KR19990075658A - Satellite Transmission Antenna Beam Pattern and Its Connection Method in Low-orbit Satellite Communication System - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a personal (cellular) communication system using a low orbit satellite. In particular, a satellite transmission for establishing a connection with a satellite having the longest stay time among several satellites capable of communication at the call request of a terminal in a low orbit satellite communication system A beam pattern of an antenna and a method of call connection thereof, the field strength of a transmission signal transmitted to a periphery of a service area of a satellite in a low-orbit satellite system with a transmission antenna beam pattern of each satellite in a service direction of each satellite, The electric field strength of the transmission signal transmitted to the periphery of the service area in the service area opposite to the direction of travel is lowered, but the strength of the received power is the highest among several satellites that the terminal can call when the terminal requires handoff. By selecting a large satellite, the service area stay time is maximized. There is an effect that makes connection and satellite.

Description

Transition antenna beam pattern of satellite in LEO satellite communication systems and call connecting method for the same

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a personal (cellular) communication system using a low orbit satellite. In particular, a satellite transmission for establishing a connection with a satellite having the longest stay time among several satellites capable of communication at the call request of a terminal in a low orbit satellite communication system A beam pattern of an antenna and a call connection method thereof.

In other words, the present invention compares only the strength of each pilot signal received from a plurality of satellites among the plurality of satellites that can be connected when the call is made by the communication terminal to maximize the talk time. It is about how to find and choose.

In addition, the present invention relates to an antenna beam pattern design method for compensating for path loss by adjusting the propagation beam pattern of the transmitting antenna in each satellite so that the strength of the received signal in the service area of the satellite is proportional to the stay time at that point. will be.

In general, personal communication systems have been rapidly developed as the need for rapid and frequent information exchange with the development of electronic communication technology and entering the information society.

The representative method of such a personal communication system is a cellular communication method. A predetermined area is divided into a predetermined number of cells (typically taking a 7-cell method), and each cell is provided with a base station for communication relay in the corresponding area. A wireless terminal (also called a cellular phone), which is connected to a control station connected to a public communication network and irregularly passes through a plurality of cell areas through communication relays of a base station or a control station in each cell, no matter what cell area exists. It is possible to make a call between CO line subscribers or terminals.

However, in the case of the cellular system described above, there are many performance differences in the call quality according to the cell (service network) design method. The reason is that if there are obstacles (mountains, buildings, ...) in the direction of propagation, Even though it is clearly in the cell area, it is incapable of depriving the user of the service right, so the cell designer should design the service network by minimizing the area where there is a small number of base stations without considering this part.

Moreover, since terminal users hope that seamless communication with anyone can be established anytime, anywhere, existing cellular systems are virtually limiting to fully satisfy the needs of these users. These days, it is emerging.

Looking briefly at the technical basis of the low-orbit satellite communication system, since the low-orbit satellite communication systems are relatively fast compared to the moving speed of pedestrians or vehicles, handoffs are caused by the movement of satellites regardless of the speed of the mobile terminal. Will be required.

In addition, the low-orbit satellite communication system is designed to show multiple satellites simultaneously for one terminal in order to compensate for the phenomenon that communication is impossible due to the satellite being blocked by a high building or other obstacles around the terminal. When the call is requested, call setup is made by selecting one of several available satellites.

In the conventional low-orbit satellite communication system, two methods are commonly used to determine a beam pattern of a transmission antenna. The first method is to maintain a uniform transmission antenna gain in a satellite service area. In addition, the second method is to compensate for the path loss caused by the difference in distance between the satellite and the ground in the service area.

The technical basis of the existing low-orbit satellite communication system has been briefly described through the above description, and the problems of the conventional low-orbit satellite communication system will be described with reference to FIGS. 1 to 3.

FIG. 1 is a diagram illustrating a case in which a method of maintaining a uniform transmit antenna gain in a service area is applied when determining a beam pattern of a transmit antenna in a conventional low-orbit satellite communication system, and is a distance from a center of a service area of a user in a satellite service area. It represents the normalized transmit and receive power strength according to. That is, as the distance from the center of the service area increases, the distance between the satellite and the ground becomes farther, and thus the path loss increases, indicating that the strength of the received signal is weak when the same power is transmitted.

Therefore, when there are several satellites that maintain a uniform transmit antenna gain in the service area at the time of call request at the terminal, and the call setup is performed with the satellite having the greatest intensity of the received signal, the received signal from each satellite Since the strength is inversely proportional to the distance between the satellite and the user terminal, the user terminal establishes a call with the nearest satellite.

However, when connecting to two satellites at the same time when a call is requested from one user terminal, even if the call is connected since it is the satellite closest to the terminal as shown in the accompanying drawings shown in FIGS. 2A and 2B, The service area stay time is not necessarily longer than the surrounding satellites.

That is, referring to the exemplary diagram shown in FIG. 2A, since the satellite A is located closer to the user terminal in the conventional method of maintaining a uniform transmit antenna gain, the user terminal is connected to the satellite A when a call is requested. In this case, since the service area stay time of satellite A is longer than the service area stay time of satellite B, the terminal is less likely to request handoff than when connecting to satellite B.

In addition, referring to the exemplary diagram illustrated in FIG. 2B, as in FIG. 2A, the satellite A is located closer to the user terminal than the satellite B, and thus the user terminal is connected to the satellite A when a call is requested.

However, in the case of the example shown in FIG. 2B, the user terminal has a longer service area stay time for satellite B than a service area stay time for satellite A. FIG. That is, a problem arises that the user terminal has a lower handoff request probability when the user terminal is connected to satellite B.

In addition to the conventional method of maintaining a uniform transmit antenna gain as described above, when determining the beam pattern of the transmit antenna in a manner that compensates for the path loss caused by the difference in distance between the satellite and the ground in the service area, that is, between the satellite and the terminal. The intensity of normalized transmit and receive power according to the distance from the center of the service area in the method of compensating the path loss of the signal with the transmit power of the satellite is shown in FIG. 3.

3, the distance between the satellite and the terminal increases in advance as the terminal moves away from the center of the service area, thereby compensating for the path loss increased in advance so that the same signal strength can be obtained at any point in the service area on the ground. Keep it.

When the method of compensating for path loss due to the difference in distance between the satellite and the ground in the service area is applied, each of the cases illustrated in FIGS. 2A and 2B is independent of the positions of satellites A and B. Receiving nearly the same signal from the satellite, the terminal is connected to a satellite that suffers less fading between satellites A and B, depending on the environment of the location where the terminal is located.

Therefore, in the above-described case, since the satellite to be connected is determined irrespective of the staying time in the service area of the satellite that can talk to the terminal, even if one of several satellites is selected, the service area stay time distribution becomes the same. .

Therefore, the satellite transmit antenna in the conventional low-orbit satellite communication system does not consider the influence of the available time distribution in the satellite of the terminal. As a result, when the terminal is connected to the satellite with the highest received signal strength among the multiple satellites that the terminal can talk to, the satellite that is closest to the nearest satellite is not the satellite that can last the longest call (the conventional method shown in FIG. 1). ), Or select the same probability (all the existing method shown in Figure 3) for all the available satellites.

An object of the present invention for solving the above problems is to compare only the strength of each pilot signal received from a plurality of satellites to the satellite that can maintain the maximum talk time of the plurality of satellites that can be connected when the call connection of the communication terminal The idea is to provide a way to select and locate the satellite with the greatest intensity.

The present invention also relates to an antenna beam pattern design method for compensating for path loss by adjusting a propagation beam pattern of a transmitting antenna in each satellite so that the strength of a received signal in the service area of the satellite is proportional to the stay time at that point. will be.

1 is a diagram illustrating a case in which a method of maintaining a uniform transmit antenna gain in a service area is applied when determining a beam pattern of a transmit antenna in a conventional low-orbit satellite communication system.

2A and 2B are exemplary diagrams of connecting two satellites at the same time when a call is requested from one user terminal.

3 is an exemplary diagram of a case where a method of compensating for path loss due to a difference in distance between a satellite and a ground is applied when determining a beam pattern of a transmitting antenna in a conventional low-orbit satellite communication system.

4 is an exemplary diagram for describing a gain of a transmitting antenna according to the present invention within a satellite service area.

5 is an exemplary diagram for explaining a reception power distribution in a satellite service area according to the present invention.

6a and 6b is a configuration diagram of a satellite antenna and the antenna in the Φ direction according to the present invention

7A and 7B are exemplary diagrams of normalized transmission power strengths and corresponding reception power strengths in the satellite service area according to the present invention.

8 is an exemplary diagram for explaining a call connection process.

A feature of the present invention for achieving the above object is to increase the electric field strength of the transmission signal transmitted to the periphery of the service area of the service direction of each satellite in the transmission antenna beam pattern of each satellite in the low-orbit satellite system A low orbit satellite characterized in that the electric field strength of the transmission signal transmitted to the periphery of the service area facing the travel direction of the service area is lowered, and the gain of the transmission antenna for the satellite service area is set by the following equation. Satellite Transmission Antenna Beam Patterns in Communication Systems:

Where θ is the irradiation angle between a straight line perpendicular to the ground and the specific direction, Φ is the azimuth angle from the satellite's traveling direction, and G (θ, Φ) is the satellite transmission antenna gain in the (θ, Φ) direction. Where X _r is the distance that the terminal located at (θ, Φ) is within the visible range of satellite communication, L is the distance between the satellite and the terminal, and K is defined as a proportional constant.

Another feature of the present invention for achieving the above object is to increase the electric field strength of the transmission signal transmitted to the periphery of the service area corresponding to the propagation direction of the service antenna in the transmission antenna beam pattern of each satellite in the low orbit satellite system, The field strength of the transmission signal transmitted to the periphery of the service area opposite to is lowered, but the gain of the transmission antenna of the service area is the angle formed by a specific direction with respect to the straight line perpendicular to the ground from the satellite and the azimuth angle from the traveling direction of the satellite. A satellite antenna for defining an antenna beam pattern in which the element and the distance between the satellite and the terminal and the terminal located at an arbitrary point in consideration of the stay distance within the satellite visible communication range are:

A power divider for distributing the transmit signal power of the satellite separated from the received signal by a duplexer, and a plurality of irradiation angle phase shifters for receiving the transmit signal power distributed by the power divider and performing phase shift of each element, And a plurality of irradiation angle element antennas that are matched one-to-one with each of the directional phase shifters.

An additional feature of the present invention for achieving the above object is that each of the irradiation angle element antenna is composed of a plurality of azimuth element antenna.

An additional feature of the present invention for achieving the above object is an azimuth power divider for distributing power by receiving a signal input to the irradiation angle element antenna, and a phase in the azimuth direction by receiving power distributed from the azimuth power divider A plurality of azimuth phase shifters for performing the transition, and a plurality of azimuth antennas that are matched one-to-one to each of the plurality of azimuth phase shifters.

Another feature of the present invention for achieving the above object is to increase the electric field strength of the transmission signal transmitted to the periphery of the service area corresponding to the propagation direction of the service antenna in the transmission antenna beam pattern of each satellite in the low orbit satellite system, The field strength of the transmission signal transmitted to the periphery of the service area opposite to is lowered, but the gain of the transmission antenna of the service area is reduced from the irradiation angle element and the direction of travel of the satellite in a specific direction with respect to the straight line perpendicular to the ground. In a call connection method in a terminal when a transmission signal is transmitted according to an antenna beam pattern in consideration of a distance component between an azimuth element and a satellite and a terminal and a stay distance within a satellite visible communication range:

Inspecting pilot signals from all accessible satellites and storing the pilot signals in large order; and determining whether the signal strength from the satellite in current communication decreases below a given threshold during the first process. A second process of requesting a handoff to a satellite existing at the highest level through the first process, and a third highest process through the third process if it is determined that the second process is reduced to a threshold value or less through the second process. In the case that the handoff request is accepted in the second step includes performing a handoff to the satellite.

As an additional feature of the present invention for achieving the above object, a fifth process of deleting data for a corresponding satellite when the handoff request is not accepted at the highest satellite through the third process, and the current access after the fifth process. If it is determined that the connection with the existing satellite is available, the method further includes a sixth process of accessing satellite data of the next rank among the satellite data stored through the first process and proceeding to the third process. There is.

Hereinafter, a preferred embodiment of the present invention will be described with reference to the accompanying drawings.

First, the technical idea to be applied in the present invention briefly, in the present invention to have the size of the received signal proportional to the service area stay time at any point in the service area in the terminal by the strength of the received signal in the direction of the satellite It is to get a standard for.

To this end, when the terminal in the service area is close to the direction of satellite propagation, it has a large reception signal, and conversely, the beam pattern of the satellite transmission antenna is designed so that the size of the received signal is smaller as it moves away from the direction of satellite propagation. do.

Accordingly, when the terminal can talk to several satellites upon call request, it can connect with the satellite having the longest stay time by selecting the satellite having the greatest signal strength.

Therefore, the satellite transmission antenna of the present invention considers the following two points in order to design the strength of the received signal at any position in the service area in proportion to the stay time in the satellite.

The first is the loss of path along the distance between the satellite and the service area. This is to maintain the same received power strength even for a user far from the center of the service area for the same purpose as the conventional method shown in FIG.

The second consideration is that, by the first consideration, the same power is received at any point in the satellite coverage area, and then the transmit power for any location in the satellite coverage area leaves the satellite coverage area at that point. The antenna gain is adjusted for each point in the satellite's service area in proportion to the time it takes.

In consideration of the above two matters, the gain of a transmission antenna for a satellite service area may be defined as shown in Equation 1 below with reference to FIG. 4.

In this case, θ of the variable used in Equation 1 means the irradiation angle formed by a straight line perpendicular to the ground from the satellite and a specific direction, the variable Φ means the azimuth angle from the traveling direction of the satellite. Therefore, the satellite transmit antenna gain in the (θ, Φ) direction is defined as G (θ, Φ). In addition, the variable X _r is the distance the terminal located at the point of (θ, Φ) is within the satellite visible communication range, the variable L is the distance between the satellite and the terminal, and the variable K is a proportional constant.

Since a low-orbit satellite usually moves at a constant speed, the stay distance and stay time in the satellite service area are directly proportional, so if the point in the service area is a point where the stay time is long in the satellite, it has a relatively large reception power. If the stay time is short, the reception power is to be small. This also means that the points of stay within the satellite maintain the same intensity of received power at the same point.

Accordingly, the maximum received power point 21 of the distribution of received power in the satellite service area 21, an arc 22 made up of points having the minimum received power, and a string 23 made up of points having the same received power. 5 is a schematic diagram attached.

The attached antenna beam pattern shown in FIG. 5 may be implemented using a phased array antenna. As shown in FIG. 4, the antenna beam pattern of the present invention has a non-uniform characteristic not only in the θ direction but also in the Φ direction. Therefore, when implementing using a phased array antenna, the patterns for the θ direction and the Φ direction should be considered at the same time.

6A and 6B show an example of an antenna configuration for satisfying the above requirements. FIG. 6A is a configuration example of a satellite antenna, and FIG. 6B is an antenna configuration in the Φ direction.

Referring to the configuration and operation of the satellite antenna shown in FIG. 6A briefly, the transmit signal power of the satellite separated from the received signal by the duplexer 31 is n antennas in the θ direction through the power divider 32. Divide into There are θ-phase phase shifters 33 at the n θ-direction antenna input terminals, respectively, so that their phases are adjusted to implement beam patterns in the θ-direction.

At this time, each θ direction antenna is composed of m Φ direction antenna array. That is, the unit θ direction antenna input signal is further divided into respective antennas in the Φ direction through the Φ direction power divider 41. In addition, the Φ direction phase shifter 42 is present at each Φ direction antenna input terminal, thereby realizing a beam pattern in the Φ direction by adjusting their phases. In this way, the antenna beam pattern of the present invention can be implemented through the phased array antenna of two stages in the θ and Φ directions.

As described above, in the present invention, the beam pattern of the satellite transmitting antenna is set to be proportional to the staying time in the service area, and the path loss according to the different distances between the satellites and the respective points in the service area is compensated for. . For example, the normalized transmit power intensity and the corresponding receive power intensity when the service area is a circle having a radius of 2000 km in a satellite having an altitude of 1000 km are shown in FIGS. 7A and 7B.

As described above, the transmission signal pattern of the satellite antenna according to the present invention has been described. In the case of using the transmission signal pattern, a signal flow diagram when a terminal in a call request handoff is shown in FIG. 8.

In step S101, the busy terminal always checks the pilot signals from all the other satellites in the vicinity, and stores them in the storage device in the order of increasing strength with respect to the satellites capable of making a call.

While storing the priorities of the plurality of satellites through the process of step S101, if the signal strength from the satellite currently in communication decreases below a given threshold, that is, it is determined in step S102 whether a handoff requirement has occurred. If it is determined that there is a handoff request, the flow advances to step S103 to request a handoff to the satellite located at the head position of the storage device through the process of step S101.

If it is determined in step S104 whether the handoff requested in step S103 has been accepted, and the handoff request is determined to be accepted, the process proceeds to step S105 to perform a handoff to the satellite and to perform the process of step S101 again.

If the satellite requesting the handoff in step S103 does not accept the handoff request, the process proceeds to step S106 to delete data for the satellite from the storage device. Then, it is determined in step S107 whether it is possible to connect to the currently connected satellite. If it is determined in step S107 that the call is unavailable, the flow proceeds to step S108 to terminate the call.

On the other hand, if it is determined in step S107 that the call is possible, the flow proceeds to step S109 to determine whether there is content stored in the storage device, and if there is data present, handoff is requested to the satellite located at the head of the remaining satellites. .

This procedure repeats the above procedure until the call ends if the handoff request is accepted and the handoff is performed and returns to the busy state. However, the call is terminated because the connection with the currently connected satellite is incapable of communication or terminates when all satellites present in the storage device do not accept the handoff request.

Accordingly, when the satellite transmit antenna of the present invention is used, handoff is performed using only pilot signals from each satellite. In this case, the selected satellite is a satellite capable of keeping a longest stay time among satellites capable of channel access.

As described above, when the satellite transmit antenna beam pattern and the call connection method are provided in the low-orbit satellite communication system according to the present invention, even when the terminal requires a handoff, the terminal receives the most among the satellites that the terminal can call. By selecting a satellite with a high power level, it is connected to a satellite whose maximum service area stay time is maximum.

In addition, in the present invention, the satellite transmit antenna designs the beam pattern such that the received power in each region in the service area is proportional to the service area stay time. Each terminal selects a satellite having the largest received power strength among a plurality of satellites that can communicate at the time of a call request or a handoff request. As a result, each terminal can have a maximum service area stay time, so that the probability of requesting handoff can be kept to a minimum. In addition, it is possible to reduce the probability of call disconnection due to a handoff failure during a call.

Since the satellite selection method of the present invention allows the particles of the terminal to compare only the strength of the received signal, the load of the terminal can be minimized in selecting a satellite having the maximum stay time.

Claims (6)

In the low-orbit satellite system, in the transmission antenna beam pattern of each satellite, To increase the electric field strength of the transmitted signal transmitted to the periphery of the service area in the service direction of each satellite, To reduce the electric field strength of the transmission signal transmitted to the periphery of the service area of the service area facing the direction of travel, A satellite transmit antenna beam pattern in a low orbit satellite communication system, wherein the gain of the transmit antenna for the satellite service area is set by the following equation: However, θ is the irradiation angle between a straight line perpendicular to the ground and the specific direction from the satellite, Φ is the azimuth from the satellite's direction of travel, G (θ, Φ) is the satellite transmit antenna gain in the (θ, Φ) direction, X _r is the distance that the terminal located at (θ, Φ) stays within the range of satellite visible communications, L is the distance between the satellite and the terminal, K is a proportional constant. In the low-orbit satellite system, the transmission antenna beam pattern of each satellite increases the field strength of the transmission signal transmitted to the periphery of the service area corresponding to the travel direction of the service area, and increases the field strength of the transmission signal transmitted to the periphery of the service area opposite to the travel direction. The field strength is lowered, but the gain of the transmit antenna in the service area is obtained from a survey angle element in a specific direction with respect to a straight line perpendicular to the ground, the azimuth element from the direction of the satellite, the distance element between the satellite and the terminal, and any A satellite antenna for defining an antenna beam pattern in which a terminal located at a point considers a stay distance within a satellite visible communication range: A power divider for distributing transmit signal power of the satellite separated from the received signal by the duplexer; A plurality of irradiation angle direction phase shifters which receive the transmission signal power distributed by the power divider and perform phase shift of the irradiation angle elements; And And a plurality of irradiation angle element antennas one-to-one matched to each of the irradiation angle direction phase shifters. The method of claim 2, Each of the survey angle element antennas comprises a plurality of azimuth element antennas. The method of claim 2 or 3, An azimuth power divider configured to distribute power by receiving a signal input to the irradiation angle element antenna; A plurality of azimuth phase shifters which receive power distributed by the azimuth power divider and perform phase shift in the azimuth direction; And And a plurality of azimuth antennas that are matched one-to-one to each of the plurality of azimuth phase shifters. In the low-orbit satellite system, the transmission antenna beam pattern of each satellite increases the electric field strength of the transmission signal transmitted to the periphery of the service area corresponding to the travel direction of the service area, and increases the field strength of the transmission signal transmitted to the periphery of the service area opposite to the travel direction. The field strength is lowered, but the gain of the transmit antenna in the service area is obtained from a survey angle element in a specific direction with respect to a straight line perpendicular to the ground, the azimuth element from the direction of the satellite, the distance element between the satellite and the terminal, and any In a call connection method in a terminal when a terminal located at a point transmits a transmission signal according to an antenna beam pattern in consideration of a stay distance within a satellite visible communication range, A first step of examining pilot signals from all accessible satellites and storing the pilot signals in large order; A second step of determining whether a signal strength from a satellite in current communication decreases below a given threshold while performing the first step; A third step of requesting a handoff to any satellite existing at the highest level through the first step if it is determined that the number is reduced to a threshold value or less through the second step; And And a fourth process of performing a handoff to the satellite when the handoff request is received from the highest satellite through the third process. The method of claim 5, A fifth process of deleting data for the satellite when the handoff request is not accepted at the highest satellite through the third process; After the fifth process, if it is determined that the connection with the currently connected satellite is possible, if it is determined that the call is available, the satellite data of the next rank among the satellite data stored through the first process is accessed to proceed to the third process. And a sixth step of the call connection method.