Study of INS-Aided GPS Tracking Performance under Simulated
Ionospheric Scintillation Associated with Plasma Bubbles

Toshiaki Tsujii, Takeshi Fujiwara, Yoshimitsu Suganuma
Japan Aerospace Exploration Agency (JAXA)
andKeisuke Matsunaga
Electronic Navigation Research Institute (ENRI)

Background (1/2)
Ionospheric effects would degrade
availability of aircraft precision
approach
GBAS①Spacial gradient of TEC would resultin wrong correction data

Purpose of this paper
Evaluation of INS-aiding
under scintillation②Scintillation would cause temporal
loss of satellite lock→ re-initialization of PR smoothing→ go around due to multiple
satellites losses
Robust Trackingby INS-Aiding

Background (2/2)
Ionospheric Anomaly• Storm Enhanced Density (SED) Rare
– Mid~High Latitude Region– Spatial Gradient： ＞400mm/km• Equatorial Plasma Bubble (EPB)– Low~Mid Latitude Region
Frequent
Ionosphere– Scintillation
EPB and signal loss-of lockobserved over Japan
12 Feb. 2000. Red color
shows the signal loss-of lock.
[Ma and Maruyama, GRL, 2006]

Move Eastward～100m/s

Plasma Bubble（Density Depletion）

Doppler aiding by INS
fD =VS

Phase Error Sources• Clock Dynamics• Phase Scintillation• Aircraft Dynamics

eRemoved by Doppler-Aiding

VRe  (v S  v R )Doppler Frequency
due to Satellite andAircraft Dynamics• Amplitude Scintillation
Phase error• Thermal NoiseINS
IF Data
Front- end

φiLoop Noise Bandwidth

Margin for Scintillation

LoopFilter

φ0
Phase Locked
Loop (PLL)

VCOCarrier

Flight test to verify fundamental
function of INS-Aiding
equipments

Nav. INS

Nav-grade GPS/INS

MEMS INS

MEMS GPS/INSInter mediate Freq. data recorded
IF frequency ： 4,130,400 Hz
sampling rate : 16,367,600 HzGPS Front-End (Left: TCXO, Right: OCXO)

Flight Profile – Take/Off Velocity (NED)

Trajectory

Beechcraft Model 65 QueenAirAcceleration(body)Effect of Doppler Aiding
Carrier phase error for each satellite( BL=3Hz, TCXO, MEMS-INS )－ Without Aiding －－ With Aiding －   7.2 mm

   3.8 mm

Effect of Aiding is demonstrated by using real data
(Without Scintillation)

Analyses of Scintillation Associated with Plasma Bubble
SATELLITE SKYPLOT
NORTH

Movement ofPlasma Bubble

Observation data of GSV4004@Naha, Japan(N26°13' 43, E127°40' 44),
on April 14, 2004 (by ENRI)

59143025
22

Local Time: 9:40pm~0:05am

145WEST

EAST
61826

15
25

①30
16

②22

21
18
SOUTH

Scintillation associatedwith Plasma Bubble① Strong Scintillation（PRN15)
12:40-13:10② Weak Scintillation（PRN22）
14:20-15:05 (GPS Time)(Local Time = UT + 9 hours)

TEC Variation during strong scintillation ①TEC Depletion due toPlasma Bubble
04/04/14 Scintillation @ Okinawa

120

100

PRN 21

TEC(TECu)

8060

PRN 154020

Other Satellites
012.7

12.75

12.8

12.85

12.9 12.95
time (hour)

1313.05

13.1

Variation of TEC @ Naha(bias not calibrated)

13.15

TEC variation @Taiwan(http://wdc.nict.go.jp/IONO2/TEC-ROTI/)

Amplitude Scintillation Parameter and PSD of Intensity
extracted from real data during Strong Scintillation ①
S4 Variation

Intensity spectral density (12:51)

04/04/14 Scintillation @ Okinawa

0.7

Frequency content of Intensity

Due to scintillation

010

0.6
0.5-2

PSD(dB/Hz)

S4

Due to0.4
Multipath
0.3

10

PRN 150.2

PRN 21Other Satellites

10-4-6

100.1
0S4 

12.7 12.75 12.8 12.85 12.9 12.95
time (hour)I2  II

21313.05 13.1 13.15

10-8 -2
1010-1010
frequency (Hz)2Scintillation Parameters and PSD areused to simulate scintillation data

101102

Phase Scintillation Parameter and PSD of Phase
extracted from real data during Strong Scintillation ①
Phase spectral density (12:51)
Frequency content of phase

04/04/14 Scintillation @ Okinawa, PRN= 150.3p2010

0.2
0.1
0-2

10
12.7

12.8

12.9
13
13.1
time (hour)
04/04/14 Scintillation @ Okinawa, PRN= 21

0.2

PSD(dB/Hz)

sigma phi(radians)

sigma phi(radians)

Sigma of Phase error

10-4-610

0.10

12.7

12.8

12.9
time (hour)

1313.1

σϕ for PRN15 (top)and PRN21 (bottom)

10-8 -2
1010-1010
frequency (Hz)

101

102

P ( f )  T  f  p

Simulation of GPS/INS Signal
Under scintillation
AircraftTrajectory

Doppler Aiding

INS Data
Simulator

Intermediate
Frequency （IF）
Data Simulator
Scintillation
ParameterS4, σϕReal
Scintillation
Data

Scintillation
Data Simulator

for this presentation

IF Data

GPSSoftware
Receiver04/04/14 Scintillation @ Okinawa

30TEC(TECu)

25

Data of Weak Scintillation ②

PRN 222015
105

TEC Variation
14.4

SATELLITE SKYPLOT
NORTH

14.5

14.6

14.7
14.8
time (hour)

14.9

15

14.8

14.9

15

14.7 14.8
time (hour)

14.9

15

0.6
S4

0.4

S40.2
509

14145

WEST

EAST
61826

15
25

sigma phi(radians)

220.2

14.6

14.7

②

σϕ

0.1
030
1614.5

30

25

①

14.4

14.4

14.5

14.6

22

Real data (from 14h24m to 14h28m24s)

21

Intensity

SOUTH

Normarized power

318

Intensity

210① Strong Scintillation（PRN15)

0

Used for Simulation in this presentation

(radians)

150

200

250

200250Phase Error

0-1② Weak Scintillation（PRN22）

100

Phase variation

1Cycle Slips for ground receiver

50

050

100
150time (sec)

Embedded in
Simulated IF data

Trajectory

42.52

Doppler Aiding Performance
Under Scintillation

0-100

0

100

200

300

400

0100

200

300

400

0

100

200
Time (sec)

300

400

42.5
143.415

143.42 143.425 143.43
Longitude (deg)143.435

143.44600

100

V e (m/s)

143.41

0-100

200
050

100

150200250Time (sec)

300

350

400

0-5-10Aircraft
Trajectory

Doppler Aiding

INS Data
SimulatorIntermediate
Frequency （IF）
Data Simulator

Scintillation
ParameterS4, σϕReal
Scintillation
Data

Scintillation
DataSimulator

4000
3000
2000

Normarized power

30-1000

-3000
-4000
200

1050100

150200250200250

Phase variation

1Phase Error
Phase
Error

0-1

1000-2000

Intensity
Intensity

20

Phase
TrackingError

GPS
Software
Receiver

IF Data

I amplitude

0V d (m/s)

400

Intensityheight (m)Velocity100

V n (m/s)

42.54

(radians)

Latitude (deg)

42.56

050

100
150time (sec)

200.5

201

201.5

202

202.5
203
Time (sec)

203.5

204

204.5

205

I-channel Amplitude Variation
due to scintillation(time from 200 to 205 seconds)

Effect of Doppler Aiding Under Scintillation

100WithoutScintillation-10-20-30

050

100

150

200

250

300

20
100-10-20-30

350

050

100

150

200

250

300

350

050

100

150
200
Time (sec)

250

300

350

60

60
40
20

With
Scintillation

0-20-4040200-20-40
-60

0

50

100
8x 10-4150
200
Time (sec)

250

300

350

Without Aiding

7Probability-60

Carrier error (deg)30

20

Carrier error (deg)Carrier error (deg)With Aiding

Effect of Aircraft Dynamics

30

Carrier error (deg)Carrier Tracking Error (deg)For two satellites

Without Aiding

6Rate of Cycle Slip

54( Carrier Error > 45 degrees)

330 % Reduction

2100.13

0.14

0.15

0.16

0.174560
Carrier Error (deg)0.18

GPS-IF data Logging System@ King Mongkut's Institute of Technology (KMITL), Bangkok
GPS Antenna(NICT)InternetLogging Control,Monitor

Measurement System(NICT)
Splitter

IF Data Logging System

IF data

GPS Front-End

IF Freq.: 4 MHz
Sampling Rate: 16 MHzPCHDD

Summary Real data of scintillation associated with plasma
bubble was analyzed and extracted intensity/phasevariation were embedded in the simulated GPS IFdata

 The improvement of carrier tracking by Doppler
aiding was demonstrated and an example showedthat the rate of cycle slip was reduced by 30 %Future work
• Collect the real scintillation data (IF) and evaluate INS-Aiding
performance under scintillation• Verify the improvement of GBAS availability by INS-Aiding under
scintillation associated with plasma bubble