Note: Descriptions are shown in the official language in which they were submitted.
CA 02531551 2005-12-23
MANAGEMENT OF A SATELLITE NETWORK USING A NETWORK BUDGET
FIELD OF THE INVENTION
The present invention relates to the field of satellite communications and
more
particularly concerns the use of a network budget in the management of a
satellite
network.
BACKGROUND OF THE INVENTION
The continuing introduction of new, advanced satellite technologies has
already
io brought about the reality of affordable interactive broadband services
delivered by
satellite directly to the subscriber. In this era of global connectivity,
satellite
delivery offers a unique advantage by increasing the reach of such services to
areas that cannot be connected through, or are underserved by, terrestrial
means.
However, the supporting satellite networks have become very large and more
difficult to build and manage, requiring tools that can handle the large
number of
complex factors affecting the system design, the on-going quality of service,
and
the overall economics of the services provided.
Link budgets are tools used in the design and running of satellite networks.
They
2o are computer programs used to determine power levels and other signal
quality
indicators in a satellite link, taking into account the various factors
affecting signals
along communications paths. Link budgets are often built using spreadsheet
applications in which well-established operations are performed using
appropriate
values for each contributing factor. Typically, the considered factors include
signal
gains and losses from precipitations and other climatic effects, satellite
transponders, power amplifiers and antennas, as well as interferences due to
atmospheric noise and other signals from the same or another satellite. These
values must be skilfully evaluated or estimated, and then manipulated within
the
link budget, as they will determine the obtained result.
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CA 02531551 2005-12-23
Satellite link budget analysis is well established for the links of networks
with a
small number of beams, such as is typical for satellites operating in the C or
Ku
frequency bands. These satellite systems are relatively simple, with
straightforward satellite and ground systems, a small number of large beams to
provide the required coverage, and only minor inter-beam considerations. In
these
cases, the link budgets pertain to individual links, or to small networks
operating
within a given beam.
More recently, in order to better support the emerging demand for direct-to-
user
io interactive services, satellite systems have introduced more complex
payloads
operating at higher frequency bands such as the Ka-band and the V-band. The
higher frequencies enable the creation of smaller spot beams, which in turn
allow
the satellite systems to provide higher power levels on the ground by
concentrating the available power. The increased power levels ensure that
direct-
to-user services can be offered with small, affordable user antennas. At the
same
time, advanced technologies are incorporated into the satellite payload and
the
ground equipment to mitigate the higher levels of propagation effects at the
higher
operating frequencies.
While these changes allow expansion of market opportunities, there is a need
for a
tool for satellite network design and management more practicle than
traditional
link budgets, in order to deal with the new factors being introduced.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the present invention, there is provided
a
method for building a network budget for a satellite network. The satellite
network
has a plurality of links, each including an uplink beam transmitted to a
satellite of
the satellite network and a downlink beam transmitted from this satellite. The
method includes, for each of these links:
a) estimating an initial power level of the uplink beam ensuring reception
thereof at the satellite;
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CA 02531551 2005-12-23
b) estimating a power level of the downlink beam at each of a plurality of
receiving locations receiving the downlink beam; and
c) estimating power variations affecting the downlink beam.
In accordance with another aspect of the invention, there is also provided a
computer readable medium having at least one module for building a network
budget for a satellite network recorded thereon. The satellite network has a
plurality of links, each including an uplink beam transmitted to a satellite
of the
satellite network and a downlink beam transmitted from this satellite. The at
least
io one module is operable to:
estimate an initial power level of the uplink beam ensuring reception thereof
at
the satellite;
estimate a power level of the downlink beam at each of a plurality of
receiving
locations receiving this downlink beam; and
1s estimate power variations affecting this downlink beam.
According to yet another aspect of the invention, there is also provided a
method
for managing a satellite network including:
a) building a network budget for the satellite network, the network budget
20 including at least one test parameter;
b) obtaining a predicted capacity of the satellite network using the network
budget; and
c) determining at least one set up parameter of the satellite network based on
the predicted capacity.
According to another aspect of the invention, there is further provided a
method for
optimizing reception of a receiver at a receiving location in a satellite
network. The
method includes:
a) building a network budget for the satellite network;
b) determining a target signal-to-noise ratio for the receiving location using
the
network budget; and
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CA 02531551 2005-12-23
c) optimizing a set-up of the receiver in order to obtain an effective signal-
to-
noise ratio close to the target signal-to-noise ratio.
Other features and advantages of the present invention will be better
understood
upon reading of preferred embodiments thereof with reference to the appended
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic illustration of components of a typical satellite
network to
io which the present invention may be applied.
FIG. 2 is a schematic representation of a network budget according to one
aspect
of the invention.
FIG. 3 is a flow chart of a method of building a network budget according to
one
embodiment of the invention; FIG. 3A represents the power variations taken
into
account in an embodiment of the method of FIG. 3.
FIG. 4 is a flow chart illustrating the steps of a method for managing a
satellite
2o network according to one embodiment of the invention.
FIG. 5 is a flow chart illustrating the steps of a method for optimizing
reception of a
receiver at a receiving location in a satellite network, according to another
embodiment of the invention.
FIGs. 6A and 6B represent link budgets obtained through a network budget
according to one embodiment of the invention, respectively for a forward and a
return link of a satellite network.
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DETAILED DESCRIPTION OF THE EMBODIMENTS
In accordance with a first aspect of the present invention, there is provided
a
network budget for a satellite network and a method of building such a network
budget.
Typically, with reference to FIG. 1, the satellite network 10 to which this
particular
aspect of the invention is directed includes at least one satellite 12 in
orbit above a
geographical region of interest, which allows the exchange of data between a
number of gateways 14 and a plurality of terminals 16. Only one gateway 14 and
io one terminal 16 are shown in FIG. 1, for simplicity. Each of the satellite
12,
gateways 14 and terminals 16 is provided with at least one antenna for
transmitting and/or receiving electromagnetic radiation, typically at
microwave
frequencies. For example, in the context of the provision of internet
services, the
gateways 14 may be in terrestrial communication with one or more internet
service
providers 18 for providing access to a data network 20 such as the internet.
Each
terminal 16 is located at the premises of a subscriber to such services, and
may
therefore be connected to a subscriber computer system 22. It will be
understood
that the provision of internet services is given here as an exemplary purpose
of the
satellite network, but that the satellite network could equally be used to
transmit
2o data in another context such as television services, telephone services,
etc.
Different types of beams are shown in FIG. 1, each operating at its own
dedicated
operating frequency. It will be noted that different beams may share the same
operating frequency. More precisely, beam A is an uplink beam transmitting
data
from the gateway 14 to the satellite 12, and beam B is a downlink beam
transmitting data from the satellite 12 to the terminal 16. Optionally, a beam
C
transmitting data from the terminal 16 to the satellite 12 and a beam D
transmitting
data from the satellite 12 to the gateway 14 may also be provided. Each set of
uplink and downlink beams allowing the transmission of information between a
gateway and a terminal is referred to as a "link". In the illustration of FIG.
1, beams
A and C form together a forward link, and beams B and D form together a return
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link. It will however be noted that communications with the satellite 12 need
not
necessarily be two-way; for example, in the context of internet services
provision,
the data to be sent back to the internet service provider 18 may be
transmitted
through phone lines or other terrestrial communication methods.
All communications with the satellite are transmitted at frequencies within a
frequency band associated with this particular satellite (such as 12). Such
frequency bands are usually standardized. For example, operating frequencies
between 4 and 8 GHz are generally associated with the C band, while the Ku
band
lo operates in the 12-18 GHz range, the Ka band operates in the 18-30 GHz
range,
and the V band in the 40-75 GHz range. A given satellite (such as 12) may have
more than one dedicated frequency band.
Higher operating frequencies allow the generation of smaller beams. Among the
frequency bands given as an example, the Ka and V bands will therefore
generate
beams having a smaller spot size, which allows the satellites to provide
higher
power on the ground. However, more beams are then required for the same
coverage area, necessitating frequency re-use to cover wide areas and provide
sufficient bandwidth for the subscribers. It will be understood that this
results in
potentially significant interference into each beam due to other beams sharing
the
same frequencies.
While the present invention is particularly advantageous in the context of
communications through the Ka band, it will be understood by one skilled in
the art
that it could equally be applied to the C band, Ku band, V band, or any other
relevant frequency band.
Referring to FIG. 2, there is shown an example of a network budget 24
according
to one embodiment of the invention. The expression network budget is used
3o herein to refer to an accounting of the relevant factors affecting the
transmission of
signals throughout the entire satellite network. In one embodiment, it is an
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CA 02531551 2005-12-23
advantageous feature of the present invention that the network budget is not
built
for just one link, as with traditional link budgets, but for the entire
satellite network,
that is, for all the links 26a, 26b, 26c, etc, transmitting data from between
the
gateways and the terminals. The network budget 24 may therefore be used on a
much larger scale compared to standard link budgets.
The network budget 24 may be embodied by a computer program including at
least one module recorded on a computer readable medium. For simplicity, the
computer program embodying the network budget 24 will be described below as a
lo single module, but it will be understood by one skilled in the art that it
may in
practice include any appropriate number of modules or sub-modules operable to
accomplish the functions described below. The module in question is operable
to
build the network budget 24 according to a method of the present invention,
the
steps of which will be described with reference to FIGs. 3 and 3A.
Referring to FI G. 3, the method 100 first includes estimating 102 an initial
power
level of the uplink beam of each link, sufficient to ensure reception of this
uplink
beam at the satellite. This estimating may for example include calculating a
curve
fit of the emitted power level of the uplink beam from the ground emitter,
that is,
the power level of the beam generated at the gateway 14 for a forward link and
at
the terminal 16 for a return link, as a function of distance from the center
of the
uplink beam. The curve fit may be performed using a third degree polynomial
fit.
Power variations affecting this uplink beam are then estimated and taken into
account. In this manner, a measure of the necessary power to ensure proper
reception of the uplink beam at the satellite 12 may be obtained.
The method 100 next includes estimating 104 a power level of each downlink
beam at each of a plurality of receiving locations within the corresponding
downlink beam. This again may involve performing a curve fit, such as a third
3o degree polynomial fit or other, as a function of distance from the center
of each
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CA 02531551 2005-12-23
downlink beam. Power variations affecting each downlink beam are then
estimated 106.
Referring to FIG. 3A, in accordance with one embodiment of the invention, the
power variations affecting either the uplink beams or the downlink beams are
based on an estimation of all factors having an impact on the quality of the
signal
of a given uplink or downlink beam, which include interference factors 42,
power
gains 28 and power losses 30.
io The interference factors 42 affecting a given beam along its path for
example
include thermal noise, equipment noise, and noise from receivers both on the
satellite and on the ground. Interference is present when multiple signals are
transmitted through a non-linear device, such as a satellite transponder.
Interference calculations also include an evaluation of the interference from
other
beams of the satellite network and from other satellites. Inter-beam
interference is
particufariy relevant when the satellite netvrork involves frequency re-use,
that is,
that at least two uplinks or two downlinks of the satellite network have a
same
operating frequency. Such will typically be the case for Ka band satellite
networks.
2o A number of attenuation factors may influence the power losses 30 for a
given link.
The relevance and impact of each such factors will vary depending on the
components of the satellite network, its geographical set up, its operating
frequency, etc.
Precipitations 36, such as rain or snow, is one factor which creates power
losses
in an uplink or downlink beam travelling in the affected geographical region.
These
losses are felt more acutely at higher operating frequencies. Although they
can
often be ignored for the C and Ku Bands, rain attenuation losses are to be
taken
into consideration for communications through the Ka and V bands, especially
in
3o regions where statistics show that such precipitations are frequent.
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CA 02531551 2005-12-23
The network budget 24 may also factor in the use of at least one fade
mitigation
technique 34, which adds to the power gains 28 by mitigating losses. A number
of
such techniques are weA known in the art for compensating for power losses in
a
satellite link. For example of fade mitigation techniques, reference may be
made to
a publication by Athanasio et al. entitled "Satellite Communications at Ku, Ka
and
V Bands: Propagation Impairments and Mitigation techniques" (IEEE
Communications Surveys & Tutorials- Third Quarter 2004), which is incorporated
herein by reference. It is an advantageous feature of the network budget 24
that all
such techniques, and others not covered by the reference, may be simulated to
io provide a measure of their effectiveness. The simulation generally involves
modelling the operation of the fade mitigation technique, and calculating its
effectiveness with a rain fade model. Available rain fade models for example
include Crane Global, ITU-R P618-x and Crane revised 2.
1s In addition to precipitations fading, other atmospheric losses 38 may also
have an
impact on the power level of an uplink or downlink beam significant enough to
warrant taking them into consideration in building the network budget.
Atmospheric
losses 38 for example include atmospheric absorption by gases, cloud, fog and
smoke, which become more significant at high frequencies. Dispersive losses
20 caused by the accumulation of water droplets from precipitations or dew on
antennas may also be taken into consideration. This phenomenon is referred to
as
antenna wetting 40. Other losses include propagation losses, as is normal for
radiation over long distances, antenna pointing error losses, and equipment
interconnection cable losses.
Each of these factors may be taken into consideration in the network budget 24
by
the inclusion of a constant loss value. For example, atmospheric absorption 38
of
all kinds may be associated with a typical loss of 0.5 dB, or any other
appropriate
value. Losses due to antenna wetting 38 may be as high as 3 dB for high
frequencies, but may be of any other value depending on the particular
9
CA 02531551 2005-12-23
characteristics of a given system or the presence of shielding or hydrophobic
coating on the antenna.
Referring back to FIG. 2, the module of the network budget 24 may be further
operable to input 44 a query to the network budget 24 and obtain as output 46
information on the satellite network responsive to this query. Advantageously,
since the network budget 24 includes the entire satellite network and not just
one
beam, the query may for example include only the geographical coordinates of
an
existing or future terminal, and the network budget 24 will be capable of
providing
to any required data relative to service to these particular geographical
coordinates.
It is not necessary to know in advance which link applies. The data in
question
may include an identification of the corresponding uplink and downlink beams,
and
a full link budget for this link. This link budget may for example include the
initial
power level of the uplink beam of this link, the power level of the downlink
beam at
1s the receiving location corresponding to said geographical coordinates,
information
on the power variations affecting the uplink and downlink beams, etc. The data
may further include the operating frequencies of the uplink and downlink
beams,
an identification of a gateway serving these geographical coordinates, a
target
signal-to-noise ratio thereat, etc. Exemplary representations of link budgets
20 obtained through an embodiment of the present invention are shown on FIGs.
6A
and 6B, respectively for a forward link and a return link.
Referring to FIG. 4, and in accordance with another aspect of the invention,
there
is also provided a method 110 for managing a satellite network. This method
may
25 be applied to satellite networks such as shown, for example, in FIG. 1. The
satellite network may operate at operating frequencies within the C, the Ku,
the Ka
and the V frequency bands, and is particularly advantageous when used for
multi-
beams, such as Ka or V band, satellite networks.
3o The method 110 for managing a satellite network first includes a step of
building
112 a network budget for the satellite network. The network budget may include
an
CA 02531551 2005-12-23
accounting of the relevant factors affecting the transmission of signals
throughout
the entire satellite network. In one embodiment, the network budget may be
built
according to the method described above with reference to FIGs. 3 and 3A.
The building of the network budget can involve providing in this network
budget at
least one test parameter. The test parameter may be embodied by any parameter
whose impact on the network budget may be tested. In one example, the test
parameter is the initial power level of at least one of the beams of the
network,
such as the uplink and/or downlink beams of a given link, all the uplink
and/or
lo downlink beams of the network, or sub-sets thereof. The network budget is
therefore built to represent the state of the network should this test
parameter
correctly represent reality.
In another embodiment, the test parameter may be at least one power variation
factor affecting at least one of the uplink or downlink beams of the network.
This
embodiment may for example be used to test estimated value for power gains,
power losses or interference effects.
The method 110 for managing a satellite network further includes a step of
obtaining 114 a predicted capacity of the satellite network, using the network
budget built in the previous step. In one embodiment of the invention, the
predicted capacity provided by the network budget may include an estimated
power level of one or several of the downlink beams at each of at least one
receiving location receiving this particular downlink beam. In this manner,
the
quality of the received signal at one or more receiving locations, such as the
location of a terminal or gateway, can be evaluated for a given test
parameter. The
obtained estimated power levels may also be compared with a predetermined
minimum acceptable power level. The estimated power level available may be an
average value or a minimal value. In another embodiment, the predicted
capacity
may be an availability percentage corresponding to the percentage of the time
for
which the power level is sufficient, at a given receiving location, to provide
the
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CA 02531551 2005-12-23
services to which the corresponding subscriber is subscribing. This value may
further be compared to a minimum acceptable availability. For example, in some
circumstances, it has been found that it may be desirable to have an average
availability of 99.8% in order to meet the expectations of subscribers as to
quality
of service in the context of internet services provision.
The method 110 for managing a satellite network also includes a step of
determining 116 at least one set up parameter of the satellite network based
on
the obtained predicted capacity. A number of alternative embodiments may be
io considered for the set up parameter. For example, the set up parameter may
be
an addition of supplementary equipment to the satellite network, or an upgrade
of
at least one component of the satellite network such as an antenna, a modem or
a
software application. In all cases, the equipment added or upgraded may be
located at a gateway or terminal of the satellite network. Required satellite
configuration changes may also be considered.
As will be understood, through the present method 110, the obtaining of the
predicted capacity of the satellite network gives valuable information as to
the
requirements necessary to maintain or improve services to subscribers, and
allows
planning accordingly. Interestingly, the building of the network budget may be
performed based on either existing or supposed characteristics of the
satellite
network. The present method 110 may also be used in a repetitive or iterative
manner, for example to obtain a set up parameter such as an equipment upgrade,
and then incorporating this upgrade in the network budget to see its effect on
the
predicted capacity. In this manner, the evolution of the satellite network may
be
optimized in a well-managed manner instead of blindly.
In another embodiment of the present method, the set up parameter may
correspond to a pricing structure for services provided through the satellite
3o network. Advantageously, by predicting the available power levels in a
given set of
circumstances, it becomes possible to predict the cost of operating the
satellite
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CA 02531551 2005-12-23
network and providing good quality of services, and therefore determine how
much
subscribers should be billed for those services.
In yet another embodiment of the invention, the method 110 for managing a
satellite network could be used prior to the deployment of the satellite
network, in a
planning phase. The present invention could therefore be used to explore
different
scenarios for setting up the satellite network and addressing its growth over
time.
In such a case, the building of the network budget may be based only on test
parameters representing planned or considered characteristics of the future
lo satellite network.
Referring now to FIG. 5, there is shown a method 120 for optimizing reception
of a
receiver at a receiving location in a satellite network, according to yet
another
aspect of the invention. The expression "receiver" is used herein to refer to
any
piece of equipment or group of equipment provided for the reception of a
signal
from a satellite, and the expression "receiving location" refers to the
location of
such equipment. In one embodiment, this method 120 is used for the
optimization
of the installation of antennas and related devices of terminals located at
subscriber premises, for example in the context of a satellite network as
illustrated
in FIG. 1. The satellite network may operate at operating frequencies, for
example
within the C, Ku, Ka and V frequency bands, and is particularly advantageous
when used for Ka band satellite networks.
The method 120 for optimizing reception first includes a step of building 122
a
network budget for the satellite network. The building 122 of the network
budget
may be similar to the building step 112 already described above.
The method 120 for optimizing reception also includes a step of determining
124 a
target signal-to-noise ratio for the receiving location, using the network
budget built
in the previous step. In one embodiment, the target signal-to-noise ratio is
determined by calculating an estimated power level available in a downlink
beam
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CA 02531551 2005-12-23
received at a particular receiving location. This may for example involve
performing a curve fit of an initial power level available in the downlink
beam as a
function of the distance of the receiving location from the center of this
downlink
beam. This curve fit may be performed using a third degree polynomial fit. The
impact of power variations affecting this downlink beam on the initial power
level
available is also estimated. Noise from equipment at the receiving location
itself
can also be taken into consideration.
Advantageously, the target signal-to-noise ratio may be a value automatically
1o outputted by the network budget, as shown in the examples of FIGs. 6A and
6B. In
one embodiment, a person installing or verifying the installation of a
receiver may
have access to the network budget from the receiving location, for example
through a computer remotely connected to the internet or a private network,
and
obtain the target signal-to-noise ratio therefrom for this particular
receiving
location. Alternatively, this person may reach a remote operator via telephone
and
obtain the target signal-to-noise ratio verbally.
The method 120 of optimizing reception also includes a step of optimizing 126
a
set-up of the receiver in order to obtain an effective signal-to-noise ratio
close to
the target signal-to-noise ratio. The effective signal-to-noise ratio
corresponds to a
value actually measured at the receiver location. By comparing this value to
the
target one predicted by the network budget, it is possible to make sure that
the
installation is in fact optimal.
Previously, optimizing a receiver installation involved measuring the
effective
signal-to-noise ratio for different orientations of the antenna and
identifying a
position at which the measured signal was maximal. The antenna was then set to
this particular position. This approach however leaves a number of
uncertainties
which may lead to installation problems being overlooked. For example, false
maxima may be present in the variation of the effective signal-to-noise ratio
as a
function of the orientation of the antenna, and the selected orientation may
not be
14
CA 02531551 2005-12-23
the optimal one. In addition, the identification of a maximum in the signal-to-
noise
ratio variation will not bring to light problems in the receiver equipment
which may
reduce reception evenly for all orientations of the antenna.
By contrast, the method 120 according to the present aspect of the invention
allows the immediate verification of the installation by providing an
empirical target
value for the signal-to-noise ratio to which the measured effective signal-to-
noise
ratio may be compared. An error margin may be allowed between the effective
signal-to-noise ratio and the target signal-to-noise ratio depending on the
degree
io of precision required in a given installation, on meteorological
conditions, etc. This
error margin may for example be of the order of 3 dB or less.
If, through the present method 120, it is determined that the installation of
the
receiver is not optimal, then appropriate corrective actions can be taken. In
one
1s embodiment, the orientation of the antenna may be further modified or
scanned in
order to find the true maximum of the variation of the effective signal-to-
noise ratio.
Should the problem not be linked to the orientation of the antenna, then the
equipment itself may be at fault, and appropriate testing may reveal that a
particular piece of equipment may need to be fixed or replaced. In such
situations,
20 the source of the problem may simply be a wire which is too long or faulty
or
wrongly configured software. Once made aware that a problem exists through the
application of the present method 120, one skilled in the art will be able to
use
appropriate techniques to locate the source of this problem and fix it.
25 Advantageously, the method for optimizing reception 120 may be performed
during the initial installation of any receiver. It may- also be performed
subsequently, at least once during a service life of the receiver, at any
appropriate
point in time. For example, this method 120 may be usefully performed upon
report of service difficulties from a subscriber, or at random or periodical
service
30 checks.
CA 02531551 2005-12-23
Of course, numerous modifications could be made to the embodiments above
without departing from the scope of the present invention as defined in the
appended claims.
16
