batches of equal length and then estimates a specified quantile, e.g., the median, for each batch. Next, 

the von Neumann randomness test is applied to check if the batch quantiles are statistically 

independent. The procedure iteratively increases the batch size while decreasing the significance level, 

until the test is passed. Lastly, the final batch size is taken to be the warm-up time. In a nutshell, this 

method requires the warm-up time to be sufficiently large so that data from the initial warm-up period 

is independent of the remaining time-series. 

Once the warm-up time is estimated, all subsequent analysis will be carried out on the steady-state 

portion of the data that follows. Note that because the time required for the device under test to reach 

a steady-state condition will vary with the device as well as the test conditions, the warm-up time must 

be estimated for each device and test condition. 
July 22, 2016

6.3.3 Quantile Estimation

Quantiles of the steady-state distribution, such as the median, 90th, and 95th percentiles will be 

estimated in a nonparametric manner for KPIs such as position error, pseudo-range error, and C/N0. 

These estimates will enable comparison of the baseline distribution for each KPI without LTE 

interference to that with LTE interference. Statistical precision of the measurements will be evaluated 

by estimating confidence intervals for each quantile. 

One difficulty in the statistical analysis stems from the fact that the time-series of device outputs is 

expected to be highly-correlated. Classical statistical estimators of confidence intervals for quantiles 

are designed for independent samples, and they break down for dependent samples. Consequently, 

special methods designed for dependent sequences are required. Point estimates and confidence 

intervals for quantiles will be estimated with the averaged group quantile method of Heidelberger & 

Lewis [4], which is based on asymptotic theory for dependent sequences. 

To compare a given quantile for the baseline and LTE interference conditions, a confidence interval for 

the difference of quantiles will be formed from the respective quantile confidence intervals. A 

conservative coverage probability for the difference confidence interval can be justified with the 

Bonferroni inequality. The results for each KPI at a specified quantile will be presented by plotting the 

difference of quantiles versus LTE power level. 

7 Outreach and Community Feedback

NASCTN will solicit comments about the test plan from the engineering community within federal and 

non-federal groups and entities. 

8 Data Management

The following measures will be taken to manage data.

• Measurements will be recorded on local storage at the measurement site and will be physically 

removed by NASCTN personnel at the end of the measurement period. 

9 Project Tasks

The following are the major tasks of the project.

Develop and Write Test Plan

External Outreach and Test Plan Review

Comments received 

Feedback Review info to Test Plan

Test Preparation

Preliminary Semi-anechoic setup and baseline tests

Semi-anechoic chamber test

Data Analysis and Report

NASCTN Data and Report Review Process (including Director)

Issue Report
July 22, 2016

10 Safety

The anechoic or semi-anechoic tests are indoor laboratory tests and subject to all the typical safety 

concerns associated with such environment. 
July 22, 2016

11 References

[1] http://www.nist.gov/ctl/nasctn/nasctn_moa2015.cfm

[2] M. A. Weiss, F. G. Ascarrunz, T. E. Parker, V. Zhang, and X. Gao, “Effects of Antenna Cables on GPS 

Timing Receivers,” Proc. 1999 Joint Mtg. IEEE Intl. Freq. Cont. Symp. And EFTF Conf., pp. 259-262, 

1999. http://tf.boulder.nist.gov/general/pdf/1384.pdf

[3] C. Alexopoulos, D. Goldsman, A. Mokashi, K-W. Tien, and J. R. Wilson, “SEQUEM: estimating 

extreme steady-state quantiles via the maximum transformation, Proc. 2015 Winter Simulation 

Conf., pp. 562-574., Dec. 2015

[4] P. Heidelberger and P. A. W. Lewis, “Quantile estimation in dependent sequences,” Operations 

Research, vol. 32, no. 1, pp. 185-208, Jan-Feb, 1984.

[5] J.C. Perdo, N.B. Carvalho, “Intermodulation Distortion in Microwave and Wireless Circuits.” Boston: 

Artech House, 2003, p. 17.

[6] Federal Communications Commission, “Comment Sought on Ligado’s Modification Applications,” 

Report no. DA 16-442. April 22, 2016. Online: 

http://transition.fcc.gov/Daily_Releases/Daily_Business/2016/db0422/DA-16-442A1.pdf
July 22, 2016

Appendix A. Estimating In-Situ Interference Response from Anechoic 

Measurement Results

A.1. Introduction.

A recurring question in the area of RF interference-effects measurements is whether such 

measurements can be better performed via radiation in propagation scenarios designed to be “realistic” 

versus measurands that seek to isolate minimize uncontrolled propagation effects. This problem is

examined and supports extrapolating measurements to real-world deployments.

A.2. Goal.

The goal of RF interference-effects measurements on victim receivers is to help understand the 

circumstances under which interference between two or more radio systems will occur in real-world 

environments and conditional scenarios. Measurements typically do not completely answer this 

question, but measurements can (and do) provide definitive data points which can be integrated into 

models, simulations and analysis for validation or prediction.

A.3. Interference Scenarios.

Any real-world interference between two radio systems will involve radiation from one or more 

transmitter(s) through (usually) one or more transmitter antenna(s) with some combination of 

frequencies and polarizations. To the first order, potential interference impacts can be predicted by a 

comparison of aggregate power levels at the receiver. The radiated waves may propagate through 

space, over terrain, through vegetation, through one or more structural barriers and thence into a victim 

receiver via (usually) another antenna. The actual amount of interference coupled into the victim 

receiver will not only be affected by all of these identified factors, but will also be a function (in fact a 

ratio) of the bandwidth of the victim receiver to the bandwidth of the transmitter. For each interference 

source, this situation can be written mathematically (in decibels) as:

Equation 1. Link attenuation model for interference signal power at the victim receiver

PPrrrr = EIRP − LLpp − LLpppppp, + GGrrrr − LLff ff + 10log10 �

BBrr

BB �

where:

Pri = Interference power coupled into victim receiver;

EIRPi = Effective isotropic radiated power radiated by the interferer in the direction of the victim 

receiver;

Lpi = Free-space propagation loss at a given separation distance between the interfering 

transmitter and the victim receiver;

Lpol,i = Loss due to polarization mis-matches;

Lfilt = Losses introduced by interference filtering (for example out-of-band rejection filters); this 

term is also known as the Off-Frequency Rejection (OFR) component of the FrequencyDependent Rejection (FDR) term;
July 22, 2016

Gr = Gain of the receiver antenna in the direction of the interference signal;

Br = Bandwidth of the victim receiver;

Bi = Bandwidth of the transmitted interference signal.

10log10(Br / Bi) is set to zero if Br > Bi. In addition, this term is known as the On-Tune Rejection (OTR) 

component of the FDR, and is typically set to zero when considering adjacent-channel interactions with 

a noise-like emission source.

Similarly, the received (“non-interfering”) signal that received by the victim device, this situation can be 

written mathematically (in decibels) as:

Equation 2. Link attenuation model for received (desired) signal power at the victim receiver

PPrrrr = EIRP − LLpp − LLpppppp, + GGrrrr

where:

Prs = Desired power level of the signal the receiver is designed to detect;

EIRPs = Effective isotropic radiated power of the intended signal radiated in the direction of the 

victim receiver;

Lps = Free-space propagation loss at a given separation distance between the transmitter 

radiating the desired signal and the victim receiver;

Lpol,s = Loss due to polarization mismatches; and

Grs = Gain of the receiver antenna in the direction of the transmitter of the desired signal;

Due to the wide range of potential values for the terms in the equation above, no practical set of end-toend radiated measurements between a transmitter and a receiver can provide a comprehensive set that 

covers all possible permutations. In particular, for the wide range of potential propagation losses, 

radiated or not, any interference-effects assessment study will need to perform a range of independent 

evaluations of the following factors:

- Propagation losses of various sorts (see above), including time-variation studies of fading losses 

in Lpi and Lps.

- Radiated power levels of the transmitters in the direction of the victim receiver;

- Gain of the victim receiver antenna in toward each of the desired signal and interfering 

transmitters;

- Polarization mismatch factors between both types of signal;

- Noise floor of the victim receiver.

The two equations above are used to compute the signal-to-interference (SIR), which is simply the 

difference between the power levels of the two signals above. Assuming that the filter losses, Lfilt, are 

the same for both the desired and interfering signals, the SIR ratio at the receiver in decibels is:
July 22, 2016

Equation 3. General form of SIR equation for signal and interference originating from different sources, passing through 

unknown propagation attenuation

SIR = PPrrrr − PPrrrr = (EIRP − EIRP ) − (LLpp −LLpp ) − (LLpppppp, − LLpppppp,) + (GGrrrr − GGrrrr) + LLff ff

− 10log10 �

BBrr

BB �

A.4. Systems Engineering Approach for Interference-Effects Measurement Studies

A systematic engineering approach to the problem of radio interference-effects measurements will not, 

as pointed out above, attempt to simultaneously roll a dozen different factors into a single 

measurement scenario. Instead, a systems-engineering approach breaks this problem into discrete 

pieces, studying and evaluating each piece independently and then combining together for an overall 

interference-effects evaluation.

The first piece in this type of systems-engineering approach is the determination of the incident 

interference radiation amplitude at which interference effects occur at the victim receiver. To the extent 

possible, this evaluation should be performed without regard to the other factors in the interference 

equation. The various other factors in the interference equation should be added into the mix in the 

final engineering study, each factor itself being the result of detailed individual studies and evaluations.

A.5. Impacts of Sharing a Single Transmit Antenna in Anechoic Tests

Combining both types of signal into the same transmit antenna reduces the number of variables in the 

received SIR during measurements. The transmit signals share the same propagation loss (LLpppppp, −

LLpppppp, = 0), polarization loss (LLrrrr − LLrrrr = 0), and victim receive antenna gain (GGrrrr − GGrrrr = 0), so the 

SIR ratio simplifies to

Equation 4. SIR in the test environment

NOTE: Only applies when sharing a single antenna

SIRTTTTTTTT = PPrrrr − PPrrrr = (EIRP − EIRP ) + LLff ff − 10log10 �

BBrr

BBii

�

In other words, the test has been designed to control the SIR to a constant level determined by 

characteristics of the testbed transmitter (its EIRP and signal transmit bandwidth) and the victim 

receiver DUT (out-of-band filtering characteristics and receive bandwidth) instead of the environment. It 

is independent of orientation or multipath, and isolates a measurable parameter (SIR) from applicationdependent environment variables, matching the systems engineering philosophy of the previous 

section.

A.6. Applying the SIR to Predicted System Performance.

The response of the victim receiver to interference are set by the SIR level and background noise (set in 

tests by room temperature thermal noise and receiver electronics). Estimating a victim receiver’s 

response to the tested interference according to the equations here requires evaluating Equation 3, and 

translating the SIR to the victim receiver performance result.

The factors not tested in the lab need to be accounted for. In most deployment scenarios, the interferer 

and desired signals should be expected at different EIRP levels and to undergo different Gr, Lp, and 

Lpol.(Each term could be modeled as random variables for Monte Carlo analysis with each term 
July 22, 2016

consisting of a well-defined probability density function). Based on the SIR equation, what needs to be 

modeled is the difference between each term.

Here is an example case of how an SIR might be estimated from hypothetical link values. It requires 

estimates for each link parameter, which in turn depend on the deployment scenario and the 

technology in use.

1) The interferer radiates at a weaker level than the desired signal:

EIRP − EIRP = +10 dB

2) Assume the interferer is much closer and undergoes substantially lower propagation loss:

LLpp − LLpp = −10 dB

3) Now assume that the interferer has linear polarization, and the desired source is circularly 

polarized, resulting in a relative mismatch of 3 dB:

LLpppppp, − LLpppppp, = +3 dB

4) Further, now assume that the interferer arrives nearer a sidelobe of the victim antenna pattern:

GGrrrr − GGrrrr = +2 dB

The sum of these values gives SIR = +5 dB. The estimate for victim receive performance, based on 

measurement data, is the measurement result at the 5 dB SIR operating point. The result is valid 

assuming that temperature and background noise conditions are similar to test conditions, and that the 

structure of the input signal used in the test closely resembles that of the deployment under 

consideration.
July 22, 2016

Appendix B. Specifications of Antenna and RF Front End

Table 8. Specifications of antenna and system

Subsystem Component Anechoic or semianechoic

Antenna Polarization RHCP

Boresight gain flatness across

1520 MHz – 1680 MHz

+/- 0.5 dB

Maximum VSWR across

1520 MHz – 1680 MHz

1.5

Manufacturer gain calibration ANSI C63.5 or SAE ARP958,

performed at 3m

System GPS test signal power output range TBD

LTE test signal power output TBD

Appendix C. Procedures for Characterization and Calibration of 

Conducted Signals

C.1. Instrument Calibration

A few baseline instrumentation calibration steps are illustrated in Figure 13. These should be taken after 

appropriate instrument warm-up time as specified by their manufacturers, respectively, and before 

characterizing the LTE and GPS signal generating paths. Procedures for these measurements are listed in 

Table 10.
July 22, 2016

Figure 13. Instrument calibration signal paths

Table 9. Calibration equipment setup. 

Test Input source Output measurement

Spectrum Analyzer

CW Calibration Sweep

CW source

CW stepped frequency sweep

1500 – 1660 MHz

1601 points, 10 ms per point

Power level (Pref1 - 10 dB)

Spectrum analyzer (at GPS 

emulator)

PSD (max hold)

1500 MHz – 1660 MHz

1601 points

Ref Level Pref1

Spectrum Analyzer 

Noise Floor

Matched termination Spectrum analyzer (at GPS 

emulator)

PSD

1500 MHz – 1660 MHz

1601 points

Network Analyzer 

Calibration

Network analyzer, port 1

(according to manufacturer 

operating manual)

Network analyzer, port 2

1 Set the reference level, Pref, to the highest power level that leads to 0 dB input attenuation, with the 

spectrum analyzer set to automatic input attenuation leveling.
July 22, 2016

Table 10. Instrument calibration measurements

Calibration Calculation and application

Spectrum Analyzer

Trace Level

Apply trace math as follows (point by point across frequency band):

Corrected trace PSD = Pref (dBm) - 10 (dB)

 - Spectrum Analyzer CW Calibration Sweep (dB)

Record this PSD for remaining tests. Do not change input attenuation 

setting, number of points, or frequency span.

Network Analyzer TwoPort CalibrationPerform a full two-port calibration on the instrument according to 

instrument operating instructions. Leave calibration on in remaining 

tests. Do not change resolution bandwidth, number of points, or 

frequency bounds.

C.2. Characterization of In-Band LTE Signal Generation

The purpose of generating the LTE in-band signal is to populate only the downlink (1526 MHz - 1536 

MHz) and/or one of the uplink bands (1627.5 MHz – 1637.5 MHz, 1646.5 MHz – 1656.5 MHz). The inband signal generation path needs to be characterized across the full calibration bandwidth (1500 MHz –

1660 MHz) to include its contribution in the conducted power output into the antenna.

The test setup is illustrated in Figure 14. The signal path is broken between the power amplifier output 

and the upstream isolator. A signal analyzer characterizes the power spectral density output by of the 

amplifier, and a network analyzer characterizes the loss between the amplifier and the input to the 

antenna. It is necessary to split the signal path measurements into two because the out-of-band 

emissions level is too weak compared to the signal analyzer noise floor.
July 22, 2016

Figure 14. LTE in-band signal generation path conducted measurements for calibrations

The calibration measurements necessary to characterize the LTE in-band signal generation path are 

listed in Table 13. The correction computations based on these measurements are listed in Table 14.

Table 11. Instrument calibrations.

Signal Test Input source Output measurement

LTE DL LTE in-band path SparametersNetwork analyzer

Port 1 – output of input 

(upstream) isolator

Network analyzer

Port 2 - Cable output (antenna 

side)

2-port S-parameters:

1500 MHz – 1660 MHz

1601 points

Narrow IF bandwidth

LTE DL PSD input LTE emulator

1526 – 1536 MHz

Spectrum analyzer (at GPS 

emulator)

PSD:

1500 MHz – 1660 MHz

1601 points

LTE UL1 LTE in-band path Sparameters(reuse the S-parameter measurement result from LTE DL tests)

LTE UL1 PSD input LTE emulator

1627.5 – 1637.5 MHz

Spectrum analyzer (at LTE 

emulator)

PSD:

1500 MHz – 1660 MHz

1601 points
July 22, 2016

LTE UL2 LTE in-band path Sparameters(reuse the S-parameter measurement result from LTE DL tests)

LTE UL2 PSD input LTE emulator

1646.5 – 1656.5 MHz

Spectrum analyzer (at LTE 

emulator)

PSD:

1500 MHz – 1660 MHz

1601 points
July 22, 2016

Table 12. In-band signal generation path calibration measurements

Calibration Calculation and application

LTE DL in-band PSD 

maximum output

The LTE downlink out-of-band power spectral density is that available 

to a 50 Ohm matched antenna. It is computed from measurements of 

Table 15 at each frequency point as

LTE In-Band DL PSD input (dBm/Hz)

- |LTE in-band path S-parameters, S21| (dB)

This expression shall be evaluated by trace math on the spectrum 

analyzer.

LTE DL in-band PSD 

output

The actual conducted power level includes the path attenuator 

setting,

LTE OOB DL PSD maximum output (dB)

- LTE OOB signal path attenuator setting (dB)

LTE UL in-band PSD 

maximum output

The LTE uplink out-of-band power spectral density is that available to 

a 50 Ohm matched antenna. It is computed from measurements of 

Table 17 at each frequency point as

LTE OOB UL PSD input (dBm/Hz)

- LTE OOB path loss (dB)

This expression shall be evaluated by trace math on the spectrum 

analyzer and may be reevaluated in different units.

LTE UL in-band PSD 

output

The actual conducted power level includes the path attenuator setting 

at each PSD frequency point as

LTE OOB UL PSD maximum output (dB)

- LTE OOB signal path attenuator setting (dB)

This value may be computed in the PC since the attenuator setting 

may not be available inside the spectrum analyzer.
July 22, 2016

Table 13. In-band signal generation path calibration corrections.

Signal Test Input source Output measurement

LTE OOB 

signal

LTE OOB path SparametersNetwork analyzer

Port 1 – OOBE attenuator input 

Network analyzer

Port 2 – Cable output 

(antenna side)

2-port S-parameters:

1500 MHz – 1660 MHz

1601 points

Narrow RBW

LTE OOB DL PSD 

input

OOBE noise emulator

(noise to DL spectral mask)

1526 – 1650 MHz

Spectrum analyzer

PSD:

1500 MHz – 1660 MHz

1601 points

LTE OOB UL PSD 

input

OOBE noise emulator

(noise to UL spectral mask)

1526 – 1650 MHz

Spectrum analyzer

PSD:

1500 MHz – 1660 MHz

1601 points
July 22, 2016

C.3. Characterization Out-of-Band LTE Signal Generation

The purpose of generating the LTE out-of-band (OOB) signal is to fill the range 1526 MHz – 1680 MHz 

with noise at the power density limit defined by an LTE spectral mask.

There are two spectral masks: one for the LTE downlink (DL) band at 1526 MHz – 1536 MHz and another 

that applies identically to operation of either uplink band (UL1 1627.5 MHz – 1637.5 MHz, UL2 1646.5 

MHz – 1656.5 MHz). Each is generated by a pre-stored waveform to be played back as OOB noise.

The test setup is illustrated in Figure 15. The signal path is broken between the ARB output and the 

corresponding downstream variable attenuator. A spectrum analyzer characterizes the power spectral 

density output by of the noise generator, and a network analyzer characterizes the loss between the 

amplifier and the input to the antenna. It is necessary to split the signal path measurements into two 

because the out-of-band emissions noise is too weak compared to the spectrum analyzer noise floor.

The instrumentation configuration for the LTE OOB signal characterization is shown in Figure 15. The 

intended OOB signal levels are weak, so the spectral density measurement is at the generator output, 

where the signal is more powerful. S-parameter measurements give the remaining attenuation to the 

antenna input. The calibration measurements in this setup to characterize the LTE in-band signal 

generation path are listed in Table 15.

Figure 15. Conducted measurement setup for calibrating LTE out-of-band signal generation
July 22, 2016

Table 14. Measurements of the out-of-band signal generation path for calibration

Calibration Calculation and application

LTE OOB DL PSD 

maximum output

The LTE downlink out-of-band power spectral density is that available 

to a 50 Ohm matched antenna. It is computed from measurements of 

Table 15 at each frequency point as

LTE OOB DL PSD input (dBm/Hz)

- |LTE OOB path S-parameters, S21| (dB)

This expression shall be evaluated by trace math on the spectrum 

analyzer.

LTE OOB DL PSD output The actual conducted power level includes the path attenuator 

setting,

LTE OOB DL PSD maximum output (dB)

- LTE OOB signal path attenuator setting (dB)

LTE OOB UL PSD 

maximum output

The LTE uplink out-of-band power spectral density is that available to 

a 50 Ohm matched antenna. It is computed from measurements of 

Table 17 at each frequency point as

LTE OOB UL PSD input (dBm/Hz)

- LTE OOB path loss (dB)

This expression shall be evaluated by trace math on the spectrum 

analyzer and may be reevaluated in different units.

LTE OOB UL PSD output The actual conducted power level includes the path attenuator setting 

at each PSD frequency point as

LTE OOB UL PSD maximum output (dB)

- LTE OOB signal path attenuator setting (dB)

This value may be computed in post-processing since the attenuator 

setting may not be available on the spectrum analyzer.
July 22, 2016

Table 15. LTE out-of-band conducted power calibration corrections.

C.4. Characterization of L1 GPS Signal Generation

The purpose of generating the L1 GPS signal is to provide GPS satellites to test the response of GPS 

receiver DUTs.

The test setup is illustrated in Figure 16. The signal path is broken between the GPS emulator and its 

corresponding downstream variable attenuator. A signal analyzer characterizes the power spectral 

density output by of the amplifier, and a network analyzer characterizes the loss between the amplifier 

and the input to the antenna. Loss through the path needs to be measured separately because the L1 

GPS level is weak compared to the signal analyzer noise floor.

Figure 16. GPS L1 signal generation path conducted measurements for calibrations

Signal Measurement Input source Output measurement

GPS L1

signal

GPS signal path loss 

(dB)

Network analyzer

Port 1 – GPS L1 path attenuator

input

(0 dB attenuation setting)

Network analyzer

Port 2 – Cable output 

(antenna side)

2-port S-parameters:

1500 MHz – 1660 MHz

1601 points

Narrow RBW

Input power 

spectral density 

(dBm/Hz)

GPS emulator

L1: 1563.42– 1587.42 MHz

Spectrum analyzer (at GPS 

emulator)

PSD:

1500 MHz – 1660 MHz

1601 points
July 22, 2016

The instrumentation configuration for the GPS L1 signal characterization is shown in Figure 15. The 

intended OOB signal levels are weak, so the spectral density measurement is at the generator output, 

where the signal is more powerful. S-parameter measurements give the remaining attenuation to the 

antenna input. The calibration measurements in this setup to characterize the GPS L1 signal generation 

path are listed in Table 17.

Table 16. GPS L1 signal generation path conducted measurements for calibrations

Calibration Calculation and application

GPS L1 output PSD The GPS L1 signal power is the power available to a 50 Ohm matched 

antenna. It is computed from measurements of Table 17 at each 

frequency as

PSDTX (dBm/Hz) = Input power spectral density (dBm/Hz)

 - GPS L1 signal path loss (dB)

 - GPS L1 signal path attenuator setting (dB)

This expression should be evaluated by trace math on the spectrum 

analyzer if possible.

GPS L1 conducted 

transmit power

The average GPS L1 conducted transmit power available to a 50 Ohm 

matched antenna is 

PTX (dBm) = GPS L1 output PSD, band power 1563.42 – 1587.42 MHz

This expression should be evaluated by trace math on the spectrum 

analyzer if possible.

C.5. Uncertainty

Signal power uncertainty estimates will be provided where feasible based on tests, noise levels, and 

procedures provided by instrument manufacturers.
July 22, 2016

Appendix D. Procedures for Characterization, Calibration, and 

Validation of Radiated Power

D.1. Calibration of Transmit Loss to Linear Polarization

The LTE radiated emission spectral masks are specified for linear polarization, but the transmit antenna 

is designed for circular polarization. If the transmit antenna radiates true RHCP, then the linear 

component corresponding to the LTE spectral mask is 3 dB weaker (3 dB of polarization loss).

Table 17 . GPS L1 signal generation calibrations

Calculation and application

Transmit Polarization 

Loss to Linear

A test for the circular polarization purity is to measure the transmit 

power from a RHCP antenna with a linear-polarized horn at two

orthogonal angles. The received power out of the horn antenna 

should be approximately the same at each angle. The ratio of these, in 

dB, is the transmit antenna’s axial ratio (AR).

The measured estimate of the polarization loss is related to the AR as

Lpol = AR + 3 dB

 = Received power H-pol (dB) – Received power V-pol (dB) + 3 dB

D.2. Calibration of Radiated Power Levels

The radiated power computations here combine conducted signal power levels (calibrated in Appendix 

C) and antenna gain (calibrated by the antenna manufacturer). The radiated power that is the result of 

this computation is therefore also taken to be calibrated.

Table 18. Radiated power level calibrations

Calibration Calculation and application

EIRP

(GPS L1, right-hand 

circular polarization)

The EIRP of the testbed antenna at boresight, given the RHCP partial 

gain of the transmit antenna, G, is

EIRP (in dBm) = PTX (dBm) + G (dBi) – Lpol (dB) + 3 

or

EIRP (in dBm/Hz) = PTX (dBm/Hz) + G (dBi) – Lpol (dB) + 3

This conducted transmit power PTX should be taken from the 

measurement “GPS L1 conducted transmit power” in Table 17.

EIRP

(LTE in-band or OOB, 

vertical polarization)

The calibrated EIRP of the testbed antenna at boresight, given the 

total gain of the RHCP transmit antenna, G, is
July 22, 2016

EIRP (in dBm) = PTX (dBm) + G (dBi) - Lpol (dB)

or

EIRP (in dBW/MHz) = PTX (dBW/MHz) + G (dBi) - Lpol (dB)

This expression applies to the uplink or downlink, and in-band or outof-band. The appropriate choice of conducted transmit power PTX 

comes from the desired choice among “LTE UL in-band PSD output” or 

“LTE DL in-band PSD output” in 

Table 14, or “LTE OOB DL PSD output” or “LTE OOB UL PSD output” in 

Table 16.

3GPP GPS Power Level 3GPP conformance test standard TS 37.571-1 defines a power level 

operating point for over-the-air tests of GPS receivers in cellular 

industry tests. The power level is defined as the incident field strength 

(or power density) equivalent to PRX = -130 dBm received with an 

antenna that has gain GRX = 0 dBi in the location of the DUT. 

The calibration here assumes this receive antenna gain is the RHCP 

partial gain as defined in the IEEE dictionary of standard terms for 

antennas.

The Friis transmission equation relates these to the EIRP and test zone 

geometry:

PRX (in dBm) = EIRP (in dBm) + GRX – 20 log10 (4πr/λ0)

where r = 3 meters is the separation distance between the DUT and 

test antennas and λ0 is the wavelength, approximately 0.19 meters. 

EIRP must be calculated with the “GPS L1, in-band” calibrated 

transmit power. Inserting these numbers the EIRP necessary to fulfill 

the 3GPP standard becomes

EIRP3GPP = -84.0 dBm

at test antenna boresight. Measurements at the levels specified in TS 

37.571-1 are achievable by adjusting the LTE in-band attenuator to

bring EIRP to this level (and adjusting the LTE OOB attenuator to 

maintain desired relative levels).
July 22, 2016

D.3. Validating radiated signal levels at the DUT

In order to validate the expected anechoic or semi-anechoic propagation behavior (Figure 8) and the 

calibrated gain level of the testbed transmit antenna, we perform an additional check on the 

propagation attenuation between the calibrated source antenna and a second calibrated validation 

antenna. The test setup is illustrated in Figure 17.

For each LTE downlink (in-band and OOB), LTE uplink (in-band and OOB), and GPS L1 signal, conducted 

power will be measured 1) at the calibrated testbed output and 2) out of the validation antenna. These 

are the “source” and “through” measurements in Figure 17. The ratio of each power measurement 

expressed in decibels, will be taken the difference between these two signals (in decibels) for each 

signal. This ratio will be reported as the propagation attenuation.

The anticipated gain of these antennas, and their separation, will be used to compute the expected loss 

according to the Friis transmission equation. This expected value will be compared against the measured 

loss.
July 22, 2016

Figure 17. Validation procedures for radiated signal levels

D.4. Chamber Validation Tests

This test plan depends received DUT power attenuating smoothly with rr2 (the square of the distance to 

the transmit antenna). Any actual test zone includes error ripples caused by multiple reflections 

between the antennas and the environment, and reflections between the transmit antenna and the 

DUT. It is therefore crucial to ensure the error components that produce these ripples are small.

The environmental reflections will be made worse if the test environment is a semi-anechoic chamber 

with a reflective floor. In this case, adding absorber on the floor between the transmit antenna and the 

DUT mitigates these reflections.

Field uniformity and multipath tests validate the that minimal contributions from reflections are preset 

in the test zone. The goal is to ensure that undesired reflections have a substantially lower magnitude 
July 22, 2016

than that of the desired LOS path. One approach is shown in the figure below. A network analyzer 

connects to the transmit antenna and the calibration antenna (or other test antenna) and performs 

scattering parameter “through” (S21) measurements, then transforms into the time domain. If the 

calibration (or test) antenna does not match the specific gain pattern of the DUT, a minimally directive 

calibration antenna is desirable so as to capture any potential multipath contributions arriving from 

different angles at the DUT test location. 

The plot of the resulting test data shows the power distribution over time as it arrives at the receiving 

antenna. If initial tests show that additional absorber is necessary to dampen reflections in the test 

chamber, follow-up tests should be able to confirm that less power arrives as undesired, time-delayed 

reflection components. 

D.5. Uncertainty

When possible, signal level uncertainty statements and analysis will be provided based on best practices 

from NIST and instrument manufacturers.

Figure 18. Setup to validate minimal multipath contribution at the location of the DUT.
July 22, 2016

Appendix E. Procedures and Considerations for Validating

Calibrations

E.1. Intermodulation Effects between Test Signals

This test plan prescribes signals that may have components at more than one (or all) of the LTE 

downlink, LTE uplink, and GPS L1 bands. Node voltages with these waveforms at nonlinear components 

of active system blocks (like amplifiers, receivers, and signal generators) may produce measurable signal 

components at new frequencies. Signals at these new frequencies are the intermodulation distortion 

(IMD) products. In passive devices like the combiner, connections between different metals form weakly

nonlinear p-n diode junctions, which producing signal content at new frequencies but at weak levels 

that may be difficult to measure. This phenomenon is called passive intermodulation distortion (PIM), 

which is a form of IMD expected to have weaker amplitude than expected in active devices.

The impacts of IMD are a concern in testing LTE interference effects upon GPS L1 if the distortion alters 

the test results. The relatively powerful LTE waveforms “bookend” the interference sources, so we take

IMD products to be important only if they are fall between LTE uplink and downlink frequencies: 1536 

MHz – 1627.5 MHz. Within this frequency span, IMD products are negligible if they can be confirmed to 

be weak relative to the OOBE noise floor.

In general, the center frequency of 

each IMD product for two input signal 

bands is determined by their signal 

band center frequencies, f1 and f2, as 

in Figure 18. Intermodulation 

products come from the mixing 

product frequencies fmn = m f1 + n f2, 

= (m+n) f1 + n Δf [5], where m and n 

can be any integer, and Δf is the 

spacing between the band center 

frequencies. The intermodulation 

products that we are concerned about happen near 

the fundamental frequencies. For these frequencies, m + n = 1, so each nth intermodulation center 

frequency is

fimd = f1 + n Δf.

Like the illustration in Figure 18, none of the intermodulation frequencies are located between f1 and f2.

Intermodulation frequencies are listed for each pair of generated band centers in the table below. Only 

the combination of LTE downlink and GPS L1 signals produce IMD products in the test band, covering 

1590.84 MHz – 1633.84 MHz (centered at 1619.84 MHz). Therefore, IMD will need to be tested with 

signals covering the LTE downlink and GPS L1 bands to ensure the IMD products are below the noise 

floor.

Figure 19. Center frequencies of intermodulation products
July 22, 2016

Table 19. Nearest high and low intermodulation frequencies produced by each pair of bands. Intermodulation products that 

need to be tested in the calibration process are shown in red.

Band 1, center frequency Band 2, center frequency

Nearest IMD 

center frequency 

(below)

Nearest IMD 

center frequency 

(above)

LTE downlink, 1531 MHz LTE uplink 1, 1632.5 MHz 1429.5 MHz 1734 MHz

LTE downlink, 1531 MHz LTE uplink 2, 1651.5 MHz 1410.5 MHz 1772 MHz

LTE downlink, 1531 MHz GPS L1, 1575.42 MHz 1486.58 MHz 1619.84 MHz

GPS L1, 1575.42 MHz LTE uplink 1, 1632.5 MHz 1518.34 MHz 1689.58 MHz

GPS L1, 1575.42 MHz LTE uplink 2, 1651.5 MHz 1499.34 MHz 1727.58 MHz