MXPA99009150A - Method and apparatus for determining the antenna orientation parameters in a satel receiver - Google Patents

Abstract

A method and apparatus for pointing or orienting a satellite antenna or a target satellite allows a user to support a commonly known geographic designator, such as a ZIP code. From the ZIP code, the longitude and latitude of the antenna is determined. The user also supports the length of the target satellite or the name of the satellite from which the length is queried. The system also makes reference to a variation model in the Earth's magnetic field in order to determine the variation in the location of the antenna and correct the parameters of orientation or aim for that variation.

Description

"METHOD AND APPARATUS FOR DETERMINING THE ANTENNA ORIENTATION PARAMETERS IN A SATELLITE RECEIVER" FIELD OF THE INVENTION The present invention relates to the field of satellite communications. More particularly, the present invention relates to an improved method for determining the initial parameters needed to correctly point a vessel or antenna of the satellite to a specific target geosynchronous satellite from which a communication signal will be received.

BACKGROUND OF THE INVENTION Geosynchronous satellites are used, for example, to transmit data, voice, telephony and analog / digital television signals from an uplink location to one or more users in various downlink locations. The geosynchronous satellites are placed in orbit in the equatorial plane of the Earth at an altitude of 35,784 kilometers. At this altitude, the satellite's orbital period is equivalent to a sidereal day (86.156 seconds). In other words, the satellite is placed in orbit in the Earth at approximately the same speed with which the Earth rotates around its axis. The result is that the satellite appears stationary for observers on the surface of the earth and can transmit communication signals along a direct line of sight to all land-based receivers that are not beyond the satellite's horizon. Typically, satellite receiving antennas include a parabolic reflector vessel that focuses the satellite signal transmitted to an antenna feed. The power converts the electromagnetic wave energy into electrical signals that can be decoded and / or presented by the end user's equipment, for example, a television set. Because the transmission of communication signals from the satellite is along a direct line of sight path, an antenna used to receive these signals from geosynchronous satellites must point exactly to the satellite in its orbital position. Antennas with large vessel openings have a greater gain than smaller vessels and therefore require that they be aimed more accurately at the broadcast satellite. The opening of the vessel is the shape of the antenna as it looks down from its axis of the plate viewer.

The parameters used to describe the direction in which the satellite antenna is pointed are typically the azimuth (measured in degrees from the true north direction at the antenna site) and elevation (measured in degrees from the local horizontal plane). The azimuth ("AZ") and elevation ("EL") required to point an antenna to a specific satellite are easily determined from simple geometric considerations once the latitude and longitude of the antenna, the length of the satellite that is being placed in white they are known. Figure 1 illustrates a typical satellite vessel 101 that is aimed to communicate with a satellite 102 in the geosynchronous orbit. As illustrated, the elevation (EL) of the vessel is the angle between the axis of the vessel radius and the horizontal plane. The azimuth (AZ) of the vessel is the angle between the vertical plane that contains the axis of the radius of the vessel and the true north (N). Satellite antenna systems typically include the necessary electronic components to monitor the azimuth and elevation of the antenna. The motorized systems capable of moving the antenna can then be placed in a feedback loop with the azimuth and elevation monitoring systems. With this circuit, the antenna can move automatically from a known orientation to one in which it is pointed exactly to a target satellite that corresponds to a specified azimuth and elevation. An azimuth of the antenna can be measured more or less using a magnetic compass to determine true north. However, because the Earth's magnetic field varies locally at every point on the surface of the Earth, the compass that reads only can not result in a perfectly accurate determination of the real azimuth of the antenna. Therefore, the satellite's point will also contain an error factor. Accordingly, there is a need in the art for a method and apparatus for aiming a satellite antenna that more accurately determines the azimuth of the satellite antenna so that the antenna can be more accurately targeted to a target satellite.

COMPENDIUM OF THE INVENTION Accordingly, an object of the present invention is to meet the needs described above and others. Specifically, an object of the present invention is to provide a method and an apparatus for more precisely determining the required azimuth of a satellite antenna so that the antenna can be more accurately targeted. A further object of the present invention is that the method and apparatus of the present invention are implemented so that they can be easily operated by an average person without training or technical capability in satellite communications. The additional objects, advantages and novel features of the invention will be pointed out in the description given below or that can be learned for those persons skilled in the art through the reading of these materials or of putting the invention into practice. The objects and advantages of the invention can be achieved through the means mentioned in the appended claims. To achieve these manifested and other objects, the present invention may be encompassed and described as a method for targeting a satellite antenna on a target satellite by determining the local magnetic variation in the earth's magnetic field; and calculating an azimuth in which the antenna is going to be aimed that is corrected for local magnetic variation. The determination of the local magnetic variation is achieved by receiving location designation data from a user designating an antenna location; and determining the local magnetic field variation that corresponds to that location.

The determination of the variation of the local magnetic field is carried out using a model that represents the variations in the magnetic field of the earth. Preferably, the model used is the International Geomagnetic Reference Field (IGRF) model. When the location designation data is received, the system of the present invention can receive the antenna's longitude and latitude if they are known, and are input by the user. Alternatively, the system may be receiving the location designation data comprising a well-known location designator, such as the ZIP Code of the antenna, admitted by the user. When the ZIP Code is admitted, the method of the present invention includes matching the ZIP Code with a longitude and latitude of the ZIP Code. The method also includes receiving target designation data from the user. The receipt of the designation data of the target satellite includes receiving the length of the target satellite if it is known and admitted by the user. Alternatively, the method may include receiving a name of the target satellite from the user and determining a satellite length by reference to a query box that correlates satellite names and lengths.

The present invention also encompasses a method for targeting a satellite antenna that does not include correction for local variation in the Earth's magnetic field. This method includes the steps of receiving a ZIP code entry by a user; from the ZIP Code, determine a latitude and longitude of the antenna and calculate an azimuth to which the antenna will be aimed to receive signals from the target satellite based on latitude and longitude. This method also includes receiving a designation of the target satellite input by a user; of the designation, determine a satellite length; and calculate an azimuth and elevation at which the antenna will be targeted to receive the signals from the target satellite based on the latitude and longitude of the antenna and the satellite length. The present invention also encompasses an apparatus for pointing a satellite antenna to a target satellite that includes a processor; a user input device through which the user can support a designation of an antenna location to the processor and a memory unit connected to the processor. The processor, using the designation of the location of the antenna gives access to a local variation model of the Earth's magnetic field stored in the memory unit and corrects the parameters to point the antenna based on the variation of the Earth's magnetic field in the location of the antenna. A query box is stored in the memory unit that correlates the ZIP Codes with latitude and longitude. When a user supports a ZIP Code or the designation of the location of the antenna, the processor gives access to the query box in the memory unit to determine the latitude and longitude of the antenna. The apparatus of the present invention may also include a drive unit controlled by the processor to point the antenna; and a compass on the antenna to monitor the azimuth to which the antenna is pointing. The processor controls the drive unit to point the antenna to the target satellite. If the processor has calculated the variation in the location of the Earth's magnetic field, the processor controls the drive unit to point the antenna to the target satellite, based on the corrected parameters for local variation in the Earth's magnetic field.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings illustrate the present invention and form part of the specification. Together with the following description, the drawings demonstrate and explain the principles of the present invention. Figure 1 is an illustration of a conventional satellite antenna. Figure 2 is an illustration of an associated electronic satellite antenna in accordance with the present invention. Figure 3 is a flow chart showing the steps of the method of the present invention to accurately target a satellite antenna to a target satellite.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES In general principle, one aspect of the present invention is the use of a lookup box to correct local variations in the earth's magnetic field when a magnetic compass is used to monitor the azimuth of a satellite antenna. The International Geomagnetic Reference Field ("IGRF") model is a recognized standard model developed by the National Space Science Data Center based on empirical measurements of variations in the Earth's magnetic field. The IGRF model can therefore be used to mathematically quantify the Earth's magnetic field as it varies across locations. Consequently, if the location of a satellite antenna is specified, it is possible to refer to the IGRF model and determine how the Earth's magnetic field varies at the specified location. This variation of the actual magnetic field of the Earth from the expected magnetic field can be used to correct the given heading of a magnetic compass to identify true north and the true azimuth of the antenna. Using the drawings, preferred embodiments of the present invention will now be explained. As shown in Figure 2, the present invention includes a system for controlling a satellite antenna 101 in order to accurately point the antenna 101 to a target satellite 102. The antenna 101 of the satellite has a drive system 206 that moves the antenna 101 to direct satellites that have different orbits. A magnetic compass 207 can be placed in the vessel 101 itself in order to provide a means by which the driving system 206 can monitor the azimuth of the antenna 101. Typically, when a satellite antenna is being used to receive, for example, the television signals, a terminal placed at the top is used which is placed with and connected to the television set to provide the television signals from the satellite antenna to the television. This terminal placed at the top includes an integrated receiver / decoder ("IRD") (201). In the present invention, the impeller system 206 of the antenna 101 is controlled by and communicates with a processor 204 that is part of the IRD 201. The IRD 201 and the processor 204 include a terminal 205 by which the IRD 201 is connected to a television set (not shown). The IRD 201 of the present invention also includes a user input device 202. The user input device 202 may be any of a number of equivalent devices. For example, the user's input device 202 may include a keypad or numeric keypad that is placed on, connected to, or remains in communication with the IRD 201. Alternatively, the user's input device 202 may include a receiver, such as an optical (IR), acoustic (ultrasonic) or radiofrequency (RF) receiver for receiving data signals transmitted by the remote control unit (not shown). By abbreviating, the user input device 202 can be any device with which a user can support the data to the processor 204 of the IRD.

In the present invention, the user through the user's input device 202 would admit the necessary data to direct a desired satellite with the antenna 101 of the satellite. As mentioned above, the first piece of data that must be known by the processor 204 to address a satellite is the geographical position of the antenna 101. If the user knows its longitude and latitude, the data can be admitted to the processor 204 with the input device 202. Without However, an object of the present invention is to allow a user to designate their location without knowing the uncommon information, such as its longitude and latitude. Accordingly, under the principles of the present invention, the user may admit some more common designation of their location. For example, a zip code, in the United States a ZIP Code can be supported with the user's input device 202. Although the use of the postal code is a simple way in which an average user can designate his location with a commonly known piece of data, the present invention is not restricted in this way. Any such well-known or easily communicated location designator can be used within the scope and spirit of the present invention. For example, a telephone code, such as area codes and prefixes, can be conceivably used. The process for using the system of the present invention shown in Figure 2 is illustrated in Figure 3. Therefore, both Figures 2 and 3 will be referred to in the following discussion. As shown in Figure 3, in block 301, the user supports the location data in the IRD 201 with the input device 202. The location data is then received by the processor 204. In block 302, the processor 204 will determine whether the user has accepted the longitude and latitude of the antenna 101. If the latitude and longitude have been admitted, the processor 204 advances to block 305. If the user has not admitted the latitude and longitude, the processor 204, in block 303 will determine whether the user has admitted another common location designator, i.e., a ZIP Code. If not, the processor 204 returns to block 301 and waits for the user to support an appropriate location designator. If the ZIP Code is supported, the processor, in block 304, gives access to a query box stored in memory unit 203. The query box will match the ZIP Code of entry with the latitude and longitude of that ZIP Code.

As will be appreciated by those skilled in the art, the user will only need to go through blocks 301 to 304 only once. Then, the latitude and longitude of the antenna 101 will be known and stored by the processor 204 in the memory unit 203. Only if the antenna 101 is replaced will the user need to re-specify the location of the antenna. The processor then advances to block 305 where the user inputs the data specifying the target satellite. In block 306, processor 204 will determine whether the user has simply admitted the length of the satellite. If done by the user, the processor 204 moves to block 309. If the user has not already done so, the processor in block 307 determines whether the user has accepted a name from the satellite or other designator 307. If the user it has not supported a satellite designator, the processor 204 moves back to block 305 and expects the user to accept the satellite data. If the user has admitted a recognized name or satellite designator, the processor 204, in block 308, gives access to the memory unit 203 for a look-up box that will associate the name or designator of the satellite with its length. Having the latitude and longitude of the antenna, the processor 204 determines the parameters that define the local variation of the Earth's magnetic field. The processor 204 can do this by calculating the necessary parameters directly from the IGRF model or can give access back to the memory unit 203 for a query box that will associate the latitude and longitude of the antenna 101, with the parameters that define the magnetic field local Then, in block 310, the processor 204 uses the accumulated data, i.e., the latitude and longitude of the antenna 101, the length of the target satellite 102, and the local variation in the magnetic field to calculate quickly and accurately the AZ and EL necessary to point the antenna 101 to the target satellite 102. The process can present the calculated AZ and EL on the screen of the connected television set. In this way, antenna 101 can be established and targeted by those without special skills or training. In addition, errors to point the antenna, which arise from an incorrectly determined azimuth due to local variation in the Earth's magnetic field, can be compensated for and eliminated. The details for the processor 204 of the IRD 201 to determine the true azimuth and elevation to accurately target an antenna 101 to a target satellite 202, will now be described. In the following equations, beats and lories are the latitude and longitude of antenna 101, respectively. Rs is the radius of the geosynchronous satellite orbit (42,162.14 km), Re is the average radius of the Earth (6378.145 km) and lon_ is the length of the target satellite. We can ignore the oblate spherical shape of the Earth as well as the height above the mean sea level of the antenna 101. These omissions have very small effects on the actual calculation of AZ / EL. Consequently, the azimuth and elevation can be calculated as follows. R = (Rs + Re - 2RsRe eos (late) eos (lons - lone)) / EL = arcsin ((Rs eos (late) eos (lons - lone) - Re) / R) AZ = arctan ((sin ( lons - lone)) / -sin (late) eos (lons lone)) Special care must be taken in the calculation of the True AZ, since arctan (x) is typically defined through the scale [-p / 2, p / 2]; that is, the arguments of positive x provide the same value of arctan (x), regardless of whether the desired angle remains in [0, p / 2] or [p, 3p / 2]. For antennas placed in the northern hemisphere, the true AZ is within the scale of (p / 2, 3p / 2). The proper calculation can be done using the function ANSÍ C atan2 (y, x) with compensation for negative results: AZ = 180.0 • atan 2 (sin (lons - lone), - sin (late) eos (lons - lone)) / p If (AZ < 0.0) then AZ = AZ + 360.0 °, where AZ has been converted into grades before checking and compensating for a negative result. In order to carry out these calculations, as described above, the latitude and longitude of the antenna 101 must be terminated, preferably by the user by admitting a basic well-known geographic designator. If the ZIP code of the United States is used under the principles of the present invention, the geographical identifier, the processor 204 must have the data stored in the memory unit 203 that correlates the ZIP Codes with latitude and longitude. These ZIP Code data can be obtained commercially and are updated periodically. The most direct approach to deriving the latitude and longitude of a ZIP Code is simply to let a five-digit ZIP Code serve as the direction to a box that stores latitude and longitude. Since the possible values of the ZIP Code vary from 00000 to 99999, this box would be about half empty because only ZIP codes 43907 are currently used in the United States. Assuming that the latitude and longitude could each be represented by a byte, the present invention would require a linear storage space of 200 kilobytes for the data correlating the ZIP Codes and the latitude / longitude. Clearly, this compression of this data would be preferable. The longitude / latitude data must be stored as quantized values. To accomplish this, latitude and longitude grid spacing may be selected through, for example, North America. Then we would determine the AZ / EL and the orientation error of the plate viewer when the next latitude and longitude grid point is used in the calculations instead of the actual latitude / longitude. With a grid in units of one degree of latitude / longitude, we find that only 1078 latitude / longitude values are required to represent all US ZIP codes in commercially obtainable files for these one-degree quantization values. Less than one storage byte is required for each latitude and longitude quantified to one degree through the area of interest. The resulting AZ / EL maximum errors for a 110 W satellite are 1.3 ° / 0.7 °, and for a 119 satellite they are 1.2 ° /O.8°, respectively. The maximum orientation error of the sheet viewer obtained for this grid is less than 0.8 °. If the separation of the grid is reduced to 0.5 °, the maximum AZ error is reduced to less than 0.7 ° and the maximum error of the plate viewer is reduced to 0.4 °. However, the required number of grid points to represent all ZIP code entries under consideration increases to 3,510. Note also that an orientation error of 0.8 ° for a 45-centimeter (18-inch) vessel results in less than a point loss of 0.6 dB and less than 0.35 dB for a 33-centimeter (13-inch) vessel. Even when the latitude / longitude to grid size of 1.0 or 0.5 degree quantification dramatically reduces the number of latitude / longitude points that must be stored in the memory unit 203, the problem of projecting a particular ZIP code towards one of these remains points. Even when ZIP codes are grouped more or less geographically, they do not undergo simple truncation strategies. For example, the following ZIP codes are projected to the next latitude / longitude in a grid of one degree: ZIP CODES LAT / LONG 92220 34 / -117 92222 33 / -115 Therefore, a truncated address such as 922 or 9222 does not can be used to consult the desired latitude / longitude in this case. However, the inventors have discovered that the ZIP codes from 02000 to 02534 can all be represented by a latitude of 42 ° and a length of -71 ° in a grid separation of one degree, while 02535 is quantized by a latitude / longitude of 41 ° / -71 °. Therefore, a query box needs only store values for ZIP Codes 02000 and 02535, while any ZIP code that falls between these two uses the stored latitude / longitude for 02000. Similar cases in which the stored data can be truncated can possibly be found. In addition, it is preferred to store only a decentralized ZIP code in an index box of the query box instead of the full ZIP code of 5 decimal places. By storing only the off-center value, that is, ZIP (j) = ZIP (j-l) + off-center (j), the number of bits required for index recovery is reduced. The algorithm simply accumulates offsets until the value of the user's defined ZIP code is exceeded. If the algorithm ends in the jfc index then (j-l) st serves as the address for a latitude / longitude query. For a grid separation of one degree, 18,926 one-byte decentered values are required to represent all 43,907 ZIP codes. This indexing algorithm will require 18,926 bytes to store the decentrations of the ZIP code and another 2 x 18,926 bytes to store the latitude / longitude quantifications for a total of 56.8 Kbytes for the one-degree separation example. However, because the total number of latitude / longitude grid points other than a separate degree required to represent the ZIP codes is only 1,078, this table of different grid point values would require a linear address space and the element 2,048 (11 bits). Therefore, more storage space can be saved by storing only the 18,926 11-bit addresses in some consolidated method of bits (which start the byte boundaries) and then having a smaller frame (2,048 x 2 bytes) of latitude / longitude. This results in a total of 18,926 bytes for the ZIP off-center, 18,926 x 11/8 = 26,024 bytes for latitude / longitude rates and 4,096 bytes for latitude / longitude resulting in 49.05 Kbytes of storage required in the 203 memory unit. To reduce the memory requirements even further, the ZIP off-center can be limited to 5 bits, so that the 11-bit latitude / longitude direction and the 5-bit offset can be stored in a single 2-byte word. Using this approach to the algorithm, results in a 203 memory unit storage requirement of 20,298 x 2 bytes = 40.6 kilobytes plus 4,096 bytes for latitude / longitude.

In its simplest form, the algorithm of the present invention does not provide error checking against an invalid ZIP code user input. However, the methods to verify the ZIP entries would include storing a 100,000 bit string where a "one" in the ZIP bit location implies a valid code and "zero" an invalid code. This requires 12.5 kilobytes of additional storage. This additional memory load can be considerably reduced by using a career-length coding algorithm. Finally, the details to determine the local magnetic variation will be explained. As briefly mentioned above, a magnetic compass is deflected from true north by variations in the local geomagnetic field. Magnetic north varies at each location on the surface of the Earth. For example, in San Diego, California, in 1929, a compass indicating magnetic north will read 13.1 ° east from true north. Consequently, if you target a target satellite with a 200 ° azimuth from true north, the azimuth to be selected as measured by a compass that reflects the local north is 200 ° - 13.1 ° = 186.9 °. In addition, the north magnetic pole moves 2 minutes of arc to the west each year, as measured from San Diego, California. This deviation can also be taken into account in the calculations carried out by the processor 204. The method to correct an azimuth calculation to point a satellite antenna using an IGRF model in North America is next. First, the user admits the geographical designation that is either reduced to latitude (lat) and length (Ion). latí = the largest integer < (lat - 6 °) / 2 loni = the largest integer < (Ion - 188 °) / 2 Once the lati and loni are determined, the parameters must be retrieved from the table of values provided by the National Space Science Data Center, as part of the IGRF model. foo = magnetic variation [latí] [loni] fio = magnetic variation [latí] [lonl + 1] foi = magnetic variation [latí + 1] [loni] fu = magnetic variation [latí + 1] [loni + 1] The parts fractions of latitude and longitude, p and q, respectively in relation to the separations of 2 ° are found by: p = (Ion -2 | _ lon / 2 _ |) / 2; and where (_ x J = the largest integer, less than or equal to x) Given these parameters, the correction for the local magnetic variation? m is calculated by a two-dimensional interpolation in the following way:? m = (1- p) (lq) foo + p (lq) f? o + q (lp) fo? + (pq-fn) The corrected azimuth is then calculated as follows: AZcompás = AZ -? m The description above has been presented only to illustrate and describe the invention, it is not intended to be exhaustive or to limit the invention to any precise form disclosed.Many modifications and variations are possible in view of the above teaching.The preferred embodiment was selected and described in order to better explain the principles of invention and their practical application The foregoing description is intended to allow other persons skilled in the art to better utilize the invention in the various modalities and with various modifications that are appropriate for the specific use It is intended that the scope of the invention be defined by the following claims.

Claims (17)

R E I V I N D I C A C I O N S

1. A method for targeting a satellite antenna on a white geosynchronous satellite that comprises: determining a local magnetic variation in the Earth's magnetic field; and calculate an azimuth where the antenna will be pointed, which is corrected for the local magnetic variation.

2. A method according to claim 1, wherein the determination of a local magnetic variation further comprises: receiving the location designation data of a user designating an antenna location; and determine the local magnetic variation that corresponds to that location.

3. A method according to claim 2, wherein the determination of the local magnetic variation is carried out using a model representing the variations in the Earth's magnetic field.

4. A method according to claim 3, wherein the use of a model comprising using the International Geomagnetic Reference Field model.

5. A method according to claim 2, wherein receiving the location designation data comprises receiving a longitude and latitude of the antenna input by the user.

6. A method according to claim 2, wherein receiving the location designation data comprises receiving a ZIP code from the antenna input by the user.

7. A method according to claim 6, wherein receiving the location designation data further comprises matching the ZIP Code with a longitude and latitude of the ZIP Code.

8. A method according to claim 1, further comprising receiving the designation data of the target satellite of a user.

9. A method according to claim 8, wherein receiving the target satellite designation data comprises receiving a target satellite length.

10. A method according to claim 8, wherein receiving the target satellite mapping data comprises: receiving a name of the target satellite; and determine a satellite length by reference to the query box that correlates the names and lengths of the satellite.

11. A method for pointing a satellite antenna to a target satellite comprising: receiving a ZIP Code entry by a user; from the ZIP Code, determine a latitude and longitude of the antenna; and calculate an azimuth at which the antenna will be oriented to receive the signals from the target satellite based on latitude and longitude.

12. A method according to claim 11, further comprising: receiving a designation of the target satellite input by a user; from that designation, determine a satellite length; and calculate an elevation at which the antenna will be oriented to receive the signals from the target satellite based on the latitude and longitude of the antenna and the length of the satellite.

13. An apparatus for aiming or orienting a satellite antenna to a target satellite comprising: a processor; a user input device through which a user can support a designation of an antenna location to the processor; and a memory unit connected to the processor. An apparatus according to claim 13, wherein the processor, using the designation of an antenna location, gives access to a local variation model of the Earth's magnetic field stored in the memory unit and corrects the parameters to point or orient the antenna based on the variation of the Earth's magnetic field at the location of the antenna. 15. An apparatus according to claim 13, further comprising a query box stored in the memory unit that correlates ZIP Codes with latitude and longitude, wherein when a user accepts a ZIP Code as the location designation of the antenna, the processor gives access to the query box in the memory unit to determine the latitude and longitude of the antenna. 16. An apparatus according to claim 15, further comprising: a drive unit controlled by the processor to orient or point the antenna; and a compass on the antenna to monitor a real azimuth toward which the antenna is oriented; wherein the processor controls the driving unit to aim or orient the antenna on the target satellite. 17. An apparatus according to claim 14, further comprising: a drive unit controlled by the processor for pointing or orienting the antenna; and a compass on the antenna to monitor a real azimuth toward which the antenna is oriented; where the processor controls the driving unit to orient the antenna to the target satellite based on the corrected parameters for local variation in the Earth's magnetic field.