Challenges and Solutions for GPS Receiver Test

Transcription

1 Challenges and Solutions for GPS Receiver Test Presenter: Mirin Lew January 28, 2010 Agenda GPS technology concepts GPS and GNSS overview Assisted GPS (A-GPS) Basic tests required for GPS receiver verification Test solutions Signal creation for GPS receiver test A-GPS test systems GNSS = Global Navigation Satellite Systems

2 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 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 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

3 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) India: GPS and GEO Augmented Navigation (GAGAN) India: Indian Regional Navigation Satellite System (INRSS) Europe: European Geostationary Overlay Service (EGNOS) Japan: Multifunctional Satellite Based Augmentation Satellite System (MSAS) Japan: Quazi Zenith Satellite System (QZSS) Regional Navigation Satellite Systems (RNSS) Intended for improved coverage over limited areas 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

4 How Does GPS Work in the Real World? Space Segment Uplink data: Satellite orbital information Position constants Clock correction factors Atmospheric data Almanac Monitor Stations GPS Data Master Control Station User Control segment GPS Transmitted Signal Satellite GPS signal has 3 components: Carrier wave: MHz (L1) & 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) L1 Carrier MHz C/A Code MHz Navigation Data 50 Hz + 90 Σ + L1 Signal (Civilian use) modulo 2 adder P Code MHz + modulator L2 Carrier MHz L2 Signal (Military use)

5 Navigation Message Navigation message 25 pages/frames 37,500 bits 12.5 minutes Sub-frame bits Sub-frame 1 6 seconds Sub-frame 3 Sub-frame 4 Sub-frame Frame (page) 1500 bits 30 seconds TL LM HO OW Satellite health and clock correction data TL LM HO OW Ephemeris TL LM HO OW Ephemeris TL LM HO OW Partial almanac & other data TL LM HO OW Almanac Telemetry word (TLM) 30 bits 0.6 seconds 8 bits preamble 16 bits reserved 6 bits parity Handover word (HOW) 30 bits 0.6 seconds 17 bits Time of week TOW 7 bits ID 6 bits parity 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. Ephemeris File Contains detailed information on the orbit of an individual satellite. Updated every 2 hours. 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.

6 Agenda GPS technology concepts GPS and GNSS overview Assisted GPS (A-GPS) Basic tests required for GPS receiver verification Test solutions Signal creation for GPS receiver test A-GPS test systems 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: 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

7 How Does A-GPS Work in the Real World? Space Segment Uplink data: Satellite ephemeris Position constants Clock correction factors Atmospheric data Almanac Monitor Stations GPS Assistance Server Master Control Station Network Downlink: Coarse Time Ephemeris Data Coarse Location (100m accuracy) Almanac Control segment Cellular Network User 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) 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)

8 Agenda GPS technology concepts GPS and GNSS overview Assisted GPS (A-GPS) Basic tests required for GPS receiver verification Test solutions Signal creation for GPS receiver test A-GPS test systems Typical Tests for GPS Receiver Verification Time To First Fix (TTFF) Cold, warm, hot start conditions Sensitivity Acquisition sensitivity Tracking sensitivity Location Accuracy Absolute and relative accuracy Moving GPS receiver accuracy Satellite tracking accuracy

9 Time to First Fix (TTFF) Time To First Fix (TTFF) For cold, warm, hot start conditions 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: Cold start: Receiver does not have time or position information, no valid ephemeris (or almanac) data (typical TTFF sec, may be up to several minutes) Warm start: Last position and approximate time known, valid almanac, no valid ephemeris data (typical TTFF 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 Sensitivity Acquisition sensitivity Tracking sensitivity Sensitivity minimum = -174dBm/Hz + C/No minimum + NF receiver 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

10 Location Accuracy Location Accuracy Absolute and relative accuracy Moving GPS receiver accuracy Satellite 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)

11 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 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 Multiple channels to simulate multiple satellites (4 to 15) Stationary and moving GPS receiver scenarios Real-time satellite power adjustments, satellite visibility on/off Custom scenario generation capability Test Challenges Met Minimum of 4 for TTFF. 15 allows you to reproduce all satellites visible from any location. Test more realistic case of moving GPS receiver as well as simple stationary case Test sensitivity, ability to reacquire satellite signals Flexibility to create scenarios for any date, time, or location TTFF Sensitivity Accuracy

12 Requirements for GPS Test Signals Impairments Feature Multipath signals (requires more channels) Reduced satellite visibility: partial or complete, elevation mask Ionospheric and tropospheric modeling Add calibrated AWGN Test Challenges Met Simulate real-world situation with reflected signals from obstructions Test loss of visibility due to tunnels, mountains, or other obstructions Account for atmospheric effects on GPS signals (refraction, delay) Add broadband noise to control C/No of GPS signal TTFF Sensitivity Accuracy Agenda GPS technology concepts GPS and GNSS overview Assisted GPS (A-GPS) Basic tests required for GPS receiver verification Test solutions Signal creation for GPS receiver test A-GPS test systems

13 Agilent GPS Receiver Test Solutions E4438C-409 GPS Personality N7609B Signal Studio for Global Satellite Navigation Systems (GNSS) MXG Signal Generator or ESG Signal Generator ESG Signal Generator Real-time GPS Signal Generation for RealManufacturing and GPS verification 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 verification without impairments PXB Baseband Generator and Channel Emulator Real--time GPS Signal Generation for R&D Real Perform standard GPS verification tests with impairments: Multipath signals (24 total channels) 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 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

14 Agilent N5106A PXB Baseband Generator and Channel Emulator Recent new features in blue Industry-Leading Baseband Performance Up 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 AWGN Up 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 Comprehensive Signal Creation Tools Multi-frame Signal Studio applications running in the PXB Arb: LTE FDD, Mobile WiMAX, W-CDMA, GSM/EDGE, 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 Investment Automated 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 hour Page 27 Real-time Satellite Simulation with 24 Channels Navigation Mode Real-world GPS satellite signals with actual navigation data Simulate up to 15 satellites 24 channels can be used for lineof-sight satellite signals or multipath 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

15 N7609B User Interface Real-time Individual Satellite Control Turn off these 5 satellites Reduce power in these 3 satellites by 6 db N7609B User Interface Screen shot from u-center software by u-blox AG 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

16 Scenario Generation (Option RFP) Create scenarios for any time, date, and location 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 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 Scenario Editing (Option RFP) Customize scenarios with multipath impairments Add multipath signals for any visible satellite Up to 24 channels (combined satellite and multipath) Specify Doppler shift, delay, and power offset for each multipath Other editing features: Delete channel Channel power offset Equalize all satellite power Trim scenario play time

17 Scenario Editing Graphical 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 2 nd 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

18 N7609B + PXB and MXG/ESG Summary 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 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 GPS technology concepts GPS and GNSS overview Assisted GPS (A-GPS) Basic tests required for GPS receiver verification Test solutions Signal creation for GPS receiver test A-GPS test systems

19 A-GPS Test Solution Overview Satellite Simulator (E4438C-409 ESG or N7609B with PXB) GPS Assistance Server Assistance Data Cellular Network User A-GPS Test Solution Overview Satellite Simulator (E4438C-409 ESG or N7609B with PXB) A-GPS Data GPS Assistance Server Assistance Data Cellular Network Assistance Data User Control Plane mode Base Station Emulator (8960 Series Wireless Communications Test Set)

20 A-GPS Test Solution Overview Satellite Simulator (E4438C-409 ESG or N7609B with PXB) A-GPS Data GPS Assistance Server Location Server Emulator (E6965A Software) User Plane mode Cellular Network Assistance Data Assistance Data User Base Station Emulator (8960 Series Wireless Communications Test Set) 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 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

21 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 ( /5.2.1) Nominal Accuracy ( /5.3) Dynamic Range ( /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) 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

22 GS-9000 Standard Capabilities: Comprehensive System for Pre-Conformance Test 3GPP Defined Test Cases 2G/3G (51.010/34.171) Sensitivity Coarse Time Alignment ( /5.2.1) Sensitivity Fine Time Alignment ( /5.2.2) Nominal Accuracy ( /5.3) Dynamic Range ( /5.4) Multi-path performance ( /5.5) Moving Scenario and Periodic Update (5.6) 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 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 For More Information Agilent Resources Application Notes: GPS Receiver Testing, Literature number EN Functional A-GPS Receiver Testing Using 8960 Wireless Communications Test Set and E4438C ESG Vector Signal Generator, Literature number EN Agilent GPS solutions: Agilent A-GPS solutions: Upcoming Webcast on Feb. 4th: How to Test A-GPS Capable Cellular Devices and Why Testing is Required Industry Resources GPS Tutorials and Links: U.S. Coast Guard Navigation Center: GPS status, almanacs, link to ephemeris data, general GPS information: European Space Agency: Information on Galileo: Russian Space Agency: Information on GLONASS, almanac:

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