MXPA98001437A - Reference of satellite beam direction using terrestrial terminals of direction of - Google Patents

Abstract

A satellite communication system has at least one satellite with an antenna that generates a beam pattern in motion on the surface of the earth, the beam pattern comprises a plurality of sub-beams, a method for determining a correction signal position for the satellite that includes: providing a reference transmitter on the ground, transmitting a signal from the transmitter in one of the sub-beams, receiving the signal with the satellite antenna and repeating the signal to a ground station, receiving the signal repeated with the terrestrial station, determine a gain of the received signal, compare the determined gain with a gain that is expected to be received based on the predetermined knowledge of the characteristics of the satellite antenna, and determine a difference between the determined gain and the expected gain to derive a correction signal indicative of a satellite position error

Description

REFERENCE OF THE SATELLITE BEAM DIRECTION USING TERRESTRIAL BEAM STEERING TERMINALS FIELD OF THE INVENTION This invention relates, in general terms, to satellite systems and, in particular, to a mobile communication satellite system utilizing low earth orbit (OBT) satellites.

BACKGROUND OF THE INVENTION OBT satellites suitable for use in a mobile communication satellite system have coverage areas for radio frequency (RF) communications that correspond to antenna patterns (traces) that sweep across the earth in the direction of the path of the satellite orbit. In general, it is important to point the satellite exactly in a given direction to orient the beam or beams of the satellite antenna pattern on the surface of the earth. In most cases, there are three directions that govern a satellite in flight. By accepted convention, these directions conform typical "aircraft" coordinates. Figure 1 shows these three directions as a roll axis direction, a pitch axis direction, and a yaw axis direction. The rolling axis is indicated in the direction of the satellite velocity vector and is in the plane of the orbit. The pitch axis is perpendicular to the axis of rolling and to the plane of the orbit. The yaw axis is perpendicular to each of the rolling and pitch axes, and is in the plane of the orbit. Nominally a satellite is pointed with its yaw axis directed towards the center of the earth. The coverage area of the communication beam, if the antenna is fixed to the satellite body, or the gimbal point of the antenna, if the antenna is directed, can be directed by tilting the satellite either in the direction of the velocity vector of the antenna. satellite, or outside the velocity vector. This is achieved by turning the satellite on its pitch axis. Likewise, the beam can be directed perpendicular to the velocity vector by turning the satellite, that is, by turning the satellite around the axis of oscillation. Finally, the satellite beam can be directed in rotation by turning the satellite around its yaw axis. Generally, commands are sent to the satellite position control system to perform these turns. The position control system is used to keep the satellite pointed in a particular direction, controlling the position of the satellite with respect to the different axes and in this way pointing the antenna pattern beam or beams in a desired direction in relation to the surface of the earth (or a desired direction in space). The OBT satellites move in space and time with the aerial beam above the ground sweeping along with the satellite, alternately covering uncovered areas on the ground. The OBT satellites can have the axes of fixed roll, pitch and yaw of the antenna, and in this way move a radiation pattern on the surface of the earth. A subsattellite point (PSS) is a point on the surface of the earth on which the yaw axis is pointed, and is located along a vector from the center of the earth to the point above the orbit where it is located. located the satellite. The PSS is defined at the intersection of this line and the surface of the earth. The antenna beam of an OBT satellite can be converted into an analog like an impulse broom, in which the yaw axis is the end of the broom and where the satellite's coverage area, that is, a region illuminated by the beam is propelled on the surface of the earth. The portion of the earth's surface that can be observed from the OBT satellite in orbit at any time is its coverage footprint. The antenna beam can be the entire fingerprint or some portion of it. The coverage area has a size and shape that typically depend on the altitude of the orbit and the angle of elevation towards the satellite from the tip of the footprint of the coverage area. The antenna beam does not necessarily need to be on a regular basis, nor have to illuminate the entire coverage area. However, for the purposes of this discussion, it is assumed that the coverage area is a circular area centered on the PSS. The satellite beam is typically divided into smaller sub-beams for communication efficiency. It is this group of sub-beams that usually require a preferential address to be specified. In addition, for this discussion it is assumed that the antenna is fixed to the body of the satellite. However, this is not necessary, and instead the antenna can be gimbal and directed to point in some direction with respect to the satellite axes. In this case, the instrumentation on the gimbal axes (either an axis or two) provides compensation information to the satellite or ground control to determine the position of the satellite. The satellite system requires reference information to maintain a preferential direction of the satellite with respect to the yaw axis (and other axes), for the antenna beam as it moves on the ground. The satellite position control system performs this function. You can use any of several conventional control methods to orient the satellite in the preferred direction. In order to develop the reference information on the position control function, it is necessary to determine the position of the satellite and therefore to determine and send commands to the position control system, in order to change the signaling direction of the satellite or antenna that is eeta creating the coverage area on the earth. This reference information has been obtained conventionally by means of earth detectors, solar detectors, agnetometers and other external reference devices. Recent advances in communication, computers and small satellite technology have made feasible a communications satellite system employing a constellation of OBT satellites in conjunction with fixed, mobile and manual user terminals. In order for one to operate with maximum efficiency, it can be appreciated that it is desirable to provide an improved method for controlling the position of individual OBT satellites.

OBJECTS OF THE INVENTION A first object of this invention is to provide reference information for control of satellite popping, either from the system's euema or fixed reference transmitters having known locations on the earth's surface. A further object of this invention is to provide a satellite position control system which compares the gains of signals received from one or more reference transmitters, placed in a known location on the earth's surface, with an expected gain indicated by a stored map. of gain contour of the satellite antenna, and which afterwards determines a correction of the poem from a difference in the received and expected gains.

BRIEF DESCRIPTION OF THE INVENTION The above and other problems are overcome, and the object of the invention is achieved by means of methods and apparatus for determining a position correction signal of an satellite. A communication satellite system has at least one satellite with an antenna that generates a pattern of mobile radiation on the surface of the earth. The radiation pattern is comprised of a plurality of sub-beams. One method of this invention determines a poem correction signal for the satellite by the following steps: a) provide at least one reference tracker at a known location on the earth's surface; b) transmitting at least one signal from the reference transmitter to at least one of the sub-hacee; c) receive the signal with the satellite antenna and repeat the received signal to a ground station. A subsequent step of method d) receives the repeated signal with the ground station; e) determines a gain of the received signal; f) compares the determined gain with a gain that was expected to be received based on a predetermined knowledge of a spatial variation in gain of the satellite antenna; and g) determines a difference between determined gain and the expected gain to derive a correction signal indicative of a position error of the satellite. The method also includes the task of transmitting the correction signal to the satellite; and correct the position of the satellite in accordance with the correction signal. The step of transmitting at least one signal from the reference trans- mitter may include the step of transmitting a plurality of signals from a reference trans- mitter; a step of transmitting a plurality of signals from a plurality of reference transmitters; or a step of transmitting a signal of the individual reference transmieoree of a plurality of them. The satellite has a preferred travel direction and a preferred orientation in space at any given point in time. Although the teaching of this invention is illustrated primarily in the context of yaw axis control, it should be understood that the teaching of this invention applies to all orientation axes. The satellite has a preferred yaw angle with respect to the direction of travel over the surface of the earth, and there is a yaw error angle, so that the actual direction of the satellite differs from the preferred direction. In this case, the determination step determines an apparent travel direction that differs from the actual travel direction by an angle related to an uncertainty with respect to the position of the satellite. For the case in which the correction signal has a value that is a function of the yaw error angle of the satellite, the method also includes the steps of transmitting the correction signal to the satellite; and correcting the position of the satellite in accordance with the correction signal by rotating the satellite around the yaw axis, to reduce the magnitude of the yaw error angle. In a currently preferred, but not limiting, mode of this invention, the signals are transmitted, repeated, and received as a multiple-code, multiple-spectrum code accee.

BRIEF DESCRIPTION OF THE DRAWINGS The features of the invention described above and others become more apparent in the following detailed description of the invention, when read in conjunction with the appended drawings, in which: Figure 1 is a useful pattern in the explanation of the orientation of the conventional axis of roll, pitch and yaw of a satellite in orbit. Figure 2 illustrates, in accordance with the teaching of this invention, a satellite having a bundle comprised of sub-hacee, and the trawl transmitter terreetree of yaw reference, also referred to in the preamble as reference terminals of beam direction satellite (TRDHSs), which are located in known places on the surface of the land. Figure 3 is a vieta that looks down on the surface of the earth from the satellite, and illustrates the angulate relationship between a satellite speed vector, a preferred address, a real address, and an apparent direction, all of which may be referred to with the sub-satellite point (PSS). Fig. 4 illustrates a satellite beam, in time, as the beam sweeps over a plurality of TRDHSe. Figure 5A illustrates the antenna gain contour emplamplaree for two sub-beams. Figure 5B is a graph showing the location of a TRDHS within the gain contours of the antenna, taken along the line of section B-B of Figure 5A. Figure 6 is a simplified block pattern of a satellite having round trip repeaters to relieve round trip service links, respectively, between a TRDHS and a terrestrial gate (CP). Figure 7A is useful in describing a method of this invention in which multiple TRDHSs (or terminal terminals) are used with single link tranemieionee. Fig. 7B is a block pattern of the satellite showing an antenna of elements in the service link receiving phase, amplification of multiple sub-beams and down converters, and a feeder transmitting antenna for transmitting the service beams of the figure 7A to a gate. Figure 7C shows several feeder link channels that correeponden to the sub-hacee in what is located at the TRDHSe of Figure 7A. Figure 8 is useful in describing a method of this invention in which a single TRDHS (or user terminal) with multiple link transmissions is used. Figure 9 is a block pattern illustrating a gate and control center for satellite operations (CCOS) interconnected by means of a terrestrial or ground data network, in which either or both of the gate or the CCOS can transmit a command link control of poetry to the satellite. Figure 10 shows a simplified block pattern of an exemplary satellite position control system; and Figure 11 is an exemplary gain contour map for a single interior beam.

DETAILED DESCRIPTION OF THE INVENTION It was noted at the outset that, although the following description is made primarily in the context of a steering reference of the yaw axis, the teaching of this invention is also applicable in general to the steering around other axes. For example, two-axis control can be effected in accordance with this invention, and control of all three axes can be achieved with a suitable detector, such as a solar detector, a magnetometer, or other suitable means. Referring now to Figure 2A, a satellite 1 is moving along the velocity vector 2 of the satellite along an orbital path x and thus moves a coverage area 3 along the earth. The coverage area 3 corresponds to a satellite beam that is typically divided, for example, into some number of sub-phases 4 concentrically, such as sub-beams 20. In general, loe eub-agoe is required to point in a preferred or preferred address 5, with a return to the yaw axis. The preferred direction may vary over time and may rotate at some specified speed. It is assumed that satellite 1 is controlled around the yaw axis, which is defined as a line between the center of the earth and the satellite. The intersection of this line with the surface of the earth is referred to herein as the satellite subsattellite point (PSS) 6. The preferred address 5 is a vector extending from PSS 6 to a point 7 on the outer edge of the coverage region 3 of the satellite antenna, or to any other convenient point. It is not necessary that the beam be centered on the PSS 6, and instead it may be at an arbitrary angle to the PSS 6 and may cover less of the entire area of the satellite coverage area. At least one terrestrial gate (CP) 8 is bidirectionally coupled to satellite 1 through an RF link or feeder link 9, comprised of an RF uplink 9a, towards an antenna receiving satellite feeder link, and a downlink 9b of RF, from a satellite Ib of satellite transmission. In accordance with this invention, at least one, and preferably a plurality, of yaw reference transmitters, also referred to herein as satellite beam direction reference terminals (TRDHSs) 10, are provided which are placed on sites. known (latitude and longitude) of the surface of the earth. Each TRDHSs 10 includes an antenna 10a, such as an antenna or ni-directional, and is capable of transmitting a signal to satellite "1, and may also be capable of receiving a signal from satellite 1. The communication of the TRDHSe 10 by second RF link (ein power link) with satellite 1. In a currently preferred, but certainly not limiting, mode of this invention, there is a total of 48 satellitee, for example, in a low earth orbit (OBT) of 1414 km The satellites are distributed in eight orbital planes with six satellites equally separated by plane (constellation of Walker) .The orbital planes are inclined at 52 ° with respect to the equator and each satellite completes one orbit once every 114 minutes.This focus provides coverage of approximately complete ground with, preferably, at least two eatélitee in view at any given time from a particular user site between approximately 70 ° south latitude and ap approximately 70 ° north latitude. As such, a user is enabled to communicate to or from any nearby point on the surface of the earth within a gate coverage area 8, to or from other points on the surface of the earth by one or more CPs 8 (eg between a public switched telephone network (PSTN) connection to CP 8) and one or more of the satellite 1. In this respect, reference may be made to the US patent. No. 5,422,647, by E. Hirshfield and C.A. Tsao, entitled "Mobile Communications Satellite Payload", which describes a type of communications satellite that has linealee amplifiers and antennas for tranemission and reception of elements in phase. The satellite payload described is suitable for use with the teaching of this invention, as well as other types of satellite repeater. The user / gate communications are carried out by means of an extended spectrum (EE) code division multiple access (CDMA) technique. The currently preferred AMDC-EE technique is similar to the TIA / EIA Interi Standard, "Mobile Station-Base Station compatibility Standard for Dual-Mode ideband Spread Spectrum Cellular System" TIA / EIA / IS-95, July 1993, although use other extended spectrum and CDMA techniques and protocols. However, Time Multiple Multiplex Access (AMDT) can also be used, such as by time sequencing of signal transmissions and applying correction methods to achieve an almost real-time approximation of the teachings described herein. Multiple Frequency Division Accesses (AMDF) can also be used, as well as combinations of these various access techniques. The low ground orbit of the satellites 1 allows low power fixed or mobile user terminals to communicate via satellites 1, each of which functions, in a currently preferred embodiment of this invention, solely as a "curved line" repeater. to receive a communications traffic signal (such as voice and / or data) from a user terminal or from a gate 8, to convert the received communications traffic signal into another frequency band, and then retransmit the converted signal . However, it should be considered that the teaching of this invention is not limited to "repeating" "curved line" technology and can work equally well with on-board processing and regenerative repeater satellites. There is no need for direct communication links or links between the satellites 1. The user terminals, and also the TRDHS 10, communicate via, for example, L-band RF links (uplink or return link) and RF link S-band (uplink or one-way link) through return and return satellite repeaters (shown in Figure 6), respectively. The return L-band RF links can operate within a frequency range of 1.61 GHz to 1625 GHz, a bandwidth of 16.5 MHz, and are modulated in accordance with the preferred extended spectrum technique in multiplex segment of 1.25 MHz. The outgoing S-band RF links can operate within a frequency range of 2.485 GHz to 2.5 GHz, a bandwidth of 16.5 MHz, and are also modulated according to the 1.25 multi-segment extended spectrum technique. MHz. The 16.5 MHz bandwidth of the forward link is divided into 13 channels with, for example, up to 128 users assigned per channel. The return link may have various bandwidths, and a given user terminal may or may not be assigned to a channel other than the assigned channel on the forward link. The gate 8 communicates with the satellitee 1 for example by means of a full duplex RF link 9 (forward link 9a (to the satellite), return link 9b (of the satellite)) operating within a frequency range generally above 3 GHz, and preferably in the C band. The C-band RF links provide two-way links to the communication power link, and also carry satellite commands to the satellite and satellite telemetry information. The feeder link 9a may operate in the 5 GHz to 5.25 GHz band, while the return feeder link 9b may operate in the band from 6,875 GHz to 7,075 GHz. Having described a currently preferred, but not limiting, mode of a communication system within which the invention of this invention can be used to take advantage, reference is now made to Figure 3 to illustrate an exemplary antenna pattern 3 of sub-hacee 4 centered on the PSS 6. The antenna pattern 3 of satellite ee moves as the satellite 1 moves along the velocity vector 2, alternately covering and discovering points on the earth. The pattern has the preferred direction 5 with respect to the velocity vector 2, and at any time it can be fixed or rotating at some speed. The accuracy of beam targeting has two components. A first component is the error angle 11, which in this embodiment of the invention is a yaw error. The yaw error is the difference between the preferred direction 5 and the actual direction 12 in which the beam is moving. The second component is an uncertainty angle 13, that is, the uncertainty of the real direction. The uncertainty gives rise to an "apparent" direction 14 of the pattern movement of the satellite beam on the surface of the earth. If a yaw axis control is not performed, the yaw error angle 11 will change with time. Considering various effects and disturbances due to orbital dynamics, thermal effects, drag, mechanical force and other factors, the yaw error angle 11 can oscillate, can remain constant with compensation, or can rotate in any direction around the PSS 6. A satellite position controller is used (Figure 10) for maneuvering the satellite 1 to point the antenna for example, in the preferred direction 5, reducing to a minimum the beam-beam error 11 (for the case of the example, the yaw error), using values and information which are obtained in accordance with the teaching of this invention. Referring now to Figure 4, one or a plurality of the TRDHSs 10 are distributed over the known land surface area in place. The beam pattern 3 of OBT satellite 1 moves through the TRDHSe 10 pattern. In time (ti to t2, where t2 = ti + t), the antenna beam 3 and the coupled PSS 6 sweep to through the surface of the earth, illuminating the TRDHSs 10 in turn and causing them to appear to move from one sub-beam to another. Referring now also to FIGS. 5A and 5B, it is shown that, assuming a perfect alignment of the actual address 12 and the preferred direction 5 of the satellite, as the satellite goes over the surface of the earth, a satellite will be received by the satellite 1. which transmits an uplink signal 1, with a mixed pattern of all loe eub-hacee 4. Loe eub-hacee 4 have individual spatial variations in gain, referred to herein as the antenna gain contours gl and g2, for the sub-beams N and M, respectively. Referring in particular to Figure 5B, it can be seen that at a certain time the TRDHS 10 is covered by a portion of the beam of the mobile satellite 1. Since the TRDHS 10 is fixed on the ground and the mixed satellite pattern 3 is moving with respect to the earth, the apparent gain of the antenna of the sub-hacee N and M, changes with time. Thus, the magnitudes of gl and g2 can be considered to vary over time. The signal from the TRDHS 10 is received at the satellite 1 of the sub-stations N and M, and is repeated by the satellite 1 to the gate 8 on the return feeder link 9b (Figure 2). Referring to Figure 6, the operation of RF links and repeaters is shown. Starting with the forward feeder link 9a (e.g., a C-band link) from gate 8 to satellite 1, reception is made via the satellite feeder link antenna 20 and a frequency translation is performed on a repeater. or receiver-transmitter 22. The transferred frequency forward signal is transmitted by the satellite antenna 24 as a forward service link 26 (eg, the S-band) for reception by means of the TRDHS 10. A link of return service 28 (e.g., band L) is transmitted by TRDHS 10 to a receiving antenna 30 of satellite 1, and a frequency translation is made on a return repeater or receiver rt 35. The return signal Frequency is transmitted by satellite antenna 32 as the return feeder link 9b for reception by means of CP 8. The principle of operation is based on receiving a signal or signal from one or more of the TRDHS s 10 at CP 8, determining where the satellite antenna pattern of the TRDHS 10 is located, and relating the determined location to a database 35 of stored antenna gain contour values. CP 8, or a satellite operations control center (CCOS) 40 or a ground operations control center (CCOT) 44 (Figure 9), can store a gain contour map for each satellite of the constellation, or a generalized map that relates to all satellites. The map can be updated periodically to reflect the changes in the satellite's po- litition, as well as changes in the operational capacity of on-board linear amplifiers generated by the various sub-beams. The map or maps can be determined by calculation, based on the geometry of satellite antennas of elements in phase, and / or can be generated empirically by measuring the gain contour values, either testing on the ground or performing tests in orbit. Figure 11 is an exemplary gain contour map for a single internal sub-beam. The signals from only one of the TRDHSs 10 are received by the CP 8, either singularly (for example, from a single sub-beam 4), or as a plurality of copies of a plurality of loe eub-hacee 4. The elaboration of a map of locations of TRDHS 10 fixed on the surface of the earth in fixed positions expected in the antenna beam map, gives as a result a calculation of the angular co-direction between the preferred direction 5 and the apparent direction 14. Eeto ee , a yaw error angle determination 11 is made from the signal received from the TRDHS 10. Referring again to FIG. 5B, based on the stored patterns of antenna gain values as a function of the gain contour. of eub-beam, the CP 8 expects to find that the signal 28 transmitted by the TRDHS 10 to, for example, the sub-hacee N and M, experience satellite antenna gain of gl 'and g2', remembering that the location of the satellite 1 is known p or CP 8 from ephemeris data of the satellite, while the location of the TRDHS 10 is known a priori. The gain can be determined from strength measurements or received signal strengths made by CP 8. However, at present, CP 8 determines that the antenna gains are gl and g2 in the sub-arrays N and M, respectively . The difference in gain (e) between the eeperated and the measured, indicates a difference between the real and actual beam orientation with respect to the fixed TRDHS 10. This difference is then used to derive a yaw correction that is emitted by the satellite pointer controller (Figure 10) to rotate satellite 1 around the yaw axis (in this example), in order to handle the beam error angular towards zero. Although described hitherto in the context of the TRDHSe 10, it should be understood that the teaching of this invention can also employ signals received from user terminals, whether mobile, manual or fixed. That is, when establishing a connection with a terminal of the user, in particular with mobile terminals and manualee, the CP 8 preferably performs a location location on the user terminal using GPS position techniques or other suitable pointer technique. The location of a fixed terminal terminal, for example one having an antenna located above an office building or a tile, can be determined initially with great precision when the antenna is first installed. Also, starting with the TRDHS 10 or user terminals, the CP 8 can also actively control the power of the terminal transmier, in order to substantially equalize the power received from each terminal. As such, the power to which a given transmitter is transmitting is also known for the CP 8. Furthermore, it should be considered that the beam steering reference technique of this invention need not be continuously active. That is, during periods of high communication load, and for an AMDC execution, it may not be convenient to assign an extension code (eg, a Walsh code) to one of the TRDHSs 10, thereby releasing the ) code (s) for use by a user terminal. During periods of low communication load, CP 18 may selectively activate one or more of the TRDHSs 10 over the forward link, assign one or code Waleh to the TRDHSs 10, and then perform the determination of the satellite popping error (per example, yaw error) in baee to the transmissions from the activated TRDHSs or 10. The teaching of this invention can operate in one of several ways or methods. For example, a method employs multiple transmission of a single TRDHS 10 (i.e., transmieionee from several TRDHSs 10 simultaneously). Another method uses multiple copies of TRDHS link, from a single TRDHS 10. An additional method employs multiple copies of TRDHS link copies from multiple TRDHSs. These different methods are summarized in the following table.

TABLE 1 Method 1- Multiple TRDHSs- Single-link transmission Method 2- TRDHS alone- Multiple link transmission Method 3- Multiple TRDHSs- Multiple linkage transmission In more detail, and referring to the figures 7A-7C, method 1 uses multiple TRDHSe 10, each one tranemitting a single return service link 18 to CP 8 through one of sub-beams 4. That is, a plurality of TRDHSs 10, which are located in different sub-hacee (SH) A, B, C, etc., each transmits a signal to satellite 1. The signals can be tranemitted simultaneously or not. If they are not transmitted simultaneously, then preferably the TRDHSs 10 mark the respective transmissions time encoding the system time in the transmission. The signals are repeated in the return link repeater of satellite 30 (FIG. 6) and received in CP 8. The received signal level, the time differences between the signals, and other link values are developed by gate 8. and to the acenadoe in a database 8A. Referring also to Figure 3, gain values of received signal are developed and the apparent direction of satellite 14 is determined. Preferred address 5 is known a priori by CP 8 and is also stored in data bank 8a. The actual direction 12 can not be known exactly, and differs from the apparent direction 14 by the angular difference referred to above as the knowledge uncertainty 13. Therefore, the angular difference, for example, the yaw error angle 11, is calculated and stores for future use, or can be transmitted directly to the satellite position controller (Fig. 10) to implement the correction. In any case, after correction, any residual error (considered by this invention) is the uncertainty of knowledge 13. Referring again to FIGS. 7A to 7C, the TRDHSs 10 are shown transmitting signal from one or more sub-beams (for example SH-A and SH-B) on the return service links 28a and 28b, respectively, which are then repeated on the connection link 9b. These signals may be transmitted, for example, by a repeater configured as the example in figure 7B, which is only one example of a suitable satellite repeater. In the example of FIG. 7B, an antenna of the service link receiver of the phased arrangement of the satellite ld receives the links 28a and 28b which are applied to low noise amplifiers (ABRs) SH-A and SH-B, and then turned down, they are simultaneously transmitted together, and appear as signals in the different channels of the connecting link (for example, A and B of Figure 7C) that correspond to loe eub-hacee A and B. Exieten varies technical to determine the apparent direction 14 shown in figure 3. A first preferred technique uses at least one of the TRDHSe 10, or some other transmitter having a known position on the surface of the earth, measures the gain of each transmitter as it is received in CP 8, and compares the values of the measured gain with the values of the expected gain known by CP 8 or by another ground station. A second technique uses only the knowledge of which channel (s) of the connection link are located in TRDHSe 10. A third technique uses the tranemission of a user aggregate of the communication instead of a TRDHS 10, which is located in one or some of the sub-hacee 4. In the latter case, for example, the users that are eeten in loe eub-agoe A and B, are better in, for example, the sub-beams C and D. If it is found that this is the case, CP 8 or another terrestrial station is allowed to eday apparent address 14, and can be determined without the use of TRDHS devices. The method 2 referred to above, that is, the multiple link transmission of a single TRDHS 10, uses a single TRDHS 10 which is transmitting a signal, but that produces multiple links. That is, the signals are automatically received in the channel of sub-beams A and B. Considering the case that the extended code division multiple access (CDMA-EE) is a preferred modality for the communication system, and in relation to FIG. 8, a service link signal of an individual TRDHS 10 is transmitted over multiple return service links 28 'and 28' '(eg, doe) using an omnidirectional antenna 10a. The multiple link 28 'and 28"are each received by satellite 1, see also figure 7B, and re-fed to sub-stations A and B. This results in a re-evaluation of the channel of the eub- you make A and B (see Figure 7C) on the return connection link 9b. The signal received at CP 8 in doe or mána canalee. The signal levels corresponding to gl and g2, as shown in FIG. 5B, are measured after directly or otherwise calculated. The gain of these signals (and / or other transmitted information) is then used to determthe apparent direction 14. As in method 1, you can make a preliminary approximation of the apparent direction 14 or use aggregate transmissions from the user. The third method referred to above, that is, the transmission of multiple links of multiple TRDHSs, can be considered as a combination of methods 1 and 2. This method provides the best accuracy of knowledge of the error angle 11. Method 3 uses TRDHSs 10 multiples each operating as in method 2. That is, a plurality of TRDHSs 10 transmits each multiple links 28 'and 28". For this case, the multiple links are received by multiple sub-beams, and the additional information relating to the gains of the different links is used to obtain a precise value for the apparent address 14. Deepuée that the apparent address 14 is determ and the angle (s) of error 11, must be provided in some way the information to satellite 1. There are several techniques to achieve the release of error information. Four different methods (designated A-D) are described as examples. This is known as: (A) individual gate address, in real time; (B) individual gate address, in non-real time; (C) address of the system, in real time; and (D) system address, in non-real time. The first two methods (ie, A and B) are considered together. In this case, satellite 1 is addressed with the resulting error value (s) (s) 11 of CP 8, which determines (n) the error value 11 and tranemite (n) the information to the satellite 1 in real time (method A) or non-real time (method B) for additional use by the satellite position control system shown in figure 10. The pointer control system includes a receiving antenna of the command link, which may be the receiver antenna of the connection link 20 shown in FIG. 6, a control receiver ld and position controller l, and a suitable position control mechanism lf (for example, flywheels, torquing torques agnéticoe, giroecopioe or propuleoree). You can include an optional on-board computer lg to calculate the required position adjustment (s) from the information received and / or to store the information received from the command address for later use. If the lg computer is not provided, then the command link carries the required position control operations, which are used by the position controller l. For example, and in the case of a determination of the yaw error angle, the position controller le and the position control mechanism lf cooperate to rotate the satellite 1 around the yaw axis (see FIG. 2) to reduce the yaw error angle (ideally) to zero. For an OBT system, satellite 1 moves over a substantial number of CPs 8. Some of the Eetae CPs 8, or all of them, may have the command capability to command satellite 1 and provide directional guidance to the member. In addition, satellite 1 (method B) can have the computer lg as part of its command and control system that can accept the reference information and store it for later use, update an address algorithm, or otherwise use the reference information. In Figure 10, CP 8 transmits the error signal (ee) 11 or the information of the poorer control derived from the error data to satellite 1. The information of the command link is received by the control receiver ld on the command link. The signal after reception, downconversion, decoding and processing is released to the onboard computer lg (method B) or directly to the position control system l (method A). In the case of the on-board computer lg, the data can be used to update a stored program to control satellite 1, either in real time (method A) or at some later time (method B). Alternatively, the signal can be released directly to the pointer controller and the setting error will be corrected. Another update is made or corrected as satellite 1 advances over the surface of the earth and paes over other CPs 8 and TRDHSs 10. In either case, the position controller gives instructions to one or more types of motion control mechanisms. to change the poem of satellite 1 to reduce the angle of error 11.

For methods C and D, that is, direction of the seventh, in real time and not real time, and now also in relation to figure 9, satellite 1 retracts the transmission of TRDHS 10 (or terminal of the ueuario) to the gate 8 on the return connection link 9b as the satellite 1 moves through the CP 8. The signals are received by the CP 8, and the error angle 11 is determined in the CP 8 as described above. However, and in this case, the resulting error angle 11 is communicated to the Satellite Operations Control Center (CCOS) 40 via a land or terreetree data network (RDT) 42. The RDT 42 is coupled together with a plurality of CPs 8 (only one of which is shown in Figure 9), CCOS 40, and other terreetree components of the satellite system, such as the Terreetree Operational Control Center (CCOT) 44. The re-emerging error angle 11 and / or other data based thereon, are received by the CCOS 40 from the RDT 42, and are communicated after (in real time or not real time) to the satellite 1 over the command link from the CCOS 40 The error signal is received by the control receiver ld (Fig. 10), is converted down, decoded and otherwise processed and formatted. The signal is then sent to the position controller directly or indirectly by the optional onboard computer for processing. The resulting information is applied to the position control mechanism lf. The real-time direction of method C may be affected, or it may use the non-real time direction of method D. Although the position correction technique has been described above mainly in the context of a cooperative effort between the TRDHSs, the satellite and at least one ground station, it should be appreciated that all the functionality of the ground station or part thereof can be incorporated into the satellite. For example, the satellite can store its own (e) map (s) of the gain contour of the antenna, can determine the gain of the signal received from the TRDHS or user terminal, can calculate its error of position (for example, yaw error), and can then apply the corrective action. Thus, even though the invention has been shown and described particularly in relation to preferred embodiments thereof, it will be understood by those skilled in the art that changes can be made in the form and detail of the part without departing from the scope and spirit of the invention. the invention.

Claims (38)

NOVELTY OF THE INVENTION CLAIMS

1. - In a communication satellite per satellite comprising at least one satellite having an antenna that generates a beam pattern in motion on the surface of the earth, the beam pattern being comprised of a plurality of sub-beams, a method to determine a position correction signal for the satellite, comprising the steps of: providing at least a reference tracer at a known position on the surface of the earth; at least one signal from the reference transmitter (at least one) in at least one of the sub-hacee; receive the signal (at least one) with the satellite antenna and repeat the received signal (at least one) to a terreetre eetation; receive the repeated signal (at least one) with the terreetre station; determine a gain of the received signal (at least one); comparing the determined gain with a gain that is expected to be received based on a predetermined knowledge of a spatial gain variation of the satellite antenna; and determining a difference between the determined gain and the expected gain to derive a correction signal indicative of a satellite position error.

2. A method according to claim 1, and further comprising the steps of: transmitting the correction signal from the earth station to the satellite; and correct the position of the satellite according to the correction signal.

3. A method according to claim 1, and further comprising the steps of: transmitting the correction signal of the terreetre eetation to a second terreetre eetation; tranemit the correction signal of the second terrestrial eetation to the satellite; and correct the position of the satellite according to the correction signal.

4. A method according to claim 1, characterized in that the transmission step includes a step of transmitting a plurality of signals from a reference transmitter.

5. A method according to claim 1, characterized in that the tranemission step includes a step of transmitting a plurality of signals from a plurality of reference transients.

6. A method according to claim 1, characterized in that the tranemising step includes a step of transmitting a signal from a single reference transmitter of a plurality of reference transmitters.

7. A method according to claim 1, characterized in that the satellite has a preferred direction of travel on the surface of the earth, characterized in that there is at least one angle of error such that the satellite travels in a real direction that differs of the preferred direction, and characterized in that the determination step determines an apparent travel direction that differs from the actual travel direction by an angle related to an uncertainty in relation to the position of the satellite.

8. A method according to claim 1, characterized in that the correction signal has a value that is a function of a yaw error angle of the satellite, and that also includes the steps of: transmitting the correction signal to the satellite; and correcting the position of the satellite according to the correction signal, by rotating the satellite around the yaw axis to reduce a magnitude of the yaw error angle.

9. A method according to claim 1, characterized in that the correction signal has a value that is a function of at least one error of axial disadjustment of the satellite, and which also comprises the following: transmission of the correction signal to the satellite; and correct at least one axial mismatch error of the satellite according to the correction signal.

10. A method according to the claim 1, characterized in that the correction signal has a value which is a function of at least one error of axial adjustment of the satellite antenna, and which further comprises the steps of: transmitting the correction signal to the satellite; and correct the axial mismatch error (at least one) of the satellite antenna according to the correction signal.

11. - A method according to claim 1, characterized in that the step of transmitting at least one signal from the reference transmitter (at least one) involves a multi-access signal of extended spectrum code division, characterized in that the pairing of repeating the received signal (at least one) to a terirtre transmission transmits the extended spectrum code division multiple access signal on at least one connection link channel, and characterized in that the step of receiving the repeated signal (eg at least one) with the terreetre station receives the multiple-spectrum repeated code access signal repeated, from the connection link channel (at least one).

12. In a satellite communication system comprising at least one satellite having an antenna that generates a beam pattern in motion on the surface of the earth, the beam pattern being comprised of a plurality of sub-hacee, a satellite position correction system, comprising: at least one reference transmitter at a known position on the surface of the earth; Means to tranemit at least one sign of the reference tranemieor (at least one) at least one of the sub-hacee; Means to receive the signal (at least one) of the antenna of the satellite and to repeat the signal received (at least one) to a ground station; means for receiving the repeated signal (at least one) with the ground station; means for determining a gain of the received signal (at least one) and for comparing the determined gain with a gain that is expected to be received based on a predetermined knowledge of a spatial gain variation of the satellite antenna; and means for determining a difference between the determined gain and the expected gain to derive a correction signal indicative of a satellite poem error.

13. The satellite position correction system of claim 12, and further comprising: means for transmitting the correction signal of the terreetre eetation to the satellite; and means in said satellite to correct the position of the satellite according to the correction signal.

14. The satellite position correction system of claim 12, and further comprising: means for transmitting the correction signal from the ground station to a second ground station; means for transmitting the correction signal from the second ground station to the satellite; and means in said satellite to correct the position of the satellite according to the correction signal.

15. The satellite position correction system of claim 12, characterized in that said transmission means transmits a plurality of signals from a reference transmitter.

16. The satellite position correction system of claim 12, characterized in that said transmission means transmits a plurality of signals from a plurality of reference trans- mitters.

17. The poetry correction system of the satellite of claim 12, characterized in that said traffic means transmits a signal of an individual reference transformer of a plurality of reference transmitters.

18.- The satellite correction correction factor of claim 12, characterized in that the satellite has a preferred direction of travel over the surface of the earth, characterized in that there is at least one error angle such that the satellite travels in a actual direction that differs from the preferred direction, and characterized in that said determining means determine an apparent direction of travel that differs from the actual travel direction by an angle related to an uncertainty in relation to the position of the satellite.

19.- The score of the poetry correction of the satellite of claim 12, characterized in that the correction signal has a value that is a function of an angle of winking error of the satellite, and that also comprises: means to transmit the signal of correction to the satellite; and means in said satellite to correct the member's poem according to the correction signal, by rotating the satellite around the yaw axis to reduce a magnitude of the yaw error angle.

20. - The satellite position error correction system according to claim 12, characterized in that the correction signal has a value that is a function of at least one error of axial desajuete of the satellite, and that also comprises: means for transmit the correction signal to the satellite; and means in said satellite to correct the axial mismatch error (at least one) of the satellite according to the correction signal.

21. The satellite position error correction system according to claim 12, characterized in that the correction signal has a value that is a function of at least one axial mismatch error of the satellite antenna, and It also includes: means to transmit the correction signal to the satellite; and means on said satellite to correct the axial mismatch error (at least one) of the satellite antenna according to the correction signal.

22. The satellite position correction system of claim 12, characterized in that said tranemission means transmit an extended spectrum code division multiple accee signal, characterized in that said repeating means include means for transmitting the access signal. spectrum division division extended at at least one connection link channel, and characterized in that said ground station includes means for receiving the repeated extended spectrum code division multiple access signal from the connection link channel (per I miss it one).

23. In a satellite communication system comprising at least one satellite having a steerable antenna that generates a beam pattern in motion over the surface of the earth, the beam pattern comprised of a plurality of sub-beams , a method for determining an antenna correction correction signal for the satellite, comprising the steps of: providing at least one reference transmitter in a known poem on the surface of the earth; transmitting at least one signal from the reference transmitter (at least one) in at least one of the sub-beams; receive the signal (at least one) with the satellite antenna and repeat the received signal (at least one) to a ground station; receive the repeated signal (at least one) with the terreetre eetation; determine a gain of the received signal (at least one); comparing the determined gain with a expected gain to be received based on a predetermined knowledge of a spatial gain variation of the satellite antenna; and determining a difference between the determined gain and the expected gain to derive a correction signal indicative of a satellite position error.

24. In a satellite communication system comprising at least one satellite having an antenna that generates a beam pattern in motion on the surface of the earth, the beam pattern being comprised of a plurality of sub-hacee, a method for determining a beam pattern correction signal for the satellite, comprising the steps of: providing at least one reference tranemieor in a known poem on the surface of the earth; transmitting at least one signal from the reference transmitter (at least one) in at least one of the sub-hacee; receive the signal (at least one) with the antenna of the satellite; comparing a gain of the received signal (at least one) with a gain that is expected to be received based on a predetermined knowledge of a spatial gain variation of the satellite antenna; and determining a correction signal of the beam pattern according to a difference between the actual gain and the expected gain.

25.- A method according to the claim 24, characterized in that the step of receiving the signal (at least one) with the satellite includes a step of retransmitting the received signal (at least one); and characterized in that the comparison and determination parameters are executed by at least one ground station.

26.- A method in accordance with the claim 25, and which also includes the tasks of: transmitting the correction signal of the terrestrial eetation to the satellite; and correct the beam pattern according to the correction signal.

27.- A method in accordance with the claim 25, and further comprising the steps of: storing the correction; transmitting the corrected correction signal from the same ground station or a different ground station to the satellite; and correct the beam pattern according to the correction signal.

28.- A method in accordance with the claim 24, characterized in that the comparison and determination steps are executed by the satellite.

29. In a satellite communication system comprising at least one satellite having an antenna that generates a beam pattern in motion on the surface of the earth, the beam pattern being comprised of a plurality of sub-beams, a method for determining a correction signal of the beam pattern for the satellite, comprising the step of: providing at least one reference transmitter at a known position on the surface of the earth; transmit at least one signal from the reference trader (at least one) in at least one of the sub-beams; receive the signal (at least one) with the satellite antenna; comparing a gain of the received signal (at least one) with a gain that is expected to be received based on a predetermined knowledge of a spatial gain variation of the satellite antenna; determining a correction signal of the beam pattern according to a difference between the actual gain and the expected gain; and correcting the beam pattern according to the correction signal and according to the information obtained from at least one position sensing means carried by said satellite.

30.- A method in accordance with the claim 29, characterized in that the step of receiving the signal (at least one) with the satellite includes a step of retransmitting the received signal (at least one); and characterized in that the comparison and determination steps are executed by at least one ground station.

31.- A method in accordance with the claim 30, characterized in that the correction step includes an initial step of transmitting the correction signal from the ground station (at least one) to the satellite.

32. A method according to claim 30, characterized in that the correction step includes the initial steps of storing the correction signal on the ground; and subsequently transmitting the correction signal from a ground station to the satellite.

33.- In a satellite communication system comprising at least one satellite having an antenna that generates a beam pattern in motion on the surface of the earth, the beam pattern being comprised of a plurality of sub-beams, a method for determining a correction signal of the beam pattern for the satellite, comprising the steps of: providing at least one trader in a poem on the surface of the earth; at least one signal from the tranemieor (at least one) in at least one of the eub-beams using a predetermined access technique; receive the signal (at least one) with the satellite antenna; comparing a gain of the received signal (at least one) with a gain that is expected to be received based on a predetermined knowledge of a spatial gain variation of the satellite antenna; and determining a correction signal of the beam pattern according to a difference between the actual gain and the expected gain.

34.- A method in accordance with the claim 33, characterized in that the predetermined access technique comprises a code division multiple access technique.

35.- A method according to claim 33, characterized in that the predetermined access technique comprises a time division multiple access technique.

36.- A method according to claim 33, characterized in that the predetermined access technique comprises a multi-frequency frequency access technique.

37. A method according to claim 33, characterized in that the tranemieor forms a portion of a terminal transceiver of the user. 38.- A method according to claim 37, characterized in that the step of receiving the signal (at least one) with the satellite includes a step of retransmitting the received signal (at least one); characterized in that the comparison and determination steps are executed by at least one ground station receiving the retransmitted signal; and characterized in that the terrestrial communication (at least one) is connected to a seven terrestrial communications to couple the user terminal to the seventh terrestrial communications.