PRESENT SATELLITE RADIO NAVIGATION SYSTEMS,THEIR PERFORMANCE

ANDUSER RECEIVER CONCEPTS

František Vejražka, Pavel Kovář, Libor Seidl,

Petr Kačmařík, Josef Špaček, Pavel Puričer

Department of Radio EngineeringCzech Technical University in Prague

Czech Republic

Abstract

This contribution gives an overview of present and future navigation systems and their augmentations such as GPS, GLONASS, GALILEO, WAAS, EGNOS, MSAT, QZSS, BEIDOU, GAGAN. Performance of the systems depends on their technical parameters. We will try to evaluate these and to present our opinion on their advantages for different applications and in various situations (reception of weak signals suffering from great attenuation under vegetation canopy, in urban canyons, influence of reflections and multipath).The last part of the contribution deals with an application of software radio technology for user receiver design and results obtained from experiments with different algorithms of processing the satellite navigation systems signals.

Terminology

Satellite (Radio) Navigation Systems

~

Radio Determination Satellite Systems

~

Systems for radio position determination using satellites

Satellite Navigation Systems

Historical Satellite Navigation Systems(not realized)

• 601

• TIMATION

•...

• GEOSTAR

• REXSTAR

GPS - NAVSTAR

Satellite Navigation Systems

Past Satellite Navigation Systems

• NNSS - Transit

• Tsikad GPS - NAVSTARrealized but cancelled

full operational

Satellite Navigation Systems

GLONASS

GPS - NAVSTAR GALILEO

in the air, not fully operational, lack of reliable satellites

projected, in development,operational from 2008

Satellite Navigation Systems

GPS-NAVSTARGLONASSGALILEO

Global systems:

Local systems:

Augmentation systems:

BEIDOU…

WAASNDGPSEGNOSMSASGAGANQZSS

→ GALILEO

Principles of Satellite Navigation Systems

• Doppler systems

• Ranging systems

Principles of Satellite Navigation Systems – Doppler Systems

satellite

fv

fv

t1+t1 t2+t2 t3+t3 t4+t4

fp

f0

crtdtff ii

tt

tt

pi

ii

ii

/Δ )(N11 Δ

Δ

0

receiver

fp

mixer

oscillator

f0 -fp

Ni

counter

time marks

startti+ti

stopti+1+ti+1

Ni = ΔFΔT+(f0/c){√[(xi+1-x)2+(yi+1-y)2+(zi+1-z)2 ] –

√[(xi-x)2+(yi-y)2+(zi-z)2]} i = 1, 2, 3

satellite

orbit T t2

t3

t1

t4

r1

r2 r3 r4

user

Principles of Satellite Navigation Systems – Ranging Systems(x1, y1, z1) (x2, y2, z2)

(x3, y3, z3)

(x4, y4, z4)

d4 = c4

(xi - x)2 + (yi - y)2 + (zi - z)2 = (c (mi - 0) )2 i = 1, 2, 3, 4

(x, y, z)

x

z

y

0 mi

0 i = di /c

0

signaltransmittedby satellite

tuser

signalreceived by user

d1 = c1

d2 = c2

d3 = c3

(xi - x)2 + (yi - y)2 + (zi - z)2 = (c i)2 i = 1, 2, 3

+1

-1

t

m

received

C(t+) code

+1

-1

t

C(t) range

code inside

receiver

- 0

R()

GPSDELAY DISCRIMINATOR

correlator

C()generátor

delay

clock

delay control

C(t+)

C(t)

0

R()

m

C*(t)

C*(t) unwanted satellite range code

C*(t) C(t)

R*()

GPSEARLY-LATE DISCRIMINATOR

correlator

C() generator

clock

m = R +

correlator

filterC(t - m) +

-

C(t - R + /2)uE()

uE()

C(t - R - /2)uL()

/2-/2

uL()

/2-/2

u() = uL() - uE()

u()

R

Receiver Principle

()2

phase lock

m

pseudorange

delay discriminator

C(t)D(t)cos(2ft)

[C(t)D(t)(1+cos(4ft))]1

2

cos(2ft)

C2(t) = 1D2(t) = 1

C(t)D(t)1

2

C(t)

C2(t)D(t) = D(t)1

2

Systems Parameters (Properties)

We will deal with systems:

• GPS – NAVSTAR

• GLONASS

• GALILEO

GPS - NAVSTAR

GPS Constellation

0°

40°

80°120°

160°

320°

280°

240°

200°17°

77°137°

197°257°

317°

satelliteoperationalspare

Equator

Right ascension of ascending node

Mea

n an

omal

y

F E D B A

Plane

Inclination 55°Semimajor axis 26561.75 km (altitude above Earth 20183,6 km)Excentricity nominally e = 0, generally e < 0,02

E1D2

C2B3

B2D1

E4C1

A4

F4A3

F3 F1

F2

D4

A1E2

D3

A2

C3B1

C4 E3

B4

C

GPS Present Signal Structure (1/3)Signal in time domain:

L1: s(t)=ACCC/A(t).D(t)cos(2πf1t)+APP(t).D(t)sin(2πf1t)

L2: s(t)=APP(t).D(t)sin(2πf1t)

Code multiplex - each satellite has own range codes CC/A(t) and P(t)

Signal in frequency domain:L2

1227,6 MHz±12 MHz

L11575,42 MHz

±12 MHz

ARNS/RNSS

1260 1559 1610

C/A

P(Y) P(Y)

MHz1215RNSS

GPS ParametersSignal Structure (2/3)Navigation Message (Data) Content:

• transmitting satellite Kepler parameters• almanac – Kepler parameters of others satellites• satellite „health“• corrections of

– satellite clock frequency– troposphere refraction

• …

Organisation of Data Frame:

54321

navigation message = 25 pages ~ 12,5 mins

frame = 1500 bits ~ 30 s ~ 5 subframes

25 pages

0987654321

subframe=10 words ~ 6 s

word = 30 bits ~ 0,6 sbit ~ 20 ms

GPS ParametersSignal Structure (3/3)Navigation Message FEC Hamming Coding

message receivedin error

errors without message ifsyndrom

bits (control)parity ,...,

bitsn informatio,...,

1000...

........................

0010...

0001...

,...,,,...,

data received

1

1

21

22221

11211

11

0S

0SHBS

HB

TT

m

k

mkmm

k

k

mk

rr

aa

hhh

hhh

hhh

rraa

GPS Services• SPS – Standard Positioning Service

only C/A code accessible

• PPS – Precision Positioning Servicefor authorized usersP(Y) code accessible

GLONASS

GLONASS Constellation

• 24 satellites (8 satellites in each of 3 planes)

• e ~ 0 (circular orbit) • inclination 64.8°• altitude 19 100

km, • orbit period 11h 15m

• angular spacing between orbits 120°

GLONASSSignal Structure• Frequencies:

– L1: fj = 1602 + 9j/16

– L2: fi = 1246 + 7i/16 [MHz]

• Modulation:– Navigation message– Pseudorandom ranging code

• Sequence of maximum length• Period 1 msec• Bit rate 511 kb/s

– 100 Hz auxiliary meander sequence – Manchester code

GLONASS Signal Structure• Data

– Hamming code (84,8)– 50 b/s in strings– 15 strings ~frame– 5 frames ~navigation message ~2.5 min

No Data Parity Time mark

2 sec

0

85 bits111110…110

1.7 sec 0.3 sec

GLONASS Constellation history

9 1012

1412 12 12

16

26

22

16

13 12 11

8 7 810

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

GALILEO

GALILEO Constellation

3 GEO satellites:• Inmarsat III

AOR-E 15.5°W F5 25.0°E

• ESA Artemis 21.5°E30 MEO satellites:

• 9 satellites in each of 3 planes (Walker constellation 27/3/1)• 3 spare satellites (1 in each plane) • e = 0 (circular orbits)• inclination 56°• altitude 23 616 km• orbit period 14h 21.6m ~ 1+2/3 rev. a day ~ ground track

repeats every 3 days

GALILEOArchitecture

USER SEGMENT

IMS

GALILEO CORE SYSTEM

TTC uplink

GCC

L-bandNAV

UHFSAR

….

REGIONALCOMPONENTS

LOCALCOMPONENTS

COSPAS-SARSATGROUND SEGMENT

MEO CONSTELLATION

External ComplementarySystems

C-band uplink

regional uplink

S-b

and

uplin

k GSS

Network

ICC

IMSNetwork

ICC

IMSNetwork IULS

Communication link

LocalInfra-

struct.

Communication link

LocalInfra-

struct.

.

.

.

.

.

.

NAV SIS NAV SIS

NAV SIS NAV SIS

INTEGRITY DETERMINATION& DISSEMINATION

NAVIGATION CONTROL &CONSTELLATION MANAGEMENT

Mission uplink

USER SEGMENT

IMS

GALILEO CORE SYSTEM

TTC uplink

GCC

L-bandNAV

UHFSAR

….

REGIONALCOMPONENTS

LOCALCOMPONENTS

COSPAS-SARSATGROUND SEGMENT

MEO CONSTELLATION

External ComplementarySystems

C-band uplink

regional uplink

S-b

and

uplin

k GSS

Network

ICC

IMSNetwork

ICC

IMSNetwork IULS

Communication link

LocalInfra-

struct.

Communication link

LocalInfra-

struct.

.

.

.

.

.

.

NAV SIS NAV SIS

NAV SIS NAV SIS

INTEGRITY DETERMINATION& DISSEMINATION

NAVIGATION CONTROL &CONSTELLATION MANAGEMENT

Mission uplink

GALILEOServices• OS – Open Service

free of charge, positioning, navigation, timing services

• CS – Commercial Serviceadded value to OS, garanteed services

• SoL – Safety of Lifeintegrity message

• PRS – Public Regulated Servicepolice, customs, ...dedicated signal, under governmental control

• SAR – Search and Rescuecoordinated with COSPAS – SARSAT

GALILEOSignals and Spectra

1164

.00

1215

.00

E5

1260

.00

1300

.00

E6

1563

.00

1587

.00

L1

1559

.00

E2

1591

.00

E1

1544

.10

SA

R d

ownl

ink

L6

≈ ≈ ≈f [MHz]

ARNS960 MHz 1214 MHz

1151 MHz 1300 MHzRNSS

1559 MHz 5250 MHz

1559 MHz 5030 MHzRNSS

ARNS

ARNS – Aeronautical Radio Navigation ServiceRNSS – Radion Navigation Satellite Service

GALILEO Signals and Spectra – BOC(m,n)

s(t) = carrier x subcarier x (ranging)code

subcarrier –

code – PRN

TS

TC

C6

S6

T1,023.10

1n

T1,023.10

1m

BOC modulation BOC(m,n)

GALILEOBOC Spectrum

-5 -4 -3 -2 -1 0 1 2 3 4 5

x 106

-40

-35

-30

-25

-20

-15

-10

-5

0

BOC(1,1) BPSK(1)

m = 1 – subcarrier frequency is 1.023 MHzn = 1 – range code chip frequency is 1.023 MHz

GALILEOBOC Correlation Function

-8 -6 -4 -2 0 2 4 6 8

x 10-6

-0.5

0

0.5

1

BOC(1,1)

m = 1 – subcarrier frequency is 1.023 MHzn = 1 – range code chip frequency is 1.023 MHz

GALILEOBOC modulation

-2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5

x 107

-40

-35

-30

-25

-20

-15

-10

-5

0

-2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5

x 107

-40

-35

-30

-25

-20

-15

-10

-5

0

-5 -4 -3 -2 -1 0 1 2 3 4 5

x 106

-40

-35

-30

-25

-20

-15

-10

-5

0

-8 -6 -4 -2 0 2 4 6 8

x 10-6

-0.5

0

0.5

1

-1.5 -1 -0.5 0 0.5 1 1.5

x 10-6

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

-1.5 -1 -0.5 0 0.5 1 1.5

x 10-6

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

BOC(1,1) BOC(5,1) BOC(5,2)

corr

ela

tion

fun

ctio

nsp

ect

rum

GALILEOSignals, Services and Spectra

I

Q

IN P

HA

SE

sin(

)

IN Q

UA

DR

ATU

RE

cos(

)

1575

.420

1561

.098

1589

.742

1559

.00

1591

.00

L1

1563

.00

1587

.00

E2 E1service modulation

codeencryption

data rate[symbol/s]

dataencryption

PRS BOC(15,2.5) yes 100 yes

OS/SoL/CS

BOC(1,1) none 250some(CS)

OS/SoL/CS

BOC(1,1) noneno data(„pilot“)

-

modulationsubcarrierfrequency

MHz

code rateMchips/s

BOC(15,2.5) 15.345 2.5575

BOC(1,1) 1.023 1.023

SoL uses the same signals as OS with integrity message

GALILEOSignals, Services and Spectra

1176

.450

1207

.140

1191

.795

E5a E5b

1164

.00

1215

.00

E5

I

Q

IN P

HA

SE

sin(

)

IN Q

UA

DR

ATU

RE

cos(

)

service modulationcode

encryptiondata rate

[symbol/s]data

encryption

OS/SoL AltBOC(15,10) none 50 none

OS/SoL AltBOC(15,10) none no data („pilot“) -

OS/SoL/CS AltBOC(15,10) none 250 some (CS)

OS/SoL/CS AltBOC(15,10) none no data („pilot“) -

Differerent signals are broadcast• on I and Q channels• in upper (E5b) and lower (E5a) part of the band

E5a and E5b may be used asa single ultra wide channel

GALILEOSpectrum, Services and Spectra

1278

.750

1268

.520

1288

.980

1260

.00

1300

.00

E6

I

Q

IN P

HA

SE

sin(

)

IN Q

UA

DR

ATU

RE

cos(

)

service modulationcode

encryptiondata rate

[symbol/s]data

encryption

PRSBOC(10,5)

TDMAgovernment 100 yes

CS PSK(5) commercial 1000 yes

CS PSK(5) commercial no data („pilot“) -

GALILEOSignal, Services and Spectra

I

Q

1176

.450

1207

.140

1278

.750

1575

.420

1544

.10

1191

.795

1268

.520

1288

.980

IN P

HA

SE

sin(

)

IN Q

UA

DR

ATU

RE

cos(

)

1561

.098

1589

.742

1164

.00

1215

.00

1260

.00

1300

.00

1559

.00

1591

.00

E5 E6 L1

1563

.00

1587

.00

E2 E1

E5a E5b

SA

R d

ownl

ink

L6

≈ ≈ ≈

GALILEOService Parameters

Open Service

(OS)

Commercial Service(CS)

Public Regulated Service(PRS)

Safety of Life Service

(SoL)

Coverage global global local global local global

Accuracyh-horizontal

v-vertical[m]

h=4, v=8dual

frequency

h=15, v=35single

frequency

<1

three frequency

access

<10 cm

localaugmented

signals

h=6.5

v=12

1local

augmentedsignals

4-6dual

frequency

Availability 99.9% 99.9% 99 – 99.9% 99.9%

Integrity No Value added service Yes Yes

BEIDOU

BEIDOU

„China‘s „Beidou“ navigation system is a regional positioning system mainly covering the country and its neighbouring areas, thus making vertical positioning impossible and limiting the number of users.“

• 3 geostationary satellites

• circular orbits

BEIDOUConstellation (Beidou 1B orbit)

Augmentations

transmiter reference

station

correctionsknown coordinates

receiver

receiver

AugmentationDifferential GPS (DGPS)

reference station

user

transmitter reference

station

correctionsknown coordinates

receiver reference

station

user receiver

AugmentationDifferential GPS (DGPS)

Augmentations• Many systems

– NDGPS– maritime systems

• Systems with satellite channel for corrections transmission– WADGPS– SBAS (ICAO) – Satellite Based Augmentation

Systems• WAAS• MSAS• EGNOS → future part of GALILEO• …

AugmentationsSBAS - Constellation

ARTEMIS

GPS

MTSATINMARSAT

INMARSAT

EGNOSMSAS

WAASGAGAN

AugmentationsSBAS - signals

Similar to SATNAV systems signals

AugmentationQZSS

AugmentationQZSS - Constellation

(1) Inclined orbital plane at approximately 45 deg from GSO

Ground track draws a figure “8” centered on the equator

４５deg

Side view

Equator

120 deg

Top view

(2) 3 satellites on the 3 orbit planes operate so that the right ascension of the nodes are each 120 degrees apart

Every 8 hours each of the 3 satellites passes over the same point on the figure “8” ground track

AugmentationQZSSSatellite visibility ensured with high elevation angle of more than 70 degrees.

The urban canyon picture

(Shinjuku area)

0 4 8 12 16 20 240

10

20

30

40

50

60

70

80

90(準天頂衛星の仰角 東京）

Time (Hr)

Ele

vation

Ang

le (

deg)

SAT1 SAT2 SAT3 GEO110GEO130GEO150

0 4 8 12 16 20 240

10

20

30

40

50

60

70

80

90(準天頂衛星の仰角 東京）

Time (Hr)

Ele

vation

Ang

le (

deg)

SAT1 SAT2 SAT3 GEO110GEO130GEO150

Elevation angle at Tokyo (24hour)

Minimum elevation angle for QZSS (approx. 70 deg)

Elevation angle for GSO sat (E130deg) Approx. 48 deg

Planed for 2010

MODERNISATION

GPS

Spectrum of Future GPSPresent state

Second civil signal L2

C/A

L21227,6 MHz

±12 MHz

L11575,42 MHz

±12 MHz

ARNS RNSS ARNS/RNSS

960 1215 1260 1559 1610

C/A

P(Y) P(Y)

L51176,45 MHz

±12 MHz

Third civil signal L5 and new military signal L1 a L2

M M

MHz

C/A P(Y) M C/A P(Y) M F1 F2

II, IIA1-28

28 sats7,4 y.

IIR1-8

8 sats7,9 y.

IIR9-20

12 satsc7,9 y.

IIF1-6

6 sats15 y.

IIF7-30

24 sats15 y.

5m

L1 = 1575,42 MHzL2 = 1227, 6 MHzL5 = 1176,45 MHz

GPS1990 2000 2010 2020 2030

L1 L2 L5Frequency and codes

10 m 0.5 m100 mPrecision 95%

24 satellites

89

97

05

97

8 satellites

12 satellites

02

4 d.6 satellites

04

06

6 satellites24 satellites

18 satellites 12 IIR+ 6 IIF

18 satellites

IIF

Comparison of Systems

Comparison of Systems

What is an advantage of modernized or new systems ???

• Systems use two or three frequencies → suppression of ionosphere refraction

• New modulation methods have– very sharp correlation function

→ better precision– broad spectrum

→ thermal noise resistance

Comparison of Systems

• New modulation methods have– very sharp correlation

function→ better precision

– broad spectrum → thermal noise resistance

– higher code rate→ easier multipath mitigation

Comparison of SystemsMultipath Mitigation

BPSK(5)BPSK(10)BOC(10,5)BOC(15,10)

Comparison of Systems• New modulation methods have

– very sharp correlation function→ better precision

– broad spectrum → thermal noise resistance

– higher code rate→ easier multipath mitigation

• Constellations ensure better satellite visibility→ lower PDOP → better precision,

integrity, …

RECEIVER ARCHITECTURERequirements

• Processing of all known and planned SATNAV signals:– GPS L1, L2, L5– GLONASS– GALILEO– Augmentations

• EGNOS• WAAS

• Flexible design and development of powerful algorithms of signal processing

• Easy implementation of them• Rapid and simple prototyping and testing

Software Defined Radio

RECEIVER ARCHITECTURERequirements

Software Defined Radio

What processor to use ???

• DSP• FPGA

RECEIVER ARCHITECTUREDSP Concept

Loops in algorithms – lower computational power

RECEIVER ARCHITECTUREFPGA Concept

No loops in algorithmsparallel processing → higher computational power

RESULTSat

CZECH TECHNICAL UNIVERSITY

Experimental receiver

Experimental Receiver CTU(first version)

• Two-channel RF unit• DSP unit – Virtex II FPGA PCI card• PC Workstation – Windows 2000

LNA

Channel 1

Channel 2

LNA

A/D FPGAVirtex II

PCI Bridge

DSP Xilinx

DSP UnitRadio Frequency UnitGNSS antenna

Synthesizer

High PowerComputer

High Frequency Part of the Receiver

ReceiverProgramming in Simulink

Processor Programming in EDK

Conclusions

• Software Radio is prospective technology for multi-systems GNSS receivers, as well as FPGA technology

• This technology make possible design of receivers for hard receptions conditions (leaves canopy, urban environment, etc.)

Thank you for your attention.Pavel Kovář

&František Vejražka

&Libor Seidl

Czech Technical UniversityPrague, the Czech Republichttp://radio.feld.cvut.cz/per

sonal/vejrazka