Controlling Satellite Communication System Unwanted Emissions
in Congested RF Spectrum
Donald Olsen
The Aerospace Corporation
P.O. Box 92957
Los Angeles, CA 90009-2957
Roger Heymann
National Environmental Satellite Service
NOAA-NESDIS
Building SSMC1, 5th Floor
1335 East-West Highway
Silver Spring, MD 20910
ABSTRACT
The International Telecommunication Union (ITU), a United Nations (UN) agency, is the agency that,
under an international treaty, sets radio spectrum usage regulations among member nations. Within the
United States of America (USA), the organization that sets regulations, coordinates an application for use,
and provides authorization for federal government/agency use of the radio frequency (RF) spectrum is the
National Telecommunications and Information Administration (NTIA). In this regard, the NTIA defines
which RF spectrum is available for federal government use in the USA, and how it is to be used. The
NTIA is a component of the United States (U.S.) Department of Commerce of the federal government.
The significance of ITU regulations is that ITU approval is required for U.S. federal government/agency
permission to use the RF spectrum outside of U.S. boundaries. All member nations have signed a treaty
to do so. U.S. federal regulations for federal use of the RF spectrum are found in the Manual of
Regulations and Procedures for Federal Radio Frequency Management, and extracts of the manual are
found in what is known as the Table of Frequency Allocations. Nonfederal government and private sector
use of the RF spectrum within the U.S. is regulated by the Federal Communications Commission (FCC).
There is a need to control “unwanted emissions” (defined to include out-of-band emissions, which are
those immediately adjacent to the necessary and allocated bandwidth, plus spurious emissions) to
preclude interference to all other authorized users. This paper discusses the causes, effects, and
mitigation of unwanted RF emissions to systems in adjacent spectra.
Digital modulations are widely used in today’s satellite communications. Commercial communications
sector standards are covered for the most part worldwide by Digital Video Broadcast - Satellite (DVB-S)
and digital satellite news gathering (DSNG) evolutions and the second generation of DVB-S (DVB-S2)
standard, developed by the European Telecommunications Standards Institute (ETSI). In the USA, the
Advanced Television Systems Committee (ATSC) has adopted Europe’s DVB-S and DVB-S2 standards
for satellite digital transmission. With today’s digital modulations, RF spectral side lobes can extend out
many times the modulating frequency on either side of the carrier at excessive power levels unless
filtered. Higher-order digital modulations include quadrature phase shift keying (QPSK), 8 PSK (8-ary
phase shift keying), 16 APSK (also called 12-4 APSK (amplitude phase shift keying)), and 16 QAM
(quadrature amplitude modulation); they are key for higher spectrum efficiency to enable higher data rate
transmissions in limited available bandwidths. Nonlinear high-power amplifiers (HPAs) can regenerate
frequency spectral side lobes on input-filtered digital modulations. The paper discusses technologies and
techniques for controlling these spectral side lobes, such as the use of square root raised cosine (SRRC)
filtering before or during the modulation process, HPA output power back-off (OPBO), and RF filters after
the HPA. Spectral mask specifications are a common method of the NTIA and ITU to define spectral
occupancy power limits. They are intended to reduce interference among RF spectrum users by limiting
excessive radiation at frequencies beyond the regulatory allocated bandwidth.
The focus here is on the communication systems of U.S. government satellites used for space
research, space operations, Earth exploration satellite services (EESS), meteorological satellite services
(METSATS), and other government services. The 8025 to 8400 megahertz (MHz) X band can be used to
illustrate the “unwanted emissions” issue. 8025 to 8400 MHz abuts the 8400 to 8450 MHz band allocated
by the NTIA and ITU to space research for space-to-Earth transmissions such as receiving very weak
Deep Space Network signals.
The views and ideas expressed in this paper are those of the authors and do not necessarily reflect
those of The Aerospace Corporation or The National Oceanic and Atmospheric Administration (NOAA)
and its National Environmental Satellite Service (NESDIS).
KEY WORDS: Unwanted emissions, RF spectrum, satellite communications, modulations,
communications technology, transmitter linearization
INTRODUCTION AND BACKGROUND
There is a need for satellite communication systems using the RF spectrum to control “unwanted
emissions,” which are defined to include out-of-band emissions (immediately adjacent band), plus
spurious emissions to preclude interference to other authorized spectrum users. The ITU, through
international treaty, sets standards for member nations and provides authorization for RF spectrum use
beyond a nation’s boundaries. Member nations determine their own sub-allocations within the ITU
regulations for their own domestic use. In the USA the NTIA regulates, coordinates, and provides
authorization for agencies of the federal government to use the RF spectrum as required by federal law.
Similarly, the Federal Communications Commission (FCC) regulates the nonfederal use of the radio
spectrum. These organizations publish documents defining the permitted levels of both in-band and outof-band transmitter power. The FCC and the NTIA work together in their respective domains to promote
a coordinated use of the various bands within the structure of the ITU limits. The Space Frequency
Coordination Group (SFCG), with input from the Consultative Committee for Space Data Systems
(CCSDS), plays a significant role in advising the ITU, including proposing spectrum mask definitions to
the ITU.
Traditionally there has not been a great emphasis by U.S. federal government agencies to use the RF
spectrum as efficiently as they might. However, due to the increasing demand for spectrum over the last
few years, the spectrum use regulators have greatly increased their emphasis on efficiency. In 2003, the
Department of Commerce was directed by the White House to prepare recommendations to improve
spectrum management. This became part of a presidential directive on using spectrum more efficiently,
titled “Improving Spectrum Management for the 21st Century.”
From that paper, President George W. Bush signed a “Presidential Determination: Memorandum for
the Heads of Executive Departments and Agencies.” He opens that memo, dated June 5, 2003, by
stating:
The existing legal and policy framework for spectrum management has not kept pace with the
dramatic changes in technology and spectrum use. Under the existing framework, the Federal
Government generally reviews every change in spectrum use. This process is often slow and
inflexible and can discourage the introduction of new technologies. Some spectrum users, including
Government agencies, have argued that the existing spectrum process is insufficiently responsive
to the need to protect current critical uses. 1
Later the President wrote,
1
Presidential Memo on Spectrum Policy, Office of the Press Secretary, June 5, 2003.
2
In May 2003, I established the Spectrum Policy Initiative to promote the development and
implementation of a U.S. spectrum management policy for the 21st century. This initiative will
foster economic growth; promote our national and homeland security; maintain U.S. global
leadership in communications technology; and satisfy other vital U.S. needs in areas such as
public safety, scientific research, Federal transportation infrastructure, and law enforcement. 2
Then in the same memo he directed:
the Secretary of Commerce to prepare recommendations for improving spectrum management.
The Secretary of Commerce then established a Federal Government Spectrum Task Force and
initiated a series of public meetings to address improvements in policies affecting spectrum use
by the Federal Government, State, and local governments, and the private sector. The
recommendations resulting from these activities were included in a two-part series of reports
released by the Secretary of Commerce in June 2004, under the title Spectrum Policy for the 21st
Century - The Presidents Spectrum Policy Initiative (Reports).
Within 1 year of the date of this memorandum, the heads of agencies selected by the Secretary
of Commerce shall provide agency-specific strategic spectrum plans (agency plans) to the
Secretary of Commerce that include: (1) spectrum requirements, including bandwidth and
frequency location for future technologies or services; (2) the planned uses of new technologies
or expanded services requiring spectrum over a period of time agreed to by the selected
agencies; and (3) suggested spectrum efficient approaches to meeting identified spectrum
requirements.3
This was followed up by a memo from the Honorable Secretary of Commerce Carlos M. Gutierrez to
the Honorable Conrad C. Lautenbacher, Jr., the Under Secretary of Commerce for Oceans & Atmosphere
within NOAA, where in part he stated that:
As directed by the Executive Memorandum, your agency’s plan must be submitted no later
than November 30, 2005, and shall include:
(1) spectrum requirements, including bandwidth and frequency location for future technologies or
services;
(2) the planned uses of new technologies or expanded services requiring spectrum over a period
of time agreed to by the selected agencies; and
(3) suggested spectrum efficient approaches to meet identified spectrum requirements.4
With funding by NOAA-NESDIS, The Aerospace Corporation has investigated technologies related to
spectrum conservation and bandwidth efficiency through analysis and development of a Geostationary
Operational Environmental Satellite (GOES-R) radio communications test bed. This test bed was
specifically tailored for the processed data uplink (PDU)/global rebroadcast (GRB) data and included an
uplink signal processor, a satellite L-band downlink traveling wave tube amplifier (TWTA), downlink
channel, and a downlink signal processor. The processing currently includes error correction encoding
and modulation for the uplink and demodulation and decoding for the downlink. It presently does not
include an uplink X-band transmitter, channel, or receiver and is connected directly to the L-band TWTA
2
USA Federal Government Presidential Determination: Memorandum for the Heads of Executive
Departments and Agencies, 30 November 2004.
3
Ibid.
4
Letter on Spectral Efficiency from Secretary of Commerce, Carlos M. Gutierrez, to Under Secretary of
Commerce, Conrad C. Lautenbacher, Jr., 10 March 2005.
3
input. The signal processors are very flexible and implemented in field-programmable gate array (FPGA)
technology. The encoding and decoding are done with an AHA company turbo product encoder/decoder
chip. The nomenclature for this chip is AHA4540A. We have built modulators and demodulators,
including phase and symbol tracking for binary phase shift keying (BPSK), QPSK, and 16 APSK.
This paper discusses technologies and techniques with which future systems such as the emerging
new-generation NOAA GOES-R satellite series in response to the above directive might more efficiently
use the limited spectrum than did prior GOES systems and also deal with an essential related issue of
controlling unwanted emissions. The technologies offer to significantly mitigate the increase in bandwidth
necessary to accommodate the greatly increased data rate required for this and future systems. These
include data compression, higher-order modulation formats, modern, more powerful, higher code rate
forward error correction coding, and improved HPA linearization for a greatly reduced OPBO. This paper
also discusses the causes, effects, and mitigation of unwanted RF emissions and increased radio
frequency interference (RFI) on systems using adjacent spectrum. These technologies reduce the
required frequency separation, called the frequency guard band, and thereby improve spectrum
utilization.
ANALYSIS AND DISCUSSION
In the big picture view, bandwidth efficiency is the ratio of the precompression cumulative GOES-R
sensor data rate to the required total RF bandwidth for transmission. Bandwidth efficiency is measured in
bits per second per hertz of channel bandwidth. Today’s digitally modulated signal emissions can extend
out to many times the necessary bandwidth on either side of the carrier and thus require a guard band
between spectrum users (this can be seen later in the paper, in Figure 3, where “roll-off rate” is
discussed). Since the power spectral density doesn’t fall off to zero immediately outside the main
modulation spectral lobe and because there are usually many spectral side lobes, bandwidth efficiency
must take into account the guard band required between the wanted signal’s spectral lobes and any
adjacent signals. This guard band is necessary to reduce the mutual RFI.
Efficient use of RF spectrum, given a certain data compression factor, requires effective use of three
features. The first is minimizing the necessary bandwidth, a frequency management term, the corner
point on the spectral mask where the downward slope starts. The second is minimizing the guard band
needed between adjacent spectrum users, and the third is limiting maximum power level of unwanted
emissions (out-of-band plus spurious emissions). The latter is done by working to meet the
recommended frequency masks on power limits issued by the NTIA and ITU and likely should include as
well, in our view, negotiations with adjacent band users.
Minimizing necessary bandwidth must be done consistently within the system trade space dictated by
allowable transmitter power and receiver sensitivity degradation from signal distortion within the limits of
link geometry, data rate, and link availability in the propagation environments. Avoiding degradation of
adjacent signal reception or limiting spectrum usage may require a steeper slope than that available with
any existing regulatory mask. The width of the guard band is set by the proximity of other adjacent
spectrum users or by the slope of the envelope of the required spectrum mask and by achievable filter
technology. The smaller value governs the spectral width.
Figure 1 shows the applicable SFCG spectral masks.5 The steeper curve is for signals with symbol
rates exceeding 2 megasymbols per second. It has a slope of about 80 dB (decibels) per decade. The
shallower curve is for lower data rates and requires a slope of only about 43 dB per decade. They
provide 16-to-1 and 6-to-1 bandwidth ratios, respectively, at the 60 dB down points. The NTIA has also
defined spectral masks for many applications. In particular the mask to which space applications signals
5
Space Frequency Coordination Group (SFCG), Figure 1 of Recommendation 22-2R2, p. 3.
4
must adhere is shown in Figure 2.6 Here dBsd stands for dB of spectral density relative to the peak
value. The necessary bandwidth is set such that the upper corners of the two-sided width of the main
frequency spectral lobe of the signal are 8 dB down from the spectrum peak on the mask rather than
having the corner point be at 0 dB, as in the SFCG mask. Furthermore the NTIA mask includes a slope
of precisely 40 dB/decade of frequency offset. The reference frequency for this ratio is with respect to the
single-sided, necessary half-bandwidth. Both masks continue outward and downward until the curves
reach the –60 dB point with respect to the peak spectrum value. After that they remain flat at a –60 dB
floor. The guard band for this NTIA mask is a factor of 19 times the half-necessary bandwidth for the
lower mask corner, a significant factor in terms of 95% loss of spectrum efficiency. This slope is much
less stringent than the 16-to-1 and 6-to-1 ratio values for the SFCG mask. Therefore the steeper curve of
the SFCG mask provides much better bandwidth efficiency than the NTIA mask provides.
Figure 1. Spectral Emission Masks
Spectrum Attenuation (dB)
0
-10
Rates > 2Mbps
-20
Rates < 2 Mbps
-30
-40
-50
-60
-70
0
1
2
3
4
5
6
7
8
9
Frequency-off-Carrier to Symbol Rate Ratio (F/Rs)
Fourier analysis shows that the customary unfiltered square modulation pulses have a
[sin(πf/Rs)/(πf/Rs)]2 normalized power spectral density normalized to 1 bit per second, as shown in Figure
3. f is the frequency offset from the signal carrier frequency and Rs is the modulation symbol rate.
Note that the roll-off rate is only 20 dB per decade and is much slower than required by the NTIA
mask, let alone the SFCG mask. Therefore, the sidebands require a relatively large guard band. When
the 60 dB down guard band is included, the bandwidth efficiency becomes 0.00133 bits per second per
Hz. One can improve the spectrum of the nominally square-shaped digital modulation time domain pulse
by rounding its corners or by post-final HPA RF filtering or by both. These reduce the high-frequency
components of the spectrum. A commonly used modulation pulse shaping results in an SRRC spectrum.
This spectrum theoretically has no energy beyond +/-Rs(1+β)/2, where Rs is the symbol rate and β is the
bandwidth expansion parameter of the SRRC signal. Figure 4 shows the normalized spectral density of
SRRC M-ary PSK signals for a typical β value of 0.35. The upper curve is the spectrum of the SRRC
only. It assumes that the data input to the SRRC filter is a series of positive or negative delta functions
(infinite impulses). The lower curve is the output spectrum when one uses square pulses as the data
input of the SRRC pulse filter. This cascade results in a spectrum that is the multiplication of the
spectrum of the square pulses with the SRRC spectrum of the pulse shaping filter. A spectral floor of –60
dB is assumed.
6
National Telecommunications and Information Administration (NTIA), Manual of Regulations and
Procedures for Federal Radio Frequency Management, rev. September 2006, Figure 5.6.1, pp. 5-44.
5
dBsd
dB relative to the maximum value of
power spectral density (psd) within the
necessary bandwidth
Figure 2. Space Services Permitted Unwanted Emission
0
-10
-20
-30
-40
-50
-60
-70
10
100
1000
10000
Frequency offset as a Percent of the Necessary Bandwidth
Figure 3. Theoretical Spectral Density of Phase Shift Keyed Modulation
with Square Pulses
Normalized Spectral Density (dB/Hz)
0
-10
-20
-30
-40
-50
-60
-70
0.1
1
10
100
1000
Normalized Frequency Offset from Carrier
Since the modulation is applied with amplitude shaping to the quadrature inputs of the M-ary PSK
modulator, the pulse shaping for spectral sideband reduction will cause the amplitude of the signal to
fluctuate proportionally with the modulation pulse during each symbol. This would not be a problem if the
upconverters that set the output frequency of the signal and the HPA that sets the output power of the
transmitter were perfectly linear. Linear means that the HPA output signal level is directly proportional to
6
the input level from the modulator over the desired amplitude range of the signal. However, a nonlinear
HPA’s saturation partially flattens the modulation amplitude peaks and partially regenerates the frequency
spectral side lobes. This process is called spectral regrowth.
When the spectral regrowth exceeds the required mask parameters or the limits reached by
negotiations with adjacent band users, the nonlinearity and its spectral regrowth can be partially mitigated
by several techniques. These include:
1. Using a pre-HPA linearizer that predistorts the signal to compensate as much as possible for the
saturation curve that typically exists in power amplifers.
2. Reducing the output power at the operating point of the HPA relative to the saturated power
output so that the linearity is improved at the cost of more output power back-off (OPBO).
3. Adding post-final HPA bandpass filtering, but this is at the cost of some loss in signal power due
to the filter insertion loss.
Figure 4. Spectral Density of SRRC and SRRC*Sinc Pulse
Shaping
Spectral Density (dB/Hz)
0
-10
SRRC
Sinc*SRRC
-20
-30
-40
-50
-60
-70
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
Frequency/Symbol Rate
The regrowth of sideband spectrum has been examined using the NOAA-NESDIS GOES-R satellite
series communications test bed to evaluate practical waveform performance in real hardware. We
included an L-band, space-qualified design TWTA (purchased from Boeing) in the test bed to examine
sideband regrowth. We implemented the modulator and demodulator in FPGA technology, including
SRRC spectral filtering, and did some end-to-end bit error rate (BER) and spectral regrowth testing with
and without linearization and variable amounts of OPBO. We examined these effects using a 16 APSK
waveform. Figures 5 and 6 document the measured spectrum for these tests. Figure 5 shows the TWTA
output spectrum with OPBO as a parameter. OPBO is referenced to the saturated power of the TWTA of
150 watts. The vertical axis should be treated as a relative power and not the absolute RF dBm power.
No linearization was used in this case. Then the TWTA was mated with a commercial analog L-band
linearizer at the input port and tuned for optimum sideband reduction. Figure 6 compares the data for the
nonlinearized TWTA with that for a linearized TWTA. It shows that the main and first sideband spectrum
levels for the linearized case with 4 dB OPBO matched that for the nonlinearized 7 dB OPBO case. The
conclusion was that linearization in this case reduced the OPBO by 3 dB for the higher sideband levels.
However, for the linearized case, the lower sideband levels are worse than those for the nonlinearized
7
case. Also the higher floor level is due to the high noise figure of the analog linearizer and is not caused
by spectrum regrowth. This can be mitigated by use of a low-noise figure analog linearizer or better yet,
by a purely digital linearizer. The peak spectrum levels have been set to the same level for easier
comparison of sidebands.
Figure 5. Attenuated L-Band TWTA Output Power Spectral Density
Versus Output Power Back-off
2-dB OPBO
-15
3-dB OPBO
-25
4-dB OPBO
5-dB OPBO
-35
Amplitude, dB
6-dB OPBO
-45
7-dB OPBO
8-dB OPBO
-55
9-dB OPBO
10-dB OPBO
-65
-75
-85
-95
1660
1670
1680
1690
1700
1710
1720
Frequency, MHz
Shannon’s limit dictates the maximum bandwidth efficiency at which one can transmit at a certain
signal-to-noise power level with error-free communications. The continuous curve in Figure 7 shows this
upper bound on the bandwidth efficiency in bits/second (bps) per Hz (capacity) versus power efficiency in
energy per bit to noise density ratio (Eb/No). It also shows the efficiency for a selection of modulation and
coding schemes for BER = 10–6.7 With modern modulation and coding techniques, one can communicate
with a signal-to-noise level that is only about 1 dB greater than Shannon’s limit for a prescribed bandwidth
efficiency. TC/16QAM (turbo code) in the graph (shown by the solid squares connected with a dotted line)
approaches that value. Shannon’s limit also dictates that increasing the modulation alphabet increases
the required signal-to-noise ratio. However, there is a large gap (on the order of 2 to 3 dB with coding)
between the Shannon limit and the measured performance for most signals using readily available
modulations and modest codes.
Adding error correction coding despite its small increase in bandwidth with high rate codes can
mitigate that gap considerably in many cases. The expansion of the bandwidth can be minimized by the
use of a high rate code. The code rate is defined as the ratio of the user data bit rate to the encoded bit
rate. The newer more powerful turbo and low-density parity check (LDPC) codes in many cases can
provide near–Shannon limit performance (within 1 dB) for code rates greater than 0.5 and up to 0.98. A
minimum value suggested for GOES-R is a 0.876 code rate, which has been used in our GOES-R
laboratory test bed. Commercially available hardware of code rate 0.876 and higher and consistent with
the DVB-S series of standards has been available for years (refer to various commercial communications
7
Wang, Charles C., The Aerospace Corporation, personal correspondence.
8
satellite electronics equipment suppliers such as Comtech and Broadcom). Attainable bandwidth
efficiencies are below the theoretical Shannon limit. Areas above the Shannon limit are not achievable.
Processing delay and decoder chip complexity increase as one tries to communicate more closely to the
theoretical limit.
Figure 6. TWTA-LTWTA Comparison - Normalized OPBO
-15
-20
-25
TWTA 7-dB OPBO,
norm.
-30
LTWTA 4-dB OPBO
-35
-40
Amplitude, dB
-45
-50
-55
-60
-65
-70
-75
-80
-85
-90
-95
1660
1670
1680
1690
1700
1710
1720
Frequency, MHz
Figure 7. Bandwidth Efficiency Versus Power Efficiency for BER = 10-6
10
6
Data Rate/BW (bps/Hz)
More Bandwidth Efficiency
8
Shannon
Theoretical
Limit
Uncoded
16QAM
4
14.5 dB
13.9 dB
3
Uncoded
QPSK
Uncoded
8PSK
3 4
2
1
2
10.5 dB
4
A
B 3
2
1
1
0
1
2
3
4
5
6
7
8 9 10 11 12 13 14 15
Eb/N0 (dB)
More Power Efficiency
9
TC: Turbo Code
CON_C: Concat. Code
TC/QPSK
CON_C/QPSK
TC/8PSK
CON_C/8PSK
TC/16QAM
CON_C/16QAM
Within each group of 4:
1 - (the leftmost one),
TC(R4/5;16K) or
CC2/3-RS(255,223)
2 - (the 2nd from left),
TC(R8/9,16K) or
CC3/4-RS(255,223)
3 - (the 2nd from right),
TC(R11/12;16K) or
PC8/9-RS(255,223)
4 - (the rightmost one),
TC(R15/16,16K) or
PC8/9-RS(255,243)
NOAA requirements in increased sensor data rate from the current 2.66 megabits per second (Mbps)
of the GOES-L and M series to roughly 150 Mbps as an upper bound for GOES-R through U series has
necessitated a migration of the sensor data downlink from the legacy L-band usage up to X band, within
the 8025 to 8400 MHz band. However, care must be exercised so that unwanted emissions from this
signal do not impact ground reception of the adjacent 8400 to 8450 MHz band allocated to space
research and particularly for deep space to Earth transmission. The GOES-R stage 2 NTIA filing with the
NTIA stipulates 180 MHz of bandwidth. If QPSK without pulse shaping and rate 2/3 error correction
coding were used, the necessary bandwidth would be 157 MHz. This would leave 23 MHz for the twosided guard band for the filter to roll off the spectrum of the signal, or 11.5 MHz per side. However, with
the bandwidth expansion factor, β = 0.35, for SRRC 16 APSK modulation and rate 0.876 coding, the
necessary bandwidth is reduced by 46% to about 85 MHz plus the guard bands. This modulation and
coding combination will allow a reduction of the complexity and signal loss associated with the HPA RF
output filtering for diplexing the receiving and the transmission bands, but it will increase the required
HPA output power after other adjustments by about 3 dB.
Spurious emissions are the other part of unwanted emissions. Out-of-band emissions are considered
for the most part to be caused by the modulation process. The spurious emissions are considered to
include intermodulation products, with such causes as nonlinear junctions, parasitics, and harmonics.
Spurious emissions are usually controlled by filtering.
COMMUNICATIONS TECHNOLOGY STATUS
The advanced state of the art and ready availability of the above technologies and techniques are
demonstrated in the DVB-S (1994), DVB-DSNG (1997), and the DVB-S2 evolution of Europe’s “Digital
Video Broadcast (DVB)” series of standards and in the equipment of the world’s suppliers to its
requirements. The DVB standard was developed for satellite television broadcast for high-definition TV
and other applications. Standards are developed as well by the DVB body for cable transmissions. The
1997 version (DVB-DSNG) added 8 PSK and 16 QAM modulations. The S2 version is designed to
squeeze high-definition video streams into existing 6 MHz channel bandwidths, including some guard
band. “The DVB standards are maintained by the DVB Project, an industry consortium with more than
270 members, and they are published by a Joint Technical Committee (JTC) of the European
Telecommunications Standards Institute (ETSI), European Committee for Electrotechnical
Standardization (CENELEC), and European Broadcasting Union (EBU).”8
This S2 standard includes modulation modes up to and including 32 APSK. This means that there
are 5 bits per symbol for the highest bandwidth-efficient mode. Other variants of APSK are 64 APSK, 128
APSK, and 256 APSK. LDPC coding is used with coding rates selected to complement the modulation
modes for uniform steps in required Eb/No and bandwidth efficiency.
The DVB-S standard has been widely accepted and used in Europe, Asia, and the USA, with
commercial equipment being designed and manufactured throughout the world. DVB-S2 provides a
range of bandwidth efficiencies up to 4.5 bit/s/Hz. Comtech and other companies are pioneering the
development of modems for ground applications that support DVB-S through DVB-S2 standard. See, for
example, data sheets of their models SLM-5650, SLM-7650, SLM-8650, CLM-9600L, CDM-Qx, CDM600, CDM-700, and CDM-8000, all of which are available online.
In addition the European Space Agency (ESA) is developing a slightly different family of waveforms
with the same family of modulation types as DVB-S2 but mates them with serial concatenated turbo
coding (SCTC). Some variations include a Reed-Solomon (RS) or Bose-Chadhuri-Hocquenghem (BCH)
outer code to reduce low BER Eb/No flaring.
8
Internet Wikipedia Encyclopedia for “DVB” May 25, 2007.
10
Further, the U.S. Department of Defense (DOD) issued a memorandum on February 10, 2006,
establishing a requirement that DVB-S2 be used in DOD-owned and -leased satellite communications
systems.9 In a paper presented at the 2006 annual Society for Photo-Optical Instrumentation Engineers
(SPIE) meeting in San Diego, CA, the authors Cragg and Brockman discussed the decision of NOAA’s
National Weather Service (NWS) to require the use of the DVB-S standard for any of its contracted
commercial satellite data broadcasts to its field offices.10
In a 2005 e-mail communication with Roger Heymann of NOAA-NESDIS, Daniel Enns of Comtech
reported (Daniel Enns is also an advisor on modulation and coding to the ATSC standards body in the
USA):
At CEFD (Comtech EF Data) we have been providing 8PSK, 16QAM satellite modem
solutions for over 10 years. We probably have well thousands [sic] satellite modems on the market
today operating in 8PSK and 16QAM links. We have provided these satellite modems both for the
commercial market as well as the Military/Government market. Our newer satellite modem i.e. [sic]
the CDM 700 and the SDM 5650. We also offer 64QAM as an option for very high data rate
throughput. We have also started to ship satellite modulators with the new DVB-S2 standard our
CDM 710 [sic]. Comtech EF Data is also the leader in the market of Forward error correction,
hence we (develop and market) modems that offer Viterbi, Viterbi+RS, Turbo Coding as well as
LDPC/BCH. NOAA would certainly be well served by adopting higher order modulation and
improved forward error correction (FEC) for the new satellite services.11
Several of the Department of Defense Air Force space programs are building or preparing to build
satellites that will support on-board modulation, coding, demodulation, and decoding of 8 PSK and 16
APSK modulations as well as SCTCs. These are being prepared for flight by around 2014. They are
currently building application-specific integrated circuits (ASIC) for these functions using technology that
lends itself to transfer to space-qualified integrated circuit production lines.
FUTURE WORK
The residual technology development remaining for the modulation and coding for space applications
such as the GOES-R series satellites is to complete the conversion of the above designs to spacequalified ASIC chips for the spaceborne transmitters and receivers through porting the ASIC design code
from the commercial chip fabrication lines into the space-qualified lines. The hardware components for
the ground-based applications already exist in commercial fabrication lines.
CONCLUSIONS ON CONTROL OF UNWANTED RF SPECTRUM EMISSIONS
Controlling unwanted RF spectrum emissions—meaning both out-of-band and spurious—is both a
national and international problem with growing RF spectrum use and congestion. For U.S. federal
bodies, the use of RF spectrum when crossing U.S. boundaries must meet both NTIA and ITU
requirements. The NTIA and ITU both specify RF spectrum masks as guidelines to limiting RF power
9
Memorandum for Secretaries of the Military Departments, “Department of Defense Policy for
Transmission of Internet Protocol DOD-Leased Lines and DOD-Owned Transponded Satellite Systems,”
John Grimes, Chief Information Officer, DOD, Feb. 10, 2006
10
Published paper, “Evolution of the NOAA National Weather Service Satellite Broadcast Network (SBN)
to Europe’s DVB-s Satellite Communications Technology Standard,” P. Cragg, NOAA NWS, et al.,
Published proceedings (manuscripts) of SPIE, “Satellite data Compression, Communications, and
Archiving,” R. Heymann, C. C. Wang, Schmit Chairs/Editors, 13–14 Aug. 2006.
11
E-mail from Daniel Enns, Head of the ATSC, digital TV standards body for the U.S., to Roger
Heymann, 8 February 2005.
11
emissions outside of a user’s assigned allocations. Further, in cases supplementing use of recommended
masks by conducting negotiations with adjacent-band RF spectrum users seems logical. Spectrum
efficiency plays a role in containing unwanted emissions. The use of advanced higher-order modulations
as discussed in the paper requires less bandwidth and will decrease the required guard bandwidth to
adjacent band users. However, if the strategy for requesting bandwidth is to base it on a lower bandwidth
efficiency signal and then improve that efficiency after the allocation is obtained, then the available guard
band would be increased and as such would reduce the out-of-band emissions on the adjacent users.
Such advanced modulations are readily available in the commercial sector through equipment built to
Europe’s DVB standards.
ACRONYM GLOSSARY
APSK
ASIC
ATSC
BPSK
BCH
BER
bps
CCSDS
CEFD
CENELEC
dB
dBsd
DOD
DSNG
DVB
DVB-S
DVB-S2
EBU
Eb/No
EESS
ESA
ETSI
FCC
FEC
FPGA
GOES
GOES-L and M
GOES-R
GRB
HPA
ITU
JTC
LDPC
LTWTA
Mbps
METSATS
MHz
NESDIS
NOAA
NTIA
NWS
amplitude phase shift keying
application-specific integrated circuit
Advanced Television Systems Committee
binary phase shift keying
Bose-Chadhuri-Hocquenghem
bit error rate
bits per second
Consultative Committee for Space Data Systems
Comtech EF Data
European Committee for Electrotechnical Standardization
decibel, defined as 10Log10 (power ratio)
dB of spectral density relative to the peak spectral density
Department of Defense
digital satellite news gathering
Digital Video Broadcast
DVB satellite
DVB-S second generation
European Broadcasting Union
energy per bit to noise density ratio
Earth exploration satellite services
European Space Agency
European Telecommunications Standards Institute
Federal Communications Commission
forward error correction
field-programmable gate array
Geostationary Operational Environmental Satellite
L and M satellites of GOES series
R satellite of GOES series
global rebroadcast
high-power amplifier
International Telecommunication Union
Joint Technical Committee
low-density parity check
linearized TWTA
megabits per second
Meteorological Satellite Services
megahertz
National Environmental Satellite Service
National Oceanic and Atmospheric Administration
National Telecommunications and Information Administration
National Weather Service
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OPBO
PDU
PSK
QAM
QPSK
RF
RFI
RS
SCTC
SFCG
SRRC
TWTA
UN
U.S.
USA
output power back-off
processed data uplink
phase shift keying
quadrature amplitude modulation
quadrature phase shift keying
radio frequency
radio frequency interference
Reed-Solomon
serial concatenated turbo code
Space Frequency Coordination Group
square root raised cosine
traveling wave tube amplifier
United Nations
United States, an alternate to USA
United States of America
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