JPH05235818A - Satellite communication system and equipment used therefor - Google Patents

Abstract

PURPOSE:To improve the data transmission efficiency by using time slots whose length differs from each other in combination in response to the distribution of data lengths of communication implemented at this time. CONSTITUTION:A center station reception section 2 demodulates a signal received by an interface 1 and corrects its error, sends a base band signal to a monitoring section 3 and sends a received packet to a center station demultiplexer section 4. A buffer 5 receives user data from the demultiplexer section 4 and composes the data subjected to packet division and gives the result to a host terminal. A slot configuration deciding section 6 outputs slot configuration information to a multiplexer section 10. The decision section 6 recognizes the quantity of occurrence of data using a long slot and a short slot based on traffic information received by the monitoring section 3 and the number of times of retransmission from the demultiplexer section 4 and revises the slot configuration when the slot configuration is inadequate. Moreover, the section 6 sends new configuration to the monitoring section 3 and a signal generating section 8 and to the multiplexer section 10 and revises the content of slot configuration information 25 into new slot configuration.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a central station: peripheral station 1: n
It is used for satellite communication for multiple access. In particular, it relates to access technology for central and peripheral stations.

[0002]

2. Description of the Related Art A conventional example will be described with reference to FIGS. FIG. 7 is an overall configuration diagram of multiple access satellite communication. FIG. 8 is a diagram showing a data transmission situation of the slotted Aloha system of the conventional example.

As shown in FIG. 7, a multiple access system is used in which a plurality of peripheral stations T1 to T4 share a communication line by one communication satellite S in a time division manner to communicate with one central station C. TDMA (Time Division Multi)
The slotted Aloha method is one of the please access channel access methods. In the slotted Aloha method, all peripheral stations T1 to T4 randomly access a time slot, which is a time-division unit of a satellite line, to transmit packet data. The advantage of this scheme is that it allows low delay transmission when the message origination rate is low. A host terminal is connected to the central station C, and user data terminals are connected to the peripheral stations T1 to T4 to form a star network.

FIG. 8 shows a data transmission situation of slotted Aloha.

When using the slotted Aloha scheme, the packet data to be transmitted must be of a length equal to the time slot. If the generated data is longer than the length of the time slot, it is divided into packets of a length that can be accommodated in the time slot. Also, if the generated data is shorter than the length of the time slot, the shortage must be filled with dummy data.

[0006]

As described above, the data generated in the peripheral stations have large variations in length. When this is transmitted by a slotted Aloha method using a time slot of a fixed length, when transmitting extremely short data such as data D2 shown in FIG. 8, most of the time slots used are However, it is inefficient because it is filled with dummy data.

If the length of the time slot is determined according to the length of the short data such as the data D2, when the long data such as the data D3 occurs, the number of divisions increases and the probability of collision increases. Get higher Further, in satellite communication, since the header part such as the preamble part is large, an increase in the number of packets causes a decrease in data transmission efficiency.

The present invention has been made against such a background. Data transmission efficiency is improved by using time slots having different lengths according to the distribution of the data length of the communication being performed at that time and combining them. An object of the present invention is to provide a satellite communication device using a slotted Aloha system with good performance.

[0009]

The present invention relates to a communication satellite connected to a host terminal and relaying a line from a central station device,
In a satellite communication system provided with a plurality of peripheral station devices that transmit and receive data to and from the central station device via this communication satellite, the central station device and the peripheral station devices use two types of long and short time slots as one frame. It is characterized in that it is provided with means for receiving and transmitting data.

It should be noted that the central station device includes means for varying the composition ratio of the two types of the long and short time slots according to the distribution of the data length that is currently in progress, and the peripheral station device is changed by the varying means. It is desirable to include means for synchronizing slot timing with the time slot composition ratio.

A second aspect of the present invention is a central station device thereof, which is a satellite communication type central station device which is connected to a host terminal and which transmits and receives data to and from a communication satellite. Is arranged in one frame to receive data, and means for varying the composition ratio of the two types of the long and short time slots according to the distribution of the data length currently in progress. ..

A third aspect of the present invention is a peripheral station device, which is a satellite communication type peripheral station device for transmitting / receiving data to / from the central station device via a communication satellite. Is arranged in one frame for data transmission, and means for synchronizing the slot timing with the time slot composition ratio changed by the changing means is included.

[0013]

As a time slot of the slotted Aloha system, two types of slots, long and short, are provided, and the central station monitors the amount of data received within a fixed time and the resending frequency of these data, so that the long slot and the short slot Calculate the slot usage rate for each, determine the ratio of the number of long slots and short slots suitable for the variation in the length of data generated in the peripheral station, and specify the slot configuration information to notify this to the peripheral station. create.

The peripheral station creates the slot timing of each of the long slot and the short slot based on the slot configuration information notified from the central station.

The data generated from the user data terminal is divided into long packet data to be transmitted in the long slot and short packet data to be transmitted in the short slot. Further, for data that has failed to be transmitted due to collision of data or the like, the number of times of retransmission is added again and the data is transmitted.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the device of the embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram of the central station apparatus of the apparatus of the present invention. FIG. 2 is a block diagram of a peripheral station device of the device of the present invention.

According to the present invention, a communication satellite S connected to a host terminal for relaying a line from the central station device 24, and a plurality of peripheral station devices 26 for transmitting and receiving data to and from the central station device 24 via the communication satellite S. In the satellite communication system equipped with
This central station device 24 and this peripheral station device 26 have a length of 2
A central station channel monitoring unit 3, a central station separation unit 4, and a transmission control unit 21 of the peripheral station device 26 are provided as means for receiving and transmitting data by arranging different types of time slots in one frame. Is characterized by.

The central station device 24 includes a slot configuration determination unit 6 as a means for varying the above-mentioned two types of long and short time slot configuration ratios according to the distribution of the data length that is currently in progress. This is a configuration including a slot timing generation unit 18 as a unit for synchronizing the slot timing with the time slot configuration ratio changed by the slot configuration determination unit 6 of the variable unit.

Next, the operation of the apparatus of the present invention will be described with reference to FIGS. FIG. 3 is a diagram showing a transmission frame configuration of the peripheral station device 26. FIG. 4 is a diagram showing a transmission frame configuration of the central station device 24. FIG. 5 is a diagram showing a transmission / reception state of the central station C and the peripheral stations T1 to T4 and a slot configuration changing process. FIG. 6 is a diagram showing a packet division situation in the peripheral station device 26.

First, the operation of the central station device 24 will be described.

The central station line interface 1 performs transmission / reception with the communication satellite S and performs frequency conversion between a high frequency band and an intermediate frequency band. The central station receiver 2 demodulates and corrects the signal received by the central station line interface 1.
The central station channel monitoring unit 3 uses a CRC (Cyclic R)
The transmission error of the received packet data is detected by using the edundancy check method. Furthermore, if there is no transmission error in the received packet data, the central station channel monitoring unit 3 determines that the data transmitted in the time slot has been correctly received, and in other cases, whether or not data collision has occurred. , Or it is determined that no data was transmitted in that time slot. Then, the central station channel monitoring unit 3 sends to the reception response signal generation unit 8 the source peripheral station address of the correctly received data, and slots the traffic information indicating how many data were correctly received in one frame. Configuration determination unit 6
To, respectively. Finally, the central station channel monitoring unit 3 uses the RE unit and PL shown in FIG. 3 among the received data.
Unit, PC unit, DATA unit, and dummy bit unit are delivered to the central station separating unit 4. The central station separation unit 4 receives the output of the central station channel monitoring unit 3, and passes the output to the host terminal connected to the central station device 24, user data (DATA), effective packet length (PL), packet re-transmission. The information for assembling (PC) is output to the central station reception data buffer 5, and the number of retransmissions (RE) is output to the slot configuration determining unit 6.

The central station reception data buffer 5 buffers the user data (DATA) received from the central station separation unit 4, and refers to the packet reassembly information (PC) and the packet effective length (PL), Peripheral stations T1 to T4
With regard to the data divided into packets, the data is reassembled into one data, and the data not divided into packets is delivered to the host terminal as it is.

The slot configuration determining unit 6 adds the slot configuration information 25 for notifying the slot configuration at that time to the multiplexing unit 1.
Output to 0. Further, the slot configuration determining unit 6 knows the amount of data generated using each of the long slot and the short slot based on the traffic information received from the central station channel monitoring unit 3 and the number of retransmissions received from the central station separating unit 4, Determine if the current slot configuration is appropriate. If the current slot configuration is inappropriate, change the slot configuration. Then, the slot configuration determination unit 6
The new slot configuration is notified to the central station channel monitoring unit 3 and the reception response signal generation unit 8 and output to the multiplexing unit 10. The contents of the slot configuration information 25 are also changed to the new slot configuration.

The central station transmission data buffer 7 receives user data from the host terminal, buffers it, and outputs it to the multiplexer 10.

The reception response signal generating section 8 uses the source peripheral station address received from the central station channel monitoring section 3 to create a reception response signal and outputs it to the multiplexing section 10.

The frame timing signal generator 9 multiplexes a frame timing signal which indicates a frame delimiter.
Output to 0. At the same time, the frame timing signal generator 9 outputs the reception frame timing used by the central station device 24 to the central station channel monitor 3 and the reception response signal generator 8.

The multiplexing section 10 time-division-multiplexes the outputs from the slot configuration determining section 6, the central station transmission data buffer 7, the reception response signal generating section 8, and the frame timing signal generating section 9, and the central station transmitting section 11 Output to.

The central station transmitter 11 adds a redundant bit for detecting a transmission error by the CRC method to the user data in the input from the multiplexer 10, encodes and modulates the user data, and then applies it to the central station line interface 1. Output.

The transmission frame from the central station device 24 is as shown in FIG. 4, and is transmitted to each peripheral station device 26. The user data is transmitted, and at the same time, a frame timing signal indicating a delimiter of frames of a fixed time length is transmitted in the broadcast mode. This frame timing signal serves as a timing reference used when the peripheral stations T1 to T4 perform transmission from their own stations, and the interval at which this frame timing signal is transmitted depends on the channel during transmission of the peripheral stations T1 to T4. It is equal to the length of the frame to be divided. The central station device 24, following the frame timing signal, a reception response signal for the data transmitted by the peripheral stations T1 to T4,
The slot configuration information indicating how many short slots and long slots the frame used for transmission by the peripheral stations T1 to T4 is divided is transmitted in the broadcast mode. The reception response signal is a transmission source peripheral station T of the data correctly received by the central station C.
The addresses 1 to T4 are arranged in the order of the used slots, and the data could not be normally received due to a slot in which no data was received, a collision between data or a transmission error, or the like. All "0" is written in the slot. The reception response signal and the slot configuration information are transmitted in units of one frame.

Next, the operation of the peripheral station device 26 will be described.

The peripheral station line interface 12 transmits / receives signals to / from the communication satellite S and performs frequency conversion between a high frequency band and an intermediate frequency band.

The peripheral station receiving unit 13 performs demodulation and error correction processing of the signal input from the peripheral station line interface 12, and outputs the processed signal to the peripheral station separating unit 14.

The peripheral station separation unit 14 receives the output of the peripheral station reception unit 13, detects the frame timing signal generated by the central station device 24 from the output, and sends the frame timing to the frame synchronization unit 17 as a reception response. Signal delivery confirmation unit 2
3, slot configuration information 25 to the slot timing generation unit 18, and user data to the peripheral station channel monitoring unit 15.
To, respectively.

The peripheral station channel monitoring unit 15 performs error detection on the user data received from the peripheral station separation unit 14 and outputs the normally received data to the peripheral station reception data buffer 16.

The peripheral station reception data buffer 16 buffers the user data received from the peripheral station channel monitoring unit 15, and delivers this to the user data terminal.

The frame synchronization section 17 determines the frame timing to be used when the local station transmits by considering the distance between the local station and the communication satellite S with reference to the frame timing transmitted from the central station C. And outputs it to the slot timing generator 18.

The slot timing generator 18 uses the slot configuration information 25 to identify the frame created by the frame synchronizer 17.
Based on, the slot timing is determined by dividing into a predetermined number of long slots and short slots.

The packetizing unit 19 receives data from the user data terminal, divides the user data into packets with the data length that can be accommodated by the DATA unit of one long slot as a unit, and outputs the packet to the peripheral station transmission data buffer 20. To do. The packetizing unit 19 also includes information (PC) necessary to reassemble the packet-divided data into one piece of data for each piece of data to be transferred to the peripheral station transmission data buffer 20, and the packet data. Data effective length (PL) of As the packet reassembly information (PC), for example, information such as whether or not the data is a part of the packet-divided data, or whether it is the last data of the packet-divided data is given. Be done.

The peripheral station transmission data buffer 20 receives the data from the packetizer 19 and sends it to the number of retransmissions (R
E) is added and then buffered, and the transmission control unit 21
Output this to. At this time, the peripheral station transmission data buffer 20 buffers long packet data to be transmitted in the long slot and short packet data to be transmitted in the short slot in separate buffers. Further, the peripheral station transmission data buffer 20 holds the data output to the transmission control unit 21 in the primary holding buffer for confirmation of delivery. Then, upon receiving a retransmission or buffer release instruction signal from the delivery confirmation unit 23, the data instructed to be released from the hold buffer is erased from the buffer, and the data instructed to be retransmitted is buffered in a dedicated buffer for retransmission data. Ring again. However, the dedicated buffer for retransmission data also has long packet data that should be transmitted in a long slot,
A separate buffer shall be provided for the short packet data to be transmitted in the short slot. Further, the peripheral station transmission data buffer 20 sets “0” as the number of retransmissions to the data just input from the packetization unit 19, and every time the data is buffered again in the dedicated buffer for retransmission,
This value is incremented by 1.

When the transmission controller 21 receives the output from the slot timing generator 18 and knows that the slot timing has come, it recognizes whether it is the long slot timing or the short slot timing, and transmits to the peripheral station. One piece of packet data for long slot or packet data for short slot is read from the data buffer 20, and is output to the peripheral station transmitter 22. At this time, the transmission controller 21
Adds the address of its own station (ADRS) to the data delivered to the peripheral station transmitter 22. In addition, the transmission control unit 21
Notifies the delivery confirmation unit 23 whether or not data transmission has been attempted in that time slot.

The peripheral station transmitter 22 adds a dummy bit and a frame sequence check field (FCS) to the input from the transmission controller 21 and further performs encoding and modulation to provide an error correction redundant bit (FEC).
Is added and output to the peripheral station line interface 12.

The delivery confirmation section 23 receives the output from the transmission control section 21, and stores in which time slot the own station tried transmission, and this and the reception response output from the peripheral station separation section 14. The response to the time slot in which the local station tried to transmit data is compared with the signal and an acknowledgment ACK (A
acknowledgment or NAK (N)
ot Acknowledgement). That is, if the reception response signal indicates the address of the own station, it is determined as a positive response ACK, and if all are "0" or the addresses of other peripheral stations T1 to T4 are determined, it is determined as a negative response NAK. Then, the delivery confirmation unit 23 instructs the peripheral station transmission data buffer 20 to retransmit the data whose response is a negative response NAK and release the data from the temporary holding buffer for the data whose response is a positive response ACK.

Next, with reference to FIG. 5, a description will be given of changes in the slot configuration in the device of the present invention.

The slot configuration determining unit 6 of the central station device 24
However, the rules for determining whether the slot configuration is appropriate or not are: (1) The slot configuration determining unit 6 manages two variables, that is, the number of long slots used and the number of short slots used.

(2) The data using the long slot is 1
The number of long slots used is "1" each time it is correctly received.
Only added. Even if one piece of data using the short slot is correctly received, the number of used short slots is incremented by "1".

(3) When the number of retransmissions of received data is not "0", the number of retransmissions is added to the number of slots used.

(4) The slot configuration determining section 6 determines the slot configuration by referring to the slot usage rate during the three frames. The calculation formula of the slot usage rate is as follows: long or short slot usage rate = number of long or short slots used for 3 frames /
The total number of slots in 3 frames.

(5) The slot configuration determination unit 6 changes the slot configuration if either the long slot usage rate or the short slot usage rate is at least twice the other. (6) The minimum number of long slots and the number of short slots in one frame are defined. Even if the usage rate of one slot is very high, the other slot is set to "0". It never happens.

In FIG. 4, the number of long slots used and the number of short slots used are shown above.

First, the first slot structure has four short slots and three long slots per frame. Then, the four peripheral stations T1 to T4 transmit data to the central station C by the slotted Aloha method. The central station C transmits the reception response signal for one frame and the slot configuration information 25 to all the peripheral stations T1 to T4 in the broadcast mode during the next frame. In frame 1, since the short slot data D1 from the peripheral station T4 and the long slot data C1 from the peripheral station T3 are normally received, the slot usage number at the end of the frame 1 is the long slot usage number =
1, the number of short slots used = 1. Further, in the first long slot of the frame 1, the data A1 transmitted by the peripheral station T1 and the data B1 transmitted by the peripheral station T2 collide with each other, so that the central station C can normally receive the data. It is not possible, and NA for the peripheral stations T1 and T2
A K response is returned. The peripheral stations T1 and T2 each generate a random number at the time of receiving the NAK response, and retransmit the data A1 and B1 with a slot interval corresponding to the random number. At this time, the number of retransmissions “1” is set in the data A1 and B1.

Retransmitted data A in frame 3
1 and B1 are output to the central station C. When data A1 is received in the first long slot of frame 3, the number of long slots used is incremented by "1" by one data reception,
Further, the number of retransmissions “1” is added, and a total of 2 is added. Data B1 in the second long slot
Is received, the number of long slots used is also “2”.
Only added.

According to the above rules, the slot configuration determining unit 6 of the central station device 24 updates the number of slots used each time one data is received. The number used is "7" and the number used for short slots is "3". Here, the slot configuration determination unit 6 calculates the slot usage rate of each of the long slot and the short slot in the three frames from frame 1 to frame 3.

The number of long slots is 9 for 3 frames.
The number of short slots is twelve. Therefore, the slot usage rate from frame 1 to frame 3 is 0.78 for the long slot usage rate and 0.25 for the short slot usage rate. At this time, since the long slot usage rate is more than twice the short slot usage rate, the slot configuration determination unit 6 determines to decrease the short slots by 2 and increase the long slot by 1. Then, the new slot configuration is applied to all peripheral stations T1 to T1.
Notify T4 in broadcast mode.

Therefore, after the frame 5, the slot structure per frame is two short slots and four long slots.

However, with respect to the data received in frame 4, since the slot configuration is being changed, the number of slots used is not updated.

Packet division in the packetizer 19 of the peripheral station device 26 will be described with reference to FIG.

Data such as the data D1 and D2 which is shorter than the length of the DATA portion of the long slot is not divided into packets and is passed to the peripheral station transmission data buffer 20 as one packet data. Data D3 and D
4, data longer than the length of the DATA portion of the long slot is divided into two or more pieces of packet data and then passed to the peripheral station transmission data buffer 20. Among these, for packet data shorter than the length of the DATA part of the short slot, such as the latter half b of the data D1 and D3, the peripheral station transmission data buffer 20 determines this as the data for the short slot, and Buffer in the buffer for.

On the other hand, for data longer than the length of the DATA portion of the short slot, such as the first half a of the data D2 and the data D3, and c and d obtained by dividing the data D4, the peripheral station transmission data buffer 20 Is determined as long slot data, and is buffered in the long slot data buffer.

[0059]

EFFECTS OF THE INVENTION By using time slots having different lengths according to the distribution of the data length of the communication being carried out at that time and combining them, satellite communication by the slotted Aloha system with high data transmission efficiency can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram of a central station apparatus of an apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram of a peripheral station device of the device of the present invention.

FIG. 3 is a diagram showing a transmission frame configuration of a peripheral station device.

FIG. 4 is a diagram showing a transmission frame configuration of a central station device.

FIG. 5 is a diagram showing a transmission / reception state of a central station device and a peripheral station device and a slot configuration changing process.

FIG. 6 is a diagram showing a packet division situation in a peripheral station device.

FIG. 7 is an overall configuration diagram of multiple access satellite communication.

FIG. 8 is a diagram showing a data transmission situation of a slotted Aloha system of a conventional example.

[Explanation of symbols]

 1 Central Station Line Interface 2 Central Station Receiver 3 Central Station Channel Monitor 4 Central Station Separator 5 Central Station Receive Data Buffer 6 Slot Configuration Determinator 7 Central Station Transmit Data Buffer 8 Receive Response Signal Generator 9 Frame Timing Signal Generator 10 Multiplexing unit 11 Central station transmitting unit 12 Peripheral station line interface 13 Peripheral station receiving unit 14 Peripheral station separating unit 15 Peripheral station channel monitoring unit 16 Peripheral station reception data buffer 17 Frame synchronization unit 18 Slot timing generation unit 19 Packetization unit 20 Peripheral Station transmission data buffer 21 Transmission control unit 22 Peripheral station transmission unit 23 Delivery confirmation unit 24 Central station device 25 Slot configuration information 26 Peripheral station device C Central station S Communication satellite T1 to T4 Peripheral station A1 to A3 data B1 to B4 data C1 C4 data D1 to D4 data

Claims (4)

[Claims] 1. A satellite communication comprising a communication satellite connected to a host terminal for relaying a line from a central station device, and a plurality of peripheral station devices for transmitting and receiving data to and from the central station device via the communication satellite. In the method, the central station device and the peripheral station device are provided with means for receiving and transmitting data by arranging two types of long and short time slots in one frame. 2. The central station apparatus includes means for varying the two types of long and short time slot composition ratios according to the distribution of the data length currently in progress, and the peripheral station apparatus is changed by the varying means. 2. The satellite communication system according to claim 1, further comprising means for synchronizing slot timing with a time slot composition ratio. 3. A central station device of a satellite communication system, which is connected to a host terminal and transmits and receives data to and from a communication satellite, wherein the central station device arranges two types of long and short time slots in one frame. A central station device of a satellite communication system, comprising means for performing reception of the time slot, and means for varying the composition ratio of the two types of long and short time slots according to the distribution of the data length which is currently in progress. 4. A satellite communication type peripheral station device for transmitting and receiving data to and from the central station device via a communication satellite, wherein the peripheral station device arranges two types of long and short time slots in one frame. A satellite communication system peripheral station apparatus comprising: means for performing transmission of the above, and means for synchronizing slot timing with the time slot configuration ratio changed by the changing means.