Lambert Wanninger, Stephan Wallstab-Freitag

Geodetic Institute, Dresden University of Technology, Germany

ION GNSS 2007, Session D2

Combined Processing of GPS, GLONASS, and SBAS

Code Phase and Carrier Phase Measurements

GPS+GLONASS+SBAS

Maxim: The more satellites the better.

but several differences:• reference systems (GLONASS) transformation• orbit accuracy (GLONASS, SBAS) weighting• observation quality (GLONASS, SBAS) weighting• inter-channel biases (GLONASS) algorithm, estimation

GPS

(30)

GPS+GLONASS

(30+11)

GPS+SBAS(30+4)

GPS+GLONASS+SBAS

(30+11+4)

# visible SV 8.4 11.7 12.4 15.7

PDOP 1.9 1.7 1.6 1.4

Orbit Accuracy GPS/GLONASS

Broadcast orbit accuracy(source: JPL, IGS)

Precise IGS orbitsGPS (final): <5 cmGLONASS: 15 cm

Observation Quality GPS/GLONASS

Code Observations: Elevation dependence of MP1

Proper weighting required receiver dependence

Station 1 / Receiver 1 Station 2 / Receiver 2

GPS+GLONASS+SBAS

Observation Equations forSingle-Difference Carrier Phases

iba

Glonassba

iGlonassba

iba

iGlonassba

iba

SBASGPSba

iba

iSBASGPSba

NhktcR

NtcR

,,,0,,

,

,/

,0,,/

,

GLONASS inter-channel bias difference [cm]: Glonasshc 0

GLONASS Inter-channel Bias Diff.

Double-Difference Residuals L1

GPS GLONASS GLONASS GLONASS inter-channel

biases removed

GLONASS Inter-channel Bias Diff.

Long-term Stability

L0 – iono.-free linear combination

GLONASS Inter-channel Bias Diff.

Temperature effects

Chilling: 20° Celsius temperature difference

no effect

but change of antenna affects inter-channel bias difference

L0 – iono.-free linear combination

GLONASS Inter-channel Bias Diff.

A priori values of [cm]

AshtechZ-18

JPS Legacy,TPS E_GGD,TPS Net-G3

Leica GRX 1200 GG PRO

TrimbleNetR5

Ashtech Z-18 0.0 0.0 2.4 -0.7

JPS Legacy,TPS E_GGD,TPS Net-G3

0.0 0.0 2.4 -0.7

Leica GRX1200 GG PRO -2.4 -2.4 0.0 -3.1

Trimble NetR5 0.7 0.7 3.1 0.0

Glonasshc 0

Baseline Results GPS/GLONASS

RTK-like processing: short baseline, 2 minutes of observations

GPS GPS + GLONASS

average # of SV 8.0 11.6

Combined Float/DGNSSStd. Dev. N/E/Up [cm] 18 / 20 / 25 15 / 19 / 20

Fixed solution# valid solutions (of 360)Std. Dev. N/E/Up [cm]

3580.54 / 0.49 / 1.00

3590.53 / 0.48 / 0.93

SBAS

Code and carrier phase observations to GEO satellites

presently• 10 SBAS satellites,• 4 over Europe,• just single-frequency

EGNOSpresently: poor broadcast orbits+clocks short baselines only

Observation Quality GPS/SBAS

Code observations: elevation dependence of MP1

dual-frequency GPS MP1

single-frequency GPS MP1´

single-frequency SBAS MP1´

SBAS

GPS GPS + SBAS

average # of SV 8.7 12.7

Combined Float/DGNSSStd. Dev. N/E/Up [cm] 16/18/22 15/17/21

Fixed# valid solutions (of 720)Std. Dev. N/E/Up [cm]

7130.44 / 0.35 / 0.89

7120.27 / 0.26 / 0.74

RTK-like processing: short baseline, 2 minutes of observations,dual-freq. GPS, single-freq. SBAS

single-frequency SBAS improves dual-frequency GPS

SBAS Carrier Phase Multipath

Double-difference residuals L1: short static baseline, 2 SBAS satellites

daily multipath pattern, but also changes in pattern:due to daily repetition of orbits, orbit maneuvers

Summary + Outlook

GLONASS• lower orbit accuracy• some receivers: lower accuracy of code observations• inter-channel biases

SBAS• presently + EGNOS only: very poor orbit accuracy • lower accuracy of code observations• single-frequency only

Bright future • GPS L5, dual-frequency SBAS• more GPS/GLONASS/SBAS satellites• Galileo / Compass / GLONASS CDMA

A bird in the hand is worth two in the bush.