Position determination using multiple base station signals

Positioning system using multi-base station signals

The present invention relates to a system for locking a terminal station of a radio communication system, in particular to a method for positioning a terminal station of a radio communication system that uses a spot beam to illuminate a geographic area in the system to provide a communication coverage.

In satellite communication systems, one example is known as a wireless communication system using spot beams. Another example is a cellular PCS system that uses a fixed beam phased antenna array. In order to achieve a cost-effective capacity to serve the mass of users, the communication system must be able to allow important available spectrum multiple times throughout the world. This can be achieved, for example, by using multi-point beam antennas that divide the illuminance of selected service areas in many smaller areas.

The most promising satellite system for this application is to place satellites in low earth orbits (LEOs), medium earth orbits (MEOs), or fixed earth orbits (GEOs). The disadvantages of satellites in fixed orbits include the need for huge antennas to create fish spot beams of the size required for 40,000 km orbital distances, and long-term signal delays across orbital distances that cause problems in two-way conversations. On the other hand, the disadvantage of satellites in low earth orbit is that the area illuminated by the focal wave due to the satellite's rotation relative to the earth will change as the satellite rotates around the earth. Although lighter in degree, medium-Earth orbit satellites still have problems with low earth orbits (LEOs) and regular earth orbits (GEOs).

Satellite systems using low or medium earth orbit satellites need to compensate for the rapidly changing propagation delays on the chain between the satellite and the terminal stations on the earth caused by the movement of the satellite relative to the earth. During communication in such a system, Doppler compensation is provided to the signal for changes in propagation delay. In order to provide this Doppler compensation, the terminal station will search for this Doppler frequency. This kind of operation will be a labor-consuming and time-consuming project, and will delay the time to connect to the system.

However, given the position of the terminal station and the orbital period information of the satellite position, the Doppler compensation can be calculated without searching for the Dougler frequency, which can speed up the call heuristic process.

Knowing the location of the terminal unit is also useful for providing many other system functions. For example, the handover of a terminal unit between the focal beam and the frequency designation can be made easier by using the known terminal unit location.

The conventional method of determining the position of the terminal station is to use the information obtained from the Global Positioning System (GPS). This GPS includes multiple MEO satellites, and each satellite transmits a known signal. From any given point on the earth, a terminal station can receive and measure three or four such signals (because there are many GPS in orbit) to determine the time delay, and therefore determine three or four terminal stations and terminals The distance between the stations. This information can then be used to determine the position of the terminal station using the triangulation method. Although this technique is quite effective in systems where multiple different satellite signals can be used by the receiver, other systems such as GEO satellite systems do not have this advantage. Therefore, it is necessary to provide different methods and systems to obtain position information of terminal stations in a radio communication system without relying on the availability of signals from multiple satellites. A group of such systems and methods are provided in the aforementioned US Patent Application No. 08/597,073. In this patent application, a technique is described in which signals generated in a satellite using polyphase array antenna beams can be used To obtain an estimate of the position of a mobile station. However, we also hope to be able to locate mobile stations for terrestrial radio communication systems other than satellites (or included at the same time).

According to a representative embodiment of the present invention, the method for positioning a terminal station is: measure the signal received from the multiple spot beams closest to the terminal station in each of the multiple base stations with phased antennas The signal strength value. For example, for each base station with phased antennas, it is related to the central spot beam of the currently operating mobile station, and the signal strength from 6 adjacent beams can be measured corresponding to the strength of the central beam. Using the information from these measurements, an exponential model of the beam shape can be used to determine the orientation of the terminal station. Using the positions from multiple base stations, explain that triangles can be used, for example, to determine the position of the terminal station.

According to other representative embodiments, the mobile station or terminal station can measure the time delay of the propagating signal from the satellite and use the information from multiple such measurements to determine its position. Then, for example, this procedure can be performed during the call setup period or during the wake-up period when the mobile unit monitors the call message.

From the following description, those familiar with the technology can further understand the features and advantages of the present invention. Please refer to the accompanying drawings when reading. Among them: the first illustration represents the beam irradiation field shape; the second illustration uses identification and The representative coordinate axis and angle of the terminal station position related to the satellite position; the third diagram shows the relative accuracy of the exponential beam model, which is a function of the angle with the beam center; the fourth diagram shows the radial mapping of the terminal station position; Fig. 5 illustrates a method of locating a terminal station according to a representative embodiment of the present invention. The sixth figure can be used to form a block diagram of an example of a base station receiver of another representative embodiment of the present invention; the seventh figure is a graph of the beam size versus direction of the receiver example of the sixth figure.

Detailed description

Before starting to explain the location of this terminal station, consider a very simplified satellite communication system in which three communication channels are used. Provide multiple antenna beams, such as 37, the number of which is determined by the fixed physical characteristics of the satellite antenna system, and is used in the so-called spot beam coverage area. The first figure shows the operational focus beam among the 37 focus beams. According to the conventional design, the gain of the worst point at the middle point between the three points (for example, the corresponding beam illumination crossing point in the first figure) can reach the maximum gain by selecting the beam width, The gain at the midpoint of the corresponding peak (beam center gain) is reduced by about 3dB. This is a typical compromise method. On the one hand, this configuration reduces the peak gain by widening the beam, thereby reducing beam loss, and on the other hand, narrowing the beam and increasing the peak gain, but it must bear a larger beam edge Loss, this loss is the same as the distance from the center. Another different design can be found in US Patent Application No. 08/179,583. This patent application explains how in a slightly different direction, the channel can perform more effective radiation beams, so that each point on the earth is close to one. The beam center of the channel. By applying this method, multiple channels can be provided to the system, so that the channel whose center is more inclined to any specific mobile station can be selected, so the loss at the edge of the beam can be changed.

In any example, a system can use all three frequency channels in each of the 37 spot beams. Applying this result, the mobile unit at the midpoint between the three beams can be used from all three frequency channels. The two beams receive equal overlapping signals on each frequency, that is, beams of two equal strengths interfere above each required signal, and the interference problem can be avoided by allocating the frequencies between the beams of the three frequency reuse field types. In the latter example, the mobile station at the midpoint between the three beams receives all three frequencies of equal intensity from three different surrounding beams, but each beam receives only one frequency, and the far side lobes Interference can be reduced. The mobile unit at the midpoint of the two beams will receive signals of equal strength for the two frequencies, while the strength of the signal received from the third frequency is smaller than that of the second frequency. The mobile unit in the center of the beam will mainly receive the frequencies of the beams whose intensity is slightly lower than the other two frequencies from the 6 surrounding beams. Therefore, a mobile station roughly determines its position based on the relative received signal strength (such as the received signal strength in the above-mentioned three frequencies). For a detailed description, please refer to US Patent Application No. 08/179,958. Hereinafter, another method for determining the position by the signal strength received from the adjacent beam is described, as described in US Patent Application No. 08/587,073.

The power received by the mobile unit from each beam depends on the size of the beam shape, and the radiation field shape obtained by the beam is determined by the combination of the radiation field shape of each element generated by the beamforming of the element and the array factor. The model that can be used to determine the power loss of the obtained field shape is an exponential model. If the beams can be fully identified, the received signal strength measured from the occupied and surrounding beams is used as a measurement value of the beam shape, and this measurement value can be used to determine the position of the mobile unit.

When it is assumed that the position of the beam center is already known, the problem of estimating the mobile position becomes a problem of estimating the user's position relative to the beam center. Given the known direction of the beam at a specific spot, the users position can be determined by two angles: the angle is the angle from the center of the beam; and the angle θ around the beam extending from the satellite in the direction of the beam center. This concept See the second figure.

Although the normalized beam shape can be determined by the following exponential equation, the beam field shape is a function of angles Φ and θ, which is:<maths><img file="TW353835B_D0001.tif" /></maths>Here, α is selected to fit the model of the positive beam field shape. When the angle is quite small, this model is quite accurate, usually within a few degrees. For example, in the 211-element array proposed in the Inmarsat EP21 satellite design, the alpha value of the approximate array field shape is found to be 0.1891 after beamforming. Under the control of the third figure and the exponential model field shape, this system simulates the field shape of beamforming. Among them, the model field shape is represented by the discovery curve with a higher (y-axis) field shape gain value. It can be seen that the exponential model adaptation method can be accurate to the state of Φ=3 degrees, where it will diverge from the simulated field shape.

In order to estimate the values of Φ and θ, use the antipodal x(Φ, θ) (note that the vector is represented by the bold x), and its expression is<maths><img file="TW353835B_D0002.tif" /></maths>Here θ is measured from the center of the beam. Now, in order to estimate the position of the mobile unit, measure its power for the signal in the current and 6 surrounding beams. The power measurement is expressed as p=[p₀,p₁,. . . ,p₆]^T. The model used to measure the i-th beam becomes:<maths><img file="TW353835B_D0003.tif" /></maths>Here i<img file="TW353835B_D0004.tif" />{0,1,. . . 6} represents the measured beam, and x_iIndicates the position of the center of beam i. Using this model can directly determine the location of the mobile unit that caused the problem. This is because the absolute power (represented by the scalar factor A in equations (4) and (5)) cannot be known. Therefore, in accordance with a representative embodiment of the present invention, relative measurements of power from beam pairs can be used to determine position. For example, the center beam can be used as a reference beam, and this beam correspondence can determine the relative power measurement. The calculated measurement value is expressed as y=[h₁,. . . ,h₆]^T, Where h_i=p_i/p₀. Using this method, the measured value and model can become<maths><img file="TW353835B_D0005.tif" /></maths>For example, h can be calculated from the mobile station_i(x), and the mobile station uses the RSSI with the reception time slot, and the time slot corresponds to the time slot received from the center beam, and then this measurement slot is used in equations (6) and (7). Now, applying the measurement model in the above equations (6) and (7) can determine the estimated value of the position of the mobile unit. In order to estimate the position of the action unit, by finding the point that makes J(x) the smallest, calculate the least square estimate of the Kalmax minimum variance of x, where J(x) is<maths><img file="TW353835B_D0006.tif" /></maths>here<img file="TW353835B_D0007.tif" />Is the estimated value of the action position, P_x,k|k-1Is the estimated value of the position covariate matrix, and Ry is the hypothetical known measured variance. choose<img file="TW353835B_D0008.tif" />And P_x,k|k-1.The initial value of. For example, for<img file="TW353835B_D0009.tif" />Choose the beam center position, and for P_x,k|k-1, The radius of the beam is used as the standard deviation of the initial estimate. For the Ry value, by assuming the worst signal-to-noise ratio value that is technically sufficient to handle, the hypothetical noise variance is selected, and then the appropriate noise variance for the power measurement corresponding to this signal-to-noise ratio. It is assumed that the noise from different beams is not correlated with each other. Then the function h(x) is given by the following formula:<maths><img file="TW353835B_D0010.tif" /></maths>Using this type in the position estimator can allow tracking the position of the mobile unit at different times and generate an estimate of the covariate of the estimator. If the measured power noise variance can also be estimated, this covariate is quite useful, and the covariate of the estimator can give the estimation result better accuracy. For example, this covariate can indicate the reliability of the position estimation and is used to more accurately predict the beam processing time.

Many different methods can be used to obtain the minimum point of J(x). Because the function h(x) is highly non-linear, an expanded Kalman filtering method can be used. Moreover, because of non-linearity, it is better to use the iterative expansion Kalman filtering method. The equivalent form of this estimate is to directly calculate the Gauss-Newton estimate from equation (8) for each update time k. Given the existing estimated value at time k, the estimated value can be calculated by x<img file="TW353835B_D0011.tif" />To refine the estimate<maths><img file="TW353835B_D0012.tif" /></maths>Here x can be obtained by solving the following linear equation:<maths><img file="TW353835B_D0013.tif" /></maths>The values of Pk and g can be obtained by the following formula:<maths><img file="TW353835B_D0014.tif" /></maths>and<maths><img file="TW353835B_D0015.tif" /></maths>Within the tolerance range, or when the estimated value can be further executed, these equations can be calculated iteratively, and the initial value of x is selected as the previous estimated value<img file="TW353835B_D0016.tif" />And use P_x,k|k-1=P_x,k-1. At the end of time k=1, the previous estimate<img file="TW353835B_D0017.tif" />Can be selected as the beam center, and select P_x,1|0=P_x,0Make the radius of the beam center a standard deviation. When the satellite movement needs to be tracked, that is, when the position determination is calculated in a relatively long period of time, an appropriate satellite movement model can be used to generate<img file="TW353835B_D0018.tif" />And P_x,k|k-1. And it must also be noted that the output common variable P is only generated when the convergence of the output result needs to be monitored._x,k-1,(Therefore, unnecessary conversion operations can be saved).

In each iteration calculation, the current estimate<img file="TW353835B_D0019.tif" />Click on the calculation /h=xh(x). Its value is:<maths><img file="TW353835B_D0020.tif" /></maths>Where i=1,2,. . . x/hi(x) of ,6 is determined by the following formula:<maths><img file="TW353835B_D0021.tif" /></maths>Using these model equations, it is now possible to use equation (8), as well as the measurement of the received beam signal strength and the model beam field shape to determine.

According to a representative embodiment of the present invention, the terminal station can be located by measuring the propagation delay of signals transmitted by one or more satellites. This representative embodiment is illustrated in the flowchart of the fifth figure. For example, in step 502, each satellite visible to the terminal station can transmit a signal. This signal includes a column containing codes with excellent correlation characteristics. Based on the reception time of the relevant spike and the absolute time of the embedded signal, in step In 506, the value of the propagation delay can be determined. In step 508, the propagation delay can be sent to the network and the position of the terminal station under the given movement information of the known satellite can be selected. Then repeat this procedure to update the position of the terminal station.

For example, this delay measurement can be performed in different traffic times. During the call setting, the satellite will receive an initiation message including terminal station ID information on the random access channel. This can provide the satellite with general information about the location of the terminal station, for example, it can be based on which array element can receive extremely strong terminal station initiated messages. During the sending of the call establishment, the terminal station can perform the above-mentioned delay measurement. For a representative system, the initiation message is long enough to perform three or four delay measurements, and the interval between each measurement is about 20 seconds. This information including beam information can be used to estimate the position of the mobile station by applying the well-known triangulation technique.

According to another representative embodiment, the positioning of the mobile terminal station can be performed by taking these delay measurements during the "waking up" period of the terminal station. The terminal station can periodically turn on the power to monitor the control channel to determine whether this channel is called to establish a connection. This delay information can then be stored in the memory device of the terminal station. Multiple such delay measurements can be stored, for example four measurements, and these measurement values can then be forwarded to the satellite so that the terminal station position can be calculated during the call establishment or call origination.

The above-mentioned representative embodiments have been described using a satellite radio communication system, for example, the radio coverage is a system provided by a spot beam generated from a satellite. However, the present invention can be configured using a ground system. In this system, the array antenna of the base station can illuminate different areas. However, because the base station is not elevated from the ground or in the case of satellites, the base station is in a mobile state. The measurement of the received signal of a single base station can be used to estimate the position of the terminal station, rather than its absolute position. Therefore, according to other representative embodiments of the present invention, signals received by multiple base stations from a terminal station can be used to calculate the position of the terminal station by applying the triangulation method.

For example, consider the architecture of the representative base station receiver in Figure 6. Among them, a fixed beam phase array antenna system is shared with different hardware components to generate multiple beams in a fixed angular direction. The phase array antenna system may include a plurality of antenna elements, and the first group of antenna systems 602 are used for receiving horizontally polarized signals, and the second group of antenna systems 604 are suitable for receiving vertically polarized signals. The beams thus received are processed by beamforming circuits 606 and 608 corresponding to the beams. In blocks 606 and 608, the next beamforming matrix technique, such as the so-called "Bulter" matrix technique, is performed. Then the received signal is further processed by the low noise amplifier 610 and the receiving circuit 612. For example, the receiving circuit 612 itself can be a signal strength measuring device, or can be combined with a demodulator that demodulates only a part of the received signal (such as sync characters or other known symbols). As described below, the receiving circuit performed depends on the number of beams that need to be selected. In this representative embodiment, four of the eight receive beams are selected in block 614 to receive mobile station signal power. However, those skilled in the art should understand that any options can be used, such as using signal power symbols such as known sync characters or other known information symbols. Then, in block 618, the synchronization operation of the received signals in the four selected beams is performed, and then the equalization operation is performed by the equalizer 618. This information is then decoded and processed using known techniques.

The seventh figure shows a representative array field shape, in which the array of the receiving architecture of the sixth figure is used to cover -60. To 60. The range of angles. It can be seen from this figure that the number of beams that can be seen by the mobile unit positioned in a specific direction corresponding to the receiver in the sixth figure is more than one. Assuming that a terminal station signal can be seen in the selected beam, and if the relative power in these signals is known, this provides the information needed to determine the angular direction of the terminal station using the above technique. Therefore, in a single base station, the position of the mobile unit can be estimated. Assuming that the azimuth estimate from one base station to one terminal station in two or more base stations has been obtained, this information can be recorded to determine the position of the terminal station using the triangulation method. The position estimation at each base station can be a time marker to get better accuracy. In addition, it can be assumed that the base stations are close enough, so the propagation difference is not meaningful. Therefore, the time mark direction estimation can be used to form a combined position estimation, and the required accuracy of the position estimation controls the time interval between the combined measurement values. For example, a position estimation accuracy of 150 meters can limit the measurement value combined with the signal received within a predetermined time period.

The above-mentioned representative embodiment does not need to be included in the base station to which the triangular method of synchronization is applied. However, if a synchronized base station can be used, better position accuracy can be obtained by combining the estimated value of the above-mentioned azimuth and the use of the difference between the signal arrival time for the azimuth measurement. For example, the time difference of signal measurement from two antennas is T₁₂. Given that the users position is X, the expected time difference can be determined by another nonlinear or equation f₁₂(X) is obtained, so another term can be added to formula (8):<maths><img file="TW353835B_D0022.tif" /></maths>And then a similar process can be performed as described above, adding other items to equations (12) and (13) to take the time delay measurement into consideration, namely<maths><img file="TW353835B_D0023.tif" /></maths>In equation (13) and add<maths><img file="TW353835B_D0024.tif" /></maths>

Those skilled in the art must understand that the present invention can be implemented in other specific forms without departing from the spirit and characteristics of the present invention. The above-mentioned embodiments are used to illustrate the present invention, but are not intended to limit the present invention. The point of view of the present invention is described by the attached patent application scope, rather than the above description, and all changes within the meaning and scope of the equivalent application of the present invention are covered within it.