International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 1

Number 4

December 2007

375

Galileo Satellite Navigation System Receiver

Concept

M. Lemanczyk & J. Demkowicz

Gdansk University of Technology, Poland

ABSTRACT: The paper presents the Galileo Satellite Navigation System’s Receiver concept. The receiving

path and the model of GNSS receiver system for the L1 signal was shown as well as Galileo services and fre-

quencies were presented.

1 INTRODUCTION

Development of services connected with the Global

Navigation Satellite System, depends directly or

indirectly, on the progress in such areas as:

− GPS systems, EGNOS, Galileo, GPS III

− wireless telecommunication systems GSM (SMS,

GPRS), UMTS, WiMax

− GIS systems (digital maps, navigation maps,

thematic maps, 3D maps)

− terminals (smart phones, PDA, mobile phones)

as well as overall of standardization, certification,

and licensing.

Within the next few years most of the mobile

phones will be equipped with the satellite navigation

systems, both GPS and Galileo. There will be revo-

lution on the telecommunication market, when the

Galileo system will be combined with the GSM and

UMTS systems, providing communication and posi-

tioning with an unprecedence accuracy.

Fig. 1. Galileo signals frequency spectrum [GERAN]

376

At the next stage, when the whole three systems

become fully functional and available: Galileo, GPS

and most probable GLONASS, there will be a sig-

nificant improvement in providing the signal inside

the buildings, better accuracy, as well as shorter time

required for collecting all the needed signals from

the space. This will be the impulse for new applica-

tions to develop, which will be only limited by the

law and privacy policy protection. GNSS receiver is

one of the GNSS segments, but is the one that is ac-

cessible to the user. That’s why research and devel-

opment, connected with such a devices can be made

independently in the R&D Centers, around the

world. The main aim of the researches is to build the

fully integrated GNSS system receiver.

2 GALILEO AND GPS SYSTEMS

Galileo and GPS are the systems that will not in-

terfere with each other but which should cooperate.

One of the establishment of the Galileo constructor

engineers was to use such a signals that they could

be received on the Earth, on such a terrain, as forest

and high-destiny housing, but even though the signal

should not interfere with the GPS signal. The same

CDMA (Code Division Multiple Access) modulation

scheme is used in the E5a and E2-L1-E1 Galileo sig-

nals, as well as the same carrier frequencies that the

GPS signals are with. Fig. 1. The same carrier fre-

quencies are used to simplify the single common

receiver construction. [Hein et al.] That is why the

integration of both systems will be easier and the

cost of this process will be minimized.

At the each moment of time the L1 C/A code of

the GPS signal do not interfere the Galileo BOC(2,2)

signals more than 0,2 dB, witch his show in the

Fig.2. L1 Galileo signal has the right hand

polarization, carrier frequency of 1575,42 MHz and

the 40,92 MHz band. The signal is divided into L1A

(used for PRS services), L1B and L1C channels. The

L1B signal is the data channel. It is generated using

the modulo 2 of the signal that has the navigation

data and the PRN code sequence. The L1C is the

pilot signal. It is generated using the modulo of the

signal with the PRN code sequence and the carrier

frequency. The L1B signal code has 4092 chips and

L1C signal has 4092 chips and additionally 25 chips.

The minimum signal power required to a proper

receive the L1 (B+C) signals from the Earth is

167 dBW.

Figure 2. Maximum GPS C/A code C/N degradation in [dB]

due to inter-system interference from a Galileo BOC(2,2) for

L1. [Hein et al.]

The Fig. 2. shows the maximum interference ratio

for the L1 signals for GPS C/A and Galileo

BOC(2,2) depending on the geographical location.

Table 1. Maximal level of interference between GPS and

Galileo signals [Hein et al.]

As show in the Table 1, the values are accepted

and the Galileo and GPS signals will not interfere

with each other. The issue is essential because of the

integration of both systems in a unified receiver. So,

for the single end-user, cooperation between Galileo

and GPS will mean greater accuracy, availability and

certainty.

From the final users perspective the Galileo sat-

ellite navigation system will be conducted through

the five available services, that is:

1 Open Service - OS – available without payments,

for all users (naturally with lower accuracy),

compatible with the GPS SPS (Standard

Positioning Service)

2 Commercial Service - CS – available for a charge,

for certain users (with greater than OS,

guaranteed! accuracy)

3 Safety of Live - SoL – available without payment,

for all users, with guaranty of action, (Quality Of

Service)

4 Public Regulated Service - PRS – available

without payment, for certain users – members of

Galileo Project, controlled by them, with a

strategic meaning (i.e. Military Defense Systems)

5 Search and Rescue - SAR – available for all users,

enabling to send reflexive message to the rescue

station

377

To accomplish these requirements Galileo uses 10

signals in 4 bands, namely E5a (1 and 2), E5b (3 and

4), E6P (5), E6C (6 and 7), L1P (8) i L1F (9 ad 10).

Some publications mention only 6 signals are

broadcasted (E5a, E5b, E6P, E6C, L1P and L1F).

The difference comes from the fact that signals are

transmitted at the same frequency, one is called data

channel (contains datas) and the second is a pilot

channel (contains the pseudo code).

Figure 3. The L1 signal simplified modulation scheme

[GERAN]

The L1 signal is used in such a services like:

Open Service (OS), Safety if Live (SoL), Commer-

cial Service (CS) and in Public Regulated Service

(PRS). The E6 signal will be used in Commercial

Service (CS) and Public Regulated Service (PRS).

The E5 signal will be available in Open Service

(OS), Safety of Live (SoL) and Commercial Service

(CS). The L1 signal depending on the usage will hale

the BOC(1,1) modulation scheme ( Binary Offset

Carrier) or the BOC(15; 2,5). The carrier frequency

will be 1575,42 Mhz and the L1 signal involves

signals with the numbers 8, 9 and 10. The E5 signal

will involve signals with numbers 1, 2, 3 and 4. For

signals numbered as 1 and 2 the carrier frequency is

1176,45 Mhz, and the modulation scheme is

AltBOC (15,10). The E5 signals with numbered 3

and 4 use the carrier frequency 1207,14 (the

modulation remains the same). The E6 signals

involves signals with numbered 5, 6 and 7. Their

carrier frequency is 1278,75 Mhz, for signal number

5 the modulation scheme is the BOC(10,5), but for

the signal numbers 6 and 7 it is BPSK-R5

modulation scheme.

3 GALILEO SYSTEM RECEIVER

3.1 Galileo transmitting path

The signal in the transmitting path for the L1 signal

for channels B and C has the following scheme (see

eq. 1).

( ) ( )

[ ]

( ) ( )

[ ]

∑

∞+

−∞=

−−

−

′

−

+∞

−∞=

−−

−

′

−

−=













−=

CLsCLc

CLc

iCL

BLsBLc

BLc

lBL

iBL

tRsigniTtrectcte

tRsigniTtrectdcte

sin)(

(1)

Because of the CASM (Coherent Adaptive

Subcarrier Modulation) modulation scheme, which

assures the stable power level transmitted from the

satellite. The common signal for the L1 frequency is

shown with the following theorem:

[ ]

( )

[ ]

( )





















+−

−−−−

−−

tftetetete

tftete

xCLBLALAL

xCLBL

222

1111

sin)()()()(

cos)()(

)(

where:

Carrier Frequency [Hz]

x-y

Ranging Code Repetition Period [Chips]

c,x-y

Range Code-Chip-Length [Seconds]

s,x-y

Subcarrier-Period [Seconds]

c,x-y

1/T

c,x-y

; Code-Chip-Rate [Hz]

s,x-y

1/T

s,x-y

; Subcarrier-Frequency [Hz]

D,x-y

1/T

D,x-y

; Binary (NRZ modulated) navigation

message signal

x-y(t)

Binary (NRZ modulated) ranging code

x-y(t)

Binary (NRZ modulated) navigation message

signal

x-y(t)

Binary (NRZ modulated) subcarrier

x-y(t)

Binary NRZ modulated navigation signal

component including code, sub-carrier (if

available) and navigation message data (if

available); (c

x-y(t)

· sc

xy(t)

· d

x-y(t)

);

x(t)

Normalised Baseband Signal (= sX-I(t) +

jsX-Q(t))

|i|

‘i’ modulo L

3.2 Galileo receiving path

Finally the Galileo receiving path for the L1 fre-

quency includes the NCO generator, I-Q demodu-

lator, pilot signal correlator and the correlator for the

data channel, as shown in the Fig.4.

Figure 4. Galileo receiver block diagram

378

The Gold codes in the corrlelator has 4092 bits.

The process of the canvassing will be relatively long

and first to run should be for the piloting signal, the

second step should be for the channel with the datas.

The filtration block should be responsible both for

signal demodulation and for the BOC phase

sequence setting (Binary Offset Carrier), as well as

for receive signal frequency.

4 CONCLUSIONS

The paper presents a few essential concepts on the

Galileo satellite navigation system and especially the

Galileo receiver. The receiver is a project undergone

in the Dep. of Geoinformatics of Gdansk University

of Technology. Unfortunately some of the Galileo

concepts are still verified and the first stage of

building the system is to be closed in the 2008 and

that is that time the Galileo concepts could be

verified and some of the parameters can be modified

or changed. Therefore the main short-time project

goal include postprocessing and testing procedure

using software simulator and raw GPS/Galileo signal

record.

REFERENCES

3GPP TSG GERAN, 2005 meeting: L1 band part of Galileo

Signal In Space ICD (SIS ICD), Galileo Joint Undertaking,

Quebec, Canada.

Guenter W. Hein, Jeremie Godet, Jean-Luc Issler, Jean-

Christophe Martin, Philippe Erhard, Rafael Lucas-

Rodriguez and Tony Pratt, 2002 Status of Galileo Fre-

quency and Signal Design, Galileo Signal Task Force,

European Commission, Brussels.