Note: Descriptions are shown in the official language in which they were submitted.
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METHODS AND SYSTEMS FOR IMPROVING
SPECTRUM UTILIZATION FOR SATELLITE
COMMUNICATIONS
TECHNICAL FIELD
[0001] The present application relates to satellite communications, and
more
particularly to methods and systems for improving spectrum utilization in
satellite
communications.
BACKGROUND
[0002] Traditionally, satellite communications have involved a fixed
routing of
uplink analog channels to downlink analog channels. The input and output
multiplexers and up/down converters are prearranged to implement the frequency
plan
for uplink and downlink.
[0003] A full digital solution is more flexible, but can be far more
costly.
Moreover, a digital payload with phased array antennas (beam steerable) uses
solid
state power amplifiers that achieve lower power output density than the
comparable
analog technology.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] Reference will now be made, by way of example, to the accompanying
drawings which show examp::, embodiments of the present disclosure, and in
which:
[0005] FIG. 1 is a block diagram of an example of a conventional analog
satellite
payload;
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[0006] FIG. 2 is a block diagram of an example of a hybrid digital-analog
satellite
payload in the Ku band;
[0007] FIG 3. shows example uplink and downlink frequency plans for the
example payload of FIG. 2;
[0008] FIG. 4 is a block diagram of another example hybrid analog-digital
payload;
[0009] FIG. 5 shows example uplink and downlink frequency plans for the
example payload of FIG. 4;
[0010] FIG. 6 is a block diagram of a further example hybrid analog-
digital
payload;
[0011] FIG. 7 shows example uplink and downlink frequency plans for the
example payload of FIG. 6;
[0012] FIG. 8 is a block diagram of an example satellite payload with
dual output
multiplexers and dual output antenna feeds on same reflector;
[0013] FIGs. 9A, 9B, and 9C shows example uplink and downlink frequency
plans for the example payload of FIG. 8;
[0014] FIG. 10 is a block diagram of an example hybrid analog-digital
payload
with dual output multiplexers and dual output antenna feeds on same reflector;
[0015] FIG. 11 shows example uplink and downlink frequency plans for the
example payload of FIG. 10;
[0016] FIG. 12 diagrammatically shows coverage areas of a regional beam
and
spot beams;
[0017] FIG. 13 shows example uplink and downlink frequency plans using a
dynamic regional spectrum reallocation;
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[0018] FIG. 14 is a block diagram of an example payload for realizing
dynamic
regional spectrum reallocation;
[0019] FIG. 15 shows example uplink and downlink frequency plans with
different reallocations;
[0020] FIG. 16 diagrammatically shows coverage areas of a regional beam and
spot beams with spatially distinct uplink locations;
[0021] FIG. 17 shows example uplink and downlink frequency plans using
shared
regional beam spectrum;
[0022] FIG. 18 shows an example portion of a payload with digital
cancellation
for realizing shared regional beam spectrum; and
[0023] FIG. 19 shows a block diagram of an example hybrid satellite
payload
without analog input multiplexer; and
[0024] FIG. 20 shows example uplink and downlink frequency plans for the
example payload of FIG. 19.
[0025] Like reference numerals are used in the drawings to denote like
elements
and features.
DETAILED DESCRIPTION
[0026] In one aspect, the present application describes a satellite
payload for
mitigating an imbalance in uplink and downlink availability for satellite
communications. The payload includes a receive antenna and amplifiers to
receive an
uplink signal containing a plurality of channels in a band of spectrum at a
satellite,
each channel having a bandwidth and each pair of adjacent channels being
separated
by a guard band; an analog-to-digital converter to covert the band of spectrum
to
digital; a digital channelizer to channelize the digitized band of spectrum to
obtain
two or more digitized guard band channels each corresponding to a respective
one of
the guard bands and to group the two or more digitized guard band channels to
create
a composite channel; a digital-to-analog converter and an RF up-converter to
convert
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the composite channel to an analog downlink channel; an output multiplexer to
frequency division multiplex the analog downlink channel with other analog
downlink
channels; and a transmit antenna to transmit the multiplexed channels as an
analog
downlink signal.
[0027] In another aspect, the present application describes a method for
mitigating
an imbalance in uplink and downlink availability for satellite communications.
The
method includes receiving an uplink signal containing a plurality of channels
in a
band of spectrum at a satellite, each channel having a bandwidth and each pair
of
adjacent channels being separated by a guard band; digitally channelizing the
band of
spectrum to obtain two or more digitized guard band channels each
corresponding to a
respective one of the guard hands; grouping the two or more digitized guard
band
channels to create a composite channel; and converting the composite channel
to an
analog downlink channel, frequency division multiplexing the analog downlink
channel with other analog downlink channels, and transmitting the multiplexed
channels as an analog downlink signal.
[0028] In a further aspect, the present application describes a satellite
payload for
satellite communications. The payload includes a receive antenna and
amplifiers to
receive an uplink signal containing a plurality of channels in a band of
spectrum at a
satellite; an analog-to-digital converter to covert the band of spectrum to
digital; a
digital channelizer to channelize the digitized band of spectrum to route each
of the
plurality of channels to a respective downlink channel in a first frequency
plan, and to
form at least one additional downlink channel; a digital-to-analog converter
and an RF
up-converter; a first output multiplexer to frequency division multiplex the
respective
downlink channels in accordance with the first frequency plan, wherein the
first
frequency plan defines a guard band between each adjacent downlink channel in
the
first frequency plan; a second output multiplexer to frequency divisional
multiplex the
at least one additional downlink channel in accordance with a second frequency
plan,
wherein the second frequency plan defines one or more supplemental downlink
channels covering the one or more of the guard bands; and one or more transmit
antenna feeds to transmit the multiplexed signals.
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[0029] In yet a further aspect, the present application describes a
satellite payload
for satellite communications. The payload includes a regional beam antenna
operable
over a regional band of spectrum; a narrowband spot beam antenna operable over
a
spot beam band of spectrum and a portion of the regional band of spectrum; a
digital
channelizer to route digitized spot beam channels to downlink channels, and
wherein
the digital channelizer is to dynamically assign one or more digitized spot
beam
channels to a part of the portion of the regional band of spectrum; a digital-
to-analog
converter to convert the digitized spot beam channels to analog; an RF up-
converter
to up-convert the analog spot beam channels; and a spot beam spectrum
amplifier to
amplify the up-converted analog spot beam channels in the spot beam band of
spectrum and the portion of the regional band of spectrum.
[0030] In another aspect, the present application describes a satellite
payload for
satellite communications to share uplink capacity. The payload includes a spot
beam
antenna operable over a spot beam band of spectrum and a portion of a regional
band
of spectrum, wherein the spot beam antenna has a spot beam coverage area; a
regional
antenna operable over the regional band of spectrum with a regional beam
coverage
area that overlaps with the spot beam coverage area, wherein the regional
antenna is
to receive an uplink signal from an uplink location geographically outside of
the spot
beam coverage area; an analog-to-digital converter to digitize signals
received by the
regional uplink antenna and the spot beam antenna to produce digitized
regional band
signals and digitized spot beam signals, respectively; a digital cancelation
circuit to
subtract the digitized spot beam signals from the digitized regional band
signals to
obtain a clean regional band signal; and a digital channelizer to route uplink
channels
to downlink channels in both the clean regional band signal and the digitized
spot
beam signals.
[0031] In yet another aspect, the present application describes a
satellite payload
for mitigating an imbalance in uplink and downlink availability for satellite
communications. The payload includes a receive antenna and amplifiers to
receive an
uplink signal containing a plurality of channels in a band of spectrum at a
satellite; an
analog-to-digital converter to covert the band of spectrum to digital; a
digital
channelizer to channelize thc digitized band of spectrum to obtain the
plurality of
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channels and to route each of the plurality of channels to a respective
downlink
channel; a digital-to-analog converter and an RF up-converter to convert each
downlink channel to an analog RF downlink channel; an output multiplexer to
frequency division multiplex the analog RF downlink channels into a band of
downlink spectrum; and a transmit antenna to transmit the band of downlink
spectrum.
[0032] Other example embodiments of the present disclosure will be
apparent to
those of ordinary skill in the art from a review of the following detailed
description in
conjunction with the drawings.
[0033] Example embodiments of the present disclosure are not limited to any
particular type of satellite or antenna.
Satellite Overview
[0034] Satellites are devices positioned in orbital space that are used
for various
purposes. In one example embodiment, the satellites are communication
satellites.
That is, they are positioned in orbital space for the purpose of providing
communications. For example, communication satellites are designed to relay
communication signals between two end-points (which may be stationary or
mobile)
to provide communication services such as telephone, television, radio and/or
internet
services.
[0035] The satellites may employ a variety of orbital paths around the
Earth. For
example, satellites may have geostationary orbits, molniya orbits, elliptical
orbits,
polar and non-polar Earth orbits, etc. Communication satellites typically have
geostationary orbits. That is, the satellites have a circular orbit above the
Earth's
equator and follow the direction of the Earth's rotation. A satellite in such
an orbit
has an orbital period equal to the Earth's rotational period, and accordingly
may
appear at a fixed position in the sky for ground stations.
[0036] Communication satellites are typically spaced apart along the
geostationary orbit. That is, the satellites are positioned in orbital slots.
The satellite
operators coordinate their use of orbital slots with each other under
international
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treaty by the International Telecommunication Union (ITU), and the separation
between slots depends on the coverage and frequency of operation of the
satellites.
For example, in at least some example embodiments, the separation between
satellites
may be between 2-3 degrees of orbital longitude. In at least some example
embodiments, the separation between satellites may be less than 2 degrees of
separation. The separation of the satellites in such a manner allows for
frequency
reuse for both uplink and downlink transmission. For example, by separating
adjacent
satellites by a distance greater than the transmitting beamwidth (i.e. the
angle,
measured in a horizontal plane, between the directions at which the power of
the
beam is at least one-half its maximum value) of an antenna associated with the
ground
station for uplink transmission, the same frequency for the communication
signals
may be employed to uplink to adjacent satellites with interference at or below
the
coordinated level. Similarly, if the separated distance between the adjacent
satellites
is greater than the receiving beamwidth of the antenna associated with the
ground
station for downlink transmission, the same frequency for the communication
signals
may be employed to downlink from adjacent satellites with interference at or
below
the coordinated level.
[0037] In order to perform communication functions, the satellite is
equipped with
various components. For example, the satellite may include a communication
payload (which may further include transponders, one or more antennas, and
switching systems), engines (to bring the satellite to the desired orbit),
tracking and
stabilization systems (used to the orient the satellite and to keep the
satellite in the
right orbit), power subsystems (to power the satellite) and command and
control
subsystems (to maintain communication with ground control stations).
[0038] The transponder of the satellite forms a communication channel
between
two end-points to allow for communications between the two end-points. The
transponder also defines the capacity of the satellite for communications.
[0039] The antenna of the satellite transmits and receives communication
signals.
More specifically, the antenna is an electronic component that converts
electric
currents (which may be generated by a transmitter) to propagating radio
frequency
(RF) signals during transmission, and converts induced RF signals to electric
currents
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during reception. In at least
some example embodiments, the antenna may be
associated with an amplifier which may amplify the power of the transmitted or
received RF signals.
[0040] The
communication signals may be microwave signals. Microwave
signals are RF signals that have wavelengths ranging from as long as one meter
to as
short as one millimeter. Equivalently, the frequency of the RF signals may
range
from 300 MHz to 300 GHz. More particularly, the communication signals are
within
certain frequency bands of microwave signals as they are more suited for
satellite
communications. For example, in at least some example embodiments, a satellite
may operate within the frequency of the C-band defined by the ITU. The C-band
is a
portion of the electromagnetic spectrum that ranges from approximately 4 GHz
to 8
GHz. That is, the communication signals are transmitted by and received at the
satellite within such a frequency range.
[0041] In some
cases, the satellite may operate within frequencies higher than 8
GHz. For example, the satellite may operate within the frequency of the Ku-
band.
The Ku-band is the portion of the electromagnetic spectrum that ranges from
approximately 10 GHz to 18 GHz.
[0042] In at least
some example embodiments, the satellite may operate within
other high frequencies, above the Ku-band. For example, the satellite may
operate
within the Ka-band frequency. The Ka-band is the portion of the
electromagnetic
spectrum that ranges from approximately 26.5 GHz to 40 GHz (at present the
assigned slots for fixed satellite service (FSS) are 27-31 GHz for uplink and
17.7-21.2
GHz for downlink).
[0043] In some
examples, the satellite may be configured to operate in more than
one band. In one example, the satellite may be equipped to receive and
transmit
signals within the C-band, Ku-band, and Ka-band.
[0044] It will be
appreciated that the satellites may operate within other
microwave frequency bands. For example, the satellites may operate in any one
of
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the defined microwave frequency bands ranging in frequencies from
approximately 1
GHz to 170 GHz. Examples of such frequency bands may include the X-band, etc.
[0045] A conventional analog payload architecture is illustrated in
Figure 1 by
way of a block diagram of an example satellite payload 10. The payload 10
includes a
receive antenna 12, such as a reflector antenna, which collects incoming RF
signal.
The received signal is amplified by a low noise amplifier 14 and the amplified
signal
is down-converted by down-converter 16 to the desired downlink frequency band.
The downconverted signal is then channelized by an input demultiplexer 18
(IMUX)
so as to map individual analog uplink channels to their corresponding downlink
channels in accordance with a predefined and fixed frequency plan. Each
channel is
then amplified using individual linearized travelling wave tube amplifiers 20
(LTWTA) with a redundancy ring switch network. The output from the LTWTAs 20
are then combined again by an output multiplexer 22 (OMUX) and fed to a
transmit
antenna 24 for transmission back to the Earth.
[0046] Some modern satellites use digital channelizers to digitize the
incoming
RF signal and make the payload more configurable. Such a digital payload
typically
includes a down-converter to convert the incoming spectrum to IF, an analog-to-
digital converter (ADC), digital multi-channel demultiplexer, digital
switching matrix,
digital-to-analog converter (DAC), up-converters, power amplifiers and
multiple spot
or phased-array antenna networks. A digital payload satellite is more
flexible, but is
also more costly, partly due to the use of a digital beamforming network,
regenerative
processor, and multi-spot/phased-array antenna networks. More significantly,
the
available solid state power amplifier (SSPA) output RF power for phased-array
signals results in a lower output power spectral density as compared to the
power
spectral density available using conventional linear travelling wave tube
amplification. In other words, the output power and efficiency of space-
qualified
LTWTA is higher than space-qualified SSPA, meaning better downlink EIRP
density
is achievable with LTWTA. The lower EIRP density available using SSPA results
in
the need for a larger receiving dish at the downlink earth station.
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Hybrid Digital-Analog Payload
[0047] In accordance with one aspect of the present application, the
uplink
frequency is digitized and channelized, but the downlink maintains a
conventional
analog transmission architecture, resulting in what may be referred to herein
as a
"hybrid" payload.
[0048] In accordance with another aspect of the present application, the
digitization of the full uplink spectrum allows for mitigating imbalance in
spectrum
allocation amongst uplink and downlink channels.
[0049] By digitizing the uplink frequency, the available frequency
resources
assigned for satellite communication by the ITU can be utilized more
efficiently
compared to a conventional payload implementation. For example, there is an
imbalance of Ku band frequency resources for the uplink and downlink band for
Region 3. Defined by the ITU, Region 3 includes most of Oceania and most Asian
countries, but excluding Russia and former Soviet Union countries. The Ku-band
uplink frequency bands are 13.75-14.00GHz (250MHz bandwidth (BW), the extended
Ku) and 14.00-14.50GHz (500MHz BW, the standard Ku), giving a total uplink BW
of 750MHz. In Region 3, the ITU has specified three available downlink
frequency
bands: 10.95-11.20GHz (250MHz, the 2"1 extended Ku), 11.45-11.70GHz (250MHz,
the 1st extended Ku), and 12.25-12.75GHz (500MHz, the standard Ku). The total
downlink BW is 1000MHz. With this mismatch, the downlink Ku-band frequency
resource cannot be fully utilized. The satellite operator can only use a
maximum of
750MHz in a wide beam or spot beam configuration. Moreover, the actual BW that
can be used in a Ku conventional spacecraft is around 648MHz because the
traditional
analog IMUX/OMUX combination required a guard-band of about 10%.
[0050] Reference is now made to Figure 2, which shows a block diagram of an
example hybrid satellite payload 100. The payload 100 in this example is for
uplink
and downlink of Ku band channels. Accordingly, the payload 100 includes a Ku
band
receive antenna 102 and a Ku band transmit antenna 114. The payload 100
further
includes the elements of a conventional analog architecture, including a LNA
redundancy network 104, Ku band down-converters 106, Ku band IMUX 108, Ku
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band LTWTA ring 110, and Ku OMUX 112. These elements function to channelize
and route the uplink band in order to implement the predetermined fixed uplink-
to-
downlink frequency plan. However, the example hybrid satellite payload further
includes a digital portion. The digital portion digitizes the entire incoming
band of
Ku spectrum and extracts the guard bands between the Ku channels. Extracted
guard
bands may then be grouped to form one or more Ku downlink channels, thereby
adding up to 10% of uplink capacity. In other words, by digitizing the uplink
band
and extracting and grouping the guard bands to form one or more downlink
channels,
the hybrid satellite payload 100 is able to recover about 102 MHz of unused
uplink
capacity.
[0051] In this example, the digital portion of the hybrid satellite
payload 100
includes an IF down-converter 116 to convert the incoming RF Ku band of
spectrum
to IF. The full down-converted band of spectrum is then digitized in an ADC
118 and
digitally channelized with a digital channelizer 120. The digital channelizer
120 in
this example sub-channelizes the digitized band of spectrum to extract
portions of the
spectrum corresponding to guard bands in the standard Ku-band analog RF plan.
A
standard Ku band channel is 54 MHz with 6 MHz guard bands. The digital
channelizer 120 then combines or groups digitized guard bands to form one or
more
composite channels. Those composite channels are then converted to analog
using a
DAC 122 and up-converted to the downlink RF frequency for Ku band using an RF
up-converter 124. The up-converted composite channels are then fed into the Ku
band LTWTA ring 110 together with the de-multiplexed analog Ku band channels
form the Ku IMUX 108. Together, they are amplified by the LTWTA ring 110 and
are multiplexed by the Ku OMUX 112 to produce the Ku downlink band of RF
spectrum that is then transmitted by the transmit antenna 114. It will be
appreciated
that the transmit antenna 114 and the receive antenna 102 may be the same
physical
antenna in many implementations.
[0052] Figure 3 diagrammatically shows example uplink frequency plan 150
and
example downlink frequency plan 160 corresponding to one implementation of the
example hybrid satellite payload 100 (Fig. 2). In this example, the uplink
frequency
plan 150 shows 12 Ku band uplink channels in a conventional frequency plan.
The
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center frequency of each 54 MHz channel is separated by 60 MHz from the centre
frequency of adjacent channels, meaning a 6 MHz guard band lies between each
of
the adjacent channels. Data may be inserted in the guard bands of the uplink
spectrum. At the satellite, the spectrum is digitized and the guard bands are
extracted
and grouped to form one or more composite channels.
[0053] In this example, the guard bands are used to form two downlink
channels
in the 2' extended Ku band between 10.95 GHz and 11.2 GHz. In the illustrated
example, the composite channels correspond to downlink channels at 11.1 GHz
and
11.16 GHz (i.e. Ku 13 and Ku14). It will be noted that, in this example, the
conventional Ku band uplink channels have been routed to Ku downlink channels
Ku01 through Ku12, each having a bandwidth of 54 MHz and separated by guard
bands, in the 1st extended Ku and standard Ku bands spanning 11.45-11.7 GHz
and
12.25-12.75 GHz, respectively.
[0054] Reference is now made to Figure 4, which shows a block diagram of
another example hybrid satellite payload 200. The payload 200 in this example
is for
uplink and downlink of C band and Ku band channels, although the figure does
not
show the uplink portion of the Ku band, which may, for the purposes of this
example,
be presumed to be a convent:onal analog Ku uplink feeding into a Ku OMUX 218.
The payload 200 is designed to digitize and extract data from the guard bands
of the C
band spectrum and to create Ku band downlink channels from the C band guard
bands. In other words, the C band guard bands are used to send uplink data
that is
then downlinked in the excess Ku band capacity.
[0055] An antenna 201 for C band and Extended C band receives signals
from
ground stations. Those signals are amplified in an LNA network 202, and the
amplified signals are fed into a conventional analog C band signal path 204,
including
a C band IMUX, LTWTA amplifiers, and C band OMUX, all configured in
accordance with a defined frequency channel routing plan. Those output signals
form
the analog C band signal path 204 are then beamed back to the Earth using a C
band
transmit antenna.
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[0056] The amplified incoming C band and Extended C band signals from the
LNA network 202 are also input to a digital processing path, which includes an
IF
down-converter 206, an ADC 208, a digital channelizer 210, a DAC 212, a Ku
band
RF up-converter 214 and a Ku band LTWTA 216 that feeds Ku band signals into
the
Ku OMUX 218. In this processing path, the C band spectrum is downconverted to
IF
and is digitized. The digital channelizer 210 then extracts the guard bands
within the
C band spectrum and group or reassembles the guard band data to form one or
more
Ku band downlink channels. These Ku band downlink channels are then converted
back to analog, upconverted to the Ku band frequency and amplified in the
LTWTA
216 before being combined in the Ku OMUX 218 with the regular Ku band channels
from the Ku band uplink/downlink payload (not illustrated). The full set of Ku
band
(and 1st extended Ku and 2'd extended Ku) channels are then transmitted using
the Ku
transmit antenna 220.
[0057] Figure 5 diagrammatically shows example uplink frequency plan 250
and
example downlink frequency plan 260 corresponding to one implementation of the
example hybrid satellite payload 200 (Fig. 4). In this example, the uplink
spectrum
250 shows 14 standard C band uplink channels and 6 extended C band uplink
channels in a conventional frequency plan. The center frequency of each 36 MHz
channel is separated by 40 MHz from the centre frequency of adjacent channels,
meaning a 4 MHz guard band lies between each of the adjacent channels. Data
may
be inserted in the guard bands of the uplink spectrum. At the satellite, the
spectrum is
digitized and the guard bands are extracted and grouped to form one or more Ku
band
composite channels.
[0058] In this example, the guard bands are used to form two downlink
channels
in the 2nd extended Ku band between 10.95 GHz and 11.2 GHz. In the illustrated
example, the composite channels correspond to downlink channels at 10.98 GHz
and
11.04 GHz (i.e. Ku 13 and Ku14). It will be noted that, in this example, the
conventional C band and extended C band uplink channels have been routed to C
band downlink channels CO1 through EC06, each having a bandwidth of 36 MHz and
separated by guard bands.
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[0059] In yet a further example, guard bands from both the C band uplink
and Ku
band uplink may be used to create composite Ku downlink channels. Figure 6
shows,
in block diagram form, one example hybrid satellite payload 300 for both C and
Ku
band uplink digitization. This example payload 300 includes a C band analog
processing path 302 and a Ku band analog processing path 304. A digital path
306
receives both the C band uplink spectrum and the Ku band uplink spectrum,
converts
both to IF, and digitizes both. The digitized spectrum is channelized,
extracting the
guard bands of both the C band spectrum and Ku band spectrum and forming
composite Ku band downlink channels from the guard band data. The composite
channels are then converted to analog, up-converted, amplified, and fed into a
Ku
band OMUX for transmission with the regular Ku band channels.
[0060] Figure 7 diagrammatically shows example uplink frequency plan 350
and
example downlink frequency plan 360 corresponding to one implementation of the
example hybrid satellite payload 300 (Fig. 6). In this example, the uplink
frequency
plan 350 shows 14 standard C band uplink channels and 6 extended C band uplink
channels in a conventional frequency plan, and 12 Ku band channels in a
conventional
frequency plan. Data may be inserted in the guard bands of the uplink spectrum
in
both the C band and the Ku band. At the satellite, the spectrum is digitized
and the
guard bands are extracted and grouped to form one or more Ku band composite
channels. Note the conventional C band downlink spectrum is not illustrated.
[0061] In this example, the guard bands from C band and Ku band are used
to
form four Ku downlink channels in the 2nd extended Ku band between 10.95 GHz
and
11.2 GHz.
[0062] It will be appreciated that, in other embodiments, various
combinations of
other bands of spectrum may be used, including Ka band, X band, etc., to send
data in
guard bands for use in creating composite Ku band downlink channels. In
further
embodiments, guard band data may be used to create composite downlink channels
for bands other than the Ku band.
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[0063] In yet another aspect, the present application discloses a hybrid
satellite
payload for a frequency plan with no uplink guard bands by using digital
channelization.
[0064] In Figure 2, the Ku band satellite payload includes a conventional
signal
path through the Ku band down-converter 106 and the Ku band IMUX 108. These
elements channelize the analog uplink signal in accordance with the pre-
designed
uplink-downlink frequency plan. The channels are then each fed into the
individual
LTWTAs 110. The parallel digital path digitizes the band of spectrum, extracts
data
from the guard bands, and groups the guard band data to form one or more
downlink
channels, which are then converted to analog and multiplexed together with the
conventionally routed analog downlink channels.
[0065] Reference is now made to Figures 19 and 20. Figure 19 shows, in
block
diagram form, an example hybrid satellite payload 370 without an analog IMUX
and
featuring full digital channelization of the uplink band of spectrum. Figure
20 shows
an uplink frequency plan 380 and downlink frequency plan 390 for the example
hybrid satellite payload 370 of Figure 19. In this example implementation,
rather than
preserving the conventional frequency plan and analog channelization, the
payload
370 digitizes and channelizes the full band of spectrum. It will be noted that
Figure
19 is the same as Figure 2, except for the elimination of the analog path,
i.e. the
elimination of IMUX 108 and Ku band down-converter 106. The payload 370
includes a digital channelizer 375 with sufficient bandwidth to digitally
channelize the
full band of spectrum (in this example, the Ku uplink band from 13.75 GHz to
14.5
GHz.
[0066] As illustrated in the uplink frequency plan 380, digital
channelization
allows for elimination of the guard bands as the full band of spectrum is
available for
data transmission.
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Parallel Output Multiplexers
[0067] In another aspect, the digital channelization of spectrum at the
satellite
allows for greater flexibility in ensuring efficient utilization of available
uplink and
downlink spectrum. In some embodiments, the downlink path may be configured to
include a second OMUX and transmit antenna feed, where the second OMUX is
designed with channels centered at the guard bands of the channels in the
primary
OMUX.
[0068] Reference will now be made to Figure 8, which shows, in block
diagram
form, an example hybrid payload 400 with dual feed downlink. In this example
the
payload 400 is configured for operation in the C band spectrum. The uplink may
include additional channel data inserted in guard bands. As illustrated, the
received
data is down-converted to IF by a down-converter 402, digitized by ADC 404,
and
channelized by digital channelizer 406. The channelizer 406 routes the
standard C
band 36 MHz channels to corresponding 36 MHz C band downlink channels, which
are then converted to analog by DAC 408, up-converted to C band frequencies by
up-
converter 410, amplified by LTWTA 412, and multiplexed by OMUX 1 414 for
output via the transmit antenna.
[0069] The channelizer 406 also extracts data from the guard bands
between the C
band uplink channels and routes that data to OMUX 2 416. The OMUX 2 416 is
configured with channels centered at one or more of the guard band frequency
of
OMUX 1 414. In some cases, the channels of OMUX 2 416 have a bandwidth that
corresponds to the respective guard bands of OMUX 1 414. In some cases, the
channels of OMUX 2 416 have a bandwidth wider than the guard bands of OMUX 1
414, which may be expected to cause interference if the channels of OMUX 1 414
are
fully utilized; however, the utilization rate of each channel may be less than
100%,
particular in the case of multi-carrier transmissions in a channel. In such as
case,
OMUX 2 416 with partially overlapping channels affords an opportunity to
improve
utilization of the available spectrum.
[0070] Figures 9A, 9B, and 9C diagrammatically show example uplink
frequency
plan and downlink frequency plans corresponding to one implementation of the
CA 02883278 2015-02-27
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example hybrid satellite payload 400 (Fig. 8). In particular, in this example
the C
band uplink frequency plan features 14 36 MHz channels separated by guard
bands.
In some cases, the guard bands may be the standard 4 MHz guard bands; however,
in
other embodiments the guard bands may have different widths, such as 6 MHz, 9
MHz, etc. The uplink frequency plan may be designed with one or more different-
sized guard bands to accommodate specialty channels using a particular
bandwidth.
In the example shown in Figure 9A, most of the guard bands are 4 MHz bands,
but a
few guard bands are 9 MHz wide.
[0071] Figure 9A also shows the corresponding downlink frequency plan via
OMUX 1, which has the same channel allocation as the uplink spectrum. In
particular, OMUX 1 shows 36 MHz channels centered with the same frequency
spacing as the uplink, leaving the same layout of guard bands. In some
embodiments,
the layout could be different, i.e. the guard bands need not have the same
arrangement
as in the uplink spectrum.
[0072] Also shown in Figure 9A is the channel plan designed for OMUX 2. In
this example, it will be noted that the channels of OMUX 2 are centered at the
guard
bands of OMUX 1. In fact, the channel bandwidths of OMUX 2 correspond to the
sizes of the guard bands of OMUX 1.
[0073] Figure 9B shows another example channel plan for OMUX 2. In this
alternative plan, the OMUX 2 channels are again centered at the midpoints of
the
guard bands of OMUX 1, but in this case the channels of OMUX 2 are wider such
that they partially overlap the OMUX 1 channels on either side of the guard
band. In
this example, the OMUX 2 channels are each 36 MHz channels (except for the
edge
channels, which are 18 MHz wide). This configuration of channels in OMUX 2
increases flexibility for dynamically allocating downlink channels between
OMUX 1
and OMUX 2 so as to maximize the used downlink frequency spectrum. For
example, in a case in which one of the OMUX 1 transponders (channels) is
operating
in a multi-carrier mode that does not occupy the full 36 MHz bandwidth of the
channel, other carriers/traffic may be routed through a partially overlapping
OMUX 2
channel for downlink over the unused portion of the spectrum. The partial
overlap of
downlink channels available through the dual OMUX configuration allows for
CA 02883278 2015-02-27
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flexibility in dynamically routing traffic so as to improve the efficient
allocation of
available spectrum, such as in a case in which the downlink traffic has a
bandwidth
wider than just the guard band of OMUX 1, and too wide to fit in the unused
portion
of an OMUX 1 channel, but narrow enough to fit within the unused portion of
spectrum in an OMUX 2 channel that partly overlaps two OMUX 1 channels.
[0074] Yet a further example is shown in Figure 9C, in which OMUX 2
features
four large bandwidth channels each overlapping three or more OMUX 1 channels.
In
this example, the OMUX 2 channel bandwidth is 143 MHz.
[0075] Combinations of these examples may also be used. For example, an
example OMUX 2 may features some channels having a bandwidth the corresponds
to guard bands in OMUX 1, and one or more channels having a larger bandwidth
that
partially overlaps the channel on either side of a guard band.
[0076] In one illustrative example, suppose that the OMUX 1 downlink
channel
centered at 3725 MHz supports 10 carrier slots, cl to c10. If the OMUX 2
alternative
1 downlink channel centered at 3745 MHz is used, then it partly overlaps the
downlink channel at 3725 MHz. In this example that may mean that carrier slots
cl-
c5 of OMUX 2 channel 3745 overlap with carrier slots c6-c10 of OMUX 1 channel
3725. In a case where only seven carrier slots are being used in OMUX 1
channel
3725, they may be allocated to carrier slots c1-c7, meaning that carrier slots
c3-c5 of
OMUX 2 are available to route other traffic. The OMUX 2 feed horn may point to
a
different geographic location than the feed horn for OMUX 1, meaning that the
excess
capacity may be used to supply signals to another location.
[0077] Figures 10 and 11 show a block diagram of an example payload 500
and
corresponding example uplink frequency plan 550 and downlink frequency plan
560,
respectively. This example payload 500 is configured to receive C band, Ku
band and
Ka band uplink spectrum, extract guard band data from the C band, Ku band and
Ka
band through digitization and channelization of that spectrum, and the
formation of
2' extension Ku band channels composed from data obtained from the digitized
guard bands. The Ku band downlink features a dual feed implementation with a
conventional Ku OMUX, shown as OMUX 1, and a second Ku band downlink
CA 02883278 2015-02-27
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channel plan via OMUX 2. OMUX 2, in this example, features channels of various
bandwidths centered at the guard bands of the Ku band channels routed through
OMUX 1. This configuration has the potential to improve downlink Ku band
utilization to about 97% in Region 3.
Dynamic Spectrum Reallocation between Spot and Regional Beams
[0078] In order to increase the capacity for broadband access, frequency
reuse
amongst multiple spot beams or hybrid multi-spot/regional beams are commonly
implemented. Usually for a given satellite, the bandwidth assigned to each
spot beam
is uniform and the frequency plan is fixed with little flexibility. However,
the actual
operational traffic loading is never evenly distributed geographically. The
capacity
demand on each spot beam may also change with time and the maturity of the
terrestrial telecommunication infrastructures. Therefore, areas with high
traffic
demand may not always have sufficient services available and the regions with
lower
demand may have spare capacity that cannot be released for use elsewhere.
[0079] A hybrid regional/spot beam payload may alleviate this problem to
some
degree, as the bandwidth of a regional beam may be used to supplement the
bandwidth of a spot beam as long as the spot beam is covered by the regional
beam.
By using digitization of uplink spectrum, capacity may be allocated
dynamically with
sub-channel routing. This may be realized by feeding the uplinks of a few
selected
spot beams and the regional beam into a digitizer and then routing the output
to the
corresponding beams according to actual traffic demand. If the capacity of the
selected spot beam is fully engaged, then the satellite may reallocate vacant
capacity
from the regional beam to resolve this imbalance traffic issue.
[0080] Reference is now made to Figure 12 and Figure 13. Figure 12 shows
an
example of a regional beam coverage area 600, and 12 spot beam coverage areas
602
(individual labelled as DOL D02, ... D12). Figure 13, shows the uplink and
downlink
frequency plans for the regional beam (RU01, RU02, RD01 and RD02) and the spot
beams, all operating in the Ka band. Left-hand circular polarization (LHCP)
and
right-hand circular polarization (RHCP) is used to allow frequency re-use. The
regional beam covers all small spots but the frequencies assigned for the
regional and
CA 02883278 2015-02-27
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spots beams are different. The uplink and downlink spot beams are indicated as
U01/D0L UO2/D02 U12/D12. The regional beam is designated as RU01/02 for the
uplink and RD01/02 for the downlink. The regional beam takes 500MHz nominal
bandwidth for each of the two orthogonal polarizations. The spot beam nominal
bandwidth is 250MHz each in one of the two polarizations, as the standard 4-
color
reuse scheme (spot beams reused with the same color are non-adjacent to reduce
the
co-pol interference) is used for the spot downlinks.
[0081] If there is a high demand on spot beam U01/D01, then, using the
input
digital channelizer, part of the regional beam RU01/RD01 capacity may be
dynamically reallocated to spot beam U01/D01,. In this example, the re-
allocatable
250 MHz frequency block of RU01/RD01 spectrum is indicated by reference
numeral
604.
[0082] Reference is now made to Figure 14, which shows, in block diagram
form,
an example payload 700 for dynamically reallocating regional beam spectrum to
a
spot beam. The payload 700 in this example includes an IF down-converter 702
into
which both the received regional beam RUO1 and received spot beam U01 are fed.
The downcoverted IF is then converted to digital and channelized by the ADC
704
and digital channelizer 706, respectively. Once digitized, the frequency
spectrum of
the two beams may be reallocated through IF routing. Since regional beam RD01
is
downlinked to a dedicated band, it will not interfere with the rest of the 4-
color reused
spot beams.
[0083] The payload 700 includes a conventional output path to the
regional beam
downlink antenna 708, including an LTWTA 710 and a bandpass filter 712 that
passes the 500 MHz of regional beam spectrum in accordance with the frequency
plan. However, the output path to a downlink spot beam antenna 714 for DO1
includes a diplexer 716 to split the output analog spot beam, which is then
passed
through a pair of channel bandpass filters: channel A 718 and channel B 720.
The
channel B bandpass filter 720 is the normal spot beam bandpass filter
corresponding
to the allocated frequency slot for spot beam D01. The channel A bandpass
filter 718
passes the shareable portion of the regional beam spectrum. The filtered
signals are
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then recombined by a second diplexer 722 and sent to the downlink spot beam
antenna 714.
[0084] The digital
channelizer 706 dynamically reallocates a portion, or all, of the
shareable regional beam spectrum from the regional beam to the spot beam if
the
regional beam does not require the spectrum and traffic demand in the area of
the spot
beam requires additional spectrum.
[0085] Reference is
now made to Figure 15, which shows example frequency plan
diagrams to illustrate the dynamic reallocation of spectrum in the example
payload
700. In this example, a first frequency plan diagram 750 shows the spectrum
without
reallocation. The uplink spectrum allocated to the regional beam is 500 MHz
between
28 GHz and 28.5 GHz. The downlink spectrum for the regional beam is 500 MHz
between 18.3 GHz and 18.8 GHz. The uplink spot beam uses 250 MHz between 28.5
GHz and 28.75 GHz, and the downlink spot beam uses 250 MHz between 19.7 GHz
and 19.95 GHz.
[0086] A second frequency plan diagram 760 illustrates the situation when
50
MHz of the regional beam spectrum is reallocated for use by the spot beam. In
this
example, it will be noted that the uplink spectrum for the regional beam is
now 450
MHz, spanning 28 GHz to 28.45 GHz, whereas the uplink spectrum for the spot
beam
is now 300 MHz spanning 28.45 GHz to 28.75 GHz. Similarly, the downlink for
the
regional beam has 450 MHz between 18.3 GHz and 18.75 GHz. The downlink for the
spot beam now uses 50 MHz from 18.75 GHz and 18.8 GHz plus its usual spectrum
from 19.7 GHz to 19.95 GHz.
[0087] A third
example frequency plan diagram 770 shows full reallocation of the
shareable regional beam spectrum to the spot beam. In this example, the
regional
beam now occupies only 250 MHz of the uplink and downlink spectrum, and its
shareable spectrum is now fully allocated to the spot beam.
[0088] In the above
example shown in Figure 14, only one spot beam, U01/D01,
is configured to use the shareable spectrum from the regional beam. However,
it will
be understood that some, or all, of other spot beams (UO2/D02, U12/D12) may
be
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configured so as to be capable of sharing the reallocatable spectrum from the
regional
beam if the those spot beams are also routed through the digital channelizer
706.
[0089] Advantageously, the digital channelizer 706 is able to reallocate
fractions
of the available sharable bandwidth from the regional beam to one or more of
the spot
beams as traffic demand changes.
[0090] The above example, illustrates the dynamic reallocation of a
portion of the
regional beam spectrum to a spot beam. In another aspect, uplink spectrum may
be
shared between a regional beam and a spot beam.
[0091] Reference will now be made to Figure 16, 17 and 18 to illustrate
an
example implementation of sharing uplink frequency spectrum between a regional
beam and a spot beam. Figure 16 shows an example of a regional beam coverage
area
800 and coverage areas 802 for various spot beams within the regional beam
coverage
area 800. Figure 16 shows an uplink location 806 for the spot beam U01/D01. It
will
also be noted that the uplink location 804 for the regional beam is outside of
the spot
beam U01/D01 coverage area 802. In this example, the regional beam uplink
location
804 happens to be outside the location of all spot beam coverage areas 802,
but it is
not necessarily case in other embodiments.
[0092] Figure 17 shows diagrams for the uplink and downlink frequency
plans.
In this example, the uplink for the regional beam spans from 28 GHz to 28.5
GHz,
and the uplink for the spot beams U01 and UO2 span 28.25 GHz to 28.75 GHz. In
other words, the allocated uplink spectrum for the regional beam and one or
more spot
beams overlaps. The block of spectrum denoted by reference numeral 810 is
"shared"
spectrum, i.e. it may be used by both the regional beam uplink and spot beam
uplink
at the same time.
[0093] Figure 18 shows a portion of an example payload 820 for sharing
uplink
spectrum between a regional beam and a spot beam. In this example, the payload
820
uses digital cancellation to separate the two signals. As illustrated, the
regional beam
antenna will receive signals from both the regional beam uplink location 804
and the
spot beam uplink location 806. Thus, the signals in the shared spectrum 810
will
CA 02883278 2015-02-27
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cause interference with each other. The spot beam antenna, having a narrow
beamwidth that excludes the regional beam uplink location 804, will only
receive the
spot beam uplink signal. Accordingly, both received signals are digitized by
ADC
822 and the spot beam uplink signal is then digitally subtracted from the
signal
received by the regional beam antenna,. which removes the interfering spot
beam
signal and leaves the regional beam signal.
[0094] Although the above example uses the Ka band for illustration, it
will be
understood that the same uplink sharing through digital cancellation may be
applied to
the C band or Ku band in other examples.
[0095] Example embodiments of the present disclosure are not limited to any
particular type of satellite or antenna.
[0096] The various embodiments presented above are merely examples and
are in
no way meant to limit the scope of this application. Variations of the
innovations
described herein will be apparent to persons of ordinary skill in the art,
such
variations being within the intended scope of the present application.
Additionally,
the subject matter described herein and in the recited claims intends to cover
and
embrace all suitable changes in technology.
