JP2853470B2 - Orbiting satellite communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an orbiting satellite communication system, and more particularly to an orbiting satellite communication system used for voice and data communication using a plurality of low-altitude orbiting satellites.

[0002]

2. Description of the Related Art Conventionally, a multiple access communication system for performing communication via a communication satellite is generally performed using a geostationary satellite in a geosynchronous orbit. Has been proposed since the early days of satellite communications in the 1950s. In recent years, with the increase in the size of the satellite launch locket, the establishment of technology for launching small satellites by tying them together with large satellites, and the development of rockets aimed at launching small satellites have led to economical miniaturization. It is now possible to launch satellites. Along with this, a satellite communication system using low-orbit orbiting satellites using a plurality of small satellites has been spotlighted. For example, "Nikkei Communication Nikkei B
No. 21 October 1991, No. P 112 3
The iridium program of Motorola Corporation in the United States as shown in "Pages 1 to 32" has been announced. FIG. 7 shows a network configuration of a satellite communication system using a general low altitude orbiting satellite group. 7, 101 to 1
03 is an orbiting satellite. The orbiting satellites 101 and 10
2 and 103, as shown in FIG.
The area of G1, the area of cells A2 to G2, and the area of cells A3 to G3 are covered. 104 to 107 are orbiting satellites 10
At least one network control station exists in the communicable area with respect to the area covered by 1 to 103. The network control stations 104 to 107 also serve as gateway stations for connecting a satellite communication channel to the subscriber network 109, performing billing management, and managing network subscribers. In particular, the network control station 107 is also a network reference station that controls the entire network.
In addition, 108 is a communication partner participating in the network,
It is a small communication terminal that can be carried around freely or mounted on vehicles. The orbiting satellites 101 to 103 irradiate a spot beam, and a cell is formed for each spot beam on the ground surface. This is why satellite communications using orbiting satellites is called satellite cellular. As is well known in terrestrial cellular in modern mobile communication systems, each cell uses a number of different frequency repetitions to make efficient use of the frequency. Also,
The use of spot beams contributes to the effective use of satellite power. Cells Ai, Bi, Ci, D
i, Ei, Gi (i = 1 to 3) indicate cells using the same frequency (for example, A1, A2, A3) for each alphabet, and among cells A2 formed by the spot beam of the satellite 102, The communication terminal 108 located
This indicates that a communication channel link is established with the network control station 105, which is a gateway station located in the communication area of the satellite 103, via communication between the satellites 102 and 103.

FIG. 8 shows the orbiting satellite group network shown in FIG. 7 after a certain period of time. That is, as time passes, the orbiting satellites 101 to 103 move relative to the earth, and the communication terminal 108 located in the cell A2 of the satellite 102 becomes the cell C1 of the satellite 101.
It shows the state located inside. Gateway 1 of communication partner
05 is still located in the communication area of the satellite 103. That is, if communication is to be continued as the satellite moves, it is necessary to prepare a completely different communication channel. FIG. 9 shows the state of FIG. 8 after a further elapse of time. This time, although the satellite has moved, the satellite used has not changed, and the communication terminal 108 located in the cell C1 of the satellite 101 at the time of FIG.
01 is located in cell B1. Also, when the communication terminal moves, the cell changes similarly, but there is no problem assuming that the orbiting satellite has moved.

[0004] In order to carry out such continuous communication, the cell in which the communication terminal is located changes with time due to the movement of the satellite, so that it is necessary to prepare a completely different communication channel.

[0005] Therefore, all the cells including the cell adjacent to the cell where the communication terminal 108 is located continuously monitor the signal emitted by the communication terminal 108. The adjacent cell detects the signal of the communication terminal 108 and switches the communication channel.

[0006]

In the conventional orbiting satellite communication system described above, when a cell in use moves out of the coverage area of the communication terminal while the mobile terminal is communicating, the next adjacent cell comes in. The cell used naturally changes when the communication continues to be used and the satellite used changes. With the change of the cell, the frequency of the used channel also changes, and a completely different link from the communication partner is established. There is a disadvantage in that it takes time to establish this link, and communication is interrupted during the transition to the next cell. Further, in the satellite, the spot beam that is in charge of each cell must monitor up to the frequency of all adjacent spot beams, which has the disadvantage that the number of receivers in the satellite becomes enormous. I have. Therefore, there is a disadvantage that the load on the satellite itself increases and the launch cost increases with the superposition of the satellites. Further, the number of communication terminals handled by one cell is very large, and it takes a long time from the cell change of the communication terminal to the setting of a new communication channel, so that the communication is interrupted.

[0007] Further, since the communication terminal has no means for monitoring the communication quality, there is a drawback that the communication quality cannot be predicted in advance.

An object of the present invention is to add a means for monitoring communication quality to a communication terminal and to add this monitoring item as one item of used cell recognition information, thereby ensuring more reliable cell replacement without disconnection of communication. It is to provide an orbiting satellite communication system that can be implemented.

[0009]

According to the orbiting satellite communication system of the present invention, a plurality of cells assign an identification number to each of the corresponding M (M is an integer) spot beams and a satellite identification number. N (N is an integer) orbiting satellites that transmit a burst signal and transmit and receive the burst signal to and from a terrestrial mobile communication terminal, and a destination to enter a cell where the satellite is located upon receiving the burst signal. Recognize the received burst signal of the cell and transmit to the corresponding orbiting satellite the location information including the spot beam identification number and the satellite identification number in both cells, which is its own identification information, and the used cell identification information including the measurement result of the line error rate. A mobile communication terminal, and a network for setting available cells and communication channels based on the used cell identification information of the mobile communication terminal. And a reference station, wherein the communication terminal,
A control channel demodulation unit for sequentially receiving and demodulating a plurality of control channels of the network reference station via a satellite, and receiving an output of the control channel demodulation unit to decode a satellite identification number and a spot beam identification number of a control channel that can be demodulated. An identification number detector, a line BER measuring unit for measuring a BER which is a line bit error rate of a control channel which can be demodulated in response to an output of the control channel demodulating unit, and a satellite identification number output from the identification number detector And an identification number / line BER storage unit for storing the spot beam identification number together with the line BER output from the line BER measurement unit at that time, and the identification number / line BER.
One or more cells that can be currently used are recognized from the satellite identification number and the spot beam identification number stored in the storage unit, and the cell with the best line BER is determined as the cell to be used now, and the cell to be used is determined. A used cell recognition unit for recognizing one or more possible cells and judging the best cell of the line BER as a cell to be used from among these cells and currently used cells; Report to the network reference station via the available satellite the cell to be used currently recognized by the used cell recognition unit,
Further, during communication, the used cell recognizing unit recognizes a cell to be used from now on, and transmits a cell to the network reference station via a channel of a satellite currently in use. .

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram of one embodiment of the present invention. . In FIG. 1, reference numerals 1 to 3 denote orbiting satellites each forming a cell with M spot beams, reference numeral 4 denotes a network reference station for controlling the entire network, and reference numeral 5 denotes a communicator participating in the network which can be carried around or mounted on a vehicle. It is a small communication terminal that can be operated.

FIG. 2 is a block diagram of each orbiting satellite of this embodiment. The embodiment of FIG. 2 includes a synchronization establishing unit 6 and M burst transmitting units 7 corresponding to M cells on the ground.
The synchronization establishing unit 6 establishes a cycle for the frame. The burst transmission unit 7 transmits a burst signal including the identification number of its own satellite and the identification number of the spot beam in a predetermined time slot for each spot beam to a control channel common to the network. It has a number of burst transmission units.

FIG. 3 is a block diagram showing the configuration of the communication terminal 5 of FIG. 1 of the present embodiment. Reference numeral 11 denotes a control channel demodulation unit for sequentially receiving and demodulating a plurality of control channels;
Is an identification number detector that receives the output 13 of the control channel demodulation unit 11 and decodes the satellite identification number and spot beam identification number of the control channel that can be demodulated. 18 receives the output 13 of the control channel demodulation unit 11 and demodulates. A line BER measuring unit 14 for measuring a line BER, which is a line error rate of the control channel, is a satellite ID number and a spot beam ID number 15 output from the ID detector, and a line BER measuring unit 18 at that time. BE output from
An identification number / line BER storage unit 16 stored together with R19, a satellite ID number and a spot beam identification number stored in the identification number / line BER storage unit 14, and a cell to be used at present from the line BER, The use cell recognition units 16 and 17 for recognizing cells to be used report a cell to be used currently recognized by the use cell recognition unit 16 via an available satellite when a call is generated, and are in communication. Is a transmitter for recognizing a cell to be used from now on by the used cell recognizing section 16 and reporting the cell to the network reference station 4 via the channel of the satellite currently used.

FIG. 4 is a block diagram showing an example of the network reference station shown in FIG. 1. Reference numeral 21 denotes a cell which can be used by a communication terminal 5 by recognizing an available cell from the cell data reported from the communication terminal 5. And a communication channel setting unit for setting a communication channel using a cell to be set.

In FIG. 1, orbiting satellites 1 to 3 irradiate M spot beams corresponding to M cells 1A to MA, respectively. The burst including the beam identification number is transmitted to a control channel common to the network. Here, the time slot to output the burst is predetermined in advance. In addition, since the synchronization with the frame generated by the network reference station 4 is established in the synchronization establishing unit 6 in FIG. 2, the bursts transmitted from the spot beams of all the orbiting satellites are synchronized.

FIG. 5 shows a state of a time slot and a burst in a control channel common to a network. The total number of cells in the system is (number of orbiting satellites N) × (number of spot beams of each satellite M), but 1
The number L of time slots in a frame is set smaller than (the number N of orbiting satellites) × (the number M of spot beams of each satellite) in order to effectively use the frame. In this case, bursts from multiple spot beams are output in the same time slot, but the irradiation area of each orbiting satellite is limited, and radio waves do not reach cells far away from each other, causing interference. There is no problem if the spot beams that output bursts in the same time slot are specified to be separated by such a distance that they do not interfere with each other.

In the communication terminal 5, a currently usable cell and a cell which can be used from now on are recognized by the used cell recognition section 16 shown in FIG. This process will be described in more detail.

In FIG. 3, the control channel demodulation unit 11
Demodulates the signal of the control channel and outputs the identification number detector 1
If the satellite identification number and the spot beam identification number are decoded in step 2, the control channel BER measured by the line BER measurement unit 18 and the decoded identification number are stored in the identification number / line BER storage unit 14 with a period T. Keep it.
The used cell recognizing unit 16 uses the identification number / line B
The history of the identification number stored in the ER storage unit 14 is read, and if it is stored, for example, k times consecutively, it is determined that the cell is usable. In addition, it may be determined that the device can be used if it has been stored b times out of a trials. Further, the used cell recognition unit 16 looks at the line BER of the control channel of the usable cell and recognizes that the cell having the control channel with the highest BER is the cell to be used. This is equivalent to selecting the cell most advantageous for the communication terminal as the cell to be used. The cell selected in this way is a cell to be used at present until communication starts, and if the cell selected during communication is changed, that cell becomes a cell to be used from now on.

After recognizing the cells that can be used now and the cells that can be used from now on, when a call is generated by the transmitter 17 of the communication terminal shown in FIG. The currently available cell identified at 16 is reported via the available satellites, and during communication, each time an available cell is generated, it is transmitted via the channel of the satellite currently using that cell. Report to network reference station 4.

In the network reference station 4, the communication channel setting unit 21 recognizes the cell used by the terminal from the cell data reported from the communication terminal 5, and immediately sets the communication channel using the cell.

Normally, in a transient state in which the used cell is changed, there is an overlapped area in which both the cell used up to now and the cell to be used can be used. Therefore, while communicating with the cell used so far,
The next cell comes into view, and the above operation is performed using this overlap period.

Further, according to the method of the present invention, in a satellite relaying a signal of a communication terminal in each cell, a spot beam in charge of each cell is changed to all adjacent spot beams. It is not necessary to monitor up to this frequency, and the number of receivers in the satellite need only be the number of spot beams.

[0022]

As described above, according to the present invention, the communication terminal monitors the line BER, and
By providing the line BER storage unit, more reliable cell identification information can be obtained when a cell being used is replaced, so that there is an effect that communication can be performed without disconnecting.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram of an embodiment of the present invention.

FIG. 2 is a block diagram of the orbiting satellite of the embodiment.

FIG. 3 is a block diagram of a communication terminal according to the embodiment.

FIG. 4 is a block diagram of a network reference station according to the present embodiment.

FIG. 5 is an explanatory diagram of a signal format according to the present embodiment.

FIG. 6 is an explanatory diagram of a cell recognition process according to the present embodiment.

FIG. 7 is a configuration diagram of a general low-altitude orbiting satellite communication system.

FIG. 8 is an explanatory diagram of a time change of the low-altitude orbiting satellite shown in FIG. 7;

9 is an explanatory diagram of a time change of the low-altitude orbiting satellite shown in FIG. 7;

[Explanation of symbols]

 1-3 orbiting satellite 4 network reference station 5 mobile communication terminal 6 synchronization establishing unit 7 burst transmission unit 11 control channel demodulation unit 12 identification number detector 13 output of control channel demodulation unit 14 identification number line BER storage unit 15 identification number detector Output 16 Used cell recognition unit 17 Transmitter 18 Line BER measurement unit 19 Output of line BER measurement unit 21 Communication channel setting unit

Claims (2)

(57) [Claims] 1. M corresponding to a plurality of cells (M is an integer)
Assign an identification number to each of the spot beams, and
N (N is an integer) orbiting satellites that transmit a burst signal with a satellite identification number and transmit and receive the burst signal to and from a terrestrial mobile communication terminal, and a cell in which the burst signal is received and located. Recognize the received burst signal of the destination cell to enter, and use the cell identification information including the spot beam identification number and the satellite identification number in both cells, which are self-identification information, and the measurement information of the line error rate. A mobile communication terminal for transmitting to a corresponding orbiting satellite, and a network reference station for setting a usable cell and a communication channel between the mobile communication terminal based on used cell recognition information of the mobile communication terminal. Orbiting satellite communication system. 2. The communication terminal, comprising: a control channel demodulator for sequentially receiving and demodulating a plurality of control channels of the network reference station via a satellite; and a control channel demodulator receiving an output of the control channel demodulator and demodulating the control channel. An identification number detector for decoding a satellite identification number and a spot beam identification number; a line BER measuring unit for measuring a BER which is a line bit error rate of a control channel which can be demodulated by receiving an output of the control channel demodulating unit; An identification number / line BER storage unit for storing the satellite identification number and the spot beam identification number output from the identification number detector together with the line BER output from the line BER measuring unit at that time; From the satellite identification number and spot beam identification number stored in the BER storage unit, one or more currently available The cell is recognized and the line BER is
Is determined to be the current cell to use, and
A used cell recognizer for recognizing one or more cells that can be used from now on and judging the best cell of the line BER as a cell to be used from among these cells and currently used cells; The cell to be used currently recognized by the used cell recognition unit is reported to the network reference station via an available satellite, and during communication, the cell to be used is recognized by the used cell recognition unit. 2. The orbiting satellite communication system according to claim 1, further comprising: a transmitter for reporting the cell to the network reference station via the channel of the satellite currently in use.