Satellite Interference and Carrier ID
(Radio Division)
1 Introduction
Satellite operators all across the globe have been suffering heavily in terms of revenue losses
because of Radio Frequency Interference (RFI). Radio Frequency Interference (RFI) highly
impacts the Quality of Service for satellite operators and their customers. With satellite
transmissions it is difficult to identify the source of this interference. This in particular
applies to occasional-use satellite transmissions and temporary feeder links, rather than to full
time DTH (Direct To Home) services, where the owners and locations of the uplinks are well
known and identified.
Realizing the acuteness and criticality of this problem, telecommunication standardization
bodies like ITU, World Broadcasting Union, ETSI to name a few as well as the consortium of
satellite operators like DVB etc. decided to come up with effective standards addressing
satellite interference globally. Keeping in mind that the number of fixed-satellite service
(FSS) earth stations used for occasional use (OU) carrier transmissions in the 4/6 GHz and
11-12/13/14 GHz FSS bands is increasing rapidly; that the OU transmissions are often
characterized by frequent changes in earth station antenna pointing, frequency, power level,
polarization sense, carrier bandwidth and modulation technique and also that the proliferation
of the use of OU transmitting earth stations, and their frequent changes in link parameters,
has caused an increase in unintentional interference to other satellite users, the various
standardization bodies came up with the Carrier ID solution to be leveraged effectively to
combat RFI problem.
In this study paper, the satellite interference scenarios are discussed briefly and how the
recommended Carrier ID solution can be employed to effectively curb it.
2 Satellite Interference and its Types
The statistics in the Figure 1 below depict the major types or reasons for satellite interference
or RFI.
Figure Satellite Interference statistics provided by INTELSAT Report 2013.
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Some of the major interference types are discussed below:
2.1 Adjacent Satellite Interference
This is generally caused due to installation errors by operator, or poor inter-system
coordination. Transmitting antenna from the uplink site is poorly pointed and hence directs its
signals to the unintended satellite. This is becoming more prevalent as two degree spacing
between satellites in the geostationary arc becomes more common.
2.2 Cross polar Interference
This arises in cases where two different terminals are uplinking signals in the opposite sense
of the same kind of polarization, for example vertical polarization (VP) adjacent to horizontal
polarization (HP), or right-hand circular (RHC) adjacent to left-hand circular (LHC)
polarization. The extent of cross polar interference then depends on the ground station
antenna cross polar gain and the cross polar discrimination margin implemented in the
system. Co-ordination of network parameters specifications between the ground stations of
the different satellite networks also plays a major role in defining the extent of this type of
interference.
2.3 Interference due to equipment faults
This includes interference internal to the satellite network (equipment and cabling faults, poor
quality transmission equipment, human error settings of polarisation and frequency etc.). No
regulations as such are in place to handle these problems and are internally handled by the
satellite operators at their ends by installing high quality equipments and carrying out proper
training of their personnel and capacity development.
2.4 Interference due to Unauthorized carriers and Deliberate Jamming
Interference due to unauthorized carriers results from carriers (with content) being
transmitted towards a satellite without any prior contract/authorisation put in place with the
satellite operator (e.g. piracy). Intentional or deliberate jamming of satellite signals is
generally achieved by carriers (often unmodulated) transmitted towards a satellite with the
intent to prevent the current signals to be transmitted. This is often geopolitically motivated
and though easy to locate yet difficult to mitigate as it requires political clearances etc.
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Satellite Interference mitigating techniques: Carrier ID
ITU is currently working on the specification for Carrier Identifier (Carrier ID) which
contains information related to the source such as operator‟s name, phone number etc., to
identify a source of a carrier to be transmitted with the uplink signals to mitigate satellite
interference. This technique has been suggested by the satellite Interference Reduction Group
(sIRG). The satellite Interference Reduction Group (sIRG) members include satellite
operators, service providers, broadcasters, and equipment manufacturers. Three working
groups were formed within the sIRG to address different segments of the satellite industry.
The Broadcast, VSAT, and Data groups are pursuing approaches to mitigate interference that
are unique to their segments of the market.
Though there are several ways by which Carrier ID can be transmitted along with the original
carrier, considering minimal adverse effects, following two methods are being considered
mainly by the ITU Working Group for the specification:
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3.1
Insert the Carrier-ID, i.e. a small string, into the network information table frame on
the original carrier
In this method, for instance, Carrier ID consisting of the manufacturer‟s name, the unique
unit serial number etc. as shown in Table 1 are inserted with comma separators into the
Network Information Table (NIT) frame of the original carrier by the transmitting service
provider to achieve traceability. The disadvantage of this method is that the decoder cannot
decode the information on NIT, if the original carrier is interfered with other carriers.
Table Carrier-ID in network information table
Carrier identifier format
Encoder manufacturer
Encoder serial number
Carrier identifier
Telephone number
Longitude
Latitude
User information
Total character count
2 character string numeric only
5 character string
12 character string
5 character string
17 character string numeric only
17 character string numeric only
8 character string
15 character string
80 character string
3.2
Overlay of the Carrier-ID data at a very low rate in a spread spectrum carrier, onto
the original carrier
In this method, for instance, Carrier-ID consisting of similar information shown on Table 1 is
embedded in the very low data rate carrier, and then sent as the spread spectrum carrier
without adding appreciable noise to the original carrier. The spread spectrum modulation
technique is used because of its robustness towards interference. Even when the host carrier
is suffering from heavy interference, the Carrier ID can be easily decoded from it. Figure 2
shows this method.
Figure Carrier ID overlay as a spread spectrum carrier onto the original carrier
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4 Carrier ID System Description
DVB came up with the specifications of Carrier ID system (DVB-CID system) which was
later adopted by ETSI in its technical specification document, namely TS 103 129. This
specification mainly deals with the technique in which overlay of the Carrier ID data in a
spread spectrum carrier onto the original carrier is done (as described in Section 3.2). Since
the Network Information Table technique or CID NIT is proposed to be phased out by
January 1, 2018 and new modulators are mainly to support DVB-CID system by January 1,
2015 as per WBU-ISOG (World Broadcasting Unions- International Satellite Operation
Group) Resolutions, so in this section focus is on the overview of the various aspects and
features of the DVB-CID technique as prescribed in the ETSI specification.
4.1 DVB CID Global Unique Identifier
The 64-bit DVB CID Global Unique Identifier is based on the IEEE-defined 64-bit extended
unique identifier and is sent in two parts of 32 bits. It can be derived from a 48 bit MAC
address or a 48 bit Space Data Association modulator identifier.
4.2 Content ID table
The Content ID table (see Table 2) lists the possible content of the Information field carried
by CID. The CID format revision code (Content ID 0) shall be transmitted; other information
is optional, and the Content ID value indicates the corresponding Information field content. If
the telephone is sent, all 3 Telephone content ID fields shall be sent. If the User Data is sent,
all 7 User Data fields shall be sent.
Table Content ID table
Content ID
Value
Information
field content
Information field content
0
Carrier ID Format (23:0) CID Format is a revision code anticipating possible changes in the
number and possible content of the Fields. This shall be set to 0x000001. All other values are
reserved.
1
Latitude(23:4) and (0) Latitude(3:1) are unused and set to '000' Interpreted based on NMEA
0183 [i.2]protocol of degrees and decimal minutes. The field is interpreted as 6 numerical
digits in binary form, plus a single bit assigned as "0" = N and "1" = South latitude.
Longitude(23:3) and (0) Longitude(2:1) is unused and set to '00' Interpreted based on NMEA
0183 [i.2]protocol of degrees and decimal minutes. The field is interpreted as 7 numerical
digits in binary form, plus a single bit assigned as "0" = E and "1" = W longitude. or 23°34'27"
E would be coded in 24 bits as 000111000111111100101000. Resolution is equivalent to 20
meters.
2
3
4
Telephone 1 of 3: (23:0): field is 72 bits made up of 18 x 4 bit BCD coded characters. This
field is user entered. Telephone 1 (23) is the MSB of the BCD code of the first digit of the
telephone number while Telephone 3 (0) is the LSB of the BCD code of the last digit of an 18
digit telephone number. The telephone number is in international format according to
Recommenation ITU-T E.123 [2] with three modifications: '+', "ext." and padding. The '+'
sign is not transmitted. In case of an extension, "ext." will be transmitted as binary code
"1101". Telephone numbers that do not completely fill the 72 bits are appended with the
appropriate number of bits to fulfil the 72 bit filed with the invalid BCD code '1111'
(padding).
Telephone 2 of 3: (23:0).
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Telephone 3 of 3: (23:0).
4
6
User Data 1 of 7 (23:0) This field is 168 bits made up of 24 x 7 bit ASCII characters. It allows
the operator to enter a user message. This field is user entered. User Data 1 (23) is the MSB of
the ASCII code of the 1st character. User Data 7 (0) is the LSB of the ASCII code of the last
(24th) character. Used Data that does not completely fill the 168 bits are appended with the
appropriate number of bits to fulfil the 168 bit filed with binary '0's (padding).
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User Data 2 of 7 (23:0).
8
User Data 3 of 7 (23:0).
9
User Data 4 of 7 (23:0).
10
User Data 5 of 7 (23:0).
11
User Data 6 of 7 (23:0).
12
13-31
User Data 7 of 7 (23:0).
Undefined.
4.3 Carrier ID system block diagram
The Carrier ID Transmitter Block diagram is shown in Figure 3. It shall be possible to disable
the CID in equipment by hardware or software.
Figure Carrier ID Transmitter block diagram
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The Carrier ID system uses Binary Phase Shift Keying (BPSK) spread spectrum modulation,
differential encoding, scrambling and a concatenated error protection strategy based on
repetition, cyclic redundancy check (CRC) and Bose-Chaudhuri-Hocquenghem (BCH) codes.
The CID carrier is assigned a Power Spectrum Density level well beneath the Data Carrier
level, thus allowing for a negligible degradation of the Data Carrier performance (typically
below 0.1 dB). At the same time, the adoption of Spread Spectrum technique, together with
the Differentially Encoded BPSK modulation and a BCH FEC (Forward Error Correction)
protection, allows for a very robust Carrier ID system. It should in fact be possible, in most
practical cases, to identify the interferer without switching-off the wanted signal.
4.4 Carrier ID frame format
The syntax and semantics of the CID Frame which is transmitted over the original carrier are
defined in Table 3. This CID Frame will contain the DVB CID Global Unique Identifier and
2 content ID's.
Table Carrier ID frame format
Syntax
CID_Frame () {
unique_word
id_high
content_id_1
content_id_information_1
crc_1
fec_1
id_low
content_id_2
content_id_information_2
crc_2
fec_2
}
No. of bits
22
32
5
24
8
42
32
5
24
8
42
Remarks
First half of the Global Unique Identifier.
1st Content ID
st
1 Content ID data
Second half of the Global Unique Identifier
2nd Content ID
nd
2 Content ID data
Content ID 0 is a mandatory field and must be sent in the Carrier ID frame. The following
example describes how the Carrier ID frame is transmitted in a general scenario. Referring to
the Content ID table (Table 2), if a user only entered their telephone number into the
modulator and did not enter any other information, the sequence becomes 0-3-4-5. The
frames sent would be as follows:
�Frame N => Content ID "0" and Content ID "3"
�Frame N+1 => Content ID "4" and Content ID "5"
�Frame N+2 => Content ID "0" and Content ID "3" (restart from the beginning)
�Frame N+3 => Content ID "4" and Content ID "5"
�Frame N+4 => Content ID "0" and Content ID "3" (restart from the beginning)
5 Carrier-ID identifying configuration and procedures
ITU is currently working on the Carrier-ID identifying configuration and as per the inputs
from various stake-holders the following description of identifying configuration and
procedures is under consideration.
Since several manufacturers are developing the devices which employ the
Carrier-ID function, providers will be required to replace or attach another device to deal
with it. As the methods of inserting or overlaying the Carrier-ID are applied for modulated
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carriers, the Carrier-ID needs to be set before sending modulated carriers in accordance with
the following procedures.
–
Open the tool provided by the manufacturer to input the information.
–
Input operator name of an antenna, latitude and longitude of an antenna, operator‟s
contact telephone number and other necessary information.
The receiving devices must have a special function implemented in them, of receiving and
identifying or decoding the Carrier-ID. However, the function of receiving the ID need not to
be installed in all receivers, but a dedicated receiver can be used by the satellite operator, to
employ the function, because the desired and the interfering signals can be received at any
receiving site. Hence, the operator, at his dedicated receiver, can receive the undesired signals
causing interference to any of his service sites and effectively pursue and solve the
interference problems. Figure 4 below shows an example Carrier ID identifying network
configuration
Dedicated
Receiver
Satellite (transponder)
Detector
Receiver
Transmitter
Demodulator
Demodulator
External
Embed
Modulator
Modulator
Intenal Embed
Figure Carrier ID identifying configuration
Once the identity of the interfering carrier is received, geo-location technique can be used to
locate the interfering ground station. This technique is being adopted by most of the satellite
operators, but there is no standard or guideline in place for the same. The following Figure 5
illustrates the concept of this technique.
Figure Geolocation technique to locate interfering terrestrial station
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In this technique, the unknown transmitter antenna is aimed at the interfered satellite,
transmitting most of its energy through the main lobe and a smaller part of its energy through
the side lobes, which reaches adjacent satellites at a very low level. When the original signal
is transmitted to two satellites that are located in different orbital positions (the interfered
satellite and the adjacent satellite), the signal travels different distances to reach the two
adjacent terrestrial stations to simulate one single monitoring point indicated on the diagram
as “Receiving stations of both satellites,” which involves a time difference of arrival (DTO)
of the order of µs. Likewise, the signal experiences a frequency difference of arrival (DFO)
of the order of Hz. These parameters, DTO and DFO, are processed in the geolocation system
and are represented by two lines that, depending on the satellites used, intersect in an area
inside the interfered satellite‟s coverage, thus tracing an ellipse with central geographical
coordinates that indicate the zone where the terrestrial station that is transmitting the
unknown signal is located.
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Merits and Demerits of Carrier ID system
6.1 Merits
Carrier ID will enable the operators and users to:
• Quickly identify interfering carriers and respond to RFI, reducing the duration of each
RFI event.
• Improve Quality of Service and reduce operating costs.
• In the longer term, lower the number of RFI events and release bandwidth being used
to overcome current and ongoing RFI events
Figure 6 below depicts the difference in the flows of identifying the possible source of
interference with a carrier with/without Carrier-ID. If the interference carrier includes
Carrier-ID, the satellite operator can reduce the time to identify the possible source of
interference and ask the service provider to stop the carrier immediately. If without CarrierID, it takes a long time for a satellite operator to identify the possible source of interference.
As a result, the damage due to the interference would be increased.
Interference occurs
Check the receiving system
With measurement tools
Ask the satellite operator to
identify interference
With/Without
Carrier-ID
Without
With
Identify the possible source of
interference by Carrier-ID
Identify the possible source of
interference
A Satellite operator asks a
provider to stop the carrier
It takes a long time to identify
Interference disappears
Identify the source
No
Yes
A satellite operator asks a
provider to stop the carrier
Interference disappears
Time
Figure Interference Identifying flow
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6.2
Demerits
• Degrades the transmitted signal as it increases the noise floor.
• It cannot be embedded on Continuous Wave (CW) signals and hence interference
caused by them cannot be easily identified.
7 Conclusion
Carrier ID is a promising technology to combat satellite interference. This system should be
harmonized all over the world so that satellite equipment manufacturers could bring out new
equipments in the market incorporating this system. Also, it will be a relief to the satellite
operators who suffer much revenue loss due to satellite interference.
In India, TEC could formulate Generic Requirements for equipments implementing Carrier
ID system to promote their usage in Indian Telecommunication networks as well.
REFERENCES
ITU-R Working document on „A carrier identification system for digital-modulation transmissions for
fixed-satellite service (FSS) occasional use (OU) carrier earth station transmissions to geostationarysatellite orbit space stations in the 4/6 GHz and 11-12/13/14 GHz FSS bands to eliminate harmful
interference‟
2. ETSI TS 103 129 V1.1.1 (2013-05) Digital Video Broadcasting (DVB); Framing structure, channel
coding and modulation of a carrier identification system (DVB-CID) for satellite transmission
3. DVB Fact Sheet - August 2013 DVB Carrier Identification DVB‟s Caller-ID solution to stop satellite
interference
4. http://www.oas.org/en/citel/infocitel/2008/septiembre/metodo-interferencia_i.asp
5. http://broadcastengineering.com/satellite/world-broadcasting-union-adopts-carrier-id-combat-satelliteinterference
6. http://satirg.org
7. Technologies to identify and/or mitigate harmful interference, International Satellite communication
workshop: "The ITU - challenges in the 21st century: Preventing harmful interference to satellite
systems“ 10 June 2013, Dr. Rob Rideout, SAT Corporation.
8. Harmful interference to satellite systems ANFR views International satellite communication workshop
“The ITU - challenges in the 21st century: Preventing harmful interference to satellite systems”
Geneva, 10 June 2013
9. WBU-ISOG Resolution document regarding Carrier ID.
10. Comtech EF Data White paper on Meta-carrier technology.
1.
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