DRAFT:

LTE Impacts on GPS

Test and Metrology Plan

Prepared by: Dr. William Young, NIST

Dr. Daniel Kuester, NIST

Dr. Adam Wunderlich, NIST

Dr. Duncan McGillivray, NIST

Dr. Marc Weiss, NIST

Mr. John Ladbury, NIST

Dr. Sheryl Genco, NASCTN

Mr. Frank Sanders, ITS

Mr. Billy Riddle, NIST

Reviewed and approved by: xxxx, xxxx
2

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....................................................................................................................................7

5.2.1 Device Under Test (DUT) Population ....................................................................................7

5.2.2 Global Positioning System (GPS) Satellites .........................................................................10

5.2.3 Augmentation Signals.........................................................................................................11

5.2.4 Long Term Evolution (LTE) Signaling Scenarios...................................................................11

5.3 Setup ...........................................................................................................................................12

5.3.1 Equipment...........................................................................................................................12

5.3.2 GPS Position Testbed ..........................................................................................................14

5.3.3 GPS Time Testbed ...............................................................................................................15

5.3.4 In-Band LTE Emulation ........................................................................................................17

5.3.5 Out-of-Band Emissions (OOBE) LTE Emulation ...................................................................19

5.3.6 Measurement Locations.....................................................................................................20

5.4 Tests to Establish Data Collection Timing ...................................................................................20

5.5 Tests at Swept LTE Levels............................................................................................................23

5.5.1 Emulate swept range ..........................................................................................................23

5.5.2 Study LTE In-Band Coexistence Margins.............................................................................23

6 Statistical Considerations....................................................................................................................24

6.1 Test Population ...........................................................................................................................24

6.2 Relevant Experimental Variables and Sources of Uncertainty ...................................................24

6.3 Analysis Plan................................................................................................................................25

6.3.1 Steady-State Assessment....................................................................................................25

6.3.2 Estimation of Quantiles and Histograms ............................................................................25

7 Outreach and Community Feedback ..................................................................................................26

8 Data Management..............................................................................................................................26

9 Project Tasks.......................................................................................................................................26
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10 Safety ..............................................................................................................................................26

11 References ......................................................................................................................................27

Appendix A. Estimating In-Situ Interference Response from Anechoic Measurement Results..............28

A.1. Introduction. ...................................................................................................................................28

A.2. Goal.................................................................................................................................................28

A.3. Interference Scenarios....................................................................................................................28

A.4. Systems Engineering Approach for Interference-Effects Measurement Studies...........................30

A.5. Impacts of Sharing a Single Transmit Antenna in Anechoic Tests..................................................30

A.6. Applying the SIR to Predicted System Performance.......................................................................30

Appendix B. Specifications of Antenna and RF Front End.......................................................................31

Appendix C. Procedures for Characterization and Calibration of Conducted Signals.............................32

C.1. Instrument Calibration....................................................................................................................32

C.2. Characterization of In-Band LTE Signal Generation........................................................................33

C.3. Characterization Out-of-Band LTE Signal Generation.....................................................................38

C.4. Characterization of L1 GPS Signal Generation................................................................................40

C.5. Uncertainty .....................................................................................................................................41

Appendix D. Procedures for Characterization, Calibration, and Validation of Radiated Power .............42

D.1. Calibration of Transmit Loss to Linear Polarization ........................................................................42

D.2. Calibration of Radiated Power Levels.............................................................................................42

D.3. Validating radiated signal levels at the DUT ...................................................................................44

D.4. Uncertainty .....................................................................................................................................45

Appendix E. Procedures and Considerations for Validating Calibrations...............................................46

E.1. Intermodulation Effects between Test Signals...............................................................................46
4

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 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 test method, but does not 

incorporate insight from any preliminary anechoic 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 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 

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. 
5

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 the L1 GPS band. 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 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. 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 Key Performance Indicators such as 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. 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 3.5-Mbps

LTE signal. A set of select GPS devices will be tested as part of test validation and the collection of a 

subset of data. 

The testing will make use of an anechoic chamber. A representative subset of available devices will be 

tested in the anechoic chamber.
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3 Scope

The purpose of the GPS receiver measurement project is to develop a rigorous 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 chamber setup. 

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, etc. Emphasis is on real-world expected LTE signals. 

However, where practical, the LTE signal levels will be elevated to a power level that produces 

noticeable degradation so as to provide data that can 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 scope is the impact of LTE on GPS performance. Specifically, LTE waveforms representing downlink 

bands will occupy 1526 MHz - 1536 MHz and 1670 MHz - 1680 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 and the 1627.5 MHz - 1637.5 MHz uplink.

The 1526 MHz - 1536 MHz and 1646.5 MHz - 1656.5 MHz pair combination represents a condition 

where the GPS devices will be in the presence of both down and uplink activity, and the architecture is 

assumed to follow the traditional cellular phone separation between up and downlink. However, since 

an architecture has not yet specified, the pair used for testing will include 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 up 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 high precision position and timing. 

Aviation, space-based, cellular, and DoD devices of all categories are not included. The test procedure 

would likely require modification to include those additional categories of devices.

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 part of 

this test.

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

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.
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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 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 

chamber tests will not include atmospheric impairments.

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.

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 each of the devices. 

The highest priority devices were included in previous testing efforts. 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 first round of testing will focus on the top two or three 

devices in each of the categories.
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DRAFT:

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

General Location and Navigation

Unit Priority Antenna

PC 

interface

Data 

format(s)

Extra 

KPIs Sub-type Website

Motorola MW810 1 Internal

RS232

USB

Bluetooth

NMEA

UBX

TAIP

NMEA 

params

First

Responder

https://www.motorolasolutions.com/content/dam/msi

/docs/business/products/mobile_computers/vehiclemounted_computers/mw810/_documents/staticfiles/

mw810_mobile_workstation_r2_user_guide.pdf

Garmin eTrex H 2 Internal USB

Flash

NMEA

GPX

NMEA 

params

Hiking https://buy.garmin.com/en-US/US/intosports/discontinued/etrex-h/prod8705.html

Garmin eTrex 30x 3 Internal USB GPX No Hiking https://buy.garmin.com/en-US/US/intosports/handheld/etrex-30x/prod518048.html

Garmin Montana 

650t 4 Internal USB NMEAGPX

NMEA 

params

Hiking https://buy.garmin.com/en-US/US/on-thetrail/montana-650t/prod75228.html

Garmin Montana 

680t 5 Internal USB NMEAGPX NMEA Hiking https://buy.garmin.com/en-US/US/intosports/hiking/montana-680t/prod523677.html

Fitbit Surge 6 Internal Bluetooth? TCX No Wearable https://www.fitbit.com/surge

Apple iPad Air 2 

(WiFi only) 7 Internal

USB

Wi-Fi 

Bluetooth

Appdependent Unknown Tablet http://www.apple.com/shop/buy-ipad/ipad-air-2

Table 2. High precision positioning devices identified for testing.

High Precision Positioning

Unit Priority Antenna PC Interface Data

format(s) Extra KPIs Website

Trimble NETR9 1

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 GR30 2

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/gnssreference-networks/receivers/leica-gr50-andgr30
9

Table 3. Precision timing devices identified for testing

Precision Timing

Unit Priority Antenna Accuracy Ext. Oscillator 

Support

Lock state 

indicator Website

Arbiter 1088B GPS 

Satellite Clock (40ns) 1

Arbiter AS0087800 

GPS Active Timing 40 ns Yes Yes http://www.arbiter.com/catalog/product/model1088b-gps-satellite-precision-time-clock-40ns.php

MicroSemi Symmetricom 

SyncServer S650

2 Microsemi Kit <15ns Yes Yes

http://www.microsemi.com/products/timingsynchronization-systems/time-frequencydistribution/network-appliancesservers/syncserver/syncserver-s650

Table 4. Development boards identified for testing.

Development Boards

Unit Priority Chipset Antenna PC 

interface

Data

format(s) Extra KPIs Website

Ublox M8 Board 1

Ublox M8 

Chrystal

Internal

External Kit

USB 2.0

RS232

NMEA

UBX

all NMEA

C/N0

https://www.ublox.com/en/product/evk-m8

SwiftNav Piksi 

v2.3.1 2

Maxim 

Integrated 

MAX2769

Internal

External Kit

USB

UART

NMEA

RINEX

Pseudorange

C/N0

https://www.swiftnav.com/sites/default

/files/swift_datasheet_030716.pdf

Adafruit Ultimate 

GPS Breakout 

Board

3

Global Top 

013

Internal

External Kit UART NMEA all NMEAC/N0

https://www.adafruit.com/products/74

6
DRAFT 5/3/2016

10

5.2.2 Global Positioning System (GPS) Satellites

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

respectively. Values selected for these conditions are similar to those in the 3GPP Specification TS 

37.571-1, though not identical. Details for the constellation are listed in Table 5. Losses from the 

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

The emulated GPS signals will not include atmospheric propagation impairment effects based on input 

that not all GPS devices are compatible.

For some devices, a “live sky” may be necessary in order to evaluate its performance. The anechoic 

facilities have the infrastructure required provide “live sky” GPS signals.

Table 5. Satellite constellation setup.

Nominal

Number of generated satellites 8 to 12

GPS L1 C/A signal for all satellites -130 dBm

Propagation conditions AWGN

Limited Exposure 

Number of generated satellites 6

GPS L1 C/A signal for 1st satellite -129 dBm

GPS L1 C/A signal for 2nd satellite -132 dBm

GPS L1 C/A signal for 3rd satellite -135 dBm

GPS L1 C/A signal for 4th satellite -138 dBm

GPS L1 C/A signal for 5th satellite -141 dBm

GPS L1 C/A signal for 6th satellite -144 dBm

Propagation conditions AWGN

Augmentation signals

WAAS -128.5 dBm

GPS constellation power levels based on hypothetical 

power available from a 0 dBi antenna in the location of 

the DUT.
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11

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. Augmentation signals such as Wide Area Augmentation Signals 

(WAAS), Real Time Kinematic (RTK), and Mobile Satellite Services (MSS) will be included as needed and 

time permitting.

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 may not be generated during tests if a cavity filter is not 

available with this passband.

Table 6. Up and downlink frequencies.

Number LTE Link 

Direction

LTE Band

(MHz)

1 Downlink 1526 - 1536

2 Downlink 1670 - 1680 

3 Uplink 1627.5 - 1637.5

4 Uplink 1646.5 - 1656.5

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 1 in relation to GPS L1 and LTE operating bands 

under consideration.
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12

Figure 1. 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.
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Table 7. Equipment for 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 1

Isolator Fairview 

Microwave

SFI1020 (or 

similar)

1- 2 GHz

Isolation > 19 dB

2

LTE amplifier TBD TBD 1

Programmable 

attenuator

Mini-Circuits

RCDAT-6000-110 

(or similar)

0.25 dB steps; 0.3 dB uncertainty 3

LTE downlink 

in-band OOB 

rejection filter

Custom TBD 1

Diplexer KP Microwave

F00150

Separates an input into separate channels - LTE downlink bands 

and uplink bands 

2

Combiner MECA

DC802-2-1.500V

800 MHz – 2200 MHz

Isolation > 22 dB

1

Antenna 

(RHCP for 

anechoic 

chamber)

ETS-Lindgren

3102 

RHCP conical log spiral

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

1

Antenna (LTE 

source for 

outdoor, 

validation 

horn)

ETS Lindgren

3115 (or similar)

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

Spectrum 

Analyzer

TBD 1

Network 

Analyzer

TBD

Signal 

generator for 

LTE OOB 

emission

TBD TBD (Requires ARB capability) 1

Time Interval 

Counter

Keysight 

Technologies

53220A (or 

similar)

Single shot resolution 100 ps 1
DRAFT 5/3/2016

14

Temperature 

monitor

TBD TBD 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 2 depicts the setup in the 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 8. 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 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.

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.
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Figure 2. Setup for position measurements in the 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].

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 3 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, 
DRAFT 5/3/2016

16

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 8. Timing data are stored to 

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

satellite. 

Figure 3 Setup for precision timing tests in the anechoic chamber.
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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. The channel is 10 MHz 

wide (half of a 10 MHz allocation) consisting of 50 available resource blocks (RBs). The base station 

compensates for the weak link with fair scheduling, limiting the number of RBs allocated to our UE; we 

assume a relatively large 35 RB (70%) allocation. The UE compensates for the weak link by transmitting 

the quadrature phase-shift keying (QPSK) at its maximum allowed EIRP following Figure 1. Proposed inband 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 4 and a 

spectrum like that in Figure 5. This uplink corresponds with 7 Mbps maximum data rate.

Figure 4. Example LTE uplink resource block allocation
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Figure 5. 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 is where a fully-allocated downlink signal is being one device near the GPS device and 

another UE is sending data to another base station. 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 
DRAFT 5/3/2016

19

determine a reasonable range of attenuation levels for test. In the 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 

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 6 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 6. 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 1. 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.
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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

Potential locations under consideration for testing are below. 

 Electronic Proving Grounds (EPG); Fort Huachuca, Arizona.

 White Sands Missile Range, New Mexico.

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 7, 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 8, at 

each LTE power level, data are captured for a time duration of tc . 
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Figure 7. Process to establish data collection time for the DUT.
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Figure 8. Process to increment LTE power for a specific waveform and collect data from the DUT.
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5.5 Tests at Swept LTE Levels

We propose here 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. If time permits, both types of testing will 

be performed.

5.5.1 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. The spectral 

shape 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 9. 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.

5.5.2 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 10. The out-of-band emission power-spectral density is fixed to that of Figure 1, 

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. 

in-band emission

out-of-band

emission Mask
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Figure 10. 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.

6 Statistical Considerations

6.1 Test Population

GPS devices from the following classes will be tested:

 general location and navigation

 high precision

 timing

 development boards

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

selection of devices chosen from each class will likely be driven by practical considerations, such as data 

accessibility. Moreover, only a single unit of each device will be tested to keep the test time and cost 

manageable. 

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

each class. 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. 

 Controlled variables: 

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)

in-band emission

out-of-band

emission Mask
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25

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) 

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

constellation, GPS signal impairments, GPS processing algorithm, receiver antenna orientation, and 

indoor environmental conditions

6.3 Analysis Plan 

6.3.1 Steady-State Assessment

The analysis of device outputs for the indoor testing is predicated on the assumption that the device is 

operating in a steady-state condition. Therefore, for each set of experimental conditions, stability of 

device outputs will be assessed as a function of time. The point at which transients are negligible will be 

identified with a pre-specified criterion. Subsequent analysis will be carried out on the steady-state 

portion of the data. 

Note that 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. Therefore, an early phase of the testing will attempt to estimate 

the time required to reach steady-state. Such estimates will inform the subsequent experimental 

procedure. 

A basic evaluation of steady-state performance will consist of applying a sliding time window to the 

data, and then estimating the mean and variance from the windowed data. For example, if the relative 

change of the mean and variance after a certain time is less than, e.g., 1%, then the time-series may be 

judged to be in a steady-state condition. 

Additional metrics for assessing steady-state performance will be investigated in pre-testing with 

available GPS device output data. Moreover, pre-test investigations will inform the choice of a specific 

criterion for steady-state performance.

If the collected time series does not satisfy the pre-determined criteria for steady-state behavior, then 

alternative methods will be applied to derive a steady-state time series from the measurements. 

Specifically, techniques such as differencing and trend estimation will be used in an attempt to generate 

stationary data from the observed time series. 

6.3.2 Estimation of Quantiles and Histograms

Assuming that the device under test has reached a steady-state condition, the steady-state distribution 

and associated quantiles, such as the median, 90%, 95%, and 99% 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 distribution for each KPI without LTE interference to that with LTE 

interference. 

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

expected to be highly-correlated. Since classical statistical methods that are designed for independent 

samples break down for dependent samples, they are not applicable in this context, and special 

methods are required. 
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26

Point estimates and 95% confidence intervals for quantiles will be estimated with the averaged group 

quantile method of Heidelberger & Lewis [3], which is based on asymptotic theory for dependent 

sequences. In addition, depending on software availability, the more robust sequential estimation 

methods of either Chen & Kelton [4][5] or Alexopoulos et al. [6] will be applied.

The steady-state distribution will first be estimated with a conventional histogram, which will provide a 

simple means to compare distributions. It is well known that the histogram is an unbiased estimator of 

the probability mass in each bin as the bin size approaches zero, even for dependent data. However, 

because the classical histogram precision estimates are not valid for dependent data, it is challenging to 

estimate and control uncertainty in the histogram. To address this issue, if possible, the method of Chen 

& Kelton [5] will be applied to obtain histogram estimates with a specified precision.

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 Anechoic setup and baseline tests

Anechoic chamber test

Data Analysis and Report

NASCTN Data and Report Review Process (including Director)

Issue Report

10 Safety

The anechoic tests are indoor laboratory tests and subject to all the typical safety concerns associated 

with such environment. 
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27

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

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

[4] E. J. Chen and W. D. Kelton, “Quantile and tolerance-interval estimation in simulation,” European 

Journal of Operations Research, Vol. 168, pp. 520-540, 2006.

[5] E. J. Chen and W. D. Kelton, “Estimating steady-state distributions via simulation-generated 

histograms,” Computers & Operations Research, Vol. 35, pp. 1003-1016, 2008.

[6] 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.

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

Artech House, 2003, p. 17.

[8] 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
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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

Pri = EIRPi − Lpi − Lpol,i + Gri − Lfilt − 10log10 (

Br

Bi

)

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);

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

Bi = Bandwidth of the transmitted interference signal.

10log10(Br / Bi) is set to zero if Br > Bi.

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

Prs = EIRPs − Lps − Lpol,s + Grs

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:

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

unknown propagation attenuation

SIR = Prs − Pri = (EIRPs − EIRPi) − (Lps−Lpi) − (Lpol,s − Lpol,) + (Grs − Gri) + Lfilt

− 10log10 (

Br

Bi

)
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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 (Lpol,s −

Lpol,i = 0), polarization loss (Lrs − Lri = 0), and victim receive antenna gain (Grs − Gri = 0), so the 

SIR ratio simplifies to

Equation 4. SIR in the test environment

NOTE: Only applies when sharing a single antenna

SIRTEST = Prs − Pri = (EIRPs − EIRPi) + Lfilt − 10log10 (

Br

Bi

)

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 

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

EIRPs − EIRPi = +10 dB

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

Lps − Lpi = −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:

Lpol,s − Lpol,i = +3 dB

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

Grs − Gri = +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.

Appendix B. Specifications of Antenna and RF Front End

Table 8. Specifications of antenna and system

Subsystem Component Anechoic 

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
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Appendix C. Procedures for Characterization and Calibration of 

Conducted Signals

C.1. Instrument Calibration

A few baseline instrumentation calibration steps are illustrated in Figure 11. 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 9.

Figure 11. 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 (Pref

1 

- 10 dB)

Spectrum analyzer (at GPS 

emulator)

PSD (max hold)

1500 MHz – 1660 MHz

1601 points

Ref Level Pref

1

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.
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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 12. 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.
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Figure 12. 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 12. The correction computations based on these measurements are listed in Table 13.
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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

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
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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 14 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 16 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.
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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
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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 13. 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 13. 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 14.

Figure 13. Conducted measurement setup for calibrating LTE out-of-band signal generation
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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 14 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 16 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.
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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 14. 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 14. 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
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The instrumentation configuration for the GPS L1 signal characterization is shown in Figure 13. 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 16.

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 16 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.
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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 linear 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 16.

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
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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 13, or “LTE OOB DL PSD output” or “LTE OOB UL PSD output” in 

Table 15.

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 dB

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

In order to validate the expected anechoic propagation behavior (Figure 6) 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 15.

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 15. 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.
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Figure 15. Validation procedures for radiated signal levels

D.4. Uncertainty

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

from NIST and instrument manufacturers.
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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 16. Intermodulation 

products come from the mixing 

product frequencies fmn = m f1 + n f2, 

= (m+n) f1 + n Δf [7], 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 n

th intermodulation center 

frequency is

fimd = f1 + n Δf.

Like the illustration in Figure 16, 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 16. Center frequencies of intermodulation products
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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