1. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
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390
A COMPARATIVE STUDY ON SPECTRAL ANALYSIS OF GLOBAL
NAVIGATION SATELLITE SYSTEMS
Boney Bose Kunnel [1]
, Susan Abraham [2]
, R Kumar [3]
,
Swarna Ravindra Babu[4]
[1][2][3]
SRM University, Chennai, India -603203
[4]
Samsung, Bengaluru, India
ABSTRACT
The introduction of new Global and regional navigation satellite systems has
simplified land, air and marine navigation. However, use of similar spectral bands would
cause notable effects such as interference, noise and performance issues on existing
navigation satellite systems. Apart from inter system and intra system interference issues
among these systems, researchers are more interested in making use of all these systems in a
single receiver to improve positioning accuracy. By analyzing the spectrums and modulations
of each of these Global Navigation Satellite Systems, it is possible to answer many queries on
interoperability and compatibility among them. Navigation satellite systems such as GPS,
Galileo, GLONASS and Compass are considered in this paper. These systems are compared
and effect of one system on another is studied using spectral analysis.
Keywords: Compass, Galileo, GLONASS, GPS, Spectral analysis.
1. INTRODUCTION
Man’s desire to explore unknown places led to inventions like the magnetic compass.
A Global Navigation Satellite System (GNSS) is a modern day compass, which uses artificial
satellites to find the user position anywhere on earth. Though 3D positioning can be achieved
by using four satellites, greater number of satellites will drastically improve accuracy. With
availability of multiple Global and regional navigation systems, even if one satellite system is
unavailable, user can make use of another system if both navigation systems offer
interoperability. The main requirements for interoperability are common or very close centre
frequency, similar kind/family of modulations and signal characteristics, common geodetic
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2. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
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and time references. [1]. Thus availability of two or more satellite navigation systems further
aids positioning accuracy.
Global Positioning System (GPS), managed by the United States DOD is the most
popular satellite navigation system. The user receiver can be fixed absolutely anywhere like
vehicles, mobile phones or even in spectacles as in those developed by Google recently. GPS
L1 C/A and L5 are considered in this paper. Galileo, managed by the European Union is
another active GNSS that provides highly accurate and guaranteed positioning services.
Galileo E1 and E5 signals are considered here. Another global navigation satellite system is
GLONASS of Russia which uses Frequency Division Multiple Access (FDMA) technique in
both L1 and L2 sub-bands [3]. Compass or Beidou Navigation Satellite system (BDS) of
China, when fully deployed will consist of five Geostationary Earth Orbit (GEO) satellites,
twenty-seven Medium Earth Orbit (MEO) satellites and three Inclined Geosynchronous
Satellite Orbit (IGSO) satellites [16].
The remainder of the paper is organized as follows: Section 2 describes various constellations
considered for spectral analysis where as section 3 explain the numerical results and figures.
The paper concludes with section 4.
2. GNSS CONSTELLATIONS
2.1.1 GLOBAL POSITIONING SYSTEM(GPS)
The United States GPS consist of 24 satellite constellation in 6 orbital planes, inclined
at 55 degrees with respect to equator. GPS signal basically consist of PRN codes and ranging
information.
2.1.2 GPS L1 C/A
GPS L1 uses Coarse/Acquisition (C/A) code which is Bi-phase modulated at a chip
rate of 1.023MHz. The C/A code is 1ms long and belongs to the family of Gold codes,
generated using shift registers where position of feedback determine pattern of sequence. The
navigation data rate used is 50Hz and is 20 ms long, thus requiring 20 C/A codes for each
data bit [1,2].
2.1.3 GPS L5
GPS L5 uses two codes namely in phase (I5) code and quadrature phase (Q5) code at
10.23Mcps. Each code is modulo-2 sum of two sub sequences XA and XB where, XA & XB
are 8190 & 8191 length codes respectively that are restarted to run for 1 ms duration (length
of 10230 chips). Data is 50 bps which is half rate convolution encoded. QPSK modulation is
performed onto an 1176.45MHz carrier [4]. The GPS L5 generation is shown in Fig 1.
2.1.4 GALILEO
2.1.5 Galileo E1
The E1 signal is composed of three channels A, B and C. E1-A is a restricted access
signal, E1-B is the data signal whereas E1-C is the data-free signal (pilot signal). Galileo E1
uses Binary Offset Carrier modulation. A basic understanding of BOC modulation is shown
in Fig 2.

3. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 2, March
representeisBOC
E1 signal has a Code length of 4092 with chipping rate of
Secondary code on pilot with length 25 chips increases repetition interval to 100. Very long
code is used to reduce effects of cross correlation from other satellites [6, 8]. Galileo E1
shares same frequency as GPS L1 which
2.1.6 Galileo E5
Galileo E5 uses an alternative of BOC modulation, Alternate Binary Offset Carrier
represented as AltBOC(15, 10). The difference from traditional BOC is that the sub
function is a complex rectangular exponential that only
centre frequency. Two PRN codes are modulated on orthogonal components. The two in
phase components E5aI and E5bI carry the data modulation whereas the two quadrature
components E5aQ and E5bQ are pilot signals. The da
convolution encoding scheme. The primary codes used in the Galileo E5 signal are 10230
chips long. Apart from primary codes, shorter and slower secondary codes are used to obtain
tiered codes. Tiered codes have very
[7].
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
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392
Fig 1: GPS L5 generation
Fig 2: BOC Modulation
)
f
f
,
f
f
BOC(
:asdrepresente
o
c
o
s
FrequencyReferencef
RateChipf
FrequencySubcarrierf
o
c
s
−
−
−
E1 signal has a Code length of 4092 with chipping rate of 1.023MHz and repeats every 4ms.
Secondary code on pilot with length 25 chips increases repetition interval to 100. Very long
code is used to reduce effects of cross correlation from other satellites [6, 8]. Galileo E1
shares same frequency as GPS L1 which is 1575.42MHz.
Galileo E5 uses an alternative of BOC modulation, Alternate Binary Offset Carrier
represented as AltBOC(15, 10). The difference from traditional BOC is that the sub
function is a complex rectangular exponential that only shifts the spectrum up or down of the
centre frequency. Two PRN codes are modulated on orthogonal components. The two in
phase components E5aI and E5bI carry the data modulation whereas the two quadrature
components E5aQ and E5bQ are pilot signals. The data rate used is 250sps with a half rate
convolution encoding scheme. The primary codes used in the Galileo E5 signal are 10230
chips long. Apart from primary codes, shorter and slower secondary codes are used to obtain
tiered codes. Tiered codes have very good auto-correlation and cross-correlation properties
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
April (2013), © IAEME
1.023MHz and repeats every 4ms.
Secondary code on pilot with length 25 chips increases repetition interval to 100. Very long
code is used to reduce effects of cross correlation from other satellites [6, 8]. Galileo E1
Galileo E5 uses an alternative of BOC modulation, Alternate Binary Offset Carrier
represented as AltBOC(15, 10). The difference from traditional BOC is that the sub-carrier
shifts the spectrum up or down of the
centre frequency. Two PRN codes are modulated on orthogonal components. The two in
phase components E5aI and E5bI carry the data modulation whereas the two quadrature
ta rate used is 250sps with a half rate
convolution encoding scheme. The primary codes used in the Galileo E5 signal are 10230
chips long. Apart from primary codes, shorter and slower secondary codes are used to obtain
correlation properties

4. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
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2.1.7 GLONASS
GLONASS uses L1 and L2 bands. L1 sub-band carrier is modulated by modulo 2
operations of PRN Ranging code, Navigation message and an auxiliary meander sequence
whereas L2 sub-band carrier is modulated by modulo 2 operations of PRN Ranging code and
an auxiliary meander sequence. The PRN ranging code is generated as Maximum length
sequence of shift register and has a period of 1 ms with a bit rate of 511 kbps. The digital data
in GLONASS is transmitted at a rate of 50bps [3]. The nominal frequencies used in
GLONASS L1 is defined as
562.5KHz∆f1602MHz,f
where,∆fK.ff
101
101k1
==
+=
K is the Frequency number (channel)
2.1.8 BEIDOU B1-I
The carrier frequency of Beidou B1 signal is 1561.098 MHz. The signal consists of
carrier frequency, ranging code and Navigation message. The final B1 signal is obtained as a
sum of in-phase and quadrature phase components out of which China has released only B1-I
signal details. The PRN code used in B1I has a Chip rate of 2.046Mcps and length 2046chips
[16]. QPSK modulation is used to generate the Beidou B1 Signal and can be represented as
follows.
)2sin().().(.
)2cos().().(.)(
j
o
j
Q
j
QQ
j
o
j
I
j
IIj
tftDtCA
tftDtCAtS
ϕ
ϕ
+Π+
+Π=
(1)
Where j is the satellite number, A is signal amplitude, C is the ranging code, D represents
data modulated on ranging code., of represents carrier frequency and j
φ represents the initial
carrier phase.
3. SIMULATION RESULTS
All simulations were performed in MATLAB. The spectrum of GPS L1 C/A and
Galileo E1 are shown in Fig 3. Both the spectrums are centred at 1575.42MHz.
Fig 3: Galileo E1 and GPS L1 Spectrums
-4 -2 0 2 4
-200
-180
-160
-140
-120
-100
-80
-60
-40
Frequency [MHz]
Power[dBW/Hz]
Galileo BOC(1,1)
GPS C/A

5. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 2, March – April (2013), © IAEME
394
As observed from Fig 4, the main lobe of GPS L1 has a bandwidth of around
2.046 MHz and contains maximum power. The side lobes have a little power distributed
among them. Galileo E1 using BOC (1, 1) has a spectrum that splits the main lobe into two
distinct parts each with 2 MHz bandwidth. Due to this split, the interference caused by
Galileo on GPS is negligible and both can co-exist on the same carrier frequency. The
spectrums of GPS L5 and Galileo E5 are plotted in Fig 4. Both these spectrums are centred at
1176.45 MHz. The main lobe occupies a bandwidth of around 20 MHz and the different
modulations used by the signals allow for interoperability. The power spectrum of
GLONASS L1 for K=-7 channel is shown in Fig 5.
Fig 4: Galileo E5 and GPS L5 Spectrums
Fig 5: GLONASS L1 power spectrum
As seen from Fig 5, the main lobe of GLONASS occupies a bandwidth of
around 1 MHz. The relatively new constellation of Beidou B1 spectrum is shown in Fig 6.
The main lobe occupies a bandwidth of 4 MHz. Since the carrier frequency of Beidou is
1561.098 MHz, it causes negligible interference to its neighbours GPS L1 and Galileo E1
also on the 15 GHz band.
-4 -3 -2 -1 0 1 2 3 4
x 10
7
-240
-220
-200
-180
-160
-140
-120
-100
-80
-60
-40
Frequency[Hz]
Power[dBW/Hz]
Galileo E5 and GPS L5 Power spectrum centred at 1176.45 MHz
Galileo E5
GPS L5
-5 -4 -3 -2 -1 0 1 2 3 4
x 10
6
-240
-220
-200
-180
-160
-140
-120
-100
-80
-60
-40
Power Spectrum of GLONASS L1 C/A Code
Frequency (Hz)
Power(dBW/Hz)

6. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 2, March – April (2013), © IAEME
395
Fig 6: Power Spectrum of Beidou B1
Correlations of various constellations are also shown below. Fig 7 shows auto correlations of
GPS L1 C/A and Galileo E1. BPSK modulation has limited ranging capability and requires
high performance receivers. BOC provides better performance at frequencies away from
centre frequency thus causing negligible interference effects on each other. Autocorrelation
of GLONASS L1 and Beidou B1 are shown in fig 8.
Fig 7: Autocorrelation of GPS L1 and Galileo E1
-6 -4 -2 0 2 4 6
x 10
6
-320
-300
-280
-260
-240
-220
-200
-180
-160
-140
Power Spectrum of BEIDOU B1 Signal
Frequency (Hz)
Power(dBW/Hz)
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
x 10
4
0
2
4
6
x 10
4 GPS L1 C/A Code
Autocorreleation
Lag
0 2 4 6 8 10 12 14 16 18
x 10
4
-5
0
5
10
x 10
4 Galileo E1 BOC(1,1)
Autocorreleation
Lag

7. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
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396
Fig 8: Autocorrelation of GLONASS L1 and BEIDOU B1
Fig 9: Normalized autocorrelations of Galileo E5 and GPS L5
Fig 9 shows the normalized correlations of GPS L5 (I code and Q code) and Galileo E5
AltBOC. The E5 has a sharp correlation peak that aids in tracking.
-5 -4 -3 -2 -1 0 1 2 3 4 5
x 10
4
0
1
2
3
x 10
4
Lags
Autocorrelation
GLONASS L1
-200 -150 -100 -50 0 50 100 150 200
0
50
100
Lags
Autocorrelation
BEIDOU B1
-250 -200 -150 -100 -50 0 50 100 150 200 250
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Lags
Autocorrelation
Correlation plots
Galileo E5
I5 code (GPS L5)
Q5 code (GPS L5)

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4. CONCLUSION
The increasing number of Global Navigation Satellite Systems is no longer a result of
resistance against American monopoly in Satellite Navigation. Various countries with Global
and regional navigation systems are trying to support one another to provide users with
accurate positioning information. The negative effects of inter system and intra system
interferences are negligible compared to the advantages when these constellations
interoperate. Once inter operability is achieved, with a single user receiver, a user can receive
and acquire signals of different constellations thus improving positioning accuracy to an
unimaginable level. The GPS L1 and Galileo E1 can interoperate without causing much
interference as BOC modulation splits the main lobe of the spectrum away from L1 centre
frequency. Similarly, Galileo E5 and GPS L5 can co-exist due to AltBOC modulation in
Galileo. Thus even if different GNSS use similar carrier frequency, effect of one constellation
on another is very less. The future works include receiving a particular frequency spectrum
and perform acquisition to obtain Doppler measurements and trying to predict another
frequency spectrum.
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