Roman BERESIK, Milos SOTAK, Frantisek NEBUS, Jozef PUTTERA

Armed Forces Academy

Satellite communication system’s detection

Abstract. In recent asymmetric warfare satellite communication systems play more and more important role in remote control of Improvised
Explosive Devices (IED). Such systems are primarily used in environment where other communication technologies have either limited or no
coverage in particular area. First stage in effective suppression of such systems misusage is possibility to monitor and in case of need cease down
unacceptable communication. Paper deals with analysis of Thuraya communication system. The goal of paper is to present results of system
analysis in terms of its configuration, time and frequency signal parameters. Base on achieved results the possible method on how to block IED
triggering is outlined.

Streszczenie. Asymetryczne satelitarne systemy komunikacyjne odgrywają ważną role w zdalnym sterowaniu urządzeniami wybuchowymi.
Systemy tego typu są stosowane tam gdzie inne systemy komunikacji są limitowane. W artykule zaprezentowano system Thuraya. Przedstawiono
parametry konfiguracji. (Detekcja satelitarnych sygnałów komunikacyjnych)

Keywords: SATCOM, Thuraya, Signal Detection, Improvised Explosive Devices

Słowa kluczowe: komunikacja satelitarna, zdalne sterowania urządzeniami wybuchowymi.

Introduction Thuraya-2 satellite acts as an on-ground spare. The

Commercial satellite communications means play an Thuraya system has been designed to be compatible with
increasingly vital role not only as public communication the GSM network. The dual-mode hand-held terminals are
means but also in military operations, where is limited or no of a similar dimension to current GSM phones. Vehicular
communication backbone available in particular area. dual-mode phones are also supported, as are satellite-
Availability of commercial satellite systems cause the mode only fixed terminals and payphones. The mobile link
potential risk of their misusing from adversary side. There operates in the L band, specifically the 1626.5–1660.5 MHz
are several scenarios how satellite communication can be for uplink (UL) and 1525.0–1559.0 MHz for downlink (DL)
misused. On of them is to coordination of adversary attacks bands. The Thuraya system is defined by global mobile
against friendly units during operations. Generally, radio ETSI standards (see more [4]).
commercial satellite systems are not hardened to be The composition of the Thuraya system elements is
protected against deliberate attacks or jamming. This is the shown in Figure 1. The system includes one or more
reason why analysis of satellite communication systems is geostationary satellites, a Satellite Operations Center
important and in many cases crucial in order point out its (SOC), a number of Gateway Stations (GS), and a large
vulnerabilities. In general, the satellite systems can be number of user terminals, referred to as Mobile Earth
divided into two basic categories [1, 2]. The first category Stations (MES). The range of possible MESs includes hand
involves Geostationary Earth Orbit (GEO) systems such as portable terminals (handsets), vehicle terminals, and fixed
INMARSAT and THURAYA, and the second one involves terminals. The Gateway stations have external interfaces to
Non-geostationary Earth Orbit (Non-GEO) systems. The existing fixed telecommunications infrastructure as well as
main systems being included in this category are to the GSM mobility management networks.
GLOBALSTAR, IRIDIUM and ICO as well. Every system
has its own architecture, coverage, signal structure and
system of frequency management. In general, main
approach for satellite communication system signal analysis
is to detect of satellite terminals activities in particular areas
both in uplink and downlink direction in order to identify
particular satellite communication systems, analyze signal
structure and if it is possible to identify single user terminal
within data stream. It is important to point out that satellite
systems share same frequency band for uplink and
downlink direction which is dedicated for SATCOM
systems. The paper presents the analysis of the Thuraya
satellite system, time and frequency signal analysis and
outcomes achieved during practical experiments.

Thuraya system overview

The Thuraya satellite system launched in 2001 by a
Fig.1. Thuraya system elements [4]
Private company Thuraya Satellite Telecommunications Co.
Ltd, based in United Arab Emirates allows 2 portable
A GS includes one or more Gateway Transceiver
terminals to communicate on a local cover Middle East,
Subsystems (GTS) which correspond to a GSM BTSs, one
North and Central Africa, Europe, Central Asia and the
or more Gateway Station Controllers (GSC), which
Indian subcontinent. The scheduled life-span of the system
correspond to a GSM BSCs, one or more Mobile Switching
is 12-15 years. The supplied services are: voice, fax and
Centers (MSC) which may be GSM MSCs, and one Traffic
data in 9,6 kb/s, SMS, INTERNET at the bit rate of 9,6Kb/s,
Control Subsystem (TCS) which has no corresponding
and localization by GPS, allowing the user to know or to
functional element in the GSM base station. The Thuraya
transmit its position by voice or by SMS.
TCS is required to support position based services, optimal
The system has the capacity for 13,750 simultaneous
routing and other satellite specific services and features, not
voice circuits with a call blocking probability of 2%. The

PRZEGLĄD ELEKTROTECHNICZNY (Electrical Review), ISSN 0033-2097, R. 87 NR 7/2011 249

found in GSM. Mobile services are provided in a large TDMA frame 24 time slots = 40 ms
regional coverage area, defined by the orbital location of the Modulation pi/4 CQPSK and others
geosynchronous satellite and the satellite payload Debit 46,8 kbit/s /channel
performance. Subscribers located anywhere in the Coding CRC, convolution codes, Golay
coverage area may have full use of the Thuraya system code, coding of Reed Solomon
services. EIRP 44-56 dBW
Satellite spot beams differ from GSM cells in that they
are large, regularly shaped and all originate from the same Physical channels
point source, i.e., the satellite, and thus are synchronized. Radio Frequency Channels
Because of their large size, several hundred kilometers in Operational frequencies in the mobile band may be
diameter, they overlap national boundaries and service anywhere within the 34 MHz L-band 1.525 GHz to 1.559
areas. GSM cells, on the other hand, are very small, GHz (downlink) and 1.6265 GHz to 1.6605 GHz (uplink);
irregularly shaped by terrain features and buildings and each carrier will be centered on an integer multiple of 31,25
originate from different geographical locations. GSM cells kHz [8]. The relation among Thuraya frequency channels is
are always assumed to be contained within a single shown in
country. These differences necessitate very different Fig.Figure 3 L-band RF carriers are configured for each
treatments. spot beam, depending on traffic demand, frequency reuse
considerations, and available spectrum as a result of
coordination with other systems using the same spectrum.
In the Frequency Division Multiplexing (FDM) scheme, L-
band downlink (forward) radio frequency (RF) carriers in the
Satellite-to-MES direction (downlink) are always paired with
L-band uplink RF carriers in the MES-to-satellite (uplink)
direction at a frequency offset of 101.5 MHz. The 34 MHz
operating frequency band is divided into 1087 paired
carriers, with carrier spacing of 31.250 kHz. When
assigning carriers to spot beams, the smallest addressable
unit is a sub-band. A sub-band is the combination of five
carriers. Any sub-band can be assigned to any spot beam,
regardless of the location of the spot beam. In addition to
carrying traffic, a subset of RF carriers is assigned to
control channels. A carrier can be either dedicated to a
Fig.2. Thuraya coverage area map as of 2010 [3] control channel or shared by both traffic and control
channels.
In the first case, the Thuraya system provides two-way
connectivity between a user terminal and a fixed network Downlink channels Uplink channels
U
subscriber, using L-band and Feeder links to the satellite
DLCh1 DLCh2 ULCh1 ULCh2

31,25 kHz

(shown with solid lines in Fig. 1). Access to fixed Usig

telecommunications networks is provided by connections …

through the Gateway Station. Fixed network connectivity 101,5 MHz

includes the Public Switched Telephone Network (PSTN); 1525 MHz 1559 MHz 1626.5 MHz 1660.5MHz

Public Land Mobile Networks (PLMNs); and Private Fig. 3. The relation among Thuraya radio channels
Networks (PN). Where DL frequency F1D is 1525.03125 MHz, F2D is 1525.06250
In the second case, the Thuraya system provides two- MHz, a is carrier spacing with value 31.25 kHz, b is channel
way connectivity between two user terminals in the same or bandwidth 27.7 kHz, UL frequency FU1 is 1626.53125 MHz and FU2
different spot beams by performing direct connection of the is 1626.56250 MHz.
two L-band to L-band connections in the satellite. This
special case of single-hopped terminal to terminal (TtT) Multiple access and timeslot structure
calls. The Thuraya satellite system is a Time Division Multiple
Access (TDMA) system. Timing configuration in the system
Relevant Thuraya parameters: is composed of hyperframe, superframe, multiframe, frame,
Cover Middle East, North and central and timeslot.
Africa, India, Central Asia and  Hyperframe: 3 hours 28 minutes 53 seconds 760
Europe, Australia and Indonesia msec in duration, including 4 896 superframes, 19
Service Telephony, fax, data short 584 multiframes or 313 344 TDMA frames.
messaging, location determination,  Superframe: 2.56 seconds in duration, including
emergency services, high power four multiframes or 64 TDMA frames.
alerting  Multiframe: 640 msec in duration, including 16
Orbital altitude GEO :35,786 km TDMA frames.
Nb of satellite 3 (1 in reserve)  Frame: 40 msec in duration, including 24 timeslots.
Life duration 12 – 15 years  Timeslot: approximately 1.67 msec (5/3 msec) in
Nb of beams / sat more than 200 [6] duration, including 78 bits.
Satellite capacity 13 750 channels
Frequency UL 1626.5-1660.5 MHz The complete timeframe structure is given in Figure 4.
Frequency DL 1525-1559 MHz
Total Band 34 MHz
Channel bandwidth 27,7 kHz (31,7 kHz guard band)
Access Method TDMA/FDM
Time slot 1.67 ms=78 bits

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 To distinguish whether the user terminal or service data are
transmitted, the data stream is arranged in logical channels.

Logical channels
The logical channels associated with the Thuraya may
either be a Traffic Channel (TCH) or a Control channel.
TCHs are intended to carry encoded speech or user data.
These are all bidirectional channels.
 TCH3: This channel carries normal speech and has a
gross information rate of 5.2 kbps, it takes 3 contiguous
timeslots.
 TCH6: This channel carries 2.4 kbps and 4.8 kbps user
data and has a gross transmission rate of 10.75 kbps, it
takes 6 contiguous timeslots.
 TCH9: This channel carries 2.4 kbps, 4.8 kbps, and 9.6
Fig. 4. Timeframe and timeslot structure [5, 7] kbps user data and has a gross transmission rate of
16.45 kbps, it takes 9 contiguous timeslots.
At the satellite, the TDMA frames on all of the radio The control channels are intended to carry signalling or
frequencies in the downlink of each spot beam will be synchronization data. There are three different categories of
aligned. The same principle is also applied to uplink. At the control channels:
MES, the start of a TDMA frame on the uplink is delayed by a) Broadcast channel is a downlink (forward) only channel
a variable amount from the start of the TDMA frame on the and consists of the following: Frequency Correction
downlink. This delay is variable to allow for signal CHannel (FCCH), GPS Broadcast Control CHannel
propagation delay. A physical channel which uses time (GBCH), Broadcast Control CHannel (BCCH), Cell
division multiplexing and it is defined as a sequence of Broadcast CHannel (CBCH).
timeslots on a single Radio Frequency (RF) channel. The b) Common Control CHannel (CCCH) consists of the
transmissions within these timeslots are known as bursts. following: Paging CHannel (PCH), Random Access
CHannel (RACH), Access Grant CHannel (AGCH),
Bursts Basic Alerting CHannel (BACH), Common Idle CHannel
A burst is a single unit of transmission on the radio path (CICH).
defined in terms of RF channel, RF power profile and c) Dedicated Control CHannel (DCCH) is a channel
modulation symbols. Bursts are sent in a defined time and resource that is dedicated for MES. They are all
frequency window where the time window is defined by a bidirectional except for the TACCH. The SACCH3
range of contiguous timeslot numbers and the frequency channel is a logical channel with the same physical
window are defined by the carrier number. Therefore, a burst structure as the FACCH3.
burst represents the physical content of one or more d) Slow TCH6-Associated Control CHannel (SACCH6):
contiguous timeslots. The fundamental unit of burst timing is Slow TCH9-Associated Control CHannel (SACCH9),
the half-symbol period. A timeslot consists of 78 half-symbol Fast TCH3-Associated Control CHannel (FACCH3),
periods, each of 5/234 ms duration. A particular half-symbol Fast TCH6-Associated Control CHannel (FACCH6),
period within a burst is referenced by a half-symbol number Fast TCH9 Associated Control CHannel (FACCH9),
(HSN), with the first half-symbol period numbered 0. In the Standalone Dedicated Control CHannel (SDCCH),
following clauses, the transmission timing of a burst is Terminal-to-Terminal (TtT) Associated Control CHannel
defined in terms of half-symbol numbers. The half symbol (TACCH), Power control subchannel.
with the lowest half-symbol number is transmitted first.
Different types of bursts exist in the system. One Time-domain signal description
characteristic of a burst is its useful duration. The useful Physical channels
duration of a burst is defined as beginning with HSN5. The The Air Interface allows multiple physical channels to share
present document defines bursts with useful durations of the same radio-frequency channel of a given spot beam
146, 224, 458, 614 and 692 half-symbol periods, based on using a TDMA scheme. Therefore, each physical channel is
total durations of 2, 3, 6, 8 and 9 timeslots. The period characterized by a sequence of timeslots on a radio-
between the useful durations of successive bursts is termed frequency channel. Once a physical channel has been
the guard period. Each burst has a guard period with allocated timeslots in a TDMA frame, it maintains the same
duration of five half-symbol periods before its useful timeslot numbers (relative to the start of the TDMA frame) in
duration and a similar guard period with duration of five half- all subsequent TDMA frames, for the duration of the
symbol periods after its useful duration, which has the effect physical channel allocation. The uplink and downlink
of centring a burst's useful duration within its timeslot(s). timeslot numbers assigned to a physical channel need not
Many bursts contain a pattern of bits known as a unique be same. Uplink and downlink physical channel timeslot
word pattern, used to resolve phase ambiguities inherent in assignments can cross TDMA frame boundaries.
the modulation. In conjunction with Thuraya system several
types of bursts are known: BACH burst, BCCH burst, CICH Logical channels
burst, DC2 burst, DC6 burst, DKABs bursts, FCCH burst, The Air Interface also allows for the possibility, in specified
NT3 burst - NT3 burst for encoded speech and NT3 burst cases, of multiple logical channels sharing a physical
for FACCH, NT6 burst, NT9 burst, RACH burst and SDCCH channel. This may be done by partitioning a physical
burst. More information about the bursts is in [7]. In channel's timeslots both by timeslot number relative to the
comparison of other satellite communication systems such start of the TDMA frame and by TDMA frame sequence.
as Inmarsat, the Thuraya system does not use special Therefore, characterization of a logical channel requires the
frequency channels for transmitting of service information. definition of a frame sequence in addition to a sequence of
This information is transmitted in frequency channels of timeslots on a physical channel.
particular spot beam together with user data (voice or data).

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Physical channel (PC) types and names Signal characteristics
By convention, the distinguishing characteristics of First experiment was focused on verification of Thuraya
physical channel types are captured in their names. frequency plan pattern in particular spot beam and also
Physical channel names start with the letters PC (physical confirmation of relationship between UL and DL channel
channel) followed by the number of contiguous timeslots frequencies. Every spot beam has predetermined frequency
used per TDMA frame. In the case of a unidirectional sub-band which is a combination of five carriers. Any sub-
channel, a suffix is added designating the channel's band can be assigned to any spot beam, regardless of the
direction, "u" for uplink or "d" for downlink. location of the spot beam. In order to prove this hypothesis
Six types of physical channels are used, as follows: the DL frequency band has been monitored by spectral
 PC2d, a physical channel with a length of two timeslots analyzer during several experimental measurements. The
for downlink only; initial condition for this experiment was that any Thuraya
 PC6d, a physical channel with a length of six timeslots mobile terminals were switched on. The results of UL band
for use only by the downlink; frequency spectrum measurement are shown in Figure 6.
 PC12u, a physical channel with a length of 12 timeslots It indicates that only one UL channel is allocated for
for use only by the uplink; particular spot beam whether the mobile terminals are
 PC3, a physical channel with a length of three timeslots; active or not. The measured frequency of active UL channel
 PC6, a physical channel with a length of six timeslots; is 1634.843750MHz. The several measurements were
 PC9, a physical channel with a length of nine timeslots. conducted in different time intervals, with the aim to obtain
information whether frequency of channels are updated or
There are only a few permitted ways in which logical not. In spite of the fact that other UL channels haven’t been
channels can populate physical channels, as described in intercepted, it is most likely that another L-band RF carriers
[7]. will be configured for each spot beam, depending on traffic
demand, frequency reuse considerations, and available
Experiments spectrum as a result of coordination with other systems
The experimental evaluation of Thuraya system’s using the same spectrum.
detection has been conducted in a basic test, shown in
Figure 5. Its structure can be divided into two essential Signal characteristics
systems. First part consists of UL monitoring subsystem First experiment was focused on verification of Thuraya
which is dedicated for UL frequency band monitoring and frequency plan pattern in particular spot beam and also
for time and frequency analysis. confirmation of relationship between UL and DL channel
frequencies. Every spot beam has predetermined frequency
sub-band which is a combination of five carriers. Any sub-
band can be assigned to any spot beam, regardless of the
location of the spot beam. In order to prove this hypothesis
the DL frequency band has been monitored by spectral
analyzer during several experimental measurements. The
initial condition for this experiment was that any Thuraya
mobile terminals were switched on. Base on captured data
via oscilloscope Agilent Infinitum 80804B, the spectrogram
of UL frequency band was computed in Matlab. The results
are shown in Fig.6.

Fig. 5. Structure of experimental test bed

Essential parts of that system are high performance

oscilloscope Agilent Infinitum 80804B with attached external
satellite antenna. User terminal consists of Thuraya mobile
station SO-2510 plugged into docking station and Thuraya
external satellite antenna. Second part of test bed is
dedicated for DL channels monitoring. It consists of
spectrum analyzer Anritsu MS2711D used for downlink
monitoring. Overall arrangement of test bed enabled
primary measurements in indoor environment.
Initially, the frequency spectrum analysis of both DL and
UL frequency band was conducted. Due to the hardware
limitations, it wasn’t possible to capture and analyze data in Fig. 6. Spectrogram of Thuraya ULCh267
DL channel and subsequently to analyze time frames
composition during the initialization, spot beam selection It indicates that only one UL channel is allocated for
and sending of system information. For this reason, primary particular spot beam whether the mobile terminals are
goal was focused on analysis of DL channels in frequency active or not. The measured frequency of active UL channel
domain and UL channels in both frequency and time is 1634.843750MHz. The several measurements were
domain. conducted in different time intervals, with the aim to obtain
information whether frequency of channels are updated or

252 PRZEGLĄD ELEKTROTECHNICZNY (Electrical Review), ISSN 0033-2097, R. 87 NR 7/2011

not. In spite of the fact that other UL channels were not can be identified as RACH logical channel which is part of
intercepted, it is most likely that another L-band RF carriers the PC12u physical channel, see [7].
will be configured for each spot beam, depending on traffic
demand, frequency reuse considerations, and available
spectrum as a result of coordination with other systems
using the same spectrum.
Subsequent experiments were focused on the
verification of relationship between UL and DL channel
frequencies. In the pattern of frequency plan, L-band DL
and UL channels have frequency offset of 101.5MHz. With
the knowledge of the UL channel frequency the DL channel
frequency can be determined by simple formula. The
relation among Thuraya channel frequencies can be found
in Fig.3. Knowing the frequency of UL RF channel in
particular spot beam, which is in our case
fUL=1634.843750MHz called ULCh267, we focus spectral
analysis in order to determine the DL channel frequency.
The computed central frequency of DL RF channel is fDL=
1533.34375MHz. The screenshot of spectral analyzer
displays (Figure 7) frequency spectrum of Thuraya DL
channel, where measured central frequency of channel is Fig. 8. Time series of the Thuraya UL bursts
fDL=1533,343MHz.
The next series of pulses is followed after time interval
0.789016s. This time interval is approximately 20 time
frames long (every time frame has duration 40ms). From
analysis it is also implied that SDCCH and TCH logical
channel can be sent within DL channel (DLCh267). The
exact composition of the DL logical channels was not
possible to determine due to the technical restriction of
experimental test bed.
The time pulse 2 has duration 4.8575ms, which are
approximately 3 time slots. Logical channel TCH3 (Traffic
channel) and FACCH3 (Fast associated control channel) [7]
can take 3 time slots, both in UL and DL direction. TCH3
and FACCH3 logical channels can be transmitted within
these signal time series as a part of permitted channel
configuration PC3. To determine either TCH3 or FACCH3
Fig. 7 Spectrum of DL frequency band logical channel is transmitted can be identified by analysis
of modulation scheme. Traffic channel TCH3 uses /4
This channel is called as DLCh267 and has level - CQPSK modulation and FACCH3 uses /4 CBPSK
113dBm. Figure 7 also shows the spectrum of adjacent modulation. Furthermore, spectral analysis of every pulse
signal which is Inmarsat DL channel at the central determines which channel frequency was used for its
frequency 1533.1MHz with bandwidth 200kHz (level - transmitting. For these particular measurements, UL
122dBm). This fact confirms the UL and DL channel channel frequency is 1634.875MHz (called as ULCh268),
composition which was analyzed. which has 31.25kHz higher value than ULCh267.
Frequency of DL channel is determined by formula fDL=fUL-
UL signal analysis 101.5MHz. In this case the frequency of DL channel is
The purpose of these experiments was to analyze UL 1533.375MHz (called as DLCh268) which was also
channel in time domain during the call initialization, to confirmed by practical measurement of DL frequency band.
determine crucial time intervals and analyze the type of the The spectrum of DL frequency band with DLCh267 and
bursts which are transmitted in UL channel during call DLCh268 is shown in Figure 9.
initialization. As initiator of call, two types of user terminals
were used.
First was GSM mobile phone and second Thuraya
mobile terminal. The second Thuraya mobile terminal was
used as answer user station. The measured time series of
UL Thuraya bursts are shown in Fig. 8. First pulse is
followed by two series of 40 pulses. Several characteristic
time periods can be recognized. The time duration of pulse
1 is 14.83750ms (pulse 1). Having information how logical
channels are organized within physical channels, there are
several logical channels which can be transmitted in UL
direction. One of them is Random Access Channel (RACH)
which is one of logical channels dedicated for call
initialization. It is used to request a Standalone Dedicated
Control Channel (SDCCH) or Traffic Channel (TCH) Fig. 9. Spectrum of downlink frequency band with DLCh267 and
allocation. The RACH comprises of 9 time slots (every time DLCh268
slot has 5/3ms) which is totally 15ms long time period. With
respecting of the measurement fault, particular time interval

PRZEGLĄD ELEKTROTECHNICZNY (Electrical Review), ISSN 0033-2097, R. 87 NR 7/2011 253

 Practical measurement showed that Thuraya system Spectral analysis showed that system determined one
allocates during call initialization two channels for single frequency channel for particular spot beam for call
connection between two mobile terminals. As was initialization and sending of the service data during
mentioned previously, channel ULCh267 is used for authorization of the user terminal. Other frequency channels
sending of channel allocation (RACH logical channel). As are allocated base on user terminal requirements, where
soon as the Thuraya control station allocates channel additional service data and user data are transmitted.
where the user traffic will be transmitted, the mobile station Practical results show that Thuraya system kept the same
tune itself to the adjacent channel (in this case ULCh268). frequency pattern in spot beam during experiments.
Subsequently, following bursts are sent via ULCh268. The Experiments showed that for successful and timely blocking
time period between pulses 3 and 2 is 35.148ms. Series of of incoming call that can be used as IED trigger from the
40 pulses (pulse 2) is followed by another series of 40 Thuraya user terminal it is necessary to keep situation
pulses. awareness about UL and DL frequency band in order to
The second series of experiments was focused on call identify the time interval (RACH) during which the
initialization time series analysis between two Thuraya connection initialization between two user terminals starts.
mobile terminals. The UL time series of two Thuraya mobile
terminals are shown in Fig.10. REFERENCES
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[9] GMR-1 05.008 (ETSI TS 101 376-5-6): "GEO-Mobile Radio
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Authors: Ing. Roman BERESIK PhD.

E-mail: roman.beresik@aos.sk
Ing. Milos SOTAK PhD,
E-mail: milos.sotak@gmail.com
Assoc. Prof. Ing. Frantisek NEBUS PhD.
Fig. 10. Time series of two Thuraya mobile terminals signals E-mail: frantisek.nebus@aos.sk
Assoc. Prof. Ing. Jozef PUTTERA PhD,
E-mail: jozef.puttera@aos.sk
Conclusions
The paper describes the experiments during which the Armed Forces Academy, Department of Electronics, Demanova
time, frequency and time-frequency analysis of Thuraya 393, 031 06 Liptovsky Mikulas 6, Slovakia,
signal was conducted. The results show that it is possible to
identify structure of time series during call initialization,
frequency channel pattern in UL and DL frequency band.

254 PRZEGLĄD ELEKTROTECHNICZNY (Electrical Review), ISSN 0033-2097, R. 87 NR 7/2011