JP2956837B2 - Satellite communication systems, terminal stations, center stations - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a satellite, one station having a center function (hereinafter referred to as a center station), and a plurality of remote stations (hereinafter referred to as terminal stations) connected to terminals such as individual users.
In particular, the present invention relates to an improvement of a random access system which is one of multiple access systems from a terminal station to a center station.

[0002]

2. Description of the Related Art A general form of a random access method is as follows.
A pure random access scheme and a slotted random access scheme.

[0003] In the pure random access method, when a data transmission request is generated from each terminal station, each station is free to make a request.
This is a method in which the data is packetized and transmitted on a shared line, but data packets transmitted from each station partially overlap on a satellite and interfere with each other, so that data is likely to be destroyed. For this reason, the random access method with a slot, which transmits the data packet so as to enter a time frame called a time slot so as not to partially overlap, has a lower probability of data destruction. Assuming that the data length is constant and the generation of data is a Poisson process, the throughput indicating the transmission efficiency is about 18% in the pure random access scheme, while about 3% in the slotted random access scheme.
7%, about twice as high.

[0004] However, even with the above-mentioned slotted random access system, further improvement in throughput cannot be expected, and data destruction due to collision of data packets occurs stochastically. In this case, the average delivery time of the data becomes longer due to the need to retransmit the data. In particular, when data that exceeds the time slot length is divided into time slot length data and sent, the average data delivery time increases.
Therefore, in systems that require higher throughput operation or systems that need to reliably deliver data longer than the time slot length in a short period of time, the time slot reservation function must be added to the conventional slotted random access method. A built-in reservation method has been considered.

[0005] The reservation method is basically to reserve a time slot by some method prior to data transmission. This reservation method can be roughly classified into an explicit reservation method in which a time slot is reserved using a reservation packet and a successful delivery of a data packet without collision once without using a reservation packet, depending on the reservation method.
There are two types of implicit reservation schemes in which the same time slot in subsequent frames is automatically reserved.
Generally, the reservation method refers to the explicit reservation method,
The present invention also relates to this explicit reservation method.

FIG. 12 shows an example of a conventional explicit reservation method.
As shown in FIG.

[0007] FIG. 12 shows that a terminal station first transmits a reservation request exclusive packet by a random access method with a slot to reserve a time slot, and if the center station can normally receive the packet without collision, the time is determined according to the reservation request. This figure illustrates a communication procedure for performing slot allocation, notifying the time slot allocation information to the packet transmitting terminal station, and the terminal station transmitting data using the allocated time slot.

FIG. 13 illustrates a communication procedure in which a terminal station first transmits data with reservation request information added thereto using a slotted random access method, and thereafter performs the same procedure as in FIG. 11 (a). Things. As an example of FIG. 13, the AA / TDMA system ("AA / TDMA-A") described in Globecom 86 Conference Records, pages 1494 to 1499, is used.
adaptive satellite access method for mini-earth st
ation network ”, Conf. Record. GLOBECOM'86, PP.1.
494-1499, Houston, TX. Dec. 1986).

[0009]

In the conventional reservation system based on the slotted random access system, when a terminal station needs to make a reservation, a reservation request dedicated packet shown in FIG. 12 or a reservation request packet shown in FIG. It is necessary to send one request information addition packet at first, but if the reservation packet collides and cannot be received normally by the center station, the terminal station repeats the reservation packet until it can be received normally by the center station. Has to be retransmitted, which takes extra time.

An object of the present invention is to reduce the time required for a center station to correctly receive a reservation packet or an urgent data packet transmitted from a terminal station by a slotted random access method without collision.

Another object of the present invention is to allow a reservation request from a transmitting terminal station to reliably reserve a time slot for remaining unreceived data, and to transmit a part of transmission data at the time of a reservation request. The aim is to reduce the time.

[0012]

According to the present invention, there is provided a center station for multiplexing transmission data to a plurality of terminal stations and transmitting the multiplexed data to a plurality of terminal stations via satellites. Receive data for own station from transmission data of
A random access method with a slot for transmitting packet data by random access and a reservation access method for transmitting packet data to an assigned time slot are used in combination, and the transmission packet data at the time of the random access is determined in advance. In a system for performing satellite communication with a terminal station that sub-packets for each slot length and transmits to the center station via the satellite, packet data transmitted from the terminal station to the center station is divided for each slot length. Means for subpacketizing, and means for adding, to each of the divided packet data, subpacket information indicating a header, the number of divided packets, and an order number indicating the order of the subpacket in a subpacket group. , Into some of the sub-packets, And means for transmitting to Umate the center station.

Further, the present invention is used in a system for communicating between a center station and a terminal station via a satellite, and a slotted random access system for randomly accessing and transmitting packet data, and an assigned time slot. And a reservation access method for transmitting packet data to the center station. The transmission packet data at the time of the random access is divided into sub-packets for each slot length and transmitted to the center station via the satellite. From the time-division multiplexed transmission data transmitted from the terminal station via the satellite, wherein the terminal station transmits the packet data transmitted from the terminal station to the center station. Means for dividing a packet into sub-packets for each slot length, and adding a header and a divided packet to each of the sub-packetized data. Means for adding sub-packet information indicating the number of the sub-packets and the order number of the sub-packet in the sub-packet group; Means for transmitting to a station.

The present invention also provides a random access method with a slot for randomly accessing and transmitting packet data, and a reservation access method for transmitting packet data to an assigned time slot. The transmission packet data is divided into sub-packets for each slot length to receive data from the terminal station transmitted via the satellite, and the transmission data is multiplexed and transmitted to a plurality of terminal stations via the satellite. A center station, wherein the center station receives the subpacket or subpacket group sent from the terminal station;
The number of unreceived subpackets in the subpacket group is determined from the number of divided packets added in the subpacket and the subpacket information having the packet sequence number, and the number of the last received subpackets for each terminal station is reserved. Means for permitting access.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

First, an outline of a satellite communication system for implementing the present invention will be described with reference to FIG. The satellite communication system includes a satellite 2-1, a center station 2-2, and a plurality of terminal stations 2- including 1 to n.
3 Communication from the terminal station 2-3 to the center station 2-2 via the satellite 2-1 uses a common communication line to randomly access each terminal station 2-3 toward a time slot on the line. Random access method with a slot for transmitting a packet through the
-3 is assigned by the center station 2-2 based on the reservation request from -3, and each terminal station 2-3 uses a reservation access method for transmitting a packet toward the assigned time slot. Communication from the station 2-2 to each terminal station 2-3 via the satellite 2-1 is performed by multiplexing transmission data to each terminal station 2-3 at the center station and transmitting the multiplexed data in the broadcast mode.
It is assumed that each terminal station 2-3 uses a time-division multiplexing method in which only the data for the own station is selectively extracted. The configurations of the center station 2-2 and each terminal station 2-3 are shown in FIGS. 5 and 6, respectively.

FIG. 4 shows that each terminal station 2-3 is connected to the center station 2-
2 shows the contents of the packet transmitted. As shown in FIG. 4, the short data 3-1 is a header such as a self-station address and subpacket information of 1/1 indicating that the data is short data (the denominator is the subpacket division number, and the numerator is the subpacket sequence number. The same applies to the following.) To form one packet having a length of one time slot. However, as shown in FIG.
After being divided, a header and sub-packet information are added to form a sub-packet. In this embodiment, the data is divided into five, and each divided data has a header, 1/5, 2/5, 3/5, 4 /
5, 5/5 sub-packet information is added and sub-packetized.

Further, as shown in FIG. 4C, when there is short data 3-3 to be transmitted urgently, in this embodiment,
Four short copies of the same contents are created by being copied four times. Each data has a header and 1/1, 2/1, 3/1, 4
/ 1, 5/1 are added and subpacketized.

FIG. 5 is a block diagram showing the configuration of the center station 2-2. The center station 2-2 is connected to the satellite 2-1.
A transmission / reception device 4-1 for transmitting / receiving data to / from the terminal station 2-3 by radio waves via the Internet and a predetermined number of time slots as time units for preventing data (packet) collision on the satellite 2-1. A reference timing creation unit 4-2 for providing a reference timing for data transmission / reception to the terminal station 2-3 by forming one frame, generating the frame signal and sending the frame signal to the terminal station 2-3; A receiving unit 4-3 for performing processing for receiving a transmission packet from the terminal station 2-3 received and output by the device 4-1 and outputting a packet true / false signal, a received packet signal, and subpacket information; -3 controls the order of data (packets) received from the terminal station 2-3 by the terminal station 2-3 and performs buffering to output the received data to the host computer. DOO interface receiver 4-4
And each terminal station 2 based on the output from the receiving unit 4-3.
-3, a traffic control unit 4-5 that outputs a traffic status signal by monitoring the number of packets transmitted and outputs a traffic control signal for controlling the number of packets; A response signal creating unit 4-6 which receives sub-packet information and a packet correct / wrong signal and outputs an acknowledgment signal (ACK) or a negative acknowledgment signal (NAK) for each received packet;
3 to determine the necessity of time slot reservation in response to the packet correct / false signal, calculate the number of required time slot reservations if necessary, and output this as a time slot assignment signal. An assignment signal generating unit 4-7 for outputting an assigned time slot signal related to an assigned time slot in one frame based on the determination and calculation results, and for receiving transmission data from the host computer to each terminal station 2-3. A host interface transmitting section 4-8 for performing buffering, the host interface section 4-8, the reference timing creating section 4-2, a traffic control section 4-5,
A multiplexing unit 4-9 for time-division multiplexing the output from the response signal creating unit 4-6 and the assignment signal creating unit 4-7, and a multiplexing output from the multiplexing unit 4-9 to the transmitting / receiving unit 4 Transmitting unit 4 for transmitting to each terminal station 2-3 in broadcast mode via -1
-10.

FIG. 6 is a block diagram showing the configuration of the terminal station 2-3. The terminal station 2-3 transmits and receives data to and from the center station 2-2 by radio waves via the satellite 2-1. The center station 2-2 receives and outputs the data from the transmitting and receiving apparatus 5-1. And the frame signal, the traffic status signal, the traffic control signal, and the acknowledgment signal (AC
K) and a negative acknowledgment signal (NAK), the time slot assignment signal, the assigned time slot signal and transmission data from the host computer which are extracted and separated, and output from the reception section 5-2. A transmission timing creating section 5-3 for establishing and maintaining frame synchronization in synchronization with the frame signal and creating a transmission time slot timing signal indicating each time position of a transmission time slot provided in a predetermined number of frames; A terminal interface receiving section 5-4 for buffering transmission data from the host computer output from the receiving section 5-2 to a terminal, and the receiving section 5-2
Receiving the time slot allocation signal and the allocated time slot signal output from the terminal, an allocation time slot signal indicating a time slot number allocated to the own station by reservation, and an empty time slot signal not reserved by another terminal station. Receiving the traffic status signal and the traffic control signal from the receiving section 5-2, and taking into account its own assigned transmission priority, and a slot managing section 5-5 for generating an empty time slot signal indicating a time slot number. In addition, in consideration of the packet retransmission number signal and the packet retransmission number signal from the packet control unit 5-12 and the sub packet control unit 5-13, the packet retransmission maximum delay time signal, the emergency transmission allowance signal, and the sub packet number control. A traffic control unit 5-6 that outputs a signal, and one time when packetized A packet buffer 5-7 that saves short data of a lot, and saves data that is longer than two time slots by dividing it into subpackets of one time slot length. If the short data is to be transmitted to the center station 2-2, a subpacket buffer 5-8 for copying the data and saving it as a plurality of subpackets, and a buffer for receiving data transmitted from the terminal to the center station 2-2. A terminal interface transmitting section 5-9 for performing ringing, identifying emergency data from the transmission data, and copying the emergency data the number of times determined based on the emergency transmission allowance signal from the traffic control section 5-6. Then, the urgency identification unit 5-10 for adding the header and the sub-packet information described in FIG. The transmission data is received from the interface transmission unit 5-9, and the data length is identified. In the case of single data, the header and sub-packet information 1/1 described in FIG. The data to be transferred to the buffer 5-7, and in the case of long data, the transmission data is divided into sub-packets, each of which is added with a header and sub-packet information to be packetized and transferred to the sub-packet buffer 5-8. Long identification section 5
-11 and the transmission of the packetized short data, and the acknowledgment signal (AC
K), a negative acknowledgment signal (NAK) and the traffic control unit 5-6
Packet control unit 5-12 for performing retransmission control based on the maximum packet delay time signal, and a slot-based random access method based on the sub-packet number control signal from the traffic control unit 5-6. The number of subpackets to be transmitted is controlled, and the acknowledgment signal (ACK) and the negative acknowledgment signal (NAK) from the receiving unit 5-2 and the packet delay maximum time signal from the traffic control unit 5-6 are also transmitted. And a sub-packet controller 5-13 for controlling transmission of sub-packets of the series of sub-packets which has not reached the center station 2-2, and a packet from the packet buffer 5-7, or , A sub-packet is read from the sub-packet buffer 5-8, and the time specified by the assigned time slot signal from the slot management unit 5-5 is read. In addition to the insertion into the lot, the sub-packet buffer 5-8 inserts a sub-packet waiting for time slot allocation into the allocated time slot from the slot management section 5-5, and the transmission time from the transmission timing creation section 5-3. A packet transmitting unit 5-14 for transmitting a packet or a sub-packet in synchronization with a slot timing signal; a packet transmitted from the packet transmitting unit 5-14;
-1 as a transmission data.

Next, the procedure of the satellite communication system according to the present invention will be described with reference to FIGS. The present invention relates to an access method of a terminal station accessing a center station by a random access method with a slot, but the description of the random access method with a slot itself will be omitted, and a part related to the invention will be mainly described.

FIG. 1 shows a conventional random access method with a slot when a long data requiring 5 time slots is transmitted from a terminal station to a center station when divided and packetized, as shown in FIG. 4 (b). FIG. 3 illustrates a communication procedure according to the present invention which enables transmission earlier than the reservation method based on the present invention. The long data is transmitted to the terminal station 2-
When the data is received by the terminal interface transmission unit 5-9 of FIG. 3, the data length identification unit 5-11 recognizes that the data is long data, and as shown in FIG. 2, data 3, data 4 and data 5 are divided into five, and each data has a header such as its own address and a denominator as the number of subpackets and a numerator as a subpacket sequence number 1/5.
Subpacket information of 2/5, 3/5, 4/5, 5/5 is added to form a subpacket, and the five subpackets are transmitted to the subpacket buffer 5-8.

The sub-packet control unit 5-13 receives the traffic status signal transmitted from the center station and received by the receiving unit 5-2 and the number of the sub-packets generated by the traffic control unit 5-6 based on the traffic control signal. Based on the control signal, the number of subpackets to be transmitted first in the slotted random access scheme is determined to be three. That is, three subpackets whose subpacket information is 1/5, 2/5, 3/5 are set as transmission subpackets to be transmitted first in one set. In the packet transmission unit 5-14, the slot management unit 5
Based on the empty time slot signal from -5, three empty time slots are randomly found, the set of three subpackets is inserted into the empty time slot, and the transmission time slot created by the transmission timing creation unit 5-3 The transmission is performed one after another according to the timing signal.

Since the set of three sub-packets is transmitted to the center station by a slot-based random access method,
In the same time slot as the time slot used by the three sub-packets, there is a possibility of collision with a packet or sub-packet transmitted from another terminal station. In this embodiment, the sub-packets having the sub-packet information 1/5 and 3/5 collide and are not normally received by the center station, but the sub-packets having the sub-packet information 2/5 are normally received by the center station without collision. Therefore, NAK 1/5, NAK 3 / -5 are respectively used as negative acknowledgment signals for subpackets that cannot be normally received by the center station, and ACK2 / 5 is used as an acknowledgment signal for subpackets that can be normally received. It is created by the creating unit 4-6, transmitted to the terminal station in the broadcast mode with the transmission terminal station address added, and only the subpacket having the subpacket information 2/5 was normally received. 1/5
A time slot assignment signal to which four time slots are assigned is created by the assignment signal creation section 4-7 for transmission of four subpackets having 3/5, 4/5, 5/5, and Transmits to the terminal station.

In the terminal station, the time slot assignment signal received / separated and output by the receiving section 5-2 is decoded by the slot management section 5-5 and output to the packet transmitting section 5-14 as an assigned time slot signal. Then, the packet transmission unit 5-14 outputs 1 /
Subpackets having subpacket information of 5, 3/5, 4/5, 5/5 are read out, inserted into time slots according to the assigned time slot signals, and transmitted.
In this case, since transmission is performed using a time slot allocated exclusively, transmission can be performed without collision. In the center station, the receiving unit 4-3 is transmitted via the transmitting / receiving device 4-1.
When the four packets are normally received, the host interface receiving unit 4-4 controls the order of data from data (1/5) to data (5/5), buffers the data, and outputs it to the host computer. .

FIG. 2 shows that the emergency data is copied into five subpackets as shown in FIG. 4 (c) and transmitted from the terminal station to the center station more reliably by the slotted random access method. The communication procedure of the present invention, as one embodiment,
It is illustrated. When the emergency data is received by the terminal interface transmission unit 5-9, the urgency identification unit 5-
10, the emergency data generated by the traffic controller 5-6 based on the traffic status signal and the traffic control signal transmitted from the center station and received by the receiver 5-2. The number of copies = 4 is determined based on the allowance signal, and the emergency data is copied four times as shown in FIG. 4 (c), and a header such as the own station address and a denominator are added to each of the total of five emergency data. 1/1, 2/1, 3/1, 4/1, 5 / with the numerator set to 1 and the numerator as the subpacket sequence number
1 sub-packet information to form a sub-packet, and the five sub-packets are stored in a sub-packet buffer 5-8.
Send to

The sub-packet control unit 5-13 controls the number of sub-packets generated by the traffic control unit 5-6 based on the traffic status signal and the traffic control signal transmitted from the center station and received by the receiving unit 5-2. Based on the signal, it is determined that the number of sub-packets that can be transmitted first by the slotted random access scheme is five, which is appropriate. The packet transmitting unit 5-14 randomly finds five empty time slots from the empty time slot signal from the slot managing unit 5-5, inserts the five subpackets into the empty time slots, and The transmission is performed one after another in accordance with the transmission time slot timing signal created in step -3.

Since the five emergency data transmission sub-packets are transmitted to the center station by the slotted random access method, packets transmitted from other terminal stations in the same time slot used in the sub-packets are transmitted. Or it may collide with subpackets. In the present embodiment, the sub packet information 1/1, 2/1, 3/1, 5
The sub-packet having sub packet information / 1 cannot be normally received by the center station because of collision, but the sub-packet having sub packet information 4/1 has been normally received by the center station without collision. It will reach the center station in a short time without retransmission.

The center station receives NAK1 / NAK1 signals as negative acknowledgment signals for subpackets that cannot be received normally.
1, NAK2 / 1, NAK3 / 1, NAK5 / 1, and AC as an acknowledgment signal for a normally received subpacket.
K4 / 1 is created by the response signal creation unit 4-6, and the transmission terminal station address is added thereto and transmitted to the terminal station in the broadcast mode, and the terminal station copies and sends the emergency sub-packet in five subpackets. The response signal confirms that at least one of the data has arrived, and ends the emergency data transmission process. When transmitting urgent data in this way, by transmitting a plurality of copied sub-packets and increasing the probability that at least one can be normally received by the center station, compared to the case of transmitting one urgent data , Delivery time can be shortened.

FIGS. 7 and 8 show the effect when 1 to 5 subpackets are transmitted in FIG.

FIG. 7 shows the throughput (horizontal axis) of the random access method with slots and the assumption that the satellite channel quality is error-free. It shows the relationship with the probability (vertical axis) that sub-packets can be received normally without collision.

FIG. 8 shows the throughput (horizontal axis) of the random access method with slots and the assumption that the satellite channel quality is error-free. It shows the relationship with the probability (vertical axis) that packets can be received normally without collision.

Assuming that the throughput is 0.3, as shown in FIGS. 1 and 2, when three sub-packets are transmitted, at least one of them is normally received by the center station, and the remaining sub-packets are transmitted. The probability of making a time slot reservation for packet transmission is 0.94, which is considerably higher than the probability of transmitting only one subpacket, 0.61. Assuming that all five sub-packets are initially transmitted together in a slotted random access scheme, the probability that all five sub-packets will be correctly received by the center station without collision is as low as 0.09. The probability that at least one sub-packet of the five sub-packets is normally received and the time slot for the remaining sub-packets is reserved is 0.99, which is close to 1.0, and the reservation can be reliably made. You can see that.

On the other hand, assuming that the throughput is 0.1, three subpackets are transmitted as shown in FIGS.
The probability that at least one subpacket is normally received by the center station and the time slot for the remaining subpacket is reserved is 0.99, and the subpacket 1
The probability is higher than 0.89 when only the number is transmitted. On the contrary, when the throughput is low as described above, even if all five sub-packets are collectively transmitted at the beginning by the slotted random access method, all the five sub-packets are normally received by the center station without collision. Probability is relatively high at 0.58. Therefore, for example, if 10 attempts are made, about 6 times out of 5 sub-packets are normally received by the center station without reservation in one transmission,
Delivery time can be reduced.

As described above, if the data is divided into sub-packets and transmitted in a plurality of sub-packets, the probability that at least one sub-packet is normally received by the center station is determined by transmitting only one packet. It is much higher than the probability of normal reception at the center station, and the effect is more significant as the throughput is higher. The probability that all the subpackets are normally received by the center station at a time is lower as the throughput is lower, and the data from the terminal station to the center station is higher. Shortening of delivery time can be expected. In this case, even if all the packets cannot be normally received by the center station, as described above, the probability that at least one subpacket is normally received is very high, and therefore, the Since there is a high probability that a time slot reservation will be made, a reduction in the data delivery time can be expected sufficiently compared to a case where only one packet is transmitted for reservation.

FIG. 9 shows a case where the throughput is 0.1 and 0.2.0.3 based on the simulation result of FIG.
This figure shows how sub-packets are transmitted when at least one sub-packet is normally received by the center station with a probability of about 0.99.

At a low throughput of about 0.1, at least one subpacket is normally received by the center station with a probability of 0.99 just by transmitting two subpackets. At a medium throughput of about 0.2, if three sub-packets are transmitted, at least one sub-packet is normally received by the center station with a probability of 0.99. When the throughput is as high as about 0.3 and five sub-packets are transmitted, at least one sub-packet is normally received by the center station with a probability of 0.99.

From the above, at least 0.99 has a probability of 1
In order for the center station to receive the sub-packets normally and to reserve the remaining sub-packets reliably, the slots are first grouped by the random access method with slots according to the throughput of the communication line from the terminal station to the center station. It can be understood that the number of subpackets to be transmitted may be adjusted.

The description of FIG. 9 assumes that the total number of transmission sub-packets is small and has little effect on the throughput of the communication line from the terminal station to the center station. In the case where the algorithm operates and the total number of packets transmitted from the terminal station may slightly affect the throughput, FIG.
0, when the throughput is low, since the total number of transmission packets is small, many sub-packets are first transmitted together by the random access method with a slot. There may be an operation mode in which only the sub-packet is transmitted so that the throughput is not significantly affected.

FIG. 11 is a flowchart showing the sub-packet transmission operation of the terminal station.

FIG. 12 shows a conventional reservation system and an emergency data transmission system. Conventionally, when packetized long data exceeding one time slot is transmitted by the slotted random access method, as shown in FIGS.
The terminal station first transmits the reservation request packet to the center station, or adds the reservation request information to the transmission data and transmits it to the center station, and obtains the time slot allocation information of the required number of time slots from the center station. , Untransmitted data is transmitted using the assigned time slot. However, in such a conventional method, when the reservation request packet or the reservation request additional data packet collides and cannot be normally received by the center station, the terminal station retransmits the packet until the center station can normally receive the packet. Therefore, the delivery of long data is delayed by the time required for retransmission.

According to the present invention, (1) the long data is divided into sub-packets, and the divided sub-packets are collectively transmitted by the slotted random access method. Has the same effect. (2) Since the reservation packet also includes transmission data, the center station may allocate time slots for sub-packets that cannot be received normally and sub-packets that have not been transmitted. (3) If all the divided packets are transmitted together and the center station can receive all of them normally, there is no need to allocate time slots (1).
For the reasons (2) and (3), the effect of shortening the transmission time of long data can be sufficiently expected.

[0043]

As described above, according to the present invention, when communicating from a terminal station to a center station via a satellite, the time required for the center station to correctly receive data transmitted from the terminal station is reduced. Is done.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a communication procedure according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a communication procedure according to an embodiment of the present invention.

FIG. 3 is a configuration diagram of a satellite communication system to which the present invention is applied;

FIG. 4 is a diagram showing transmission packet data used in the present invention;

FIG. 5 is a block diagram of a center station 2-2.

FIG. 6 is a block diagram of a terminal station 2-3.

FIG. 7 is a diagram illustrating a relationship between a throughput and a packet arrival probability.

FIG. 8 is a diagram illustrating a relationship between a throughput and a packet arrival probability.

FIG. 9 is an explanatory diagram showing a transmission method according to the degree of throughput.

FIG. 10 is an explanatory diagram showing a transmission method according to the degree of throughput.

FIG. 11 is a flowchart showing a sub-packet transmission operation of the terminal station.

FIG. 12 illustrates a conventional method.

FIG. 13 is a diagram illustrating a conventional method.

[Explanation of symbols]

 2-1: Satellite 2-2: Center station 2-3: Terminal station.

Claims (3)

(57) [Claims] 1. A center station for multiplexing data transmitted to a plurality of terminal stations and transmitting the multiplexed data to the plurality of terminal stations via a satellite, receiving data for the own station from the transmitted data from the center station, and Random access method with a slot for transmitting packet data by accessing a slot and a reserved access method for transmitting packet data to an assigned time slot, and the transmission packet data at the time of the random access is set to a predetermined slot. In a system for performing satellite communication with a terminal station that transmits a packet to the center station through the satellite by subpacketing the packet data for each length, packet data transmitted from the terminal station to the center station is divided by slot length and divided into subpackets. And a header, the number of divided packets, and the Means for adding subpacket information indicating the sequence number of the packet in the subpacket group, and forming the subpacket and transmitting some of the subpacket groups together to the center station A satellite communication system comprising: 2. A system for communicating between a center station and a terminal station via a satellite, wherein a random access method with a slot for randomly accessing and transmitting packet data and a packet for an assigned time slot are provided. In combination with a reserved access method for transmitting data, the transmission packet data at the time of the random access is divided into sub-packets for each slot length and transmitted to the center station via the satellite, and the satellite is transmitted from the center station. A terminal station for receiving data destined for itself from time division multiplexed transmission data transmitted through the terminal station, wherein the terminal station transmits the packet data transmitted from the terminal station to the center station for each slot length. Means for dividing the data into sub-packets, and adding a header, the number of divided packets, and the Means for adding subpacket information indicating the sequence number of the packet in the subpacket group, and forming the subpacket and transmitting some of the subpacket groups together to the center station And a terminal station used in a satellite communication system. 3. The transmission packet data at the time of random access, wherein a random access method with a slot for transmitting packet data by random access and a reservation access method for transmitting packet data to an assigned time slot are used together. Is a center station that divides the data by slot length, converts it into subpackets, receives data from terminal stations transmitted via satellites, and multiplexes transmission data to transmit to a plurality of terminal stations via satellites. Means for receiving the subpacket or subpacket group sent from the terminal station, and subpacket information in the subpacket group from subpacket information having the number of divided packets added to the subpacket and a packet sequence number. Judge the number of unreceived sub-packets, and make reservation access to each terminal station for the number of the last received sub-packets. Center station used satellite communication system characterized in that a means for variable.