JP2020080571A - Method for maintaining signal-to-noise ratio at user terminal in satellite system - Google Patents

Abstract

To provide an earth orbit communication satellite and a user terminal used therefor.SOLUTION: A system and a method for maintaining a signal-to-noise ratio when a user terminal switches beams include a user terminal that generates beam aiming information. The beam aiming information is used to change a time at which the user terminal switches communication from a first beam to a second beam transmitted from the satellite, or adjusts the attitude of the satellite, thereby being used to correct any error in the directivity of the beam transmitted from the satellite to the user terminal.SELECTED DRAWING: Figure 1

Description

RELATED STATEMENT This case claims priority to US Patent Application No. 62/241449, filed October 14, 2015, which is incorporated herein by reference.

  The present invention relates to an earth orbit communication satellite and a user terminal used for it.

  A non-geostationary satellite system comprises a group or constellation of satellites orbiting the earth at altitudes other than geosynchronous orbit (about 36000 kilometers above the earth's surface). Non-geostationary satellite systems in the low earth orbit (LEO) have less propagation loss and less propagation delay than earth-synchronous satellite systems due to the lower orbits of non-geostationary satellites. As a result, such satellites are more suitable than geostationary satellites for interactive communications such as Internet services.

  Geostationary satellite systems have an orbital period equal to the earth's rotational period, and therefore appear to the earth as a fixed position in the sky. Non-geostationary satellites move relatively faster and thus appear to observers on the ground as they pass overhead from horizon to horizon. Due to this relative movement between the non-geostationary satellite and the earth, such satellites move in and out of range of the user terminal on the ground. Such terminals therefore have to switch their communication link from one satellite to the next (ie handoff) in order to achieve continuous communication.

  In some systems, wireless transmissions from satellites to user terminals are in the form of multiple independent beams directed in different directions. Thus, in addition to terrestrial user terminals competing with inter-satellite handoffs, there is a handoff between individual beams of individual satellites as the coverage area of the satellite passes through a particular user terminal.

  In the optimal situation, each satellite is properly oriented in space such that the beam emanating from it "points" in a specified direction. However, the reality is that there may be errors in the satellite's attitude, in addition to any other errors for the individual beams, so that the beams do not point exactly according to the system design. Such inaccuracy in beam aiming results in poor signal-to-noise ratio (SNR) at the user terminal.

  Beam aiming affects SNR in two ways. One way is that if two adjacent satellites in the constellation point at a slight distance from each other, there may be a gap in ground coverage between these satellites. The second way SNR can be affected is that a single satellite points in a slightly wrong direction and the dividing line between the two user beams from that satellite has shifted its position on the surface of the earth. (For example, forward or backward). This dividing line is defined as where the signal strengths from both beams are equal. In a system where a user terminal switches its telecommunication connection from one beam to the next based on time (as calculated a priori from ephemeris and knowledge of the location of the terminal), a dividing line is expected If shifting from position, the terminal will experience unequal signal strength before and after the shift.

  Currently, there are several ways to address this issue. One way is to use common techniques in mobile telephony, where the user terminal compares the power of the signal currently being received with the power of other beams received on other channels. . As soon as the received power of the other beam exceeds the received power of the signal currently being received, the user terminal performs the switching. At that time, the received signal strengths of the two beams are very close to each other, and the SNR hardly changes. However, this approach results in a significant amount of overhead traffic. The second way to address the problem is to design each satellite with very tight tolerances (up to 0.2 degrees) in beam pointing. However, this requires relatively more expensive hardware in the satellite, in addition to tight manufacturing tolerances. Cheap satellite control systems are unlikely to meet this tolerance. The third approach is to accept that a relatively poor quality of service is provided to the user.

  This first approach results in excessive amounts of telecommunications traffic, the second approach attempts to avoid the problem, and the third approach ignores the problem. Neither of these approaches is particularly satisfactory.

U.S. Application No. 14/627577

The present invention provides a system and method for maintaining a signal to noise ratio when a user terminal switches communication from one beam transmitted from a satellite to the next. The present invention is
Rather than using traditional approaches to determine when to handoff (i.e., compare received power on a channel), timing-based approaches may be used,
The relationship between the angular offset and the timing mismatch can be defined,
The information gained from the relationship is then
May be used to adjust the beam switching time (so that the user terminal receives equal signal strength from both beams) and/or
It is based on some insights that the satellites can be fed back so that they can make the necessary attitude adjustments so that the switching time adjustments are unnecessary.

  There are many reasons why the power received at a user terminal at a particular time is not at the expected level. The reasons are deviations in the attitude of the satellite (pitch, roll, yaw), that individual beams can be mechanically displaced, fluctuations in beam shape, fluctuations in beam intensity, and satellites being accurately positioned in their orbits. Including that it may not be located. Each of these issues is characterized by some parameter (eg, satellite orbit position, beam azimuth, etc.). Also, each of these issues will result in timing errors.

  More specifically, ideally, when the power received at the user terminal is the same for both beams, the user terminal switches its communication from one satellite beam to the next. This results in a constant signal-to-noise ratio when the user terminal switches beams. This switching is executed according to the schedule. Specifically, the user terminal receives a look table that indicates which satellite and which beam of the satellite the user terminal should communicate with at a particular time. The information in the table assumes that the beams are all pointing exactly as expected. If they are not, the switching times are erroneous, as caused by any of the problems mentioned above. Therefore, the received power level does not remain unchanged during the switch, but there is a change, typically a reduction, in the received power. This results in a reduction in signal to noise ratio.

  According to the present teachings, beam aiming information is obtained by a user terminal. Specifically, the user terminal obtains a power reading received from the beam as a function of time. The system retrieves that data and compares it to the expected power level. From that comparison, information can be extracted that correlates to errors in satellite attitude (ie, roll, pitch, and yaw). In addition to determining the error in satellite attitude, the measurement data can capture other types of error as well.

  Finally, the beam aiming information generated by the measurements obtained from the user terminal is (1) for changing the time at which the user terminal switches communication from the first beam to the second beam, or (2) It is used to adjust the attitude of the satellite, thereby correcting any error in the directivity of the beam transmitted from the satellite to the user terminal.

FIG. 1 shows a satellite system 100 for delivering Internet services to homes. FIG. 3 is a diagram showing beams transmitted from satellites of system 100. It is a figure which shows the influence of the roll error in the beam transmitted from a satellite. It is a figure which shows the influence of the pitch error in the beam transmitted from a satellite. It is a figure which shows the influence of the yaw error in the beam transmitted from a satellite. FIG. 6 shows the power received by a user terminal as a function of the position of the user terminal within the coverage area under the satellite for a satellite with 16 beams. FIG. 6 illustrates a method for determining pitch error according to an exemplary embodiment. FIG. 6 illustrates a method for determining pitch error according to an exemplary embodiment. FIG. 6 illustrates a method for determining yaw error and pitch error according to an exemplary embodiment. FIG. 6 illustrates a method for determining yaw error and pitch error according to an exemplary embodiment. FIG. 6 illustrates a method for determining yaw error and pitch error according to an exemplary embodiment. 6A-6C show further details of the method shown in FIGS. 5A-5B and 6A-6C for determining yaw and pitch errors. 6A-6C show further details of the method shown in FIGS. 5A-5B and 6A-6C for determining yaw and pitch errors. 6A-6C show further details of the method shown in FIGS. 5A-5B and 6A-6C for determining yaw and pitch errors. 6A-6C show further details of the method shown in FIGS. 5A-5B and 6A-6C for determining yaw and pitch errors. FIG. 6 illustrates a method for determining roll error according to an exemplary embodiment. FIG. 6 illustrates a method for determining roll error according to an exemplary embodiment. FIG. 6 illustrates a method for determining roll error according to an exemplary embodiment. FIG. 6 illustrates a method for jointly determining roll error, pitch error, and yaw error, according to an example embodiment. FIG. 6 illustrates a method for jointly determining roll error, pitch error, and yaw error, according to an example embodiment. FIG. 3 shows a first embodiment of a method according to an exemplary embodiment of the invention. FIG. 6 shows a simulation map of additional beam errors including individual beam aiming offsets, variations in beam shape, and variations in beam intensity. FIG. 11b shows a map of the beam allocation area on the ground from the parameters used in the simulation map of FIG. 11a. FIG. 6 shows a second embodiment of a method according to an exemplary embodiment of the invention.

  Exemplary embodiments of the present invention relate to a satellite system 100 for providing low cost broadband internet services anywhere on earth. Embodiments of the invention generally use any number of satellites (i.e., one or more) to produce a ground-measurable beam of radiation (e.g., optical, RF, or otherwise). It is applicable to non-geostationary satellites.

  FIG. 1 illustrates an exemplary embodiment of a satellite system 100 and its operating environment. The system 100 includes a core network 102, a gateway antenna 104, a LEO satellite 106, and a user terminal 108. The system 100 sends data from the Internet 50 to user devices 70 (eg, televisions, computers, tablets, smartphones, or other devices capable of receiving and/or sending data) and vice versa.

  The core network 102 receives/transmits data from/to the Internet 50. Among other functions, core network 102 routes data packets to multiple gateway antennas 104 for transmission to multiple LEO satellites 106. Similarly, the core network 102 receives data packets from multiple LEO satellites via multiple gateway antennas. In addition to including internet content and the like, the data packet includes system-related information, as discussed further below.

  For simplicity, FIG. 1 shows a single LEO satellite 106, but it should be understood that system 100 includes multiple such LEO satellites, referred to as a “constellation”. For example, in some embodiments, the constellation includes a very large number of satellites, such as 720 satellites. In some embodiments, the satellite constellation is organized into multiple orbital "planes," each orbital plane at a different altitude. Typically, but not necessarily, there is an equal number of satellites in each orbital plane.

  In the embodiment shown in FIG. 1, user device 70 receives data from and/or transmits data to satellite 106 via user terminal 108. User device 70 is shown as located within structure 60. In some other embodiments, the user device 70 is used outdoors, as supported by a suitable enhanced telecommunications connection between the user terminal 108 and the user device.

  In the exemplary embodiment, user terminal 108 is shown attached to a residential structure 60. In some other embodiments, the structure 60 is a non-residential building, such as a company (eg, office building, restaurant, warehouse, etc.), hut, or slow moving vessel such as a cruise ship. Typically, one user terminal 108 is installed at each location (eg, home, office, etc.) to provide internet connectivity. One embodiment of user terminal 108 is provided in US Application No. 14/627577, filed Feb. 20, 2015, entitled "User Terminal Having A Linear Array Antenna With Electronic And Mechanical Actuation System."

  As shown in FIG. 2, LEO satellite 106 comprises multiple versions of at least two different types of antennas. The antenna 205 is for communication with the gateway antenna 104, and the antenna 207 is for communication with the user terminal 108. In the exemplary embodiment, antenna 207 is a wireless antenna for transmitting wireless signals towards the surface of the earth. Such transmissions are shown as beams 210, each of which provides a footprint 212 on the surface of the earth. When the user terminal 108 is within the footprint 212 of one of the beams 210, that user terminal receives such data from its wireless transmission.

  Upon initial commissioning of the user terminal 108, the user terminal will be empty until it acquires and tracks one of the satellites 106 (i.e., by listening to pilot signals transmitted by all satellites in the satellite constellation). Perform a fast scan of. Once the user terminal 108 has completed sign-in and is authenticated (including transferring its exact location to the system), the user terminal 108 receives the "satellite and beam" look-up table via the control channel. To do. This table indicates which particular satellite 106 and which beam 210 of the satellite the user terminal 108 should communicate with at a given time. The look-up table is updated regularly (eg, daily, etc.) as the ephemeris information is updated.

  The use of the information contained in the look-up table is based on implicit assumptions, namely that it accurately indicates where the beam transmitted by the satellite is expected and that it is transmitting at the specified amount of power. Based on. This assumption is likely to be incorrect in most cases, so the switch times specified in the table will be erroneous.

  For example, an offset in one or more of the satellite's roll, pitch, or yaw will change the aiming direction of that beam. 3A to 3C show the influence of the above error on the beam aiming direction. In these figures, arrow 314 represents the direction of flight of satellite 106 in its orbit.

  FIG. 3A illustrates the effect of satellite roll on beam pointing direction. Although shown rolled in the clockwise direction, it will be appreciated that the satellite may rotate in the clockwise or counterclockwise directions. "Roll" is when the axis of rotation is parallel to the flight direction. Arrows 316 indicate the direction in which beams 210 (and their respective footprints 212) shift as a result of rolling. The shift is "left" or "right" in the figure, orthogonal to the direction of flight of the satellite.

  FIG. 3B shows the effect of satellite pitch on the beam pointing direction. Although shown pitched in the counterclockwise direction, it will be appreciated that the satellites can rotate in the clockwise or counterclockwise directions. "Pitch" is when the axis of rotation is orthogonal to the direction of flight. Arrows 316 indicate the direction in which beams 210 (and their respective footprints 212) shift as a result of pitch. The shift is "forward" or "rearward" in the figure, parallel to the direction of flight of the satellite.

  FIG. 3C shows the effect of satellite yaw on beam pointing direction. Although shown yawed in the clockwise direction, it will be appreciated that the satellite can rotate in the clockwise or counterclockwise directions. "Yaw" is when the axis of rotation is orthogonal (and out of plane) to the direction of flight. Arrows 316 indicate the direction in which beams 210 (and their respective footprints 212) shift as a result of yaw. The shift is "clockwise" or "counterclockwise" when viewed from above.

  FIG. 4 shows a computer estimate of the power received by the user terminal 108 under one of the satellites 106. In this figure, the satellite transmits 16 beams. For each beam, the received power exhibits a characteristic "hump" shape with a peak 418. Depending on where the user terminal is on the ground relative to the satellite, the user terminal may see power at peak 418, or less power 420 when on the slope. The "valley" between the humps is where the power received from adjacent beams is equal. When the power received at the user terminal coincides with such a trough, it is when beam switching should occur so that the user terminal does not see any step changes in the received power.

  Suppose FIG. 4 shows the power received at multiple user terminals when the beam is pointing in the nominal direction. The time that any particular user terminal should switch between beams is based on when the received power is in the "valley" for that particular user terminal. Consider what happens if the aiming direction of the beam is offset from its nominal value due to, for example, satellite roll, pitch, or yaw. The time at which the power received at the user terminal corresponds to the power level at the valley is changed. As a result, if user terminal 108 was to switch to a different beam at the times specified in the look-up table, the power received at the user terminal would not correspond to the power level at the valley. The result is a step change (and typically a decrease) in received power at the switch.

  The rest of this specification discloses a method of correcting a beam that is not exactly pointing to the expected location as a result of satellite attitude offsets or other problems. That is, a mathematical relationship based on geometric and trigonometric considerations between arbitrary offsets and timing discrepancies is developed and used to maintain the signal to noise ratio at the user terminal.

  When the angular offset is small, the timing discrepancy is also small and the mathematical relationship can be approximated by a linear relationship. As a result, the timing discrepancy can be approximately represented as a linear function of the three angular offsets. At least three equations are needed to solve for three unknowns, in this case three angular offsets. As previously shown, one estimate of timing mismatch can be represented as a linear function of three angular offsets. This provides one linear equation. In addition, the two timing discrepancy estimates provide the two additional equations needed to derive the values for the three unknown angular offsets.

  The additional timing discrepancy estimates can be used to determine the “optimal” set of solutions for the three unknowns. That is, a system of linear equations that uses more equations than unknowns is commonly called an "overdetermined system." The covariance matrix discussed below can then be used with the linear equations to find the "optimal" set of solutions for the three unknown angular offsets.

  5A and 5B show a method for measuring pitch. A single user terminal 108 in the path of the satellite 106 receives the expected received power profile 522 as a function of time (eg, from the satellite system core network 102 of FIG. 1, etc.). The user terminal 108 measures the received power. The received power value is curve fitted and compared to the profile 522, as shown in FIG. 5B. The arrival time difference X between the peak power 523 (expected value) and the peak power 525 (measured value) is obtained. This amount of error time is a measure of pitch error, as discussed further below.

6A-6C show a method for measuring pitch and yaw together. This technique requires more than one user terminal. The same principle of "peak" arrival time is used. Thus, two user terminals 108 ₁ and 108 ₂ in the path of satellite 106 will have their respective profiles of expected received power 522 ₁ and 522 ₂ as a function of time (eg, from satellite system core network 102 of FIG. 1, etc.). To receive. The user terminal measures the received power. The received power values are curve fitted and compared to respective profiles 522, as shown in FIGS. 6B and 6C. FIG. 6B shows the arrival time difference A between the peak power 523 ₁ (expected value) and the peak power 525 ₁ (measured value) for the user terminal 108 ₁ . FIG. 6C shows the arrival time difference B between the peak power 523 ₁ (expected value) and the peak power 525 ₁ (measured value) for the user terminal 108 ₂ .

  7A-7D provide more detail about the determination of pitch and yaw errors. FIG. 7A shows a footprint of four beams and shows a scenario where the time when the peak received power is measured at the user terminal matches the expected time for the peak received power. In other words, there are no pose (or other) errors. FIG. 7B shows the yaw error. The arrival time error is shown as T_yaw in FIG. 7B. FIG. 7C shows both yaw and pitch errors. The arrival time error for the pitch is denoted as T_pitch. As can be seen from FIG. 7C, the mean of the arrival time error for the two user terminals indicates the pitch and the difference of the arrival time error for the two user terminals indicates the yaw.

Referring now to FIG. 7D, in order to determine the pitch angle θ and yaw angle Φ from the time error amount related to pitch (t_pitch) and the time error amount related to yaw (t_yaw), the 3D coordinates of the satellite and the user terminal are always Must be known. From the GPS on the satellite, the altitude (alt) and velocity (v) of the satellite are known. The distance "L" between user terminals is known from their GPS receiver. For small pitch and yaw angles, trigonometry is used to determine pitch and yaw, as shown in FIG. 7D, as follows.
Pitch angle θ=t_pitch*v/alt [1]
Yaw angle Φ=t_yaw*v/L [2]

8A-8C show a method for measuring the roll angle β. This technique requires a small group of user terminals 108 _i , i=1,n such that n equals 6 as a practical minimum. The user terminals are arranged in a column that is essentially perpendicular to the flight direction of the satellites 106. At some instant, all user terminals report power measurements. Power measurements may be plotted, as shown in FIG. 7B. When these points are connected, they define a curve with a characteristic hump shape. The peak of the curve can then be estimated. This plot is compared to the plot of predicted power for each user terminal at the time of measurement. The shift of actual power vs. predicted power (left <-> right) correlates with roll angle. For small roll angles, trigonometry is used to determine the roll, as shown in FIG. 8C, as follows.
Roll angle β = distance / altitude [3]

  For small angle errors, the methods shown in Figures 5A-5B, 6A-6C, 7A-7D, and 8A-8C work well with simultaneous roll, pitch, and yaw errors. Is.

9A and 9B show an alternative method for simultaneously determining roll, pitch, and yaw. As shown in FIG. 9A, a plurality of user terminals 108 _i , i=1,n are arranged in a line across the path of satellite 106. The user terminals may alternatively be randomly placed as long as there are enough user terminals to observe all beams 210 from satellite 106. As shown in FIG. 9B, each user terminal 108 _i measures the received power during a certain time period.

Referring again to FIG. 4, the computer model of the beam pattern can predict what power will be received at any particular user terminal at all times. As a result, the total power error can be calculated as the sum of the squared differences between the measured power and the predicted power over all time and over all user terminals according to equation [4].
Power error = Σ _{all terminals and all times} (power _meas -power _predicted ) ² [4]
The computer model can be manipulated to include any and all values of roll error, pitch error, and yaw error in its prediction. A “brute force” technique to solve this problem is to calculate the total power error for all combinations of roll error, pitch error, and yaw error, for example, with a granularity of 0.1 degree, and then the most It is to choose the case with a small total power error. In the absence of measurement noise, this method would have an error of about ±0.05 degrees.

  Any number of estimation methods known to those skilled in the art can be used to mitigate the effects of measurement noise. One method is to "smooth out" the total power error data by computing the average of all adjacent cases for each case and then choosing the smallest power error from the resulting operation according to Equation [5]. "It is to be.

Where i, j, and k are indices for the particular case of roll, pitch, and yaw, respectively.

  Any measurements obtained are susceptible to measurement errors, and each estimate of timing mismatch (eg, due to improper satellite attitude) is corrupted by such measurement errors. The error is a random variable, of course its value is unknown. However, the variance of the error can be estimated from knowledge of the receiver noise and analysis of the method used to derive the mismatch estimate from the received signal. Different discrepancy estimates are generally not statistically independent. In fact, there are many reasons why a particular mismatch estimate may be correlated. The method used to calculate the variance of the mismatch estimates can also be used to estimate the cross-correlation between the estimates. The variance and correlation estimates are collectively referred to as the "covariance matrix."

  FIG. 10 shows a method 1000 for maintaining a signal to noise ratio (SNR) at a user terminal when switching between beams. Method 1000 uses the techniques described above for determining aiming error (ie, roll, pitch, and yaw).

  According to task 1001, the user terminal measures the received power from the satellite beam. Task 1002 allows the user terminal to process the measurement results along with their location (eg, GPS coordinates, etc.), typically, but not necessarily, as part of the satellite system core network (eg, see FIG. 1). Send to the system. The referenced information is transmitted from the user terminal to the satellite, the satellite to the gateway antenna, and the gateway antenna to the data processing system. In addition to sending the information received from the user terminal to the gateway antenna, the satellite also obtains its own position data (eg, GPS coordinates, etc.) and sends it to the data processing system, according to task 1003. GPS coordinates for satellites are obtained during the time period when the user terminal is measuring the received power.

  Task 1004 causes the data processing system to capture the received power measurements and all of the GPS data and calculate a beam aiming estimate for the satellite. In accordance with task 1005, the data processing system determines a best estimate of satellite aiming error.

  At this point in the method, processing can proceed in any one of two ways. According to task 1006a, the aiming information is transmitted to the satellite via the gateway antenna. Finally, in task 1007a, the satellite modifies its attitude based on the transferred information.

  Alternatively, the process can continue at task 1006b, the aiming information is sent to the user terminal, and the user terminal adjusts its beam switching schedule.

  The user terminals whose power levels are measured may be those of the actual customer (for services provided by the system), or they may be terminals belonging to the operator of the system. In some alternative embodiments, a specialized receiver device created for the purpose of measuring and recording power levels rather than using a user terminal.

  In addition to satellite attitude deviations, there are other possible sources of timing mismatch. For example, individual beams can be mechanically misaligned, variations in beam shape, variations in beam intensity, the satellite may not be located exactly at its defined position in its orbit, etc. Each such cause is characterized by some parameter (eg, satellite orbit position, beam azimuth, etc.). For each of these parameters, the yaw, pitch, and roll are used to derive the mathematical relationship between all parameters (including yaw, pitch, and roll) and the value of the timing discrepancy for a particular measurement. For, the equivalent steps may be performed. Then a linear approximation of the relationship is generated, which results in one linear equation at all unknown parameters. Additional measurements are obtained until at least as many linear equations as there are unknowns are present. The system of equations is then solved to find solutions to all unknown parameters. If there are more equations than unknowns, the least squares method can be used to find the "best" solution. This more complex analysis will be described in more detail here.

  Figure 11a shows an exaggerated version of all simulations of these effects. FIG. 11b shows a map of the terrestrial beam allocation area from the same parameters that were used to generate FIG. 11a. The boundary between the beams is where the received power from adjacent beams is equal, and thus where beam switching should occur.

  If the beam allocation map can be recalculated based on the measured user terminal data, the beam switching schedule can be modified appropriately to improve SNR. One technique for calculating this map is disclosed below.

Consider data from a set of user terminals that measure and store power data under a single beam. Each data point has a power z, a user terminal position and a collection time t. The error is constant over a time measurement interval (e.g. minutes, etc.), and assuming that we use GPS coordinates from satellites and user terminals, all data can be converted to a single point in time, but collected at different points. Can be done. The analogy is that of an office scanner where a one-dimensional array of pixels, each with a strong time history, can produce a two-dimensional image of the scanned object. Therefore, each data point is here an equivalent [x,y,z] point in space, where x and y are latitude and longitude coordinates that are no longer associated with any user terminal location. The beam power is assumed to be closely approximated by the generalized parabolic equation.
z=a1*x ² +a2*x+a3*y ² +a4*y+a5*x*y+a6 [6]
With enough [x,y,z] points (ie a minimum of 6), a set of equations, all based on equation n[6], is a least-squares method for unknown a1, a2, a3, a4, a5, a6. Available to solve by.
State = Pseudo Inverse (H)*z [7]
Where the “state” is the solution of [a1 a2 a3 a4 a5 a6] and H is the x ² , x, y ² , y, and x*y data from the set of equations based on equation [6] Is an array containing all of, and z is the power data associated with the x,y data. This analysis is performed for all satellite beams, one at a time. Once the analytic function is reconstructed for all beams, the beam allocation map can be calculated. The beam allocation map was calculated by taking in all the beam powers from the satellites for each position on the ground and then selecting the beam with the highest received power.

  FIG. 12 shows a method 1200 for maintaining a signal to noise ratio (SNR) at a user terminal when switching between beams. Method 1200 uses the techniques discussed above in connection with FIGS. 11A and 11B.

  The first three tasks (1201-1203) of method 1200 are the same as method 1000 shown in FIG.

  At task 1204, a data processing system that is typically, but not necessarily, part of the satellite system core network (see, eg, FIG. 1) receives the data (power/time/location) received from the user terminal. Convert and use GPS data to convert it to a pure location format (ie, see above discussion associated with equation [6]). At task 1205, the data processing system uses a regression analysis such as least squares to obtain an analytic function for each beam (ie, see the discussion above associated with equation [7]). An analytical function is obtained for each satellite beam.

  A beam allocation map is generated from the analytic function according to task 1206, the map is simply the maximum of all functions at each position on the ground. According to task 1207, the beam allocation map is sent to all user terminals. Finally, each user terminal adjusts its beam switching schedule based on the map.

  Method 1200 is directed to adjusting beam switching schedules to compensate for beam aiming errors. Those skilled in the art will appreciate that the techniques disclosed herein may be adapted to allow a satellite to correct its attitude error by finding the position of the peak of the analytic function for each beam. Will. The average value over the peak positions of all beams on the ground can be used to calculate roll, pitch, and yaw errors that can be fed to the satellite.

  This disclosure describes a few embodiments, and that many variations of the invention can be readily devised by those skilled in the art after reading this disclosure, and the scope of the invention is as follows: It should be understood that it should be determined by the scope of the claims.

50 Internet
60 structures
70 User device
100 satellite system, system
102 core network
104 gateway antenna
106 LEO satellite, satellite
108 User terminal
108 ₁ User terminal
108 ₂ User terminal
205 antenna
207 antenna
210 beams
212 footprint
314 arrow
316 arrow
418 peak
420 power
522 Profile
522 ₁ profile
522 ₂ profiles
523 Peak power
523 ₁ Peak power
523 ₂ peak power
525 peak power
525 ₁ peak power
1000 ways
1200 ways

Claims (15)

A method for maintaining a signal to noise ratio at a user terminal when the user terminal switches communication between a first beam and a second beam, the first and second beams being non-stationary. Transmitted from a satellite, the method
Defining a mathematical relationship between at least one of the satellite's pitch offset, roll offset, and yaw offset and a timing mismatch resulting from said offset, wherein said timing mismatch is said first Reference time for switching communication between the second beam and the second beam, and communication between the first beam and the second beam such that the signal to noise ratio remains constant. The difference between the time to switch the step, and
Adjusting the time at which the user terminal switches communication between the first beam and the second beam based on the mathematical relationship.   Of the pitch offset, the roll offset, and the yaw offset at the user terminal by measuring the power received in at least one of the first beam and the second beam as a function of time. The method of claim 1, further comprising determining at least one of the.   Determining at least one of the pitch offset, the roll offset, and the yaw offset generating a curve fit of the measurement of power received as a function of time acquired by the user terminal. The method of claim 2, further comprising: Determining at least one of the pitch offset, the roll offset, and the yaw offset,
Comparing the curve fit with a reference profile of expected power received by the user terminal as a function of time;
4. The method of claim 3, further comprising determining an offset between the peak value of the curve fit and the peak value of the reference profile.   The method according to claim 2, wherein at least two user terminals measure the received power as a function of time to measure the pitch offset and the yaw offset together.   The method of claim 2, further comprising at least six user terminals measuring received power as a function of time to measure roll offset. Pitch offset, roll offset, and yaw offset are determined simultaneously, and the method
Measuring at a plurality of user terminals the power received from all beams transmitted from the satellite as a function of time, including the first and second beams;
Generating a prediction of the power received at the user terminal as a function of time,
Calculating the total power error as the sum of squared differences between the measured received power and the expected received power over all user terminals. A method for maintaining a signal to noise ratio at a user terminal when the user terminal switches communication between a first beam and a second beam, the first and second beams being non-stationary. Transmitted from a satellite, the method
The first beam and the second beam by defining a mathematical relationship between at least one of the satellite pitch offset, roll offset, and yaw offset and the timing mismatch resulting from the offset. A step of determining an aiming error of the timing mismatch, the reference time for switching the communication between the first beam and the second beam, and the signal-to-noise ratio remains constant. Is a difference between the time for switching the communication between the first beam and the second beam, such that
Transmitting information to the satellite about the aiming error of the first beam and the second beam;
Adjusting the attitude of the satellite to correct the aiming error of the first beam and the second beam.   Of the pitch offset, the roll offset, and the yaw offset at the user terminal by measuring the power received in at least one of the first beam and the second beam as a function of time. 9. The method of claim 8, further comprising determining at least one of the.   Determining at least one of the pitch offset, the roll offset, and the yaw offset, generating a curve fit of the measurement of power received as a function of time acquired by the user terminal. 10. The method of claim 9, further comprising: Determining at least one of the pitch offset, the roll offset, and the yaw offset,
Comparing the curve fit with a reference profile of expected power received by the user terminal as a function of time;
11. The method of claim 10, further comprising determining an offset between the peak value of the curve fit and the peak value of the reference profile.   10. The method of claim 9, wherein at least two user terminals measure the received power as a function of time to measure pitch and yaw offsets together.   10. The method of claim 9, wherein at least six user terminals measure received power as a function of time to measure roll offset. Pitch offset, roll offset, and yaw offset are determined simultaneously, and the method
Measuring at a plurality of user terminals the power received from all beams transmitted from the satellite as a function of time, including the first and second beams;
Generating a prediction of the power received at the user terminal as a function of time,
9. The method of claim 8, further comprising: calculating a total power error as a sum of squared differences between the measured received power and the expected received power over all user terminals. A method for maintaining a signal to noise ratio at a user terminal when the user terminal switches communication between a first beam and a second beam, the first and second beams being non-stationary. Transmitted from a satellite, the method
Measuring at least the power received from the first beam at the user terminal;
Transmitting from the user terminal the received power measurements and the location of the user terminal to a data processing system;
Transmitting from the satellite to the data processing system one or more positions of the satellite obtained while the power measurements were being measured by the user terminal;
In the data processing system, generating predicted received power levels at the user terminal for all possible combinations of aiming errors of the satellites;
Selecting in the data processing system the best estimate of satellite aiming error from all possible combinations thereof;
Transmitting from said data processing system to said one of (a) satellite and (b) a user terminal said best estimate of satellite aiming error,
(i) if the best estimate is sent to the satellite, then the method:
In the satellite, further comprising the step of correcting the aiming error based on the best estimate thereof,
(ii) if the best estimate is sent to the user terminal, the method:
The method further comprising adjusting a beam switching schedule at the user terminal.