Global Navigation Satellite SystemsResearch efforts in Luleå

Staffan Backén, LTU

Dr. Dennis M. Akos, LTU

Presentation Outline

Crash Course in GNSS (GPS, Galileo) Constellation Signal Structure Signal Processing Positioning – Accuracy - Augmentations GNSS in Space

Research efforts in Luleå Thesis - Phased Array Antenna

How? Why 1 & 2 & example Hardware Design – Dataset Recording Research Status

Questions?

GNSS CC - GPS Constellation

Minimum 24 satellitesPeriod of 11 hours 58 minutesSix circular orbits,

20200km above the earth - MEOInclination angle of 55° relative to the equator

Passive system Virtual stars

GNSS CC – Signal Structure

CDMA – All three systems (Glonass with a twist)Modulation

GPS BPSK (QPSK)Glonass BPSKGalileo Boc(1,1), Boc(10,5), AltBoc(15,10) – not finalized

GPS transmitted and received power at L1:Satellite antenna input ≈ 27WReceived power ≈ 5×10-14 W/m2 → Received signal below thermal noise floor

E5a/L5 E5b L2 E6 SAR

1164

1176

.45

118?

1207

.14

121412

1512

27.6

1237

1260

1278

.75

1300

1544

1545

1559

1563

1575

.42

1587

1591

Frequen

cy

(MHz)

E2 L1 E1

Galileo bands GPS bands Galileo SAR downlink

GNSS CC - Signal Processing

AcquisitionFind a specific satellite signal buried in noise

Code trackingDecode time stamp

Carrier trackingDecode data bits

PositioningFour satellites required for 3D position + timeAccuracy ≈ 7m RMSError sources

MultipathIonospheric, tropospheric delay Ephemeris inaccuracies

Augmentation systemsSBAS

WAAS (America)EGNOS (Europe)MSAS (Asia)

DGPS, AGPS etc

User location xu=(xu, yu, zu)

Satellite 1 position xs1=(xs1, ys1, zs1)

Range r1

Satellite 2 position xs2=(xs2, ys2, zs2)

Satellite 3 position xs3=(xs3, ys3, zs3)

Satellite 4 position xs4=(xs4, ys4, zs4)

Range r2

Range r3

Range r4

GNSS in Space - Considerations

Software altitude/speed limit – commercial low cost receiver To counteract missile development … 18000 m, 515 m/s

Roll issue Antenna direction not fixed relative to the earth

Higher doppler More extensive acquisition when traveling very fast

GNSS satellite antenna pattern Directed towards earth

Predictable motion Kalman filter

GNSS Research Efforts in Luleå

Dr. Dennis M. AkosSoftware Receivers

Bi-static Radar

Dr. Dennis M. AkosSoftware Receivers

Bi-static Radar

GNSS courseGNSS courseStudent Projects

Ex: GPS/INSRapid Acq.

Student ProjectsEx: GPS/INS

Rapid Acq.

Staffan BackénPh.D. student

Antenna ArraysQuantization

Staffan BackénPh.D. student

Antenna ArraysQuantization

Tore LindgrenResearch Engineer

VRS Algorithms

Tore LindgrenResearch Engineer

VRS Algorithms

Antenna Array Principle – Nulling Example

GNSS Antenna Arrays – why #1?

GNSS Antenna Arrays – why #2?

Example of Beam Forming

IF Data Recording Setup

Front end 1

Front end 8

USB2 board

16.3676MHz Rubidium oscillator

8 • 2 bits 16.3676MHz

33MB/s

•

••

Antenna Array Layout

GroundplaneAluminum1m diameter

Antenna elementsCommercial GPS patch antennas

Spacingλ/2 ( ≈ 9,5 cm)

Typical Front End Design

Research Status Completed

Hardware design and implementation Antenna array USB2 transfer – hardware, firmware and host program

Dataset recording Several dataset during a day

In progress Verifying dataset

Antenna phase center determination Coming up

Algorithm development Adaptive algorithms, pre and/or post correlation beam forming

Future work Interference mitigation

New hardware platform required …