3. The Eutelsat Monitoring System
In this chapter the system that provides the monitoring functions is presented, as regard both hardware and software components.
3.1 – The Eutelsat Teleport
Eutelsat has its own Teleport located in Rambouillet, approximately 60 kilometres from Paris. It is the place in which antennas for satellite communications are installed, so it’s the spot through which Eutelsat controls its satellite and offers different services to its customers: it makes up part of the entire Eutelsat network.
It was created in 1964 and used for military purposes until the 80s; at first it was propriety of France Telecom, but finally Eutelsat bought it on 1 September 2004. It covers an area of 80 hectares, of which 7 are used for the Teleport, and over one hundred antennas are installed there.
In the Teleport mainly 3 kinds of activities are located:
• In-House Requirements, that is all those operations concerned with Eutelsat’s requirement for controlling its fleet: Satellite Control Systems, Communication System Control (for payload monitoring activities), Opensky (a customer
service realized to get Internet contents via satellite), In-Orbit Testing platforms (necessary to test performance of satellites during their life);
• Providing Services for costumers, in order to let them to transmit contents to satellites via the Teleport, without forcing to get the necessary hardware to do itself; for example, Eutelsat is able to offer a complete package in getting contents (cp. AXN™ Entertainment Company) from Sony Studios located in
London and for transmitting them over the space segment via the Teleport of Rambouillet;
• Hosting third part equipment, providing power supply, assistance and surveillance for those enterprises that require a secure and reliable place to keep their hardware for the access to the satellites.
3.2 – The Communication System Control (CSC)
The CSC is the main user of the Payload Monitoring System. This branch of Eutelsat has actually a direct link with those customers which transmit contents to satellites, offering a service 24/7.
This important service is offered by an internal supervision group and by some operators. Let’s understand why this section is completely necessary to Eutelsat’s activities.
3.2.1 – How it works
Here all the operations of the CSC are described. Please keep in mind that the philosophy of it is to guarantee that the Eutelsat’s network would be most “clean” as possible, in order to offer the best service to customers.
The first CSC team is responsible for the surveillance of each carrier that use Eutelsat’s Space Segment; actually, when a customers signs a contract with the commercial department, the planning department assigns to him a fixed bandwidth and power level in a well determined TXP over the satellite which will cover the region of interest in order to match customer’s requirement for the downlinked signal. Clearly, there is lot of kind of contracts can be made every time, but they can usually be divided into two: a long-time or an occasional rent of resources.
In both cases Eutelsat needs to monitor if a certain transmission occupies the “right place” in the satellite at the “right time”, and the only way to do this is having a Monitoring System that can observe all the satellites, analyzing directly the signals coming down from them. For example, it could happen that a customer transmits to a frequency completely different by that assigned, disturbing other transmissions.
Instead, the operators are responsible for other procedures. Here are listed the most important ones:
• When a permanent or an occasional carrier requires an access to the satellite (for example a TV operator that wants to transmit a match or a news in live broadcast), he needs to contact the CSC for getting the authorization to “access at time-up”: in that moment the operator checks if the identified carrier has the permissions to occupy the assigned bandwidth; he can do it because he’s directly connected with the billing department and he can get a
mask where he can verify all the parameters of the transmission (see Image 3.1).
(Image 3.1 – A booking mask for an uplink transmission)
If all is correct, he uses the Monitoring System to scan the appropriate frequencies on the apposite satellite. When the operator is connected, he leads the earth station through three steps: first of all he asks him to transmit a clean carrier at reduced power (-20 dB respect to the nominal power), in order to
see if the transmitting antenna is well oriented and aligned with respect to polarization. If it isn’t, it could be the responsible for a Cross-Polar interference that could disturb other transmissions. In the Image 3.2 we can see this phenomenon; during this operations it was asked to the carrier to rotate his own antenna, in order to try to reduce the bad effect on the other polarization (red line).
When each parameter is correct, the operator orders to get the clean carrier to the nominal power, that is the power assigned by Eutelsat and calculated during the discussion with the customer to optimize the operating conditions on a transponder with the communication requirements of the sevice, checking again if there is any disturb; at last, to transmit the modulated carrier is required, checking all the bandwidth and spectrum.
Image 3.3 and 3.4 show these steps; note that a particular care is paid to the Cross-Pol component, highlighted by the red line.
(Image 3.4 – A modulated carrier step)
• Concerning Cross-Pol interferences again, operators call the CSC if they find unauthorized services in his assigned bandwidth; having no idea who belongs the transmission on the other polarization, and any authority to contact another carrier, he asks to Eutelsat’s CSC to check and to solve the problem. The CSC reserves the right to cut carriers that cause interference to other users, and can invite to respect all the parameters controlling the equipment is well installed and configured. In the Image 3.5 we find an example of a Cross-Pol interference: the interfering carrier (line red) disturbs the other polarization
(line blue) approximately at 12565,42 MHz: actually, we can see a spurious lobe that would affect the transmission near that frequency.
As explained before, CSC will call the offending operator transmitting the carrier and will ask to set properly all the equipment to solve the problem. We repeat that if for any reason the interference can’t be cancelled, Eutelsat will remove by the spectrum the dangerous content.
• When a carrier changes his own equipment, like for example an antenna or other components, he can require to Eutelsat to measure his transmission, in order to have the certainty that the EIRP in the downlink path is sufficient to reach the necessary parameters. We’ll understand in the next chapters how this request makes reliable measures necessary.
3.3 – The initial structure of the Satellite Monitoring System
The main purpose of this work has been to upgrade the original structures of Rambouillet_1 and Rambouillet_2; the reasons that led it will be shown in the next chapter.
In the following paragraphs the original structure of the monitoring system is described, and a particular emphasis is dedicated to the French site.
3.3.1 – Monitoring Sites
Each satellite has a particular footprint, that is it can cover with the downlink beam(s) a geographic area. Usually, the footprints are described schematically, showing a region with concentric lines, each of them identified by a number expressed in dBW showing the power that is transmitted to a certain point on the earth surface. The
Image 3.6 shows a typical footprint for Hot Bird 6; clearly more power comes down, smaller antennas we need for getting the necessary level to the receiver.
(Image 3.6 – HB6 Footprint)
Taking into account the regions covered by the satellite, a location for a monitoring site is chosen. Generally, a site can look at more satellites, all those can light it up with a sufficient power.
At the moment, Eutelsat has got 10 monitoring sites spread all around the world. An important thing is that one satellite can be reached by more sites, in order to have more data collected by different hardware.
The Image 3.7 shows the geographical location of them together with the satellite fleet updated at January 2007, Table 3.1 shows which satellites are monitored by each
site, while Table 3.2 shows us the available resources. Finally, in Tables 3.3a and 3.3b a more detailed report on Rambouillet and Rambuoillet_2 is written, in order to introduce the reasons according to which the system has been improved.
Site Satellites Site Satellites
Cameroon W4 Rambouillet AB2
Dubai SESAT2 AB3
W1 EB4
Dubna W4 EB9
Johannesburg EB4 EXPA3
SESAT1 SESAT1
W2 TC2D
W3A W1
W4 W2
Makarios AB2 W3A
AB3 W6
AB4 Rambouillet_2 AB1
EB2 EB1
SESAT2 EB3
W5 HB6
W6 HB7A
New York AB1 HB8
AB2 TELSTAR-12
W3A
Sao Paulo AB1
AB2
TELSTAR-12
Monitoring Site # Monitored # Antennas # Monitoring # Calibrated
Satellites Devices Antennas
Cameroon 1 1 1 -Dubai 2 2 1 -Dubna 1 2 1 -Johannesburg 5 5 (1 Mnt) 2 (1 Mnt) -Makarios 7 10 2 -New York 2 2 1 -Rambouillet 11 12 8 (Prev: 6) 10 Rambouillet_2 8 10 (Prev: 9) 3 -Sao Paulo 3 3 1 -Singapore 1 2 1
Satellite Coverage Antenna
AB2 European West Transmit TR 04
AB3 Steerable Transmit-STH ASM 02
AB3 Superbeam Transmit-SBH ASM 02
AB3 Superbeam Transmit-SBV ASM 02
AB3 Widebeam Transmit-WBH ASM 02
EB4 East Wide ASM 01
EB4 West Super ASM 01
EB4 West Wide ASM 01
EB9 East Super TR 06
EB9 East Wide TR 06
EB9 West Wide TR 06
EXPA3 Steerable Transmit ASM 11
SESAT1 East Transmit ASM 10
TC2D Transmit Beam ASM 04
W1 East Transmit TR 08
W2 East Transmit TR 03
W3A EuropeA East Transmit TR 02
W3A EuropeB Transmit X TR 02
W3A EuropeB Transmit Y TR 02
W6 East Transmit TR 05
Satellite Coverage Antenna
AB1 European Transmit ASM 06
EB1 East Transmit ASM 08
EB1 Steerable 1 Transmit ASM 08
EB1 Steerable 2 Transmit ASM 08
EB3 Spot A Transmit TR 09
EB3 Spot B Transmit TR 09
EB3 Spot C Transmit TR 09
EB3 Spot D Transmit TR 09
HB6 Ka Transmit ASM 09
HB6 Ku East Transmit TR 07
HB7A East Transmit TR 07
HB7A West Transmit TR 07
HB8 East Transmit TR 07
HB8 West Transmit TR 07
TELSTAR-12 European Transmit ASM 12
W3A EuropeC Transmit ASM 07
3.3.2 – Rambouillet Monitoring Site before upgrading
As formerly described, Rambouillet monitoring system is responsible for the monitoring of 11 satellites; for achieving this objective, 12 antennas and 6 Monitoring Devices was originally used.
The detailed scheme is shown in the Image 3.8.
Signals from satellites are collected by two types of antennas: ASM (Automatic Spectrum Monitoring), installed for the use with the old management system (called RAMSES), and TCR (Telemetry Command and Ranging) the work of which is not only receiving signals repeated by satellites, but also being the instrument that allow to measure their position and velocity; we refer reader to specific documentation if more details are needed.
After passing through an antenna, the transmission is amplified by a LNA and then, via a waveguide, taken to an Amplifier Divider Module (ADM) that amplifies and repeats it to 8 outputs. The first 6 were linked to as much RF Switches, while the remaining two ports to the TLS™ and SatId™ Geolocation Systems, that allow to locate, with a variable uncertainty, on the Earth surface an interference present into a TXP. Finally, each switch is connected to a Monitoring Device, that is a Spectrum Analyzer that allows getting measures on signals, which are directly used by the CSC Team during its work. The interface that permits the communication between the system and users will be afterwards described.
3.3.3 – Rambouillet_2 Monitoring Site before upgrading
The Image 3.9 presents the structure of Rambouillet_2 Monitoring System. Thanks to it, 9 antennas monitored 8 satellites. The mainly difference in comparison with the site mentioned above is that before we was able to find two independent installations: TLS-1, TLS-2 and ASM-13 were isolated by the rest of antennas, using exclusively one Spectrum Analyzer (TLS-ASA).
3.3.4 – The SIECAMS® interface
The entire monitoring system can be managed remotely, using an interface called “SIECAMS” developed by SIEMENS™. Image 3.10 tries to briefly explain its functioning.
The interface is directly connected to a Front End Controller (FEC) that collects all the data coming from the Local Area Network (LAN) and that provides to send all the instructions produced by users to the appropriate device. As we can see, users can communicate with the system via the SIECAMS® interface.
(Image 3.10 – Monitoring System structure)
It can manage instructions coming from/directed to the following main devices: • Antennas. For example via SIECAMS® it’s possible to configure paths for
signals directed to Spectrum Analyzers, specifying gain/attenuation factors, frequencies, thresholds and all the calibration values.
• Rf Switching Units (RSU). It’s possible to communicate with those devices that transmit the signals received by antennas to the right Spectrum Analyzer; for example it’s possible to specify on which input port a particular signal is coming into and all the Ethernet parameters for the device, without changing them directly on the hardware.
• Powermeters and Powerheads. Managing all the hardware connected to the calibration subsystem is possible; please refer to the dedicated chapter for more informations.
• Monitoring Devices. The most important feature of SIECAMS® is to collect, elaborate and recording all the data coming from Spectrum Analyzers; usually they can have a LAN interface included in them, or they can communicate with all the system via a gateway that translates TCP/IP contents to the GPIB protocol and vice versa.
The main part of the SIECAMS® interface is the “Status Window”, where you can find a list of alarm elaborated by the system. Actually, during the Background monitoring all the carriers listed in the program are scanned by monitoring devices and nominal values of EIRP, Center Frequency and Bandwidth are compared with the actual ones. If these are so different in order to pass thresholds defined by the system administrator, an alarm is generated and added to the list shown in the Image 3.11.
(Image 3.11 – The Siecams Status Window)
A CSC controller’s job is to scan periodically this list and start all the necessary procedures to delete alarms. For example, a very common one is the H-EIRP and it occurs when a carrier passes the authorized EIRP it can transmit to the satellite; it’s very important taking into account this sort of warnings, because if the EIRP is too high, the satellite can be damaged by the transmission, so there is the need to quickly identify the responsible and telling him to normalize its flow if he doesn’t want to be excluded by the TXPs.
Other alarms can communicate differences with nominal values about centre frequency and bandwidth of transmissions, because they can damage other customers
The image below describes the other main functions of this tool.
(Image 3.12 – Block Diagram of SIECAMS® Configuration Explorer)
The first thing that an administrator can do is configuring all the devices used by the Monitoring System, without setting them physically, but via the common Ethernet bus. What has to be understood is that SIECAMS® is a tool that permits a large scalability of the system, because adding a satellite or a carrier to be monitored is a very easy operation, entirely done via software.
First of all, the Space Segment can be set up, giving specifications about:
• Satellites: identification, position, slant ranges from different monitoring. This last datum is used for calculating the Path Loss in the EIRP balancing equation.
• Transponders: identification, uplink and downlink polarizations, uplink and downlink centre frequencies, total bandwidth, downlink frequency shift and PSD of the entire transponder.
• Carriers: each carrier in a TXP can be configured, with regard to identification the service it carries on, frequencies, bandwidth and modulation features, thresholds for generation of alarms in the main window.
Also the following hardware of Ground Segment can be configured:
• Antennas: over frequencies and polarizations that can be received via the antenna, we can find specifications about the calibration subsystem (see further). But the most important section is dedicated to the steerable antennas (that is equipped with an engine and driven by an Antenna Control Unit), because via this section, they can be oriented automatically to the satellite of interest, after a detailed calculation is done.
• Path Devices: like RF switches, the connections of which can be configured. For example specifying on which port a particular signal is entering is possible.
• Monitoring Devices: the most used function in SIECAMS® is the data exchange between users and monitoring devices, in order to be efficiently used by the CSC team. Usually, PSD and data are organized into a matrix and sent as a digital payload, subsequently elaborated by the interface for getting graphs and measured parameters.
• Calibration Hardware: all the devices for calculation of the various Path Gains can be managed. Next chapters will treat more precisely this problem.
Furthermore, both background and foreground monitoring functions are available in SIECAMS®. As said below, the first type takes place when monitoring devices are idle; it consists in a periodical scanning of all carriers stored in the configuration, verifying EIRP, Centre Frequency and Occupied Bandwidth of each transmission. Instead, CSC operators can activate the foreground mode and they have three ways to do that:
• Line Up: it consists of continuously scanning the portion of transponder that hosts the carrier has to be lined up. SIECAMS® provides the PSD, the relevant EIRP and centre frequency of the carrier. Moreover it can provide also visualization of Cross-Pol component, automatically selecting the correct transponder. On the other hand an operator can manually select on which monitoring device of which site measures have to be done.
• Realtime Mode: basically it performs a continuous scanning of a frequency band, displaying the PSD as only result and allows adopting the most important monitoring device settings.
• Remote Control Mode: it’s very similar to the previous one, with only the exception that it allows operators also to send raw commands to monitoring devices, as they were in front of spectrum analyzers.
3.4 – The Calibration Issue
As explained before, one important function of SIECAMS® is the computation of EIRP of any carrier from the measured power, according to following equation:
s r path sa G G L P EIRP= ! ! + (3.1) where: sa
P is the carrier power (dBW) at SA input; generally the system takes into account (subtracts) the measured noise power;
r
G is the receive antenna gain to injection point (dB) and is stored as gain versus frequency tables;
s
L is the Free Space Loss (dB) calculated taking into account the slant range stored into the database.
But the relevant quantity of the equation above is the Gpath (Path Gain), that is how much dB have to be subtracted to the measurement of the spectrum analyzer to get the correct EIRP at satellite.
(Image 3.13 – A generic path in the Monitoring System)
Signal received by the antenna has to pass through both amplifying and attenuating stages; so, each contribute has to be considered to get the correct result for users. The problem is that the a priori measurement is possible, but not so accurate, because lot of factors intervene: couplers and cables attenuation, frequency depending of amplifiers, reliability of switches respect to nominal values; it follows that nominal calculation of path gain is possible, but not useful for a system that requires as much precision as possible because of the reasons previously explained.
This fact led the system developers to provide a way to accurately calculate how many dBs have to be taken into account on each monitoring path and on each work frequency of the interested hardware. SIECAMS® can perform this Calibration automatically through a simple imbedded system. Here is a brief description.
(Image 3.14 – The Calibration Subsystem)
Into each calibrated antenna, inside a thermostatic box, we can find two couplers, two switches, a fixed frequency signal generator and a Power Head. Let’s see the functioning of the system.
As explained above, the path gain is frequency sensitive, that is for the same path different values have to be considered. It’s for this reason that in the RF Room a signal generator is present: it can generate a clean carrier (a sinusoidal signal) of different frequencies (all that the antenna can work at), at a fixed power level (generally -30 dBm). This signal is injected directly at the input of the LNA and here is measured by a Power Meter through the Power Head; for reasons of alignment,
synchronization with the reference signal generator present into the antenna. The same signal is also measured by the SA needs to be calibrated; at this point the interface compare the values of the signal and, observing the difference, calculates which is the Path Gain at that frequency. The same procedure is then repeated for different frequencies. Clearly, not all the spectrum can be calibrated, but the system calculates gains for a certain number of points and after storing them into a table, makes a linear interpolation. Depending of the accuracy the users need, various calibration techniques are configured. Concerning the number of measures have to be made for each path the following calibration types are present:
• Initial Calibration: is performed when the new path is installed. Usually as much frequency values as possible are considered; it’s very important, because the system will base itself on these measures to upgrade periodically the tables;
• Path Calibration: is very similar to the previous one, but generally less points are calculated; it’s usually performed weekly or when a small change in the system architecture takes place; be aware that it takes few minutes to be calculated, so it can be made too often, otherwise the interested monitoring device can’t be used for ordinary work;
• Delta Calibration: is projected to avoid the problem above: it’s less precise but so more quick because it calculates values on a little number of point; it’s usually done every day.
As the calibration signals can be interpreted as real ones, various techniques on which frequency values choose are scheduled.
• Linear Path Verification: is the simplest but the most efficient way to compile calibration tables: it consists to divide the entire spectrum in equal portions considering as much points as possible; the problem is that it could be possible that measures on a busy transponder could be altered;
• Outside Transponders: after analyzing the real traffic on the satellite, SIECAMS® can select those frequencies are at the limits of carriers lined up, in order not to disturb useful measures.
A big problem as far as calibration is that not all the antennas can be equipped with necessary hardware, so a monitoring system can work without it; this situation can led not to have reliable measures over carrier, so other techniques have to take place in order not to give wrong informations. This issue will be treated in the 5th chapter, where two possible solutions are shown.
