Challenges and Solutions for GPS Receiver Test and Solutions for GPS Receiver Test Presenter: Mirin Lew January 28, 2010 ... Geostationary satellites transmit correction and integrity

Challenges and

Solutions for GPS

Receiver Test

Presenter: Mirin Lew

January 28, 2010

© 2010 Agilent Technologies

Agenda

• GPS technology concepts

• GPS and GNSS overview

• Assisted GPS (A-GPS)

• Basic tests required for GPS receiver verification

• Test solutions• Test solutions

• Signal creation for GPS receiver test

• A-GPS test systems

GNSS = Global Navigation Satellite Systems


GPS and GNSS Overview

GPS: Global Positioning System

• System owned and operated by the U.S. government

• Civilian service freely available to users worldwide

• Military service available to selected agencies onlyagencies only

GNSS: Global Navigation Satellite System

• General term for any satellite-based navigation system

• Includes multiple systems worldwide


Global Navigation Satellite Systems (GNSS)

Galileo

– Joint effort of European Community and European Space Agency

– 2 test satellites in orbit, contracts awarded for first 14 satellites, up to 32 satellites operational by 2014

– Interoperability agreement signed with GPS

– 4 services (open service, paid commercial service, safety of life service, public regulated service) as compared to 2 GPS services (public and private)

Global Orbiting Navigation Satellite System (GLONASS)

– Russian system first launched by Soviet Union in 1982

– Became non-functional for most applications in the 1990’s

– Currently being restored, 22 satellites in orbit as of Dec. 2009

– Particularly good coverage over upper latitudes (Northern Europe)

Compass (Beidou-2)

– Chinese system

– 3 satellites are up, 12 satellites by 2012 to provide regional service

– Eventually 30 satellites


GNSS Related Systems

Satellite Based Augmentation Systems (SBAS)Geostationary satellites transmit correction and integrity data for GNSS

system over the GNSS frequency. Provides increased positioning accuracy.

North America:

Wide Area

Augmentation System

(WAAS)

Europe:

European Geostationary

Overlay Service (EGNOS)

Japan:

Multifunctional Satellite

Based Augmentation

Regional Navigation Satellite Systems (RNSS)Intended for improved coverage over limited areas

(WAAS)Based Augmentation

Satellite System (MSAS)

Japan:

Quazi Zenith Satellite

System (QZSS) - 2013

India: Indian

Regional Navigation Satellite System

(INRSS) - 2012

India:

GPS and GEO Augmented

Navigation (GAGAN)


GPS Technology Overview

• Constellation of 24 active satellites in orbit (up to 32 satellites total)

• Each satellite transmits its current location and time

• Each satellite transmission is synchronized to the rest by atomic clock

• Minimum of 4 satellites required for 3D location calculation

• Major segments of the system

• Space: Satellites or Space Vehicles (SV) orbiting the

Earth twice a day at 20,200 km

• Control: Ground stations provide navigation

information update and SV control

• User: GPS receiver


How Does GPS Work in the Real World?

Space Segment

Uplink data:Satellite orbital information

Position constantsClock correction factors

GPS Data

Monitor Stations

MasterControl

Station

User

Clock correction factorsAtmospheric data

Almanac

Control segment


GPS Transmitted Signal

L1 Carrier 1575.42 MHz

C/A Code 1.023 MHzL1 Signal

(Civilian use)+Σ

90˚

Satellite GPS signal has 3 components:• Carrier wave: 1575.42 MHz (L1) & 1227.60 MHz (L2)

• Ranging (pseudo-random) codes: Coarse acquisition (C/A) code and precise (P) code

• Navigation message: 50 bit/s contains ephemeris data (detailed orbital information for the

transmitting satellite) and almanac data (more general orbital information for all satellites)

Navigation Data 50 Hz

P Code 10.23 MHz

L2 Carrier 1227.6 MHz

(Civilian use)

L2 Signal

(Military use)

modulo 2 adder

modulator

+

+

+


Navigation Message

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Navigation message

25 pages/frames37,500 bits12.5 minutes

Frame (page)

1500 bits30 seconds

Sub-frame 2

300 bits

6 secondsSub-frame 1 Sub-frame 3 Sub-frame 4 Sub-frame 5TLM

HOW

1 2 3 4 5 6 7 8 9 10

Satellite health

and clock

correction data

Ephemeris Ephemeris Partial

almanac &

other data

Almanac

TLM

HOW

1 2 3 4 5 6 7 8 9 10

TLM

HOW

1 2 3 4 5 6 7 8 9 10

TLM

HOW

1 2 3 4 5 6 7 8 9 10

TLM

HOW

1 2 3 4 5 6 7 8 9 10

8 bits

pre

am

ble

16 bits

reserved

6 bits

parity

7 bits

ID

17 bits

Time of week

TOW

6 bits

parity

30 seconds

Telemetry word (TLM)30 bits0.6 seconds

Handover word (HOW)30 bits0.6 seconds

TLM

HOW correction data

TLM

HOW

TLM

HOW

TLM

HOW

TLM

HOW

Worst Case: 30 seconds to receive full ephemeris data

12.5 minutes to receive full almanac data


Almanac and Ephemeris Files

Almanac File

Contains data on the health and general orbital information for every satellite in the constellation.

Updated weekly.

http://www.navcen.uscg.gov/GPS/almanacs.htm

Ephemeris File

Contains detailed information on the orbit of an individual satellite. Updated every 2 hours.Contains detailed information on the orbit of an individual satellite. Updated every 2 hours.

http://cddis.gsfc.nasa.gov/gnss_datasum.html#brdc

• Data from the almanac can be used to create a scenario file that contains the

satellite information for a specific date, time, and location.

• Ephemeris data files can be used to create a GPS signal that more accurately

represents the actual signals broadcast at that date, time, and location.


Agenda





• Test solutions



GNSS = Global Navigation Satellite Systems


Assisted GPS (A-GPS)

• Technique for cellular network to assist mobile phone’s GPS receiver to lock to

satellites and achieve location fix more quickly

– Fulfills U.S. FCC’s E911 directive which mandated fast and accurate location of mobile

phones by emergency services

– Needed due to low GPS signal levels that may be seen by mobile phones when indoors or

in areas without direct view of sufficient satellites

– Allows mobile phone’s GPS receiver to acquire location fix much more quickly

• Base station provides “assistance data” to mobile phones. Data includes:• Base station provides “assistance data” to mobile phones. Data includes:

– Navigation: precise satellite orbital information

– Almanac: coarse orbital information

– Time of Week: GPS time

– Ionosphere: single frequency (L1) correction factors

– Reference location: initial estimate of location

– Acquisition assistance: data to aid in locating or tracking satellites

– Real-time integrity: list of bad satellites

– UTC model: leap second time correction for GPS time


How Does A-GPS Work in the Real World?

Space Segment

Uplink data:Satellite ephemeris

Position constantsClock correction factors

Monitor Stations

MasterControl

Station

User

Clock correction factorsAtmospheric data

Almanac

Control segment

GPS AssistanceServer

Cellular Network

Network Downlink:Coarse TimeEphemeris Data

Coarse Location(100m accuracy)Almanac


A-GPS Operation

• Assistance Data Transportation

• Control plane: Uses dedicated messaging on network control channels

• User plane: Uses existing standard Internet protocol (IP) based data

connections; also called Secure User Plane Location (SUPL)

• A-GPS Modes

• Mobile station/user equipment (MS/UE) Assisted (older method)• Mobile station/user equipment (MS/UE) Assisted (older method)

– MS/UE supplies GPS measurements to network

– Network combines with assistance server data, calculates and transmits

location back to mobile

– Typically used with control plane

• MS/UE Based (newer method)

– MS/UE uses assistance data to calculate location

– Transmits location back to BS

– Used with user plane (less network dependent)


Agenda





• Test solutions




Typical Tests for GPS Receiver Verification

Time To First Fix (TTFF)

Sensitivity

Cold, warm, hot start conditions

Acquisition sensitivity

Location Accuracy

Acquisition sensitivity

Tracking sensitivity

Absolute and relative accuracy

Moving GPS receiver accuracy

Satellite tracking accuracy


Time to First Fix (TTFF)

• Time between start of GPS signal and the acquisition of a location fix by the GPS receiver

• May be tested under different conditions or states of the GPS receiver:

Time To First Fix (TTFF)

For cold, warm, hot start conditions

• May be tested under different conditions or states of the GPS receiver:

– Cold start: Receiver does not have time or position information, no valid ephemeris (or almanac) data (typical TTFF 30-50 sec, may be up to several minutes)

– Warm start: Last position and approximate time known, valid almanac, no valid ephemeris data (typical TTFF 30-40 sec)

– Hot start: Time and last position known, valid almanac and ephemeris (typical TTFF 1-5 sec)

• Need to specify satellite power level when testing TTFF

� Test requires a multi-satellite GPS signal with valid navigational messages


Sensitivity

Sensitivityminimum = -174dBm/Hz + C/Nominimum + NFreceiver

Sensitivity

Acquisition sensitivityTracking sensitivity

• Minimum level of signal that allows GPS receiver to acquire or track the GPS signal (may also be specified in terms of C/No)

– Acquisition sensitivity: minimum level to successfully perform TTFF under cold start (typically around -140 to -150 dBm)

– Tracking sensitivity: minimum level to maintain location fix once it has been attained (typically -150 to -160 dBm)

� Test requires multi-satellite GPS signal with valid navigational messages for TTFF, and real-time satellite power control to reduce power levels to test sensitivity


Location Accuracy

• Absolute location accuracy: Closeness of the receiver’s calculated

Location Accuracy

Absolute and relative accuracyMoving GPS receiver accuracySatellite tracking accuracy

• Absolute location accuracy: Closeness of the receiver’s calculated location fix to the ideal (simulated) location

• Relative location accuracy: Compares location fixes between tests

• May be tested for both stationary and moving GPS receivers

• Satellite tracking accuracy: Track location of single satellite

� Tests require multi-satellite GPS signal for location fix, repeatable test scenarios, moving GPS receiver scenarios, and ability to vary power and other satellite parameters to test tracking


Secondary GPS Verification Tests

Calculate reacquisition time

• Time required to resume location fix following loss of

signal

RF interference measurements

• Measures the ability of the GPS receiver to operate in

the presence of interfering (jamming) signals (second RF

source required)


Why You Need GPS Simulation

GPS simulation offers the following advantages over “live” satellite signals:

• Repeatability

– Ensure exact replication of the signal conditions for each test

• Flexibility

– Use different scenarios to simulate different locations and times, with different – Use different scenarios to simulate different locations and times, with different

satellites and orbits

• Control

– Use standard test scenarios throughout your process

• Stress Testing

– Turn individual satellites on/off and change satellite power

– Reduce satellite visibility

– Introduce specific, known impairments


Requirements for GPS Test Signals

GPS Signal Simulation

Feature Test Challenges Met

Multiple channels to simulate multiple

satellites (4 to 15)

Minimum of 4 for TTFF. 15 allows you to

reproduce all satellites visible from any

location.

Stationary and moving GPS receiver Test more realistic case of moving GPS

TTFF AccuracySensitivity

Stationary and moving GPS receiver

scenarios

Test more realistic case of moving GPS

receiver as well as simple stationary case

Real-time satellite power adjustments,

satellite visibility on/off

Test sensitivity, ability to reacquire satellite

signals

Custom scenario generation capability Flexibility to create scenarios for any date,

time, or location

Requirements for GPS Test Signals

Impairments

Feature Test Challenges Met

Multipath signals (requires more

channels)

Simulate real-world situation with reflected

signals from obstructions

Reduced satellite visibility: partial or

complete, elevation mask

Test loss of visibility due to tunnels,

mountains, or other obstructions

TTFF AccuracySensitivity

complete, elevation mask mountains, or other obstructions

Ionospheric and tropospheric modeling Account for atmospheric effects on GPS

signals (refraction, delay)

Add calibrated AWGN Add broadband noise to control C/No of

GPS signal


Agenda





• Test solutions




Agilent GPS Receiver Test Solutions

RealReal--time GPS Signal Generation for R&Dtime GPS Signal Generation for R&D

• Perform standard GPS verification tests with impairments:

• Multipath signals (24 total channels)

• Real-time control of satellite visibility and power

PXB Baseband

Generator and Channel Emulator

MXG Signal Generator or ESG Signal Generator

RealReal--time GPS Signal Generation for time GPS Signal Generation for

Manufacturing and GPS verificationManufacturing and GPS verification

• Perform standard GPS verification tests

ESG Signal Generator

E4438C-409 GPS Personality

N7609B Signal Studio for Global SatelliteNavigation Systems (GNSS)

• Real-time control of satellite visibility and power

• Introduce atmospheric effects (ionospheric and

tropospheric)

• Add calibrated AWGN

• Edit or create new scenarios (option RFP)

• Up to 15 visible satellites

• Moving GPS receiver scenarios

• Up to 8 hours simulation time (8 channels)

• A-GPS Pre-conformance Solution with the 8960

• Perform standard GPS verification tests

• Time To First Fix (TTFF)

• Accuracy

• Sensitivity

• Pre-configured scenarios

• 8 satellites simulation

• Up to 4 hours simulation time

• A-GPS Bench-top Solution with the 8960

Basic GPS verificationwithout impairments Advanced GPS verification

with impairments for full characterization


N7609B Signal Studio for GNSS

PERFORMANCE: Create the GPS signals required for full GPS receiver verification

FLEXIBILITY: PXB/MXG platform will allow signal creation of other wireless standards

EXPANDABILITY: Integrate into A-GPS pre-conformance system with 8960 addition


Agilent N5106A PXBBaseband Generator and Channel Emulator

Industry-Leading Baseband PerformanceUp to 6 baseband generators (BBG)

120 MHz BW & 512 MSa of playback memory per BBG

Support I/Q outputs or upconvert to RF with ESG/MXG

512 MSa RF and digital I/Q signal capture

Advanced Channel Emulation with AWGNUp to 8 real-time faders with up to 24 paths/fader and dynamic fading

Supports MIMO fading and channel models, antenna setup, and custom correlation matrix

Recent new features in blue

custom correlation matrix

Comprehensive Signal Creation ToolsMulti-frame Signal Studio applications running in the PXB

• Arb: LTE FDD, Mobile WiMAX, W-CDMA, GSM/EDGE, 802.11 WLAN, digital video, LTE TDD, TD-SCDMA

• Real-time: LTE FDD, GPS, DVB-T/H

• Support Matlab, SystemVue, ADS waveform playback

Save Time, Maximize the Value of Your InvestmentAutomated power calibration including RF instruments in seconds

Leverage existing MXA for RF input, MXG/ESG for RF output, and N5102A for digital I/Q input/output

On-site upgrade of baseband and I/O cards in one hourwww.agilent.com/find/pxb

Page 27© 2010 Agilent Technologies

Real-time Satellite Simulation with 24 ChannelsNavigation Mode

• Real-world GPS satellite signals

with actual navigation data

• Simulate up to 15 satellites

• 24 channels can be used for line-

of-sight satellite signals or

multipath signalsmultipath signals

• Up to 8 hours playback time with 8

satellites

• Stationary (static) or moving GPS

receiver (dynamic) scenarios

Screen shot from u-Center software by u-blox AG


N7609B User Interface Real-time Individual Satellite Control

Reduce power in

Turn off these5 satellites

Reduce power in these 3 satellitesby 6 dB

Screen shot from u-Center software by u-blox AGN7609B User Interface


24 Channel Simulation Static Test Mode

Test satellite tracking capability of a GPS receiver or IC

• 24 channels

• Select SV PRN ID

• Individual power, delay (in chips or ms), and Doppler shift settings

• Custom 30-bit GPS word input

• Unlimited playback time


Scenario Generation (Option RFP)

• Create static or dynamic scenarios for

stationary or moving GPS receivers

• Up to 15 satellites (depends on

scenario)

• Specify moving scenarios through a

NMEA (GGA) format file

• Include ionospheric or tropospheric

Create scenarios for any time, date, and location

• Include ionospheric or tropospheric

impairment models

• Specify elevation mask for urban

canyon environment

• For A-GPS:

– Input ephemeris data into the

scenario

– Output ephemeris and A-GPS

assistance data for each scenario


• Add multipath signals for

any visible satellite

• Up to 24 channels (combined

satellite and multipath)

• Specify Doppler shift, delay,

and power offset for each

Customize scenarios with multipath impairments

Scenario Editing (Option RFP)

multipath

• Other editing features:

• Delete channel

• Channel power offset

• Equalize all satellite

power

• Trim scenario play time


Scenario EditingGraphical Display of Channels & Satellites vs. Time


N7609B + PXB and MXG/ESG Summary

Reliability and repeatability in GPS signal simulation

Perform standard GPS receiver tests– Time to First Fix (Cold, warm, or hot start conditions)

– Location accuracy (Relative, absolute, moving receiver, satellite

tracking)

– Sensitivity (acquisition and tracking)

– Interference testing (requires 2nd RF source)

Flexibility in configuring and customizing GPS receiver tests signals

– Stationary or moving GPS receiver conditions

– Satellite channel power adjustments in real-time

– Introduction of multipath signals

– Reduced satellite visibility (partial or complete loss of visibility)

– Introduce ionospheric and tropospheric impairments

– GPS signals with calibrated AWGN


N7609B + PXB and MXG/ESGSummary

Scenario generation capability• Stationary or moving GPS receiver scenarios

• NMEA (GAA format) file input mode for scenario creation

• Up to 8 hours playback time with 8 channels

Scenario editing

• Create custom scenarios with the following editing capabilities

• Multipath impairment• Multipath impairment

• Individual satellite power adjustments

• Deletion of specific satellites visibility during the scenario playback period

Static test mode

• Test GPS tracking capability for any combination of satellite PRNs (varying

Doppler shift, power, and delay settings)

Ability to integrate into A-GPS test solution with the 8960


Agenda





• Test solutions




A-GPS Test Solution Overview


Satellite Simulator(E4438C-409 ESG or

N7609B with PXB)

User

Assistance Data

Cellular Network

Server





N7609B with PXB)

A-GPS

User

Assistance Data

Cellular Network

Base Station Emulator(8960 Series Wireless

Communications

Test Set)

ServerData

Control Plane mode

AssistanceData





N7609B with PXB)

A-GPS

User

Assistance Data

Cellular Network

Base Station Emulator(8960 Series Wireless

Communications

Test Set)

Server

Location Server Emulator(E6965A Software)

Data

User Plane mode

AssistanceData


CTIA Over-the-Air (OTA) Mobile Phone Testing

• U.S. wireless carriers require compliance to

CTIA specs, which mandate OTA A-GPS testing

• Key test is Total Isotropic Sensitivity (TIS),

performed in an anechoic chamber with antenna

positioning system: measures GPS receiver

sensitivity under A-GPS conditions and GPS

antenna patternsantenna patterns

• Test systems available from Agilent partners

ETS-Lindgren and Satimo, incorporating E4438C

ESG signal generator with Opt. 409 GPS

personality, 8960 with Lab Application, and

custom test software/drivers


Design Verification and Pre-Conformance Test

GS-9000 A-GPS Design Verification Test Systems:Scalable systems for R&D engineers who are designing and testing A-GPS

capabilities in chipsets and mobile devices. Solutions cover GSM, W-CDMA, and

cdma2000.

GS-9000 Lite

R&D Product Life Cycle

Prototype Phase Pre-Certification Certification

GS-9000 Standard


GS-9000 Lite Capabilities:

Bench top System for R&D

3GPP Defined Test Cases 2G/3G (51.010/34.171)

Sensitivity Coarse Time Alignment (70.11.5.1/5.2.1)

Nominal Accuracy (70.11.6/5.3)

Dynamic Range (70.11.7/5.4)

GPS and A-GPS measurements

TTFF (time to first fix)

Raw satellite data (Satellite ID, C/No, Doppler, Code Phase,

and Pseudo Range Error)and Pseudo Range Error)

Reporting of latitude and longitude with mobile based

methodology

2D error calculation and reporting

Multiple GPS scenarios (8)

Flexibility to test beyond the standards for R&D

Individual satellite power control

GPS time advancing

Sensitivity searches

Power sweeps

User friendly GUI, test executive, test automation


GS-9000 Standard Capabilities:

Comprehensive System for Pre-Conformance Test

GPS and A-GPS Measurements

� Support A-GPS over the user plane with the

E6965A Location Server Emulator (SUPL server)

TTFF (time to first fix)

Raw satellite data (Satellite ID, C/No, Doppler,

Code Phase, and Pseudo Range Error)

� Positions estimation with Mobile-Assisted

methodology

Reporting of latitude and longitude with mobile

based methodologybased methodology

2D error calculation and reporting

� Multiple GPS scenarios (12)

Flexibility to test beyond the standards for R&D

Individual satellite power control

GPS time advancing

Sensitivity searches

Power sweeps

� User defined GPS scenarios

Complete test executive for test plan creation and execution

3GPP Defined Test Cases 2G/3G (51.010/34.171)

Sensitivity Coarse Time Alignment (70.11.5.1/5.2.1)

� Sensitivity Fine Time Alignment (70.11.5.2/5.2.2)

Nominal Accuracy (70.11.6/5.3)

Dynamic Range (70.11.7/5.4)

� Multi-path performance (70.11.8/5.5)

� Moving Scenario and Periodic Update (5.6)


For More Information

Agilent Resources

Application Notes:

GPS Receiver Testing, Literature number 5990-4934EN http://cp.literature.agilent.com/litweb/pdf/5990-4943EN.pdf

Functional A-GPS Receiver Testing Using 8960 Wireless Communications Test Set and E4438C ESG Vector Signal Generator, Literature number 5989-9141EN http://cp.literature.agilent.com/litweb/pdf/5989-9141EN.pdf

Agilent GPS solutions: www.agilent.com/find/gps

Agilent A-GPS solutions: www.agilent.com/find/agps

Upcoming Webcast on Feb. 4th: “How to Test A-GPS Capable Cellular Devices and Why Testing is Required” www.agilent.com/find/A-GPSwebcast

Industry Resources

GPS Tutorials and Links:

http://www.ublox.com/en/tutorials-links-gps.html

http://www.trimble.com/gps/index.shtml

U.S. Coast Guard Navigation Center: GPS status, almanacs, link to ephemeris data, general GPS information: http://www.navcen.uscg.gov/gps/default.htm

European Space Agency: Information on Galileo: http://www.esa.int/esaNA/galileo.html

Russian Space Agency: Information on GLONASS, almanac: http://www.glonass-ianc.rsa.ru



Documents

Challenges and Solutions for GPS Receiver Test and Solutions for GPS Receiver Test Presenter: Mirin Lew January 28, 2010 ... Geostationary satellites transmit correction and integrity