RO Instrument Design Considerations

for the New GNSS Signals

IROWG-2 Workshop

Estes Park, Co USA, 2012

Magnus Bonnedal

Anders Carlström

Thomas Lindgren

Jacob Christensen

Contents:

• The present: MetOp-GRAS

• The future: GRAS-2

• New GNSS Signals: Galileo

• RO simulation results

• Conclusion

IROWG-2 Workshop 2012, Estes Park, Colorado RUAG Space 2

GRAS MetOp CGRAS MetOp B

GRAS MetOp A

GPSOS

NPOESS

SWARM

Operational Production Phase

6 units

New Generation:

- Modular

- Compact

- Front end RFASICS

- UART i/f

- Compact antenna

Sentinel-1 A

Production Phase

6 units

New Features:

- 1553 i/f

- Dynamic Nav solution

- Choke ring antenna

- S/C multipath analysis

RO

RO

POD POD

Sentinel-2 A

Sentinel-3 A

EDU

Sentinel-1 B

2:nd

generation ordered

6 units

POD

Sentinel-2 B

Sentinel-3 B

GPS: L1 C/A + L2 Codeless tracking

ROEartCARE

GPS L2C

Galileo, Compass, Glonass CDMA

GRAS-2

Sentinel-1 C

POD

Sentinel-2 C

Sentinel-3 C

3:rd

generation anticipated

6 units

GNSS Receiver Development

IROWG-2 Workshop 2012, Estes Park, Colorado RUAG Space 3

GRAS Performance

Characteristics:

650 occ/day

Ultra stable frequency reference < 1e-12

Wide coverage high gain antennas

Excellent RFI rejection

OL sampling at 1 kHz (high observability)

Range model performance Doppler model performance

10-2

10-1

100

101

10-8

10-7

10-6

10-5

10-4

10-3

Frequency (Hz)

Spectr

al density o

f D

opple

r nois

e (

m2/s

2H

z)

Thermal noise

USO clock drift

Total Doppler Error

GNSS clock drift

GRAS data

USO PLL phase noise

Integration range

Variable upper integration limit

depending on geometry

Doppler measurement performance

IROWG-2 Workshop 2012, Estes Park, Colorado RUAG Space 4

GRAS-2 Performance

Requirements:

GPS L1, L5

GALILEO E1, E5

COMPASS

GLONASS CDMA

0.5 mrad bending angle accuracy

Nominal data:

• Mass: 8 kg

• Power: 25 W

• Data rate: 200 kbps – 1 Mbps

Characteristics:

1300-2400 occ/day

Ultra stable frequency reference < 0.5e-12

Wide coverage high gain antennas

Open loop sampling for continuous measurements

IROWG-2 Workshop 2012, Estes Park, Colorado RUAG Space 5

GRAS Experience

Complex atmosphere

Ground interference

Co-channel interference

LEO Longitude [deg]

Occ L

atitu

de [

deg]

Distrubution of L1 NPD increase of 2.0 dB. North = 0

180oW 120oW 60oW 0o 60oE 120oE 180oW 90oS

60oS

30oS

0o

30oN

60oN

90oN

0 20 40 60 80 100 120 140 160 18015

20

25

30

35

40

45

50

55C/A C/No for Case 10 from WOP file: ALLModFreqFile1kHzDataLinCase10.

C/N

o [

dB

Hz]

Time since start of occultation [s]

IROWG-2 Workshop 2012, Estes Park, Colorado RUAG Space 6

Galileo Signals

0 2 4 6 8 10

-0.5

0

0.5

Time (us)

E1 CBOC-B signal

-10 -5 0 5 10-40

-30

-20

-10

0

Frequency (MHz)

-2 -1 0 1 2-0.5

0

0.5

1

E1 CBOC-B cross-correlation

-2 -1 0 1 2-0.5

0

0.5

1

Relative code offset (us)

E1 CBOC-C cross-correlation

Signals of particular interest for GRAS-2:

E1 (CBOC) data 250 Hz (-B) and pilot (-C)

E5 (BPSK 10 MHz)

Cross-correlation between signals varies over time

due to the relative motion between them.

Experience from GRAS is that cross-correlation

interference may be up to 5 dB above thermal

noise, interfering with the acquisition process.

-2000 -1500 -1000 -500 0 500 1000 1500 2000-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

Cross-correlation GAL code 2 and 1

Relative code offset (us)

Rela

tive a

mp

litu

de (

dB

)

Cross-correlation between Galileo E1 CBOC (B and C):

-24 dBc peak relative to signal being tracked (B or C)

(~3 dB better than GPS C/A)

-38 dBc average (~6 dB better than GPS C/A)

IROWG-2 Workshop 2012, Estes Park, Colorado RUAG Space 7

Galileo Signals: Bending Angle Accuracy

RMS budget at 35 km

Interference between

Galileo/GPS/Compass/Glonass

signals accounted for

Signal power increases

(no codeless tracking)

More co-channel interference

GNSS clock improvements

10-2

10-1

100

101

10-8

10-7

10-6

10-5

10-4

10-3

Frequency (Hz)

Spectr

al density o

f D

opple

r nois

e (

m2/s

2H

z)

Thermal noise

USO clock drift

Total Doppler Error

GNSS clock drift

GRAS data

USO PLL phase noise

Integration range

Variable upper integration limit

depending on geometry

535250494755C/No (dBHz)

-171

-116

E5a-I,Q

-171

-119

E5a-Q

-173

-119

L2 P(Y)

-168-168-171Noise and interference power density (dBm/Hz)

0.46

0.40

1.13

0.33

0.57

0.35

0.84

-55

1e-12

1e-12

-118

E1c

Galileo signals

Pilot only

Bending angle accuracy budget

Budget Parameters

0.390.46Total Bending Angle Meas. Error (urad)

0.400.40Bending angle Doppler sensitivity (urad mm-1 s)

0.961.14Total Doppler Meas. Error (mm/s)

0.330.30LO phase noise error (mm/s)

0.570.53USO Allan Deviation Error (mm/s)

0.350.67GNSS Allan Deviation Error (mm/s)

0.590.70Thermal Noise Error (mm/s)

-55-55LO phase noise at 1 Hz offset (dBc/Hz)

1e-121e-12USO Allan deviation @ 1-10 s gate time

1e-122e-12GNSS Allan deviation @ 1 s gate time

-115-115Received signal power at lower frequency (dBm)

E1b,cL1 C/ASignal component

Galileo signals

Pilot + Data

Metop-GRAS

535250494755C/No (dBHz)

-171

-116

E5a-I,Q

-171

-119

E5a-Q

-173

-119

L2 P(Y)

-168-168-171Noise and interference power density (dBm/Hz)

0.46

0.40

1.13

0.33

0.57

0.35

0.84

-55

1e-12

1e-12

-118

E1c

Galileo signals

Pilot only

Bending angle accuracy budget

Budget Parameters

0.390.46Total Bending Angle Meas. Error (urad)

0.400.40Bending angle Doppler sensitivity (urad mm-1 s)

0.961.14Total Doppler Meas. Error (mm/s)

0.330.30LO phase noise error (mm/s)

0.570.53USO Allan Deviation Error (mm/s)

0.350.67GNSS Allan Deviation Error (mm/s)

0.590.70Thermal Noise Error (mm/s)

-55-55LO phase noise at 1 Hz offset (dBc/Hz)

1e-121e-12USO Allan deviation @ 1-10 s gate time

1e-122e-12GNSS Allan deviation @ 1 s gate time

-115-115Received signal power at lower frequency (dBm)

E1b,cL1 C/ASignal component

Galileo signals

Pilot + Data

Metop-GRAS

IROWG-2 Workshop 2012, Estes Park, Colorado RUAG Space 8

RO Simulator Environment Objective: (EUMETSAT Study)

Relate instrument characteristics to bending angle performance.

Establishing GRAS-2 acquisition and tracking strategies.

Validating S/W patches for GRAS enhancements.

ECMWF DMI RUAG

Wave Optics

Propagator

A(t), Φ(t) @ fi

Coded Signal

Module

Wave Optics

Inversion

a(a)

DError

Characteristics

Receiver

Module

A(t), Φ(t)

Model Atmosphere Retrieved Atmosphere

Atmosphere

Profile

N(h), a(a)

Baseband

30 MHz

Corr. fcn

1 kHz

0 20 40 60 80 100 120 140 160 18015

20

25

30

35

40

45

50

55C/A C/No for Case 10 from WOP file: ALLModFreqFile1kHzDataLinCase10.

C/N

o [

dB

Hz]

Time since start of occultation [s]

0 100 200 300 400 500 600 700 800 900 1000-3

-2

-1

0

1

2

3

noise and

co-channel

IROWG-2 Workshop 2012, Estes Park, Colorado RUAG Space 9

Simulation Model Results

GRAS Simulation GRAS Data

(ESA study)

IROWG-2 Workshop 2012, Estes Park, Colorado RUAG Space 10

Simulation model results

GRAS Simulation GRAS-2 Simulation

IROWG-2 Workshop 2012, Estes Park, Colorado RUAG Space 11

GRAS Instrument Simulations

GRAS Simulation GRAS Data

IROWG-2 Workshop 2012, Estes Park, Colorado RUAG Space 12

GRAS Instrument Simulations

GRAS Simulation GRAS-2 Simulation

IROWG-2 Workshop 2012, Estes Park, Colorado RUAG Space 13

Conclusion

GRAS-MetOp continuous to provide valuable experience

for the GRAS-2 instrument development

New GNSS signals provide new opportunities but is also a

source of increased interference in the GNSS bands

Improved simulation tools provide realistic atmosphere

cases for validating the GRAS-2 tracking principles