U.S. patent application number 14/931463 was filed with the patent office on 2016-03-10 for method and system for controlling a communications carrier's power spectral density (psd) using spread spectrum for matched spectral allocation.
The applicant listed for this patent is Comtech EF Data Corp.. Invention is credited to Michael Beeler, Wallace Davis, Cris M. Mamaril.
Application Number | 20160073359 14/931463 |
Document ID | / |
Family ID | 46235002 |
Filed Date | 2016-03-10 |
United States Patent
Application |
20160073359 |
Kind Code |
A1 |
Mamaril; Cris M. ; et
al. |
March 10, 2016 |
Method and System for Controlling a Communications Carrier's Power
Spectral Density (PSD) Using Spread Spectrum for Matched Spectral
Allocation
Abstract
A method of reducing adjacent satellite interference, the method
comprising monitoring, by a processor, a power spectral density
(PSD) of a signal transmitted by a remote transmitter, determining,
by the processor, that the PSD of the signal transmitted by the
remote transmitter is above a predetermined level, and reducing the
PSD of the signal transmitted by the remote transmitter by
adjusting at least one of a spread spectrum spreading factor, a
power level, a modulation factor, and a forward error correction
(FEC) rate using a modulator while maintaining a constant spectral
allocation and center frequency of the signal.
Inventors: |
Mamaril; Cris M.; (Mesa,
AZ) ; Beeler; Michael; (Jefferson, MD) ;
Davis; Wallace; (Scottsdale, AZ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Comtech EF Data Corp. |
Tempe |
AZ |
US |
|
|
Family ID: |
46235002 |
Appl. No.: |
14/931463 |
Filed: |
November 3, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13406969 |
Feb 28, 2012 |
9178605 |
|
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14931463 |
|
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61578763 |
Dec 21, 2011 |
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Current U.S.
Class: |
455/13.1 |
Current CPC
Class: |
H04W 52/243 20130101;
H04B 7/0678 20130101; H04W 76/20 20180201; H04W 52/36 20130101;
H04L 1/0041 20130101; H04L 1/0003 20130101; H04B 7/18513
20130101 |
International
Class: |
H04W 52/36 20060101
H04W052/36; H04B 7/06 20060101 H04B007/06; H04L 1/00 20060101
H04L001/00; H04W 52/24 20060101 H04W052/24; H04B 7/185 20060101
H04B007/185; H04W 76/04 20060101 H04W076/04 |
Claims
1. A method of reducing adjacent satellite interference, the method
comprising: monitoring, by a processor, a power spectral density
(PSD) of a signal transmitted by a remote transmitter; determining,
by the processor, that the PSD of the signal transmitted by the
remote transmitter is above a predetermined level; and reducing the
PSD of the signal transmitted by the remote transmitter by
adjusting at least one of a spread spectrum spreading factor, a
power level, a modulation factor, and a forward error correction
(FEC) rate using a modulator while maintaining a constant spectral
allocation and center frequency of the signal.
2. The method of claim 1, further comprising maintaining a
communications link between the remote transmitter and a remote
receiver while reducing the PSD of the signal.
3. The method of claim 2, further comprising applying one or more
predetermined timing parameters by the modulator when more than one
of the spread spectrum spreading factor, the power level, the
modulation factor, and the forward error correction (FEC) rate are
adjusted.
4. The method of claim 1, further comprising interrupting a
communications link between the remote transmitter and a remote
receiver while reducing the PSD of the signal.
5. The method of claim 1, wherein the PSD of the signal is reduced
by adjusting only the modulation factor while maintaining a
constant spectral allocation and center frequency of the
signal.
6. The method of claim 1, wherein the PSD of the signal is reduced
by adjusting only the FEC rate while maintaining a constant
spectral allocation and center frequency of the signal.
7. The method of claim 1, wherein the PSD of the signal is reduced
by adjusting only the power level while maintaining a constant
spectral allocation and center frequency of the signal.
8. The method of claim 1, wherein the signal transmitted by the
remote transmitter is a non-spread waveform.
9. The method of claim 8, further comprising transitioning the
non-spread waveform to a spread waveform wherein the non-spread
waveform and the spread waveform have a same spectral
allocation.
10. The method of claim 9, wherein the PSD of the signal is reduced
by adjusting only the modulation factor while maintaining a
constant spectral allocation and center frequency of the
signal.
11. The method of claim 9, wherein the PSD of the signal is reduced
by adjusting only the FEC rate while maintaining a constant
spectral allocation and center frequency of the signal.
12. The method of claim 9, wherein the PSD of the signal is reduced
by adjusting only the power level while maintaining a constant
spectral allocation and center frequency of the signal.
13. The method of claim 9, further comprising applying a spread
factor of a type 2 N while transitioning the non-spread waveform to
a spread waveform.
14. The method of claim 9, further comprising applying an integer
spreading spread factor while transitioning the non-spread waveform
to a spread waveform.
15. The method of claim 9, further comprising applying a fractional
spreading spread factor while transitioning the non-spread waveform
to a spread waveform.
16. A system for reducing adjacent satellite interference, the
system comprising: a remote transmitter configured to transmit a
signal to a remote receiver; a processor configured to: monitor a
power spectral density (PSD) of the signal transmitted by the
remote transmitter; and determine that the PSD of the signal
transmitted by the remote transmitter is above a predetermined
level; and a modulator configured to reduce the PSD of the signal
transmitted by the remote transmitter by adjusting at least one of
a spread spectrum spreading factor, a power level, a modulation
factor, and a forward error correction (FEC) rate while maintaining
a constant spectral allocation and center frequency of the
signal.
17. The system of claim 16, wherein the modulator is further
configured to maintain a communications link between the remote
transmitter and the remote receiver while reducing the PSD of the
signal.
18. The system of claim 17, wherein the modulator is further
configured to apply one or more predetermined timing parameters by
the modulator when more than one of the spread spectrum spreading
factor, the power level, the modulation factor, and the forward
error correction (FEC) rate are adjusted.
19. The system of claim 16, wherein the modulator is further
configured to interrupt a communications link between the remote
transmitter and a remote receiver while reducing the PSD of the
signal.
20. The system of claim 16, wherein the modulator is further
configured to reduce the PSD of the signal is by adjusting only the
modulation factor while maintaining a constant spectral allocation
and center frequency of the signal.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This document is a continuation of earlier U.S. application
Ser. No. 13,406,969, entitled "A Method and System for Controlling
a Communications Carrier's Power Spectral Density (PSD) Using
Spread Spectrum for Matched Spectral Allocation ," to Cris Mamaril
et al., which was filed Feb. 28, 2012, now pending, which
application claims the benefit of the filing date of U.S.
Provisional Patent Application No. 61/578,763, entitled "A Method
and System for Controlling a Communications Carrier's Power
Spectral Density (PSD) Using Spread Spectrum for Matched Spectral
Allocation" to Cris Mamaril et al., which was filed on Dec. 21,
2011, the disclosures of which are hereby incorporated entirely by
reference herein.
BACKGROUND
[0002] 1. Technical Field
[0003] Aspects of this document relate generally to
telecommunication systems and techniques for transmitting data
across a telecommunication channel.
[0004] 2. Background Art
[0005] In all forms of communications, the objective is to develop
smaller antennas that provide higher performance while occupying
less space. The natural result of using a smaller antenna is that
the beam patterns become wider as the antennas necessitate a less
sharply focused signal transmission and the result is energy being
received in undesirable locations. The options to mitigate the
problem of off-axis emissions are as follows: 1) use a larger
antenna, which may not be an option due to space requirements; 2)
lower the transmitted power resulting in less overall power being
used for the transmission link; or 3) using a combination of
decreasing the power while using signal processing techniques such
as Forward Error Correction (FEC) or spread spectrum to mitigate
the effects of the reduced transmission power or smaller antenna.
In the art, the amount of power per unit bandwidth (e.g. Watts/Hz
or dBW/Hz) is known as the Power Spectral Density (PSD). For a
given amount of power, a smaller antenna emits the power over a
wider area, resulting in higher off axis emissions. Conversely, a
larger antenna emits the same amount of power with lower off axis
emissions.
[0006] For example, in satellite communications, as the size of the
antenna is reduced, a resulting and negative aspect of the
reduction to the size of the antenna aperture is that off-axis
emissions increase, resulting in less energy being directed into
the bore sight to the intended target receiver or satellite and
more energy ending up in the off-axis (not into the bore
sight).
[0007] Therefore, a need exists for a method and system that
addresses communications on the move (COTM) or satellite on the
move (SOTM) products in which the antennas are small (small
aperture size), resulting in higher adjacent satellite interference
(ASI) conditions being experienced due to the wider transmission
beam from the antenna. The result is that the PSD may be higher
than can be tolerated on the adjacent satellites (off axis
emissions).
[0008] Development of a method and system that allow a transmission
device to operate at an established transmission configuration, but
keep the spectral allocation as a constant value (e.g. remaining
within the 3 dB bandwidth) is advantageous. Many devices in the art
suffer from problems when changing the transmission carrier signal
characteristics that result in the symbol rate having to be
adjusted. Therefore, a need exists for a method and system that
allow a transmission carrier signal's spectral allocation to remain
at or near a desired (e.g. 3 dB) bandwidth, but use spread spectrum
techniques, namely Direct Sequence Spread Spectrum (DSSS) to
effectively lower the PSD by while holding the spectral allocation
as a constant value during operation.
SUMMARY
[0009] Implementations of a method of reducing adjacent satellite
interference may comprise monitoring, by a processor, a power
spectral density (PSD) of a signal transmitted by a remote
transmitter, determining, by the processor, that the PSD of the
signal transmitted by the remote transmitter is above a
predetermined level, and reducing the PSD of the signal transmitted
by the remote transmitter by adjusting at least one of a spread
spectrum spreading factor, a power level, a modulation factor, and
a forward error correction (FEC) rate using a modulator while
maintaining a constant spectral allocation and center frequency of
the signal.
[0010] Particular implementations may comprise one or more of the
following features. The method may further comprise maintaining a
communications link between the remote transmitter and a remote
receiver while reducing the PSD of the signal. The method may
further comprise applying one or more predetermined timing
parameters by the modulator when more than one of the spread
spectrum spreading factor, the power level, the modulation factor,
and the forward error correction (FEC) rate are adjusted. The
method may further comprise interrupting a communications link
between the remote transmitter and a remote receiver while reducing
the PSD of the signal. The PSD of the signal may be reduced by
adjusting only the modulation factor while maintaining a constant
spectral allocation and center frequency of the signal. The PSD of
the signal may be reduced by adjusting only the FEC rate while
maintaining a constant spectral allocation and center frequency of
the signal. The PSD of the signal may be reduced by adjusting only
the power level while maintaining a constant spectral allocation
and center frequency of the signal. The signal transmitted by the
remote transmitter may be a non-spread waveform. The method may
further comprise transitioning the non-spread waveform to a spread
waveform wherein the non-spread waveform and the spread waveform
have a same spectral allocation. The PSD of the signal may be
reduced by adjusting only the modulation factor while maintaining a
constant spectral allocation and center frequency of the signal.
The PSD of the signal may be reduced by adjusting only the FEC rate
while maintaining a constant spectral allocation and center
frequency of the signal. The PSD of the signal may be reduced by
adjusting only the power level while maintaining a constant
spectral allocation and center frequency of the signal. The method
may further comprise applying a spread factor of a type 2 N while
transitioning the non-spread waveform to a spread waveform. The
method may further comprise applying an integer spreading spread
factor while transitioning the non-spread waveform to a spread
waveform. The method may further comprise applying a fractional
spreading spread factor while transitioning the non-spread waveform
to a spread waveform.
[0011] Implementations of a system for reducing adjacent satellite
interference may comprise a remote transmitter configured to
transmit a signal to a remote receiver, a processor configured to
monitor a power spectral density (PSD) of the signal transmitted by
the remote transmitter and determine that the PSD of the signal
transmitted by the remote transmitter is above a predetermined
level, and a modulator configured to reduce the PSD of the signal
transmitted by the remote transmitter by adjusting at least one of
a spread spectrum spreading factor, a power level, a modulation
factor, and a forward error correction (FEC) rate while maintaining
a constant spectral allocation and center frequency of the
signal.
[0012] Particular implementations may comprise one or more of the
following features. The modulator may be further configured to
maintain a communications link between the remote transmitter and
the remote receiver while reducing the PSD of the signal. The
modulator may be further configured to apply one or more
predetermined timing parameters by the modulator when more than one
of the spread spectrum spreading factor, the power level, the
modulation factor, and the forward error correction (FEC) rate are
adjusted. The modulator may be further configured to interrupt a
communications link between the remote transmitter and a remote
receiver while reducing the PSD of the signal. The modulator may be
further configured to reduce the PSD of the signal is by adjusting
only the modulation factor while maintaining a constant spectral
allocation and center frequency of the signal. The modulator may be
further configured to reduce the PSD of the signal by adjusting
only the FEC rate while maintaining a constant spectral allocation
and center frequency of the signal. The modulator may be further
configured to reduce the PSD of the signal by adjusting only the
power level while maintaining a constant spectral allocation and
center frequency of the signal. The signal transmitted by the
remote transmitter may be a non-spread waveform. The modulator may
be further configured to transition the non-spread waveform to a
spread waveform wherein the non-spread waveform and the spread
waveform have a same spectral allocation. The modulator may be
further configured to reduce the PSD of the signal by adjusting
only the modulation factor while maintaining a constant spectral
allocation and center frequency of the signal. The modulator may be
further configured to reduce the PSD of the signal by adjusting
only the FEC rate while maintaining a constant spectral allocation
and center frequency of the signal. The modulator may be further
configured to reduce the PSD of the signal by adjusting only the
power level while maintaining a constant spectral allocation and
center frequency of the signal. The modulator may be further
configured to apply a spread factor of a type 2 N while
transitioning the non-spread waveform to a spread waveform. The
modulator may be further configured to apply an integer spreading
spread factor while transitioning the non-spread waveform to a
spread waveform. The modulator may be further configured to apply a
fractional spreading spread factor while transitioning the
non-spread waveform to a spread waveform.
[0013] Aspects and applications of the disclosure presented here
are described below in the drawings and detailed description.
Unless specifically noted, it is intended that the words and
phrases in the specification and the claims be given their plain,
ordinary, and accustomed meaning to those of ordinary skill in the
applicable arts. The inventors are fully aware that they can be
their own lexicographers if desired. The inventors expressly elect,
as their own lexicographers, to use only the plain and ordinary
meaning of terms in the specification and claims unless they
clearly state otherwise and then further, expressly set forth the
"special" definition of that term and explain how it differs from
the plain and ordinary meaning. Absent such clear statements of
intent to apply a "special" definition, it is the inventors' intent
and desire that the simple, plain and ordinary meaning to the terms
be applied to the interpretation of the specification and
claims.
[0014] The inventors are also aware of the normal precepts of
English grammar. Thus, if a noun, term, or phrase is intended to be
further characterized, specified, or narrowed in some way, then
such noun, term, or phrase will expressly include additional
adjectives, descriptive terms, or other modifiers in accordance
with the normal precepts of English grammar. Absent the use of such
adjectives, descriptive terms, or modifiers, it is the intent that
such nouns, terms, or phrases be given their plain, and ordinary
English meaning to those skilled in the applicable arts as set
forth above.
[0015] Further, the inventors are fully informed of the standards
and application of the special provisions of 35 U.S.C. .sctn.112,
6. Thus, the use of the words "function," "means" or "step" in the
Description , Drawings, or Claims is not intended to somehow
indicate a desire to invoke the special provisions of 35 U.S.C.
.sctn.112, 6, to define the invention. To the contrary, if the
provisions of 35 U.S.C. .sctn.112, 6 are sought to be invoked to
define the claimed disclosure, the claims will specifically and
expressly state the exact phrases "means for" or "step for," and
will also recite the word "function" (i.e., will state "means for
performing the function of [insert function]"), without also
reciting in such phrases any structure, material or act in support
of the function. Thus, even when the claims recite a "means for
performing the function of . . . " or "step for performing the
function of . . . ," if the claims also recite any structure,
material or acts in support of that means or step, or that perform
the recited function, then it is the clear intention of the
inventors not to invoke the provisions of 35 U.S.C. .sctn.112, 6.
Moreover, even if the provisions of 35 U.S.C. .sctn.112, 6 are
invoked to define the claimed disclosure, it is intended that the
disclosure not be limited only to the specific structure, material
or acts that are described in the preferred embodiments, but in
addition, include any and all structures, materials or acts that
perform the claimed function as described in alternative
embodiments or forms of the invention, or that are well known
present or later-developed, equivalent structures, material or acts
for performing the claimed function.
[0016] The foregoing and other aspects, features, and advantages
will be apparent to those artisans of ordinary skill in the art
from the DESCRIPTION and DRAWINGS, and from the CLAIMS.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a representation of a geographically diverse
satellite network with a hub earth station terminal communicating
with multiple remote sites.
[0018] FIG. 2 is a representation of an implementation of a
satellite repeating relay.
[0019] FIG. 3 is a representation showing an implementation of a
typical satellite that contains multiple transponders in which the
odd transponders are one type of polarization and the even
transponders are a second type of polarization.
[0020] FIG. 4 is representation of emissions from a remote terminal
including a corresponding bore-sight and off-axis emissions to a
satellite in an orbital arc of the remote terminal.
[0021] FIG. 5 is a representation of emissions from a remote
terminal including a corresponding bore-sight and off-axis
emissions to a satellite in the orbital arc in which adjacent
satellites are not illuminated.
[0022] FIG. 6 is a graphical representation depicting an example of
occupied bandwidth remaining the same when spreading is introduced
and PSD is dynamically lowered.
[0023] FIG. 7 is a block diagram of a modulator using an
implementation of the described method and system.
[0024] FIG. 8 is a block diagram of a demodulator using an
implementation of the described method and system.
[0025] FIG. 9 shows various modulation and FEC coding combinations
(MODCOD) versus Eb/No and Es/No.
DESCRIPTION
[0026] This disclosure, its aspects and implementations, are not
limited to the specific components, frequency examples, or methods
disclosed herein. Many additional components and assembly
procedures known in the art consistent with a method and system for
controlling a communications carrier signal's power spectral
density (PSD) using spread spectrum for matched spectral allocation
techniques are in use with particular implementations from this
disclosure. Accordingly, for example, although particular
implementations are disclosed, such implementations and
implementing components may comprise any components, models,
versions, quantities, and/or the like are known in the art for such
systems and implementing components, consistent with the intended
operation.
[0027] This disclosure relates to a method and system for
controlling a communications carrier signal's power spectral
density (PSD) using spread spectrum. The method and system provides
the user with the ability to control the power spectral density
(PSD) by operating the transmission carrier signal at a constant
occupied spectral allocation while adjusting the power and
spreading factor to ensure the PSD remains at or below an
acceptable level. The method and system makes provisions for
adjusting the overall carrier signal power, but further compensates
by adjusting the spreading while keeping the spectral allocation at
a constant value, resulting in the PSD being controlled. An
additional aspect of the control is the ability to dynamically
adjust the Forwarded Error Correction (FEC) while adjusting the
transmission carrier power and level of spreading--in essence the
adjustment of the FEC, may be an additional control aspect of
lowering the PSD in concert with the level of spreading and power.
One result of the described method and system is no interruption to
service. Existing art requires service interruption.
[0028] The ability to change a system from non-spreading to
spreading and then dynamically change the spreading results in a
condition at which the power, bandwidth, chip-rate configuration,
etc. creates an outage of the system during the change. Particular
implementations of the described methods and systems provide a
hitless way to ensure the PSD may be managed, that does not result
in an impact to the operation of the equipment.
[0029] This disclosure relates to a method and system for
controlling a communications carrier signal's power spectral
density (PSD) using spread spectrum techniques. For point-to-point,
point-to-multipoint and multipoint-to-multipoint networks that
utilize a repeating relay, such as a space-based satellite
repeating relay or an airborne repeating relay, the amount of power
spectral density (PSD) that is received by the intended receiver
(desired satellite) is beneficial. However, for unintended
receivers (adjacent satellites) the higher the PSD, the more
interference is received resulting in degradation to services that
may be in operation on the adjacent satellite.
[0030] In satellite communications, and in the present art, there
are numerous ways to ensure the amount of adjacent satellite
interference is mitigated. The techniques include, but are not
limited to, using a larger antenna to focus the beam into the
desired bore sight (desired satellite), using spread spectrum to
lower the PSD, using a Forward Error Correction (FEC) code that
results in lowering the PSD, or using brute force techniques such
as decreasing the transmitted power used for transmitting the
carrier signal.
[0031] In the art, if it is determined that a transmission site's
carrier signal has a PSD that is too high, typically the options
for lowering it include: introducing spread spectrum; increasing
the occupied spectrum; and/or changing the power emitted from the
site. In the present description, implementations of the method and
system allow a carrier signal to remain at the original occupied
spectral allocation and simply invoke spread spectrum,
specifically, in one particular implementation, Direct Sequence
Spread Spectrum (DSSS), at the original symbol rate (when operating
without spreading). Implementations of the described method and
system ensure that the spectral allocation remains as a constant
while adjusting the PSD.
[0032] More specifically, the introduction of spread spectrum
results in the PSD being reduced. For each factor of two (2) for
the spreading (spread factor) the power spectral density is reduced
by 3 Decibels (3 dB). Therefore, the PSD is reduced by a factor of
two for each level of spread factor that is introduced. Holding the
occupied spectral allocation to a constant value, equivalent to the
non-spread spectrum symbol rate, which is also known in the art as
the chip rate, with the introduction of spread spectrum, the power
of the carrier signal may be reduced by an equivalent amount of
power for each increase of spread factor.
[0033] For implementations of the described method and system, with
the introduction of spread spectrum, the ability to carry user data
is reduced. To compensate for the introduction of spread spectrum,
the modulation (MOD) and FEC coding (COD) may be adjusted to
provide a more spectral efficient bits/Hz rate to help mitigate the
reduction in efficiency of the spread spectrum. The combination of
the parameters in implementations of the described methods and
systems may result in a hitless manner to minimize the interference
as a result of PSD than is available in the existing art.
[0034] Particular implementations for a method and system for
controlling a communications carrier signal's power spectral
density (PSD) using spread spectrum for matched spectral allocation
techniques disclosed herein may be specifically employed in
satellite communications systems. However, as will be clear to
those of ordinary skill in the art from this disclosure, the
principles and aspects disclosed herein may readily be applied to
any electromagnetic (IF, RF and optical) communications system,
such as terrestrial broadcast network without undue
experimentation.
[0035] The requirement to regulate the PSD has previously been
addressed by airborne, satellite and terrestrial antenna
manufactures as long as antennas have been produced.
Implementations of the described method introduce the ability to
provide a hitless (i.e. without link interruption) manner to modify
or adjust the waveform/signal/carrier characteristics in a manner
that allows the PSD to be controlled. While some implementations of
the described system and methods may result in controlling the PSD
in a completely or substantially hitless manner, one of ordinary
skill in the art would also recognize that other implementations
may not be entirely "hitless" when switching from a normalized to a
spread configuration.
[0036] In the art, the PSD may be addressed in many ways: the most
obvious is to change the physical geometry of the antenna by making
the aperture larger (larger parabolic aperture or larger surface
area with more active elements for a satellite antenna) or longer
(longer boom or more elements) for terrestrial, but the geometry is
highly dependent on the operating frequency and space available to
mount the antenna. A larger physical geometry results in a sharper
beam from the antenna. If the geometry cannot be changed or space
is limited, then the next step that may be taken is to lower the
power spectral density in the waveform by introducing spread
spectrum, more FEC to the data, lowering the modulation index, or
lowering transmitted power. As each aspect is changed, there is a
trade off that must be considered when making changes to the
waveform. As power is lowered, more FEC is needed or the modulation
index must be lowered. Conversely, if spread spectrum is
introduced, then the data rate is reduced. Implementations of the
described method and system do affect the bandwidth, but using the
aforementioned degrees of freedom, the effects may be adjusted to
mitigate the reduction in power, bandwidth, etc. to achieve a level
of optimal operation.
[0037] FIG. 1 shows a typical satellite configuration having three
sites, a hub earth station terminal 100 is communicating over a
satellite repeating relay 110 to two geographically diverse remote
sites 120, 130.
[0038] FIG. 2 illustrates a typical satellite based repeating relay
100 used in the art with no onboard processing. The repeating relay
contains an input (receive antenna) 200 which receives the incoming
carrier signals, Orthogonal Mode Transducer (OMT) 210 that
separates the various electromagnetic (EM) polarizations, Bandpass
Filter (BPF) 220 that filters the frequency spectrum, amplifier
(e.g. a Low-Noise Amplifier (LNA)) 230 that allows the received
carrier signals to be power amplified, multiplexer 240 which
separates the various frequency spectrum to the appropriate
transponder, frequency converter 250 that converts to the downlink
frequency, linearizer 260 that linearizes any non-linearity due to
the amplifiers, an amplifier 270 that amplifies before transmitting
back to the destination, a multiplexer 280 that multiplexes to the
proper EM polarization configuration and feed to the OMT 290 to the
transmit antenna 300 feed for relay. The configuration of the
transponders of the repeating relay 110 may be comprised of a
single transponder or a plurality of EM transponders with or
without overlapping frequencies as shown in FIG. 3.
[0039] FIG. 4 shows a typical small antenna where the PSD is being
exceeded and the result is that the desired satellite 400 at zero
(0) degrees (bore sight) is being illuminated, but the adjacent
satellites 410, 420 are being illuminated at a level above an
acceptable PSD. In the existing art, the options are to replace the
antenna with one or more desirable characteristics, introduce
spread spectrum, reduce the power, lower the modulation index, or
change the FEC configuration to reduce the PSD. All the described
actions result in the carrier signal being interrupted. The result
of any or a combination of the possible actions results in the PSD
being reduced and the results may be observed in FIG. 5.
[0040] As shown in FIG. 6, in a particular embodiment of the
described method and system, while keeping the occupied bandwidth
constant (same as the non-spread symbol rate), spread spectrum may
be introduced at the same rate as the symbol rate. The symbol rate,
in units of symbols per second (sps), then transitions from sps to
a chip rate, in chips per second (cps). The two quantities are the
same and remain the same number, but mean something different when
transitioning from spread spectrum to non-spread spectrum. In a
baseline configuration, the carrier signal may be operating in a
non-spread spectrum configuration and if it is deemed the PSD is
too high, then while keeping the symbol rate (the rate that symbols
are transitioned), a spread spectrum waveform may result by
spreading each modulated symbol by a spread factor. Implementations
of the method and system may use spread spectrum that uses an
integer, non-integer or 2 N type spread factor. Therefore, the
nomenclature of a symbol must be removed and replaced by a chip
occurring at the same rate as the previous symbol time. By reducing
the symbol rate and simultaneously chipping the symbols by the
appropriate factor, the result is a constant bandwidth. An aspect
of novelty of the method and system is that by holding the occupied
bandwidth to a constant value and keeping the chip rate equal to
the symbol rate, the complexity of the transmission and receiving
equipment is significantly simplified. The result of using
implementations of the described method and system may go in and
out of spread spectrum and adjust the spread factor on-the-fly
without the need of having the carrier signal interrupted as the
occupied spectrum remains as a constant value.
[0041] Implementations of the described method and system continue
to allow the use of power level, modulation index and FEC coding
rate to be adjusted as degrees of freedom to change the PSD and the
bandwidth available for carrying user data.
[0042] FIG. 7 shows an implementation of a modulator using an
implementation of the described method and system. The modulator
comprises a data input 700 that may have a data formatter 710,
followed by a parallel to serial serializer 720 followed by a
randomizer/encoder 730 for energy dispersal and possible FEC
encoding, followed by a bit to symbol mapper 740. Operation up to
this point in the modulation flow may be a common modulator in the
current art. To implement implementations of the method and system,
a symbol chipper 750 may be inserted where each symbol may be
chipped. When the carrier signal can meet the PSD limits, the
symbol chipper 750 may be set to 0 and the symbols flow through
symbol chipper 750 in an unaltered fashion. If the power spectral
density is not met, then the symbols may be chipped. The symbol
chipper 750 may operate as either an integer chipper (1, 2, 3, 4,
etc.), non-integer chipper (1.1, 1.2, 1.3, 1.4, etc.) or as a 2 N
chipper. The output of the symbol chipper 750 becomes the standard
modulator design flow with a constellation mapper 760, followed by
a pulse shaping filter 770, by non-limiting example a Nyquist
filter, square root raised cosine filter or other pulse shaping
filter, that outputs a modulated output 780 that may also be power
amplified and frequency up-converted.
[0043] FIG. 8 shows an implementation of a demodulator using an
implementation of the described method and system. The demodulator
comprises a carrier signal input 800 and may include a gain control
810 to set the desired input level, followed by an analog to
digital converter (ADC) 820 to convert the input from an analog
input to a digital input, followed by a decimator 830 to reduce the
input sample rate, followed by a pulse shaped filter filter 840 for
smoothing the input samples. Operation up to this point in the
demodulation flow may be a common demodulator in the current art.
The input then may flow to a chip to symbol despreader 850 where
the chips are removed and the carrier signal is reconstituted as a
symbol based carrier signal. The output of the chip to symbol
despreader 850 becomes the standard demodulator design flow with a
symbol to bit converter 860, followed by a de-randomizer/decoder
870 to remove the randomization of the data and possibly a decoder
for performing the FEC decoding, followed by a serial to parallel
converter 880 and output as a native data stream 890.
[0044] The following are particular implementations of a method and
system for controlling a communications carrier signal's power
spectral density (PSD) using spread spectrum for matched spectral
allocation techniques and are provided as non-limiting
examples:
EXAMPLE 1
[0045] A satellite network using X-Band is configured to support a
mobile site that operates with a 0.45 m antenna. The antenna
provides an acceptable level of performance that allows the carrier
signal being transmitted from the mobile terminal using 1.0 Msps
QPSK 0.780 FEC. The resulting PSD to the adjacent satellites is
designed to operate at 1.0 dB below the desired PSD limit. After
being placed in service, it is determined the PSD is now 2.0 dB
above the required limit when the mobile terminal is in motion.
Therefore, the adjacent satellite operators have requested that in
conditions at which the PSD is above the acceptable limit, the
mobile terminal immediately transitions to a configuration
resulting in acceptable PSD operation. Using an implementation of
the described method and system, and upon detection of motion, the
mobile terminal immediately moves from 1.0 Msps QPSK 0.780 FEC to a
spread factor of 2 and the data rate is reduced in half. The
resulting carrier signal configuration occupies the same bandwidth
but has 3 dB more margin as a result of the change. The power can
now be reduced by 3 dB and the link can still be closed. At no time
does the mobile terminal using an implementation of the method and
system experience a drop in service or require the carrier signal's
symbol rate to be reconfigured.
EXAMPLE 2
[0046] In particular implementations of the system described in
Example 1, the satellite uses C-Band resulting in the same
operation of PSD.
EXAMPLE 3
[0047] In particular implementations of the system described in
Example 1, the satellite uses Ku-Band resulting in the same
operation of PSD.
EXAMPLE 4
[0048] In particular implementations of the system described in
Example 1, the satellite uses Ka-Band resulting in the same
operation of PSD.
EXAMPLE 5
[0049] In particular implementations of the system described in
Example 1, the satellite uses V-Band resulting in the same
operation of PSD.
EXAMPLE 6
[0050] A satellite network using Ku-Band is configured to support a
remote site that operates with a 0.2 m antenna. The extremely small
antenna provides an acceptable level of performance that allows the
carrier signal to be transmitted from the remote site using 48 Ksps
BPSK 0.488 FEC. The resulting PSD to the adjacent satellites
indicates that carrier signal is operating at the maximum
acceptable PSD limit. After being placed in service, it is
determined that the PSD is now 9.0 dB above the required limit.
Therefore, the adjacent satellite operators have requested that in
conditions where the PSD is above the limit, the site must
immediately transition to a configuration that results in lower PSD
operation. Using an implementation of the described method and
system, upon detection by an operator, agency, etc. of being over
the PSD limit, the site must be moved from 48 Ksps BPSK 0.488 FEC
to a spread factor of 8 and data rate reduced to 1/8. The resulting
carrier signal configuration remains at 48 Kcps BPSK 0.488 FEC and
PSD is realized to drop by 9.0 dB. At no time does the site using
the method and system experience a drop in service or require the
carrier signal's symbol rate to be reconfigured. The site may
operate in this manner until the site can be repaired.
EXAMPLE 7
[0051] In particular implementations of the system described in
Example 6, the satellite uses C-Band resulting in the same
operation of PSD.
EXAMPLE 8
[0052] In particular implementations of the system described in
Example 6, the satellite uses X-Band resulting in the same
operation of PSD.
EXAMPLE 9
[0053] In particular implementations of the system described in
Example 6, the satellite uses Ka-Band resulting in the same
operation of PSD.
EXAMPLE 10
[0054] In particular implementations of the system described in
Example 6, the satellite uses V-Band resulting in the same
operation of PSD.
EXAMPLE 11
[0055] A satellite network using C-Band is configured to support a
remote site that operates with a 0.45 m antenna. The extremely
small antenna provides an acceptable level of performance that
allows the carrier signal to be transmitted from the remote site
using 64 Ksps BPSK 0.488 FEC. The resulting PSD to the adjacent
satellites appear to be operating at the maximum acceptable PSD
limit. After being placed in service, it is determined the PSD is
now 10.0 dB above the required limit. Therefore, the adjacent
satellite operators have requested that in conditions where the PSD
is above the limit, the site must immediately transition to a
configuration that results in lower PSD operation. Using an
implementation of the described method and system, upon detection
by an operator, agency, etc. of being over the PSD limit, the site
must be moved from 64 Ksps BPSK 0.488 FEC to a spread factor of 10
and a data rate of 1/10th. The resulting carrier signal
configuration remains at 64 Kcps BPSK 0.488 FEC and PSD is realized
to drop by 10.0 dB. At no time does the site using the method and
method experience a drop in service or require the carrier signal's
symbol rate to be reconfigured. The site may operate in this manner
until the site can be repaired.
EXAMPLE 1
[0056] In particular implementations of the system described in
Example 11, the satellite uses X-Band resulting in the same
operation of PSD.
EXAMPLE 13
[0057] In particular implementations of the system described in
Example 11, the satellite uses Ku-Band resulting in the same
operation of PSD.
EXAMPLE 14
[0058] In particular implementations of the system described in
Example 11, the satellite uses Ka-Band resulting in the same
operation of PSD.
EXAMPLE 15
[0059] In particular implementations of the system described in
Example 11, the satellite uses V-Band resulting in the same
operation of PSD.
EXAMPLE 16
[0060] A satellite network using Ku-Band is configured to support a
remote site that operates with a 0.30 m antenna. The extremely
small antenna provides an acceptable level of performance that
allows the carrier signal to be transmitted from the remote site
using 80 Ksps BPSK 0.488 FEC. The resulting PSD to the adjacent
satellites appear to be operating at the maximum acceptable PSD
limit. After being placed in service, it is determined the PSD is
now 3.5 dB above the required limit. Therefore, the adjacent
satellite operators have requested that in conditions at which the
PSD is above the limit, the site must immediately transition to a
configuration that results in lower PSD operation. Using an
implementation of the described method and system, upon detection
by an operator, agency, etc. of being over the PSD limit, the site
must be moved from 80 Ksps BPSK 0.488 FEC to a spread factor of
2.24. The resulting carrier signal configuration remains at 80 Kcps
BPSK 0.488 FEC and data rate of 1/(2.24) and PSD is realized to
drop by 3.5 dB. At no time does the site using an implementation of
the method and system experience a drop in service or require the
carrier signal's symbol rate to be reconfigured. The site may
operate in this manner until the site can be repaired.
EXAMPLE 17
[0061] In particular implementations of the system described in
Example 16, the satellite uses C-Band resulting in the same
operation of PSD.
EXAMPLE 18
[0062] In particular implementations of the system described in
Example 16, the satellite uses X-Band resulting in the same
operation of PSD.
EXAMPLE 19
[0063] In particular implementations of the system described in
Example 16, the satellite uses Ka-Band resulting in the same
operation of PSD.
EXAMPLE 20
[0064] In particular implementations of the system described in
example 16, the satellite uses V-Band resulting in the same
operation of PSD.
[0065] In places where the description above refers to particular
implementations of telecommunications systems and methods, it
should be readily apparent that a number of modifications may be
made without departing from the spirit thereof and that these
implementations may be applied to other telecommunications system
and method implementations.
* * * * *